Casein, degradation/hydrolysis

Figure 10.22 Schematic representation of the hydrolysis of casein (a) by lactococcal cell envelope proteinase (CEP), and (b) degradation of an hypothetical dodecapeptide by the combined action of lactococcal peptidases oligopeptidase (PepO), various aminopeptidases (PCP, PepN, PepA, PepX), tripeptidase (TRP), prolidase (PRD) and dipeptidase (DIP).

The results given above indicate that there is no obvious advantage of substituting the existing batch process for production of ISSPH by a membrane reactor process. However, this does not in general mean that continuous protein hydrolysis in a membrane reactor will be uneconomical. For example if the substrate is more completely degradable than soy protein (casein might be such a substrate), it is expected that in a small scale plant (where the capital costs would favour the membrane reactor) the membrane reactor process could be very attractive. The production of protein hydrolysates for dietetic and medical use, could well be considered in this context. 

There have been a limited number of studies on the effects of enzymic modification of protein concentrates on functional properties other than solubility. Studies on functional properties, as modified by enzymic treatments, emphasize foam formation and emulsifying characteristics of the hydrolysates. Treatment of chicken egg albumen alters the functional properties of the egg proteins in terms of foam volume and stability and the behavior of the proteins in angel food cakes (25). Various proteolytic enzymes were used to degrade the egg albumen partially. However, proteolytic enzyme inhibitors indigenous to the egg proteins repressed hydrolysis of the egg proteins compared with casein. 

Few studies have focused on the biodegradability and environment-friendly aspects of protein-based products which degrade naturally or in compost. The construction of protein networks can induce marked changes in the conformation and resistance to enzymic hydrolysis and chemical attack of proteins [219]. However, Garcia-Rodenas and co-workers [220] showed that the susceptibility of casein and wheat... 

In stored foods containing natural bixin (9 -ds isomer), in the presence of light, aU-trans-bixin may result and, by its hydrolysis, all-trfl s-norbixin. In cheeses containing bixin, these substances bind to phosphoproteins (e.g. to some caseins), causing pink discoloration of products. In addition to tra s-isomers, some degradation products of bixin may also arise, such as methyl ester of d -trans-4,8-dimethyltetradeca-2,4,6,8,10,12-hexaenoic acid and aromatic hydrocarbons (e.g. m-xylene). 

Scheme 4 shows another kind of biological hydrolysis, the putrefactive degradation of casein [11]. The later reaction is also a hydrolysis, but in contrast to the hydrolysis of PHB the resulting degradation products (amino acids) are used in the anabolic cycle forming new proteins. 

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