EVALUATING THE EFFICACY OF RADIATIVE DRY SANITATION TECHNIQUES ON 
SALMONELLA-INOCULATED STAINLESS STEEL SURFACES POST VISIBLE 
CLEANING 

By 

Kasey L. Nelson 

A THESIS 

Submitted to 
Michigan State University 
in partial fulfillment of the requirements   
for the degree of 

Biosystems Engineering – Master of Science 

2024

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ABSTRACT 

Salmonella cross-contamination in flour production facilities remains a recalcitrant 

problem, requiring effective low-moisture cleaning and sanitation. For research on this topic to 

be effective, dry inoculation methods must accurately model the powder accrual and the transfer 

of Salmonella from flour to equipment surfaces. Additionally, radiative sanitation technologies 

could provide quick and effective surface sanitation, given a sufficient intensity. Therefore, it is 

necessary to understand the relationship between radiation dosage and Salmonella reduction on 

stainless-steel (SS) surfaces. The objectives of this research were to (1) develop a replicable 

methodology employing electrostatic powder coating technology to apply inoculated, fabricated 

all-purpose flour onto SS surfaces, (2) generate the efficacy data for radiative dry sanitation 

technologies (UV-C, Far UV-C, and Infrared) achieving minimum 3 log reduction of Salmonella 

(log CFU/cm2), and (3) develop surface inactivation models for the Salmonella on visibly clean 

SS surfaces in low-moisture environments. All-purpose wheat flour was fabricated and 

inoculated with a 6-strain Salmonella cocktail. The inoculated flour was adhered to #304 and 

#316 grade SS using an electrostatic powder coating apparatus. Subsequently, the SS was 

cleaned with a brush until visibly clean and then exposed to UV-C, Far UV-C, and IR radiation. 

Thereafter, the surface inactivation models were developed based on the log population counts 

remaining on SS surfaces and the total energy deposited as a function of the applied radiation 

intensity and the duration of radiation exposure. The dry powder coating inoculation 

methodology proved to be consistent and replicable at pilot scale, achieving ~4 log CFU/cm2 on 

the surface of #304 brushed finish and #316L brushed finish SS coupons. Furthermore, this study 

demonstrated the potential application of UV-C and IR technologies for dry sanitation on 

visually clean, stainless steel surfaces across various grades and finishes. 

 
 
ACKNOWLEDGEMENTS 

My sincerest thanks to Dr. Sanghyup Jeong, my major advisor. His ability to distill 

complex engineering problems that seem impossible to solve into actionable tasks that further 

scientific understanding toward current issues in food production cannot be overstated. His 

guidance, advice, and patience helped me overcome many roadblocks to my success. 

I also greatly appreciate my committee members, Dr. Bradley Marks, and Dr. Teresa 

Bergholz. I would not have been able to succeed without their collective expertise and insight, 

especially with their limited and highly valuable time.  

Next, thank you to the Food Safety Engineering Laboratory staff, specifically Michael 

James and Dr. Ian Hildebrandt, for their assistance with a large amount of small things: 

equipment, troubleshooting, best laboratory and modeling practices, and answering minor but 

important questions. Additionally, thank you to Phil Hill for fabricating components of my 

experimental equipment. 

Thank you to my fellow graduate students and undergraduate coworkers. My work would 

not have been feasible without their support. Thank you to Ian Klug for his eagerness to help 

with experimentation, his innumerable hours of help, and company. Thank you to my family and 

friends, who cheered me on from near and far, and to the Nokomis Cultural Heritage Center, 

which was a source of community and generational knowledge throughout the course of my 

degree. 

And finally, thank you to Nicole Hall, whose single suggestion to research the microbial 

safety of flour during a team meeting in my sophomore year changed the course of my academic 

career.  

Chi-miigwech to you all for your support. 

iii 

 
This work is supported by the Agriculture and Food Research Initiative, Sustainable Agricultural 

Systems Program grant no. 2020-680-31822 from the USDA National Institute of Food and 

Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this 

publication are those of the author(s) and do not necessarily reflect the view of the U.S. 

Department of Agriculture.  

iv 

 
 
 
TABLE OF CONTENTS 

LIST OF TABLES ......................................................................................................................... vi 

LIST OF FIGURES ...................................................................................................................... vii 

INTRODUCTION .......................................................................................................................... 1 

LITERATURE REVIEW ............................................................................................................... 3 

MATERIALS AND METHODS .................................................................................................. 27 

RESULTS ..................................................................................................................................... 49 

CONCLUSIONS........................................................................................................................... 66 

BIBLIOGRAPHY ......................................................................................................................... 69 

v 

 
 
 
 
LIST OF TABLES 

Table 1: Survey of studies utilizing UV-C and IR in low-moisture food sanitation 
experimentation............................................................................................................................. 16 

Table 2: Treatment factors applied to stainless steel coupons ...................................................... 41 

Table 3: Descriptive statistics and 95% confidence intervals for inoculated, non-irradiated 
control samples for different sanitation experimental runs ........................................................... 52 

Table 4: Maximum intensity values at specified distances from the emitter ................................ 56 

Table 5: Relative humidity changes during infrared radiation treatment ..................................... 59 

Table 6: 95% Confidence intervals of the required dosage to meet a target sanitation efficacy 
(log CFU/cm2) ............................................................................................................................... 61 

vi 

 
 
 
 
LIST OF FIGURES 

Figure 1: Accumulated wheat meal on a milling attachment after milling inoculated and 
equilibrated wheat berries ............................................................................................................. 23 

Figure 2: A stand mixer with a grinding attachment .................................................................... 29 

Figure 3: Sieving system used for flour fabrication. From top to bottom, a lid, a U.S. Standard 
No.’s 20, 70, 100, and 200 mesh, followed by a sieve bottom ..................................................... 31 

Figure 4: #304 brushed finish (left), #316L brushed finish (center), and #304 mirror finish (right) 
stainless steel coupons .................................................................................................................. 32 

Figure 5: Stainless steel coupon preparation ................................................................................ 33 

Figure 6: Labeled photo of equipment used for electrostatic powder coating within an 
equilibrated chamber ..................................................................................................................... 34 

Figure 7: Brushing protocol to create visibly cleaned coupons .................................................... 36 

Figure 8: Coated #304 SS brushed finish (A) and #304 SS mirror finish (B) coupons ................ 37 

Figure 9: The sanitation treatment chamber with racks and two slots (8 cm × 2.2 cm) (in pink) on 
top of the chamber for housing the selected technologies ............................................................ 38 

Figure 10: Distance measurements within the sanitation chamber ............................................... 39 

Figure 11: UV-C 254 nm device (A), Far UV-C 222 nm excimer lamp (B), and infrared lamp 
and ballast (C) ............................................................................................................................... 40 

Figure 12: Sanitation of visibly cleaned SS coupons using UV-C (A), Far UV-C (B), and IR 
devices (C) .................................................................................................................................... 41 

Figure 13: Simulated coupon surface used for UV-C and Far UV-C intensity measurements .... 43 

Figure 14: UV-C intensity measurement set-up within the sanitation treatment chamber ........... 44 

Figure 15: (A) Modified #304 SS coupon with 0.11 diameter cm hole with affixed thermocouple, 
(B) A 10 x 10 x 2.5 cm block of high temperature fiberglass insulation with a circular indentation 
cut out to house the coupon in the center, and (C) IR irradiance measurement device with a 
visible channel .............................................................................................................................. 46 

Figure 16: 95% confidence intervals of wheat berry Salmonella populations throughout the 
milling process. Pre-grind (unground berries) and post-grind (berries milled into wheat meal). 
Mean populations are listed to the right of each interval plot ....................................................... 49 

Figure 17: 95% confidence intervals for wheat meal and flour particles within each respective 
U.S. Standard Mesh after one 5 minute sieving cycle. Mean populations are listed to the right of 
each interval plot ........................................................................................................................... 50 

vii 

 
Figure 18: Microscopic images of coated (left) and brushed to visibly clean (right) #304 SS, 
brushed finish, at 10X magnification ............................................................................................ 51 

Figure 19: 95% confidence intervals of Salmonella populations on coated and visibly cleaned 
stainless steel coupons .................................................................................................................. 52 

Figure 20: UV-C intensity data at the center of a coupon surface with varying distances from the 
emitter (λ = 254 nm) ..................................................................................................................... 53 

Figure 21: UV-C intensity data at separate locations on coupon surface, 5 cm from emitter (λ = 
254 nm) ......................................................................................................................................... 54 

Figure 22: Far UV-C intensity data at the center of a coupon surface with varying distances from 
the emitter (λ = 222 nm) ............................................................................................................... 55 

Figure 23: IR intensity data at the center of a coupon surface with varying distances from the 
emitter ........................................................................................................................................... 56 

Figure 24: UV-C Salmonella sanitation efficacy (log CFU/cm2) vs. length of exposure (min) at 
specified intensities ....................................................................................................................... 57 

Figure 25: Far UV-C Salmonella sanitation efficacy (log CFU/cm2) vs. length of exposure (min) 
at specified intensities ................................................................................................................... 58 

Figure 26: IR Salmonella sanitation efficacy (log CFU/cm2) vs. length of exposure (min) at 
specified intensities ....................................................................................................................... 59 

Figure 27: Sanitation efficacy (log CFU/cm2) vs. dosage (mJ/cm2) ............................................. 61 

viii 

 
 
INTRODUCTION 

Problem Statement 

Recent outbreaks and recalls of low-moisture food products such as flour have been 

linked to Salmonella, raising significant public health concern. Ensuring cleanliness and 

sanitation in low-moisture food production is critical for maintaining product safety and 

protecting public health. Challenges in these low-moisture environments include the need to 

limit water usage in the cleaning and sanitation processes to prevent the outgrowth of pathogens, 

yeasts, and molds. The prohibition of water as a sanitation compound carrier in dry environments 

necessitates alternative, more labor-intensive cleaning and sanitation approaches to meet similar 

sanitation efficacies to other industry sectors. 

Significant knowledge gaps exist in research related to dry sanitation, particularly 

regarding ideal food contact surface inoculation strategies, the application of efficacious and 

practical dry sanitation technologies, and the generation of sanitation parameters for future 

reference. 

To mimic potential contamination in dry processing environments, a dry inoculation 

methodology is essential. This method must use minimal moisture and reflect the realities of 

powder accrual on equipment surfaces during production. Food-grade stainless steel is a 

commonly used surface in food production environments, and characteristics such as chemical 

composition (grade) and the surface finish can affect the survival of adherent bacterial 

populations. An ideal inoculation method would leave detectable bacterial populations on the 

surface after cleaning, enabling the assessment of the effectiveness of dry sanitation 

technologies. 

1 

 
Although several proof-of-concept studies have explored non-aqueous sanitation 

technologies, such as electromagnetic radiation for low-moisture foods and food contact 

surfaces, many lack consistent, crucial data needed for industrial application, including radiation 

intensity, the distance from the emitter to the target surface, and the inactivation models on the 

target surface. 

Goals and Objectives 

The objectives of this experiment were to: 

1.  Develop a replicable and consistent electrostatic powder coating dry inoculation 

methodology that can achieve Salmonella populations (> 4 log CFU/cm2) on stainless 

steel surfaces after brushing to “visibly clean.” 

2.  Generate the efficacy data for several radiative, non-aqueous sanitation technologies 

(UV-C 254 nm, Far UV-C 222 nm, Infrared) on visibly clean stainless steel surfaces 

achieving minimum 3 log reduction of Salmonella (log CFU/cm2) by varying the total 

energy deposited. 

3.  Develop surface inactivation models for Salmonella on stainless steel surfaces for each 

radiative sanitation technology in low-moisture food production environments. 

2 

 
 
 
LITERATURE REVIEW 

Recent Outbreaks of Salmonella Linked to Flour Products 

Foodborne pathogens in low-moisture foods (LMFs) pose significant concerns for food 

manufacturers, public health agencies, and consumers. The rise in outbreaks and recalls related 

to low-moisture foods has heightened public awareness of the risks associated with their 

consumption. 

In the United States, numerous recalls have involved Salmonella contamination in flour 

and wheat-containing products. In 2008, a salmonellosis outbreak was linked to S. Agona 

occurred in wheat and rice cereal (Centers for Disease Control and Prevention, 2008), and within 

the same year, a New Zealand-based Salmonella Typhimurium phage type 42 outbreak was 

linked to consumption of contaminated raw flour (McCallum et al., 2013). In 2018, S. Mbandaka 

was found in cereal, which was subsequently recalled. Most recently, in 2023, recalls of all-

purpose flour (Centers for Disease Control and Prevention, 2023a), and raw chocolate chip 

cookie dough (Centers for Disease Control and Prevention, 2023b) were linked to S. Infantis and 

S. Enteritidis, respectively. 

Additionally, previous outbreaks linked to other low-moisture foods include a 1998 

outbreak of S. Agona in toasted oats cereal (Centers for Disease Control and Prevention, 1998), a 

2003 outbreak of S. Enteritidis PT 30 in almonds (Centers for Disease Control and Prevention, 

2004), a 2007 outbreak of S. Tennessee in peanut butter (Centers for Disease Control and 

Prevention, 2007), a 2009 outbreak of S. Montevideo outbreak in black and red pepper (Centers 

for Disease Control and Prevention, 2010), and a 2013 outbreak of S. Mbandaka in tahini 

(Centers for Disease Control and Prevention, 2013). 

3 

 
The recurrent outbreaks of Salmonella, including those in low-moisture foods such as 

cereals and flours, underscore its critical importance in food safety protocols, highlighting the 

need for stringent contamination prevention measures across diverse food products. 

Salmonella 

Salmonella is a Gram-negative, rod-shaped enteric bacteria. They can be classified into 

typhoidal and non-typhoidal strains, each causing different health effects and outcomes for those 

infected. The most common infectious serovars in the United States are S. Enteritidis, S. 

Newport, and S. Typhimurium (Centers for Disease Control and Prevention, 2016). 

Certain strains of Salmonella (Typhi, Paratyphi A, B, and C) can cause life-threatening 

illnesses when present in the host’s bloodstream. Typhoidal strains of Salmonella can only be 

shared between humans (Bennett, 2020), usually through a fecal-oral route. Typhoidal strains are 

associated with typhoid fever, which typically presents as a severe, lengthy fever in conjunction 

with headache, constipation, or diarrhea (CDC Yellow Book, 2024b). Without medical treatment, 

serious complications may arise, including gastrointestinal hemorrhage. Untreated cases may last 

up to a month and can have a fatality rate of 10–30% (CDC Yellow Book, 2024b). 

Non-typhoidal strains have multiple reservoirs for transmission to human hosts, whether 

they be zoonotic or environmentally based. Common sources include domestic animals, raw food 

products, or contaminated water sources (CDC Yellow Book, 2024a). Non-typhoidal 

salmonellosis typically present with severe diarrhea, fever, heavy abdominal cramping, and loss 

of appetite. 

As of 2011, 1.2 million cases of non-typhoidal Salmonella occurred annually in the 

United States (Scallan et al., 2011). The considerable burden of illness has significant impacts on 

public health. 

4 

 
Unique Challenges: Salmonella and Low-Moisture Foods 

Low-moisture foods, which have a water activity (aw) below 0.86, lack the environmental 

and physical characteristics that typically support the survival of foodborne microbes. The lower 

the water activity for a food product, the less water is available for pathogen use, serving as a 

barrier to pathogen growth. Particularly, some strains of Salmonella can express resistance to 

processing steps such as drying and thermal treatment due to their thermal and desiccation 

resistance (Liu et al., 2018; Smith, et al., 2016). Some examples include Salmonella Enteritidis 

PT 30 (ATCC BAA-1045), known for its thermal resistance and linked to almond outbreaks from 

2003–2004 (Centers for Disease Control and Prevention, 2004), and Salmonella Reading (Moff 

180418), which demonstrates both thermal and desiccation resistance in low-moisture food 

powders (Wei et al., 2020). 

Prevalence and Viability of Salmonella in the Flour Milling Process 

To understand how Salmonella accrues in milling end-products, field studies have been 

conducted to survey the microbiological backgrounds of incoming wheat from across the globe 

as a point of entry into the milling process. 

A 2003 Australian study by Berghofer, et al. surveyed nine mills owned by three 

companies, conducting APC counts, total coliform counts, spores, and yeast tests to determine 

the microbiological background of wheat within Australia (n=650). The study found minimal 

populations of E. coli and Salmonella, with no pathogenic Salmonella serovars found in the 

samples, although two strains of environmental Salmonella were isolated. Notably, most wheat 

contaminants were present on the outer layers of the grain (i.e., wheat bran and germ) (Berghofer 

et al., 2003). The study also highlighted early discussions on product recontamination via milling 

equipment. 

5 

 
Additional microbiological surveys of wheat, corn, oats, whole wheat, and durum were 

taken from 2003–2005 in research by Sperber (2007). After sampling wheat from 2003–2005 

(n=4,358), the study found a low prevalence of Salmonella (0.14%) in tested samples. 

Later research by Sabillón, et. al, investigated the varying microbial load of hard red 

winter wheat produced in the midwestern United States (Sabillón et al., 2016). Three different 

lines of hard red winter wheat were grown in separate locations and exposed to different 

environmental conditions over two growing seasons. Like Berghofer, et al., the wheat samples 

(n=81) were tested for microbes and fungus related toxins using APC, yeasts, molds, and 

coliform bacteria tests. Samples selected for Salmonella testing were enriched using buffered 

peptone water and transferred into tetrathionate broth, a selective medium. The study did not 

detect the presence of Salmonella or E. coli in any samples. Importantly, the microbial load of 

wheat varied depending on growth location, with environmental factors like seasonality, relative 

humidity, and rainfall further impacting microbial load. More research was needed to 

characterize the microbial load of wheat for large sample sizes to better reflect the large scale, 

multi-seasonal, and continuous nature of wheat processing. 

Lastly, Myoda, et al. conducted a three-year study that sampled wheat prior to entering 

the milling process (n=5,176) (Myoda et al., 2019). Wheat samples, including hard red spring, 

hard red winter, soft red winter early, and soft red winter late, were tested for E. coli and 

Salmonella, with 3,891 of the samples tested and 1.23% of testing positive for Salmonella (0.110 

± 0.448 MPN/g, ~41 MPN per 375 g sample) (Myoda et al., 2019). 

Overall, the microbiological surveys highlighted a low prevalence of Salmonella and 

other foodborne pathogens in wheat products, a finding that contrasts with the rising number of 

outbreaks and recalls. 

6 

 
Fate of Salmonella During Flour Processing and Post-Processing 

Given the reported low prevalence of Salmonella in incoming wheat, one might wonder 

why are extra populations are measured in milling end products. Factors influencing the survival 

of Salmonella in flour, such as fluctuations in relative humidity within the processing system, 

shifts in the water activity of products, and cross-contamination from soiled equipment, explain 

this necessity. 

Generally, the flour milling process reduces water usage to inhibit the growth of 

pathogens, molds, and yeasts. During tempering, a step in the milling process, a minute amount x 

of water (1–3% of the wheat berry mass) is used to bring the wheat berries to their optimal 

moisture content before milling, although the total added amount of water can vary due to 

several factors including initial moisture content (Posner & Hibbs, 2005). This step may seem 

counter-intuitive to prevent the growth of unwanted microbes. Notably, a study by Lin, et. al, 

found that significant increases in wheat grain aw during the tempering process did not 

significantly increase native microbes (mesophiles and coliforms) or intentionally added 

pathogen populations (2023). 

Nonetheless, research by Sperber and the North American Millers’ Association 

emphasized the importance of limiting water use beyond tempering: the addition of moisture to 

products can cause growth of pathogens, molds, and yeasts once the aw is greater than 0.85 

(Sperber & North American Millers' Association, 2007). The fluctuation of water activity inside 

the products during processing can also have a detrimental effect on product safety. Carter, et. al 

determined that tempered wheat held at aw > 0.70 for over 24 h could cause unwanted mold 

growth on wheat berries (Carter et al., 2015). Therefore, monitoring the relative humidity and 

7 

 
moisture content of the wheat and the production environment is an important consideration for 

product quality and safety. 

This observation of minimized water use contrasts sharply with the sanitation methods 

prevalent in other industries, where aqueous sanitizers are widely used, especially in clean-in-

place operations for dairy and juice processing. In low-moisture environments, water cannot 

serve as a carrier fluid for chemical compounds to inactivate pathogen, mold, and yeast, making 

equipment sanitizing challenging. Additionally, moisture introduced during the sanitation could 

affect the quality and safety of subsequent products. 

Even with the strict control of moisture, Salmonella and other pathogens can contaminate 

equipment with low levels in a viable state. Research by Kusumaningrum, et. al found that S. 

Enteritidis, when allowed to contaminate surfaces at high levels (7 log CFU/100 cm2) was 

detected on #304 stainless steel after 96 hours post-contamination (Kusumaningrum et al., 2003). 

At moderate levels (5 log CFU/cm2), S. Enteritidis was detectable until 24 hours passed. 

Although 24 hours is a relatively short period, residual populations on stainless steel surfaces 

within the processing line can cross-contaminate the next batch of flour. 

A later study in 2021 by Sabillón et al., investigated the prevalence of generic E. coli on 

relevant equipment surfaces in a flour mill. . Milling equipment was swabbed to enumerate any 

potential E. coli, coliforms, yeasts, and molds remaining on equipment surfaces from incoming 

wheat grain to flour packaging. Quantifiable amounts of Enterobacteriaceae (2.3 ± 1.0 log 

CFU/cm2) were found within the inside walls of the flour grinding machines. In comparison, the 

flour handling and storage equipment had 1.1 ± 1.6 log CFU/cm2, specifically within the finished 

flour mixer (Sabillón et al., 2021). 

8 

 
After production, flour is often stored for extended periods before consumption. The 

survival rates of heat and desiccation-resistant Salmonella strains in low moisture foods post-

production has been previously studied (Syamaladevi et al., 2016; Villa-Rojas et al., 2017; Xu et 

al., 2019). Thus, recurring consumption of the contaminated product could cause multiple 

occurrences of illness, emphasizing the importance of sanitation during and after production in 

low moisture food environments. 

Sanitation In Low-Moisture Environments 

Current practices for sanitation in low-moisture food processing environments use 

multiple techniques and tools to inactivate microorganisms on equipment after cleaning, the 

physical removal of debris. One standard technique is the use of non-aqueous chemical sanitizers 

which can be applied directly to food contact surfaces to inactivate microbes. Although effective, 

some non-aqueous sanitizers include water as part of their formulation, introducing undesirable 

moisture into the processing environment. Harada & Nasciemento found that a quaternary 

ammonium compound +isopropyl alcohol solution (specifically, didecyldimethylammonium 

chloride (0.015% v/v), sequester, isopropyl alcohol (25% v/v) and water) inactivated pathogens 

on stainless steel and polypropylene, albeit with a “weak performance” (Harada & Nascimento, 

2021) in comparison to the other dry sanitation technologies used within the study. 

While “non-aqueous” sanitizers are not the ideal method for dry sanitation, they are 

employed in some food production environments such as almond processing (Du et al., 2010) 

due to a lack of feasible alternatives, especially since the solution can flow into cracks and 

crevices (Kane et al., 2016). The preferred dry-sanitation method should be non-aqueous, safe for 

both the product and personnel, cost-effective, and require short exposure times for treatment 

efficacy. Two potential non-aqueous technologies that could be used alongside non-aqueous 

9 

 
sanitizers, ultraviolet-C (UV-C) radiation and infrared radiation (IR), utilize different 

wavelengths of electromagnetic radiation to inactivate pathogens. 

Overview of Electromagnetic Radiation 

There are two main models of classifying electromagnetic radiation: the classical model 

and the quantum model. The classic model describes the oscillations of electric and magnetic 

fields by interactions between charged particles (Zhabinskaya & University of California Davis, 

2023a). The quantum model describes the excitation of photons to different quanta. The higher 

the quanta, the higher the frequency of the particle, hence the higher radiative energy the particle 

can possess (Zhabinskaya & University of California Davis, 2023b). The dual nature of 

electromagnetic radiation being both an electromagnetic wave and a particle allows for a range 

of applications toward pathogen control in different food products and food contact surfaces. 

Given enough energy, select wavelength bands of electromagnetic radiation (X-ray and 

gamma) can promote ionization, where an atom gains or loses electrons within atomic valence 

shells through collisions with energetic particles. Ionizing radiation can effectively inactivate 

microbes in a variety of mediums by removing electrons from biological molecules that are 

crucial for survival. However, this phenomena poses a significant risk to human health. 

Alternatively, non-ionizing, lower energy radiation sources such as infrared and ultraviolet can 

effectively inactivate microbes in food processing environments. 

Infrared Radiation. Infrared radiation is a form of electromagnetic radiation between 

700–1000 nm that is invisible to the human eye. The inactivation principle involves heating the 

target microorganism until it can no longer function. Molecules within the microorganism absorb 

IR, causing vibrations that increase the temperature of the cell. Bacteria, including Salmonella, 

can be thermally inactivated in both normal or desiccated states (Xu et al., 2020). 

10 

 
IR can penetrate thin surfaces and access hard-to-reach cracks and crevices on surfaces 

and equipment that are normally inaccessible to tools and hands. IR can be generated using 

various sources such as heat lamps, ceramic and metal shielded heat coils, and quartz halogen 

tubes. Key considerations for implementing IR include the housing materials, IR absorption, the 

distance between target surface or product and the IR emitter, and duration of exposure. 

Ultraviolet Radiation. Ultraviolet radiation (UV) is a form of electromagnetic radiation 

with a frequency above visible light, having shorter wavelength than both IR and visible light. 

UV can be further classified into three main wavelength bands: UV-C (100–280 nm), UV-B 

(280–315 nm), and UV-A (315–400 nm) (International Organization for Standardization, 2007). 

Ultraviolet radiation uses shorter, more powerful wavelengths in comparison to infrared 

radiation. UV-C rays specifically provide ionizing energy to break bonds within DNA and RNA 

molecules toward the inactivation of microorganisms. 

Exposure to UV-C radiation leads to the dimerization of the pyrimidine bases (thymine, 

uracil, and cytosine) in eukaryotes, prokaryotes, and viruses. Dimerization occurs when the 

double carbon bond between thymine and cytosine (or uracil) absorbs UV-C radiation and severs 

(Goodsell, 2001). The severed bond can reattach to the next base on the same DNA strand and 

has several notable variations in chemical structure (Batista et al., 2009; Napoleao et al., 2023). 

Dimerized DNA and RNA bonds are mutagenic and cannot be used for normal genetic 

replication, protein synthesis and other cellular functions. Nucleic acids are especially 

susceptible to UV-C wavelengths within the 200–300 nm range (Beck et al., 2016; Hessling et 

al., 2021). UV-C radiation effectively inactivates bacteria, fungi, and viruses on various products 

and surfaces, requiring specific wavelengths and UV-C dosages tailored to the critical 

inactivation parameters of the target microorganism. 

11 

 
UV-C can be generated by mercury lamps, light emitting diodes (LEDs), excimer lamps, 

or pulsed xenon lamps. Common low-pressure mercury bulbs emit UV-C at 254 nm, which are 

often used within UV-C disinfection systems and have a wide array of data available for dosage 

experiments (Giese & Darby, 2000). LED lamps can be modified to emit UV-C between 200–

280 nm. Excimer lamps emit UV-C at 222 nm. Pulsed xenon lamps have a wide range of emitted 

radiation (200–1000 nm) but require filtering of the emitted waves to meet a target wavelength 

(Demeersseman et al., 2023). 

Safety of UV-C Generating Devices 

UV-C can cause damage to human skin and eyes, including facial erythema (skin 

reddening) and photokeratitis (“snow-blindness”) (Ramos et al., 2020; Sliney, 2013). UV-C 

emitted at 254 nm has been found to alter oxidative stress and inflammatory response pathways 

on reconstructed human skin models in comparison to 222 nm, a lower, Far UV-C wavelength 

(Napoleão et al., 2023). 

Recent research has indicated that Far UV-C has a reduced risk of skin and eye damage in 

comparison to 254 nm UV-C. A study by Buonanno, et al. claimed that 222 nm UV-C “produces 

almost no premutagenic UV-associated DNA lesions in a 3D human skin model and it is not 

cytotoxic to exposed mammalian skin” (2017). The study also achieved ~3 log reduction of 

methicillin-resistant Staphylococcus aureus using Far UV-C at a UV fluence of ~15 mJ/cm2 

(Buonanno et al., 2017). Additional research by Kaidzu, et al., found that Far UV-C radiation did 

not penetrate beyond the corneal limbus, the border between the cornea and white of the eye, in 

rat and porcine corneas (2022). However, 254 nm penetrated to the basal cell layer where corneal 

limbus cell replication occurs and exhibited signs of DNA dimerization (Kaidzu et al., 2022). 

12 

 
Far UV-C has been used in hospital settings, which are similar to dry processing 

environments due to the frequent sanitation of surfaces to prevent cross-contamination and 

disease. A 2023 study by Navarathna, et al. used a filtered 222 nm Far UV-C device in 

comparison to sodium hypochlorite disinfectant wipes on non-porous, high-touch surfaces, 

including bedrails, tables, and workstations (n=86). The UV-C device was positioned 2.54 cm 

from each target surface (confirmed with a built-in indicator) and emitted UV-C for 30 s with an 

intensity of ~3.6 mW/cm2. The contact surfaces for the UV-C device had a mean 22.2 CFU per 

25 cm2 pre-treatment and had an 81.4% reduction in surface populations (~4.1 CFU) post-

treatment (Navarathna et al., 2023). The device was suggested for use when manual disinfection 

is infeasible or as a substitute for moderate disinfection capabilities. 

If UV-C generating devices at lower wavelengths can inactivate pathogens with 

comparable population reductions and intensities such as UV-C 254 nm, Far UV-C devices may 

pose as a “safer alternative” for sanitation personnel when applied to low-moisture food contact 

surfaces. 

Applications of UV-C and IR for Low-Moisture Food Safety 

Although research on UV-C and IR based sanitation methods for low-moisture foods and 

their contact surfaces is limited, notable studies exist. 

A 2011 study by Hamanaka, et al., studied the effects of synergistic UV and IR radiation 

on Rhodotorula mucilaginosa, a yeast that can impact fig fruits, using UV-C (253.7 nm) and IR 

(950 nm) sources. The findings showed that UV-C and IR had different levels of efficacy 

(Hamanaka et al., 2011). Specifically, IR treatment resulted in a 1 log reduction of Rhodotorula 

mucilaginosa on fig surfaces within 30 seconds (Hamanaka et al., 2011), whereas UV-C 

treatment achieved a 2.5 log reduction in the same duration. Remarkably, a 3 log reduction in 

13 

 
populations occurred after a sequential 30 second dose of IR followed by UV-C (Hamanaka et 

al., 2011). 

Another study by Ha & Kang investigated the effect of UV-C and IR on red pepper 

powder inoculated with S. Typhimurium and E. coli O157:H7. The study achieved a 3.34 log 

reduction in Salmonella populations within red pepper powder samples after 5 min of concurrent 

IR and UV-C exposure (Ha & Kang, 2013). 

A 2021 study by El Darra, et al. measured the effects of IR, UV, and ozone on dried onion 

flakes and black pepper. The study used a 100 W IR bulb, a 4 W UV-C lamp, and a 25 W ozone 

purifier to inactivate E. coli on the samples in a custom-made decontamination system. After a 

sequential treatment of ozone for 2.5 min followed by concurrent UV and IR for ten min, black 

pepper samples received a 4.20 log reduction in E. coli populations, a higher kill than the 

technologies being used sequentially (El Darra et al., 2021). The study showed the potential for 

further work using the synergistic effects of UV-C and IR in low-moisture foods. 

An in-depth study by Nyhan, et. al, investigated the efficacy of different UV-C 

inactivation technologies within inoculated low-moisture food powders (onion powder, cheese 

and onion powder, chili powder, and garlic powder) with additional observations on plastic 

surfaces. UV-C lamps and UV-C LEDs, each at different wavelengths, were used to inactivate L. 

monocytogenes, E. coli, B. subtilis, and S. Typhimurium in the target products. The study used a 

wide range of UV-C wavelengths, from 254 nm, 270 nm, to 365 nm to examine potential 

differences in efficacy. There were significant differences in efficacy depending on the food 

product, UV-C device, and applied wavelength. S. Typhimurium had over a 4 log CFU reduction 

in populations after a five second treatment using a 270 nm UV-C LED mounted 2 cm from the 

target surface (Nyhan et al., 2021). This study had the highest reduction with the shortest time in 

14 

 
comparison to other literature, likely due to the minimized distance between the UV-C LED 

emitters, the target surface, and selected low-moisture food powders. 

Applications of UV-C and IR Toward Low-Moisture Food Contact Surfaces 

Most of the research on food contact surface sanitation experiments involves food-grade 

stainless steel (SS), which is commonly used in food manufacturing equipment. 

Research by Gabriel et. al, used UV-C and cold atmospheric plasma on stainless steel to 

inactivate S. enterica. The study determined the time for a 2 log reduction on the surface of #304 

stainless steel with a 2B finish to be 462.56 ± 560.15 s (mean ± SD), approximately 7.7 min 

(Gabriel et al., 2018). Harada and Nasciemento also studied multiple dry sanitation methods on 

stainless steel, along with polypropylene. UV-C, dry heat, ozone, and non-aqueous sanitizers 

were used to inactivate Listeria monocytogenes biofilms. After generating a Weibull model to 

characterize the various methods of inactivation, it was found that UV-C required 390 min of 

exposure to achieve a 5 log reduction in populations on stainless steel, while dry heat required 

170 min. The time for a 5 log reduction decreased significantly for polypropylene, requiring only 

6.1 min for UV-C and 54 min for dry heat (Harada & Nascimento, 2021). 

A compilation of studies using UV-C and IR in low moisture foods and food contact 

surfaces is featured in Table 1. 

15 

 
Table 1: Survey of studies utilizing UV-C and IR in low-moisture food sanitation experimentation 

Citation 

Food product / 
surface 

Pathogens of 
interest 

Technologies 

Treatment Parameters 

Wattage 

Wavelength (if 
applicable) 

Intensity of 
radiation 

Length of 
exposure 

Distance 
from 
surface 

Achieved log 
reductions  

 (Ha & Kang, 
2013) 

Red pepper powder 

E.coli O157:H7, S. 
Typhimurium 

Near infrared 
(Quartz halogen 
infrared heating 
lamp), UV 
germicidal lamp 

NIR: 500 W 

 Not specified 

2.62 mW/cm2 

0-5 min 

Not 
specified 

NIR-UV: 3.34 (5 
min, Salmonella) 
synergistic 

 (Bozkurt & 
Uslu, 2022) 

Petri dishes  

Staphylococcus 
aureus, Bacillus 
cereus, E. coli, 
Klebsiella 
pneumoniae 

Philips UV-C 
TUV PL-L 36W 
/ 4P Germicidal 
light bulb 

12.2 W 

262 nm 

Not specified 

10 s, 20 s, 30 s, 
45 s, 1 min, 2 
min, 4 min, 10 
min 

24 cm 

UV: 45s (17.95 
CFU/mL, log 
5.74), 30s (19.50 
CFU/mL, log 
5.70), 20s, (30 
CFU/mL, log 
5.52), and 10s 
(241.04 CFU/mL) 

(Hamanaka et 
al., 2011) 

Fig fruit, yeast cells 

Rhodotorula 
mucilaginosa  

WASAKI 
Electric Co. Ltd 
(IR + UV lamps) 

Not specified 

IR: 950 nm 
UV: 253.7 nm 

IR: 14.8 
mW/cm2/nm 

UV: 31.7 
mW/cm2 

15 s, 30 s, + 
combinations for 
each technology 

8 cm 
(fruit), 13 
cm (petri 
dish) 

IR: 1 log (30 s), 
UV: 2.5 log (30 
s), IR-UV: 3 log 
(30 s sequential) 

(El Darra et al., 
2021) 

Dried onion flakes, 
black pepper 

E. coli 

IR lamp, UV 
lamp, ozone 

IR: 100 W 
UV: 4 W 

UV: 254 nm 

Not specified 

0–30 min (5 min 
intervals) 

Not 
specified 

Sequential IR and 
UV: ~4 log (2.5 
min)  

16 

 
 
Table 1 (cont’d) 

 (Kim et al., 
2023) 

Black peppercorn 

S. Typhimurium 

Vacuum 
ultraviolet, 
Near-infrared 
radiation 

IR: 500 W 
VUV: 42 W 

UV: 185, 254 
nm 

IR: 141.75 
μW/cm2/nm 
VUV: 4.7 
mW/cm2 

5, 10, 15, 20 min 

17 cm  

Combined 
IR+UV: ~1.74 log 
(5 min) 

(Nyhan et al., 
2021) 

onion powder, garlic 
powder, cheese and 
onion powder and 
chilli powder 

L. monocytogenes, 
S. Typhimurium, B. 
subtilis 

UV mercury 
lamps, UV-C-
LEDs, and 
UVA-LEDs 

50 W 

UV: 254, 270, 
365 nm 

Not specified 

5, 10, 20, 40 s 

2 cm 

(Ruiz-
Hernandez et 
al., 2021) 

Peanuts, almonds 

S. Typhimurium 

UV-C lamp 

Not specified 

254 nm 

 10 mW/cm2 

2.5–30 min 

10 cm 

~ 3.5 log (40 s, 
onion powder, S. 
Typhimurium) 

2.39 log (30 min, 
almonds) 

 (Kim et al., 
2016) 

Sliced cheese 

E. coli, S. 
Typhimurium, L. 
monocytogenes 

UV-C LEDs, 
UV-C lamp 

UV-C lamp: 
16 W 

266, 270, 275, 
279 nm 
(LEDs), 254 
nm (Lamp) 

4–5 µW/cm2 

"Treatment 
times for the 
doses were 
calculated by 
dividing UV 
doses by 
intensities with 
an appropriate 
conversion 
factor." 

4 cm 

Not specified 

(Gabriel et al., 
2018) 

 (Harada & 
Nascimento, 
2021) 

Stainless steel 

Salmonella enterica 

UV-C lamp  

15 W 

~254 nm 
(253.97) 

33.588 mW/in2 

0–180 s 

9.8 cm 

3.3 log (10 s, 
#304 SS 2B) 

Polypropylene, 
stainless steel 

L. monocytogenes 

UV-C light  

8 W 

254 nm 

 6.5 mW/cm2 

0,5,10,15,30 min 

15 cm 

1.5 log (5 min) 

17 

 
 
Table 1 (cont’d) 

(Bae & Lee, 
2012) 

Polypropylene, 
stainless steel 

S. Typhimurium. S. 
aureus, L. 
monocytogenes 

UV Sterilizer, 
model DS701 

15 W 

253.7 nm 

0.24 mW/cm2 

30 min, 1, 2, 3 h 

18 cm 

(Yoon et al., 
2018) 

Pork, chicken, 
cabbage, milk, and 
distilled water 
transferred onto 
stainless steel and 
polypropylene 

E. coli, S. 
Typhimurium, L. 
monocytogenes, S. 
aureus 

UV Sterilizer, 
model DS701 

15 W 

253.7 nm 

0.24 mW/cm2 

0, 30, 60, 120 
min 

~22 cm 

3.06 log (3 h, 
stainless steel, S. 
Typhimurium) 

~3.15 log (120 
min, stainless 
steel, S. 
Typhimurium 
within chicken 
residues) 

18 

 
Importantly, some of the critical processing parameters used for radiative technologies 

featured in Table 1, such as the intensity of the emitted radiation, are not reported in all studies. 

The absence of these values obstructs practical comparisons between studies and the generation 

of dosage models. 

Knowledge Gaps Within Current Literature: Dry Inoculation Methodologies 

Current literature on cleaning and sanitation reveals knowledge gaps in the ideal 

inoculation methodology for simulating cross-contamination scenarios, and in determining the 

appropriate application parameters for dry sanitation techniques on low-moisture foods and food 

contact surfaces. 

Modeling equipment surface contamination during low-moisture food processing can be 

achieved by directly inoculating the target food product. However, the chosen inoculation 

methodology can affect the survival rates of pathogens within the food matrix. Research by 

Hildebrandt, et. al emphasized how inoculation methodologies influence the behavior of 

Salmonella in low-moisture food products like flour (Hildebrandt et al., 2016). These methods 

simplify the experimental design, promote thermal and desiccation resistance of the selected 

strains, allow for analysis of worst case storage and thermal treatment scenarios in low-moisture 

foods, and improve experimental replicability. Yet, they do not accurately simulate potential 

contamination scenarios in dry processing environments. Additionally, certain liquid broth-based 

inoculation methods may inadvertently increase moisture level in the food product and the 

processing environment unless specific equilibration steps are followed post-inoculation. 

Additional research into other inoculation methods such as biofilm formation for 

sanitation experimentation has been studied. A study involving Listeria monocytogenes biofilm 

formation on #304 SS surfaces adhered 4.89 ± 0.03 log CFU/cm2 (mean ± SD) of non-planktonic 

19 

 
L. monocytogenes cells on SS after 3 h of contact with liquid broth agitated with a magnetic stir 

bar (de Oliveira et al., 2010). The liquid broth was used as the medium for bacterial attachment 

to the surface, which does not replicate initial contamination scenarios in dry environments. 

However, biofilm formation can occur in dry processing environments due to “microscopic 

surface wetness,” where visibly dry surfaces are covered in microdroplets and liquid films (Orevi 

& Kashtan, 2021). A review of dry surface biofilms in the food processing industry 

contextualized the role of microscopic surface wetness and biofilm formation. While the 

processing environment is dry, wet biofilms can form and persist on equipment, especially on 

irregular surfaces, grooves, and hard-to-reach areas like nooks and crannies (Alonso et al., 2023). 

In the selected studies, microbial transfer was observed from a dry, biofilm contaminated surface 

to the target food powder. Similarly, modeling contamination from an inoculated powder to a dry 

food contact surface could be relevant for understanding sanitation practices in dry 

environments. 

Multiple experiments have utilized the strategy of inoculating food contact surfaces with 

powder and have explored variations, including the use of spherical beads or inoculated powders 

as the vector of microbial transfer. A portion of a 2022 study by Liu, et al. investigated multiple 

transfers of Salmonella from #316 stainless steel and polypropylene beads (d=3.18 mm) to low-

moisture foods and dry powders to evaluate the efficacy of system purges using uninoculated 

low-moisture foods. Approximately 11 log CFU/ml of Salmonella was adhered to the beads with 

an initial concentration of 8.09 ± 0.58 log CFU/cm2 (mean ± SD) on #316 SS. 1 g of whole 

wheat flour, corn meal, and NaCl were separately mixed with three beads of each material type 

and had multiple exposures with uninoculated products. The change in Salmonella populations 

20 

 
on the surface of the #316 SS beads after a single whole wheat flour rinse was 0.34 ± 0.65 log 

CFU/cm2 (Liu et al., 2022). 

A recent experiment by Chen & Snyder used glass beads, spot inoculation, and milk 

powder as modes of pathogen transfer to food contact surfaces such as high density polyethylene 

(HDPE), #304 SS polished 2B finish, and rubber. 30 g of inoculated beads, separated by 

microorganism (S. Enteritidis PT 30, E. faecium, L. innocua, and E. coli) were combined with 

four sterile coupons of a target surface, sealed in a sample bag, and shaken for 5 min to inoculate 

the coupons, among other inoculation methodologies, and exposed to a custom-designed 

mechanical dry cleaning process. For powder inoculation, 10 g of dried inoculated milk powder 

was sealed in a sample bag with four coupons and mechanically mixed for 5 mins using a 

stomacher. Initial Salmonella populations on the glass-bead inoculated #304 SS coupons were 

2.1 ± 0.8 log CFU/coupon (mean ± SD). After dry cleaning, the residual populations were 0.6 ± 

0.6 log CFU/coupon, resulting in a 1.5 ± 1.2 log reduction (Chen & Snyder, 2023). In 

comparison, the milk powder method had initial populations of 3.3 ± 0.2 log CFU/coupon, post 

cleanings populations of 2.0 ± 0.4 log CFU/coupon, and a resultant log reduction of 1.2 ± 0.4 log 

CFU/coupon. The glass bead inoculation methodology had lower initial populations in 

comparison to the other inoculation strategies, highlighting the potential applications of powder-

based inoculation methodologies onto SS surfaces. 

Inoculating powdered food matrices to simulate cross-contamination onto food contact 

surfaces yields higher pathogen populations on surfaces compared to glass beads. However, this 

method might not transfer sufficient pathogens to the target surface to accurately represent 

potential cross-contamination scenarios. If the residual Salmonella populations on the target 

surface are too low, it becomes challenging to quantify sanitation parameters, as the inactivation 

21 

 
achieved by the technology may fall within the margins of experimental error. Thus, for the 

inoculated food powder strategy to be more widely applicable in dry sanitation, the initial 

populations within the powder should be approximately 7–8 log CFU/g to ensure high enough 

starting levels and to replicate the approximate initial populations used in other low-moisture 

food studies. This microbial load can be achieved in flour through a lawn-liquid inoculation 

methodology explored by Hildebrandt, et al. (2016), applicable only if wheat berries (flour 

precursors) are inoculated and equilibrated before milling, thus preventing any net moisture 

increase in the system. 

In summary, the ideal method for inoculating dry food powder for use in dry sanitation 

studies should (1) minimize water usage, (2) use a relevant contaminated food product as the 

cross-contamination vector, (3) maintain high initial population levels to ensure adequate transfer 

to target food contact surfaces for sanitation experiments, and (4) keep water activity and relative 

humidity low throughout the experiment to mirror typical environmental conditions during 

processing. 

Understanding how powdered food matrices adhere to food-contact surfaces could more 

accurately represent contamination scenarios in low-moisture food processing systems, offering 

insights for refining the dry powder inoculation method. 

Powder Adhesion onto Food Contact Surfaces 

In general, powder processing, involving mechanical actions such as sifting and grinding, 

produces dust that disperses and settles on all available surfaces, requiring cleaning (Figure 1). 

22 

 
Figure 1: Accumulated wheat meal on a milling attachment after milling inoculated and 
equilibrated wheat berries 

Particle adhesion to surfaces primarily occurs through electrostatic attractions. Particles 

can become charged through friction from particle-to-particle collisions or from externally 

applied voltages, with electrical charge facilitating attraction between particles (Prasad et al., 

2016). Charged particles can be generated in several ways, including the triboelectric effect, 

where electric charge transfer and generation occur through physical contact or friction (Bailey, 

1998). Another method is corona discharge, involving the application of voltage to a powder to 

charge its particles (Bailey, 1998). 

Charged particle adhesion to surfaces presents challenges in pharmaceutical processing 

and food production, especially within product lines (Ghori et al., 2015). In dry food processing 

systems, the accumulation of food particulate dust with triboelectric charge on food contact 

surfaces is widespread. However, the accumulation of charged powder on surfaces can also have 

advantageous applications in food processing; both electrostatic and non-electrostatic charging 

methods are often used for uniform coating of food products with spices and seasonings 

(Somboonvechakarn & Barringer, 2012). These coating principles can be deliberately applied to 

surfaces. Simply stated, by applying a voltage to a selected powder, the powder can adhere to an 

23 

 
 
electrically grounded surface due to the electric charge gradient between the particle and the 

surface. Powder coating, which involves uniformly applying and distributing powdered paint 

particles onto metal surfaces, is widely used in the automotive industry (Pilcher, 2001) and 

general manufacturing processes to enhance corrosion resistance (Fedrizzi et al., 2007). 

Low-moisture food powder adhesion and removal from stainless steel surfaces has been 

recently studied. Klug, et. al, found that at lower relative humidities (20 and 40%), triboelectric 

charging significantly increased the adhesion rates of custom-fabricated all-purpose flour (U.S. 

Standard Mesh No.’s 60–80) on #304 electropolished SS coupons (2023) by using a simple 

triboelectric charging tube device. This was a novel approach to modeling equipment 

contamination in LMF processing systems. However, the study only used tribocharging as the 

method of charged particle adhesion to stainless steel surfaces and did not investigate the 

differences in composition and surface finish of the stainless steel. 

Using electrostatic powder coating to adhere charged low-moisture food powders onto 

food contact surfaces could be a practical method for simulating the accumulation of food 

powder on equipment surfaces during processing. Incorporating Salmonella into food powders 

might offer an innovative way to affix inoculated food powders onto equipment surfaces. This 

approach could potentially secure high microorganism populations within dry foods to stainless 

steel food contact surfaces without introducing excess moisture, thereby altering pathogen 

behaviors such as desiccation and thermal resistance, and simultaneously simulating potential 

contamination scenarios. If the adhered powder exhibits high levels of Salmonella (>8 log 

CFU/g), it could leave sufficient populations on the target surface area to evaluate the 

effectiveness of new contamination methods. If there are consistent and replicable populations (> 

24 

 
4 log CFU/cm2) remaining on the surface post-cleaning, it will be enough to determine 

significant differences in Salmonella populations before and after sanitation treatments. 

When selecting the target SS surface, considerations should include the SS composition 

(grade), and surface finish. The roughness and microscopic grooves of the target surface could 

influence powder adhesion and microbial transfer. 

Knowledge Gaps Within Current Literature: Dry Sanitation Methodologies 

Considerations for evaluating new electromagnetic sanitation technologies should include 

exposure time, emitter-target distance, and radiation intensity for creating descriptive dosage 

models. In challenge studies, targeting a 5 log reduction in pathogen populations on foods and 

surfaces is recommended (National Advisory Committee on Microbiological Criteria for Foods, 

2010). This study suggests that achieving a surface inoculation of > 5 log CFU/cm2 and then 

reducing populations by 5 log would reduce surviving populations to below the limits of 

detection. Instead, aiming for a >3 log reduction might be more feasible with dry sanitation 

technologies, reflecting the reduced efficacy of sanitation in dry environments in comparison to 

thermal and chemical inactivation studies. 

Variations in treatment duration, the distance between the radiation source and the target 

surface, and unspecified radiation intensity in prior studies (Table 1) limit the usefulness and 

applicability of these findings. In some prior research, exposure times extended to hours, 

impractical for continuous operation of processing lines. Differences in distance affect the ability 

to replicate experiments and compare them with other studies; as distance from the source 

increases, radiation intensity decreases due to the inverse square law. Additionally, not specifying 

25 

 
the radiation intensity or using incorrect units1 for reporting it hinders comparisons across studies 

of UV-C technologies. Without the intensity value, it is impossible to calculate the radiation dose 

applied to microorganisms on the target surface. Clarifying the term “intensity” as it applies to 

UV-C and IR technologies could improve understanding of how radiation affects the target 

surface. 

Consistently reporting sanitation parameters will propel sanitation innovations forward, 

offering a preliminary, evidence-based parameters for dosage modeling. This provides both 

industrial and academic researchers with a solid starting point for future experiments and the 

potential adoption of these technologies. 

1 The term intensity has different definitions and SI units depending on the scientific branch of inquiry. In physics, 
intensity is the power transferred per unit area (W/m2). Confusingly, intensity has been used as a common term to 
refer to different quantities such radiant intensity (W/sr), spectral intensity (W/sr.m), specific intensity (spectral 
radiance) (W/m2/nm), radiance (W/sr.m2), irradiance (W/m2), and radiant exitance (W/m2), among others. 

26 

 
 
 
MATERIALS AND METHODS 

Bacterial Strain and Culture Preparation 

Salmonella enterica strains Agona (447967), Montevideo (488275), Tennessee (K4643), 

Enteritidis Phage Type 30 (ATCC BAA-1045), Mbandaka (698538), and Reading (Moff 

1804180 were sourced from the Center for Food Safety and Applied Nutrition (Bedford Park, IL, 

US). Cultures were stored in a −80 °C cooler within an 80% (v/v) sterile glycerol solution prior 

to resuscitation. 

To create stock and working plates, cultures were taken out of the freezer and left to thaw 

for 5 min. One loop (10 µl) of each strain was placed into individual 9 ml of room temperature 

tryptic soy broth (TSBYE) (BBL, BD, Sparks, MD, US) supplemented with 0.6% yeast extract 

(m/v) (Bacto, BD, Sparks, MD, US), then vortexed. The cultures were incubated at 37°C for 24 ± 

2 h. After incubation, each strain was streaked onto individual plates (15 × 100 mm) of tryptic 

soy agar (Difco, BD, Sparks, MD, US) with 0.6% yeast extract (TSAYE) to isolate colonies to 

create a stock plate. Stock plates were incubated at 37°C for 24 ± 2 h, wrapped in Parafilm, and 

stored for up to six months. 

From the stock plate, one colony of each strain was harvested aseptically using a 10 µl 

inoculum loop into individual 9 ml tubes of TSBYE, vortexed, and incubated at 37°C for 24 ± 2 

h. One loop (10 µl) of culture was streaked onto individual TSAYE plates and incubated at 37°C 

for 24 ± 2 h to create a working plate. Working plates were wrapped in Parafilm and stored up to 

one month. To create additional working plates, individual colonies were harvested from the 

stock plate. 

27 

 
 
Wheat Berry Preparation and Inoculation 

Hard red winter wheat and soft white wheat berries (Palouse Farms, Palouse, WA, USA) 

were purchased from an online retailer. An 80/20 ratio (m/m) of hard red winter wheat and soft 

white wheat berries were used as a basis for all-purpose wheat flour fabrication. The 80/20 wheat 

berry ratio was prepared in 1000 g batches for each experimental run. For the purposes of this 

research, an “experimental run” groups data and results gathered within the same day using the 

same batch of wheat berries. The wheat berry mixture was partitioned into a large 25.4 cm × 38 

cm sample bag (Whirl-Pak LLC, Nasco Sampling, Pleasant Prairie, WI, USA), hand mixed, and 

spread into an even layer on a quarter-sheet aluminum pan within a custom equilibration 

chamber, set to 45% relative humidity, for 48 ± 2 h to equilibrate to a water activity (aw) ~0.45 

prior to inoculation. 

1 ml of each Salmonella culture was pipetted onto large (150 mm × 15 mm) TSAYE 

plates and spread using an L-shaped spreader. The lawn plates were incubated at 37°C for 24 ± 2 

h. After, the lawns were harvested in 9 ml of 0.1% (m/v) buffered peptone water (BPW) (Difco, 

BD, Sparks, MD, US) using an L-shaped spreader. The harvested cultures were dispensed into a 

single 250 ml centrifuge bottle using a 5 ml glass auto-pipette. The combined Salmonella 

cultures were centrifuged for 15 min (SLA-1500, 4500 rpm, 3000×g). After centrifugation, the 

supernatant was poured off the inoculum, and the pellet was resuspended in 25 ml of BPW. The 

initial Salmonella populations in the inoculum were ~11.4 log CFU/g. 

The inoculum was pipetted to the uninoculated, equilibrated wheat berry mixture. The 

sample bag containing the wheat berries was sealed and hand massaged for 5 min to distribute 

the inoculum on the surface of the berries. After, the berries were allowed to dry on a sterilized 

half sheet plastic tray lined with absorbent pads for 15 min. This step removed excess moisture 

28 

 
 
from the inoculum and facilitated equilibration of the berries. Once dried, the berries were placed 

back into the original sample bag, then transported to a custom equilibration chamber. Here, they 

were evenly distributed on an aluminum half-sheet pan (457 × 330 × 25 cm). They underwent 

further equilibration at 45% relative humidity for an additional 48 ± 2 h, achieving a water 

activity level of approximately 0.45. 

The aw of the uninoculated and conditioned wheat berries was measured prior to 

inoculation using a water activity meter (Model 4TE, Decagon Devices, Pullman, WA, USA). 

Samples of background microbial populations for each wheat berry variety were plated onto 

tryptic soy agar (TSA) (Difco, BD, Franklin Lakes, NJ, US). 

Wheat Milling and Sieving 

The inoculated wheat berries were milled and sieved to simulate a worst-case initial 

contamination scenario where contaminated wheat berries were used for flour fabrication. 

Figure 2: A stand mixer with a grinding attachment 

A KitchenAid mixer (model K5-A, KitchenAid, Troy, MI, US) and milling attachment 

were placed within in a laminar flow biosafety cabinet (Figure 2). 1000 grams of the inoculated 

29 

 
 
 
 
wheat berry mixture was poured into the grinding attachment. The berries were ground into the 

KitchenAid mixing bowl at mixer speed 4 (~125 rpm). The mixing bowl was suspended using a 

plastic sample bag holder to accrue the ground wheat meal and prevent unnecessary spread of 

contaminated products. After grinding, the bowl containing the wheat meal was transferred into a 

1.82 m × 1.21 m chemical fume hood (NLS 637, Fisher American, Rockford, IL, US) that 

housed a mechanical sieve (Model H-4330, Humboldt Manufacturing Corporation, Elgin, IL, 

USA). The relative humidity of the hood (~33% for all experimental runs) was displayed using a 

digital hygrometer (model TP50, ThermoPro, Inc., Duluth, GA, US). 

The wheat meal was sieved for 5 min using US standard mesh sizes No.’s 20, 70, 100 

(Figure 3) and 200 to fabricate all-purpose flour from the wheat meal, following 21 C.F.R 137 

requirements (Title 21 C.F.R. § 137.105) First, wheat meal (~300 g) was added to the No. 20 

sieve along with a small rubber ball to promote proper sieving. The meal was sieved in portions 

since 1000 g could not be sieved simultaneously. On average, the wheat meal took three 5 min 

cycles to sieve all 1000 g of the fabricated wheat meal. 

30 

 
Figure 3: Sieving system used for flour fabrication. From top to bottom, a lid, a U.S. Standard 
No.’s 20, 70, 100, and 200 mesh, followed by a sieve bottom 

To follow US standards for flour, all particles that did not pass through the No. 70 mesh 

(> 212 µm) were discarded into a biohazard container. After each 5 min sieving cycle, particles 

that passed from the No. 70 mesh to the No. 200 mesh were classified as “flour” and collected 

into an 18 oz. sample bag for later use using a sterile spoon. From the initial 1000 g of wheat 

meal, approximately 80–100 g of all-purpose flour was produced through the milling process, 

intended for utilization in the powder coating inoculation methodology section. Coarse particles 

that could not be classified as flour were disposed of after the sieving process. 

To assess the effects of sieving on Salmonella populations adhering to the wheat berries 

throughout the milling process, triplicate samples of the berries were collected before grinding, 

after grinding, and from each sieve following a single 5 min sieving cycle. 

31 

 
 
Stainless Steel Coupon Preparation 

Twenty stainless steel circular rounds (14 gauge, 0.19 cm thickness, 6.43 cm diameter) 

were custom fabricated (Stainless Supply, Monroe, NC, USA) with three grades and surface 

finishes (#304 brushed, #316L brushed and #304 mirror finish). The circular coupons were used 

to simulate metal equipment surfaces in a production line. One coupon from each stainless steel 

grade and finish was set aside from the sampling stock for reference and imaging purposes 

(Figure 4). 

Figure 4: #304 brushed finish (left), #316L brushed finish (center), and #304 mirror finish 
(right) stainless steel coupons 

The mass of each coupon was measured using a benchtop balance (OHAUS Explorer, 

model E02140, Parsippany, NJ, US), with the measurement recorded and hand-etched near the 

rim of each coupon using a handheld rotary tool (Dremel, model 395, type 5, Robert Bosch Tool 

Corporation, Mount Prospect, IL, USA). 

Before each experimental run, the coupons were sterilized by autoclaving at 121.8°C for 

30 min (121348 Pa) to inactivate Salmonella residues from previous experiments. Inside a 

chemical fume hood, the coupons were placed into a 1 quart metal paint can, an acetone-safe 

container holding 250 ml of acetone. The can was sealed using a rubber mallet, and the coupons 

were submerged for 15 min to eliminate surface resides, following procedures established in 

prior work (Suehr, 2020) (Figure 5). 

32 

 
 
 
Figure 5: Stainless steel coupon preparation 

The coupons were first removed and placed onto a wire cooling rack for 1 min to 

facilitate acetone evaporation. Subsequently, they were submersed in a container filled with 

deionized water for one minute, ensuring the removal of any residual acetone from their surface. 

After, the coupons were placed evenly distributed on the wire rack. Excess water was removed 

using kimwipes and paper towel and transferred to a drying oven (~100°C) for 10–30 min to dry 

completely and prevent rusting. Once dried, the coupons were allowed to cool to room 

temperature before use in electrostatic powder coating. 

Evaluation of Electrostatic Powder Coating Inoculation Methodology 

The fabricated all-purpose flour was applied to stainless steel surfaces using a powder 

coating gun. The goal was a target population of > 5 log CFU/cm2 on the coated coupons and > 4 

log CFU/cm2 on the surface of visibly cleaned coupons. 

33 

 
 
 
The powder coating set-up was housed within a modified silica blasting chamber (Model 

SBC 420, Atlas Auto Equipment, Greenfield, IN, USA), which contained a clamp stand, a 46.9 

cm x 37.8 cm x 28.3 cm gasket box with the front panel removed (model 1933, Sterilite 

Corporation, Townsend, MA, US), a small handheld vacuum (model 47R51, Bissell, Walker, MI, 

US), a humidity controller (model IHC-200, INKBIRD Tech. C.L., Shenzhen, CN), and a 

humidifier (model VUL520W, Kaz USA, Incorporated, Malaborough, MA, USA) (Figure 6). 

Figure 6: Labeled photo of equipment used for electrostatic powder coating within an 
equilibrated chamber 

During experimental runs, the gasket box was secured in position using the metal notch 

on the chamber’s far back wall while the clamp stand’s position was maintained with a reference 

line marked by tape. The combined 45° angled PVC pipe and 20.3 cm straight PVC pipe (7.62 

cm nominal diameter) localized the area of powder accrual onto the surface of the portable 

benchtop scale and the SS coupon (OHAUS Navigator, model NV223, Parsippany, NJ, USA). 

34 

 
 
To inoculate the stainless steel coupons, the powder coating gun (model 917288, 

Craftsman, Towson, MD, US) was suspended 39 cm from the bottom of the chamber using a 

clamp stand. The grounding wire from the powder coating gun power source was fixed to 

metallic surfaces on the scale using a piece of electrical tape. The relative humidity inside the 

powder coating chamber was maintained at 45% using a humidity controller and a humidifier to 

represent average low-moisture food processing conditions. The initial relative humidity within 

the chamber was recorded at the beginning of each experimental run. 

40 g of the inoculated all-purpose flour was added to the coating gun’s powder reservoir. 

For mass measurements during powder coating, a portable benchtop laboratory scale was used. 

The scale was tared, and a coupon was placed and tared on it. The powder coating gun’s trigger 

was secured in position with electrical tape and activated by an on-off switch on a separate 

power strip. 

Upon activation, the inoculated wheat flour in the powder cup was expelled through the 

high voltage tip of the gun. It then dispersed through the PVC pipe apparatus, primarily 

depositing onto the selected coupon type and to a lesser extent on the sensing surface of the 

scale. Once the scale registered a mass of 0.2–0.3 g (accounting for both flour and air pressure), 

the powder coating gun was turned off. Any excess flour on the surface of the scale was brushed 

off using a soft-bristled, 5 cm wide pastry brush with polyester bristles (Model 5552503, Vikan, 

Skive, DK), leaving only the flour adhered to the coupon, with a target value of approximately 

0.1 g, was documented in a laboratory notebook. 

#304 and #316L SS brushed finish coupons were coated with inoculated flour (n=48). 

Half of the coated samples were transferred into sample bags without a brushing step as negative 

controls. Subsequently, the remaining half were brushed to a “visibly clean” state using the soft-

35 

 
bristled brush described earlier, with the brush being alternately chosen from a stock of two per 

each experimental run. In this experiment, “visually cleaned” was defined as the absence of 

particles visually detectable to the naked eye, a criteria used in prior research (Daeschel et al., 

2023; Moretro et al., 2020). All experimental runs were conducted in triplicate. 

To create a visibly cleaned surface, the coupon was smoothly brushed ten times from top 

to bottom, starting from the northern edge of the coupon to the southern edge, followed by a 

180° rotation of the brush to use the opposite side for brushing ten times from left to right from 

the western coupon edge to the eastern edge (Figure 7). The visibly cleaned coupon was placed 

aside into a small metal tray and removed from the chamber. The assumed mass of remaining 

particles was 0.01 g, 1/10 of the adhered mass for Salmonella population calculations since trace 

amounts of flour particles remained on the surface after visibly cleaning. 

Figure 7: Brushing protocol to create visibly cleaned coupons 

Microscope images of the untreated, coated, and visibly cleaned coupons were taken 

using a trinocular microscope (series SM-1T, AmScope, Irvine, CA, US) with an attachable 

camera (model MU1000-HS, AmScope, Irvine, CA, US), at 10 magnification. 

36 

 
 
Application of UV-C, Far UV-C, and IR Radiation 

For the sanitation experimentation, the powder coating inoculation methodology was 

applied to #304 SS brushed and mirror finish coupons (Figure 8) to evaluate the effect of surface 

finish on sanitation efficacy. Samples (n=206) were visibly cleaned using the same methods 

described in Figure 7. Each experimental sanitation run was conducted in triplicate. Negative 

controls (n=68), which were coated and visibly cleaned, were used for comparison with treated 

samples. 

Figure 8: Coated #304 SS brushed finish (A) and #304 SS mirror finish (B) coupons 

After being taken out of the powder coating chamber, the coupons were brushed once 

from top to bottom (northern edge to southern edge) to clear off any additional particles that 

clung to the coupon surface from their time inside the chamber after being visibly cleaned. The 

underside of the coupon was then carefully wiped a delicate task wipe that had been sprayed with 

75%, 200 proof ethanol, to inactivate any residual Salmonella populations that could affect the 

results following the sanitation treatment. Subsequently, the prepped coupon was placed into a 

labeled plastic sample weigh boat, facilitating safer and more efficient transport from the powder 

coating chamber to the chamber where UV-C, Far UV-C, and IR radiation technologies were 

applied for sanitation. 

37 

 
 
An equilibration chamber (Economical glove box, model 34788-00, Cole-Parmer, Vernon 

Hills, IL, USA) was used to house the sanitation technologies used in the experiment (Figure 9). 

The equilibration chamber was set to approximately 45% relative humidity and verified before 

treatment using a precision handheld psychrometer (model RH 390, Extech Instruments, 

Knoxville, TN, US). 

Figure 9: The sanitation treatment chamber with racks and two slots (8 cm × 2.2 cm) (in pink) 
on top of the chamber for housing the selected technologies 

Two 8 cm × 2.2 cm slots were cut into the top plexiglass sheet to accommodate the 

sanitation technologies, facilitating easy removal and replacement of each sanitation device as 

required by different experimental run. For each experiment, the chamber included a repurposed 

metal sample holding rack with metal notches, an HDPE cutting board (25.4 × 25.4 × 1.27 cm), 

and three plexiglass sheets (31.1 × 22.8 × 0.5 cm). The distance from the sanitation device was 

adjusted using these sheets, accommodating the slight variations of the suspended height of each 

emitter. Distances of 10 cm and 15 cm from the device were measured and fixed by adjusting the 

metal notches on the wire rack, considering the height of the sheet under the sample (Figure 10). 

38 

 
 
The sample at a 5 cm distance was positioned on one HDPE sheet atop three plexiglass sheets, 

while those at 10 and 15 cm distances were set on one plexiglass sheet within their designated 

metal notches. 

Figure 10: Distance measurements within the sanitation chamber 

To generate UV-C at a wavelength of 254 nm, a Biolux® 6 W UV-C irradiating strip 

fixture (model 40-1106, Atlantic Ultraviolet Corporation, Hauppauge, NY, US) and a mercury 

bulb were used. For far UV-C at a wavelength of 222 nm, a 40 W Excimer Far UV-C lamp 

(model FRL-EMY-8-40W-FUVC-KT-120V, Larson Electronics, Kemp, TX, US) using corona 

discharge was used. IR was generated by a 500 W quartz infrared heater lamp (model QIH-120-

500T/S, Ushio America Incorporated, Cypress, CA, US) that emitted IR from a horizontal burn 

position. The IR bulb was housed within a custom fabricated SS fixture. The fixture was 

fabricated from a 31.8 × 5.1 × 0.2 cm #303 SS bar, with a 22.2 cm rectangular hole removed 

from the bottom for IR bulb installation by the Department of Biosystems and Agricultural 

Engineering Fabrication Shop (Michigan State University, Esat Lansing, MI, US). Eight 2.54 cm 

39 

 
 
diameter holes were cut into the stainless steel bar to allow for heat removal. The exposed wires 

from the IR bulb were mounted between heat-resistant ceramic standoffs (1.9 cm × 0.95 cm 

diameter) and secured using 1.9 cm long Philips head screws and 0.95 cm diameter #316 

stainless steel washers. High-temperature stranded wires with fiberglass and mica insulation 

were used to connect the IR bulb to a variable voltage controller switch (model 55150-SU 

E1030I, Sunlite, Brooklyn, NY, US) and then to a three-pronged power cord (Figure 11). The 

voltage was set to a maximum of 120 V for all experimental runs that required IR. To prevent 

overheating, excess heat from the IR device was dissipated using a 6.6 W fan (97 mm × 33 mm 

BBQ Blower Fan, WDERAIR, Shenzhen Shaoyuanqiao Technology CO. Ltd., Shenzhen, CN), 

which directed air flow from right to left through the metal housing and over the bulb. Beneath 

the IR fixture, there was a 15.2 cm × 15.2 cm Ultra-High-Temperature Quartz Glass sheet 

capable of withstanding temperatures up to approximately 1150 °C. This sheet mitigated the 

impact of heat on the plexiglass sheet on the top of the equilibrated chamber (Figure 9), and the 

impact of cooling air flow onto the sample coupon. 

Figure 11: UV-C 254 nm device (A), Far UV-C 222 nm excimer lamp (B), and infrared lamp and 
ballast (C) 

Visibly cleaned coupons were placed in a sample boat within the chamber and positioned 

on the wire rack at the chosen distance from the emitter. 

Each device was controlled using a power strip. When the device was powered on (Figure 

12) a handheld timer was started concurrently to mark the length of exposure. The device was 

40 

 
 
turned off once the predetermined exposure time was reached, as indicated by the timer (Table 

2). 

Table 2: Treatment factors applied to stainless steel coupons 

Technology 
UV-C 254 nm 

Far UV-C 222 nm 

Infrared Radiation 

Distance From Emitter 
5 
10 
15 
5 
10 
15 
5 
10 
15 

Length of Exposure (min) 
[0.33, 0.66, 1, 2, 3, 5, 10, 20] 
[0.33, 0.66, 1, 5, 10] 
[0.33, 0.66, 1, 2, 3, 5, 10] 
[0.33, 0,66, 1, 2, 3, 5, 10, 20] 
[0.33, 0.66, 1, 5, 10] 
[0.33, 0.66, 1, 2, 3, 5, 10] 
 [1, 2, 3, 5, 10, 20, 60] 
[1, 5, 10, 60] 
[1, 2, 3, 5, 10, 60] 

The experimental design of the sanitation portion explored the sanitation method, with 

three levels (UV-C, Far UV-C, IR), the distance from the emitter (i.e. intensity) with three levels 

(5, 10, 15 cm from the emitter), and the length of exposure, which ranged from 10 s to 60 mins 

(Table 2). Due to the exploratory nature of the sanitation experimentation, various exposure 

times were tested and selected to meet the > 3 log CFU/cm2 reduction goal on the stainless steel 

coupons. 

Figure 12: Sanitation of visibly cleaned SS coupons using UV-C (A), Far UV-C (B), and IR 
devices (C) 

After the target exposure time was reached, the weigh boat and treated coupon were 

removed from the chamber, cooled as necessary, and transferred into labeled 18 oz sample bags. 

41 

 
 
 
 
 
 
  
 
 
Changes in relative humidity changes following a 60 min IR treatment were monitored using a 

handheld psychrometer, with readings taken at 10 min intervals. 

Intensity Measurements 

Intensity refers to the power (radiant flux) per unit area of electromagnetic radiation 

reaching a surface, measured in W/m2. It has the same units as irradiance, the radiant flux 

received by a surface per unit area, and radiosity, the radiant flux exiting a surface per unit area. 

In this study, intensity refers to the irradiance of SS coupons exposed to UV-C, Far UV-C, and IR 

radiation, since the radiation impinges on the surface (and microorganisms) from a single 

direction. 

The theoretical intensity of the energy emitted from the radiation source to a target 

surface can be described using the inverse-square law (Equation 1) with the assumption that 

energy is emitted in a spherical manner from a point source to a surface. The intensity of the 

radiation on a surface at a specified distance from the emitter was calculated from the following 

equation (1): 

I = 

P
A

=

P
4πr2 

(1) 

Where I is the intensity (W/m2), P is the power of the emitter (W), A is the surface area of 

the sphere (m2), and r is the distance from the emitter to the target surface (m). It is common in 

literature to report UV-C intensity values in mW/cm2. 

The UV-C radiation intensity for both UV-C devices was measured using a UV-C light 

meter (Model UV512C, General Tools & Instruments LLC, Secaucus, NJ, US). Intensity values 

were filtered as average values on the device display prior to recording the intensity 

measurements using the AVG function within the device. 

42 

 
 
A #304 brushed finish SS coupon was traced onto a plastic sample boat to model UV-C 

exposure on the surface of the coupon (Figure 13). 1 cm circles were cut on the model coupon 

tray at the center of the coupon, 1.6 cm from the center, and 3.2 cm from the center, 

corresponding with the middle of the coupon surface, the mid-edge, and outer edge, respectively, 

to allow access for the 1 cm diameter sensing region of the UV-C light meter. 

Figure 13: Simulated coupon surface used for UV-C and Far UV-C intensity measurements 

The sample coupon surface was placed at (5, 10, 15 cm) from the emitter using a clamp 

stand within the equilibrated sanitation treatment chamber (Figure 14). The intensity of incident 

energy at 5 cm was recorded for all technologies with several variations. Initially, the intensity 

was recorded with a “cold-start,” meaning the intensity measurement started concurrently with 

powering of the technology. Then, additional measurements were taken after the device was 

powered for 5 min to determine the intensity after a 5 min “warm-up” time. 

43 

 
 
For UV-C, the intensity at separate locations on the coupon were measured using the 

“cold-start” method to determine intensity variations across the surface, using a method adapted 

from Bolton & Linden (2003).  

The intensity values reported in this study for dosage modeling were recorded under 

“cold-start” conditions to represent the probable use of the technologies on the processing line, 

where “warm-up” time may be minimized or disregarded to reduce the downtime of equipment 

for sanitation. 

Figure 14: UV-C intensity measurement set-up within the sanitation treatment chamber 

The experimental IR intensity (W/cm2) was calculated using an alternative method based 

on heat transfer principles, considering the primary effect of IR on a surface is heating. Given its 

44 

 
 
minimal thickness, the coupon was considered as a lumped system. The equation (2) below 

characterizes the total energy absorbed by the coupon exclusively through its surface: 

q = mcp(Tfinal − Tinitial) 

(2) 

Where q is the energy emitted to the coupon surface (J), m is the mass of the coupon (kg), 

cp is the specific heat of the #304 SS. Tfinal is the recorded temperature (°C) of the coupon at the 

point where the percent change in temperature per minute was less than 10%. Tinitial is the starting 

temperature of the coupon (°C). To calculate the IR intensity on the surface, q was divided by 

both the surface area of the coupon and the time to reach Tfinal. 

The intensity of the emitted infrared radiation was recorded using a modified temperature 

measurement device (Figure 15). A 1.1 mm hole was partially drilled into the center of a #304 

brushed finish coupon to implant the tip of a 36 G T-type thermocouple which was used to record 

the incident temperature at the surface of the coupon. The thermocouple tip was secured in the 

hole using autoclave tape, and the hole was then filled with heat-resistant thermal paste to 

remove air that could skew temperature measurements (Figure 15 A). The coupon was encased 

within high-temperature resistant fiberglass insulation (Figure 15 B) to shield the thermocouple 

wire from high temperatures. A rectangular channel was cut into the insulation to route the 

thermocouple wire out of the equilibrium chamber. Intensity measurements were recorded over 

60 min with a sampling rate of 2 s using a temperature data logger (model RDXL4SD, OMEGA 

Engineering Incorporated, Norwalk, CT US). 

45 

 
 
Figure 15: (A) Modified #304 SS coupon with 0.11 diameter cm hole with affixed thermocouple, 
(B) A 10 x 10 x 2.5 cm block of high temperature fiberglass insulation with a circular indentation 
cut out to house the coupon in the center, and (C) IR irradiance measurement device with a 
visible channel 

Dosage Calculations 

Dosage refers to the intensity (W/m2) of incident electromagnetic radiation impinged on a 

surface over a measured length of exposure (s). A more accurate term for dosage, especially for 

UV-C radiation, is fluence or radiant exposure, since incident UV-C light passes through most 

microorganisms with a minimized percentage of absorption (Bolton & Linden, 2003). In general, 

dosage refers to the total incident energy absorbed by a surface. In this study, dosage refers to the 

fluence of SS surfaces exposed to UV-C, Far UV-C, and IR radiation. Dosage can be simply 

described Using Equation 3 (Demeersseman et al., 2023): 

Dosage = Intensity × length of exposure 

(3) 

Where dosage is J/m2, intensity is W/m2, and length of exposure is in seconds. For the 

purposes of this experiment, dosage was reported in mJ/cm2 to remain consistent with generally 

used units of intensity (mW/cm2). 

Plating and Enumeration 

5 ml of BPW was added aseptically to all bagged stainless steel coupon samples, whether 

the samples were coated, visibly treated, or exposed to dry sanitation technologies. The bags 

were closed and hand massaged for 1 min to distribute the diluent across the surface of the 

46 

 
 
 
coupon and to collect any remaining flour particles. Additional samples of Salmonella 

populations on the soft-bristled brush were diluted in 5 ml BPW. The samples were serially 

diluted in 9 ml buffered peptone water, plated onto modified tryptic soy agar (MTSA) (+ 0.05% 

ammonium ferric citrate (Alfa Aesar, Tewksbury, MA, US) + 0.03% sodium thiosulfate 

pentahydrate (Fisher Chemical, Waltham, MA, US), (Difco, BD, Franklin Lakes, NJ, US) and 

incubated at 37 °C for 48 ± 2 h. Any black colonies found on the surface of the media were 

considered as a colony forming unit and were recorded within a laboratory notebook. Population 

counts and log reductions were recorded and calculated using a spreadsheet, Microsoft Excel 

(version 2404 Microsoft, Redmond, WA, US). To determine the limits of detection (LOD), one 

colony forming unit at the highest dilution level used within the study was used to calculate the 

corresponding populations (log CFU/cm2). For samples with a single serial dilution that plated 

the entirety of the diluent, the limit of detection for Salmonella was −1.5 log CFU/cm2. For 

samples with multiple serial dilutions, the limit of detection was −1.1 log CFU/cm2. The LOD 

for samples with multiple serial dilutions was lower because not all the diluent was plated onto 

agar plates. The residual diluent in the sample bag contained Salmonella populations that were 

not enumerated. In contrast, the single dilution samples plated all of the diluent on agar plates, 

enumerating all Salmonella that were present within the diluent and sample bag. 

Statistical Analysis 

General descriptive statistics for Salmonella populations (mean, standard deviation, 

standard error) were generated using the descriptive statistics procedure. Salmonella populations 

were analyzed using a general linear model procedure (GLM) within ANOVA to determine the 

significance (α=0.05) of factors and their interactions. ANOVA was conducted on the milling 

process (grind, sieve size), coating experiments (SS grade, SS finish, brushing treatment), and 

47 

 
negative control samples (experimental run) to determine significance of factors. Following this, 

all-pairwise comparisons of the means were conducted using Tukey’s T-test (α=0.05) to reduce 

the chance of type I error through the comparison of multiple variables. 

The relationship between dosage and Salmonella reduction for each technology (UV-C, 

Far UV-C, and IR) was described using a linear regression model. The quality of the model was 

assessed using reported R2 and RMSE values. Model parameters and their 95% confidence 

intervals were calculated from the linear regression. The estimated slope parameter and its 95% 

confidence interval was used to calculate the dosage required for a target sanitation efficacy (log 

reduction, CFU/cm2). Analysis of covariance (ANCOVA) was employed to determine whether 

the sanitation technology used had a significant effect on the predicted dosage model (α=0.05). 

The data analysis was conducted using Minitab, a commercial statistical analysis software 

(Minitab 21, State College, PA, US). 

48 

 
Grinding and Sieving 

RESULTS 

Following the inoculation of the raw wheat berries, the impact of the milling process on 

Salmonella populations were observed. There was a significant reduction (p=0.007) after the 

wheat berries were ground into wheat meal (Figure 16). 

Figure 16: 95% confidence intervals of wheat berry Salmonella populations throughout the 
milling process. Pre-grind (unground berries) and post-grind (berries milled into wheat meal). 
Mean populations are listed to the right of each interval plot 

After the sieving process, more samples of inoculated flour were collected from 

individual sieves. The factor of mesh size was found to be significant (p=0.034), with pairwise 

comparisons showing that samples from No. 200 mesh had significantly lower Salmonella 

populations than those from No. 20 mesh (Figure 17). 

49 

 
 
 
Figure 17: 95% confidence intervals for wheat meal and flour particles within each respective 
U.S. Standard Mesh after one 5 minute sieving cycle. Mean populations are listed to the right of 
each interval plot 

After completing the grinding and sieving process, the average Salmonella populations in 

the fabricated flour prepared for the powder coating experiment were 7.94 ± 0.11 log CFU/g, 

indicating a loss of <1 log CFU/g during milling. 

Evaluation Of Powder Coating Inoculation Methodology 

The electrostatic powder coating device was able to adhere inoculated flour on stainless 

steel surfaces (Figure 18). 

50 

 
 
Figure 18: Microscopic images of coated (left) and brushed to visibly clean (right) #304 SS, 
brushed finish, at 10X magnification 

Before starting sanitation trials, the effectiveness of the dry inoculation methodology was 

assessed. Preliminary trials were conducted to evaluate the impact of stainless steel grade, finish, 

and brushing to visually clean state on Salmonella populations. ANOVA showed there were no 

significant differences in coated and brushed populations between each stainless steel grade 

(p=0.22). The Salmonella populations on the coupons were significantly different (p<0.001) after 

visibly cleaning, with ~ 4 log CFU/cm2 remaining on the surface (Figure 19). There were no 

significant differences in Salmonella populations adhered to #304 SS brushed finish and mirror 

finish coupons (p=0.480). 

51 

 
 
Figure 19: 95% confidence intervals of Salmonella populations on coated and visibly cleaned 
stainless steel coupons 

The consistency of Salmonella application on SS coupons for sanitation experimental 

runs was measured using a one-way ANOVA on inoculated, non-irradiated control samples 

(Table 3). There were no significant differences in negative control populations between runs 

within the sanitation portion of the experiment (p=0.06). The mean Salmonella population for all 

visibly cleaned non-irradiated control samples were 3.09 ± 0.16 log CFU/cm2 (mean ± SD). 

Table 3: Descriptive statistics and 95% confidence intervals for inoculated, non-irradiated 
control samples for different sanitation experimental runs  

Factor 
Run 1 
Run 2 
Run 3 
Run 4 
Run 5 
Run 6 
Run 7 

N 
3 
3 
3 
3 
3 
3 
3 

Mean 
3.0279 
2.9468 
3.2987 
3.1624 
3.1468 
3.0682 
2.983 

SD 
0.0967 
0.1723 
0.1542 
0.0296 
0.0756 
0.1098 
0.188 

52 

95% CI 
(2.8679, 3.1878) 
(2.7869, 3.1068) 
(3.1388, 3.4586) 
(3.0024, 3.3223) 
(2.9869, 3.3068) 
(2.9082, 3.2281) 
(2.823, 3.143) 

 
 
 
Intensity 

The maximum intensity values for UV-C were 6.62 mW/cm2 after 60 s of exposure at the 

surface of the emitter for no warm-up time, and 7.98 mW/cm2 after 60 s of exposure with a 5 

min warm-up time (Figure 20). Intensities measured 5, 10, and 15 cm from the emitter decreased 

as distance increased. 

)
2

m
c
/

W
m

(
y
t
i
s
n
e
t
n
I

9.00

8.00

7.00

6.00

5.00

4.00

3.00

2.00

1.00

0.00

0

10

20
30
40
Length of exposure (s)

50

60

0 cm (No warm-up)

0 cm (+ 5 min warm-up)

5 cm

10 cm

15 cm

Figure 20: UV-C intensity data at the center of a coupon surface with varying distances from the 
emitter (λ = 254 nm) 

At close distances to the emitter (5 cm), the UV-C intensity varied at separate locations 

on the #304 stainless steel coupon. Intensity measured at the edge of the coupon was shown to be 

approximately 0.20 mW/cm2 lower than at the center (Figure 21). This effect was minimized at 

further distances (10 and 15 cm). 

53 

 
 
 
1.20

1.00

0.80

0.60

0.40

0.20

)
2

m
c
/

W
m

(
y
t
i
s
n
e
t
n
I

0.00

0

10

20
30
40
Length of exposure (s)

50

60

Center of Coupon

16 mm from Center

32 mm from Center (Coupon Edge)

Figure 21: UV-C intensity data at separate locations on coupon surface, 5 cm from emitter (λ = 
254 nm) 

The maximum intensity values for Far UV-C were 10.13 mW/cm2 after 60 s of exposure 

at the surface of the emitter for no “warm-up” time, and 11.72 mW/cm2 after 60 s of exposure 

with a 5 min “warm-up” time (Figure 22). Intensities measured 5, 10, and 15 cm from the emitter 

decreased as distance increased. Because the UV-C and Far UV-C intensity values plateaued 

under 60 s for each specified distance (5, 10, 15 cm), the maximum intensity value achieved at 

the end of recording per specified UV device (60 s, Figures 20 & 22) was referenced for dosage 

modeling. 

54 

 
 
 
14.00

12.00

10.00

8.00

6.00

4.00

2.00

0.00

)
2

m
c
/

W
m

(
y
t
i
s
n
e
t
n
I

0

10

20
30
40
Length of exposure (s)

50

60

0 cm (No warm-up)

0 cm (+ 5 min warm-up)

5 cm

10 cm

15 cm

Figure 22: Far UV-C intensity data at the center of a coupon surface with varying distances 
from the emitter (λ = 222 nm) 

The intensity of IR at 0 cm from the emitter was not recorded due to fire hazard. The 

maximum intensity of IR radiation 5 cm from the emitter was 0.22 mW/cm2 after 60 min of 

exposure (Figure 23). Intensities measured 5, 10, and 15 cm from the emitter decreased as 

distance increased. Because the IR temperature profile did not plateau until approximately 30 

min of recording, the intensity values at each specified distance were selected at the measured 

lengths of exposure for sanitation efficacy data (1, 5, 10, 20 and 60 min) for use in dosage model 

calculations. 

55 

 
 
 
)
2

m
c
/

W
m

(
y
t
i
s
n
e
t
n
I

0.25

0.2

0.15

0.1

0.05

0

0

5 cm

10 cm

15 cm

500

1000

1500

2000

2500

3000

3500

4000

Length of exposure (s)

Figure 23: IR intensity data at the center of a coupon surface with varying distances from the 
emitter 

The measured intensity values were consistently lower than the theoretical intensity 

values calculated using the inverse square law for each technology and distance (Table 4). The 

largest discrepancy was observed between the theoretical and experimental IR intensity values. 

Table 4: Maximum intensity values at specified distances from the emitter 

Technology 

Maximum Intensity Values (mW/cm2) 

10 cm 
Experimental  Theoretical  Experimental  Theoretical  Experimental  Theoretical 

15 cm 

5 cm 

UV-C 
Far UV-C 
IR 

1.04 
2.29 
0.16 

19.10 
127.32 
1591.55 

0.85 
1.25 
0.10 

4.77 
31.83 
397.89 

0.44 
0.68 
0.06 

2.12 
14.15 
176.84 

56 

 
 
 
 
 
 
 
 
 
 
Application of UV-C, Far UV-C, and IR Radiation 

Both time and intensity were varied to capture a diverse range of radiation exposure 

dosages. A 3 log reduction in Salmonella populations at the maximum intensity was targeted for 

each sanitation technology. 

UV-C reached an average 3.41 ± 0.12 log reduction (mean ± SD, log CFU/cm2) after 20 

min of exposure at 1.04 mW/ cm2. Figure 24 displays the range of data collected for sanitation 

efficacy at varying exposure times and intensity values for UV-C radiation. 

4

3.5

3

2.5

2

1.5

1

0.5

)
2

m
c
/
U
F
C
g
o
l
(
y
c
a
c
i
f
f
E
n
o
i
t
a
t
i
n
a
S

0

0

Maximum Intensity (1.04
mW/cm^2)

Maximum Intensity (0.85
mW/cm^2)

Maximum Intensity (0.44
mW/cm^2)

5

10

15

20

25

Length of exposure (min)

Figure 24: UV-C Salmonella sanitation efficacy (log CFU/cm2) vs. length of exposure (min) at 
specified intensities 

Far UV-C reached an average 1.68 ± 0.07 log reduction after 10 min of exposure at 2.29 

mW/cm2. Figure 25 displays the range of data collected for sanitation efficacy at varying 

exposure times and intensity values for Far UV-C radiation. However, the full data was not 

acquired due to the unexpected failure of the Far UV-C device. 

57 

 
 
 
 
 
 
3

2.5

2

1.5

1

0.5

)
2

m
c
/
U
F
C
g
o
l
(
y
c
a
c
i
f
f
E
n
o
i
t
a
t
i
n
a
S

0

0

Maximum Intensity (2.29
mW/cm^2)

Maximum Intensity (1.25
mW/cm^2)

Maximum Intensity (0.68
mW/cm^2)

5

10

15

20

25

Length of exposure (min)

Figure 25: Far UV-C Salmonella sanitation efficacy (log CFU/cm2) vs. length of exposure (min) 
at specified intensities 

IR reached an average 2.98 ± 0.09 log reduction after 60 min of exposure at 0.23 mW/ 

cm2 from the emitter. Figure 26 displays the range of data collected for sanitation efficacy at 

varying exposure times and intensity values for IR radiation. 

58 

 
 
 
 
 
 
3.5

3

2.5

2

1.5

1

0.5

)
2

m
c
/
U
F
C
g
o
l
(
y
c
a
c
i
f
f
E
n
o
i
t
a
t
i
n
a
S

0

0

Maximum Intensity (0.23
mW/cm^2)

Maximum Intensity (0.14
mW/cm^2)

Maximum Intensity (0.09
mW/cm^2)

10

20

30

40

50

60

70

Length of exposure (min)

Figure 26: IR Salmonella sanitation efficacy (log CFU/cm2) vs. length of exposure (min) at 
specified intensities 

Due to the high amount of heat emitted by the IR device, relative humidity fluctuated 

throughout the treatment. Relative humidity and ambient temperature changed in the sanitation 

equilibration chamber (initially set to aw ~0.45) during a 60 min treatment (Table 5). 

Table 5: Relative humidity changes during infrared radiation treatment 

Time (min)  Relative Humidity (%)  Ambient Chamber Temperature (°C) 

0 
10 
20 
30 
40 
50 
60 

41.3 
37.4 
33.9 
29.5 
27.0 
25.4 
24.7 

20.2 
25.4 
28.7 
28.0 
30.1 
30.0 
32.3 

59 

 
 
 
 
 
 
Dosage 

The relationship between Salmonella reduction and dosage applied to the #304 SS 

brushed finish coupons for all three sanitation technologies was expressed with individual linear 

regression analyses and ANCOVA. The regression equations for UV-C, Far UV-C, and IR are 

featured in equations 4–6. 

log (

𝑁0
𝑁

)  = 0.6074 + 0.11555 × UV-C Dosage (mJ/cm2) 

log (

𝑁0
𝑁

) = 0.4272 + 0.06147 × Far UV-C Dosage (mJ/cm2) 

log (

𝑁0
𝑁

) = 0.3029 + 0.17579 × IR Dosage (mJ/cm2) 

(4) 

(5) 

(6) 

A high percentage of the variation in the reduction could be explained by the models, 

with R2 values of 87.90, 86.82, and 94.48% for UV-C, Far UV-C, and IR respectively. 

Additionally, the RMSE for UV-C, Far UV-C, and IR models were 0.27, 0.17, and 0.18, 

respectively indicating a good model fit. The linear regression predicted constant coefficients 

significantly greater than 0 for each model (p<0.001). ANCOVA revealed that the interaction 

between dosage and sanitation technology was significant (p<0.001), indicating that the rate of 

reduction was significantly different between technologies. IR radiation displayed the highest 

reduction rate, followed by UV-C and Far UV-C (Figure 27). 

60 

 
 
 
 
Figure 27: Sanitation efficacy (log CFU/cm2) vs. dosage (mJ/cm2) 

The predicted reduction rate parameters from the linear regression were used to calculate 

the range of dosages predicted to achieve a target reduction value 95% of the time. Predicted 

intercept parameters were not included in the calculations to provide a more conservative dosage 

estimate. Target reduction values ranged from 1 to 5 log reductions (Table 6). 

Table 6: 95% Confidence intervals of the required dosage to meet a target sanitation efficacy 
(log CFU/cm2) 

Sanitation Efficacy 
(reduction) 

log CFU/cm2 
1 
2 
3 

IR Dosage 

UV-C Dosage 

Far UV-C Dosage 

mJ/cm2 
(5.26, 6.19) 
(10.53, 12.37) 
(15.79, 18.56) 

mJ/cm2 
(7.66, 9.94) 
(15.33, 19.88) 
(22.99, 29.82) 

mJ/cm2 
(14.02, 19.38) 
(28.03, 38.75) 
(42.05, 58.13) 

61 

 
 
 
Discussion 

The electrostatic powder coating dry inoculation method achieved higher than 5 log 

CFU/cm2 on the surface of stainless steel coupons on coated coupons. In comparison to other 

studies, the biofilm method from De Oliviera (2010) adhered 4.89 ± 0.03 log CFU/cm2 onto 

#304 SS. Powder coated #304 SS coupons in this study achieved 5.45 ± 0.59 log CFU/cm2. The 

milk powder transfer method by Chen & Snyder (2023) adhered 3.3 ± 0.2 log CFU/coupon and 

had 1.2 ± 0.4 log CFU/coupon of Salmonella populations remaining on #304 SS after cleaning. 

In comparison, the average populations on visibly cleaned coupons for the sanitation portion of 

this experiment were 3.09 ± 0.16 log CFU/cm2. With similar resultant populations in comparison 

to other studies, the powder coating method is a promising dry inoculation methodology for 

cleaning and sanitation studies. 

The powder coating methodology has several advantages in comparison to other food 

contact surface inoculation strategies. First, the inoculation method does not use liquid broths to 

adhere microorganisms to the target surface, minimizing the amount of moisture introduced into 

the experimental environment. Secondly, this method does not rely on biofilm formation or glass 

beads to transfer and inoculate target surfaces with microorganisms. Because of this, the method 

can directly simulate Salmonella contamination from the food product itself to relevant 

equipment surfaces instead of using an unrelated intermediate in the process. Lastly, the method 

does not require mechanical actions such as mixing the target surfaces in a sealed container to 

accrue inoculated powders on the target surface. Instead, the inoculated powder is adhered 

through electrostatic charge, which replicates dust accrual on surfaces generated by equipment 

during operation. Incidentally, the inoculated wheat berry grinding process used in this study 

displayed this phenomenon of dust accrual on the surface of an aluminum grain milling 

62 

 
attachment without the use of an electrostatic powder coating gun (Figure 1). Comparisons of 

microorganism populations between surfaces inoculated using the electrostatic coating gun and 

the triboelectrically-charged powder generated by milling equipment are another potential 

avenue for determining an ideal dry powder inoculation strategy. 

Of the selected technologies, IR had the highest log reduction per dosage (Figure 27), 

followed by UV-C and Far UV-C. However, relying solely on the dosage metric for technology 

decisions can be deceptive. Despite having the highest reduction per dosage, the length of 

exposure (~60 min) needed to achieve a 3 log reduction for IR at its highest measured intensity 

was over twice that needed for UV-C (~20 min) or Far UV-C (~25). This is because the 

measured intensity of the IR was appreciably lower than the UV technologies (Table 5). This 

highlights the importance of understanding the time needed to achieve a given dosage for each 

technology. Of the technologies and radiation intensities available for use in this study, none 

were able to achieve > 3 log reduction in populations within short exposure times (< 5 mins). As 

it currently stands, the long time required for radiative sanitation technologies to achieve 

appreciable amounts of kill on equipment surfaces limits its uses within a food processing 

environment. 

The log reduction per dosage for UV-C was significantly greater than Far UV-C. This 

indicates that the 254 nm wavelength was more efficient in inactivating Salmonella in 

comparison to 222 nm. This agrees with the conclusions reported by Hessling, et al., which 

discussed the phenomena of 254 nm wavelengths having a higher relative absorption by DNA 

and proteins compared to 222 nm (Hessling et al., 2021). However, further considerations 

towards human health and safety must be made when selecting UV-C wavelength. The 222 nm 

wavelength has been shown to be less harmful to ocular membranes and skin in comparison to 

63 

 
the 254 nm wavelength (Napoleão et al., 2023). Therefore, UV-C should be prioritized in 

situations where human exposure is minimized, such as within enclosed spaces, the inside of 

equipment, planar surfaces, and the underside of conveyor belts. Far UV-C has potential 

applications for areas where sanitation personnel may be present during the cleaning and 

sanitation process or in open spaces. 

IR technologies may be a viable solution for inaccessible areas in conductive equipment. 

IR can penetrate through surfaces while UV-C cannot. However, elevated temperatures during 

experimentation revealed an important consideration in the use of IR radiation in low moisture 

processing environments. The IR device reached a maximum temperature of 153.6°C at 5 cm 

from the emitter after 57 min of exposure. A major safety consideration in low-moisture food 

processing environments with IR is the risk of dust explosions. Dust explosions can occur from 

five factors (known as the dust explosion pentagon): oxygen, heat, fuel, dispersion, and 

confinement (Occupational Safety and Health Administration, 2015). If a heat source is added to 

an environment with airborne particles, the risk of dust explosion can increase. Therefore, IR 

surfaces should be separated from dusty surfaces and used sparingly, only for hard-to-reach 

nooks and crannies where UV-C cannot penetrate, such as between tightened nuts, bolts, and 

washers on equipment. 

The theoretical and experimentally retrieved intensity values for each technology were 

different than expected. In particular, the discrepancies between the theoretical and 

experimentally achieved IR intensity values (Table 5) may be due to the assumption that all 500 

W of energy from the emitter was being applied to the target surface as a point. In reality, the 

radiation was emitted in a top down (linear) fashion. Additional calculations to determine the 

view factor of emitted radiation from the rectangular ports in the sanitation equilibration 

64 

 
chamber (Figure 9) and the circular surface of the coupon may improve the accuracy of the 

theoretically calculated intensities. Factors such as the emissivity of the radiating surfaces, the 

absorptivity of the coupon, and any intervening medium's impact on radiation propagation 

should also be considered. Additionally, refining the view factor calculations to account for 

geometric alignments and surface orientations can further enhance the predictive accuracy 

regarding radiation heat transfer. The IR passed through an optically clear temperature-resistant 

piece of glass that prevented the sanitation equilibration chamber top from melting under the 

intense heat of the IR emitter, which may have impacted the IR emitted to the target surface. 

Additionally, as evidenced in Figure 23, the intensity varied on the surface of the coupon 

depending on the location of the UV-C light sensor. Miniscule adjustments to the intensity 

measurement set up (Figure 14) may have impacted the recorded intensity values for each 

technology. 

Importantly, the application of the dosage models and suggestions are dependent on 

environmental factors and the nature of the processing line. One technology does not fit all low 

moisture food processing situations. These technologies are beneficial for closed systems and 

spot treatments, especially as a “passive” form of sanitation that requires minimal labor from 

personnel. Radiative sanitation technologies are additional tools to increase the amount of 

hurdles for microorganism survival and cross-contamination in dry processing environments. 

65 

 
 
 
CONCLUSIONS 

Objective 1: Develop Replicable and Consistent Electrostatic Powder Coating Dry 

Inoculation Methodology 

•  The dry electrostatic powder coating methodology consistently and reliably adhered 

inoculated, custom fabricated flour to the surface of #304 brushed finish, #304 mirror finish, 

and #316L brushed finish coupons. The inoculation method adhered greater than an average 

5 log CFU/cm2 of Salmonella populations to the surface of #304 brushed finish and #316L 

brushed finish SS coupons. Visibly cleaned coupons achieved ~4 log CFU/cm2 on the surface 

of #304 brushed finish and #316L brushed finish SS coupons. 

•  Stainless steel finish and grade did not significantly impact the Salmonella populations 

adhered using the dry powder coating methodology. 

•  The consistency and replicability of the inoculation methodology had mixed success. The 

initial visibly cleaned population counts used in the sanitation portion of the experiment were 

lower than those achieved in the evaluation of the powder coating methodology portion on 

#304 SS (3.09 ± 0.16 log CFU/cm2 vs. the initial 3.92 ± 0.57 log CFU/cm2). However, there 

were no significant differences between the average visibly cleaned populations between 

sanitation experimental runs. The largest standard deviation observed for a sanitation run was 

0.17 log CFU/cm2 (Table 3). This showed that the inoculation method was both consistent 

and replicable with minimized variability within a single run. 

Objective 2: Evaluate Performance of Non-Aqueous Sanitation Technologies 

•  Two of the radiative technologies used in this study (UV-C and IR) achieved a sanitation 

efficacy of > 3 log CFU/cm2 on the surface of #304 brushed finish coupons. Far UV-C did 

not achieve this target due to equipment malfunction. 

66 

 
•  UV-C 254 nm had the highest sanitation efficacy with the shortest length of exposure, 

followed by Far UV-C and IR. 

Objective 3: Generate A Descriptive Model for Salmonella Population Reductions on 

Stainless Steel Surfaces 

•  Three individual linear regression models were developed to describe the dosages 

obtained experimentally on SS surfaces. 

•  The dosage required to achieve a target sanitation efficacy (log reduction) was calculated 

using the 95% confidence intervals generated from the ANCOVA of the linear regression 

models. 

•  Suggestions were provided for the implementation of each radiative technology. 

Future Work 

•  This study kept the relative humidity in the powder coating chamber and sanitation 

chamber constant with a target value of 45%. More research is needed to characterize the 

impact of relative humidity toward the efficacy of non-aqueous sanitation technologies. 

•  The wheat berry milling process generated a fine layer of inoculated dust on the surface 

of the milling attachment without the use of an electrostatic powder coating gun. The 

utilization of triboelectric charge in inoculated powders should be explored as an 

alternative dry inoculation method for food contact surfaces. 

•  This study focused on stainless steel food contact surfaces for inoculation due to their 

ubiquity and electrical conductivity. The electrostatic powder coating method should be 

explored with other electrically grounded food contact materials, such as HDPE, in low-

moisture food production environments. 

67 

 
•  The intensity in this experiment was modulated by increasing the distance between the 

target surface and the radiation emitter. Further research into high intensity devices will 

also be beneficial. 

•  Further investigation into the synergistic effects of UV-C and IR radiation on 

contaminated surfaces may reduce the exposure time required for targeted sanitation 

efficacies. 

68 

 
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