Why produce deteriorates and what you must do to prevent it.Marketing,

Hardenburg, Robert E.

English

Research Papers in Economics

Perishables Distribution in the 1970’s
Refrigeration Requirements for Perishables
Why produce deteriorates and
what you must do to prevent
it
70
‘$ Robert E. Hardenburg
Fe,d Research Horticulturist
Horticultural Crops
Research Branch
Market Quality Research Div
A. R. S. - U. S. D. A.
s on
Everyone who stores, ships, or markets fruits and vegetables should
try to keep these products in field-fresh condition. Keeping produce fresh for con-
sumers should be the goal. Maintaining good quality after harvest is not simple.
Many kinds of produce are highly perishable. Produce is often handled by many
people before reaching consumers and transcontinental shipment may be involved.
Some food handlers are not sufficiently aware of the need for careful handling and
for adequate refrigeration.
Today we think nothing of having a lettuce and tomato salad in midwin-
ter, although the lettuce was shipped from the Imperial Valley of California and
the tomatoes may have come from Mexico or the southern tip of Florida. The
network of rail lines and highways carrys a continuing supply of food to our tables.
Yet waste in marketing fresh produce still runs into million of dollars annually.
In 1965, the U. S. Dept. of Agriculture estimated that the annual loss of fruits
and vegetables in shipping, unloading, processing, and retailing had a market
value exceeding $250 million. 1/ This 10SS would be greater if losses in StOrage
—
and those due to a decline in quality were given a dollar valuation.
Why Produce Deteriorates --Why are fruits and vegetables so subject
to deterioration? Fruits and vegetables when removed from the plant are com-
posed of living tissues. They continue to respire and carry on certain other life
processes. After harvest these processes often result in loss in quality. Res-
piration is one of the most important In respiration, stored food, such as sugar,
is used and the product loses food value. Its quality is being lowered. In respira-
tion, energy is also produced and the excess is thrown off as heat, and heat often
has harmful effects. Much of the need for refrigeration to maintain commodity
temperatures during storage or transportation can be attributed to respiration.
For example, a car of asparagus can produce enough heat of respiration during
a cross-country trip to require meltage of 4 tons of ice just to prevent self-heat-
ing, with no cooling of the load.
if Anonymous. 1965. Losses in Agriculture. U. S. Dept. Agr. , Agr. Hand.
291.
104The respiration rate is a g“ood index of the rate of living. Fruits and
vegetables that respire the fastest give us the greatest handling problems, as
they are the most perishable. Refrigeration is the best method of slowing res -
pirat&n and other life processes. Strawberries respire about 10 times as fast
at 70 F. as at 32°, and sweet corn respires about 8 times as fast at 70° as at
32°, (Table 1). With fresh pr~duce our goal in quality maintenance is to retard
the rate of living without stopping the various processes altogether.
Tablel. Respiration rate of produce at 32°, 40°, and 70° F.
C02 production (reg. /kg. /hr. )
Product 320 400 70°
Apples 3 4 56
Peaches 5 8 72
Strawberries 15 27 149
Potatoes 3 6 13
Celery 7 11 64
Sweet corn 30 43 228
Another factor in the perishability of procluce is that fruits and vegetables
are usually well covered with countless micro-organisms, bacteria and mold
spores, some of which will cause decay if given the right conditions, The spore
load on produce can be demonstrated easily by dipping a specimen in an agar cul -
tur e and then watching the fungi develop. Deterioration due to decay is probably
the greatest source of spoilage during marketing. Refrigeration is the best
method of preventing decay because low temperatures control the growth of most
micro-organisms.
Prompt precooking after harvest to remove field heat and to retard
metabolism is highly desirable for many kinds of produce. This may be accom-
plished by hydrocooling in ice water (e. g. , peaches), by vacuum cooling (e. g. ,
lettuce), or in forced air precooking rooms (e. g. , strawberries). Precooking
is of little value if produce is not refrigerated afterwards. After precooking,
produce should be moved promptly into storage or into refrigerated cars or
trailers.
Refrigeration Benefits --Refrigeration is of value for numerous rea-
sons other than decay control and retarding respiration. Ripening and aging
may often be retarded. With apples, 1 day at ’70° F. causes as much softening
as 2 days at 50°, 4 days at 40°, or 8-10 days a.t 32°. Peaches soften at a rate
of 2 pounds a day at 600, but only 0. 2 pound a day at 32°. With sweet corn 5(Y70
of the sugar may be lost in a single day at 70°, while only about 570 will be lost
in a day if it is held at 32°0
105Loss of vitamins is another form of deterioration in which refrigera-
tion plays a key role. Freshly harvested asparagus will lose 50~0 of its vitamin
C content in 1 day at 68° F. , whereas it takes 4 days at 50° or 12 days at 32° to
lose this amount.
Many color changes associated with aging can be delayed by refrigera-
tion. The yellowing of celery, cabbage, and broccoli are examples. Broccoli
may show some yellowing in 1 day on a non-refrigerated counter~ while in a re-
frigerated display case broccoli will remain green at least 3-4 days.
The relationship between temperature and rate of deterioration var-
ies considerably among commodities and diseases. However, a reasonably ac-
curate generalization, assuming a deterioration rate of 1 at 30° for a fruit such
as apples, is shown in Table 2. With certain exceptions, the best temperature
to slow down deterioration resulting from a fruit’s living processes or from
pathogens is the lowest temperature that can safely be maintained without freez -
ing the commodity. This would be 1 to 2 degrees above the freezing point of the
fruit or vegetable in modern storage plants. Actual freezing of produce must be
avoided as ice crystal formation within cells is injurious.
Table 2. Approximate relationship of temperature and deterioration rate due
to physiological processes and microorganisms
Temperature Deterioration
0 F. rate
68’, 8-10
50 4-5
41 3
37 2
32 1.25
30 1
Loss of moisture with consequent wilting and shriveling of produce is
perhaps the most obvious way in which freshness is lost. Here again refrigera-
tion is beneficial in reducing moisture loss, because the water -holding capacity
of air decreases as the temperature is lowered. Produce will lose moisture to
the surrounding air almost anytime the humidity of the air is less than saturated.
When one realizes that most fruits and vegetables are composed of from 80 to
95~0 water, it is easier to understand how they can wilt and shrivel so readily.
Moisture losses can be minimized by lowering the air temperature, by raising
the relative humidity, by reducing air movement, and by protective packaging.
High relative humidities of 85 to 9570 are recommended for most per-
ishable horticultural products to retard softening and wilting from moisture 10Ss.
106A few exceptions, such as dry onions, garlic, dates, pumpkins and winter squash,
are listed in Tables 3 and 4,,
Recommended Refrigeration- - Refrigeration requirements for specific
fruits and vegetables are so varied that generalizations are difficult. The major -
ity, however, maintain their h-arvest freshness longest in storage, in transit,
and in wholesale warehouses if stored at 32° F’. and 90~0 relative humidity. Tab-
les 3 and 4 list the recommended storage requirements for many kinds of fresh
produce. These are optimum temperatures tc) minimize deterioration. During
food distribution, temperatu.res a few degrees higher than these recommenda-
tions for brief periods will not unduly increase spoilage.
A useful rule-of-thumb to minimize deterioration is to hold cool-
season vegetables at temperatures just above their freezing point but hold warm-
season vegetables and tropical fruits just above 50° F. Cool-season vegetables
include broccoli, celery, cabbage, carrots, lettuce, and cauliflower. For these
vegetables the recommendation is cool quickly and keep cold. Warm-season
vegetables include tomatoes, cucumbers, squash, eggplant, okra, melons, green
beans, and sweet potatoes. They grow best under warm conditions. These warm-
season vegetables and most tropical fruits are subject to chilling injury, which of-
ten appear after removal frc)m chilling temperatures, include internal breakdown,
surface pitting, increased decay, and failure to ripen properly,
Table 3. Recommended temperature and relative humidity for fresh fruits
in commercial storage.
Commodity Temperature Relative Humidity
(°F) (70) -
Apples 1 / 30-38 90
Apricots
Avocado s ~/
Bananas
Berries
Cherriesl /
Cranberr~es
Dates ~/
Figs, Fresh
Grapefruit
Grapes
Lemons l_/
Limes
Mangos
Oranges l_/ (Calif. & Ariz. )
oranges (Fla. & Texas)
Peaches & nectarines
Pears
Persimmons
31-32
40-55
56-58
31-32
30-32
36-40
0 or 32
31-32
50-60
31-32
38-55
48-50
55
38-44
32
31-32
29-31
30
90
85-90
90-95
90-95
90-95
90-95
75 or less
85-90
85-90
90-95
85-90
85-90
85-90
85-90
85-90
90
90-95
90
1/ — Variety differences exist. See U. S. Dept. Agr. , Agr. Handbook No. 66
for further information.
107Commodity Temperature Relative humidity
(°F) (%)
1/ Pineapples_ 45-55 85-90
Plums & prunes 31-32 90-95
Pomegranates 32 90
Tangerines 32 85-90
k..
108Table 4. Recommended temperature, and relative humidity for fresh vegetables
in commercial storage. ~1
Commodity Temperature Relative humidity
(0 F) (%)
Artichokes 32 90-95
Asparagus 32-36 95
Beans, green 40-45 90-95
Beans, lima 32-40 90
Beets 32 95
Broccoli 32 90-95
Brussel sprouts 32 90-95
Cabbage 32 90-95
Carrots 32 90-95
Cauliflower 32 90-95
Celery 32 90-95
Corn, sweet 32 90-95
Cucumbers 45-50 90-95
Eggplant 45-50 90
Lettuce & endive 32 95
Melons, cantaloupes 32-40 85-90
Melons, other 45-50 85-90
Mushrooms 32 90
Okra 45-50 90-95
Onions & garlic 32 65-70
Onions, green 32 90-95
Peas, green 32 90-95
Peppers, sweet 45-50 90-95
Potatoes, early-crop ~’ 40-50 90
Potatoes, late-crop ~/ 38-40 90
Pumpkins 50-55 70-75
Radishes 32 90-95
Rhubarb 32 95
Spinach & kale 32 90-95
Squashes, winter 50-55 50-75
Squashes, summer 45-50 90
Sweet potatoes 55-60 85-90
Tomatoes, mature-green 55-60 85-90
Tomatoes, firm-ripe 45-50 85-90
Turnips, rutabagas 32 90-95
~/ Some differences due to maturity, variety, intended use, or region of pro-
duction exist. Consult U. S. Dept. Agr. , Agr, Handbook No, 66 for fur-
ther details.
2 J Temperatures near 70° — F. are recommended for chip manufacture.
~f Temperatures of 50-55° F. are recommended for chip manufacture.
109Tomatoes are one of the cold-sensitive vegetables that have definite
temperature requirements. Mature-green tomatoes do not “tolerate tempera-
tures below 55° F. for more than a few days without showing subsequent chill-
ing injury. Desirable temperatures for long-distance shipment of tomatoes are
in the range of 55° - 65°. These temperatures will permit some ripening of the
fruit to take place enroute. After arrival, temperatures of 65° - 70° are com-
monly used for rip~ning tomatoes. Tomatoes will not ripen normally at tem-
peratures above 80 .
Desirable transit temperatures for fresh fruits and vegetables are
usually similar to those recommended for storage. For produce that keeps
best at 32° F. , thermostats in mechanically refrigerated vehicles should be set
at 34°. However, pears for immediate distribution should be shipped at 45° -
55° so that they will ripen somewhat in transit.
Proper refrigeration in wholesale warehouses is vital to maintain top
quality in produce. Wholesalers should provide 32° F. storage for about half
the produce they handle. Enough refrigeration capacity should be installed to
maintain a year-around temperature of 32° and a relative humidity of 90yo.
Higher temperatures and lower humidities will accelerate quality loss and in-
crease wastage. Neither desirable air temperatures nor humidities can be
maintained if excessive air exchange occurs between cold storage rooms and
warmer areas. Operators should consider the use of air curtains when doors
to the cold room must be opened often, or for prolonged periods.
While not all fresh fruits and vegetables should be stored at 32° F. in
wholesale warehouses, controlled storage conditions are desirable for all. Some
wholesalers now provide controlled temperature in their general storage areas.
The best temperature for this area is 50°. This temperature is satisfactory
for produce subject to chilling injury and for short storage of potatoes and onions.
Bananas and green tomatoes require special ripening conditions. Bananas are
ripened to meet schedules at 58° to 68°; tomatoes at 55° to 70°.
It is impossible to classify all fruits and vegetables into two groups
(32° and 50° F, ) for wholesaling and be completely accurate. However, this
is a useful grouping for persons who do not have a wide selection of controlled-
temperature rooms. Optimum storage requirements and transport recommenda-
tions for each kind of produce are listed in U. S. Department of Agriculture Hand-
books No. 66 and No. 195.2/
Check Temperatures -- People responsible for produce should make
frequent use of thermometers. Product temperatures should be taken period-
ically in bulk containers at various locations. It is short-sighted to rely on just
one or two aisle thermometers to evaluate produce temperatures. And thermom-
eters of good quality are essential; accurate temperatures cannot be expected
from a poor one.
2/
— For sale at $1. 00 each from the Superintendent of Documents, U. S. Govern-
ment Printing Office, Washington, D. C. 20402
110Storage and Shipping Mixed Commodities--At times it may be necessary
to store or ship different products together. This may or may not be safe. With
some products there is a cross-transfer of odors. For short periods, as in dis-
tribution to retail stores, mixed loading usually is not harmful, but operators
should be aware of possible harmful combinations.
Deciduous fruits can-generally be stored or shipped together if they
have the same temperature requirements, Recently, several mixed loads of
grapes and plums were shipped from California and the plums were rejected on
arrival. The cars inadvertently, were fumigated with sulfur dioxide which is a
common practice to control decay of table grapes, but the sulfur dioxide severe-
ly damaged the plums. Combinations that should be avoided in storage rooms
are apples or pears with celery, cabbage, carrots, potatoes, or onions; celery
with onions or carrots; and citrus fruits with any of the strongly scented vege-
tables. Pears and applies acquire an earthy taste and odor when stored with
potatoes. Also, odors from apples and citrus fruits are readily absorbed by
meat, eggs, and dairy products. It is recommended that onions, nuts, citrus
fruit, and potatoes each be stored separately.
Volatiles such as ethylene, which are emitted by some products, may
be harmful to others. Lettuce and carrots may be damaged by the ethylene
given off by apples, pears, and numerous other fruits. Ethylene stimulates
ripening of many fruits and vegetables. This ripening effect is negligible at
low temperatures (e. g. , 32° F. ), but may be important at higher temperatures.
For this reason, products such as cucumbers, peppers, and acorn squash, in
which retention of green color is desirable and which need to be stored at 45°
- 50°, should not be stored with apples, pears, tomatoes, or other ethylene-
producing crops. Much more information is needed on advantages and disad-
vantages of storage or transport of mixed commodities.
Summar y--Refrigeration requirements of fresh produce were review-
ed briefly. Admittedly, some of the temperature and environment requirements
of different commodities do not coincide with conditions under which mixed loads
are handled and shipped. Assuming that fruits and vegetables are harvested with
good quality, the use of desirable temperatures is most important in preventing
deterioration. In addition, use of various supplements to refrigeration will help
insure good quality for the consumer. Requirements for quality maintenance
are listed below:
10 Harvest at optimum maturity and quality
20 Precool promptly to remove field heat if necessary
30 Provide adequate refrigeration throughout marketing
4. Provide high relative humidity to minimize moisture
5. Handle carefully to avoid mechanical injury
6. Handle rapidly to minimize deterioration
7. Provide protective containers and packaging
loss
8. Use approved chemical, heat, or modified-atmosphere
preservative treatments.
111Obviously, these requirements are becoming quite well known. Each
year more produce arrives at our supermarkets with excellent quality to please
the shopper.
The illustrations on pages 108, 112 and 113 are from slides used by
Dr. Hardenburg. These and others are available with text in film strip No.
C 48 (Revised July 1968) Fedelal Extension Service, U. S. Department of Ag-
riculture, Washington, D. C. 20250.
,,
112113

PERISHABLES DISTRIBUTION IN THE 1970'S: REFRIGERATION REQUIREMENTS FOR PERISHABLES

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