Frozen pork roasts, strawberries, snap beans, and peas were stored for 12 months at 0" F., at 10" F., and in a freezer alternately fluctuating between 0" and 20" F. in a repeating, 6-day cycle. Palatability tests, vitamin analyses, and determinations of other criteria of food quality were made periodically.
Fat rancidity was evident after 4 months at temperatures above zero, but did not occur during 1 year at 0 " F. Ascorbic acid losses during storage at 10" F. or at fluctuating temperatures ranged from half of the total in peas to two thirds of that present in strawberries and four fifths of that in snap beans.
At 0' F., all of this vitamin was retained in the peas, and only one third was lost from the other products during a 1-year storage period. Palatability changes in general paralleled these chemical changes. The thiamine content of pork was not affected by the storage temperatures or storage period. Exposure of frozen food used in this study to temperatures fluctuating between 0" and 20" F. resulted in quality changes similar to those occurring in food stored at 10" F.
The quality of the food stored under both of these conditions was definitely inferior to that stored at 0" F. This suggests that exposure of frozen foods to temperatures above 0" F. rather than merely temperature fluctuation may be a major factor influencing deterioration of food quality.
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Work at Purdue (9) indicated that temperature fluctuation over the range -5" to -15" F. was not deleterious to frozen pork. Workers at Minnesota (4) stated that for frozen fruits and vegetables, constant storage temperature is not important if the storage temperature is 5" F. or less. In their study, the temperature fluctuated from 0 " $0 -20" F. with no impairment in food quality in a 6-month period.
DuBois and Colvin ( 8 ) studied ascorbic acid in frozen peaches subjected to smell temperature fluctuation three or four times daily, and reported that, as a result of fluctuating temperatures between 5" and -5" F., 50% of the originally added ascorbic acid was lost in 1 year, whereas like packs stored at a relatively constant temperature of 0" F. lost but 32% of the vitamin C during storage. Their data, however, dispute the significance of this statement.
If undesirable effects from varying temperatures are to be expected, they will be found in the freezing range above 0" F., the usually recommended storage temperature. Furthermore, this is the range most likely to be encountered in freezer cabinets or lockers subject to temperature fluctuation. No data are at hand, to evaluate the effects on frozen food of temperature variations in the range of 0 " to 20 ' F.
