General References

G. V. Barbosa-Cánovas and H. Vega-Mercado, Dehydration of Foods, Chapman and Hall, New York, 1996.

D. A. Corlett, HACCP User's Manual, Aspen Publishers, Gaithers-burg, Md., 1998.

J. F. Diehl, Safety of Irradiated Foods, 2nd ed., Marcel Dekker, New York, 1995.

W. A. Gould, CGMP's /Food Plant Sanitation, CTI Publications, Baltimore, Md., 1994.

W. A. Gould, Unit Operations for the Food Industries, CTI Publications, Baltimore, Md., 1996.

D. R. Heldman and D. B. Lund, Handbook of Food Engineering, Marcel Dekker, New York, 1992.

S.D. Holdsworth, Aseptic Processing and Packaging of Food Products, Elsevier, New York, 1992.

P. Jelen, Introduction to Food Processing, Prentice-Hall, Engle-wood Cliffs, N.J., 1989.

N. G. Marriott, Essentials of Food Sanitation, Chapman and Hall, New York, 1997.

N. N. Potter and J. H. Hotchkiss, Food Science, 5th ed., Chapman and Hall, New York, 1995.

G. L. Robertson, Food Packaging: Principles and Practice, Marcel Dekker, New York, 1993.

R. P. Singh and D. R. Heldman, Introduction to Food Engineering, 2nd ed., Academic Press, New York, 1993.

K. J. Valentas, E. Rotstein, and R. P. Singh, Handbook of Food Engineering Practice, CRC Press, New York, 1997.

R. C. Wiley, Minimally Processed Refrigerated Fruits and Vegetables, Chapman and Hall, New York, 1994.

James Faller University of Illinois Urbana, Illinois

FOOD PROCESSING: EFFECT ON NUTRITIONAL QUALITY

The definition of processing is "a natural phenomenon marked by gradual changes that lead toward a particular result"; "a series of actions or operations conducing to an end"; or "a continuous operation or treatment especially in manufacture" (1). Food processing, therefore, refers to the series of actions involved in order to prepare and preserve a food supply by some continuous operation or treatment to achieve as a goal a safe, high-quality product with extended shelf life.

Changes that occur to food quality may be thought of as two types: deterioration and spoilage. Deterioration involves changes in quality induced by physicochemical and/ or biochemical reactions taking place with or without the intervention of a physical environment (such as oxygen, carbon dioxide, water, light, heat, etc). Spoilage, on the other hand, generally refers to changes in quality due to action of biological agents such as bacteria, molds, or insects. Effects of deteriorative reactions and spoilage agents on food quality result in changes in both sensory properties (ie, appearance, flavor, texture) and nutritive value (vitamin content, protein value, etc). The extent to which these reactions can occur depends on the sensitivities and types of food products considered. For example, certain fruits such as strawberries or raspberries may be readily spoiled by the presence of molds. Green peas or beans, on the other hand, lose flavor and result in undesirable textures due to enzyme-induced reactions.

Through various types of food processing, quality factors can be maintained or extended, the extent of which depends on the food product to be considered. By canning fruits and vegetables (eg, pears, peaches, peas, beets) with proper heat sterilization and packaging, these products will not suffer spoilage, although they may deteriorate to some extent in terms of color, flavor, and texture. The extent of these changes depends on a wide array of factors, including storage conditions after packaging. Factors affecting quality of food products include: (1) initial quality of the raw materials and handling from harvesting to the manufacturing plant; (2) pretreatment (including cleaning, sanitizing, washing, aspiration, screening, filtration, chlorination, fumigation, etc); (3) sorting (removal of extraneous materials); (4) peeling, coring, dehairing, de-feathering, husking, stemming, and so on; (5) disintegration/physical separation in cases where grinding, pulping, pressing, or expelling are needed, generally followed by screening, filtering, or centrifugation; and finally, of course (6) the final finished food manufacturing step. These final manufacturing steps comprise a myriad of different types of food processes including clarification/filtration; crystallization; curing/smoking; dehydration; evapo ration and distillation; fermentation; foaming; mixing/ shearing operations (whipping, kneading, blending); forming/shaping; heating/cooking; maturation/aging; or cooling/freezing.

To discuss the effects of food processing on nutritional quality, it is important to have an understanding of some of the basic types of food manufacturing available, their historical development and why they are used. Table 1 provides a very brief chronological sequence of events that have taken place in the development of food processing since the beginning of time. Although in a very subjective way there has been general interest in the effect of processing treatments on product integrity, most traditional processes have developed by accident over time. Any true acknowledgement of nutritional or overall quality of foods has only become more of a science and concern during the last half of the twentieth century. As knowledge expands on the effects of microorganisms and chemicals on man, the standards for purity and safety increase. The standards in the United States, for example, are largely determined by state and federal food and drug agencies as well as individual food industry standards.

In addition to introducing various types of manufacturing techniques and some of the processing parameters that influence quality of foods, it is also important to include a brief discussion on chemical kinetics, which encompasses the study of the rates at which chemical reactions proceed. It is through a basic understanding of kinetics of degradation of nutrients and general physical characteristics in combination with a thorough knowledge of how their reactions rates are affected by different processing conditions that a food technologist can optimize a food process to achieve the highest quality possible and predict a maximum shelf life for that product. The area of kinetics in food systems has received a great deal of attention in past years, primarily due to efforts to optimize or at least maximize the quality of food products during processing and storage. A good understanding of reaction kinetics provides a better idea of how to formulate or fortify food products to preserve and/or extend the existing nutrients or components in a food system or minimize the appearance of undesirable breakdown products. Although limited kinetic information is presently available for food systems or ingredients, several researchers have compiled kinetic data on various quality attributes, including enzyme and protein changes (2), flavor changes (3), physical/textural changes (4), and vitamins and pigments (5,6), in order to facilitate the development of mathematical formulas for the optimization of a given food process. The interaction of the study of kinetics and its relationship to food processing and maintaining optimum food quality will be discussed in a later section. Since a complete discussion of all types of food manufacturing and their effect on quality of foods is beyond the scope of this article, only a few selected processes that are representative of various influencing processing variables that may affect a food product will be presented.

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