242 Produce Degradation: Reaction Pathways and their Prevention
8.8.4 VITAMINS AND MINERALS
Storage of fruits and vegetables also affects the stability of vitamins. The type and
amount of vitamins lost depend on the prior treatment of the produce before storage
and the storage conditions. For example, trimming, dicing, or slicing of fruits and
vegetables before storage enhances losses of water-soluble vitamins (vitamins C, B-
group, E) through leaching. Vitamin C also becomes susceptible to degradation by
oxidation (Salunkhe et al., 1991). Thermal processing treatment prior to storage
significantly reduces the amount of thermolabile vitamins such as vitamin C and
thiamine. Canning of produce prior to storage also causes degradation of the ther-
molabile vitamins. Storage temperatures and time are also important for the retention
of vitamins. For example, retention of thiamine in canned spinach stored for
12 months at 50°F was 96%, but retention decreased to 71% when the fresh vegetable
was stored at 50°F for the same length of time (Kadam and Salunkhe, 1998). In
general, the decrease in vitamin content is more rapid at higher than at low storage
temperatures. Retention of other vitamins, including vitamin C, niacin, carotene,
and riboflavin, is also adversely affected by the storage time and conditions. Reten-
tion of minerals is not significantly affected during storage of fruits and vegetables.
However, prestorage treatments such as thermoprocessing, canning, and chopping
may reduce the quantity of minerals in fruits and vegetables. High-temperature
storage over an extended period of time may also enhance mineral redox reactions
and interactions, forming complexes that are not bioavailable (Salunkhe et al., 1991).
8.8.5 PIGMENTATION
Storage affects the content of pigments in fruits and vegetables, including chlorophyll
and carotenoids. Generally, due to ongoing respiration, chlorophyll content decreases
while concentration of other pigments may either increase or decrease depending
on the storage temperatures, maturity, and variety. For example, in sweet potatoes,
carotene content and total carotenoid pigments decreased during storage at low
temperatures. Very small, immature tomatoes stored at 10°C maintained chlorophyll
longer than larger, mature ones. Carotene content (provitamin A) shows little loss
in sweet potatoes during 4 months of storage at 24°C, while significant losses of
β-carotene occurs in kale (17%), collards (30%), turnip greens, and grapes held at
10°C instead of 0°C. Carrots show an increase in carotene during the first months
of storage, even allowing for water loss and storage at different temperatures (Paull,
1999). There is a steady increase in lycopene and other pigments during tomato
ripening at 15 and 30°C, while at less than 1°C and above 30°C no lycopene synthesis
takes place (Paull, 1999).
Therefore, the stability of nutrients and other healthy components is dependent
on several storage conditions, including duration, temperature, and atmospheric
conditions. The primary storage objective should be directed at fostering ideal
conditions to enhance nutrient retention and bioavailability (e.g., β-carotene),
decrease losses (e.g., vitamin C), and increase consumer acceptability via adequate
but not excessive ripening.