EVALUATION OF CHILLING METHODS ON BROILER CARCASS APPEARANCE,
TEXTURE, SENSORY AND MICROBIAL QUALITY

By

Kishorekumar Kalapurackal Janardhanan

A THESIS

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

MASTER OF SCIENCE

Animal Science

2011

ABSTRACT
EVALUATION OF CHILLING METHODS ON BROILER CARCASS APPEARANCE,
TEXTURE, SENSORY AND MICROBIAL QUALITY

By

Kishorekumar Kalapurackal Janardhanan

Three experiments were conducted in this study to determine the effect of two or
three chilling methods [water immersion chill (WIC), air chill (AC), and evaporative air
chill (EAC)] on broiler carcass appearance, quality, and microbial contamination. In
experiment I, results indicated that carcass temperature was reduced and moisture was
picked up in the most effective way in WIC, followed by EAC and AC. WIC carcasses,
however, showed the highest moisture loss upon cutting and storage among the three
chilling methods. In experiment II, moisture content, cooking yield, and shear force of
skinless breasts were not significantly different regardless of chilling methods. The 24 hstored breast fillet from WIC showed higher pH than AC or EAC. WIC showed a higher
CIE L* value on skinless breast than either AC or EAC. However, AC yielded higher CIE
a* and b* values compared to other two chilling methods. When gels were made from
breast muscle, no significant difference was found in cooking loss, moisture content,
shear stress or shear strain. Consumer sensory tests showed a higher juiciness score
for AC fillet than WIC and EAC fillets, with no significant difference for flavor, texture
and overall acceptability. In experiment III, no significant differences were seen between
air and water chilled carcasses for Escherichia coli or coliforms or for the incidence of
Salmonella and Campylobacter.

DEDICATION

To Sonu and Dev, with love

iii

ACKNOWLEDGEMENTS
I would like to express sincere gratitude to my advisor, Dr Iksoon (Ike) Kang, for
his overwhelming support for my research program and both my professional and
personal development. I wish to extend my gratitude to the members of my guidance
committee members Dr. Darrin Karcher, Dr. Gale Strasburg, Dr. Elliot Ryser and Dr.
Perry K.W. Ng for their valuable support and suggestions for the successful completion
of my research work. I also would like to show my appreciation to Dr. Alden M. Booren
for his valuable advice in this program. Dr. Janice Harte was instrumental in our project
taking care of the sensory evaluations for this study. I would like to mention Dr. Steve
Bursian, graduate coordinator for his valuable advice throughout the program. I am
grateful to Dr Jong. Y. Jeong and Dr. Lei Zhang and Ms. Nicole Hall for their help in
this research work. Without their help, it would not have been possible to finish this work
in time. I am indebted to MSU meat laboratory managers Mr. Tom Forton and Ms.
Jennifer Dominguez for their tireless help in setting up the meat lab and sample
preparation.
I would like to thank my lab mates Thanikarn Sansawat, Gerald Hessel and
Marianela M.I for their endless support. I am thankful to Yuwares Malila and Katherine
Stanchak for wise conversations in our office.
Finally, I am grateful to my family, my mother Mrs. Padmam Janardhanan and
my farther Mr. Janardhanan. Without them, I would not even think about to start my
master program at MSU. I am highly indebted and short of words for my wife Sonika
and my son Devadathan who spared my absence for the time I spent in Michigan State
University.
iv

TABLE OF CONTENTS

List of Tables

vii

List of Figures

viii

List of Abbreviations

ix

Chapter 1. Introduction

1

Chapter 2. Literature Review
5
2.1 Introduction
6
2.2 Air Chilling
7
2.3 Water Immersion Chilling
7
2.4 Evaporative Air Chilling
8
2.5 Chilling Efficiency of WIC, AC and EAC
8
2.6 Weight Gain or Loss of WIC, AC and EAC
8
2.7 Moisture and Purge Loss from WIC, AC and EAC
9
2.8 Effect of Chilling Methods on Visual Appearance of Broiler Carcass
9
2.9 Effect of Chilling Methods on Visual Appearance of Raw Broiler
Muscle
10
2.10 Effect of Different Chilling Methods on pH
11
2.11 Effect of Chilling Methods on Broiler Breast Muscle Tenderness
11
2.12 Sensory Qualities of Broiler Breast Muscle from Different Chilling
Methods
11
2.13 Microbial Contamination of Broiler Carcass Based on Different Chilling
Methods
12
2.14 Antimicrobial Treatment in Chilling Methods
13
Chapter 3. Moisture Content, Processing Yield, and Surface Color of Broiler Carcasses
Chilled by Water, Air, or Evaporative Air
14
3.1 Abstract
15
3.2 Introduction
16
3.3 Materials and Methods
18
3.3.1 Broiler Carcass Processing
18
3.3.2 Chilling Treatments, Deboning, and Storage
19
3.3.3 Chilling Yield, Fabrication Yield, and Purge Loss
20
3.3.4 Color Measurements and Moisture Content Determination
20
3.3.5 Visual Carcass Evaluations
21
3.3.6 Statistical Analysis
22
3.4 Results and Discussion
22
3.5 Acknowledgments
29

v

Chapter 4. Breast Meat Quality and Consumer Sensory Properties of Broiler Carcasses
Chilled by Water, Air, or Evaporative Air
35
4.1Abstract
36
4.2 Introduction
36
4.3Materials and Methods
39
4.3.1 Broiler Carcass Preparation
39
4.3.2 Chilling Treatments, Deboning, Storage, and Sampling
39
4.3.3 Color Measurements
40
4.3.4 pH Value and Moisture Determination
41
4.3.5 Chicken Breast Gel Preparation, Cooking Yield, and Torsion
Test
41
4.3.6 Cooking Yield and Shear Force Measurements
42
4.3.7 Consumer Acceptance Evaluations
43
4.3.8 Statistical Analysis
44
4.4. Results and Discussion
44
4.5 Acknowledgments
49
Chapter 5. Microbiological Quality of Water-Immersion and Air-Chilled Broilers
5.1 Abstract
5.2 Introduction
5.3 Materials and Methods
5.3.1 Broiler Carcass Rinse Samples
5.3.2 Microbiological analysis
5.3.3 Statistical Analysis
5.4 Results and Discussion
5.5 Acknowledgements

54
55
55
57
57
58
59
60
63

Literature Cited
Literature Cited

67
68

vi

LIST OF TABLES

Table 3. 1. Effects of chilling methods on chilling yield, cutting yield, and 24 h purge
loss of broiler carcasses
30
Table 3.2. Effects of chilling methods on moisture content in five different parts of
broiler carcasses after 24 h storage
31
Table 3.3. The surface skin color for five different locations in broiler carcasses
chilled by water, air, or evaporative air chilling
32
Table 3.4.
Mean values of broiler carcasses appearance after water, air, or
evaporative air chilling

33

Table 4. 1. Effects of chilling methods on the properties of raw and cooked broiler
breast fillets
50
Table 4. 2. Effect of chilling methods on moisture content, cooking yield, and
functional properties of gels made from broiler breast meat

51

Table 4. 3. Effect of chilling methods on consumer sensory attributes of cooked
broiler breasts after 24 h of storage
52
Table 5.1.

Comparison of chilling parameters between air and water chilling

64

Table 5.2. Populations (log CFU/ml) of mesophilic aerobic bacteria (MAB), E. coli,
coliforms and Campylobacter recovered from broiler carcasses before and after AC and
WIC
65
Table 5.3. Prevalence of Salmonella and Campylobacter on broiler carcasses before
and after AC and WIC.
66

vii

LIST OF FIGURES

Figure 3.1.
Temperature change profiles of broiler breast fillets during water chilling
(WC), air chilling (AC), or evaporative air chilling (EAC).
34
Figure 4.1. Temperature change profiles of broiler breast fillets during WC, AC, or
EAC: ■- water chilling, ▲- air chilling, ●- evaporative air chilling.
53

viii

LIST OF ABBREVIATIONS

AC

Air Chilling

CIE

Commission Internationale de l’Eclairage

EAC

Evaporative Air Chilling

US

United States

WC

Water Chilling

WIC

Water Immersion Chilling

ix

Chapter 1
Introduction

1

Air chill (AC) technology in poultry processing is gaining popularity in the United
States (US) especially after the revision of US federal regulation (USDA, 2001).
According to the revised regulation, poultry carcass is minimally allowed to retain water
as an unavoidable consequence of processing for the food safety requirements. Water
immersion chill (WIC) technology has been used in the United States as the most
common chilling method because it is efficient and economical compared to other
chilling methods. Studies have been conducted to compare “AC and WIC” or “AC and
evaporative air chill (EAC)” on fresh broiler meat for quality improvement, chilling yield
and shelf life extension (Mielnik et al., 1999; Young and Smith, 2004; Huezo et al.,
2007a, b; Carroll and Alvarado, 2008). However, not many studies have been carried
out for the effect of three chilling methods (AC, WIC and EAC) on broiler quality
especially in the US.
The objective of this study was to evaluate the effect of the three chilling methods
on broiler carcass appearance, moisture change, textural quality, breast value, sensory
profiles and microbial contamination. For convenience, this study was divided into three
experiments: 1) evaluation of moisture content, processing yield, surface color, and
visual appearance of broiler carcasses, 2) comparison of breast meat quality, protein
functionality and consumer sensory properties of broiler fillets, and 3) assessment of
microbiological quality of water-immersed or air-chilled broilers.
Regarding carcass color, visual appearance of finished products is an important
purchasing factor and influenced by both chilling and scalding methods (Northcutt,
1997). Air chilling requires soft scalding for skin color protection (no discoloration) while
water chilling normally utilizes hard scalding for easy defeathering. Evaporative air
2

chilling can use both scalding methods, although soft scalding is preferred over hard
scalding (Veerkamp, 1985, 1991; Sams, 2001). Scalding influences both skin color and
carcass weight change while chilling methods affect carcass swelling or shrinkage
(Veerkamp 1981, 1986, 1991). For example, air chilling resulted in moisture loss (1.52%) while water chilling gained up to 4% moisture (Young and Smith, 2004; James et
al., 2006). Evaporative air chilling also resulted in a weight gain of 1-3% depending on
the amount and frequency of water spraying (Veerkamp, 1991; Thomson et al., 1974).
Protein functionality, moisture content, marinade uptake, and cook loss of the
broiler carcass were different between AC and WIC (Young and Smith, 2004; Huezo et
al., 2007a; Carroll and Alvarado, 2008). Eating quality of air-chilled carcasses was
preferred over water chilled carcasses potentially due to less water content and washing
effect (Veerkamp, 1991; Gazdziak, 2006). The textural quality of muscle protein is
affected by the freshness of protein source because the freshness factor mainly affects
the folding state of the long chain protein polymer (Kang and Lanier, 2000). Water
binding ability of muscle protein is associated with the gel structure and firmness
(Hermanson, 1979; Hamann and MacDonald, 1992).
Many pathogenic organisms (Salmonella, Clostridium perfringens, Listeria
monocytogenes, and enterohaemorrhagic Escherichia coli) can survive in poultry
carcasses even after chilling (US FDA, 1992; Mead, 2004). Water chilling was banned
in the European Union to minimize the chances of cross-contamination from carcass to
carcass during chilling in a common bath (EEC, 1971; Thomas, 1977). Previous studies
comparing different chilling methods reported mixed results from “less contamination by
AC” (Knoop et al., 1971; Sanchez et al., 2002; Lindblad et al., 2006) to “ no difference”

3

(Burton and Allen, 2002; James et al., 2006) between WIC and AC, and to “ more
contamination by AC” (Allen et al., 2000; Berrang et al., 2008).
Therefore, the objective of this study was to evaluate the effects of two or three
chilling methods (WIC, AC, and EAC) on broiler carcass quality, fillet value, protein
functionality, and microbial contamination. Results from this research could help US
broiler processors implement and optimize air-chilling technology for greater consumer
acceptability.

4

Chapter 2
Literature Review

5

2.1 Introduction
Air, water, and evaporative air chilling are three chilling methods used in the
poultry industry. The chief objectives of poultry chilling are to increase food safety for
consumers and extend product shelf-life for marketing (Sams, 2001). According to
studies, different chilling methods impact different attributes to the final product quality
such as moisture content, flavor, appearance, texture, and microbial contamination
(Petrak et al., 1999; McKee, 2001; James et al., 2006). Currently, food safety is an
increasingly important public issue that needs to be controlled from farm to fork.
Pathogenic organisms such as Salmonella, Campylobacter, Clostridium perfringens,
Listeria monocytogenes and enterohaemorrhagic Escherichia coli can be found in
poultry carcass (Wempe et al., 1983; Izat et al., 1988; Capita el al., 2004) According to
USDA regulations in poultry processing, the poultry carcass temperature should be
reduced to 4.4 oC or less within 4-8 hrs in relation to the weight of the carcass after
slaughter (USDA, 2009). The poultry industry has attempted to obtain higher efficiency
in chilling, improve microbial control, reduce installation cost and adapt to regulatory
requirements without decreasing the product quality. As a result, the chilling systems
are continuously upgraded and updated (International Commission on Microbiological
Specifications of Foods, 2005; James et al., 2006). Carcass characteristics such as
wetness/dryness, visual appearance, purge-related wet pad in tray-packs (external),
shear force, cooking loss, and eating quality are affected by the method of chilling
(McKee and Sams, 1998; Mielnik et al., 1999; Alvarado and Sams, 2002; Young and
Smith, 2004; James et al., 2006; Huezo et al., 2007a; Carroll and Alvarado, 2008;
Zhuang et al., 2008, 2009).

6

2.2 Air Chilling
The benefits of AC are improved quality, minimal water consumption, reduced
waste water management, and reduced labor (during and after chilling). However, AC
is less efficient compared to water and evaporative air chilling (Pederson, 1979;
Veerkamp, 1989; McKee, 2001). The European community has used commercial air
chilling for more than 35 years after water immersion chilling (spin-chilling) was banned
in 1977(Brant,1974; Stadelman, 1974; Thomson et al., 1974). The banning occurred to
reduce cross contamination from carcass to carcass during the water chilling in
common water-tanks (Thomas, 1977). Commercial production of air chilled poultry
started in the US in 1988 (Gazdziak, 2006). After the introduction, air chilled poultry
gained popularity over the time in the US potentially due to the higher quality of endproducts (Bailey et al., 1987; Huezo et al., 2007a, b; Carroll and Alvarado, 2008). In
addition, the revised USDA regulation for restricting moisture content in poultry carcass
is another reason for increasing interest of AC in the United States (USDA, 2001).
2.3 Water Immersion Chilling
WIC has long been used to effectively chill poultry carcasses in the United
States. In water chilling, eviscerated birds and water move in opposite directions so
that carcass temperature can be reduced in increasingly cold and clean water towards
the end. WIC also decreases bacterial contamination through washing and results in a
generally lower total bacterial load (Mead and Thomas, 1973; Blood and Jarvis, 1974;
Thomson et al,. 1979; Waldroup et al,. 1992; Blank and Powel, 1995; Allen et al., 2000;
Bilgili et al., 2002; Northcutt et al., 2006). However, better bacterial reduction in WIC
was obtained by the adding of chlorine to the water (Mead et al., 1994; James et al.,

7

2006). Although WIC is still the most popular method of poultry chilling in the United
States, its popularity is challenged frequently due to the issues of post-chill purge, reshackling, waste water management and cross contamination.
2.4 Evaporative Air Chilling
A mixed type of water and air chilling, called Evaporative Air Chilling (EAC), was
developed in order to obtain the advantages of both AC and WIC. In this process, birds
move in a shackle line through a cold room where cold water is sprayed frequently. EAC
minimizes weight loss, reduces skin discoloration, and improves heat transfer
(Veerkamp, 1989; Barbut, 2002; International Commission on Microbiological
Specifications of Foods, 2005).
2.5 Chilling efficiency of WIC, AC and EAC
WIC reduces broiler carcass temperature to 4 oC or less in 45 min while AC takes
130 to 150 min (Huezo et al., 2007 a,b; Zhuang et al., 2009). In air chill, the chilling time
of a poultry carcass is affected by carcass weight, water/ ice combination of chilling
medium, temperature/humidity of the chilling room, chilling method, air velocity and
hanging method (James et al., 2006). Evaporative air chill showed better chilling
efficiency than AC chiefly due to the water sprayed during chilling (Mielnik et al., 1999;
James et al., 2006). More specifically, Mielnik et al. (1999) reported that EAC was more
efficient (1.8 kcal/kg) than AC in heat transfer in the same chilling time (50 min).
2.6 Weight gain or loss of WIC, AC and EAC
WIC was reported to increase carcass weight from 4.6% to 9.3% after chilling
(Huezo et al., 2007b; Zhuang et al., 2008), while the weight of AC carcasses decreased
by 0.8 to 2.5% (Veerkamp, 1981; Huezo et al., 2007b). Moisture retention was highest

8

in WIC carcasses followed by EAC and AC (Veerkamp, 1981, 1986; Mielnik et al., 1999;
ICMSF, 2005; James et al., 2006; Huezo et al., 2007a; Zhuang et al., 2008).
2.7 Moisture and Purge loss from WIC, AC and EAC
According to Young and Smith (2004), WIC carcasses lost about half (5.7%) of
the moisture gained (11.5%) during chilling and further processing. The percentage of
water uptake was greater in smaller carcasses compared to large carcasses (Essary
and Dawson, 1965). Mean moisture values of breast and leg with skin on it were 74.9 %
and 70.9 % respectively, while the moisture of the meat and skin was not affected by
the chilling method (Mielnik et al., 1999). Similarly, Zhuang et al. (2008) found no
moisture difference between WIC and AC when chicken breasts were obtained after 4h
post-mortem. The water absorbed during chilling is normally held between skin and
muscle, not with in muscle (Lentz and Rooke, 1958; Klose et al., 1960). Absorbed water
in WIC carcasses neither increases the moisture content of the muscle nor the cooking
yield (Hale and Stadelman, 1973). Upon marination, AC fillets showed higher solution
pick-up and cooking yield than WIC fillets. This might be due to the high moisture loss,
which is more in AC compared to WIC where water is retained (Huezo et al., 2007a;
Carroll and Alvarado, 2008).
2.8 Effect of Chilling Methods on Visual Appearance of Broiler Carcass
Chilling methods can influence the quality and visual appearance of carcasses
thus causing an important factor in the acceptability (James et al, 2006). Light scattering
and increased lightness in WIC are due to the loss of stratum corneum from hard
scalding and absorption of water (Graf and Stewart, 1953; Sams, 2001; Huezo et al.,
2007a). A higher L* value or increased lightness in WIC compared to AC might be due
9

to the loss of epidermis during washing, agitation and carcass-contact to each other
(Huezo et al., 2007a). Surface dehydration is another reason for the low L* value in AC.
However, spraying carcasses with water in EAC can prevent surface dehydration.
(Mielnik et al.,1999; Huezo et al., 2007a). The darker color of AC carcasses might be
due to carcass drying during chilling and visibility of the underlying muscle through skin
(Huezo et al., 2007a). Using soft scalding, Huezo et al. (2007b) reported a lower CIE a*
(red) value for breast skin in WIC compared to AC. However, no significant difference
on breast skin was reported in comparative study between AC and WIC (Mielnik et al.
1999). Huezo et al. (2007b) reported that WIC yielded the lowest CIE b* (yellowness)
followed by EAC, and AC for poultry carcasses. Because of surface drying, AC resulted
in an undesirable appearance of the carcass skin (Veerkamp, 1981; Sams, 2001).
Currently, however, in the US most (89%) of broiler carcasses (9 billion broilers) are
sold as value added products or/and retail cuts while the left over (11%) are delivered
as whole carcasses (National Chicken Council, 2009). As a result, the visual defects
may be of less importance (Corry et al., 2007) and rehydration of dried skin can reduce
the appearance defects after packaging (Sams, 2001).
2.9 Effect of Chilling Methods on Visual Appearance of Raw Broiler Muscle
No significant differences between WIC and AC were reported for L*, a*, and b*
values of raw breast fillets (Fleming et al., 1991; Huezo et al., 2007a; Zhuang et al.,
2009). However, a significant lower L* value was found in air chilled breast compared to
WIC or EAC (Carroll and Alvarado, 2008). An increased L* value for WIC carcass might
be due to the washing of water soluble proteins such as myoglobin, hemoglobin, and
cytochrome C (Heuzo et al.,2007b). Heuzo et al (2007b) conducted a correlational study

10

between color values of the raw breast filler and weight loss of AC carcasses. They
concluded that the higher weight loss in AC carcasses correlates to higher a* value and
lower L* value.
2.10 Effect of different Chilling methods on pH
WIC fillets had a higher pH (5.8) than AC fillets when evaluated after 150 min
post-mortem (Huezo et al. 2007b). However, Mielnik et al. (1999) reported no significant
pH difference between AC and EAC. In the study conducted on carcasses from different
plants, Carroll and Alvarado (2008) reported a higher pH in AC compared to WIC.
2.11 Effect of Chilling Methods on Broiler Breast Muscle Tenderness
Broiler breast meat tenderness is usually measured using Allo-Kramer and
Warner-Bratzler shear force. However, a more sensitive razor blade technique was
developed for measuring tenderness in poultry meat (Cavitt et al., 2004; Meullenet
et al., 2004). No statistical difference was found in the Allo-Kramer shear values
between WIC and AC when fillets were deboned 3 h post-mortem. However, the shear
value for WIC fillets was 2kg/g higher compared to the AC carcass (Huezo et al.,
2007a). Unlike the results of Huezo et al (2007 b), Carroll and Alvarado (2008) reported
significantly lower shear force in AC carcasses than WIC carcass when fillets were
deboned 24 h post-mortem.
2.12 Sensory qualities of Broiler Breast Muscle from Different Chilling Methods
Significant improvement in juiciness was noticed in AC compared to WIC by Lee
et al., (2008). Flavor and texture profiles were similar for AC and WIC carcasses
(Zhuang et al, 2009). Odor, tenderness and overall acceptability of AC and WIC were
also not significantly different (Pedersen, 1982). Gel structure and firmness are

11

correlated with water binding ability and protein integrity (Hermansson, 1979; Hamann
and MacDonald, 1992).
2.13 Microbial Contamination of Broiler Carcass based on Different Chilling
Methods
Cross contamination can occur through aerosols in AC (Fries and Graw; 1999,
Mead et al., 2000). However, moisture absorption and retention by air-chilled carcasses
is minimum, thus offering a higher meat quality end product compared to WIC (Huezo et
al., 2007a, b; Carroll and Alarado, 2008; Jeong et al., 2010a,b). Previous studies
reported mixed results for microbial contamination on carcasses: no difference in
microbial load between AC and WIC (Burton and Allen, 2002; James et al., 2006), less
contamination in AC (Sanchez et all, 2002) and higher contamination in AC (Allen et al.,
2000; Fluckey et al., 2003; Berrang et al., 2008).
Comparing AC and WIC separately at two different facilities, Sanchez et al
(2002) reported a lower incidence of Salmonella and Campylobacter in AC carcasses.
However, this study used different stunning, scalding, and carcass washing procedures.
Farm and flock variation will also influence final microbial load on the carcass
(Wedderkopp et al., 2001; Fluckey et al., 2003; Heuer et al., 2008). Addition of chlorine
in WIC has resulted in considerable reduction in the bacterial load of the carcass to safe
limits (Lillard, 1990; Dickens and Cox, 1992; James et al., 1992; Waldroup et al,. 1992;
Allen et al., 2000; Bilgili et al., 2002).
Campylobacter jejuni is more susceptible to injury compared to Escherichia coli
in chlorinated water used in WIC and this might be the reason for lower populations of
Campylobacter (Blaser et al., 1986). Surface drying of the carcass was suggested to

12

reduce Campylobacter (Oosterom et al., 1983; Lindblad et al., 2006). However, the
reduction is transient and minimal after packaging (Thomas, 1977).
Populations of aerobic bacteria, E. coli and coliform bacteria decrease on broiler
carcasses during processing with no such reduction found for Salmonella and
Campylobacter (Fluckey et al., 2003). However, Cason et al., (1997) observed no
correlation among aerobic bacteria, Salmonella and Campylobacter on broiler
carcasses at various processing stages including defeathering, before chilling and after
chilling.
2.14 Antimicrobial Treatment in Chilling Methods
Antimicrobial treatments have shown both bactericidal and bacteriostatic effects
depending on the concentration used (Palumbo and Williams, 1994). Listeria
monocytogenes inoculated frankfurters upon treating with 1% cetylpyridinium chloride
have shown initial bactericidal property and bacteriostatic effect later at 42 days of
storage. (Singh et al., 2005). Cecure® (cetylpyridinium chloride) can be used at the rate
of 0.5-0.7% in a poultry processing plant for controlling microbial contamination (Beers
et al., 2006).

13

Chapter 3
Moisture content, processing yield, and surface color of broiler carcasses
chilled by water, air, or evaporative air

14

3.1 Abstract
This study was conducted to investigate the effects of water chilling (WIC), air
chilling (AC), and evaporative air chilling (EAC) on the moisture content, processing
yield, surface color, and visual appearance of broiler carcasses. For the WIC treatment,
one group of birds was hard scalded and submersed into ice slush, whereas for AC,
one group of birds was soft scalded and exposed to blowing air (1.0 m/s at 0° and for
C)
EAC, or one group of birds was soft scalded and exposed to blowing air and a cold
water spray (every 5 min).During chilling, carcass temperature was reduced most
effectively by WIC (55 min), followed by EAC (120 min) and AC (155 min). After chilling,
both WIC and EAC carcasses picked up moisture at 4.6 and 1.0% of their weights,
respectively, whereas AC carcasses lost 1.5% of their weight. On cutting at 5 h
postmortem, WIC carcasses showed the highest (2.5%), EAC showed the second
highest (0.4%), and AC showed the least (0.3%) moisture losses. After 24 h of storage,
almost 83% of the absorbed water in the WIC carcass parts was released as purge,
whereas EAC and AC carcasses maintained weights close to the pre-chilled weights. In
an instrumental color evaluation and a visual evaluation by panelists, AC carcasses
showed a darker appearance, more yellow color, and more surface discoloration
compared with WIC or EAC carcasses.

15

3.2 Introduction
The three most common methods of poultry chilling in industry are air (AC), water
(WIC), and evaporative air chilling (EAC; Sams, 2001). Previous research has shown
that each of the chilling methods results in a different quality of finished products, such
as microbial contamination, moisture content, flavor, appearance, and meat texture
(Petrak et al., 1999; McKee, 2001; James et al., 2006). Chilling of poultry carcasses is
necessary to prevent microbial growth, and the United States federal regulations require
that the carcass temperature must reach 4.4°C or lo wer within 4 to 8 h, depending on
the post-slaughter carcass weights (USDA, 2009). Of the three methods, WIC has
traditionally been used in the United States, whereas AC has been commercialized for
more than 35 years in Europe.
Recently, however, AC is gaining popularity in the United States from both
consumers and processors, especially after the revision of the US federal regulations
(USDA, 2001) restricting moisture retention on poultry carcasses. In AC, cold air is
blown into both the abdominal cavity and the exterior of the thick parts (e.g., breast,
legs) of the carcass to improve the efficacy and uniformity of chilling (Barbut, 2002). Air
chilling, although inferior to WIC in chilling efficiency, offers great potential for quality
improvement (less cross contamination and a better taste), minimizes water
consumption, reduces waste water management, and is labor saving during or after
chilling (Pederson, 1979; Veerkamp, 1989; McKee, 2001).
Evaporative air chilling, a mixed type of AC and WIC, was developed to combine
the advantages of both methods. During EAC, cold water is sprayed onto carcasses at
periodic intervals while they are moving on the shackle line in an AC room. As a result,

16

EAC can improve heat transfer, minimize weight loss, and reduce skin discoloration
compared with AC (Veerkamp, 1989; Barbut, 2002; International Commission on
Microbiological Specifications of Foods, 2005). In moisture pickup, EAC was reported to
have from zero change to a minimal change (±1%), depending on the frequency of
water spraying and the velocity of cold air (Thomson et al., 1974; Evans et al., 1988;
Veerkamp, 1989, 1991).
In scalding, AC requires a soft scald to prevent skin discoloration caused by the
loss of the epidermis during picking, whereas the color of WIC carcasses is maintained
if a hard scald is used (Veerkamp, 1991; Sams, 2001). Evaporative air chilling was
initially designed for a hard scald but could also be used with a soft scald (Veerkamp,
1985). It is generally recognized that both chilling methods and scalding types can
influence carcass skin color (yellowness or whiteness), swelling, shrinkage, and the
finished carcass weight (Veerkamp, 1981, 1986, 1991). Mielnik et al. (1999) found that
chicken chilled by EAC had a lighter and less intense yellow color than those chilled by
AC because the sprayed water prevented the surface from dehydrating and maintained
a lighter skin color. Northcutt (1997) reported that both carcass color and visual
appearance are important because consumers receive their first impressions visually,
and based on this impression, they often decide whether to buy the product.
Recently, several researchers have evaluated case-by case effects of either AC
and WIC, or AC and EAC on fresh broiler meats for quality improvement, chilling yield,
and shelf life extension (Mielnik et al., 1999; Young and Smith, 2004; Huezo et al.,
2007a, b; Carroll and Alvarado, 2008). However, not much research has been
conducted on the effects of the 3 chilling methods (WIC, AC, or EAC) on broiler carcass

17

appearance, moisture, and processing yield, especially in the United States. Adapting a
new technology with a sizable investment is not an easy decision, especially for poultry
plants that already have a WIC system. Without practical and scientific information on
broiler products chilled by different methods, consumers lack sufficient information to
make a purchasing decision. Therefore, the objective of this study was to evaluate the
effects of the 3 different chilling methods (WIC, AC, and EAC) on broiler carcass quality,
including the surface color, visual appearance, and status of moisture change (gain or
loss) after chilling and during further processing.
3.3 Materials and Methods
3.3.1 Broiler Carcass Processing
A total of 99 male birds (Ross 708, approximately 46-day-old broilers; 3
replicates of 33 birds each) were obtained from a local broiler producer. After birds were
withdrawn from feed for 12 h and cooped in plastic cages, the birds were transported to
the Michigan State University poultry processing laboratory. On arrival, the birds were
shackled, electrically stunned for 3 s (40 mA, 60 Hz, 110 V), and bled for 90 s by
severing both the carotid artery and jugular vein on one side of the neck. In each
replication, a group of 11 birds was subjected to hard scalding (56.7° for 120 s) for
C
WIC, whereas 2 groups of 11 birds received soft scalding (50° for 220 s) for either AC
C
or EAC. The birds were defeathered in a rotary drum picker (SP38SS Automatic
Pickers, Brower Equipment, Houghton, IA) for 25 s, manually eviscerated, and washed.
Carcasses were hung on a shackle, allowed to drain for 5 min, weighed to obtain a prechill weight, and tagged on the wing. The tagged carcasses were assigned to 1 of 3

18

chilling treatments. Three separate replications from different flocks were conducted
using the same procedure on 3 different days.
3.3.2 Chilling Treatments, Deboning, and Storage
In each replication, for the WIC treatment, 11 hard scalded carcasses were
submersed in ice slurry (approximately 0.2°C, 7.6 L /bird), with a 30-s agitation every 5
min for the entire chilling period. After chilling, carcasses were hung on shackles,
allowed to drain for 5 min, and weighed to obtain a post-chill weight. For both AC and
EAC, 2 industrial-size fans (BF30DD portable air circulator, Ventamatic Ltd., Mineral
Wells, TX) were installed separately to blow cold air toward the carcasses. Two sets of
11 soft-scalded carcasses were randomly hung by the hocks on a stainless steel bar to
expose them to either a continuous air flow (1.0 m/s) for AC or both the air flow and
0.4° water spraying (0.5 L/carcass) by a manual sp rayer (RL Pro sprayer 997P, RootC
Lowell Manufacturing Co., Lowell, MI) for EAC every 5 min during the chilling. In
addition, both temperature (1.7 ± 0.4° and RH (88 ± 4%; 4410 traceable digital
C)
humidity/thermometer, Control Company, Friendswood, TX) of the chilling room were
monitored every 15 min. After AC and EAC, the carcasses were removed from the
shackles and weighed (postchill weight). For each chilling method, one carcass (a
medium weight) was used for monitoring the internal breast temperature every 5 min
with a digital thermometer/ logger (800024, Sper Scientific Ltd., Scottsdale, AZ) until a
temperature of 4° was reached.
C
Immediately after chilling, each carcass was weighed and the surface skin color
was measured instrumentally on both sides of 5 carcass areas (breast, wings, thighs,
drumsticks, and scapulae). Carcasses were then individually packaged in freezer bags

19

(S. C. Johnson & Son Inc., Racine, WI) and held on ice in the same chilling room before
conducting a visual evaluation approximately 1 h after chilling. Following the evaluation
and at 5 h postmortem, all carcasses were fabricated into breast, thighs, drumsticks,
and back, each of which was weighed immediately after fabrication, individually placed
in a freezer bag, and stored on ice for 24 h. The following day, all the parts were reweighed to obtain 24-h post fabrication weights. The parts were then deboned,
deskinned, vacuum-packaged, and frozen for subsequent moisture determination.
3.3.3 Chilling Yield, Fabrication Yield, and Purge Loss
Four measurements (chilling yield, fabrication yield, purge loss of parts, and total
purge loss) were made from 10 carcasses per chilling method as follows: percentage
chilling yield = (postchill carcass weight/prechill carcass weight) × 100%, fabrication
yield = (immediate post fabrication weight of total parts/prechill carcass weight) × 100%,
purge loss of each part = [(immediate post fabrication weight of each part − 24-h post
fabrication weight of each part)/(immediate post fabrication weight of each part)] ×
100%, and total percentage purge loss (average) = [(immediate postfabrication weight
of total parts − 24-h post fabrication weight of total parts)/(immediate post fabrication
weight of total parts)] × 100%.
3.3.4 Color Measurements and Moisture Content Determination
Moisture content of the boneless, skinless meat and the skin color were
determined on 10 carcasses per chilling method. Commission Internationale de
l’Eclairage (CIE) L*, a*, and b* values (where L* refers to lightness, a* refers to
redness, and b* refers to yellowness) were measured on the surface skin of the breast,
wings, thighs, drumsticks, and scapulae after chilling, using a chromameter (8-mm
20

aperture, illuminant C; CR-400, Konika Minolta Sensing Inc., Osaka, Japan) that was
calibrated with a white plate (L*, 97.28; a*, −0.23; b*, 2.43). Areas were selected that
were free of any obvious blood-related defects, such as bruises, hemorrhages, or full
blood vessels (Fletcher et al., 2000). Six readings of CIE L*, a*, and b* were obtained
for each part (3 readings/side) of the breast, wings, thighs, drumsticks, and scapulae.
Moisture content was determined in duplicate on both sides (boneless and skinless) of
the 5 carcass parts by the weight loss after 16 to 18 h of drying in a dry oven (Yamato
DX 400, Yamato Scientific Co. Ltd., Tokyo, Japan) at 102° (method 950.46B, AOAC,
C
2000).
3.3.5 Visual Carcass Evaluations
The visual appearance of 10 carcasses/chilling treatment was assessed by a 10to 12-member trained panel under fluorescent light (34 W Warm White light; F40/
Spec./RS/EW/Alto, Philips Lighting Company, Somerset, Versailles, KY). Panelists
consisted of students, staff, and faculty members from Michigan State University. After
opening the bags, all carcasses were coded with a 3-digit random number, arranged on
white enamel plates, and then sequentially presented to the panelists in a random
order. All panelists received the carcasses in the same order. Prior to the evaluation, 3
training sessions were conducted with corresponding photographs, which were
prepared from preliminary tests. Through the training, all panelists were trained on
responses to obtain a consistent evaluation with the following 9-point scale: intensity of
yellow color (9 = extremely yellow, 1 = not yellow), intensity of white color (9 = extremely
white, 1 = not white), appearance defects 1 (dark spots; 9 = extreme defects; 1 = no
defects), appearance defects 2 (bleached-looking spots; 9 = extremely defects, 1 = no

21

defects), and surface moisture (dryness or wetness; 9 = extremely wet, 1 = extremely
dry). The evaluations were performed at the poultry processing facility in the meat
laboratory at Michigan State University and were replicated 3 times throughout this
study.
3.3.6 Statistical Analysis
All experiments were replicated 3 times. Data were statistically analyzed using
the GLM procedure of SAS (SAS Institute, 2002) as a randomized block design. If
significance was determined (P < 0.05) in the model, dependent variable means were
separated using the least significant difference procedure of SAS (SAS Institute, 2002).
Visual carcass evaluation data were pooled across panelists and were analyzed as
described previously.
3.4 Results and Discussion
The internal carcass temperature was 39.9° at the beginning and decreased to
C
4° with average chilling times of 55, 155, and 12 0 min for WIC, AC, and EAC,
C,
respectively (Figure 3.1). It is commonly known that immersion carcass chilling in water
(45 to 50 min) is more efficient and faster than chilling in air (130 to 150 min) (Zhuang et
al., 2009; Huezo et al., 2007a, b). Zhuang et al. (2009) reported that the average of
initial carcass temperature, when carcasses were commercially obtained and
transported to their laboratory, was 32.1° and rea ched 4° in 45 min for WIC and in
C
C
130 min for AC. In the current study, we noticed slightly longer times (55 and 155 min)
for the WIC and AC treatments, probably because of the high initial carcass
temperature (39.9° upon processing on-site, diffe rent processing factors (e.g., waterC)
to-ice ratio, velocity, or air temperature), and different carcass weights. James et al.

22

(2006) showed that the chilling time of poultry carcasses was affected by various
factors, such as the carcass weight, water-ice mixture, starting temperature, air
velocities, hanging conditions, temperature and humidity of the chilling room, and
chilling method. Evaporative air chilling exhibited a chilling rate between the WIC and
the AC, probably because the sprayed water improved the evaporative heat loss more
than the air, as noted previously (Mielnik et al., 1999; James et al., 2006). Mielnik et al.
(1999) reported, based on both temperature differences and known carcass weights
that carcasses subjected to a 50-min EAC lost 1.8 kcal/kg more than carcasses
subjected to AC during the same time period. James et al. (2006) summarized results
from 3 chilling systems in a review paper and showed that the chilling rate in a water
immersion system was far faster than the chilling rate in air, whereas EAC was between
the two. After chilling, WIC carcasses had the highest chilling yield (104.6%), whereas
EAC and AC carcasses showed an intermediate yield (101.0%) and the least yield
(98.5%), respectively. These results are consistent with previous findings on moisture
retention in the order of WIC > EAC > AC (Veerkamp, 1981, 1986; Mielnik et al., 1999;
ICMSF, 2005; James et al., 2006; Huezo et al., 2007a; Zhuang et al., 2008). Recently,
Zhuang et al. (2008) reported that AC carcasses lost 2.4% of their weight after 150 min
of chilling, whereas WIC carcasses gained 4.6% of their weight after 50 min. Veerkamp
(1991) also indicated a weight gain (1.0%) in subscaled broilers when the weight
change is carried out by weighing carcasses just prior to the carcass weight equipment
and after chilling.
Water-chilled carcasses, after fabrication at 5 h postmortem, resulted in the most weight
loss, from 104.6 to 102.1% (2.5%), whereas EAC carcasses had an intermediate

23

decrease, from 101.0 to 100.5% (0.5%), and AC carcasses had the least decrease,
from 98.5 to 98.2% (0.3%; Table 3.1). Young and Smith (2004) compared the moisture
retention of WIC and AC carcasses after cutting at 24 h postmortem and reported that
WIC carcasses lost 5.7% of the moisture gained (11.7%) after fabrication, whereas AC
carcasses had no loss at all. These results were similar to the results of the current
study, although their timing (24 h postmortem) of carcass fabrication was different from
ours (5 h postmortem). The yield difference between the two studies could have
resulted from different water uptakes (4.6 vs. 11.7%) after chilling and different carcass
weights (1,824 vs. 1,328 g) before chilling. Essary and Dawson (1965) showed that the
percentage of water uptake was greater in smaller carcasses than in larger ones.
The total purge of the 5 carcass parts (breast, wings, thighs, drumsticks, and
back), after cutting up and overnight storage, was significantly greater for WIC
carcasses (1.3%) compared with AC (0.5%) or EAC carcasses (0.5%; Table 3.1). This
demonstrated that WIC carcasses were likely releasing more of the absorbed water
than EAC carcasses during cutting and extended storage. Similarly, Young and Smith
(2004) reported that WIC carcasses had a greater purge than AC carcasses when foreand hindquarters were stored for 24 h.
Moisture content of the breast and thighs was not significantly affected by the 3
chilling methods, whereas other muscles (wings, drumsticks, and scapulae) showed
some variation (P > 0.05; Table 3.2). Similarly, no moisture difference was reported for
breast and leg muscles when they were chilled by AC and EAC (Mielnik et al., 1999) or
by WIC and AC (Zhuang et al., 2008).

24

In the drumsticks and scapulae, moisture content was the highest (P < 0.05) for
WIC samples, followed by AC and EAC samples. Nevertheless, the ranges of moisture
content in both drumsticks (77.0 to 77.6%) and scapulae (75.1 to 76.5%) were less than
1.5% across the 3 chilling methods, indicating that moisture changes inside the meat
were relatively small, regardless of the chilling method. These results support the view
that most absorbed water was loosely held and trapped under the skin or between
muscles so that the muscle absorbed the least amount of water, whereas the skin
absorbed the greatest (Lentz and Rooke, 1958; Klose et al., 1960).
Chilling methods affected color values (CIE L*, a*, and b*) on the carcass surface
(Table 3.3). The CIE L* values (lightness) on the skin surface were higher (P < 0.05) in
WIC carcasses for all 5 areas (breast, wings, thighs, drumsticks, and scapulae) than in
AC or EAC carcasses, except for the wings and drumsticks in EAC carcasses.
Generally, WIC carcasses exhibited a lighter surface color for the 5 different locations. It
seems that the loss of stratum corneum (the outer layer) from hard scalding and water
absorption during WIC were responsible for the light scattering and intense lightness
(Graf and Stewart, 1953; Sams, 2001; Huezo et al., 2007a). Huezo et al. (2007a)
reported that one reason for the significantly lighter (higher L*) skin in WIC than AC
carcasses might be the loss of some epidermis during agitation, washing, and carcassto-carcass contact. On the other hand, AC carcasses always had a darker (lower CIE L*
values; P < 0.05) surface than did WIC and EAC carcasses for all 5 locations, except for
the breast and thighs in EAC carcasses (Table 3.3). It was suggested that the skin on
AC carcasses dried during cooling, became more translucent, and was darker because
the underlying muscle was visible through the skin (Huezo et al., 2007a). Unlike the

25

lighter and darker comparison between WIC and AC carcasses, EAC produced mixed
outcomes: lower CIE L* values (darker) in 3 locations (breast, thighs, and scapulae)
compared with WIC carcasses but higher CIE L* values (lighter) in 3 locations (wings,
drumsticks, and scapulae) compared with AC carcasses. These results can be
explained by the exposure of the carcasses to both air and water. Mielnik et al. (1999)
and Huezo et al.(2007a) reported that surface dehydration in AC reduced lightness on
the carcasses, which could be prevented by water spraying during EAC.
The CIE a* value for WIC carcasses was always the highest (more red; P < 0.05)
on the 5 carcass parts except the breast, followed by AC and EAC. In contrast, Huezo
et al. (2007a) pointed out that the breast skin of WIC carcass was significantly less red
(lower a* values) than that of AC carcasses after chilling. These conflicting results might
be related to differences in the scalding temperature. In fact, the WIC carcasses in this
study were hard scalded, whereas soft scalding was used in their study. Nevertheless,
Huezo et al. (2007a) observed 2.0 CIE a* units on the breast skin of soft-scalded AC
carcasses after chilling, which was similar to the result in the present study (CIE a* of
2.1). Evaporative air-chilled carcasses had the lowest (P < 0.05) CIE a* values in all
locations except the breast, showing no significant difference (less redness) from AC
carcasses. In a comparison of EAC and AC, Mielnik et al. (1999) reported no significant
difference in a* values on the breast skin, although no additional observations were
reported for other locations. The chilling methods also resulted in different CIE b* values
for carcasses. Water-chilled carcasses were the least yellow (lowest CIE b*; P < 0.05)
among the 3 treatments for the 5 locations, again except for the breast, for which EAC

26

was intermediate between WIC (the least) and AC (the most; P < 0.05), as in previous
results (WIC < AC) ( Huezo et al., 2007a).
Both carcass color and visual appearance are very important because they have
a substantial effect on sales appeal. James et al. (2006) reported that different chilling
methods can influence product quality and visual appearance. In the present study, the
effects of the 3 chilling methods on broiler carcasses were evaluated by trained
panelists for 5 visual attributes: 1) intensity of yellow color, 2) intensity of white color, 3)
appearance defects 1 (dark spots), 4) appearance defects 2 (bleached-looking spots),
and 5) surface moisture (dryness-wetness; Table 3. 4). The yellowness skin score was
the highest in AC carcasses, followed by EAC and WIC carcasses, which were similar
to the instrumental values (CIE b*; Table 3.3 and 3.4). The intensity of yellowness in
AC carcasses has been explained by the retention of epidermal tissue (i.e., stratum
corneum) ( Graf and Stewart, 1953; Thomas et al., 1987; Sams, 2001) and surface
dehydration (Mielnik et al., 1999; Huezo et al., 2007a), whereas the least yellowness in
WIC carcasses has been explained by the removal of the tissue (Thomas and
McMeekin, 1980; Thomas et al., 1987, James et al., 2006). Water-chilled carcasses
were not different (P > 0.05) from AC or EAC carcasses in the intensity of the white
color. However, AC carcasses were less white than EAC carcasses (Table 3.4).
Regarding appearance defects 1 (dark spot), the highest score (P < 0.05) was
given to AC carcasses; whereas the lowest score (P < 0.05) was given to WIC
carcasses. In carcass surface moisture (dryness vs. wetness), WIC carcasses received
the highest (P < 0.05) wetness score (7.4), AC carcasses received the highest (P < .05)
dryness score (2.4), and EAC carcasses received an intermediate score (5.5). In

27

appearance defects 2 (bleached-looking spots), WIC carcasses received a lower score
(P < 0.05) than AC and EAC carcasses, which were similar (P > 0.05) to each other.
These results suggest that the darker color of and dark spots on AC carcasses were
related to the combination of the outer skin loss (even though soft scalded) and surface
dehydration during AC, which were reduced with water spraying in EAC. Previous
research has indicated that AC can cause the carcass skin to have an unattractive
appearance because of the drying effect (Veerkamp, 1981; Sams, 2001). However, the
visual defects would be of less importance (Corry et al., 2007) as the proportions
of cut-up parts (sometimes without skin) and value-added products increase. In 2007,
89% of 9 billion broiler carcasses were sold as cut-up parts or further processed
products, and the remainder (11%) were sold as whole carcasses (National Chicken
Council, 2009). In addition, the dried skin can rehydrate after packaging, offsetting the
defects in appearance (Sams, 2001).
In conclusion, the 3 chilling methods (WC, AC, and EAC) tested in this study
affected both carcass appearance and product quality, such as moisture pickup, water
retention, and surface color. Water-chilled carcasses resulted in a higher moisture
pickup at the end of chilling, but a greater moisture loss occurred during further
processing and extended storage. The purge from WC carcasses would induce more
microbial contamination and faster spoilage of the final products. However, both
AC and EAC showed relatively less moisture gain after chilling and almost no purge
during further processing. Although AC carcasses showed darker and more frequent
visual defects (dark and bleached-looking spots), the discoloration can be reduced by
EAC or is less of a concern as increasing portions of carcasses are processed further.

28

Water chilling appears to be more effective in reducing the temperature during chilling,
but AC could provide more advantages after chilling, such as less water consumption, a
reduced amount of wastewater, no purge, and a potentially improved shelf life.
3.5 Acknowledgments
The authors thank the Midwest Poultry Consortium (St. Paul, MN) and Michigan
Agricultural Experiment Station (East Lansing) for funding for this research.

29

Table3. 1. Effects of chilling methods on chilling yield, cutting yield, and 24 h purge loss of broiler carcasses

1

Chilling
2
yield

(%)

a

WIC

104.64
±0.31

AC

98.51
± 0.12

EAC

100.98
±0.19

c

b

a-c

4

Cutting
3
yield

(%)

Chilling

b

98.06
± 0.19

a

99.72
± 0.16

a

99.58
± 0.18

Purge loss (%)
Breast
a

1.49
± 0.17
b

0.81
± 0.09
b

0.76
± 0.06

Wing
a

1.07
± 0.09
b

0.44
± 0.05
b

0.54
± 0.04

Thigh
a

1.26
± 0.19
b

0.23
± 0.03

WIC = water chilling; AC = air chilling; EAC = evaporative air chilling.

3
4

a

0.69
± 0.13
b

0.24
± 0.03

Measured immediately after chilling.
Measured after cutting at 5 h postmortem
Measure after overnight storage

30

b

0.32
± 0.04

Means ± SE within a columm with unlike superscript letters are different (P < 0.05).

1
2

b

0.23
± 0.03

Drumstick

Backbone
a

1.42
± 0.13
b

0.32
± 0.05
b

0.35
± 0.04

Overall
a

1.28
± 0.19
b

0.47
± 0.04
b

0.49
± 0.04

Table 3.2. Effects of chilling methods on moisture content in 5 different parts1 of broiler carcasses after 24 h storage

Treatments

2

Breast (%)
a

WIC

75.70 ± 0.09
a

AC

75.49 ± 0.18

EAC

75.56 ± 0.13

a,b
1

a

Wing (%)
a

76.09 ± 0.14
a

76.05 ± 0.18
b

75.50 ± 0.21

Thigh (%)
a

76.04 ± 0.15
a

76.24 ± 0.14
a

76.01 ± 0.13

Drumstick (%)
a

77.60 ± 0.09
b

77.28 ± 0.09

Means ± SE within a columm with unlike superscript letters are different (P < 0.05).

Deboned and deskined.

2

WIC = water chilling; AC = air chilling; EAC = evaporative air chilling.

31

c

76.99 ± 0.10

Scapula (%)
a

76.49 ± 0.13
b

75.86 ± 0.16
c

75.06 ± 0.28

Table 3.3. The surface skin color for 5 different locations in broiler carcasses chilled by water, air, or evaporative air
chilling

Traits

1

63.14 ± 0.23
63.32 ± 0.22
3.24 ± 0.13

AC

2.07 ± 0.09

EAC

1.79 ± 0.09

WIC

4.72

AC

4.32

EAC

a-c

AC

WIC

CIE b*

64.94 ± 0.25

EAC

CIE a*

Breast

WIC
CIE L*

Chilling

3.75

a
b
b

a

b
b

a

ab
b

Wing

Thigh

a

a

68.89 ± 0.16

68.49 ± 0.22

b

b

67.18 ± 0.19

66.98 ± 0.32

a

b

69.27 ± 0.23
a

4.14

b

3.18

67.11 ± 0.33
a

3.38

3.08

± 0.12

2.72 ± 0.09
0.90 ± 0.20

2.19

c

c

c

5.95

c

4.63 ± 0.16

± 0.25

b

a

± 0.13

b

2.71 ± 0.13

a

a

61.13 ± 0.24
4.03

2.70

7.00

b

59.61 ± 0.24

± 0.10

± 0.13

± 0.20

a

61.46 ± 0.21

2.82 ± 0.22

± 0.12

± 0.17

Drumstick

a

± 0.19

6.78

± 0.23

4.95

b

b

a

± 0.38

1.47

Means ± SE within a columm with unlike superscript letters are different (P < 0.05).
32

b

c

68.90 ± 0.24
b

70.17 ± 0.22
a

4.62

± 0.10

3.31

c

2.14

a

70.87 ± 0.16

± 0.12

c

± 0.30

Scapula

b

± 0.15
± 0.12

c

2.80 ± 0.12
c

4.74 ± 0.22
a

± 0.20

7.65

± 0.29

6.50

b

± 0.32
± 0.36

1

WIC = water chilling; AC = air chilling; EAC = evaporative air chilling.

Table 3.4. Mean values of broiler carcasses appearance after water, air, or evaporative air chilling

Chilling

Intensity of yellow
color

WIC

1.74 ± 0.06

AC

3.84 ± 0.12

EAC

3.10 ± 0.11

2

c

a

a-c

b

Intensity of
white color

Appearance
1

defect (dark-spot)

ab

c

4.00 ± 0.14

1.57 ± 0.05

b

a

3.77 ± 0.11

4.15 ± 0.13

a

b

4.33 ± 0.12

2

Appearance defect
(bleach-like spot)

1.90 ± 0.09

b

1.93 ± 0.09
a

3.78 ± 0.13
a

3.97 ± 0.15

Surface moisture
dryness/wetness
a

7.41 ± 0.10
c

2.35 ± 0.12
b

5.49 ± 0.12

Means ± SE within a columm with unlike superscript letters are different (P < 0.05).

1

Scores based on 9 point scale, where 9 = most yellow, most white, extremely defected and extremely wet, and 1 = least
yellow, least white, none and extremely dry.
2
WIC = water chilling; AC = air chilling; EAC = evaporative air chilling

33

Figure 3.1. Temperature change profiles of broiler breast fillets during water chilling
(WC), air chilling (AC), or evaporative air chilling (EAC).

Interanl temperature (℃)
℃

45
40

WC

35

AC

30

EAC

25
20
15
10
5
0
0

15

30

45

60

75

90 105 120 135 150

Chilling time (min)

34

Chapter 4
Breast meat quality and consumer sensory properties of broiler carcasses
chilled by water, air, or evaporative air

35

4.1Abstract
Three poultry chilling methods, namely, water chilling (WIC), air chilling (AC),
and evaporative air chilling (EAC), were compared to evaluate their effects on broiler
breast meat quality and consumer sensory characteristics. A total of 189 birds were
processed with 1 of the 3 chilling methods. One-third of the birds were hard scalded
(57.7° 120 s) and subjected to WIC (an ice slurry immersion at 0°C). The
C,
remaining birds were soft scalded (50° 220 s) and randomly assigned to either AC
C,
(blowing air, 1.0 m/s) or EAC (blowing air plus each carcass sprayed with 0.5 L of
0.4° water) in a chilling room (0.9 ± 0.4°C). Wate r chilling reduced the carcass
C
temperature most efficiently (57 min), whereas AC and EAC were the least (125 min)
and intermediate (93 min) in efficiency, respectively. No significant difference was
found among the chilling methods in moisture content, cooking yield, and shear force
of deskinned breast fillets stored overnight. However, the pH (5.6) of 24-h stored
fillets was higher in WIC fillets than in AC (5.5) and EAC (5.5) fillets. For the surface
color of skinless breasts, WIC carcasses showed a higher Commission
Internationale de l’Eclairage (CIE) L* value than AC or EAC carcasses, whereas
AC carcasses exhibited more redness (higher CIE a*) and yellowness (higher CIE
b*) than the other 2 chilling methods. When raw breast meat was made into cooked
gels, no significant difference was observed in cooking loss, moisture content, shear
stress, and shear strain, regardless of the chilling method. In consumer sensory
evaluations, AC breasts had a higher juiciness score than did WIC and EAC breasts,
but no significant difference was found for flavor, texture, and overall acceptability.
4.2 Introduction

36

A poultry processing technique referred to as air chilling (AC) has been
commercialized in the European Community for more than 35 yr, but more recently,
it has been drawing the attention of members of the poultry industry in the United
States (Thomson et al., 1975; Carroll and Alvarado, 2008). The primary objective of
poultry chilling, regardless of the chilling type, is to reduce microbial growth to a level
that will maximize both food safety and product shelf life for consumers and
marketing (Sams, 2001). Chilling systems continue to evolve as the industry strives
to achieve greater efficiency (shorter chilling), reduce capital costs, improve
microbial control, and adjust to changing regulatory requirements without any
reduction in product quality (International Commission on Microbiological
Specifications of Foods, 2005; James et al., 2006). To date, however, water chilling
(WIC) has traditionally been used as a major chilling method in the United States
(James et al., 2006).
The advantage of WIC has recently been challenged by many factors, such
as cross-contamination, wastewater management, reshackling, and postchill purge
(Bailey et al., 1987; Sams, 2001; Sanchez et al., 2002; Smith et al., 2005; Huezo et
al., 2007a,b). In Europe, AC has been commercialized since WIC was banned in
1977 (Lillard, 1982). A primary reason for the ban was the potential for increasing
cross-contamination during chilling (Thomas, 1977). In AC, the carcasses are usually
soft scalded (50 to 53°C) to prevent skin discolora tion, whereas hard scalding (60 to
64° is preferably chosen for WIC because of easie r feather removal and a lower
C)
bacteria level than the carcasses in soft scalding (Notermans and Kampelmacher,
1975; Sams, 2001). Evaporative air chilling (EAC) also was developed as an
alternative to AC, having improved heat transfer and reduced skin discoloration.
Recently, several poultry processors in the United States have adopted the AC
37

technology and have promoted AC chicken, using a premium, natural, or organic
brand (Dudlicek, 2005; Gazdziak, 2006).
Chilling methods can have variable effects on broiler carcass meat, both
externally (dryness or wetness of the carcass surface, visual appearance of the
carcass color, and the purge-related wet pad in tray packs) and internally (shear
force, cooking loss, and eating quality) ( McKee and Sams, 1998; Mielnik et al.,
1999; Alvarado and Sams, 2002; Young and Smith, 2004; James et al., 2006; Huezo
et al., 2007a; Carroll and Alvarado, 2008; Zhuang et al., 2008, 2009). For breast
meat tenderness and sensory properties, Carroll and Alvarado (2008) reported that
the shear force value was significantly higher (less tender) in WIC fillets than in AC
fillets, and that the AC fillets were significantly differentiated by consumer panelists
for texture and flavor. Having an ideal texture and improved flavor, AC chicken was
reported to be preferred over WIC chicken (Veerkamp, 1991; Gazdziak, 2006).
However, Huezo et al. (2007a) reported that the color and tenderness of raw and
cooked breasts were not affected by the chilling method (WIC or AC), whereas fillets
from WIC carcasses had a significantly lower cooking yield than those from AC
carcasses. Mielnik et al. (1999) noted that moisture content in the skin and breast
meat, cooking loss, and pH values were the same between AC and EAC. Some data
published in the United States have compared the properties of AC and WIC on
meat quality and sensory profile (Huezo et al., 2007a; Zhuang et al., 2009), but
limited research has been conducted comparing the 3 chilling methods (WIC, AC,
and EAC). Information is needed on the functional characteristics of both raw and
processed breasts from different chilling methods because an increasing portion
(89%) of raw broiler meat is processed further and marketed (National Chicken
Council, 2009). Therefore, the objective of this study was to compare the effects of
38

the 3 chilling methods on raw fillets, processed meats, and the consumer sensory
properties of broilers.
4.3 Materials and Methods
4.3.1 Broiler Carcass Preparation
A total of 189 male birds (approximately 46-d-old broilers; 63 birds/replication)
were obtained from a local broiler producer. In each of 3 replications, the broilers
were taken from different flocks of the producer and processed on different days.
After withdrawing the birds from feed for 12 h and cooping them in plastic cages,
they were transported by truck to the poultry processing facility in the meat
laboratory at Michigan State University. On arrival, the birds were electrically
stunned for 3 s (40 mA, 60 Hz, 110 V) and bled for 90 s by severing both the carotid
artery and jugular vein on one side of the neck. In each replication, 1 group of 21
birds was subjected to hard scalding at 56.7°C for 120 s for WIC, whereas 2 groups
of 21 birds were soft scalded at 50° for 220 s for either AC or EAC. The birds were
C
defeathered in a rotary drum picker (SP38SS automatic pickers, Brower Equipment,
Houghton, IA) for 25 s. After manual evisceration and washing, each of the
carcasses was tagged on the wing and assigned to one of three chilling treatments.
4.3.2 Chilling Treatments, Deboning, Storage, and Sampling
In each replication, 21 hard-scalded carcasses were submersed for WIC in a
tank of an ice and water mixture (approximately 0° , 7.6 L/bird) and agitated every 5
C
min in a chilling room (0.9 ±0.4° After chilling , each carcass was hung by the
C).
hocks in shackles on a stainless steel bar and allowed to drip for 5 min. For AC or
EAC, each of 21 carcasses from soft scalding was hung by the hocks on a stainless
steel bar and exposed to a continuous air flow (1.0 m/s) in the chilling room. Two
industrial-size fans (portable air circulator; BF30DD, Ventamatic Ltd., Mineral Wells,
39

TX) were installed to blow cold air toward the carcasses of the 2 chilling treatments.
For EAC, cold water (approximately 0.4° was manua lly sprayed (model RL Pro
C)
sprayer 997P, Root-Lowell Manufacturing Co., Lowell, MI) onto carcasses (0.5
L/carcass) every 5 min, whereas the carcasses in AC received the blowing air only
during chilling. Both temperature (0.9 ±0.4° and RH (87 ± 4%; model 4410
C)
traceable digital humidity/thermometer, Control Company, Friendswood, TX) of the
chilling room were monitored every 15 min. In each chilling condition, 1 of the midsized carcasses was selected and the internal breast temperature was recorded
every 5 min with a digital thermometer/logger (model 800024, Sper Scientific Ltd.,
Scottsdale, AZ) until the internal temperature reached 4°
C.
On completion of chilling, the carcasses were removed from the shackle line,
individually packaged in freezer bags (S. C. Johnson & Son Inc., Racine, WI), and
held in the same chilling room before deboning the breasts. After 5 h postmortem,
both sides of each breast were manually deboned and skinned. The surface color
[Commission Internationale de l’Eclairage (CIE) L*, a*, and b*] measurement was
immediately taken on the skinless breast fillets. Each of the right and left fillets was
individually placed in plastic bags and stored on ice for later analyses. The following
day, anterior portions (approximately 20 g) from 10 left fillets/treatment were used to
determine pH values and moisture content of raw breast muscle. The remaining
portions of the fillets were ground together, made into a cooked gel, and used for the
evaluation of moisture content, cooking yield, and torsion values. The other 10 left
fillets were cooked for determinations of cooking yield and shear force. For
consumer sensory evaluations, all 20 of the right fillets were used.
4.3.3 Color Measurements

40

Commission Internationale de l’Eclairage L*, a*, and b* values were measured on
the surface of skinned raw fillets immediately after chilling by using a chromameter
(CR-400, 8-mm aperture, illuminant C; Konika Minolta Sensing Inc., Osaka, Japan)
calibrated with a white plate (L*, 97.28; a*, −0.23; b*, 2.43). Six CIE L*, a*, and b*
readings (3 readings/side) were obtained for each replication.
4.3.4 pH Value and Moisture Determination
After 24 h of storage, the pH value was measured with a pH electrode (model
13-620-631, Fisher Scientific Inc., Houston, TX) attached to a pH meter (Accumet
AR15, Fisher Scientific Inc., Pittsburgh, PA) after homogenizing 5 g of raw meat in
25 mL of distilled, deionized water. Moisture content was determined on each of the
raw breasts and cooked gels after 16 to 18 h of drying at 102°C in a drying oven
(Yamato DX 400, Yamato Scientific Co. Ltd., Tokyo, Japan) following method
950.46B of AOAC (2000). The weight loss after drying was recorded as the moisture
content.
4.3.5 Chicken Breast Gel Preparation, Cooking Yield, and Torsion Test
For the breast gel preparation, each of the left raw fillets (without the anterior
portions) was cut into 4 pieces and pooled according to chilling treatment. The
pooled meat (1,500 g of meat, 68% of a batch) was first chopped with ice (15%) in a
bowl chopper (Vertical- Cutter Mixer 5190, Stephan Machinery Corp., Columbus,
OH) for 30 s at 1,500 rpm and then emulsified with additional ice (15%) and sodium
chloride (2%) for 2.5 min at 2,100 rpm. The batter was stuffed into pre-weighed
stainless steel cylindrical tubes that were sprayed with vegetable oil to prevent
sticking on removal of the cooked gels. The tubes were capped, reweighed, and put
into a water bath (model 25, Precision Scientific Co., Chicago, IL) at 80° for 20 min.
C
41

After cooking, the tubes were immediately cooled in ice for 15 min, sealed in plastic
bags, and stored overnight in a refrigerated room (3° The following day, the gels
C).
were removed from the tubes, and the 3 parts (cooked gel, empty tube, and cap)
were individually weighed to determine cooking yield.
Prior to a torsion test, the gels were warmed in plastic bags at room
temperature for 2 h and then cut perpendicularly to a length of 3.0 cm by using an
adjustable Plexiglas-cutting device. Styrene disks were glued to each end of the
testing samples. The samples were then milled into a dumbbell shape (10 mm in
diameter at the midsection) by using a shaping machine (KCI- 24A2, Bodine Electric
Co., Raleigh, NC). Each specimen was placed on a viscometer (DV-III Ultra,
Brookfield Engineering Laboratories Inc., Middleboro, MA) and twisted at 2.5 rpm. At
the breaking point, both shear stress and shear strain were calculated with the
recorded torque and elapsed time by using the equations given by Hamann (1983).
Ten specimens were evaluated for each treatment for 3 separate replications.
4.3.6 Cooking Yield and Shear Force Measurements
For the evaluation of cooking yield and shear force, 10 left fillets (aged 24 h)
per treatment were individually weighed, placed on stainless trays on a stainless
steel rack, and covered with foil. The fillets were cooked to an internal temperature of
76.7° in a preheated convection oven (Bloccos-101/ AA, The G. S. Blodgett Corp.,
C
Burlington, VT) at 177°C following USDA-Food Safety and Inspection Service (2001)
guidelines. Temperature was monitored with 2 thermocouples inserted to the thickest
parts of 2 breast samples on 2 trays. Both thermocouples were attached to a digital
thermometer/ logger (model 800024, Sper Scientific Ltd., Scottsdale, AZ). During
cooking, all trays were rotated once for uniform cooking. After cooking, the fillets
were removed from the trays, individually wrapped with foil, and stored overnight at
42

3° in plastic bags. The following day, the cooked breasts were brought to room
C
temperature and weighed again to determine cooking yield. Cooking yield was
calculated by the following equation: (cooked breast weight)/(raw breast weight)
× 100. Shear force was determined according to the razor-blade method described
by Cavitt et al. (2004) and Meullenet et al. (2004). A texture analyzer (TAHDi,
Texture Technologies Corp., Scarsdale, NY) was calibrated with a 5-kg load cell; the
razor blade (height, 24 mm; width, 8 mm) was set at 10 mm/s, and the test was
triggered by a 10-g contact force. The shear force value (N) was calculated as the
maximum force recorded during the shear. Two shear force measurements per
breast fillet were made.
4.3.7 Consumer Acceptance Evaluations
A total of 210 consumer panelists (70/replication) evaluated the broiler breasts
(20 right fillets/chilling) chilled by 1 of 3 chilling treatments. The panelists recruited
were students, staff, and faculty members at Michigan State University. After 24 h of
storage, the breasts were cooked according to USDA-Food Safety and Inspection
Service (2001) guidelines, as described previously for cooking yield. Immediately
after cooking, the central portion of each breast was trimmed to approximately 5 × 6
cm. The trimmed breasts were then wrapped with aluminum foil and kept at 60° in
C
a warmer (RO230-C, 22-Quart Roaster Oven, Rival, Milford, MA) until sensory
testing was completed within 2 h. On serving, the prepared breast was cut again into
4 pieces (approximately 12 to 15 g; a total of 80 pieces/ treatment). One piece from
each treatment was labeled with a 3-digit random number and placed on a polyfoam
tray with a cover. The tray, with 3 samples, was randomly presented to each
panelist. Both filtered water and unsalted crackers were provided for mouth

43

cleansing between samples. Sensory evaluations were conducted in individual
booths equipped with a touch screen computer and controlled lighting.
Questionnaires were prepared and data were collected using Sensory Information
Management Systems software (Sensory Computer Systems, Morristown, NJ).
Panelists were asked to evaluate the samples for flavor, texture, juiciness, and
overall acceptability on a 9-point hedonic scale (9 = like extremely; 1 = dislike
extremely). They were also encouraged to make comments on their decisions
4.3.8 Statistical Analysis
All experiments were replicated 3 times. Data were statistically analyzed using
the GLM procedure of SAS (SAS Institute, 2002) as a randomized block design. If
significance was determined (P < 0.05) in the model, dependent variable means
were separated using the least significant difference procedure of SAS (SAS
Institute, 2002). Consumer sensory evaluation data were pooled across panelists
and analyzed as described previously.
4.4. Results and Discussion
Carcass chilling time is one of the critical parameters in the design of any
chilling system, and carcass temperatures have been noted to affect meat quality
(James et al., 2006). In this study, the internal temperature of carcasses before
chilling was 40.7° which was reduced to 4°C or be low during chilling, with average
C,
times of 57, 125, and 93 min for WIC, AC, and EAC, respectively (Figure 4.1). These
results are similar to the trend shown in previous research (James et al., 2006;
Zhuang et al., 2009). Huezo et al. (2007b) found that the initial internal temperature
of carcasses before chilling averaged 32.8°C and th at the chilling times to 4.4°
C
were 35 and 90 min for WIC and AC, respectively. The lower initial temperature and
reduced chilling time were due to the different processing conditions: their carcasses
44

were transported from a commercial processing line to the laboratory before
measuring the initial breast temperatures and subsequent chilling. Veerkamp (1985)
and Mielnik et al. (1999) noted that, compared with AC, EAC had an increase in heat
transfer by the evaporation of water.
The pH values of broiler breasts, measured after chilling and holding for 24 h
postmortem, are shown in Table 4.1. Water-chilled breasts had a higher pH value
(5.6) than did AC (5.5) and EAC (5.5) breasts, which were not significantly different.
Previously, Huezo et al. (2007b) indicated that more portions of WIC fillets,
compared with AC fillets, had pH higher than 5.8 at 150 min postmortem, probably
because of an accelerated rigor mortis in the extended AC. Carroll and Alvarado
(2008) reported other results of the higher pH in AC than in WIC. However, their
outcomes were obtained from broiler fillets chilled differently in different plants, which
might not be an accurate reflection of 24-h pH had the broilers been processed in the
same facility and from the same flock. In the case of AC and EAC, no significant pH
difference between the 2 chilling methods was found in our study, which was similar
to the report of Mielnik et al. (1999).
None of the 3 chilling methods (WIC, AC, and EAC) resulted in a significant
difference (P > 0.05) in moisture content and cooking yield of broiler breasts
measured after 24 h of storage (Table 4.1). Similar results were also reported in 2
separate research studies, which showed no moisture difference between WIC and
AC after 24 h of storage (Zhuang et al., 2008) and no moisture difference between
AC and EAC (Mielnik et al., 1999). Hale and Stadelman (1973) indicated that the
weight gained in WIC was lost during storage of the fresh product. It appeared that
the absorbed water in WIC simply came out as purge during value-added cutting and
overnight storage, and did not increase muscle moisture content or cooking yield.
45

When breast fillets were marinated, AC fillets had a higher solution pickup and
cooking yield than WIC fillets, which was expected because of the increased
moisture loss and ability to retain more marinade than the WIC fillets (Huezo et al.,
2007a; Carroll and Alvarado, 2008).
Both Allo-Kramer and Warner-Bratzler shear force have commonly been used
for evaluating tenderness in broiler breast meat, but a razor-blade method was
recently introduced as more advantageous in predicting poultry meat tenderness
(Cavitt et al., 2004; Meullenet et al., 2004). In this study, the shear force value of
cooked breast meat was determined by the razor-blade method after 24 h of storage
(Table 4.1). Although no differences (P > 0.05) in shear force values were
determined among the 3 chilling treatments, WIC breast meat had a numerically
(13.7 N) higher value than AC breast meat (12.0 N) or EAC breast meat (11.4 N).
Similarly, Huezo et al. (2007b) found that the Allo-Kramer shear values of WIC fillets
were approximately 2 kg/g higher, with no statistical difference, compared with the
shear values of AC fillets when the fillets were deboned at approximately 3 h
postmortem. In 2008, Carroll and Alvarado observed that shear force was
significantly higher (less tender) in WIC fillets than in AC fillets when deboned at 24 h
postmortem.
On chilling and deboning at 5 h postmortem, the 3 chilling methods affected
the surface color of broiler breast fillets (Table 4.1). Water chilling resulted in the
highest (P < 0.05) CIE L* value of breast fillets, whereas AC showed the lowest (P <
0.05) CIE L* value (darker) among the 3 chilling methods. Similarly, Carroll and
Alvarado (2008) and Mielnik et al. (1999) found that AC breasts had a lower L* value
(darker color) than WIC or EAC breasts. For redness, the CIE a* value was the
highest (P < 0.05) in the AC breasts, and no significant difference (P > 0.05) was
46

found between WIC and EAC breasts. For yellowness, AC breasts had a higher (P <
0.05) CIE b* value than WIC breasts, and EAC showed an intermediate value.
Several research studies have reported no significant difference between WIC
and AC in L*, a*, and b* values of raw breast fillets (Fleming et al., 1991; Huezo et
al., 2007a; Zhuang et al., 2009). However, Huezo et al. (2007a) noted a significant
correlation between the weight loss of AC carcasses and the color values of raw
breast fillets: the higher the weight loss of AC carcasses, the lower the L* values and
the higher the a* values of raw fillets. They also speculated that the increase in L*
values of WIC carcasses may have resulted from the removal of water-soluble
proteins (myoglobin, hemoglobin, and cytochrome C).
The cooked breast gels stored for 24 h were evaluated for moisture content,
cooking yield, and textural properties (shear stress and strain; Table 4. 2). Moisture
content and cooking yields of the gels were not significantly affected by any chilling
method. These results were coordinated with the previous observation of no
moisture difference in the raw fillets (Table 4.1), although the moisture content on the
surface of fillets might not be the same, considering the different L* values (Table4.
1). In accordance with the moisture and cooking yield results, shear stress and strain
values of the cooked breast gels among the 3 chilling treatments were not
significantly different. Both gel structure and firmness were reported to be closely
related to water-binding ability and protein integrity (Hermansson, 1979; Hamann
and MacDonald, 1992).
Table 4.3 shows the mean consumer sensory scores of cooked breast fillets
evaluated by 210 individuals. Overall, the scores for flavor, texture, and overall
acceptability were similar (P > 0.05) in all breast samples, indicating that the 3
chilling methods did not affect sensory properties. Similarly, Zhuang et al. (2009)
47

reported that the flavor and texture profiles of AC broiler breasts were not different
from those of WIC samples. Pedersen (1982) obtained similar results for odor,
tenderness, and overall acceptability when comparing AC and WIC chicken. Among
the 3 chilling methods in this study, AC resulted in a juiciness score (P < 0.05) higher
than those for WIC and EAC, which were similar to each other. Similar results were
observed by Lee et al. (2008), who reported that both AC products (no water added)
showed higher juiciness scores than 2 of the 4 WIC products (2 for 15% chicken
broth-enhanced products; 2 for products with 2 to 3% water retained) when the 6
different commercial brands (2 AC and 4 WIC products) were evaluated. The only
WIC product obtaining higher tenderness than the AC product was from the chicken
enhanced with 15% chicken broth.
In conclusion, 3 values (pH, color, and juiciness) of broiler fillets were affected
by the 3 different chilling methods (WIC, AC, or EAC). Water chilling, rather than AC
or EAC, showed the most efficient chilling rate. In the consumer sensory test, no
treatment difference was found among the 3 chilling methods, with the exception of
higher juiciness scores for the AC samples.
To date, WIC has been a common chilling method in the United States,
mainly because of the chilling efficacy and absence of weight loss. Currently, the
generic advantages of WIC are being challenged by the water shortage, cost of
waste management, and revised USDA rules. Water chilling appears to have some
straightforward advantages during chilling; however, AC possesses more potential
advantages after chilling, such as reduced water consumption, reduced waste
management, and a juicier product. Additional information is required on the overall
benefits of the 3 chilling methods to compare not only the poultry chilling rate, but
also the entire processing, including product safety, value-added processing, the
48

reduction in fresh water consumption, and environmentally friendly processing for the
future.
4.5 Acknowledgments
The authors thank the Midwest Poultry Consortium (St. Paul, MN) and
Michigan Agricultural Experiment Station (East Lansing) for providing funding.

49

Table 4. 1. Effects of chilling methods on the properties of raw and cooked broiler
breast fillets

Properties

1

Water

Air

a

pH
Moisture (%)

75.1 ± 0.13

Cooking yield (%)

75.9 ± 1.32

Shear force (N)

13.7 ± 1.25

CIE L*

53.4 ± 0.28

CIE a*

2.9 ± 0.11

CIE b*

b

5.6 ± 0.02

2.6 ± 0.14

5.5 ± 0.02

a

a -c

a

75.4 ± 0.21

a

a

74.4 ± 1.07

a

a

12.0 ± 0.34

a

c

49.6 ± 0.29

b

a

3.4 ± 0.09

b

a

3.4 ± 0.22

Evaporative-air
b

5.5 ± 0.02
a

75.6 ± 0.10
a

75.5 ± 1.24
a

11.4 ± 0.40
b

51.1 ± 0.26
b

3.0 ± 0.09
ab

3.0

± 0.19

Means ± SE within a row with no common letter are different (P < 0.05).

1

pH, moisture, cooking yield, and shear force values were measured after chilling
and holding for 24 h postmortem, and CIE L*a*b* values were measured
immediately after chilling and being skinned. Number of observations in each
chilling, n = 60 (pH); 10 (moisture); 30 (cooking yield); 60 (shear force); 360 (L*a*b*,
each).

50

Table 4. 2. Effect of chilling methods on moisture content, cooking yield, and
functional properties of gels made from broiler breast meat

Properties

1

Water

Air
a

Moisture (%)

85.8 ± 2.46

Shear stress (kPa)

25.6 ± 0.67

Shear strain

a

78.8 ± 0.06

Cooking yield (%)

78.8 ± 0.16

1.3 ± 0.05

a

a

85.3 ± 1.68

a

a

Evaporative-air

a

25.8 ± 0.64

a

a

1.3 ± 0.04

a

78.7 ± 0.12
a

86.5 ± 1.97
a

25.7 ± 0.84
a

1.4 ± 0.04

Means ± SE within a row with no common letter are different (P < 0.05).

1

All values were measured from the cooked and 24 h stored gels. Number of
observations in each chilling, n = 10 (moisture); 15 (cooking yield); 30 (shear
stress/strain).

51

Table 4. 3. Effect of chilling methods on consumer sensory attributes of cooked
broiler breasts after 24 h of storage

Attributes

1

Water

Air

a

Flavor

6.4 ± 0.11

Juiciness

6.2 ± 0.12

Overall acceptability

a

6.4 ± 0.11

Texture

6.3 ± 0.11

a,b

Evaporative-air

6.4 ± 0.11

a

a

6.7 ± 0.11

b

a

6.6 ± 0.12

a

a

6.2 ± 0.11

a

6.5 ± 0.11
a

6.4 ± 0.12
b

6.0 ± 0.13
a

6.5 ± 0.11

Means ± SE within a row with no common letter are different (P < 0.05).

1

All values were measured from the central portions of cooked breasts after chilling
and holding for 24 h postmortem. Scores based on 9-point hedonic scale, where 9 =
like extremely and 1 = dislike extremely. Number of observations in each chilling, n =
210 (each attribute).

52

Figure 4. 1. Temperature change profiles of broiler breast fillets during WC, AC, or
EAC: ■- water chilling, ▲- air chilling, ●- evaporative air chilling.

53

Chapter 5
Microbiological Quality of Water-Immersion and Air-Chilled Broilers

54

5.1 Abstract
Carcass chilling during broiler processing is a critical step in preventing growth of
pathogenic and spoilage bacteria. The objective of this study was to compare the
microbiological quality of air- and water-chilled broiler carcasses processed at the
same commercial facility. For each of four replications, 15 broilers were collected
from the same commercial processing line after evisceration, after spraying with
cetylpyridinium chloride (a cationic disinfectant), and after air chilling or water
immersion chilling (WIC). All carcasses were quantitatively examined for mesophilic
aerobic bacteria, Escherichia coli, coliforms, and Campylobacter as well as for the
presence of Salmonella and Campylobacter. No significant differences (P < 0.05)
were seen between air and water chilling for E. coli or coliforms or for the incidence
of Salmonella and Campylobacter. Lower numbers of Campylobacter were
recovered from WIC than from air-chilled carcasses (P < 0.05), but the incidence of
Campylobacter on WIC carcasses was similar, suggesting that some Campylobacter
organisms were injured rather than killed during WIC. In-line spraying with the
disinfectant effectively decreased the incidence of Salmonella and Campylobacter on
prechilled carcasses; however, cells presumably injured by the sanitizer recovered
during chilling. Therefore, on-farm intervention strategies remain critically important
in minimizing the spread of microbial contaminants during processing.
5.2 Introduction
Chickens are known to harbor many pathogenic microorganisms including
Salmonella, Campylobacter, Clostridium perfringens, Listeria monocytogenes, and
Enterohemorrhagic Escherichia coli (Wempe et al., 1983; Izat et al., 1998; Capita et
al., 2004). During poultry processing, the carcass must be quickly chilled to prevent
microbial growth. Water immersion chilling (WIC) is the most widely used method to
55

lower carcass temperature in the United States. During chilling, the eviscerated birds
are submerged in cold water that is flowing counter to the direction of carcass
processing. In addition to reducing carcass temperature faster than other chilling
methods, WIC also decreases the bacterial load (Mead et al., 1973; Blood and
Jarvis, 1974; Thomson et al., 1979; Waldroup et al., 1992; Blank and Powel, 1995;
Allen et al., 2000; Bilgili et al., 2002; Northcutt et al., 2006;) with larger microbial
reductions obtained by adding a chlorine-based sanitizer to the water (James et al.,
2006; Mead et al., 1994). However, since WIC increases carcass weight (Young and
Smith 2004;Jeong et al., 2011a), the Food Safety and Inspection Service of the U.S.
Department of Agriculture (USDA) now limits the amount of water retained (USDA,
2001) with any additional water required to be listed on the label.
Commercial air chilling (AC) of fresh poultry dates back almost 35 years in the
European Community after spin-chilling was banned in 1977 (Brant,1974;
Stadelman, 1974; Thomson, 1974) to minimize cross-contamination during WIC
(Thomas, 1977). Although microbial cross-contamination can also occur during AC
through aerosols (Fries and Graw, 1999; Mead et al., 2000), air-chilled broiler
carcasses are not prone to water uptake and are of potentially higher quality (Carroll
and Alvarado, 2008; Huezo et al., 2007a,b; Jeong et al., 2011 a,b). When Carroll
and Alvarado (2008) compared AC and WIC, AC broiler carcasses had improved
color, marination pick-up, tenderness, and shelf life. However, the microbiological
benefits of AC are less clear. While Sanchez et al. (2002) found AC to be superior to
WIC, others have reported similar (Burton and Allen, 2002; James et al., 2006) or
higher microbial populations (Allen et al., 2000; Berrang et al., 2008) for AC
carcasses. These differences may be due to variations in the prechill carcass
microflora and bacterial load, the type of chiller equipment, antimicrobials used in the
56

chiller water, and sampling techniques with the large number of variables
complicating any direct comparison between chilling methods.
Air-chilled poultry was first produced commercially in 1998 in the United
States (Gazdziak, 2006.) and has continuously grown in the poultry industry due to
an end product of potentially higher quality (Barbut, 2002; Carroll and Alvarado,
2008; Huezo et al., 2007a,b). While still predominant in the United States, the
practice of WIC has been recently challenged due to cross-contamination,
wastewater management issues, reshackling, and postchill purge (Bailey et al.,
1987; Huezo et al., 2007a, b; Sams, 2001; Sanchez, 2002; Smith et al., 2005). In
order to meet new customer requirements, some poultry processors have either
partially or fully switched to AC. However, it is not yet known how such carcasses
from the same facility may differ microbiologically. Therefore, this study was
designed to assess the number of mesophilic aerobic bacteria (MAB), coliforms, E.
coli, and Campylobacter, as well as the prevalence of Salmonella and
Campylobacter on air- and water-chilled broiler carcasses that were commercially
processed at a single facility.
5.3 Materials and Methods
5.3.1 Broiler carcass rinsed samples
During each of the four visits, broiler carcass rinse samples were collected
from 60 approximately 46-day-old broilers (Hubbard M99/Ross 708) at a commercial
broiler processing plant. Carcass rinse samples were collected onsite from 15 birds
after evisceration and carcass washing, after spraying with cetylpyridinium chloride
(Cecure, Safe Foods Corp., North Little Rock, AR) (plant visits 2, 3, and 4 only), and
after AC or WIC. To eliminate residual effects from this disinfectant, 15 birds with two

57

additional ones (for temperature monitoring) passing through the antimicrobial spray
cabinet were immediately rinsed with tap water before AC.
After, 50 min of WIC, 15 carcass rinse samples were collected after the
internal breast temperature decreased below 50C as measured by inserting a digital
thermometer probe (Model 800024, Sper Scientific, Ltd., Scottsdale, AZ) into the
center of the broiler breast. For AC, 17 birds were individually hung on the shackles
of a cart which was moved into a cold room (0.5 ± 0.40C) equipped with an industrialsize fan (portable air circulator, BF30Dd, Ventamatic, Ltd., Mineral Wells, TX) to blow
cold air (1.0 m/s) over the carcasses. Digital thermometer loggers (Model 800024,
Sper Scientific) were inserted into two extra medium-sized carcasses, by visual
evaluation, to monitor the internal breast temperature. Rinse samples from the
remaining 15 carcasses were collected after, 150 min when the internal breast
temperature decreased below 50C.
For carcass rinse samples, broiler carcasses removed at the previously
discussed points during processing were sampled following the USDA Food Safety
and Inspection Service wholecarcass rinse method (USDA, 2010). Carcasses were
placed into 12-liter sterile sample bags (VWR International, Radnor, PA) and
manually rinsed with 400 ml of buffered peptone water with a rocking motion for one
min. All carcass rinse samples were then placed in an ice chest, transported back to
Michigan State University, and analyzed within 6 to 7 h of collection.
5.3.2 Microbiological analysis
Serial 10-fold dilutions of the carcass rinsate were surface plated (0.1 ml) in
duplicate on standard method agar (Acumedia, Lansing, MI) to enumerate MAB. E.
coli and coliforms were quantified by using Petrifilm E. coli/Coliform count plates (3M
Microbiology Products, St. Paul, MN).
58

Campylobacter was assessed both quantitatively and qualitatively. For
Campylobacter enumeration, 0.25 ml of the carcass rinse sample was plated on
each of four Campy-Cefex agar plates (Acumedia). These plates were then placed in
1-gal (NNN-liter) resealable plastic bags that were flushed with a mixture of 5% O2,
10% CO2, and 85% N2 (Airgas Great Lakes, Lansing, MI) and incubated at 420C for
48 h. In addition to direct plating, 30-ml aliquots of the carcass rinse sample were
added to 4-oz (NNN-liter) Whirl-Pak bags (Nasco, Modesto, CA) containing 30 ml of
2x Blood-Free Bolton’s enrichment broth (Oxoid LTD., Basingstoke,UK). These bags
were then flushed with the same gas mixture and incubated at 420C for 48 h with the
enriched sample and then streaked onto Campy-Cefex agar plates that were
incubated as previously described for Campylobacter enumeration. Five to 10
presumptive Campylobacter colonies from each treatment were examined
microscopically for typical cellular morphology and motility and then confirmed by the
Campy detection system (Remel Inc., Lenexa, KS).
Salmonella was qualitatively assessed by adding 30 ml of the carcass rinse
sample to 30 ml of buffered peptone water (Acumedia) followed by 20 h of incubation
at 370C. Thereafter, 30 ml of this preenrichment was transferred to 30 ml of 2|
Rappaport-Vassiliadis broth (Acumedia) and incubated at 420C for 20 h. An aliquot
of 120 ml of this enrichment was then examined for Salmonella by using Reveal
Salmonella test kits (Neogen Corp., Lansing, MI). All positive samples were streaked
onto brilliant green sulfur and xylose lysine tergitol-4 agar (Acumedia), incubated at
370C for 24 h, and then inspected for typical Salmonella colonies to confirm the
Reveal Salmonella results.
5.3.3 Statistical Analysis

59

The general linear model and Duncan’s multiple range test (SAS Institute,
Cary, NC) were used to assess the quantitative data for statistically significant
differences

at

P

<

0.05.

Prevalence

differences

for

Salmonella

and

Campylobacterwere determined using the chi-square test and Fisher’s exact test
whenever the expected frequencies were less than 5%. Multiple comparisons for
proportions were determined by using the freq procedure and SAS macro compprop
when the chi-square/Fisher test was significant (P < 0.05).
5.4 Results and Discussion
Carcass chilling is a critical step in preventing microbial growth during broiler
processing. Immersion chilling predominates in the United States with air chilling
being commonly used in Europe. Given the USDA rules (USDA, 2001) to accurately
declare any water retained by carcasses resulting from chilling processing, AC is
now being viewed as a promising alternative in the United States. Thus far, all
microbial baseline data in the United States have been based on WIC with similar
data needed for AC.
In our study, the broiler carcass temperature before chilling as measured in
the center of the breast averaged 36.60C, with this temperature decreasing to 3.7
and 2.80C after 150 min of AC and 50 min of WIC, respectively. Total chlorine
concentration in the chilling water ranged from 50 to 90 ppm with free chlorine
ranging from 0.4 to 0.8 ppm. The temperatures of air chilling room and immersion
chilling water were 1.0 ± 0.2 and 0.5 ± 0.40C, respectively.
The mean bacterial populations during poultry processing are shown in Table
5.2. Carcass rinse samples analyzed at each of the four processes (after
evisceration, after disinfectant spraying, and after AC or WIC) had mean MAB
populations of 2.98, 1.64, 2.16, and 1.79 log CFU/ml, respectively. In addition, all
60

post evisceration samples yielded significantly lower (P< 0.05) MAB populations on
water-chilled than on air-chilled carcasses. Similar results were also observed for
Campylobacter with WIC significantly (P < 0.05) more effective than AC in
decreasing the numbers of Campylobacter. While disinfectant spraying decreased
the numbers of E. coli, coliforms, and Campylobacter in carcass rinse samples by
1.76 (98%), 2.01 (95%), and 1.56 (99%) log CFU/ml, respectively, air and waterchilled carcasses yielded statistically similar E. coli and coliform populations with the
numbers of Campylobacter significantly lower (P < 0.05) on water than on air-chilled
carcasses.
Salmonella was not detected (1 CFU/30 ml of carcass rinsate) on broiler
carcasses after disinfectant spraying; however, statistically similar Salmonella
populations were observed after AC and WIC (Table 5.3). Similarly, water and air
chilling significantly decreased the incidence of Campylobacter from 91.94% to 51.67
and 67.74%, respectively, with no significant difference (P < 0.05) observed between
the two chilling methods.
In our study, no significant differences were seen in the incidence rates for
Salmonella or Campylobacter on carcasses after AC or WIC. However, Sanchez et
al. (2002) reported a significantly lower incidence for both Salmonella and
Campylobacter in air-chilled than in water-chilled broilers. In their study, two different
facilities, one in Missouri for WIC and the other in Nebraska for AC, used potentially
different stunning, scalding, and carcass washing procedures. It is generally agreed
that farm-to-farm and flock-to-flock variation in microbial populations as reported by
others (Fluckey et al., 2003; Heuer et al., 2008; Wedderkopp et al., 2001) could
account for the observed differences in Salmonella and Campylobacter prevalence
after chilling. In contrast to the study described (Sanchez et al., 2002), our air and
61

water-chilled birds were processed at the same facility under identical conditions.
Since our only variable was the method of chilling, variations due to other processing
parameters (e.g., origin of farm, conditions during stunning, scalding, evisceration,
and washing) were minimized.
The bacterial reductions obtained in our study during WIC are consistent with
most other published reports (Allen et al., 2000, Bilgili et al., 2002; Dickens and Cox,
1992; James et al., 1992; Lillard, 1990; Waldroup, 1992). Compared to WIC, AC
yielded similar reductions for E. coli and coliforms but was less effective against
Campylobacter (Table 5.2). In work by Blaser et al. (1986), C. jejuni was more easily
injured and inactivated in chlorinated water than E. coli, which helps explain the
lower Campylobacter populations in rinse samples from WIC carcasses. Although
skin surface drying may lead to temporary reductions in Campylobacter (Oosterom
et al., 1983; Lindblad et al., 2006), this impact of drying is minimized after packaging
(Thomas, 1977). In agreement with our findings, other previous studies reported
greater microbial reductions on poultry carcasses after WIC as opposed to AC (Allen
et al., 2000; Fluckey et al., 2003) with Berrang et al. reporting lower bacterial
populations on carcass halves that were water- rather than air-chilled.
In the present study, application of cetylpyridinium chloride to the carcasses
as an in-line antimicrobial spray before chilling significantly reduced the levels of
MAB, E. coli, and coliforms as well as the incidence of Salmonella and
Campylobacter. Antimicrobial treatments have shown both bactericidal and
bacteriostatic effects depending on the concentration used (Palumbo and
Williams,1994) A 1% cetylpyridinium chloride treatment of frankfurters inoculated
with L. monocytogenes had an initial bactericidal effect and a bacteriostatic effect
during 42 days of storage (Singh et al., 2005). Using Cecure, the actual spray
62

concentration of cetylpyridinium chloride ranged from 0.5 to 0.7% in the poultry
processing plant (Beers et al., 2006). In this study, the cetylpyridinium chloride
antimicrobial treatment was likely bacteriostatic rather than bactericidal since higher
populations were observed after chilling.
Levels of MAB, coliforms, and E. coli have been routinely used as indicators
of microbial quality and shelf life. In a previous study, Cason et al. (1997) found no
correlation between populations of aerobic bacteria, Salmonella, and Campylobacter
on broilers after defeathering, before chilling, or after chilling. Although Fluckey et al.
(2003) reported decreased numbers of aerobic bacteria, E. coli, and coliforms on
broiler carcasses during processing; this same pattern was not observed for
Salmonella or Campylobacter. Our results also indicate that aerobic bacteria,
coliforms, and E. coli should not be used as potential indicators of pathogens.
Based on our findings, similar reductions were seen in the numbers of E. coli
and coliforms, as well as the incidence of Salmonella and Campylobacter on broiler
carcasses after AC and WIC. However, WIC in water containing 50 to 90 ppm
chlorine was more effective in reducing the level of Campylobacter. In addition, no
microorganisms (MAB, E. coli, coliforms, Salmonella, or Campylobacter) were found
in the chlorinated chilling water (data not shown). Although the in-line antimicrobial
spray

treatment

effectively

decreased

the

incidence

of

Salmonella

and

Campylobacter on prechilled carcasses, cells injured by this treatment likely
recovered during carcass chilling, reinforcing the need for on-farm Salmonella
control programs.
5.5 Acknowledgements
The authors thank the Animal Agricultural Initiative and Michigan State
University AgBioResearch for providing funding.
63

Table 5.1. Comparison of chilling parameters between air and water chilling
Chill

Carcass

WIC
AC

Total

Free

temperature

temperature

chlorine

chlorine

before chill (°
C)

Treatment

Carcass

after chill (°
C)

(ppm)

(ppm)

36.6

2.8

50-90

0.4-0.8

50

36.6

3.7

not available

not available

150

n = 4 observations repeated at least 3 times

64

time
(min)

Table 5.2. Populations (log CFU/ml) of mesophilic aerobic bacteria (MAB), E. coli,
coliforms and Campylobacterrecovered from broiler carcasses before and after AC
and WIC

Treatment

After evisceration
After disinfection

E. coli

MAB

2.98 ± 0.41
1.64 ± 1.07

After AC

2.16 ± 0.51

After WIC

1.79 ± 0.63

a
c
b
c

1.79 ± 0.59
0.03 ± 0.16
0.52 ± 0.49
0.48 ± 0.56

a

Campylobacter

Coliforms

a
c
b
b

2.12 ± 0.55
0.11 ± 0.38
0.83 ± 0.64
0.75 ± 0.65

a
c
b
b

1.57 ± 0.93
0.01 ± 0.09
0.62 ± 0.68
0.21 ± 0.42

a
c
b
c

Mean values ± SEM with different letters in the same column are significantly
different (P < 0.05).
n = 15 observations repeated at least 3 times

65

Table 5.3. Prevalence (%) of Salmonella and Campylobacter on broiler carcasses
before and after AC and WIC
Treatment
After evisceration

Salmonella
11.29

After disinfection

0.00

AC

25.81

WC

12.90

a

a

b

a

a

Campylobacter
91.94
4.35
67.74
51.61

a

c

b

b

Mean values ± SEM followed by different letters in the same column are
significantly different (P < 0.05).
n = 15 observations repeated at least 3 times

66

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