Group Title: Food technology and nutrition mimeo report
Title: Vegetable life after harvest
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Permanent Link: http://ufdc.ufl.edu/UF00094974/00001
 Material Information
Title: Vegetable life after harvest
Series Title: Food technology and nutrition mimeo report - Florida Agricultural Experiment Stations ; 59-1
Physical Description: 20 leaves : ; 28 cm.
Language: English
Creator: Showalter, R. K.
University of Florida -- Agricultural Experiment Station
Publisher: Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla.
Publication Date: 1959
Copyright Date: 1959
 Subjects
Subject: Vegetables -- Handling -- Florida   ( lcsh )
Vegetables -- Postharvest technology -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (leaves 18-20).
General Note: Cover title.
General Note: "February, 1959."
General Note: "A paper presented in the symposium on 'Recent research on post-harvest physiology' at the joint session of the American Society for Horticultural Science and the American Society of Plant Physiologists sections of the Association of Southern Agricultural Workers, Memphis, Tennessee, February 3, 1959."
Statement of Responsibility: by R.K. Showalter.
 Record Information
Bibliographic ID: UF00094974
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 435493715

Full Text





Food Technology and Nutrition Mimeo Report 59-1
February, 1959







VEGETABLE LIFE AFTER HARVEST

By

R. K. Showalter
Horticulturist

Florida Agricultural Experiment Stations
Gainesville, Florida





A paper presented in the symposium on

"Recent Research on Post-Harvest Physiology"

at the joint session of the American Society for Horticultural

Science and the American Society of Plant Physiologists sections


of the

Association of Southern Agricultural Workers


Memphis, Tennessee, February 3, 1959








VEGETABLE LIFE AFTER HARVEST


By
R. K. Showalter



A number of advances have been made recently in our knowledge of

factors affecting the storage life of vegetables. During their grow-

ing period vegetables manufacture and store food. After harvest the

process is reversed and stored foods supply energy to maintain life.

Length of storage life is governed chiefly by transpiration, respira-

tion, and attacks by decay organisms. Water loss by transpiration

with consequent wilting and shriveling is most easily controlled by

maintaining a high relative humidity.

POST HARVEST RESPIRATION

Respiration of fresh vegetables can not be stopped except by

killing as in heat sterilization. However, respiration rates can be

retarded by lowering the temperature or modifying the atmosphere.

Several investigators have suggested that the cumulative CO2 produc-

tion may be a measure of the storage life. Thus apples, cucumbers,

and bananas each produce a total of 18 to 20 grams CO2 per kg. of

fruit. This assumes that a given amount of respirable substrate is

available for respiration and that the produce reaches the end of

its useful life when this substrate is exhausted. Even though as-

paragus respires 59 times faster than potatoes (21), the storage

life of both can be prolonged by lowering their temperatures. Many

vegetables have a more or less predictable increase in storage life







- 2 -


at decreasing temperatures down to 320 F.

Vegetables with high respiration rates, such as asparagus, sweet

corn, broccoli, and peas, are often the most perishable, and their

storage life is consumed rapidly after harvest. For example, Lip-

ton (14) in a recent study of asparagus deterioration at 10 tempera-

tures, found that the total storage life ranged from 2 1/2 days at

860 to 44 days at 36. The high rates of deterioration were gener-

ally accompanied by high rates of respiration.

VACUUM COOLING PROCESS

Since respiratory activity is usually high if the vegetable

temperature is high following harvest, the rapid removal of field

heat is important. Vaclum cooling is a recent development for ex-

tracting heat quickly from lettuce, sweet corn, cabbage, celery and

other leafy vegetables. The temperature reduction is produced by

extremely rapid evaporation of water from these vegetables when they

are subjected to an almost complete vacuum. When the air pressure

is reduced to about 4.6 mm. of mercury, the boiling point of water

is 320. Evaporation within the vegetable tissue requires heat to change

water to vapor. During the change from a liquid to a vapor phase

much field heat is removed and the evaporative cooling is continued

until the vegetable temperature is slightly above 320. The vapor-

ization of one pound of water lowers the temperature of 100 lbs. of

leafy vegetables about 100 F.








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A. Vacuum Cooling and Moisture Loss

Since there is a water loss of about one percent for each 100 F.

of cooling, one might expect excessive wilting. However, no visible

wilting or injury is usually noted immediately after vacuum cooling.

After shipment and storage of vacuum cooled lettuce there is slightly

more wilting of the outer leaves as compared with ice-packed lettuce.

However, more bruising injury and decay are usually found in ice-

packed lettuce so that vacuum cooling yields a larger quantity of

marketable lettuce.

Early studies were made by Barger (1) to determine if minute in-

juries occurred on the surface of lettuce heads, grapes, and straw-

berries during the vacuum cooling. No differences in appearance or

weight loss were found between vacuum cooled and non-treated checks

during subsequent storage. Thus it appears that the water vapor

molecules originating from all parts of the fruit or vegetable eva-

porate without injuring the cells. Also when the moisture loss occurs

from all parts of the produce, wilting is not as apparent on the

outside.

I have found in current studies that vacuum cooled sweet corn

had temperatures of 350 400 compared with 55 600 temperatures

obtained by hydrocooling. Fifteen percent more total sugars were

retained by the vacuum cooled corn during storage for 2 to 8 days.

The loss of five percent moisture during vacuum cooling resulted in








-4-


objectionable denting of kernels during storage. This denting was

eliminated by adding water to the ears before and after the cooling

process (29). Thus, in connection with this more effective precool-

ing method, new water relationships became apparent.

B. Wetting with Water Maintains Sweet Corn Moisture

Many vegetables absorb enough water during hydrocooling, icing,

or sprinkling to prevent wilting during marketing. Even though corn

kernels are covered by lignified pericarp, several workers have found

that all surfaces readily absorb water (30). Since corn can be vac-

uum cooled and other vegetables with relatively impervious skins can

not be cooled by this method, it may be assumed that water also is

readily transpired from the kernel surfaces. The moisture content

of the kernels after several days storage was not as high in those

ears which were dipped in water only subsequent to vacuum cooling

as in those dipped before and after cooling. To prevent denting it

appears that surface water is necessary when the diffusion pressure

deficit is greatest at the moment the vacuum is released.

STORAGE LIFE AT LOW TEMPERATURES

Recent studies have been made by Parsons (17, 18, 19) on the

storage life of three vegetables which responded favorably to low

temperatures. Lettuce was in much better condition at 320 than at

380 after 6 weeks storage. After 8 weeks storage there was 18 per-

cent more edible celery at 320 than at 38, and none remained at 45.









- 5 -


Cabbage stored well at 32 and 380 for 8 weeks, but the heads were

greener and more turgid at 32. Storing these vegetables in film

lined crates or film packages greatly reduced the moisture losses and

retained more of the original green color.

CHILLING INJURY

Not all vegetables have an increase in storage life as their

temperature is lowered to 320. Some vegetables are susceptible to

chilling injury at 320 to 500, while others may be frozen and thawed

without permanent injury. In the latter group we find parsnips with

a freezing point of 300. Tomatoes also have a freezing point of

300, but they may be injured at temperatures below 50. Instead

of the water soaked areas caused by freezing, the symptoms of chil-

ling injury are circular pits on the surface, discoloration, failure

to ripen properly and susceptibility to decay. Such vegetables as

cucumbers, peppers, egg plants, watermelons, sweet potatoes, squash,

snapbeans and tomatoes are subject to chilling injury. Several re-

cent investigations dealing with the deterioration, respiration and

biochemistry of chilling injury have been made, but the actual mech-

anism and true cause are still unknown.

A. Physiology of Chilling Injury

Eaks and Morris (7) evaluated the physiology of chilling injury

by the responses of cucumbers to chilling and non-chilling tempera-

tures. cucumbers stored at five temperatures from 550 to 860 all








- 6 -


produced approximately 20 grams CO2 per kg. of fruit during their

entire storage life. Cucumbers held at chilling temperatures produced

the following amounts of CO2: 50 18 grams, 410 6 grams, 320 -

3 grams. Cucumbers exposed to chilling temperatures and transferred

to 77, produced less than 20 grams CO2, the amount depending upon

the severity of chilling. At non-chilling temperatures the rate of

CO2 production decreased with duration of storage, whereas at 500

and below, the rate increased with time to a plateau and then de-

creased. The increasing rate occurred at the same time as the de-

velopment of chilling injury as measured by the degree of surface

pitting, and the decline occurred as the tissue died.

The storage life of cucumbers at non-chilling temperatures in-

creased from 16 days at 86 to 62 days at 55. Lower temperatures

reduced the storage life instead of increasing it as for the vegeta-

bles previously discussed. The average storage life was 48 days at

500, 18 days at 41O, and 24 days at 32.

B. Symptoms of Chilling Injury

High relative humidity has been found to delay pitting of cu-

cumbers and peppers (16). The severity of the localized desiccated

areas was inversely proportional to the relative humidity of the

storage atmosphere. Chilling injury develops slowly. Cucumbers

held at 320 appeared field fresh for about two weeks. Eaks and

Morris (11) then reported small droplets of exudation on the surface








- 7 -


which indicated a disturbance in physiological balance. It is not

known whether desiccation of epidermal cells is the cause or effect

of pitting. Histological studies showed that cells near the pitted

area had lost most of their water content.

Differences in cell permeability resulting from chilling injury

of sweet potatoes was found by Lieberman et al (13). The leakage

from cut slices of sweet potatoes stored at 450 increased rapidly

during a 3 to 10 week period. Leakage from potatoes held at 600

remained constant. There was approximately 5 times much leakage

from the chilled tissue slices as from the non-chilled slices, and

almost all of the leakage consisted of potassium ions.

Chilling temperatures also produce color differences in vege-

tables. Cut sweet potatoes darken rapidly after prolonged storage

at low temperatures. Lieberman et al recently found that the dark

pigment formed in sweet potatoes may be associated with the formation

of chlorogenic acid and the decrease in ascorbic acid after 5 to 6

weeks chilling at 45. Tissue extracts from sweet potatoes chilled

for a shorter period did not turn black. Chemical analyses for the

major constituents of vegetables have generally failed to give spe-

cific information on the mechanism of chilling injury.

The localization of chilling injury was studied by Eaks and

Morris (8) by exposing one half of intact cucumbers to 350 and the

other half to 55. When the cucumbers were transferred to 770 after








-8-


8 days, the chilled ends appeared slightly fresher than the non-

chilled ends. However, severe pitting developed on the chilled ends

after 3 days and decay after 4 days. Decay failed to develop on

the non-chilled portions after 8 days. If a toxic substance was

responsible for the injury, it was not translocated, or it was des-

troyed in the warmer end.

In 1941 Ramsey and Wiant (22) wrote that nothing was known re-

garding the cause of russeting in green beans. These brown surface

lesions were frequently a serious marketing problem, and no fungi or

bacteria could be found in them. In 1958, Lewis (12) reported that

russeting was influenced by temperature, length of storage, and

sprinkling. Beans held at 320 or 400 for 5 or 10 days became severe-

ly russeted and discolored during the succeeding 1-day period at

750- 800. Unlike the chilling injury of cucumbers and peppers which

was inhibited by high humidity, this injury of beans was more pro-

nounced on sprinkled than on non-sprinkled beans. Russeting develops

slowly, since beans held 4 days or less at 320 did not show much

injury when moved to higher temperatures. This indicates that chil-

ling injury is reversible up to a certain point. Eight days of

continuous refrigeration were required to produce visible symptoms

of chilling.

C. Mechanism of Chilling Injury

When cucumbers were stored 2 days at 320, 4 days at 41, and








- 9 -


8 to 16 days at 500, followed by transfer to 77, no visible symp-

toms of chilling appeared, but some change had occurred which affected

the respiratory rates to varying degrees.

The activity of mitochondria from sweet potatoes stored at 450

and 60 were compared over a 10 week period (13). There was very

little difference in activity during the first 4 to 5 weeks, but

after the 8th week phosphorylation was about eliminated. This data

indicates that the chilling effects on the mitochondria were rever-

sible during the first 4 weeks.

In another recent study Lewis (11) showed that temperatures

affect the protoplasmic streaming differently in chilling-sensitive

and insensitive plants. By observing individual cells with a micro-

scope he noted that the streaming in tomato, watermelon, honeydew

melon and sweet potato plants practically ceased after 1 or 2 minutes

at 500, and it ceased entirely at 40 or 32. In contrast, the

streaming in radishes and carrots proceeded at 360 and 320. Proto-

plasmic streaming proceeded slowly for 3 days at 320 in the chilling

insensitive plants and resumed rapid streaming in 1 to 2 minutes when

returned to 680. However, for the tomato, increasing the exposure

time at 320, increasingly delayed the resumption of streaming when

transferred back to 68. If the exposure exceeded about 24 hours the

streaming failed to resume.

Tomato fruits are also susceptible to chilling injury before









- 10 -


ripening when held at temperatures of 320to 500. The symptoms, which

are not usually apparent when the tomatoes are at chilling tempera-

tures, consist of susceptibility to Alternaria rot, mottled, off-

color red ripening, and dark, sunken surface scars. After prolonged

holding at low temperatures the physiological processes may be so

impaired that ripening will not occur when the fruits are returned

to favorable ripening temperatures.

Chilling of tomatoes may occur before or after harvest and both

are cumulative. Several years ago McColloch pointed out the high

correlation between growth of Alternaria lesions and the number of

days that mature-green tomatoes were stored at chilling temperatures.

It is interesting to note that the increased susceptibility to in-

fection takes place slowly and is also reversible as was the injury

to cucumbers, beans, and sweet potatoes. Thus, tomatoes held at

320 to 400 for 3 to 5 days ripened satisfactorily at higher tempera-

tures. Whereas, after 9 to 12 days chilling the ripening was un-

satisfactory, and after 17 to 21 days all the tomatoes decayed with-

out ripening (23).

The reversible nature of chilling in tomatoes was recently con-

firmed by Lewis (10) who reduced the harmful effects of 320 storage

by interrupting the chilling periods with periods of non-chilling

temperatures.








11 -

D. Maturity Affects Tomato Chilling Injury

This discussion of tomatoes has dealt only with those harvested

before ripening. Recently, increasing attention has been focused on

vine ripened tomatoes. Difficult handling problems were presented

by the following factors:

1. Long time required to market tomatoes from distant produc-

tion areas.

2. Rapid ripening and softening rates after harvest.

3. Consumers' rejection of soft ripe tomatoes.

A partial solution to these problems may be found in precooling,

controlled transit temperatures, and possibly modified atmospheres.

In 1957 McColloch (15) found that pink tomatoes in cartons could

be precooled from 930 to 450 500 in 21 hours by circulating 320

air. When they were harvested showing 25 30 percent color, pre-

cooled to 500, and held for 3 days at 500, the tomatoes had 40 to

70 percent red color. If held 3 days at 550, they were 63 to 75

percent colored. Thus, it is evident that temperatures must be con-

trolled rather accurately to retard ripening and maintain tempera-

tures above 500.

There is some evidence that pink and ripe tomatoes can be stored

successfully at lower temperatures. Scott and Hawes (27) showed

that pink and ripe tomatoes could be stored at 320 for 6 days, and

then ripening completed at 720, with no evidence of chilling injury






- 12 -


or impairment of flavor. Storage for 12 days at 32 before the ripen-

ing was complete did produce off flavor. These findings approximate

those of McColloch for mature green tomatoes as stated above where

3 to 5 days chilling was not injurious at subsequent higher tempera-

tures.

In 1958 McColloch (4) reported that firm ripe tomatoes could be

stored for 42 days at 320 with a decay loss of only 3 percent. Ripe

tomatoes stored better at 320 than at 380 in these tests. The toma-

toes were edible, had a good appearance, but had softened. It was

recommended that these tomatoes be eaten within a few hours after

removal from 320. These results were somewhat striking. It appears

that chilling injury develops much slower, or not at all, in ripe toma-

toes, and that they can be handled at temperatures as low as 320 to

prevent over ripening.

Recent studies (24) in California have shown that the ripening

rate of vine ripened tomatoes can be decreased by increased CO2 and

decreased 02 during storage at 680 for 2, 4, and 8 days. The use of

modified atmospheres to control ripening during transit periods of

4 days or less seemed to hold promise, but longer periods reduced the

number of marketable tomatoes.

E. Summary of Chilling Injury

In summarizing the subject of chilling injury it may be defined

as physiological injury resulting from low storage temperatures above





- 13 -


the freezing point of the tissue. Some of the first evidences of

chilling injury are prompt ceasing of protoplasmic streaming, changes

in respiration rate and leakage from tissues. During later stages

pitting or color changes occur, chlorogenic acid increases and as-

corbic acid decreases. Chilling effects are reversible only to a

certain breaking point beyond which vegetables soon decay or die.

It appears to me, on the basis of the papers reviewed, that pitting,

desiccation of epidermal cells, and decay are secondary symptoms

caused by increased cell permeability, leakage, plasmolysis, and

production of a toxic material. Since pitting can be delayed by

high relative humidity, pitting must be one result of rapid water

loss.

Mitochondria from chilled and non-chilled tissue showed equal

activity during the 1st four weeks of chilling and then the activity

in the chilled tissue rapidly declined. It appeared that mitochondria

were not affected by temperature, but rather by the accumulation of

a toxic substance. The fact that chilling injury can be reduced by

intermittent periods of non-chilling temperatures further suggests

the production and elimination of a harmful substance.

IRRADIATION

This discussion of factors affecting post harvest vegetable

life would not be complete without including irradiation. The ef-

fects of irradiation on deterioration by microorganisms and on normal

living processes must both be considered. It has been known for many








- 14 -


years that ionizing radiation would kill bacteria, but only during

the last 15 years has this approach been considered for extending the

storage life of fresh vegetables. When radiation passes through mic-

roorganisms or vegetable tissue it causes ionization in the proto-

plasm of the cells. The number of ionizations are increased by in-

creased amounts of radiation, but the actual number occurring in

living tissue have not been measured. Estimates of the number of

ionizations produced by one rep of radiation in an average sized

cell vary from 2 to 2,000. It is known that high doses produce

considerable alteration of the chemical composition, normal physi-

ology, and even structure of living cells (6).

A. Effects of Irradiation on Microorganisms

Many studies have been made to determine the effects of radia-

tion on various spoilage organisms. It has been difficult to meas-

ure any specific type of cell damage even though the organism may

be lethally injured upon entering division. Thus, bacteria may show

no drop in respiration rate after exposure to 60,000 reps, and yet

only one in 10,000 of these bacteria will be able to multiply.

Doses of 100,000 to 500,000 reps will kill most of the common

spoilage organisms. However, to kill the spores of the same species

and get complete sterilization 2 to 5 million reps are required.

Thus two classifications of radiation treatments for controlling

deterioration by microorganisms have been established (28). The






- 15 -


lower doses, below 500,000 reps, may be considered pasteurization

since they require post-irradiation refrigeration to prevent the

growth of residual organisms.

B. Effects of Irradiation on Vegetable Physiology

Another application of radiation has been sprout inhibition in

root crops. Much research has been done on irradiating potatoes.

Sparrow (32) reported in 1956 that irradiated potatoes were stored

satisfactorily for 10 months at room temperatures and 2 years at

420 without sprouting, with low weight loss, and with little soften-

ing or wrinkling. Sawyer and Dallyn (25) found that 8,000 reps of

gamma irradiation entirely inhibited sprouting of sweet potatoes and

onions, and 10,000 reps were equally effective for Irish potatoes.

In 1956 when a large quantity of potatoes were irradiated and

stored under commercial conditions it was discovered that storage life

was not actually increased because of a high incidence of decay. The

sprouting was inhibited by several high levels of radiation, but the

potatoes darkened after peeling and had off odors. The increase in

decay was attributed to a delay in suberization following irradia-

tion and the prevention of periderm formation. Since the function

of periderm is protection from drying of the tissues, the increased

weight loss was understandable.

Heiligman (9) evaluated doses of 5,000 to 200,000 reps for

potatoes, and found that a minimum of 10,000 reps inhibited sprouting,








16 -

while the higher levels increased weight loss and decay. Schwimmer

et al (26) studying some physiological responses to potato irradia-

tion found an increase of 210 percent in sugars, darker colored chips

after processing, and a slower rate of greening than in non-irradiated

tubers. The increase in sugars may be related to an increased res-

piration rate found in irradiated tubers or an enzymatic hydrolysis

of starch. In 1957 Sparks (31) confirmed the minimum dose to be

10,000 reps for sprout control of potatoes. However, his non-irrad-

iated potatoes, which had sprouted, had lost less weight after 3

months than any of the irradiated treatments. He also observed that

cells in the periderm of irradiated tubers were dead and plasmolyzed

after 6 months. Chamberlain (3) says potato irradiation is neither

ready for commercial acceptance nor the scrap heap.

The lack of enzyme inactivation is a serious disadvantage in

using radiation for increasing fresh produce storage life. Enzymes

may not be inactivated by radiation doses of 10 to 20 times the

magnitude required for sterilization. Thus, long-time storage with-

out refrigeration will probably require heat destruction of the en-

zymes. Microwave heating for uniform temperatures throughout the

material may have possibilities for enzyme inactivation.

C. Storage Life After Irradiation

Fruits and vegetables vary widely in their response to irradia-

tion; some are damaged seriously by low doses, while others will

withstand doses that considerably lengthen their storage life.






17 -

Pentzer (20) states that most fruits were injured by 200,000 to

300,000 reps, but peaches withstood 400,000 reps and grapes and to-

matoes 500,000 reps. Radiation looked promising for tomatoes, peach-

es, grapes and strawberries. Dennison (5) has shown that storage life

of lychees can be extended by cobalt-60 irradiation which reduced

deterioration by fungi.

Alternaria decay of tomatoes has been inhibited enough to leng-

then the storage life for 7 to 10 days at room temperatures (33).

Retention of sweetness and tenderness of fresh corn on the cob was

also reported after irradiation of 200,000 reps and 3 weeks storage

at 40. The softening effects of gamma irradiation on carrots, beets,

and apples were measured by Boyle et al (2), and tentatively related

to degredation of pectin and cellulose in the tissues.

Research on irradiation of many kinds of foods, both fresh and

processed, is being conducted in more than 100 laboratories in the

United States. Many of the results have been unfavorable from a

practical viewpoint because of the development of off flavors, colors

and odors. However, radiation research requires many new approaches,

and much progress has been made on the causes and remedies for the

detrimental effects.

It appears now that irradiation will only supplement refrigera-

tion for many fresh fruits and vegetables. Irradiation will probably

take its place in the future along with modified atmospheres, anti-

biotics, chemicals, and low temperatures for extending vegetable life

after harvest.








- 18 -


LITERATURE CITED


1. Barger, W. R. Further tests with vacuum precooling on fruits
and vegetables. U. S. Department of Agriculture H. T. & S.
Office Report No. 244 Aug., 1949.

2. Boyle, F. P., Z. I. Kertesz, R. E. Glegg, and M. A. Connor.
Effects of ionizing radiations on plant tissues. Food Research
22: No. 1 89-95. 1957.

3. Chamberlain, W. E. Radiation preservation. Food Processing
18: No. 10 43-47. 1957.

4. Cook, H. T., C. S. Parsons, and L. P. McColloch. Methods to
extend storage of fresh vegetables aboard ships of the U. S.
Navy. Food Technology 12: No. 10 548-550. 1958.

5. Dennison, R. A. Studies on handling and preservation of lychees.
Annual report, Fla. Agr. Exp. Station pp. 107-108. 1957.

6. Dick, W. E. Atomic Energy in Agriculture. 1957. Philosophical
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7. Eaks, Irving L. and L. L. Morris. Respiration of cucumber fruits
associated with physiological injury at chilling temperatures.
Plant Physiology 31: 308-314. 1956.

8. Eaks, Irving L. and L. L. Morris. Deterioration of Cucumbers
at chilling and non-chilling temperatures. Proc. Amer. Soc.
Hort. Sci, 69: 388-389. 1957.

9. Heiligman, F. Effects of ionizing radiation on white potatoes.
American Potato Journal 34: No. 6 153-157. 1957.

10. Lewis, D. A. Physiological studies of tomato fruits injured by
holding at chilling temperatures. Univ. of Calif. Ph.D. thesis.
1956.

11. Lewis, D. A. Protoplasmic streaming in plants sensitive and in-
sensitive to chilling temperature. Science 124: 75-76. 1956,

12. Lewis, W. E. Refrigeration and handling of two vegetables at
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No. 276. 1958.






- 19 -


13. Lieberman, Morris, C. C. Craft, W. V. Audia, and M. S. Wilcox.
Biochemical Studies of Chilling Injury in Sweet Potatoes. Plant
Physiology 33: 307-311. 1958.

14. Lipton, Werner J., and Leonard L. Morris. Effect of holding
temperature on deterioration and respiration of asparagus.
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15. McColloch, L. P. Better quality tomatoes through temperature
control and careful handling. Proc. 12th National Conference
on Handling Perishable Agricultural Commodities. 1958.

16. Morris, L. L. and H. Platenius. Low temperature injury to cer-
tain vegetables after harvest. Proc. Amer. Soc. Hort. Sci.
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17. Parsons, C. S. Effects of temperature, packaging and sprinkling
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18. Parsons, C. S. Effects of temperature and packaging on the
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19. Parsons, C. S. and R. C. Wright. Effects of temperature, trim-
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Amer. Soc. Hort. Sci. 68: 283-287. 1956.

20. Pentzer, W. T. Better methods of preserving the quality of
fresh fruits and vegetables. Proc. Fla. State Hort. Society
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21. Platenius, Hans. Effect of temperature on the respiration rate
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22. Ramsey, Glen B. and James S. Wiant. Market diseases of fruits
and vegetables, U. S. Dept. of Agriculture Misc. Publication
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23. Ramsey, G. B., J. S. Wiant, and L. P. McColloch. Market dis-
eases of tomatoes, peppers and eggplants. U. S. Department of
Agriculture Handbook No. 28. pp. 13-15. 1952.

24. Rappaport, Lawrence, L. L. Morris, and A. E. Watada. The ef-
fect of modified atmospheres on the ripening behavior of tomato
fruits. Amer. Soc. Hort. Sci. Abstracts 1957 meeting, paper
No. 253.






- 20 -


25. Sawyer, R. L. and S. L. Dallyn. Vaporized chemical inhibitors
and irradiation two new methods of sprout control for tuber and
bulb crops. Proc. Amer. Soc. Hort. Sci. 67: 514-521. 1956.

26. Schwimmer, S., H. K. Burr, W. 0. Harrington and W. J. Weston.
Gamma irradiation of potatoes: effects on sugar content, chip
color, germination, greening, and susceptibility to mold. Amer-
ican Potato Journal 34: No. 2 31-41. 1957.

27. Scott, L. E. and J. E. Hawes. Storage of vine-ripened tomatoes.
Proc. Amer. Soc. Hort. Sci. 52: 393-398. 1948.

28. Shea, K. G. Food preservation by radiation as of 1958. Food
Technology 12: No. 8 6-16. 1958.

29. Showalter, R. K. Effect of wetting and top icing upon the
quality of vacuum cooled and hydrocooled sweet corn. Proc.
Fla. State Hort. Soc. 70: 214-219. 1957.

30. Shull, Charles A., and S. P. Shull. Temperature coefficient of
Absorption in seeds of corn. Botanical Gazette 77: 262-279.
1924.

31. Sparks, W. C. The effect of gamma rays from fission product
wastes on the storage and anatomy of potato tubers. Amer. Soc.
Hort. Sci. Abstracts 1957 meeting, paper No. 280.

32. Sparrow, A. H. A new method of potato sprout inhibition by
exposure to irradiation. American Potato Yearbook. pp. 17-18.
1956.

33. U. S. Army Quartermaster Corps. Food Preservation by irradia-
tion. Progress Report on Research. 1957.




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