Temperature Effects on Produce Degradation 637
during cooking. Tubers for frying are stored at 10 to 15°C, depending on the cultivar
and its respective sugar conversion characteristics. Many cultivars for chips accu-
mulate excessive sugar if stored at temperatures less than 15°C. Thus, cultivars for
chips often are stored at 15 to 20°C. New cultivars are being developed that will
not accumulate sugar at temperatures as low as 5 to 10°C. Tubers can be stored for
2 to 12 months, depending on quality at harvest, quality of storage facilities, variety,
and whether or not sprout inhibitors are used. Sprout inhibitors may be applied in
the field before senescence begins, on the tubers as they are graded and packaged,
or in storage after curing is completed.
Most potatoes are stored in common, air-cooled storage, although refrigeration
sometimes is used, mainly as an auxiliary source of cooling.^55 Uniform air and tem-
perature distribution are essential in maintaining good storage conditions. Light should
be excluded from potato storage because it causes the production of chlorophyll (which
gives the potatoes a green color) and the formation of solanine, a bitter, toxic compound.
Almost all sweet potatoes are susceptible to chilling injury; however, cultivars
differ in their level of susceptibility (Figure 20.9).^56 Cured sweet potatoes were less
susceptible than uncured ones, possibly due to the beneficial effects of suberization
and periderm formation.
20.5.2 GRAPES
Storage temperature has a significant effect on the final quality of grapes.^11 Harvested
grapes were found to deteriorate more in 1 h at 32°C than they did in 1 d at 4°C or
1 week at 0°C.
Eastern-type grapes, native American cultivars (Vitis labruscana and its hybrids
with Vitis vinifera), and French-American hybrids cannot be stored successfully for
more than 1 to 2 months.^57 However, if storage is desired, they should be stored at
–0.6 to 0°C with RH of 80 to 90% immediately after picking. Eastern cultivars are
not usually fumigated with sulfur dioxide.
Recommended storage for California-type table grapes (Vitis vinifera) is at –1.1 to
–0.6°C and 87 to 92% RH.^57 Although some cultivars can be stored satisfactorily at
temperatures as low as –2.8°C, cultivars with low sugar content have been damaged
by exposure to –1.7°C. Grapes are usually stored in rooms by themselves since the
sulfur dioxide fumigation that is needed for mold control during extended storage
may be harmful to other products.
Like all fruits, grapes are living tissue carrying on respiration during storage.^11
Compared with most fruits, grapes have a very low respiration rate; however, the
heat being evolved by this process can be a significant factor in maintaining fruit
quality. For example, if grapes have been cooled to 4°C and then the boxes are
stacked so that no heat enters or leaves the space occupied by the fruit, the heat of
the fruit will rise 2°C during 8 d of storage. However, if the initial temperature of
the fruit is 20°C, then the temperature rise during storage will be about 10°C, a level
sufficient to aggravate problems of decay.
Decay is a constant problem during grape handling. Two tools are effective in
minimizing this problem: proper temperature management and timely and thorough