Nutritional and Chemical Changes in Casein During Heat Treatment

After a brief survey of human requirements for protein, the policy of the United Nations towards closing the protein gap and sources of cheap proteins and their processing is followed by a review of biological, microbiological, chemical and biochemical methods of evaluating protein quality. The effects of heat on proteins and their in vivo absorption are discussed.
The chemical and nutritional methods used to analyse heated casein are described and the results obtained are discussed. Samples were processed either in solution or dry at temperatures between 100 and 130° for up to 8 hours. Only small changes in gel filtration pattern of casein processed in solution were observed and dry casein was chosen for further investigation as heating resulted in definite’ changes in both alkaline solubility and filtration pattern of this material. A decrease in NPU was observed only after denaturation had occurred. In samples subjected to severe heat treatment, there were losses of aspartic acid, threonine, serine, cystine, histidine and lysine. The alkali-soluble and insoluble fractions of some samples heated to 120 and 130° were separated and compared with the corresponding total heated samples.
The NPU, BV, digestibility and RNV of each sample were similar to values obtained far the corresponding fractions and the reasons for this are discussed, There were similarities in the availabilities of the essential amino acids in each sample and its fractions. Each soluble fraction differed in total amino acid content from the corresponding total sample and insoluble fraction, the latter two being similar. A shortened MEAA index based on available methionine + cystine, lysine and tryptophan, the PPD index, the chemical score based on available methionine and the pepsin digestibility of some samples of casein have been examined.