Nutrient Loss 239
Temperature has a strong influence on the nutritional composition of fruits and
vegetables, especially the vitamins. Loss of vitamin C is generally more rapid at
higher storage temperatures and slower in acid fruit than in more neutral commodities
(Watada, 1987). About 40% of vitamin C is lost from tangerines at higher storage
temperatures (7 to 13°C) over 8 weeks, while there is a negligible loss in lemons at
the same storage period. The loss is, however, significant at 24°C. In grapefruit
stored at 8 and 12°C, the loss is not significant for up to 2 months (Paull, 1999).
Immature potatoes show a rapid loss of vitamin C during the first weeks of storage,
while mature tubers show minimal loss.
Leafy vegetables lose vitamin C postharvest, but it is frequently unclear if this
loss is due to temperature or water loss. Kale, collards, turnip greens, spinach, grape,
cabbage, and snap beans exposed to conditions favorable for water loss have more
rapid water loss. However, wilting is much less important than temperature. The
loss of vitamin C in kale is 0.32% per hour at 10°C and 0.05% per hour at 0°C with
slow wilting, but when exposed to rapid wilting conditions the rate is 0.69 and 0.11%
per hour, respectively (Paull, 1999). Optimal temperature needs to be maintained to
minimize loss of vitamin C, particularly because 97% of the vitamin C in the U.S.
diet is derived from fresh fruits and vegetables (Goddard and Matthews, 1979).
There are few reports on vitamin B 1 (thiamin) and niacin losses during storage.
Potato tubers have an insignificant loss of vitamin B 1 and niacin after 30 weeks of
storage at 5°C and a slight loss at 10°C. Small losses are found during storage of green
beans, peaches, and sweet potatoes (Watada, 1987; Elkin, 1979). Folic acid losses of
up to 40% can occur in potatoes stored at 7.5°C for 8 months (Augustin et al., 1978).
A key temperature-related factor is relative humidity (RH). Many studies in
storage facilities indicate that temperature is strictly controlled, but the relative
humidity is not. Relative humidity (RH) is influenced by air exchange rate, temper-
ature distribution in the storage room, the type of commodity, and the packing
materials used. There are some practical difficulties in maintaining RH in large
storage rooms within a narrow range, particularly when the RH is high (Paull, 1999).
These difficulties occur more when the RH is high because a small fluctuation in
temperature (< 0.5°C) can result in condensation on cool surfaces. RH has a signif-
icant impact on the nutritional quality of fruits and vegetables during storage. Wilting
of leafy vegetables leads to loss of vitamin C (Paull, 1999). The loss of vitamin C
in kale increases under slow wilting conditions from 0.05 to 0.11% per hour under
high wilting (low RH) conditions. Reducing water loss not only reduces leaf yel-
lowing, but it also increases sweetness and retards protein degradation and the loss
of vitamin C in Brassica juncea (Lazan et al., 1987). Carotene (provitamin A) loss
is enhanced by storage at 0°C and a rapid wilting rate vs. a slow wilting of from
5 to 0% for kale and 13 to 2% for collards (Ketsa and Pangkool, 1994).
8.7.2.2 Packaging
Packaging is important in reducing nutrient losses in fruits and vegetables. Modified
atmosphere packaging is particularly important because it reduces the rate of respi-
ration in fruits and vegetables (Salunkhe and Kadam, 1998). Respiration is a complex
process in which sugars and starch are converted into CO 2 and water. Respiration