Commercial food processing preserves food quality and extends shelf life by destruction of food-spoilage microorganisms and certain endogenous enzymes, which could otherwise promote spoilage and/or reduce nutritive value. Since all processed foods have to be stored until they are consumed, proper food packaging is essential to maintain preservation. Time and temperature during processing and storage are closely controlled in good manufacturing practice. Distribution controls, however, are less stringent, except for very perishable products. While there are innumerable benefits to food processing nearly every food preparation process reduces the amount of nutrients in food. In particular, processes that expose foods to high levels of heat, light, and/or oxygen cause the greatest nutrient loss. Nutrients can also be "washed out" of foods by fluids that are introduced during a cooking process. It should be noted that the macronutrient and vitamin content of foods are more likely to be affected by processing than the mineral content. The main factors contributing to vitamin losses are oxidation (air exposure), heat (temperature and time), catalytic effect of metals, pH, action of enzymes, moisture, irradiation (light or ionizing radiation), and various combinations of these factors. Some vitamins are sensitive to processing and storage, while others are more or less stable. The water-soluble vitamins are susceptible to leaching losses during commercial washing and blanching, and domestic cooking. Vitamin C is very susceptible to chemical oxidation during processing, storage, and cooking.
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