Deterioration of foods and raw agricultural products which can be converted into foals is primarily the result of microbial growth, enzymatic deterioration, and chemical changes that occur after harvest or slaughter. Food scientists and technologists have utilized dehydration, high and low temperature processing, chemicals, and radiation to inhibit these deteriorative reactions and protect our food supply.Thermal processing is one of the most common and effective methods of food preservation and is used alone and in combination with other preservation techniques. The principal effect of thermal processing is protein denaturation, resultinn in the destruction of micr~organisms and the inactivation of microbial and native deteriorative enzymes in a food.Most people think of processing as being only detrimental to the nutritional value of foods because of the potential destruction of a food's proteins, lipids, and vitamins. However, thermal processing can be beneficial and is required if we are to maintain a safe, wholesome, and nutritious food supply and obtain the maximum nutritive value of some foods.The nutritive value of manv foods is increased bv the thermal destruction of toxic proteins and peptides, enzyme inhibitors, antivitamins, and other natural toxicants in foods which seriously affect their nutritive value. Numerous researchers have shown that. in order to obtain the highest nutritive value of legumes, proper heat treatment is required to destroy naturally occurring trypsin inhibitors, hemagglutinin, and other toxic substances present in legumes. Heat treatment also improves the diaestibilitv and availahilitv of the sulfur amino acids of plantproteinsil-3).Thenutritive value of plant proteins has been the subject of a great deal of research since these foods are an important dietary source of protein for many segments of the world's ~ -population, and naturally occurring toxicants are more commonly associated with plant than animal foods.
ProteinsHeat damage of proteins results from the destruction of amino acids within a protein, reactions of proteins with nonprotein componentsin a food or food system, or by inter-and intra-protein reactions in the presence or absence of oxygen (4). Studies concernine chanees in amino acid content of ~u r e . .
"protein preparations as a function of temperature and time have shown that tryptophan, methionine, cystine, basic amino acids, and P-hydroxy amino acids are readily destroyed as compared with acidic and neutral amino acids in pure casein or lysozyme preparations (5). Cysteine is heat labile and readilv destroved at temperatures onlv sliehlv above 100°C.
. -.whichis representative oilower commercial processing tem: peratures. At higher temperatures, 115-145°C, other sulfur compounds, including hydrogen sulfide, methylmercaptan, dimethylsulfide, and dimethyldisulfide have been identified as destruction products of sulfur-containing amino acids (6).Although various researchers have reported losses in the amino acid pattern of a protein as a result of thermal des...
