Because of the effects of respiration, other enzymes, autoxidation, and
desiccation (loss of water), the raw product temperature and the time
between harvest and preservation are of utmost importance to preserving
high-quality fruits and vegetables.
Ideal handling conditions vary with the product. Small berry and stone
fruits, asparagus, green beans, beets, broccoli, corn and leafy greens,
to name a few, should be preserved the same day of harvest, for highest
quality. Apples, peaches, pears, plums and tomatoes, if harvested at
firm maturity, should be ripened a few days before preserving them.
Other fruits and vegetables may be stored from a week to months before
preservation without significantly lowering their quality.
From a nutritional standpoint, if after harvest the handling and
preservation of these crops are carefully planned and implemented,
quality of the preserved products can be equal to food prepared from
fresh market fruits and vegetables.
Fruits and vegetables are recognized as significant sources of vitamins
A, the B family, C, minerals, and fiber.
Vitamin A, pro-carotene, is heat-stable and insoluble in water but is
subject to a minor loss caused by autoxidation. Therefore, losses in
home preserved foods are insignificant.
Of the water-soluble vitamins, ascorbic acid (C) and thiamin (B_1) are
subject to serious loss upon heating foods. Riboflavin (B_2) is subject
to loss when raw or preserved foods are exposed to light.
[Illustration: Removing the skins from peaches before canning.]
Significant losses of water-soluble vitamins and minerals occur when
food contacts water, such as in washing, blanching, cooking or canning
foods. As would be expected, losses due to leaching of water-soluble
vitamins and minerals rise with increased cut or exposed food surface
areas, repeated exposures to water, and more time in water, especially
when heated.
The effects on fiber in preserved food is much the same as in fresh
cooked foods.