In comparing the healthfulness of fresh versus processed fruits and vegetables, much tends to be relative. Healthfulness of fresh products is influenced by their contents of healthful constituents, e.g., vitamins, minerals, protein, fiber, anticarcinogens, as well as unhealthful and toxic substances, such as glycoalkaloids, nitrates and nitrites, oxalate, cyanide, heavy metals, glucosinolates, enzyme inhibitors, antienzymes, lectins and hazardous chemical residues. Fresh product surfaces can carry spoilage and possibly pathogenic microorganisms. Quantities of two important vitamins, A and C, can easily vary within species by a factor of two. In addition to cultivar differences, cultural and preharvest factors affecting nutrient content include soil type/fertility/moisture, growing location/season/year, light intensity/duration and stage of maturity at harvest. Apples, pears, potatoes and cabbage, among others, may be stored for months before being marketed as “fresh” product. Mechanical damage and improper temperature/humidity during harvesting, transporting, storing and distributing can destroy nutrients.
Thermal processing (canning) destroys heat labile nutrients and antinutrients (lectins, antitrypsin), kills microorganisms and can improve digestibility. Duration and severity of thermal processes vary with process type, package size and composition, etc. Dehydration involves varying degrees of heating and exposure to oxygen with similar good/bad effects. Freezing better retains heat labile nutrients, but substantial losses can occur during storage. Processed foods must be protected by packaging.
When properly processed, packaged and stored, a given fruit or vegetable can be as healthful, or more so, than a fresh counterpart. Conditions of storage and preparation of either fresh or processed products in the home or institution can have further adverse effects on their healthfulness.