Fruits and vegetables stored for a long time before being consumed suffer significant vitamin losses due to the slow progress of enzymatic decomposition. Vitamin C is particularly sensitive in this regard: in apples stored at home the vitamin C content can be reduced by about a third of the initial value after only two or three months, while the B vitamins undergo very slight variations.
Vegetables are subject to even greater losses: if stored at room temperature after a few days they lose practically all vitamin C.
TYPE OF PACKAGING: riboflavin, cobalamia, folate, ascorbic acid, tocopherols and vitamin K are particularly sensitive to light.
FREEZING: Thiamine, riboflavin, nicotinic acid and pyridoxine are well preserved in frozen meat. In vegetables, ascorbic acid losses of up to 25% can occur.
WHITENING: treatment, to inactivate the enzymes, to which the vegetables are subjected before being canned or frozen. The reduction of the vitamin content varies according to the time and temperature at which the process takes place. Losses are believed to vary between 13 and 60% for vitamin C, between 2 and 30% for thiamine and between 5 and 40% for riboflavin.
DEHYDRATION: The most consistent losses concern ascorbic acid (10 - 15%).
BOX STORAGE: Losses occur during the preparation phase (heating and sterilization). During the storage period, losses are negligible.
STERILIZATION: It mainly concerns the tremolable vitamins. For example, high-temperature sterilization and milk pasteurization can lead to vitamin C losses of up to 20%, while there is no significant loss of vitamins A and D.
COOKING: During normal cooking operations in water of fresh vegetables, vitamin losses of up to 60 - 70% can be encountered, in particular of water-soluble vitamins such as B1, B2 and C.
REDUCTION OF THE LIPID CONTENT: involves a reduction in the content of fat-soluble vitamins.