EFFECT OF ADDED COLLOIDS ON THE
PALATABILITY AND THE
QUANflT‘.’ 0? JUBCE DRAINED FROM
YHAWE’D STRAWSERMB

Thesis for the Emma af M. 5.
MiGflGAN STATE COLLEGE
iiiian Anne Gab-w
1952

 

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, thesis entitled
’ , 4 EFFECT OF ADDED COLLOIDS ON THE
A ' " . PLLATABILITY AND HE QUANTITY 0? JUICE
'. \w DRAINED IRON mm STRAWBMIIS
‘ I ,' ‘ '. ' presented by
t . ' Lilian Anne Gabay
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EFFECT OF ADDED COLLOIDS ON
THE PALATABILITY AND THE
QUANTITY OF JUICE WIRED

FROM mm SMWBERRIES

3:
Lilian Anne Gabay

A THESIS

Submitted to the School of Graduate Studies of’Midhigan
State College of’Agrtculture and.Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of l'oode and. Nutrition
School of Home Economics

1952

ACKNOWLEDGMENT

The writer wishes to express her gratitude
to Dr. Pauline Paul for her guidance throughout
the study, and to May Bay, Maura 3ean, Ruth Beegle,
Dorothy Dunsing, Annanell anb, Alice Seelinger,
and Andrea Wagoner for their cooperation in serving
on the scoring panel.

She would also like to express her appreciation
to Jean Friend for her encouragement and teen in-

terest in this project.

279569

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . .
REWIEH'OF LITERATURE . . . . . .
The pectic substances . . .
Gelatin . e . . . . . . . .

Homlcellulcmé e e e e e e

0

Characteristics of a standard.product

Objective tests . . . . . .
METHODS 01' PROCEIIJRE . . . . . .
Design of experiment . . .
Preparation for freezing .
Preparation of eirnpe . .
Preparation for scoring . .
Objective tests . e . e . .
Leakage test . . . . .
Moisture content . . .
Specific gravity . e .
Viscosity . . e e e .
Subjective tests . e . . .
DISCUSSION OF RESULTS . . . . .
Palatability scores. . . .

General appearance

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Luster . . . . . . . . . .

Odor . e e . .,. . . . e .

Flavor of berry . e . . .

Flavor of Juice . . . e .

Texture of berry . . . . .
Consistency of juice . . .

General Conclusion . . e e
Objective tests . . . . e . . .
Leakage of juice . . . . e

Specific gravity . . . . .
Viscosity . . e e . . . e

Hoisture content . . . . .
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Number

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LIST OF TABLES

Title
Quantity of ingredients per carton . . . .
Sirup for fifty cartons of each treatment.
Mean.pslatability scores . . e . . . . . .
Average lean scores and F—vslues . . . . .
Mean.per cent leakage of juice. . . . . .

Mean.specific gravity of sirup . . . . . e

Mean specific gravity of sirup and equivalent
per cent sucrose solution. . . . . . . . . . .

Mean viscosity of sirup as indicated.by minutes
in Ostvald.71scosineter. . . . . . . . . . . . .

Mean moisture contents of berries. . . . . . . .

Mean moisture contents Of Bil-Upe e e e e e e e e

. . 33

. . 36

. . 37

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IKIBOWCTIOK

INRODUCTIOH

Fruits and vegetables deteriorate rapidly after they reach.prime
condition in the garden or orchard. Many of the choicest kinds have
lost their freshness by the time they reach the consumer. A.possible
solution to the problem is to freeze fruits and vegetables shortly after
they are picked. In that way, the color. flavor. and nutritive value are
preserved for a much longer time. Freezing preserves the freshness of
foods better than any other method of food.preservation.

Small fruits are especially adapted to freezing. In fact, small
fruits are not easily preserved by other methods because they are fragile
and delicate in flavor. In addition. the preparation of small fruits for
freezing is comparatively simple.

Among the small fruits which are frozen. strawberries have been a
favorite item for a long time. However, the texture and appearance of
the frozen straiberries are not always satisfactory. Sometimes an excess
of juice leaks from the berries when they are thawed. this results in a
flabby texture and.apparent reduction in volume. When the berries appear .
flabby. they are unpalatable and do not resemble the fresh.product.

l.possible way to reduce the amount of leakage during thawing'vould
be to treat the berries with.a.protective agent prior to freezing. The
additive must be one which.vill decrease the leakage without impairing

the appearance or flavor of either the berries or the sirup.

The following study was made with a view toward finding a.possible
protective agent for frozen strawberries. Some investigators had found
that low methoxyl pectin was effective in reducing leakage by the forma-
tion of a gel on the out surfaces of the berries. This colloid was in-
cluded in the study, therefore, for comparative purposes. Since low
methoxyl pectin is not readily available to the homemaker, it seemed
advisable to include other substances which were capable of forming gels
and.which.were easily Obtained. Powdered commercial pectin and plain
gelatin were selected. A.powdered methylcellulose was also used for one
of the treatments. This colloid has been reported to be useful as a
thickening agent in a number of foods. It was thought, therefore, that
the product might be used as a protective agent for frozen strawberries.

Since one of the best tests for any food is its eating quality,
organoleptic evaluations were made by a scoring panel.' However. certain
objective measurements were necessary for a more complete study. Drained
weights of the berries were obtained to calculate the amount of'judce
lost on thawing. Specific gravities of the sirups were determined before
freezing and after thawing, and converted to the equivalent per cent
sucrose solutions. The difference between the two values was some indi-
dation of the dilution of the sirup by the juices exuded from the berries.
Per cent moisture contents were determined to compare with the results of
the leakage and the specific gravity tests. Since each of the colloids
was expected to form a gel, it seemed advisable to include viscosity

tests in the study to compare the final consistencies of the sirups.

REVIEW OF nmmmn

REVIEW OF LITERATURE

Vorkers in the field of frozen foods early recognized that one of
the problems in the freezing of strawberries was the great loss of Juice
when the product was thawed.

Voodroof (28) reported that the loss of plant Juices was due to the
irreversible precipitation of cell contents. There was a liberation of
I'bound water“ and water previously present in the vacuoles. Host of
this water was not reabsorbed on thawing. Thus. flabbiness and loss of
structure were due to the breakdown of cell contents which formerly gave
support to the walls.

Josyln (12) stated that the decrease in weiglt of frozen fruits
after thawing was due to (a.) water which was separated as ice during
freezing and not reabsorbed during thawing. (b.) leakage of fluids
through the tissues which were injured by freezing. and ((3.) osmotic
action of the sugar or sirup in which the fruit was packed.

Considerable study was made on the protective action of various
salts, sugar. and sirup which would affect the osmotic properties of the
fruit. Sucrose sirups aided in the retention of fresh appearance and
texture (6. 7, 13, 1‘4, 18. 22), but they were not effective in bringing
about an appreciable decrease in the amount of exuded Juice. Calcium
salts did not have a noticeable firming effect on frozen strawberries
(1. 11). he use of pectin to protect fruit tissues by the formation of

a gel was also reported in the literature.

_I_'_h_e_ 3.9.9.312 Substances

Boss. (21) pointed out in 1921 that the naturally present pectic
substances helped to influence the texture and firmness of plants. He
believed that if the pectin content of fruits could be regulated. an im-
provement in the freezing preservation could be expected.

Although it was impossible to regulate the pectin content of the
cell. some investigators pointed out that it was possible to add pectin
to frozen foods as an external protective agent. One of the first avail?-
able reports on the subject was a patent issued to Cowgill (5) in 1938
for the use of a ”non-acid pectin in non-hydrated, non-gelatinous con-
dition'. In the case of berries, the pectin was dispersed throughout
the fruit with or without sugar. The concentration of colloid was such
that the pectin content of the exuded juice was approximately the same
as the natural pectin content of the original berries. Apparently. the
pectin in Cowgill's sirup helped to prevent oxidative changes.

Other investigators, especially Baker (1). believed that a pectin
gel on the surface of the berries would reduce the leakage of Juice as
well as prevent oxidation. It was found that certain pectins were able
to form gels without a higi concentration of sugar. The ability of pectins
to for: gels varied according to the methoxyl content of the pectin mole?-
cules. Pectins with more than seven per cent methoxyl groups required a
soluble solids content of over 50% for proper Jelly formation. When
pectins contained less than seven per cent nethoxyl. they were able to

produce firm gels with traces of polyvalent cations (usually calcium) at

a much lower solids content. These discoveries led to investigations on
the possibility of using low methonl pectins for frozen strawberries.
Baker (1) in 1941 reported the addition of pectins ranging from 3.5
to 11$ methoxyl content to frozen strawberries. He found that the methoxyl
content was the most important factor in determining the behavior of the
pectin. A cold two per cent solution of a pure pectin having a five per
cent nethoxyl content reduced the loss of Juice upon thawing by one-
third. Pectins of high nethoxyl content. including the comercial
pectins. were not effective in reducing the loss of Juice. The pectin

solutions produced the best results when they were below 60° 1‘, Better

comparisons were found with sliced than with whole berries. because there
was not as much variation in size and surface conditions. Baker also
found that the sliced berries treated with low methoxyl pectin had better
color. shape. and general appearance than the other samples. Small
amounts of calcium salts. alone or in combination with pectin. were not
as effective as pectin alone. Evidently. these salts combined readily
with the added low methoxyl pectin. preventing the formatim of a gel
with the natural salts present in the strawberry juice.

Since Baker‘s work gave promising results with the use of low methi-
oxyl pectin. further studies were made a few years later. Buck. Baker.
and Hottern (3) reported that pectinates reduced the leakage of Juice from
frozen sliced strawberries. cherries. raspberries. and peaches. In eddie-
tion. the fruit was more glossy and retained more of its natural color.

The pectinates combined with the calcium of the fruit to form a gel on the

surface. Although some juice was withdrawn from the fruit. most of it

 

was held in a gel state and did not drain off or separate from the fruit
on thawing. These investigators found that 0.h2% of a pectin with a
methoxyl content of 6.10% gave a 33% reduction in drainage. Increased
qmntities of the pectin continued to reduce the drainage, but the lumps
of gel detracted from the appearance of the product. In their work
there was no correlation between the amount of drained Juice and the
different characteristics and properties of the pectins. such as
methonl content. calcium Optimum. gel power. or method of demethoxyla—
tion.

Grab. Yegener. and Beer (11) treated strawberries with low nethoxyl
pectin and with alginates. Both types of samples showed a definite in-
crease in per cent drained weight. though the low methoxyl pectin gave
the most marked results. The flavor was unchanged in both treatments.
but the color and appearance were improved by the low methoxyl pectin.
he authors recommended low methoxyl pectin in a concentration of 0.2 to
05$ by weight of berries for optimum results.

The California Fruit Growers' Exchange (’4) published information on
freezing strawberries with the addition of low methoxyl pectin to the
sugar sirup. The colloid caused a sealing of cut berry surfaces and a
subsequent decrease in leakage. Here apparent results were obtained
with sliced berries than with whole ones. The benefits of the low
nethoxyl pectin were more noticeable when it was added in sirup rather
than with dry sugar. The recommended concentration of low methoxyl

pectin was 0.10 to 0.15% by weight of berries. Untreated berries

usually lost 60-65% of their total weight on thawing. Losses from ber-
ries treated with low methoxyl pectin usually did not exceed hfifl,

Vegener. Baer. and.Rodgers (25) experimented with the addition of
low nethoxyl pectin. kelp extractive. and Irish moss extractive to whole
and sliced strawberries. They found that there was a marked.increase in
drained.weight in all samples. However. the low methoxyl pectin was
considered best from the standpoint of increasing drained weight with
the smallest quantity of colloid. There was a greater uncrease in
drained weight with 60% sirup than with dry sugar. inc differences be-
tween the controls and the sirup packed samples were more noticeable with
the whole berries than the sliced ones. except with the low methoxyl
pectin. In addition to an increase in drained.weight. the treated samples
were more glossy and retained their shape better than the controls. The
authors recommended a level of 0.15% low methoxyl pectin and 0.3 to 0.3%
of the other colloids for best results.

Xaloyereas (16) studied the preservation of’color. flavor. and
texture of strawberries as affected by the addition of various substances.
including a combination of 0.1%;pectin and 0.1% calcium chloride. It is
assumed that a high methoxyl pectin was used. but the report does not
state this fact specifically. The pectin-calcium.chloride increased the
firmness of the berries but did not improve the taste. color. and aroma.

The addition of a minute quantity of pectin to frozen cherries was
suggested.by Fitzgerald (10). He pointed out that cherry Juice contained
mostly invert sugar which resisted crystallization. In addition. the

Juice was low in natural pectin. The untreated Juice was more or less

111““- even at 0° 1'. because of the soluble solids content. Iitzgerald
felt that the pectin would increase the viscosity of the Juice and re-
duce the possibility of package leakage.

All of these reports in the literature indicated that improvements
in the quality of frozen fruits were possible with the addition of pectic

substances.

I Gelatin

To the author's lumwledge. no mention is made in the literature con-
cerning the use of gelatin to improve the quality of frozen strawberries.
more are many accounts of its use in other foods. however. The ability
to for: a reversible gel makes gelatin a very important addition to
many foods. According to Bronson (2) one of the principal uses of
gelatin is that of a stabilizer in ice cream. A relatively small amomit
of gelatin was found to prevent the growth of large ice crystals. It
also gave other desirable characteristics to ice cream which. in his
opinion. were not obtained from other stabilizers. Bronson also mentions
that gelatin is used widely in packing houses for coating specialty meat
products and in canned meats to absorb Juices which separate during the

cooking process.

flethylcellulose

Although there are reports in the literature advocating the use of
powdered methylcellulose in certain foods. there is no information on

its use in frozen strawberries. Certain properties of this colloid make

it useful in food applications. Among these are its thickening ability

 

and colloidal suspending properties. Methylcellulose differs from agar-
agar and gelatin in that it forms a gel on heating instead of on cooling.
As the temperature increases, the viscosity of the solution decreases
until a gel point is reached (8).

Hethylcellulose was suggested as a thickening agent in sugar-free
sirups for diabetic patients (8). it was also recommended for patients

with wheat allergies in the preparation of breads without gluten (8).

_C_h_atracteristics gt; a Standard Product

The ultimate goal in the freezing preservation of strawberries is to
maintain the natural state of the fruit as much as possible. However.
freezing does cause certain inevitable changes in the fruit. It is
necessary to consider a standard product as one which has the least
amount of these changes. he United States Department of Agriculture
(2‘4) has set up certain standards for grades of frozen strawberries.
These standards, though intended primarily for commercially-packed
berries. can be applied in part to any frozen strawberries. "U. S. GRADE
A or U. 8. ”NOT is the quality of frozen strawberries that possess simi-
lar varietal characteristics; possess a bright. practically uniform.
typical color: are practically free from defects: possess a good character;
possess a normal flavor and odor...‘ (22). According to these specifics:-
tions. strawberries of top quality have a good characteristic bright red
or pink color. they are reasonably free from a dull. grey. or reddish—
brown cast. There are no extraneous materials and no undevelOped or

damaged berries in the carton. The berries are free from off-flavors

10

and objectionable odors of any kind. The factor of character refers to
the texture and degree of disintegration. as evidenced by crushed or
mushy strawberries. If the berries possess a good character they are
fleshy. reasonably firm. and practically intact. (2’4)

Tressler and Evers (23) state that probably the best index of the
quality of frozen fruit is the determination of the drained weight when
thawed under standard conditions. They point out that if fruit is over-

mature. roughly handled. or frozen slowly. the drained weight will be low.

Objective Tests

In order to evaluate the effect of the added colloids on frozen
strawberries. certain objective tests have been performed on the berries
and sirups. The per cent soluble solids of the drained sirup was usually
determined with a refractometer (3. 25). ‘Ihe concentration of the drained
sirup was determined by the use of a hydro-eter and read directly as
Balling degrees. Kethley and co-workers (17) and Marsh (20) determined
the specific gravity of the simps. Baker (1) also included tests on
the viscosity of the drained Juices. These workers determined the
leakage of Juice by obtaining the drained weight of the berries.

Unfortunately. there is no standard method for determining the
leakage of Juice. Each investigator who studied the leakage of frozen
fruits followed his own plan or modified another worker‘s method. All
of the determinations were based on the same principle. however. It was
believed that the loss in weight on thawing was due to a loss in moisture

from the berries. A comparison of the drained weight with the original

11

weight was an indication of the per cent leakage from the frozen product.
Since there were many sources of error in the various methods. the
figures for leakage found in the literature were not taken as absolute
values. However. the tests were useful for qualitative comparisons to
evaluate various procedures in the freezing preservation of fruits.

One of the first methods described in the literature was used by
Woodroof (28). He thawed a weighed frozen mass in an aluminum funnel
lined.with filter paper. .After 2h hours at room temperature. the
filtrate and residue were weighed and the per cent less of Juice was
calculated.

Woodroof (27) later modified this method. He thawed the fruit in
100 c. c. separatory funnels with lids and stopcocks and in 1,000 c. c.
metal funnels with lids. Ehe liquid was collected in graduated cylinders.
when the product reached 60° F. under laboratory conditions. the liquid
portion was measured and the fruit was weighed. Woodroof found that the
longer the material stood. or the higher the temperature attained. the
greater the amount of leakage.

Joslyn and Marsh (1“) thawed their samples for 16 hours and
drained.the fruit for two minutes on‘a screen. They pointed out that
it was difficult to remove all of the Juice. sirup. or water from the
product by draining. They felt that the data could be used only for
comparative purposes.

As part of a quality control program. Evers and Hutchings (9)

suggested using the drained weight of frozen fruits as a criterion of

12

quality. They drained the thawed fruit for two minutes on a standard
screen and compared the drained weight with the weight after removal
from the freezer.

'Viegand (26). working with.sma11 containers of frozen berries. de-
termined.the drained.weight after thawing the product at room temperature
for 2“ hours.

ihe thawing conditions used'by Marsh (20) consisted of thawing the
fruit for 16 hours at room temperature. After that time. the material
was drained for two minutes on an 8—mesh screen. Harsh.weighed the
fruit and sirup and determined the specific gravity of the sirup.

rho investigators who studied the effect of low methozyl pectin on
the leakage of strawberries used the following methods: Baker (1)
erposed.the fruit to a temperature of 80° F. for two hours. He did not
give further details of the leakage test. however. Buck. Baker. and
Hottern (3) allowed the fruit to stand in open.packages until the berries
reached room temperature. This usually took four to five hours. Then.
they drained the fruit on a four-inch hemispherical twelve-mesh sieve
for ten minutes. They determined the weight of the drained Juice.
soluble solids content. and viscosity. Vegans r. Beer. and Rodgers (25)
defrosted the fruit in a room with a temperature of 21° 0. until the
center of the frozen mass reached 10-16° C. The berries were drained
for two minutes on an eightemesh screen. Records were kept of'the drained
weight of the fruit. and the volume. weight. and.per cent soluble solids

of the sirup.

13

Some investigators felt that when the fruit was thawed in air.
moisture from the air condensed on the product. When the food.reached
room temperature. evaporation occurred. This led to many errors. Iethp
ley. Gown. and Bellinger (17) mentioned that in their earlier studies.
they used a.procedure similar to Woodroof's (28) first method. They
found that there was such a wide variation in the results that only
qualitative conclusions could be made. After further study. they found
that the errors could be decreased by thawing the frozen mass in a sol-
vent immiscible with water. Strawberries were thawed.under mineral
spirits (previously saturated with.water) in a room maintained at 68° F.
t l O. The leakage was determined one hour after the fruit reached room
temperature. The berries were rolled on two paper towels in succession
and.weighed. 'hen leakage was expressed by weight loss. the variation
was 1’ 16% of the mean. When the volume of the Juice was considered. as
in their previously used method. the variation was t 30% of the mean.

Kaloyereas (15) suggested thawing frozen fruit for 214 hours in a beeh-
er containing petroleum ether or Skelly Solve 3. previously saturated with

water. He believed that the use of the immiscible solvent gave better

results because it helped to reduce the crushing effect of the berries.

 

METHODS OF PROCEDURE

HE'iflODS 0F PROCEDURE
Design of Experiment

Sliced Dunlap strawberries were frozen under laboratory conditions
in 50% sucrose sirup to which one of the following colloids was added:
powdered msthylcellulose. commercial pectin. low methoxyl pectin and
pure gelatin. The samples were compared objectively and subjectively
with a control in 50% sing to determine whether the colloids affected
the leakage of juice and the palatability of the product.

After the strawberries had been stored for O. 1.. 1t. 7. and 9
months. they were tested for leakage of juice. viscosity and specific
gravity of sirup. and moisture content of both berries and sirup. The
palatabili ty was judged by members of the Foods and Nutrition staff.

'hvo replications of the objective tests and three replications of the
subjective tests were made at each storage period.

For each evaluation period. three pint-sized cartons of strawberries
were needed: one for scoring. one for leakage and specific gravity tests.

and one for moisture oontmt and viscosity tests.
Preparation for Freezing

In order that the berries would be fresh when prepared for freezing.
they were processed within 214 hours of picking. 'me berries were approxi-

mately of the same maturity. Ihey were stored in a walk-in cooler until

needed througnout the day.

 

15

One crate at a time was removed from the cooler. Four or five
quarts at a time were washed in a large pan of cold tap water until there
was no sand or grit present. The berries were drained in colanders.
hulled. and cut into slices five to six millimeters thick.

1 two-hundred gram portion was put into each.pint-sized waxed
freezer carton. Onenhundred sixty grams of the appropriate sirup was
added. Crumpled.parchment paper was placed on top before the lid was
closed so that the top berries would remain immersed in sirup. The car-
ton was covered. labeled. and.put into the freezer immediately. After
“8 hours. the samples were taken to the locker plant to be stored at
0° F. until needed.

The average yield was about two cartons per quart of fresh straw-

berries.
Preparation of Sirups

A sufficient amount of each sirup was made at one time for all fifty
pint-sized cartons of each sample. The preportion of colloid added to
each sirup was calculated on the basis of’per cent by weight of berries
in each freezer carton. The sugardwater ratio in the 50% sucrose sirup
‘wes calculated on the basis of'per cent by volume of solution: that is.
on the basis of one cup water (237 grams) and one cup sucrose (200 grams).

The contents per carton are listed in Table l. The total amounts of
ingredients and the methods of preparation of the sirups for fifty cartons

of each.treatment are listed in Table 2.

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18

Preparation for Scoring

One carton of each sample was thawed for 18 hours in a household
refrigerator. At the end of the thawing time. the berries were placed in

appropriately marked vessels for the judges to score.
Objective Tests

Leakage Test

A. modification of the method of Kethley. Gown. and Bellinger (17)
was used to determine the amount of juice which leaked from the thawed
berries. The principle of the procedure is the comparison of the weigit
of the thawed. drained berries with the original weight of the berries
before freezing. The difference between the two weights is the amount
of juice which leaked from the berries on thawing.

The thawing was carried out in beakers containing mineral spirits1
in 8. 20° 6. water bath. The solvent was first saturated with distilled
water by filling a separatory funnel about one-half full with the solvent
and adding distilled water until the funnel was three-fourths full. The
mixture was shaken vigorously fifty times and allowed to settle for one
minute. The distilled water. which settled to the bottom. was drained
off and dis carded.

One-thousand grams of the solvent was weighed into a 3.000 ml. beaker

which was placed in the water bath. A sample of berries was removed from

 

l Stoddard‘ s Solvent.

 

18

Preparation for Scoring

One carton of each sample was thawed for 18 hours in a household
refrigerator. At the end of the thawing time. the berries were placed in

appropriately marked vessels for the judges to score.

Objective Tests

Leakage Test

A modification of the method of Kethley. Gown. and Bellinger (17)
was used to determine the amount of juice which leaked from the thawed
berries. lhe principle of the procedure is the comparison of the weight
of the thawed. drained berries with the original weight of the berries
before freezing. The difference between the two weights is the amount
of juice which leaked from the berries on thawing.

The thawing was carried out in bankers containing mineral spirits1
in e 20° 0. water bath. The solvent was first saturated with distilled
water by filling a separatory funnel about one-half full with the solvent
and adding distilled water until the funnel was threeafourths full. The
mixture was shaken vigorously fifty times and allowed to settle for one
minute. n1. distilled water. which settled to the bottom. was drained
off and dis carded.

One-thousand grams of the solvent was weighed into a 3.000 ml. beaker

which was placed in the water bath. A sample of berries was removed from

1 Stoddard's Solvent.

 

19

the freezer. Iillhe cardboard carton was removed by slitting it on the
sides and tearing it away from the frozen mass as quickly as possible
without loss of sample. men. the frozen mass was placed in the mineral
spirits. Each beaker was covered to prevent undue exposure to the air.
fhe samples were left .in the solvent for three and one-fourth hours

(one hour after the center of the mass had reached 20° 0.).

After the berries were thawed. they were drained for three minutes
on a wire screen. ihe drained berries were placed on a pad of paper
towels and rolled gently for one minute to absorb some of the moisture
on the outside of the berries. Then. they were placed on a second set

of. paper towels and rolled gently for one minute more. The drained and

blotted berries were weighed.

Moisture Content

A semi-automatic moisture tester2 was used to determine the moisture
cutest of the berries and of the juice.

Each sample was thawed for 18 hours in a household—type refrigerator.
After thawing. the sample was drained for three minutes on a wire screen.
{the drained berries were placed on a pad of paper towels and rolled
gently for one minute to remove the surface liquid. 'this was repeated.
he blotted berries were blended in a Waring blender for one minute.
Duplicate ten-gram portions of the blended sample were transferred to
weighing pans by means of a wide-mouthed pipette. The samples were dried
at 95° 0. for approximately six and one-half hours. or until the differ-

enee between two successive half-hour readings was no greater than 0.0%

 

2 Brabender

 

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20

moisture content.

A.similar methodnwas used to determine the moisture content of the
sirup-juice combination which drained from the berries on the wire screen.
Duplicate ten-gram samples were obtained by pipetting;the liquid into the
weighing pans. The sirups were dried at the same temperature and for

approximately the same length of time as the berries.

ecific Gravit
_a____2
The specific gravity of the sirup-juice combination was determined

by using a hydrometer. The sample for this test was obtained from the
liquid which was drained from the berries in the leakage test. (The
sirup—juice combination had been separated from the solvent by'means of
a separatory funnel.) The specific gravity of the thawed sirup-juice

was compared with the specific gravity of the sirup before freezing.

Viscosity

An Ostwald Viscosimeter was the instrument used in this test. The
source of the sample‘was the sirup-juice combination which drained from
the berries for the moisture tests. This liquid contained tiny seeds
and other solid particles from the strawberries. In addition. there
were gel particles present in some of the sirups. All of these sub-
stances tended to interfere with the flow of the sirup through the
capillary. To overcome this difficulty. the liquid.was strained through

six layers of clean cheese cloth into small beakers. By means of a

pipette. 5 in. of the liquid was placed in the bottom bulb 'or the

 

21

viscosimeter in a 20° 0. water bath. ‘Beadings were recorded in minutes

required to flow from the top bulb through the capillary tube.
Subjective Tests

The berries were scored for general appearance. color. luster. odor.
flavor of berry. flavor of juice. texture of berry. consistency of juice.
and general conclusion. The judges were asked to record their comments
on any outstanding features noted. A.sample of the score card is given
in the Appendix.

 

 

 

DISCUSSION 01' WTS

DISCUSSION 0! RESULTS

Palatability Scores
The mean scores of the strawberries in each evaluation period are
given in Table 3. The samples were scored on the basis of one to seven.
as shown on the sample score card.in the.lppendix. A score of seven in-
dicated an excellent product. a score of one a very poor product. in a

given characteristic.

General.Appearance
The samples containing the commercial.pectin.were judged as having

the best general appearance. They had a deeper red color than the
others and were quite lustrous. The slices appeared to be fairly firm
in texture.

The samples containing the low metnoxyl pectin received good scores.
also.‘ The berries probably were more responsible for the relatively
high appearance scores rather than the sirup. however. The sirup tended
to have a somewhat mottled appearance. especially when the samples were
first opened. The pectin caused a certain amount of gel formation. The
presence of colorless particles detracted from the appearance. according
to some of the judges.

Good scores were also given to the controls and to the methylcellulose
samples. though the latter samples were more lustrous than the controls.

The lowest scores for general appearance were given to the samples

23

 

 

 

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AeoesHsaoov n oHpsa

Table 3 (Continued)

 

Commercial

Pectin

Low Met‘hoxyl

Control
Pectin

Methyl- Gelatin

Storage Time

Characteristic

cellulose

 

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26

treated with.gelatin. At every scoring period they were much.paler than
the others and much less lustrous. The sirup contained fairly large
pieces of gel which appeared unpleasant. The slices appeared mushy and
soft in texture. Sometimes the sirup was objectionably frothy.

Though the differences in general appearance scores were highly
significant between samples. the differences between storage periods
were not significant. Apparently. the use of the colloids affected the

appearance of the strawberries. but storage did not.

Differences in scores for color were highly significant between
treatments and.storage periods. There was also a significant interaction
between storage and replication. indicating that the judges did not al-
ways score the same sample the same way for each replication at a given
storage period.

The commercial.pectin and low methoxyl pectin samples were given
the highest scores for color. Both of these samples had a deeper red
color in the berries than in the sirup.

Good scores were also given to the methylcellulose samples and the
controls. The gelatin samples received the lowest scores for color.
These samples were the only ones which were pale throughout the study.
Apparently. the presence of the gelatin had a bleaching effect on the
pigment in the berries as soon as they were frozen. however. the color
scores for all samples were slightly lower at the last storage period

than they were at the beginning. Some oxidation might have occurred

27

causing a slight change in color in all of the samples.

A.possible explanation for the significant interaction between
storage and replication is the relative position of each sample with
respect to the'window in the scoring room. The order of the displayed
samples varied at each replication. When a given sample‘was near the
window it might have appeared to have a different color than when it
was farther away. This source of error was controlled as much as pos-
sible, however, by lowering the shades and using artificial light during

scoring.

£12232

There was a.higbly'significant difference between luster scores
for different treatments. The low methoxyl pectin samples were Judged
to be the most lustrous. This contributed greatly to the appetizing
appeal of the product.

Good scores‘were also given to the commercial pectin, methylcel-
lulose. and gelatin samples. the latter having the lowest of the three.
The controls received the lowest luster scores among the five samples.
The results indicated that the addition of colloids had a definite

effect on the luster of the final product.

Odor
In general there was not much difference in scores for odor between

the treatments. The scores for all of the samples were good. though they

28

tended to go down somewhat with storage. The decrease in odor scores may

have been due to a slight oxidation of the ”fruity" odor during storage.

as suggested.by the work of Fitzgerald (10) and Luts and co-workers (19).
One of the Judges felt that a true strawberry odor was lacking at

the beginning of the project.

Flavor 3f; Berry

There were no significant differences between flavor scores for the
various treatments. It would appear that the addition of the colloids
did not influence the flavor of the berries. A few Judges did detect an
"off-flavor” in the methylcellulose samples. however. One Judge called
it an 'oxidized' flavor. The flavor of the gelatin samples was referred
to as “sour" and I'old" by two different Judges.

In general the scores decreased with an increase in storage. These
results are in agreement with the reports of Joslyn and.Harsh (1h). They
state that during freezing and thawing some fruits and vegetables acquire
a peculiar flavor and odor which are sometimes undesirable. They be-
lieve that anaerobic respiration in closed containers may be the cause.

Sometimes off-flavors are attributable to the permeability of paper
containers. allowing absorption of foreign cold storage odors and flavors.
The foreign flavors may even come from the containers themselves.

Joslyn and Marsh (1“) found that fruit exposed to air during freezing
or thawing became dark and discolored.and developed unnatural flavors if

active oxidases were present. It was impossible to inactivate the oxi-

deses by heat without destroying the delicate fruit textures and flavors.

 

29

3.1.2.12; 2.1: Less

The control sample was rated the highest for flavor of Juice at four
out of the five storage periods. In addition. there was a significant
difference between the scores for all the treatments. These results inp
dicate that the addition of these colloids influenced the flavor of the
sirups.

One of the Judges stated that the low methoxyl pectin sirup had a
slightly 'glue-like' flavor. Several Judges commented on an "off-flavor"
in the methylcellulose sirup.

The methylcellulose sirup was rated lowest for flavor. It had.s
definite “woody' flavor which.was detrimental to the product. In general.

however. the Judges did not reJect this sample completely.

Lum- a: £222
In general all of the samples had good texture after thawing. Home

of them were consistently flabby or unduly soft. though occasionally a
few of the Judges felt that some of the berries were somewhat soft in
texture. ‘

‘1 significant difference between storage periods was noted. The
. berries tended to become softer and less desirable in texture as the

storage time increased.

consistency.gg Juice
The commercial pectin samples and the controls received the highest
scores for consistency of Juice. The methylcellulose scores were also

good for this characteristic.

30

The low nethoxyl pectin and.ths gelatin samples were not rated as
high as the others. Apparently. the Judges did not favor the presence of
gel particles and the thickness of these sirdps. as evidenced.by the
significant difference between treatments.

There was also a significant interaction between storage and treat-
ment. indicating that the treatments did not give the same effect at the
different storage periods. The changes were erratic rather than.con-

sistent with increasing storage.

General Conclusion

The controls were given the highest scores for general conclusion,
probably due to superior flavor and consistency of the Juice. Fairly
good scores were also given to the samples containing the commercial
pectin. methylcellulose. and low methoxyl pectin. The gelatin samples
received the lowest scores for this characteristic.

is one might expect from the scores for the individual characteristics
there were highly significant differences in general conclusion between the
various treatments and storage periods. In general. the scores decreased
as the storage period increased. Host of the strawberries were accept-
able to the maJority of the Judges up to the seven months' storage period.
.Lfter that time. however. the development of off-flavors in some of the
samples caused.individual Judges to reJect them. The sample which re-
ceived the largest number of reJections was the gelatin sample. The
methylcellulose sample also received e.relatively large number of re-
Jections from individual Judges. The average mean scores and.FLvalues are

listed in Table h.

 

 

31

 

 

 

 

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32

ObJective Tests

.14.ng

The results of the leakage tests are given in Table 5. The dif-
ferences in leakage were highly significant between treatments and
storage periods. The samples which.lost the least amount of Juice were
those which.had been treated with low methoxyl pectin. The gelatin
samples lost the most Juice through leakage.

In general. the berries lost less Juice as the storage period in-
creased. The average for the seven months‘ storage period was less
than the average for the nine months' period. however.

Although the differences in amount of leakage were great enough to
be statistically significant. they do not appear to be large enough to
have any practical significance. Indeed. with the exception of the low
nethezyl pectin. the addition of colloids seemed to increase rather than

decrease the leakage.

gpecific Gravity
Table 6 shows the mean specific gravity of each sirup after thawing.

There was a significant difference between treatments. The control
sirup had the lowest average specific gravity. The low methoxyl pectin
and commercial pectin sirups had the highest average specific gravity.
One might have expected the specific gravity of the low methoxyl pectin
sirup to be relatively high because this sample had the lowest per cent
leakage. It is difficult to explain the reason for the high.specifie

gravity of the commercial.pectin sirup. since this sample had a

33

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35

comparatively high per cent leakage.

Table 7 lists the mean specific gravity and the equivalent per cent
sucrose solution for each sirup before freezing and after thawing. In
each case. the specific gravity initiallywas equivalent to a its-19$
sucrose solution. After the sirups were thawed. their specific gravities
were equivalent to 32-33% or 33-31% sucrose solutions. Though statistical-
1y there was a significant difference between the specific gravities of
the sirups after thawing. the data show that the values for specific
gravity in terms of equivalent sucrose solutions were similar. Apparently.
the dilution by exuded Juice was about the same for all treatments.

These per cent sucrose solution equivalents are only approximate be-
cause there were other substances present in the sirups besides sucrose

and water.

Viscosity
Table 8 is assummary of the viscosity of the sirups after thawing.

he sirup containing the methylcellulose was the most viscous. The
least viscous sirup was the one treated with gelatin. The gelatin sirup
might be expected to be the least viscous. since this treatment resulted
in the most leakage of Juice and consequent dilution of the sirup after
thawing. None of the other figures for viscosity. however. are consist-
ent with the data for leakage. In general. the viscosities increased
with storage.

Unfortunately. there are no valid figures for viscosity before

freezing so that comparisons could be made to detamine the relative

36

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amounts of dilution by exuded Juice. The unfrozen sirups tended to gel
in the viscosimeter before the readings could be taken.
The data for viscosity after freezing can be used to compare the

relative thickness of each sirup.

Moisture Content

Tables 9 and 10 list the data for mean per cent moisture content of
berries and Juice. respectively. The berries treated with low methoxyl
pectin had the highest per cent moisture content. Those whidi were treated I
with commercial pectin had the lowest per cent moisture content. All of
the averages were similar. indicating that the colloids did not markedly
influence the loss of moisture from the herries.

he figures for moisture content of sirup are in close agreement with

the data for specific gravity.

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SUl'iMl‘fiY AND CONCLUSIONS

Sliced Dunlap strawberries were frozen in 50% sucrose sirup under
laboratory conditions. The experimental treatments included addition of
one of the following colloids: gelatin. methylcellulose. commercial
pectin. or low methoxyl pectin. The samples were stored for 0. 1. M. 7.
and 9 months at approximately 00 1'. At each storage period the berries
were scored subJectively for palatability. In addition. tests were made
for leakage of Juice. viscosity and specific gravity of sirup. and
moisture content of berries and sirup.

The results indicated that in some cases the colloids affected the
palatabili ty and. in one case. the leakage of Juice. The gelatin yielded
an unpalatable product with pale. flabby berries and mottled. frothy
simp. Methylcellulose caused an off-flavor in the sirup. though the
luster of the berries was somewhat increased. Low methoxyl pectin im-
proved the appearance of the berries in luster and color. but marred
the appearance of the sirup with particles of gel. Commercial pectin
improved the appearance of berries and sirup in color and luster.

The only colloid which reduced the leamge was the low methoxyl
pectin. but the reduction was very slight and of no apparent practical
significance. Most of the other treated samples had a higher per cent
lea‘r'age than the controls.

From the foregoing experiment. the following conclusions can be made:

1.

3.

The addition of gelatin in a concentration of 0.5%‘by
weight of berries did not improve the frozen straw-
berries.

Conmercial pectin in a concentration of 3.5% by weight
of berries improved the appearance of the strawberries.
but did not reduce the leakage of Juice.

Low methoxyl.pectin in a concentration of 0.15% by
weight of berries reduced the leakage of Juice slightly.
It also improved the color and luster of'the'berries.
but marred the appearance and consistency of the sirup.
Methylcellulose in a concentration of 0.5%‘by'weight
of berries did not reduce the leakage of Juice. bud

it did affect the flavor of the sirup unfavorably.

W038

 

10

11

12

13
1h

 

REFERENCES

Baker. G. L. 19M. Pectin as an aid in freezing fruits. 1. Its
application in the freezing preservation of strawberries.
l'eod Ind. 11: 55.

Bronson. '. 1‘. 1951. Technology and utilisation of gelatin. Food
Tech. 5: 55. . '

23113153. 3.. G. L. Baker. and H. H. Hotter-n. 191434. Pectinates
improve frozen fruit. Food Ind. L6} 113.

California Fruit Growers Exchange. 1914‘]. Exchange pectin m.
Trade publication. Ontario. California.

Cowgill. w. w. 1933. U. 5. Patent 2,137,205. Cited in Baker (1).

Diehl. n. 0., J. n. Magness. o. a. Cross. and v. B. Bonney. 1930.
The frozen pack method of preserving berries in the pacific
northwest. U. 8. Dept. of Agr. Tech. Bull. 1R8.

. and K. 1'. warner. 1916. Freezing. to preserve home grown
foods. U. 8. Dept. of Agr. Cir. 709.

Dow Chemical Company. 1919. The new methocel. Trade publication.
Midland. Michigan.

Evers. Clifford L. and Barbara. L. Hutchings. 19’”. Quality
control in the pacmged frozen. fruit industry. Fruit Products
Jour. _2.§.: 136.

Fitzgerald. Gerald L. 1950. Why you freeze it that way. Food
Ind. _2_2_: 261.

Grab. I. 6.. Jr.. J. B. Vegener. and B. E. Bast. 1918-8. Firming
strawberries before freezing. food Packer g3: 39.

Jaclyn. H. A. 1930. Preservation of fruits and vegetables by
freezing storage. Calif. Agr. Exp. Sta. Circular 320.

1930. lhy freeze fruit in sirup! l'ood Ind. _2_: 350.
. and G. L. Marsh. 1933. Changes occurring during freezing

storage and thawing of fruits and vegetables. Calif. Lgr.
h. Sta. 31111. 551.

16

17

18

19

20

21

22

23

2h

25

26

27

28

 

Kaloyereas. S. 191”. Drip as a constant for quality control of
frozen foods. Food Research .13: 1419.

19117. Strawberry studies. A new method of determining
firmness. Fruit Products Jour. 21: 6.

Kethley. T. V.. V. 3. Cown. and T. Bellinger. 1914-9. Develop new
test for gaging leakage from frozen fruits and berries. Food
Ind-e fl: 179e

Lute. J. 14.. J. S. Caldwell. and H. H. Moon. 1932. Frozen pack:
studies on fruit frozen in small containers. Ice and Befrig.
$2 111.

. and A. T. Myers. 1933. The quality of dif-

 

ferent varieties of eastern strawberries when frozen in small
packages. Fruit Products Jour. 11: 7.

Marsh. G. L. 1932. Observations on the loss in weight of fruits
after thawing and the value of the I'weight balance' in frozen
pack foods. Fruit Products Jour. _1_l_8 335.

Rosa. J. T. 1921. he hardening process in vegetable plants.
Univ. of Missouri Research 31111. he. - Cited in Baker (1).

Tressler. D. K.. and C. W. Du Bois. 19110. Freezing and storage of
foods in freezing cabinets and locker plants. New York State
Agr. Exp. Sta. Bull. 690.

Tressler. D. 3.. and C. I. Evers. 19117. no freezing preservation
of foods. he Avi Publishing Company. Inc.. New York. p. 808.

United States Department of Agriculture. Production and Harketing
Administration. 19119. United States standards for grades of
frozen strawberries. Mines.

Wegener. J. 3.. B. H. Baer. and P. D. Rodgers. 1951. Improving
the quality of frozen strawberries with added colloids. Pood
Tech. 5: 76.

Viegand. I. H.. 1931. The 'frozen-pack' method of preserving berries.
Oregon Agr. hp. Sta. Dull. 275.

Woodroof. J. C. 1938. Kicroscopic studies of frozen fruits and
vegetables. Georgia Agr. Exp. Sta. Bull. 201.

Woodroof. J. G. 1931. Preservation freezing. Some effects on qual-
ity of fruits and vegetables. Georgia Jar. Exp. Sta. Bun. 168.

APPMDIX

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