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THESIS

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This is to certify that the

thesis entitled

Studies of Temperature, Cultivars and Biochemical
Control and Their Effect on Reducing Sugar Content
of Michigan Grown Potatoes

presented by

Kevin Halfmann

has been accepted towards fulfillment
of the requirements for

 

 

Master of Sciencedegree in Food Science

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/ Major professor
April 24, 1997

 

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STUDIES OF TEMPERATURE, CULTIVARS AND
BIOCHEMICAL CONTROL AND THEIR EFFECT ON
REDUCING SUGAR CONTENT OF MICHIGAN GROWN POTATOES

By

Kevin S. Halfmann

A THESIS

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

MASTER OF SCIENCE

Department of Food Science and Human Nutrition
1997

ABSTRACT
STUDIES OF TEMPERATURE, CULTIVARS AND
BIOCHEMICAL CONTROL AND THEIR EFFECT ON
REDUCING SUGAR CONTENT OF MICHIGAN GROWN POTATOES

BY

KEVIN S. HALFMANN

Proper storage temperature is critical in helping to control reducing sugar
accumulation in potato tubers. This study involved conducting variety and
temperature comparison studies to understand storage performances of certain
tuber selections at specified temperatures. There was also an attempt to determine
if Sucrose-G-Phosphate Synthetase (SPS) had a role in regulating sugar metabolism
of specific tuber selections.

The selections which maintained acceptable reducing sugar contents
(<.02%) were NDOl496-l , ND2676-10, NY102 and NDA2031-2.

In the temperature comparison, 45 ° F storage resulted in tubers with the
highest reducing sugar content. Storage at 50 ' F resulted in tubers with the lowest
reducing sugar content.

SPS activity was slightly higher in reconditioned tubers vs.
nonreconditioned tubers.

The storage period from week 11 through week 19 contained the most
significant rise in reducing sugar during the study.

The Norchip variety had a correlation between current glucose levels and

sucrose levels 4 weeks previous.

ACKNOWLEDGEMENTS

I would like to thank Dr. James Price who provided many hours of time
and support. I would also like to thank the members of my committee, Drs. Gale
Strasburg and Mark Uebersax. I would like to give special thanks to Dr. Roger
Brook also a member of my committee and coordinator of this project for his time,
support, suggestions and contributions.

This research was funded by a special USDA grant. Thanks also to
Bishop Farms, and Sackett Potatoes.

I would also like to thank my family for their help and support and
especially my wife Stephanie for helping to guide me to the completion of this

work.

iii

TABLE OF CONTENTS

Page
List of Tables ................................................................................................................... vi
List of Figures .................................................................................................................. viii

INTRODUCTION ................................................................................................ 1
OBJECTIVES ....................................................................................................... 3
LITERATURE REVIEW ..................................................................................... 4
Storage Practice for Potatoes used in Processing ..................................... 4
Correlation of Reducing Sugar Content and Chip Color ......................... 4
Studies of Reducing Sugars in Potatoes ................................................... 5
Factors Affecting Reducing Sugars in Potatoes ....................................... 5
Temperature Comparisons of Stored Potatoes ......................................... 6

Effect of Reconditioning .......................................................................... 7

Low Temperature Storage ........................................................................ 7

High Temperature Storage ....................................................................... 8
Variety Comparisons ................................................................................ 8
Storage Performance History of the Snowden Variety ............................ 9

Effect of Gluconeogenesis on Reducing Sugar Content .......................... 9
Carbon Partitioning in Potatoes ............................................................... 1 1

Effect of Senescence on Reducing Sugar Content ................................... 11

Effect of Sucrose on Reducing Sugar Content ......................................... 12
Carbohydrate Metabolism During Sprouting ........................................... 12
Regulation Effect of Enzymes on Reducing Sugar Content .................... 12
Starch/Sugar Interconversion in Stored Potatoes ..................................... 13
Biochemical Control of Starch Breakdown in Stored Tubers .................. 14

Key Regulatory Enzymes ......................................................................... 14
Sucrose-6-Phosphate Synthetase .............................................................. 15

Effect of Temperature and pH on SPS Activity ....................................... 16

SP8 Effect on Gluconeogenesis ............................................................... l7
Difficulties in Previous Enzyme Assays on Potato Tubers ...................... 17
MATERIALS AND METHODS .......................................................................... 18
Potato Harvesting and Collection ............................................................. 18

Potato Storage ........................................................................................... 18
Suberization Period .................................................................................. 19
Variety Comparison Study ....................................................................... 19
Temperature Comparison Study ............................................................... 20
Reconditioning Period .............................................................................. 21

Sugar Analysis Samples ............................................................................ 21

Chip Samples ............................................................................................ 23
Extraction and Assay for SP8 Enzyme ..................................................... 23
Tubers used in Enzyme Assay ............................................................ 23

Extraction ............................................................................................ 25

Assay ................................................................................................... 25

Statistical Analysis .................................................................................... 26

iv

RESULTS AND DISCUSSION ............................................................................ 27
Storage Temperature Study Comparison of Glucose

Content in Selections ................................................................................. 27
Effect of Late Season Storage on Temperature
Comparison Tuber Varieties ..................................................................... 3O
Glucose Levels in the Variety Trial ........................................................... 32
Critical Storage Time in Reducing Sugar Accumulation .......................... 36
Reducing Sugar Levels and Chip Color Scores of
Standard Chipping Potatoes ....................................................................... 38
Discussion of Color Scores in Variety Trial .............................................. 40
Effect of Reconditioning ............................................................................ 43
Utilizing Sucrose as an Indicator of Future Glucose
Levels Within the Tuber ............................................................................. 45
Results of Sucrose-6-Phosphate Synthetase Enzyme Assay ....................... 50
CONCLUSIONS .................................................................................................... 52
SUGGESTIONS FOR FUTURE WORK ............................................................... 53
REFERENCES ....................................................................................................... 55
APPENDICES ........................................................................................................ 62
APPENDIX A Sugar Analysis Data ................................................................ 62
APPENDIX B Color Score Data ..................................................................... 70
APPENDIX C Statistical Analyses ................................................................. 72
APPENDIX D SPS Analysis Data .................................................................. 78

TABLE 1

TABLE 2

TABLE 3

TABLE A1

TABLE A2

TABLE A3

TABLE A4

TABLE B1

TABLE B2

TABLE C1

TABLE C2

LIST OF TABLES

1994-1995 Variety and Temperature Comparison Study;
Tuber Selections and Originations ................................................

Procedure for Juicing Stored Tubers .............................................

Procedure for Chipping Stored Tubers ..........................................

Glucose Percentage of Tubers in Variety and
Temperature Study .........................................................................

Sucrose Percentage of Tubers in Variety and
Temperature Study .........................................................................

Average Reducing Sugar Content of Tubers in Variety Trial .......

Effect of Reconditioning on Stored Tubers ...................................

Color Scores (Agtron) for Chips ....................................................

Rankings for Chip Color Scores vs. Ranking of Tuber
Reducing Sugar Content in Variety Trial (Lowest to Highest) ......

Statistical Analysis of Variety Trial ...............................................

Correlation Coefficients of Previous Sucrose Percentage
and Current Glucose Percentage of Selections in Variety
Comparison .....................................................................................

vi

Page

19

22

24

62

65

68

69

7O

71

72

75

TABLE C3

TABLE D1

Correlation Coefficients of Previous Sucrose Percentage
and Current Glucose Percentage of all Selections
Combined in Variety Comparison .................................................. 77

Sucrose Phosphate Synthetase (SPS) Content in
Selected Reconditioned and Non Reconditioned
Tubers ............................................................................................. 78

vii

LIST OF FIGURES

Page

FIGURE 1 Gluconeogenesis Pathway ......................................................... 10
FIGURE 2a Storage Temperature Comparison for Snowden selection ........ 28
FIGURE 2b Storage Temperature Comparison for E5535 selection ............ 28
FIGURE 2c Storage Temperature Comparison for W870 selection ............. 29
FIGURE 2d Storage Temperature Comparison for W87OII selection ........... 29
FIGURE 3 Average weekly reducing sugar content in tubers

in Storage Temperature Comparison ......................................... 31
FIGURE 4a Monthly glucose percentage average for NY-102,

ND-2676-10, NDO-1496-l and NDA-2417-6 selections

in the Variety Comparison ......................................................... 33
FIGURE 4b Monthly glucose percentage average for BO-l78-34,

NDA-2031-2, Suncrisp and AF -875-15 selections

in the Variety Comparison ......................................................... 34
FIGURE 4c Monthly glucose percentage average for Atlantic,

NY-95, NDA-2471-8 and Norchip selections

in the Variety Comparison ......................................................... 35
FIGURE 5 Glucose content in tuber selections Atlantic, NY-102,

and AF-875-15 during critical storage time ............................... 37

viii

FIGURE 6

FIGURE 7a

FIGURE 7b

FIGURE 8

FIGURE 9a

FIGURE 9b

FIGURE 9c

FIGURE 9d

FIGURE 10

Weekly average glucose content of tubers in Variety
Comparison ................................................................................

Chip color score vs. glucose content in selections
from Variety Comparison ..........................................................

Chip color score vs. glucose content in selections
from Variety Comparison ..........................................................

Effect of reconditioning on three potato selections
after 26 weeks of storage at 45 deg. F .......................................

Average sucrose values in Variety Comparison
1 week prior to average glucose values .....................................

Average sucrose values in Variety Comparison
2 weeks prior to average glucose values ...................................

Average sucrose values in Variety Comparison
3 weeks prior to average glucose values ...................................

Average sucrose values in Variety Comparison
4 weeks prior to average glucose values ...................................

Sucrose percentage in Norchip selection 1 week
prior to glucose percentage .......................................................

ix

39

41

42

44

46

46

47

47

49

INTRODUCTION

Proper long term storage of potatoes to be used in processing is of
great concern to growers and processors because tubers may sprout,
rot and/ or accumulate undesirable levels of reducing sugars if
proper storage conditions are not maintained. Growers would like to
store tubers at temperatures as low as possible to conserve heat
energy, decrease incidence of sprouting and maintain weight by
decreasing respiration. However, the low temperature conditions
which benefit tubers in many ways may be detrimental to processing
quality because because reducing sugar accumulation is enhanced by
low temperature storage for many reasons.

For these economic reasons, a variety comparison is necessary
to know the storage performances of certain tuber cultivars at
specified temperatures.

During the variety comparison, the emphasis was on the
reducing sugar content in the tuber. One particular variety,
Snowden, has emerged as top processing potato in Michigan.
Snowden has also shown promise to be a variety that will produce
acceptable chips at cold storage temperatures.

Studies also focus upon optimal long term storage temperatures
of the tubers.

It is also important to understand the biochemical control of
starch breakdown. It is likely that there will be significant

breakthroughs in fruit and vegetable biotechnology in the near
future. The alteration of genes can make fruits and vegetables more
disease resistant and increase their postharvest quality. In altering
the genetic structure of the potato, it is necessary to know which
constituents are important to enhance storage and processing quality
of the tubers.

Because the enzyme, sucrose-6-phosphate synthetase is
thought to play an important role in starch/ sugar interconversion, it
has been studied in an attempt to understand regulation in the
metabolism process. The enzyme analysis was done during late
season tuber storage at the reconditioning phase. During
reconditioning, reducing sugar levels are known to have a higher
magnitude of change than during normal storage. Consequently, the
enzyme's importance during starch/ sugar interconversion may be

magnified during this stage.

OBJECTIVES

To compare storage performance as a function of reducing sugar
content for selections of Michigan grown potato tubers.

To optimize long term storage temperature for selections of Michigan
grown potato tubers.

To observe any correlations between potato tuber reducing sugar
content and previous sucrose content in an attempt to utilize sucrose as
a predictor for future reducing sugar content trends in tubers.

To understand the significance of the enzyme sucrose-6-phosphate
synthetase in biochemical pathways of the potato tuber.

LITERATURE REVIEW

Storage Practice for Potatoes used in Processing
The general tuber storage practice is to undergo an initial

suberization period at SS°—60°F for 2-3 weeks (Chase, 1981). This

allows the acceleration of healing bruised and damaged areas of the
tuber. Potatoes to be used in processing are then held at a ,.
temperature of SO°-S 2°F at a constant humidity level of 95%. The 5
storage period may last from 3-8 months depending on the needs of

 

the processing industry but the typical storage time is 6-8 months.
Near the end of the storage period, the temperature is usually raised
to 55°-60°F to increase respiration and metabolize excess sugars that
have accumulated during storage. This "reconditioning" phase may
not be necessary with some selections but it is generally utilized with
most processing tubers.
Correlation of Reducing Sugar Content and Chip Color

One of the most critical processing factors in the potato chipping
industry is the color of the chip. In previous work involving the
measurement of reducing sugars in potatoes, a correlation was
evident between reducing sugar level in stored potatoes and the color
of the fried chip (Shallenberger et al., 1959; Pritchard and Adam,
1994). Reducing sugar molecules are able to be a reducing agent
because they have a free hydrogen atom on them. The terms
‘reducing sugar’ and glucose are used synonomously in potato tuber
research articles as glucose is the predominant reducing sugar in
tubers. A high reducing sugar level in a tuber yields a darker
colored chip due to the Maillard reaction (Shallenberger et al., 1959).

The Maillard reaction is non-enzymatic browning of a food product
and requires a reducing sugar, amino group and heat for the reaction
to be carried out.

Fuller and Hughes (1984), noted that tuber glucose content was
closely related to chip color. This observation was made after
analyzing fructose, glucose, sucrose and total sugar content of tubers
stored for 8-9 months at 45°F. Glucuse content in tubers should be
no higher than .03596 to produce chips which have acceptable color in
the industry (Sowokinos and Preston, 1988).

Studies of Reducing Sugars in Potatoes

There has been considerable research done regarding the
optimal tuber variety and storage temperature needed to attain a
reducing sugar content feasible for producing marketable chips
(Rastovski and van Es, 1981).

More recent studies have focused on the mechanism associated
with sugar accumulation among certain varieties at cold storage
temperatures (_>_45°F). It has been established that various cultivars
accumulate unacceptably high reducing sugar levels at different rates
particularly during low temperature storage (Burton, 1965; Coffin et
al., 1987). Sugar accumulation also occurs during late season storage.
This phenomenon is known as senescent sweetening and is
irreversible unlike cold storage sweetening.

Factors Affecting Reducing Sugar Content During Storage

There are many factors which have proven to affect reducing
sugar content of potato tubers during storage and many more that
have been hypothesized to have an influence. Sugar is a key in the
metabolic process of plants (Rastovski and van Es, 1981). Therefore,

everything that affects metabolism is also likely to affect the
reducing sugar content.

The physical parameters which can affect reducing sugar
content of tubers in storage have been reported to be storage
temperature, humidity level and 02 content (Burton, 1965). Less than
optimum levels of these factors increase the stress level of the stored
tubers which leads to an increase in reducing sugar content.

Many studies ( Sowokinos, 1987; Pollock and ap Rees, 1975)
have focused upon enzymatic control of reducing sugar content. The
most widely studied enzyme within the metabolic process of potato
tubers has been invertase (Dixon and ap Rees, 1980). Invertase
causes the breakdown of the non-reducing sugar sucrose into the

reducing sugars glucose and fructose.

Temperature Comparisons of Stored Potatoes

Temperature plays a key role in the rate of respiration in all
fruits and vegetables. Because cold temperature storage slows
respiration, glucose is slow to be converted into the final products,

water and C02. This creates an excess of reducing sugars in potatoes

stored at temperatures in the range of 40°-45°F.

Storage temperature may also play a significant role in starch
breakdown, the source of reducing sugars. Cottrell et al., (1993) have
determined that the activity of starch hydrolytic enzymes in tubers is
higher during the first few weeks of storage at 3 7°F than during
storage at 50°F.

There have been many studies in determining the optimum

storage temperatures of tubers for seed, whole tubers for

consumption and tubers for processing. Linnemann et a1. (1985)
measured the reducing sugars glucose and fructose as well as the
non-reducing sugar, sucrose over a 12 week period. It was
determined that all three sugars were temperature dependent over
this time. Sucrose content rose from .2 g/ 100 g fresh weight to .8

g/ 100g fresh weight during this period at 28°C. Glucose and fructose
decreased from .2g/100g fresh weight to .05 g/ 100g fresh weight at
the same time and temperature.

W

Reducing sugar may accumulate at 45°-5 5°F storage and cause
unacceptable color development in processed products.
Reconditioning at 55°-60°F has been shown to lower reducing sugars
to an acceptable level. Kim and Lee (1993) reported that after
normal storage at 4 1°F for 1 month, potatoes which were
reconditioned at 60°F slowly decreased in reducing sugar content.
This decrease continued constantly at reconditioning temperatures.
Low Temflature Storage

When storing potato tubers at 55°F and below, a major concern
is the activity of the enzyme invertase. The activity of invertase can
increase glucose levels of many tuber selections to ranges that are
unacceptable for chipping (Rastovski and van Es, 198 1).

Storage at temperatures of 45°F or below may induce chilling
stress on tubers and increase reducing sugar content. The mechanism
of this increase is thought to be hormone induced (Isherwood, 1976).
Sweetening can then result from certain hormones which alter

enzyme activity.

Guy (1990) and Thomashow (1990) reported that chilling alters
the lipid composition of cell membranes, particularly the amyloplast
membrane integrity. This increases the enzymatic activity at specific
steps in metabolic pathways of carbohydrate metabolism which could
account for an increase in reducing sugar accumulation.

High Tempgature Storage

At storage temperatures in excess of 50°F, the reducing sugar
content in potato tubers normally remains at an acceptable level for
processing. One of the main reasons for this is the reduction of
invertase activity by an invertase inhibitor which is active at these
temperatures (Rastovski and van Es, 1981). However, there are
disadvantages of storage at high temperatures. The incidence of
sprouting is increased at high temperature storage. The rate of
respiration is also increased thus accelerating the onset of senescence.
There is also an economic concern because high temperatures require
substantial heat energy into potato stores in cold climate areas.
Mehta and Kaul (1988) studied the feasibility of storing potatoes at
high temperatures in a tropical region. They found that although the
reducing sugar level was acceptable, the level of sprouting was
increased.

Varieg; Comparisons

Potato varieties have been compared with respect to
parameters such as disease resistance, yield and specific gravity for
many years. Tuber storage performances with regard to reducing
sugars have not been compared until recent years. Sinha et a1.
(1992) evaluated variety performances for specific gravity, yield,

chip color, glucose and sucrose based upon growing conditions and

harvest date. Barichello et al. (1990) studied biochemical differences
between 2 potato cultivars (Norchip and ND 860-2) at low
temperature (45°F) storage. It was determined that although post
harvest storage significantly reduced respiration rate for both
cultivars, the ND 860—2 tuber exhibited a higher respiration rate than
the N orchip variety.

The cold chipping ND 860-2 selection has been the subject of
other studies to determine the physiological trait which is associated
with accumulation of lower levels of reducing sugar. Schwobe and
Parkin (1990) concluded that the ND 860-2 variety had a lower
reducing sugar content because it had a lower Glucose Forming
Potential (GFP). GFP is defined by Sowokinos (1987) as the ability of
a potato clone to convert sucrose into glucose.

Storage Performance Histog of the Snowden Variety

One characteristic that has been found in only a very few potato
selections is the ability to produce acceptable colored chips directly
out of cold temperature storage. This phenomenon is known as "cold
temperature processability" (CTP) (Coffin et al., 1987). Snowden is a
new Michigan grown cultivar which seems to have the ability to
develop an acceptable reducing sugar content and CTP. Sinha et al.
(1992) compared many selections of potatoes grown in Michigan. In
a two year study, it was found that Snowden had one of the lowest
levels of reducing sugar among the selections and consequently
produced light colored chips.

Effect of Gluconeogenesis on Reducing Sugar Content
Figure 1 shows the gluconeogenic pathway in stored tubers and

the important enzymes involved. During storage at low temperatures

l0

 

 

GLYCOLYSIS

Z

 

P .
5. PGM 2. S S SUCROSE 6-? +UOP

. 3. SSP-PTose
¢ UTP PP: pi
/
G! P t—LA) UDP GLUCOSE SUCROSE

l.
UPPLose 4.1 Invertase

 

AMYLOPLAST GLUCOSE + FRUCTOSE

 

 

GLUCONEOGENESIS

 

Enzymes represented are (l) UDPglucose pyrophOSphorylase. (2) sucrose 6-? synthase,
(3) sucrose 6-? phosphatase, (4) acid invertase. (S) phosphoglucomutase and
(6) phosphohexose isomerase.

Figure 1. Gluconeogenesis Pathway

From Sowokinos (1990)

 

11

(< 50°F), glycolysis is inhibited and gluconeogenesis with glucose as
the end product is favored (Burton, 1965). There is also an increase
of sucrose in most tuber selections at temperatures where

gluconeogenesis is favored.

Carbon Partitioning in Potatoes
The history of sugar and starch availability during tuber growth

is important in determining reducing sugar performances during
storage. One of the main factors affecting the quantity of reducing
sugar content in potato tubers is the supply of sucrose and the
method of tuber storage. Carbon partitioning in plants have been the
subject of many reviews. This process is initiated by carbon fixation
during photosynthesis (Dwelle, 1990). Following fixation the carbon
is then partitioned between sugar and starch and stored in the plant
leaf. During tuber growth, this storage pool is available to the tuber
(Oparka et al., 1986). Most of the storage energy is taken up in the
form of sucrose. The storage uptake by the growing tuber is driven
by mass flow. The rate of storage uptake is variety dependent.
When the sucrose has been translocated to the tuber, it is then
partitioned between starch (SO-70%), structural polysaccarides (5-
10%) and storage sucrose (remainder) (Mares and Marschner, 1980).
Effect of Senescence on Reducing Sugar Content

Sowokinos (1990) summarized the factors which lead to
increased reducing sugar levels during senescence. These factors
include:
A) hormones

B) membrane structure and function

12

C) compartmentalization and concentration of key ions, substrates,
enzymes and other effectors
D) enzyme synthesis and/ or activity

Sowokinos et al. (1987) found that during senescence, electron
rnicrographs showed that bi-layers of the amyloplast membrane were
beginning to separate.

If the physical condition of the tuber is changed during
senescence, membrane structure could become damaged leading to a
change in concentration of important enzymes in carbohydrate
metabolism.

Effect of Sucrose on Reducing Sugar Content

Current sucrose content in the stored potato tuber may be used
as an indicator for an upcoming increase in glucose level. Sucrose is a
12 carbon non-reducing sugar that occupies a critical position in
tuber development (Sowokinos and Preston, 1 98 8). In carbohydrate
metabolism, sucrose is broken down by invertase into glucose and
fructose. Sucrose is also used as a measure of the chemical maturity
of the tuber.

Carbohydrate Metabolism During Sprouting

The incidence of tuber sprouting is higher as storage
temperature is increased. There have been studies to determine if
quantifies of sucrose, the main transport sugar, increase during
sprouting. Davies and Ross, (1987) found that sucrose quantity did

not significantly increase in sprouting tubers.

13

Regulation Effect of Epmes on Reducing Sugar Content

Cold induced sweetening of stored potatoes is related to the
sensitivity of key metabolic enzymes at low temperatures. This
sensitivity slows the glycolytic rate in tubers resulting in high glucose
accumulation. Phosphofructokinase (PFK) and pyruvate kinase are
two important enzymes in glycolysis which have shown particular
sensitivity to cold storage temperatures (Dixon and ap Rees, 1980) .
These enzymes have different equilibriums when exposed to cold
storage than during storage at optimal temperatures. PFK catalyzes
the conversion of fructose-6-phosphate to fructose 1 ,6 bisphosphate
in the first step of glycolysis. Pyruvate kinase is suggested to play a
role in determining the level of intermediates in the glycolytic and
oxidative pentose pathway and indirectly influence PFK (Dixon and ap
Rees, 1980).

Starch/ Sugar Interconversion in Stored Potatoes

Glucose accumulates in stored potatoes by the metabolic
transformation of starch into sugars. Sucrose is the predominant
sugar in stored tubers and may remain as such, be converted back to
starch or hydrolyzed into fructose and glucose.

The sucrose level in tubers just prior to harvest is normally low
(around .2596). However, after the stolon connection to the plant has
been severed, the starch/ sugar interconversion rate changes. The
intensity of this change depends on the tuber variety and the
temperature at which it is stored. In many cases, starch/ sugar
interconversion rate change results in the accumulation of undesired

reducing sugars (Fuller and Hughes, 1984).

14

The effect of temperature on the metabolism of stored tubers
was shown by Dixon and ap Rees (1980) when labeled [14C] glucose
was introduced into the tuber by boring a well into the flesh and
placing the [14C] glucose dilution into the wells at flesh temperatures
of 34° and 77°F. The majority of the labeled glucose was found in CO;
at 77°F. However at 34°F, the labeled glucose was diverted from
respiratory pathways to the production of sucrose.
WWW

It has been proposed that biochemical control of reducing sugar
accumulation in cold stored tubers is a result of enzymes in the
glycolytic pathway which are cold labile (Pollock and ap Rees 1975;
Dixon and ap Rees, 1980). However, the mechanisms controlling
enzyme activity in planta are still not very well understood.

There has been a recent attempt to depict a global picture of
the metabolism of tubers in storage. The difficulty in this is that
biochemical changes depend not only on the storage conditions but
also the preharvest conditions of the tubers. Muller-Rober et al.
(1992) studied the consequences of the inhibition of ADP-glucose
phosphorylase (ADPase) in tubers as an attempt to use this as a
global parameter of metabolism. They determined that ADPase
inhibition causes a decrease in starch biosythesis and an increase of
the major sucrose synthesizing enzyme, sucrose phosphate synthase.
Key Regulatory Emmes

Many of the important enzymes involved in starch/ sugar
interconversion are believed to be those within the glycolytic
pathway. Phosphofructokinase and pyruvate kinase are two enzymes
which have been extensively studied. There are other enzymes

15

which have not been studied as much but have been hypothesized to
play an important role in starch/ sugar interconversion such as
sucrose phosphate synthase and sucrose-6-phosphate synthetase.
Sucrose-6-Phosphate Smthetase

One enzyme which has not been extensively studied but may
play a vital role in regulating sucrose synthesis in potato tubers is
sucrose-6- phosphate synthetase (SPS). SPS catalyzes the following

reaction:

Fructose-6-Phos. + UDP Glucose ——> Sucrose-6-Phos. + UDP

Pressey (1969) studied SPS activity in tubers at different maturities
and found that its activity was lower in less mature tubers than in
older potatoes. Dwelle (1990) found the activity of SPS to be
influenced by genetics of the potato, photoperiod, CO; concentration
and water stress. Sowokinos (1990) assayed the activity of SPS in
tubers susceptible to cold sweetening and found that the enzyme was
more active at cold storage temperatures (38°F) than at 48°F.

One theory concerning SPS activity is that it may regulate
source-sink manipulations. Source-sink manipulations are rate
changes in the carbon partitioning of starch as a function of demand
for sucrose. For example, when sucrose demand was decreased by
excision of pod from the soybean plant, Ciha and Brun (1978)
observed that while photosynthesis rates decreased, starch
accumulation within the plant increased. Mendicino (1960)
concluded that the only metabolic function of SPS is its involvement
in sucrose biosynthesis. Rufty and Huber (1983) followed the

16

changes in activity of SPS within soybean plants as it responded to
source-sink alterations and found that its activity confirmed the
following previously demonstrated characteristics of a regulatory
enzyme:

1) Exhibited sigmoidal enzyme kinetics characteristic of a regulatory
enzyme.

2) Source—sink alterations had a negative correlation with SPS
activity and the partitioning of carbon into starch.

3) At its highest rate of activity, during sucrose formation, SPS
activity was low compared to other enzymes involved in sucrose
formation which means that any changes in activity may significantly
alter sucrose formation .

It is behaved that SPS regulation involves both fine metabolic
control and coarse metabolic control (Sowokinos, 1990). Coarse
metabolic control by plants involves maintaining a certain level of
enzyme synthesis whereas fine metabolic control involves the
variation of preexisting enzyme activity.

Effect of Temperature and pH on SPS Activity

Pressey (1969) studied SPS activities of stored tubers, and
found that enzyme activity increased gradually after harvest but a
greater increase was noted in cold stored tubers. Sowokinos (1990)
found that tubers which are susceptible to cold storage sweetening
and stored at low temperatures, tend to have higher SPS activity.

Partially purified SPS has a reported broad pH range from 6-8
with optimum pH at 6.9 (Harbron et a1, 1981). This range falls within
the pH of potato tubers. Therefore, SPS will be close to its highest
activity within the potato tuber.

17

SPS activity may also be indirectly affected by low temperature
storage. Sowokinos et a1, (1985) assayed particular enzymes when
the amyloplast membrane was altered due to cold storage. The
activities of UDP-glucose pyrophosphorylase, invertase and a-
amylase were not affected by this phenomenon. However, the
activities of phosphorylase and SPS were significantly elevated.

SPS Effect on Gluconeogenesis

SPS is considered to be an important factor in regulating
gluconeogenesis. Figure 1 shows the role of SPS within the
gluconeogenic pathway. Sowokinos (1990) stated that UDP glucose
pyrophosphorylase, invertase and SPS are the most critical enzymes
in regulating gluconeogenesis.

Difficulties in Previous Enzme Assays of Potato Tubers

Previous studies of various metabolic pathways and
measurement of enzymatic activities in potato tubers have
encountered numerous problems (Kruger, 1995). These problems can
be caused from interferences within enzymatic interactions and the
formation of phenolic compounds formed during preparation of
extracts. Another source of error in tuber enzyme activity

measurement has been the excessive activity of phosphatases.

METHODS AND MATERIALS

Potato Harvesting and Collection
The potatoes used in the variety comparison were grown in a

sandy loam soil plot with optimum management production
techniques at the Montcalm Research Farm; Michigan State
University Agricultural Experiment Station in Montcalm
County. A complete listing of the tuber types used in the
variety study is in Table 1. They were harvested October,

1994 and dug with a plot harvester. The tubers were then
manually picked up and placed into mesh bags and transported

to storage cubicles at Michigan State University.

Potato Storage
The potato tubers used in this study were stored in

temperature controlled stainless steel cubicles (1.7m long, 1.3m
wide, 2.4m high). Tubers were separated by variety into
46crnx61cm standard potato lugs. These lugs were periodically
rotated with each other to assure sufficient air flow to all
tubers in the cubical. Controlled 95% humidity conditions were
achieved with an Emerson Model #850 humidifier.

The air flow was controlled by electric fans located at the top of
the cubicles. These fans ran whenever cooling was needed
except when the door was opened. There was no exchange of

air outside of the cubicles.

18

19

W W

NDA 2417—6 Montcalm Research Site,
Montcalm County, MI

NDA 2031-2
NDO 1496-1
NDA 2471-8
BO 178-34
AF87S-15

N orchip
NY102
ND2676-10
NY95
Suncrisp

Atlantic

5535 Bishop Farms,
Pinconning, MI
Snowden

W8701 Sackett Potatoes
Mecosta, MI
W8701 1

Table 1. 1994-1995 Variety and Temperature Comparison
Study; Tuber Selections and Originations.

20

During the storage period, tubers were periodically
inspected for disease and/ or rotting. If rotting was detected,
the affected tuber was removed to prevent spreading to other
tubers.

S l . l' P . 1

Following the harvest, tubers were initially stored at a
temperature of 5 5°F for 2 weeks to facilitate wound healing.
After this period, the tubers were subjected to changes in
temperature of 1°F/ 2 days until the desired storage
temperature was reached.

V ' m ' n

The tubers in the variety comparison study were all
stored in the same cubicle at a temperature of 45°F with a
humidity level of 95 96. There was approximately 90 pounds of
tubers for each of the 12 selections in the variety comparison
for a total of about 1 100 pounds in the cubicle.

Winger

The temperature comparison study involved four
different types of tubers. There were three different varieties:
Snowden, W-870 and E—5535. The W-870 variety had two
entries which were grown at different farms.

The varieties were separated into subsets so that they
could all be stored at four different temperature treatments:

21

1) Storage at 45°F for the duration of the study.

2) Storage at 50°F for the duration of the study.

3) Storage at 65°F for 1 month initially then at 50°F for the
remainder of the study.

4) Storage at 65°F for 2 months initially then at 50°F for the
remainder of the study.

R n . . . P

Near the end of the storage period, three tuber selections
that were part of the variety comparison (NDA-2417-6,
Norchip and BO-178-34) were split into two groups. The first
group remained at the storage temperature of 45 °F. The
second group was exposed to a temperature increase of 1°F/ 2
days until a final reconditioning temperature of 5 5°F was
reached. The second group remained in the reconditioning
phase until the end of the experiment. The reconditioning
phase lasted for 3 weeks.

8 An i S 1

Samples of eight tubers from both the variety comparison
and the temperature comparison were taken weekly for sugar
analysis.

The sugar analysis followed the procedure of Sowokinos
and Preston (1988)(Table 2).

After thawing the frozen samples to room temperature, a
Yellow Springs Instrument (YSI) model 2700 sugar analyzer

 

22

 

- Sample size of 8 tubers from each selection/ treatment.
- Cut samples to obtain total of 200 g potato centers.

- Blend in Acme Juicerator to obtain potato juice.

- Dilute potato juice with distilled water to a total volume of 430 ml.
- Chill dilution at 38°F for 1 hour.

- Freeze dilution until time of sugar analysis.

- Thaw dilution at time of sugar analysis and determine sucrose
concentration using YSI 2700 analyzer.

 

 

Table 2. Procedure for J uicing Stored Tubers

23

was used to determine the glucose and sucrose concentrations.
The analyzer was located at Techmark Inc., Iansing, MI.

The YSI analyzer measured reducing sugar in grams of
free glucose/liter of solution. The following calculation was
made to obtain 96 glucose:

(x)g/l x 430ml/ 200g = (x2)(.00215) = 96 glucose

Chip Samples
Chip samples were produced each month during the

study (Table 3).

The rinsed slices were placed in canola oil at 360°F
(182°C) in a Hotpoint?m chip frier. The fry time was for 115
seconds (recommended by Gould (1989)) or until the water had
cooked out of the chip.

The chip samples were visually scored based upon color
by four individuals with previous experience in color scoring.
The visual scoring was based on the use of the Snackfood
Association's 1 to 5 color chart using 0.5 increment steps
(Snackfood Association; Alexandria, VA, undated).

W
U ineEnz Ass

Tubers from the variety comparison (Norchip, NDA2417-
6 and BOl78-34) were used in the enzyme assay. The tuber
samples were split into two groups; Group 1 had no
reconditioning and Group 2 were reconditioned at 5 5°F. A total

of 18 assays were performed. A sample of tubers from each

 

24

 

— Sample size of 8 tubers from each selection/ treatment.

- Cut tuber in half through stem.
- Cut 5-6 slices per tuber, approximantly .020" thickness.
- Rinse slices in distilled water.

- Fry slices in 350°F canola oil for 115 seconds.

 

 

Table 3. Procedure for Chipping Stored Tubers

25

variety in Group 1 were assayed in duplicate before
reconditioning. After 10 days of reconditioning, a sample of
tubers from each variety in both Group 1 and Group 2 was
assayed. The sample size for the assays was 6 tubers.

moron

Crude extract for enzyme assays was prepared according
to a modified method of Harbron et al. (1980) for spinach leaf.
Fifty grams of potato obtained from center cuts of 6 uniform
sized potato tubers were mixed in a Waring blender for 1.5
minutes with 100 ml of extraction medium containing 0.02 mM
Tris HCl buffer (pH 7.6) containing 5 mM Z-mercaptoethanol.
The homogenate was squeezed through two layers of
cheesecloth and then centrifuged for 20 minutes at 40,000 g in
a refrigerated centrifuge (Sorvall RC 2—B, Dupont Instruments,
Newtown, CT). The supernatant was fractionated by addition
of solid ammonium sulphate; protein which precipitated
between 35 and 50% salt saturation was collected by

centrifugation and dissolved in 2.5 ml of 0.01 M ADA-NaOH
buffer (pH 6.5) containing 10 mM MgC12 and 0.1 M NaCl.

26

A553)!

The enzyme assay was based on a method used by
Harbron et al. (1980) for spinach leaf. Enzyme activity was

measured by the following:

extract

1
UDP-Glucose + fructose-6-phosphate _.

sucrose-6-phosphate + UDP

Changes in SPS activity was determined by measuring the
amount of sucrose-6-phosphate end product in assays. The
extracts were taken to Techmark Inc. for analysis on a YSI
model 2700 glucose/ sucrose analyzer.

S ' An i
Statistical analysis was performed using the SAS and
Minitab programs for Microsoft Windows.

RESULTS AND DISCUSSION

S T S m ' f G1 C n in
Selecu'nns

Storage temperature did not have a significant effect on
glucose content in the Snowden variety. This variety has
maintained a low glucose content throughout storage for the
previous 2 years of this study. Because of the previous history
of low reducing sugar levels in this and other studies, it is
hypothesized that the Snowden variety cannot produce enough
glucose to show any significant influence that storage
temperature may have on it. Figure 2a shows the consistently
low glucose levels in Snowden after 6 weeks of storage
regardless of temperature.

Another variety, E5535 has had increasing glucose levels
in this study as storage progressed for the past 2 seasons. In
this study, storage temperature did show an effect on glucose
content in E5535. Figure 2b shows that tubers stored at 45°F
experienced the highest average glucose content. E553 5 stored
at 65°F for 2 months had a high late season glucose level and
may have been affected by senescence near the end .of storage.

Figure 2a and 2b shows the glucose levels in W870 and
W87OII. Storage at 50° was the optimum of the four
temperature treatments in maintaining glucose at a minimum
level for this variety.

27

28

 

 

    

 

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29

 

Glucose %

 

 

 

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30

Figure 3 shows the average glucose content of the 4 tuber
selections; E5535, Snowden, W870 and W87OII stored at 45°F
was .030 96, at 50° was .008 96 at 65° for 1 month was .013 96
and stored at 65° for 2 months was .01 1 96.

The most significant difference in the average glucose
content among subgroups in the temperature comparison was
the low glucose level for tubers stored at 50°F compared to the
other temperature treatments. This indicates that regardless of
the selection, the optimum temperature for maintaining a low
glucose level was 50°F.

There was not a significant difference in average glucose
level between those stored at 65°F for 1 month or for 2 months.
A possible reason for this is that the tubers were exposed to the
65°F treatment at the beginning of storage. If the treatment of
high temperature for differing times was applied at the end of
storage, there may have been a more significant variance in

glucose levels due to senescent sweetening.

Eff f S n8 nT m tureCom 'sonTu
V . .

The physical state of all of the tubers from the
temperature comparison during late March and early April was
of lower quality than what they were earlier in storage. The
most prominent attributes were a high degree of sprouting and

water loss which may have affected membrane structure and

 

Glucose 96
P
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at

31

 

 

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32

function leading to senescent sweetening. Of the four
temperature comparison varieties, W870 exhibited the highest
degree of what seemed to be senescent sweetening with end of
storage reducing sugar readings of .1396 at 45°, .0596 at 50°, .0496
at 65° for 1 month and .0596 at 65° for 2 months. This is in
contrast to acceptable ( <.0296) reducing sugar levels for W8 70
throughout the rest of the storage period.

Gluco VI in eV ’e Tri

Table A1 in the appendix shows the average glucose
content for all tuber selections during storage. The tuber
selection with the lowest average glucose level throughout the
variety trial was NDOl496—1 with an average level of .008 96
glucose (figure 4a). Conversely, the selection with the highest
glucose content was Norchip (figure 4b) with an average level of
.092 96 glucose, over 10 times higher than NDO 1496-1 stored at
the same temperature.

It is possible that the respiration rate of NDO 1496-1 was
fast enough to maintain a low level of glucose during the
variety trial storage temperature while the N orchip variety
could not convert the accumulated glucose to C02 and water
quickly enough. Another possibility is that NDOl496-1
respiration was not as inhibited due to temperature as in the
other selections with a higher average reducing sugar content

which may have allowed it to metabolize more glucose.

33

 

 

 

 

 

 

 

 

 

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34

 

 

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35

 

 

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36

Other selections in the variety trial which maintained an
acceptable average glucose content (< .02 96) included ND 2676-
10 (.009 96) (figure 4a), NY 102 (.009 96) (figure 4a) and NDA
2031-2 (.015 96) (figure 4b) .

The selection BOl78-34 started with an acceptable
glucose content for the initial 9 storage weeks (figure 6b), but
then experienced a dramatic rise from week 10 through week
13. The increase in glucose subsided after week 14 and even
decreased in many of the subsequent weeks. However, this
decrease was not enough to bring BOl78-34 into the acceptable
reducing sugar range for the remainder of the storage period.

Many selections in the variety trial also experienced an
increase of glucose during the latter part of storage particularly
from storage week 25 until the end of the study. NDA203 1-2,
NY-95 and Atlantic selections were the most evident of this
increase with glucose readings at least 75% higher at the end of
storage than storage week 24. These results indicate late

season sweetening.

Cri' S Tim inR in S Acumul 'on

During this study, an important timeframe for reducing
sugar accumulation in stored tubers was storage week 1 1
through week 19. Figure 5 shows reducing sugar content of the
selections Atlantic, AF-875-15 and NY-102 from storage week
13 through week 17.

37

 

 

 

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38

Atlantic and AF175-15 experienced sharp rises in glucose
content during this period. There was probably no change in
respiration rate of these selections at this time. There may
have been a change in the activity of one or more enzymes in
the carbohydrate metabolic pathway for the conversion of
glucose to the final products; C02 and water. These selections
also had a significantly high glucose level at the end of storage.

Conversely, the selection NDOl496-1 did not have a great
change in reducing sugar content. This selection had a low level
of glucose present at the end of storage.

Figure 6 shows the weekly average glucose content of
tubers within the variety comparison. A dramatic rise is noted
at storage week 1 1 as the average glucose content is .04 96 . The
average then drops steadily until week 16 as the trend reverses
to a weekly increase until week 20.

It is possible that these dramatic reducing sugar
increases could have been lessened with a slight temperature
increase during this critical storage period. The increased
temperature may have heightened respiration levels in the
tubers to allow for metabolism of the reducing sugars.

Based upon these and previous potato selection storage
experimental results, it may be possible in some cases to predict
the range of glucose within tubers based upon the magnitude of
reducing sugar increases during the 12th through 18th weeks of
tuber storage.

39

 

 

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Standard chipping varieties N orchip and Atlantic had
unacceptably high glucose sugar levels throughout the variety
trial storage period with averages of .09296 and .03 796. Norchip
in particular was significantly higher in average reducing sugar
content than all other varieties in the variety storage trial
(a=.05 ) (table Cla in the appendix).

Normal storage temperatures for these standard chipping
potatoes is around 5 2°F which is considerably warmer than the
45°F storage temperature during this study. It is possible that
the respiration rate could be affected adversely enough to not
be able to break down the glucose as fast as it is produced.

 

i f C r r ‘ V ' Tri

A complete list of the color scores is in appendix table B1 .
The selection which had the best average color score in the
variety trials was NDO 1496-1 with a 2.4 average Agtron
reading. NDO 1496-1 also had the lowest average glucose level
in the trial.

Figures 7a and 7b shows a comparison of the level of
glucose vs. the chip color scores for selections in the variety
trial. A distinct linearity can be seen in the graph due to the
positive correlation between chip color and glucose 96 in the
Norchip variety. However, this linearity is not as evident in
most other selections.

41

 

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43

Table B2 in the appendix shows the rankings of chip color
scores and tuber glucose levels. All tubers selections with
average glucose levels at <02 96 had chip color scores of 2.9 or
lower. This further confirms what has already been published
the importance of acceptable reducing sugar levels to achieve
chip colors acceptable to the standards of industry.

Near the end of the storage experiment, three tuber
selections (Norchip, BO 178-34 and NDA2417-6) were selected
to be analyzed at both reconditioning temperature and at the
normal storage temperature. Figure 8 shows that all three
selections had a slightly lower glucose level at the reconditioned
temperatures than those stored at normal storage temperatures.

Table A4 in the appendix shows the glucose level at
reconditioned storage conditions and regular storage conditions.
The probable reason for this is that larger amounts of glucose
were converted to CO; and water because of a higher respiration
rate in the reconditioned potatoes. The respiration rate in each
of the reconditioned selections was increased due to the higher
storage temperatures. *

BOl78-34 was the only selection that had a significantly
lower glucose level after reconditioning with a drop of .02396.
The reason for the more significant glucose drop during
reconditioning in BOl78-34 than in the other tuber selections

44

 

 

Effect of Reconditioning on Norchip

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.12 _ I
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W 12-Apr 19-Apr 26-Apr
Date
Figure 8. Effect of reconditioning on three selected potato varieties after

26 weeks of storage at 45 deg. F.

 

 

 

45

may be due to the varying rates of respiration. B0178-34 may
have a lower 'respiration burst' than the other selections which
would cause it to respire more slowly during the reconditioning
period. Respiration burst has been defined as a sudden change
in respiration due to fluctuating storage temperatures
(Rastovski and van Es, 1981).

Uu-in SJ- 0, r 1.1: In' - or fF tur Glu se -v- Wiuu'
them

In addition to monitoring weekly glucose levels, the non
reducing sugar, sucrose was analyzed in all tubers in the study.
The data for weekly sucrose readings is in table A2 in the
' appendix. Sucrose has been hypothesized to provide a possible
signal to the magnitude of future glucose levels in the tuber. If
current sucrose content in stored tubers can be used as a
predictor of future glucose levels, the storage conditions can be
manipulated to change the potato respiration rate, thus enabling
a more desirable glucose level.

Glucose percentage data from this study was compared to
sucrose percentage data from 1 , 2 , 3 and 4 weeks previous to
determine if there was a correlation between them. Figures 9a-
9d track glucose percentage in all selections in the variety
comparison with sucrose percentage from 1-4 weeks previous.
Table C3 in the appendix shows the correlation data for this
analysis.

There was not a high correlation in sucrose percentage

vs. glucose percentage in all selections collectively regardless of

46

 

 

 
   
 

Avg. Suc. %

 
   
 

GIucoee/Sucron “I.

Avg. Glu “I.

 
 

 

 

l

 

 

 

0
2 a 4 s s 7 a 91011121314151517101920212223242526272529
Week!
Figure 9a. Average sucrose values in Variety Comparison 1 week prior to
average glucose values.
0.1
“9 Avg. Suc.%

Avg. Glu. °/.

Glucose/Sucrose 'l.

 

 

 

 

 

34567091011IZiJHis16t71019202122232‘2525272029
Weekl

 

 

 

Figure 9b. Average sucrose values in Variety Comparison 2 weeks prior to

average glucose values.

 

 

Glucose/Sucrose 'I.

Glucose/Sucrose Y.

0. i
0.09
0.00
0.07 -
0.06 ‘
0.05

0.03
0.02
0.01

 

Figure 9c.

 

Figure 9d.

47

 

 

 

Avg. Suc. %

Avg. Glu. °/.

 

 

9 10” 1213 It Is i617il 19 20 21 22 23 z: 25 25 27 23 29

Week I

 

 

Average sucrose values in Variety Comparison 3 weeks prior to

average glucose values.

 

 

Avg. Suc. %

 

 

 

 

Average sucrose values in Variety Comparison 4 weeks prior to
average glucose values.

 

48

the number of weeks previous. The highest correlation was
sucrose percentage 2 weeks previous with .40 correlation
coefficient.

In addition to analyzing all selections from the variety
trial, individual selections were analyzed for correlation
between current glucose percentage vs. sucrose levels 1, 2, 3
and 4 weeks previous. Table CZa and CZb in the appendix has
the correlation data for this analysis.

Data from selections such as AF-875-15 and Norchip
which had higher amounts of glucose than other selections in
the study, also had the strongest correlation of previous sucrose
content vs. current glucose levels. However, even these
selections did not indicate a strong correlation between
previous sucrose levels and current glucose levels. The
correlation may appear more evident in these selections than in
other selections because there is much more glucose in these
tubers.

There is evidence of a strong correlation between current
glucose levels and sucrose percentage 1 week previous in the
Norchip variety from weeks 8-19 (figure 10). This influence is
not as evident after week 19. The lesser correlation after week
19 may have to do with other factors influencing N orchip
glucose levels such as late storage season respiration rate
changes.

The differing levels of strength of correlation between

prior sucrose levels and current glucose levels within tubers

49

 

 

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50

may be because of the higher degree of reducing/nonreducing
sugar contained in selections such as Norchip over selections
with lesser amounts. Another possible reason for the differing
correlations may be due to differences in metabolism among the
selections. It may require a longer period of time in the
pathways of other selections to metabolize sucrose into glucose.
Therefore, consideration should be given to determine for any
tuber selection the time required to metabolize 1 unit of sucrose

into the subsequent amount of glucose.

R fSu O'o-HIIISEnZo-g‘ur‘-..‘ Asa

A key enzyme in the pathway of metabolizing glucose
Sucrose-6-Phosphate Synthetase was assayed during the
reconditioning study of BOl78-34, Norchip and NDA 2417-6.
The completed data from the study can be found in table D1 in
the appendix.

There was little variance in the SPS activity among the
varieties. However, there was some variance in SPS content of
tubers that had been reconditioned versus those that had not
been reconditioned. In theory, the SPS activity should be
higher in tubers undergoing reconditioning than tubers held at
normal storage conditions. This is because reconditioning
temperatures are closer to the optimum SPS temperature for it’s
activity.

As SPS activity increases, it is able to decrease activation

energy required in the reaction of Glucose-6-Phosphate +

51

Fructose-G-Phosphate -> Sucrose-6-Phosphate during
gluconeogenesis. This would have caused the reaction to be
more favorable in the direction of Sucrose-6-Phosphate
formation which would lead to a higher amount of sucrose
formed and possible an increase in reducing sugar.

A possible reason for the lack of variance may have been
the method of measuring SPS activity. SPS activity was
measured by the sucrose end product formed in the reaction
that it facilitated. It may be more accurate to directly measure
SPS activity spectrophotometrically than to indirectly measure
activity based upon end product formed. It is known that SPS
activity level is very low compared to other enzymes studied in
potato tuber metabolism. Therefore, it is important to utilize
the most sensitive method of measurement available in

determining SPS activity.

CONCLUSIONS

The best performing tuber selection in the variety comparison
in regarding low reducing sugar content was NDO-1496-l. This
selection had a glucose content of no higher than .021 % throughout
the study. Established varieties in the chipping industry such as
Norchip and Atlantic maintained a consistently high glucose content

during the study.

The temperature study revealed that of the four temperature
treatments, 50°F was the optimum for keeping reducing sugar levels at
a minimum. Storage temperature had little impact on reducing sugar
levels on the Snowden variety which has a history of having a
consistently low glucose content.

The correlation between glucose content of all selections of
tubers in the variety comparison and previous sucrose content was
low. The correlation was low regardless of the number of weeks
previous that sucrose was analyzed. A few individual selections such
as ND-2676-10 and AF-875-15 that were analyzed revealed a slight
correlation. Therefore, it may be possible to predict future glucose
levels in some tuber selections based upon current sucrose values.

There was little variance detected in SPS activity among
selections in the reconditioning study. This lack of detection may be
due to lack of sensitivity in the indirect method of analysis. Because
of the lack of variance, it was not possible to determine biochemical
significance of SPS in this study.

52

SUGGESTIONS FOR FUTURE WORK

The cubicles in which the tubers for this experiment were
stored in were lacking in proper airflow capacity. This may
have allowed an improper ratio of CO2 and O2 gasses in the air
which may have hindered proper respiration in the tubers. In
addition to improper airflow conditions, the temperature control
of the cubicles was less than optimal for the temperature
comparison portion of the study. The fluctuation of
temperature was +/- 2°F. The fluctuation for the temperature
comparison of the tubers should be less than +/- 1° F. In future
studies of tuber storage at MSU, the current cubicles should
have an airflow system implemented in them that can be
controlled by the researcher. New thermostats should also be
installed so that the temperature conditions may be controlled
more precisely.

A critical storage time for tubers was determined in this
experiment in which reducing sugar content increased more
during this period than any other time during storage. Future
tuber storage experiments may include a comprehensive
analysis of this critical storage time. For example, at storage
week 1 1 at normal 50° F storage, divide tuber selection into 2
subgroups: 1 group stays at the 50° storage and the other group
has it's temperature increased to 55°F until the end of the
critical storage period. Weekly reducing sugar analysis could

53

54

determine if there was a difference in reducing sugar level

between the 2 subgroups.

There was a possible correlation between the sucrose
content of some tubers and reducing sugar content 1 week
following. Further studies into this t0pic may include an
attempt to determine the period of time it takes to hydrolyze 1
mole of sucrose into glucose and fructose at a certain

temperature for a particular potato variety.

In future studies of SPS in potato tubers, a different
assay should be investigated to analyze activity. It is possible
that the YSI analysis was not sensitive enough in determining
the amount of sucrose produced when the enzyme was added.

It is possible that a spectrophotometric assay may be more
accurate in determining SPS activity than measuring the sucrose

end product.

Continuing to identify significant enzymes in the pathway
of formation of reducing sugar will be an important area of
study for potato researchers. It is becoming more feasible for
biogenetic engineers to manipulate genes in plants for a desired
effect. Researchers in the potato field must be able to
effectively interface with bioengineers in developing more
resistance to disease, decrease tuber respiration problems and
generation of a tuber variety that can maintain a low reducing

sugar level during cold storage.

REFERENCES

REFERENCES

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SS

S6

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57

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S9

Pollock, C.J. and ap Rees, T. 1975. Activities of enzymes of sugar
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61

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APPENDICES

APPENDIX A

Data from Sugar Analyses

62

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00.. 00-05 0.000 0.000 0.005 0.000 0.000 0.000 0.000 0.000 0.000 0.000
2033.0 0.005 0.00. 0.000 0. . 00 0. . 0 0. . 05 0.. 0.00 0. . 50 0. . 00
00:00.00 0.05 0.050 0.000 0.000 0.00 0.005 0.000 . 0.000 0.000 0.00
>0-000. 0 0.000 0.005 0.000 0.000 0.000 0. . 00 0.. .0 0.. .0 _ 0.. . 0.. N0
z<-.0~ 0.000 0.000 0.000 0.000 0.000 0.005 0.000 0.050 0.000 0.00.
20>.n50.-0 0.000 0.000 0.000 0.000 0. . 00 0. . 00 0050 0.00. 0.00 0.000
2<.00 0.000 0.000 0.000 0.000 0.000 0.000 0.050 0.00 0.005 0.00.
>33..." 0.000 0.000 0.005 0.00» 0.000 0.000 0.00. 0.000 0.000 0.000
200.500-. 0.050 0.000 0.050 0.00. 0.050 0.05 0.000 . 0.05. 0.00 .0.050
20.~000-. 0 0.000 0.000 0.00 0.00 0.000 0.050 0.000 0.00 0.000 0.000
00000.50 0.000 0.005 0.. N0 0.00 0.00 0... 0.00 0.. .0 0.00 0.00
00000.00 0.00 0.. 0. .00 0.000 0.00 0.000 0.000 0.005 0.000 0.000
00000.00.
00000.00.» 0.00 0.00. 0.000 0.005 0.05 0.00 0.000 0.000
5.00050 0.00 0..0~ 0.55 0.55 0.000 0.. .0 0.00 0.00 0.00» 0.05
50000.00 0.000 0.000 0.000 0.00 0. . 0 0.00 0.. .0 0.000 0.000 0.050
$000.00..
$000.00.» 0.000 0.000 0.000 0.000 0.005 0.000 0.00. 0.005
0:300:50 0. . 0. 0.000 0.000 0.00 0.000 0.000 0.005
0:05.00300 0.000 0.000 0.000 0.000 0.005 0.000 0.00. 0.005
0:053:00.
0305003000 0. .05 0.00 0.000 0.00 0.005 0.050 0.05.
5.000-...50 0. .00 0. . n5 0. . 00 0.000 0.000 . 0.00 0.000
30000-300 0.00 0.. .5 0.000 0.. .0 0.000 0.00 0.000 0.000
<<-000_.-00-.
50.000300-» 0.. . 0.000 0.000 0.00. 0.000 0.05 0.050

 

 

 

5.000 0:0 5-000.. <33 0.02: 0. 02.03:. 3.30.
00-. 30.00.00 «.0300 0. 3.0 33003.03 .0. . 30:3 00.03 030030 002: .0 00 000.
00-» 30.00.00 «.0300 0. 3.0 33003.03 .0. N 30:30 00.03 0300.00 005.: .0 00 000.

00.0.0 >N0.

000.000 00.0 0.03 0000.0 .: <0..0.< 00300000?

 

 

66

000.000 00.00:.000

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0mr......... 5.00.. . . <<00.. .» .20.... .0 $30.. .5 <<00.. .0 $30.. .0 <<00r .0 $000.. .0 5.00.. .0 <<00.. »0
.».»0.05 .»0»0005 .00000 .30000 .20000 .3200 30.000 ».0.00 5.5000 ».»..00

20>-»00.-» 0.000 0.000 0.000 0.000 0.05. 0.005 0.005 0.050 0.05. 0.05.
ZO)-»5.0-0 0.. .0 0.»0» 0.050 0.050 0.050 0.000 0.000 0.00. 0.00 0.05.
00.. 00.05 0.00 0.000 0.005 0.000 0.00» 0.00. 0.00. 0.000 0.00. 0.00
2033.0 0.000 0.00 0.000 0.. .0 0.0» 0.00 0.00 0.05. 0.000 0.00
0039.00 0.00. 0.000 0.000 0.00 0.00 0.000 0.000 0.00. 0.00M 0.00
>0-000-.0 0.000 0.05» 0...» 0..»0 o...» 0.... 0.... 0.50 0.0. 0.00
Z<-.o» 0.00 0.00» 0.050 0.00» 0.000 0.005 0.005 0.00. 0.00. 0.000
20>.»50.-0 0.000 0.000 0.00» 0.000 0.00» 0.05 0.000 0.005 0.0» 0.. .0
Z<-00 0.00. 0.00 0.050 0.000 0.000 0.00. 0.00. 0.000 0.000 0.000
>303..." 0.000 0.000 0.000 0.000 0.050 0.000 0.05 0.05 0.00 0.000
ZOO-.500. 0.05 0.000 0.000 0.050 0.050 0.050 0.050 0.050 0.050 0.05.
ZO.»000-.0 0.000 0.00» 0.000 0.000 0.000 0.00» 0.00» 0.000 0.000 0.00.
M00005... 0.00 o.»0» 0.0 0.00 0.00 0.»00 0.»00 0.50 0.00 0.»05
m0000-0o 0.05 0.000 0.00» 0.005 0.00 0.050 0.050 0.00. 0.000 0.000
m0000-00. 0.0». 0.0»5 0.0»0 0.0»0 0.00» 0.050 0.000 0.055 0.000 0.050
m0000-00.» 0.0»0 0.005 0.00. 0.05» 0.050 0.000 0.000 0.005 0. . 0. 0.»05
2000-50 0.050 0.000 0.00 0.000 0.000 0.000 0.00 0.000 0.000 0.000
2-00000 0.050 0.050 0.050 0.00. 0.000 0.000 0.000 0.000 0.05 0.000
2000.00. 0.0» 0.0»0 0.0»0 0.050 0.00. 0.005 0.05. 0.000 0.000 0.. .0
$0000.00.» 0.000 0.0»0 0.050 0.000 0.00. 0.005 0. . 00 0.005 0. . . 0. . 5.
023200.750 0.000 0.000 0.005 0.000 0.00 0.000 0.000 04.000 0.00. 0.000
0:0200:-0O 0.050 0.000 0.050 0.00 0.00» 0.000 0.000 0.000 0.000 0.000
0:0200:-00-. 0.000 0.00» 0.000 0.000 0.05. 0.00 0.000 0.000 0.000 0.000
0:933:00-» 0.050 0.05. 0.000 0.000 0.00 0.000 0.00. 0.005 0.000 0.000
<<000-=-50 0.00. 0.000 0.00 0.005 0.00. 0. . »» 0.00» 0.005 0. . 00 0.. .»
<<000-=-00 0.000 0.000 0.050 0.000 0.00. 0.00 0.00» 0.005 0.000 0.000
<<.000...00-. 0.0»0 0.050 0.055 0.000 0.005 0.000 0.000 0.000 0.000 0.00»
2-000.700-» 0.000 0.00. 0.005 0.000 0.005 0. . .0 0. . » 0.000 0. . o. o. 05

 

 

 

<<-000 0:0 2.000.. <33 0.0.2: 0. 0.20.3. 3.30.
00-. 30.0030 0.0300 0. 3.0 33003.03 .0. . 30:3 00.03 030030 00.2: .0 00 000.
00.» 30.00.00 0.0300 0. 3.0 33003.03 .0. » 30:30 00.03 030030 005.: .0 00 000.

40.0.0 >»0.

000.000 00.0 0.0.: 0000.0 .: <0..0.< 00300000?

 

67

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0.2.02... <<aar w. Saar nu <<oar 00 <<oax wa (<8: 00 .28.. M0 Saar n0 <<aar n0 <<oar 00
~0~0000 000000 00.200 03.000 030000 3200 ~.0. .000 ~{.0000 A3000

20>.000.-~ 0.000 0.000 0.000 0.050 0.030 0.0?— 0.050 0.000 0.0.
20).»... 00 0.05M 0.0.. 0.000 0.050 0.000 0.000 0.00. 0.000 0.030
00.. 00.05 0.000 0.00. 0.00» 0.000 0.000 0.000 0.000 0.00 0.000
2:83.: 0.... 0.00 0.. .N 0.00 0.000 0.00» 0.00N 0.00» 0.000
0.52.2. 0.003 0.00. 0.000 0.00N 0.00 0.000 0.000 0.00N 0.00.
>m000..0 0.. 0.00 0..0. 0.000 0.000 0.000 0.000 0.. .5 0.00
Z<..0~ 0.00N 0.00. 0.000 0.000 0.00 0.00. 0.000 0.00 0.000
20>-NA0.0 0..0. 0.00 0.0» 0..00 0.00 0.... 0...0 0.0» 0.00
Z<00 0.000 0.0.: 0.050 0.000 0.00 0.050 0.0... 0.00M .0000
2.0:..." 0.000 0.000 0.000 0.000 0.000 0.00. 0.000 0.000 0.000
200-. .00.. 0.000 0.00» 0.000 0.00. 0.00 0.000 0.050 0.00; 0.00.
20-~000-.0 0.000 0.000 0.005 0.000 0.000 0.000 0.000 0.005 0.000
m0000$0 0.00 0.000 0.00 0.. N 0.33 0. . 00 0. . 0. 0.. .0 0.000
m000000 0.000 0.000 0.050 0.00. 0.000 0.005 0.00. 0.00 0.000
m000000. 0.000 0.000 0.00. 0.000 0.000 0.. N 0.. .0 0.00. 0.~0~
m000000.~ 0.000 0...~ 0.0 0.00 0.». 0.0.0 0.30» 0..0~ 0.0~0
50000.50 0.000 0.00. 0.000 0.0 0..». 0..»0 0..00 0.00A 0.000
<<000.00 0.000 0...» 9.00 0.00 0.. .0 0.. .0 0.00 0.0 0050
<<00000.. 0..00 0.~.~ 0.».0 0.0 0.000 0.~00 0.005 0.»; 0.000
5000000.» 0.00» 0.~00 0.000 0.~00 0.00 0.0 0. . N. 0.00 0.0..
0:923:50 0.00~ 0.000 0.00. 0.005 0.00. 0.000 0.000 0.000 0.000
0:923:00 0.00. 0.005 0.000 0.000 0.000 0.. .0 0. . 00 0. . 00 0.. N~
0:923:00. 0.000 0.~00 0.000 0.~0. 0.00.. 0.0 0. . 00 0. . 00 0. . 00
0:923:00-» 0.00 0.0» 0.00 0.00. 0.~00 0.00 0.».0 0.00 0.»...
2000-..-00 . 0.00 0.00. 0.00» 0.. 0.000 0.00. 0.000 0.000 0.00»
<<000-=.00 0...0 0..~. 0...0 0...0 0.00 0.00 0.00 0.00. 0.0
<<000=00-. 0... 0.00 0.00 9.00 0.00. 0.00. 0.00n 0.5; 0.00
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.2000 :2. .2000: $38 085: a. 0:333 .23?
00-. 50.023 «830a m. in 33:23:; .9 . 30:... .533 $2550 092: 8 00 can.
00-0 .3323 «330a 2 3.... 83:92:; .9 n 30:16 00.06 «82.30 09:: 8 00 can.

.368 bun.

0:033 008 30:. 0:38 .: <93; 003323?

 

68

Average Reducing Sugar Content of Tubers in

 

Vanety Tnal
Week Glucose %
1 0.010
2 0.009
3 0.007
4 0.011
5 0.014
6 0.016
7 0.019
8 0.022
9 0.022
10 0.019
11 0.042
12 0.035
13 0.032
14 0.038
15 0.029
16 0.032
17 0.040
18 0.040
19 0.041
20 0.034
21 0.034
22 0.036
23 0.033
24 0.032
25 0.033
26 0.035
27 0.032
28 0.041
29 0.046

Table A3. Reducing Sugar Data from Tubers in Variety Trial

69

Effect of Reconditioning on Stored Tubers

B 1.. l:l°i: \I E In l:l°/:
Norchip
Apr. 5 .090 .090
Apr. 12 .055 .055
Apr. 19 .116 .118
Apr 26 .099 .096
BO-178-34
Apr. 5 .038 .038
Apr. 12 .030 .030
Apr. 19 .038 .019
Apr 26 .010 .042
NDA-2417-6
Apr. 5 .019 .019
Apr. 12 .016 .016
Apr. 19 .015 .021
Apr 26 .014 .019

Table A4. Reducing Sugar Data from Reconditioned Tubers.

APPENDIX B

Color Score Data

70

00.0.. 000.00 302.0... .9. 0.5.0

 

 

00.030: ....30.30.... 020......“ 2.0:...

.90.. . :00 .0-00. EM E E E
20> 0..—00 .0 0:0 0.. 0.0 0 0x. PM
20> 0.0.0-0 A80. NM
20> 0.00.-N .0 NM 0.0 P0 0.0 Mk. 0.0
200 7.00-. .0 .0 No 0.0 0.0 N... 0.0
20> N030 ..0 0 0.0 0.0 0 0.0 0.0
.00 .00-00 .0 PM 0.0 0 00 N0 0
00 .00-0.. NM
>0 0.00-.0 N PM 0.0 0... 0.0 a 0.0
208:... .x. 0 0.0 A... 0.0 PN 0.0
208:... A80. 0.0
5 .8 N0 No 0.0 0 0 0:0 0.0
2.0 0000.0 0.0 N 0 0.0 0x. 0 0.0
2< 00 0.0 0 0.0 0.0 0... 0 0
00:010.. 0 N0 0.0 0 0.0 0.0 0x.
>..0:..n 0.0 0.0. 0.0 0.~ 0.0 0.0
muuuu 0031 0.0 0 A 00 N 0.0
£0.00 00...“ 0.0 0.0 0.0 0 0 0.0
0:95.00 00...“ N NN .0 . .0 N 0
£000: 00...“ 0.0 0.0 0 0.0 0 P0
muuuu 00...” 0.0 0... 0.0 0 PM 0 0.»
€0.00 00.....- N.0 N00 NN N... PM 0 0.0
000500.. 00....H MN .0 N.» 0.0 ..N N... 0.0
2000: 00am 0.0 0.0 .x. 0x. ..0 PM 0
0.0000 00...“ A. 30...... 0.0 ..0 No 0.0 N 0.0
2000 00...... A. 30...... 0.0 .0 P0 .0 0 0.
000500.. 003.“ A. 30...... 0.0 0.0 .0 ..~ 0.0 uh
$0000.. 00...... A. 30...... PM PM 0.0 NA. 0.0 0.0
amuu 00%? 300...“. N . 0.0 N... 0. 0.0
€0.00 00...... AN 300:5. 0.0 0.0 N0 0 0.0
000200: 00.. AN 30.5.0. N 0.0 .x. N 0
£000: 00.. 3300...... 0.0 0.0 N... 0.0 0

N—uumuppwu
Color Score Data

0000010—01000'

P
so

NNPN
LAND-1d

N N N N
O O O O
Iable Bl.

va
\JUJO

71

2.3.3.00 ..0.. 0..... 00.0.. 08.00. <0. .0350 0a 0.00.... 02.0030 0:00.. 00:23. .: <0...0J.
0...... A0058. .0 0.0—.80

00.0020:

 

200 .000.
20 0000.0
Z< .00
20> 000.0
20> 00.00
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00:01m0

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20> 000.0

Z< 00

208:...

B0. .3... 0:03 035. A005

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0.0
0.0
0.0
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.0

..

.0

B0. 00.0.. LEE.

0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0..

0..

0..

00::

 

.0

.0

.0

Color Score Rankings

Table 82.

APPENDD( C

Statistical Analyses Data

General 3130:: nod-ls Procedure

Tukey's Studentixod Range (880) Test for variable:

RESPONSE

NOTE: This test controls the type I experimentwise error rate.

= 0.000274
4.658

d Ranges

95 at: 307 H82

ot studentiee

Alphnl 0.05 Confidencot 0.
Critical Value

...
3
i
Y
b
d
e m
f.
a w u
e n a m.
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dimpf.
nmUm
01$ C
e
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Comparison

2635663795
7296776156
6226779026
7993340667
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5121
6121

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21..
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30560113366
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1
4
2
6
0
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-0.016655
0.006690

-0.030983
-0.007638
'0.006086
-0.006017
-0.001880
-0.001534

0 21
66153621711

99999999999

mmwervg

II!
It!
it!
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3"
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8980116261
3746333712
6693666691
7550017224.
0112233466
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009017

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'0.023345
-0.006690

-0 .037672

-0.021017
-0.012776
-0.012707
-0.008569
-0.008224

00000

0 21
49153621711

m-_NVN <02

t one...
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96 669996129
68 798778266
50 737880135
06 248896112
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00
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2.52

Comparisons of Reducing Sugar Content Among Tubers in Variety Comparison.

Table C la.

73

General Linear Models Procedut‘
Tukoy'. Studentisod Range (880) Test for variablc: RESPONSE
NOTE: rhis teat control. the type I experimentwiso error rate.

Alphas 0.05 cong14.n¢.. 0.95 at: 307 uses 0.000274
Critical Value at Studentised Ranoe= 4.553.

Comparison; 3ifinificant at tho 0.05 lcvol are indicated by '**"

Simultaneous Simultaneous
Lower Difference Upper
VAR Confidence Between Confidence
Comparison Limit Means Limit
1 - 4 -0.060983 -0.046655 -0.032328 5*-
°? 1 - 9 -0.044328 -0.030000 -0.015672 :::
- 1 - 8 -0.037638 -0.023310 -0.008983
0” 1 - 10 -0.036086 -0.021759 -0.007431 ***
<3 1 - 5 -0.036017 -0.021690 -0.0o7362 *"
C“ 1 7 3 -0.031880 -0.017425 -0.002970 :;:
.g 1 - 6 -0.031534 -0.017207 -0.002879
£3 1 - 2 -0.020534 -0.006207 0.008121
1 7 7 -0.009293 0.005034 0.019362
2: 1 - 12 -0.009052 0.005276 0.019603
1 - 11 -0.007845 0.006483 0.020810
7 - 4 -0.066017 -0.051690 -0.037362 7*:
7 - 9 -0.049362 -0.035034 -0.020707 *7.
7 - 8 -0.042672 -0.028345. -0.014017 *7
E§ 7 7 10 -0.041121 -0.026793 -0.012466 ...
__ 3 7 5 -0.041052 -0.026724 -0.012397 5"
7 3 -0.036914 -0.022459 -0.008004 75*
7 - 6 -0.036569 -0.022241 -0.007914 57*
7 ' 2 -0.025569 -0.o11241 0.003086
7 - 1 -0.019362 -0.005034 0.009293
.7 7 12 -0.014086 0.000241 0.014569
' 11. -0.012879 0.001448 0.015776
1 - 4 -0.066259 -0.051931 -0.037604 ...
O - 9 -0.049603 -0.035276 -0.020948 mt
'7 - 8 -o.042914 -0.028586 -0.014259 '9'
up ' 10 -0.041362 -0.027034 -0.012707 5*:
r~ - 5 -o.041293 -0.026966 -0.012638 7"
up ' 3 -0.037156 -0.022701 -0.008246 ***
cs - 6 -0.036810 -0.022483 -0.008155 ***
C3 - 2 -0.025810 -0.011483 0.002845
' 1 -0.019603 -0.005276 0.009052
2! - 7 -0.014569 -0.000241 0.014086
' 11 -0.013121 0.001207 0.015534
- 4 -0.067465 -0.053138 -0.038810 ...
—~ - 9 -0.050810 -0.036483 -0.022155 6..
“5 - 8 -0.044121 -0.029793 -0.015466 ...
Ch - 10 -0.042569 -0.028241 -0.013914 44*
<3 - 5 -0.042500 -0.028172 -0.01384s 4'4
._ 7 3 -0.038363 -0.023908 -0.009453 54*
7 6 -0.038017 -0.023690 -0.009362 ...
£3 ‘ 2 -0.027o17 -0.012690 0.001638
:5 ' 1 -0.020810 -0.006483 0.007845
' 7 -0.015776 -0.0o1448 0.012879
- 12 -0.015534 -0.001207 0.013121
Table C l b. Compansons of Reducmg Sugar Content Among Tubers in Variety Comparison.

74
General Linear.uodela Procedure
Tukey'a Studentiaed Range (380) feat for variable: RESPONSE
NOTE: This teat controls the gyp. x .xperimentuise error ree..

Alphas 0.05 Confidence! 0.95 at: 307 uses 0.300274
Critical v.10. ot Otudentiaed RanO“ 4-65

55°39‘55““. iiflflificent at the 0.05 level are indicated by
Simultaneous Simultaneous

Lower Difference , Upper
VAR Confidence Between Confidence
Comparison Limit Means Limit 638 e n
5 7 4 - . 9293 -0.024966 -0.010
5 7 9 ‘-g.332638 -0.008310 0.00331;
5 7 3 -0.015948 -0.001621 0.0 ‘259
CL 5 7 10 -0.014396 -0.000069 0.018720
'9’ 5 7 3 -0.010190 0.004265 0.018810
5 5 7 5 -0.009845 0.004483 0'019810 r"
= 5 7 2 0.001155 0.015483 0.0260“ n.
3 5 7 1 0.007362 0.021690 0.031052 n.
”1 5 7 7 0.012397 0.026724 0.04 293 "I
5 7 12 0.012638 0.026966 0'055500 ‘.‘
5 7 11 0.013845 0.028172 0.04
- 775 at:
5 7 4 - . 3685 -0.029230 0.014
5 ’ 7 9 ‘-g.837030 -0.012575 0.001220
<5 5 7 3 -0.020340 -0.005885 0.000121
6? 5 7 10 -0.018789 -0.004334 0.010190
°° 5 7 5 -0.018720 -0.004265 0.01 673
r~ 5 7 5 -0.014237 0.000218 0.013673
'7 5 7 2 -0.003237 0.011218 0.021880 ...
5 7 1 0.002970 0.017425 0.03691‘ g,“
8 3 ‘12 723222: 3113732 1:27...
- ° ' ° sea
5 7 11 3.009453 0.023908 0.038363
5 - 1 '6'
5 7 4 - .043776 -0.029448 0.01512
5 7 9 -3.027121 -0.012793 0.00133:
“7 5 7 8 -0.020431 -0.006103 0.003776
" 5 7 10. -0.018879 -0.004552 0.009“5
' 5 7 5 -0.018810 -0.004483 0.00 37
V5 5 7 3 -0.014673 -0.000218 0.01;:28
55 5 7 2 -0.003328 0.011000 0.02 a. ."
LL 5 7 1 0.002819 0.012201 0.0355 0 m.
5 7 12 0.008155 0.022483 0.036817 ."
‘5 5 7 11 0.009362 0.023690 0.0380
I!
2 ' 4 -0.054776 -0.040448 -0.026121 :"
7 - -0.023793 -0.009466 "'
v: 5 7 3 -32331531 -0.017103 -0.002336 ."
FL 5 7 10 -0.029879 -0.015552 -0.001155 ...
77 5 7 5 -0.029810 -0.015483 -0.00 237
5“ 5 7 3 -0.025673 -0.011218 0.003328
‘7 5 7 5 -0.025328 -0:011000 0.00053‘
5 7 1 -0.008121 0.006207 0.035569
5: 5 7 7 -0.003086 0.011241 0.0 5810
5 7 12 -0.002845 0.011483 0.027017
E3 5 ' 11 70.001638 0.012690 0.02
TableClc.

Comparisons of Reducing Sugar Content Among Tubers in Variety Comparison.

NDA-203 1-2

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

NDA-2417-6

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

BO—178-34

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

Table C28.

.279
.457
.488
.390

(-).251
.014

(-).078
(-).289

.012
.040
.155
.248

75

NY-IOZ

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

NDA-2471-8

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

NY-95

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

Percentage of Selections in Variety Comparison.

(-).144
(-). 178
(-). 185
.016

.227
.140

(-).072
(-). 1 18

(-).142
(-).008
(-).018
(-).291

Correlation Coefficients of Previous Sucrose Percentage and Glucose

ngchip

 

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

__Smcrim

.265
(-).013
.273
.041

 

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

AF-875-15

Sucrose 1 week previous:

Sucrose 2 weeks previous:
’ Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

Table C2b.

.059
.128
.052
.310

.250
.398
.400
.460

76

Alan—tie

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

NDO- 1 496-1

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

ND2676- 10

Sucrose 1 week previous:

Sucrose 2 weeks previous:
Sucrose 3 weeks previous:
Sucrose 4 weeks previous:

Percentage of Selections in Variety Comparison.

.240
.276
.034
.006

.163
.015
(-).023
(-).095

.133
.230
.073
.102

Correlation Coefficients of Previous Sucrose Percentage and Glucose

77

Correlation Coefficients of Previous Sucrose Percentage and Glucose Percentage of all
Selections Combined in Variety Comparison

 

Sucrose Percentage 1 Week Previous as Indicator: 0.347
Sucrose Percentage 2 Weeks Previous as Indicator: 0.400
Sucrose Percentage 3 Weeks Previous as Indicator: 0.193
Sucrose Percentage 4 Weeks Previous as Indicator: 0.328
Table C3. Correlation Coefficients of Previous Sucrose Percentage and Glucose

Percentage of all Selections Collectively in Variety Comparison.

APPENDD( D

SPS Analysis Data

78

Sucrose Phosphate Synthetase (SPS) Content in
Selected Reconditioned and Non Reconditioned

Tubers

Selection

Replication 1
.125

Norchip Reconditioned
Norchip Not Reconditioned
80178-34 Reconditioned
30178-34 Not Reconditioned
NDA2417-6 Reconditioned
NDA2417-6 Not Reconditioned
Standard 1 Unit

Standard 2 Units

Table D1. Data from SPS Analysis.

SPS Content (grams /1iter)

.082

.090

.056

Replication 2
.057
.099
.064
.076
.074
.054
.072

.084

"711111111111111111111“