Nutritional quality changes

Kidmose, U. and Martens, H. (1999). Changes in texture, microstructure and nutritional quality of carrot slices during blanching and freezing. J. Food Sci. Agric. 79,1747-1753. 

Based on a review of all the data gathered for reduced-acid FCOJ, it is apparent that any changes that do occur are of an insignificant nature and do not alter the nutritional quality of the processed orange juice. The product of commerce is of equivalent quality to the more popular product, frozen concentrated orange juice. 

Limiting essential amino acids covalently attached to proteins by using activated amino acid derivatives can improve the nutritional quality and change the functional properties of proteins. The best chemical methods for incorporating amino acids into water-soluble proteins involve using car-bodiimides, N-hydroxysuccinimide esters of acylated amino acids, or N-carboxy-a-amino acid anhydrides. The last two methods can give up to 75% incorporation of the amount of amino acid derivative used. With the anhydride method, as many as 50 residues of methionine have been linked to the 12 lysine residues of casein. The newly formed peptide and isopeptide bonds are hydrolyzed readily by intestinal aminopeptidase, making the added amino acids and the lysine from the protein available nutritionally. 

Pectinases, cellulases and hemicellulases are used for clarification of fruit juices, juice extraction, improvement of cloud stability of vegetable and fruit juices and nectars, liquefaction and maceration of fruits and vegetables, reduction of cooking time of pulses and improvement of rehydration characteristics of dried vegetables. The chemical basis of these treatments and of the consequential changes in sensory and nutritional quality are discussed. 

Undesirable changes in nutritional quality of foods are initiated by the autoxidation or enzymic oxidation of unsaturated lipids to lipid hydroperoxides. Lipid hydroperoxides and their products of decomposition can react with food components, such as amino acids, proteins and certain other biochemicals. These reactions and the potential role of hydroperoxides in causing mutagenicity are reviewed. 

Several changes which can adversely influence the nutritional quality occur in proteins that are subjected to severe alkaline treatments. Losses in the amino acids (lysine and cystine, particularly), drops in digestibility, and reduction in net protein utilization all increase as the severity of the alkaline treatment increases ( ). Increases in either temperature or pH of treatment caused similar results. Decreased intestinal absorption amino acids was attributed to LAL-like cross-links and racemization. Kraus and Schmidt (68) also observed a reduction in digestibility of milk proteins as treatment temperature increased from 30 to 90°C at pH 12. 

When we speak of nutritional quality of plants we are referring primarily to their suitability as food for animals and man. This changes the picture markedly for the needs of animals are not always the same as those of plants. It is also necessary to know whether the plant product is to be used as the sole food of animals, as is common when they are kept on pasture for long periods. If the plant product constitutes only a small part of the ration, then any nutritive deficiencies can readily be supplied from other sources or from manufactured substances. For example, com that is deficient in lysine is a poor food when used as the sole feed, but with outside sources of lysine there is no problem. Likewise, if cobalt, which is not needed by crops, is deficient in feed products, it can be supplied to mminants as inorganic salts, or to other animals as vitamin B 2. 

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