Plastein reaction, applications

Another major application of the plastein reaction is nutritional improvement of proteins by the incorporation of limiting amino acids (8). A plastein containing approximately 7% methionine was produced from soy protein hydrolyzate and L-methionine ethyl ester in the presence of papain. This material was shown to be utilized as a source of methionine in the rat, producing a PER of 3.38 when incorporated into soy protein diets to give a methionine level of 2.74% of protein. 

More details of the plastein reaction and its application to remove pigments such as chlorophyll, or to remove off-flavor components such as the beany taste of soybeans, are shown in Figure 2. The protein of the food system is solubilized and denatured (in order to achieve proteolysis), a protease is added, and the hydrolytic reaction is allowed to proceed. On partial hydrolysis of the protein the pigments and flavor constituents are released from the protein they are removed, the hydrolyzate is concentrated, and resynthesis and/or rearrangement of the amino acid sequence of the polypeptides is catalyzed by the same or a different protease. Resynthesis also can be carried out in the presence of added amino acid esters in order to improve the nutritional/functional properties of the protein. 

The plastein reaction was also investigated for the possible use of proteins in novel food applications. This was done via establishing a relationship between the microenvironmental conditions of the plastein reaction and the amino acid composition of the products. At low substrate concentration, produced by manipulation with additives, the plastein reaction was enhanced via the condensation pathway 174,75]. The plastein activity in the presence of a-chymotrypsin as catalyst increased with substrate concentration in the range of 10-30% (w/v). The substrate of this plastein reaction was a peptic hydrolysate of albumin obtained at 40°C, pH 7.0. The content of hydrophobic amino acids, in this case lie, Leu, Val, and Tyr, increased in the plastein products, while the content of Asp, Glu, Ser, and... 

Watanabe, M., Aral, S. Xhe plastein reaction and its applications. In Developments in Food Proteins -6 (Ed. Hudson, B.J.F.), p. 179, Elsevier Applied Science London. 1988... 

The period after extracting SPIs and just before spray-drying provides an opportunity for treating with enzymes or chemicals. Although considerable research in succinyl-ated and acetylated derivatives has occurred, these modifications are not allowed in food and are restricted to industrial applications. Likewise, the enzyme-catalyzed reaction plastein synthesis, the reassembling of proteins from peptides, is not practiced in domestic commercially prepared food proteins. 

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