Enzymatically modified soy protein

Adler-Nissen and Olsen (40) studied the influence of peptide chain length on the taste anT functional properties of enzymatically modified soy protein. The emulsifying capacity of modified proteins could be improved significantly compared to unmodified control samples by controlling the extent of hydrolysis. 

Adler-Nissen, J. and Olsen, H.S. 1979. The influence of peptide chain length on taste and functional properties of enzymatically modified soy protein In Functionality and Protein Structure , Advances in Chemical Series 92 (A. Pour-El ed.), pp. 125-146. American Chemical Society, Washington, DC. 

The Influence of Peptide Chain Length on Taste and Functional Properties of Enzymatically Modified Soy Protein... 

The improvement of the whipping properties of enzymatically modified soy proteins and casein has already been of use in the baking industry. For example, Gunther (25) has patented a method for producing these products by pepsin hydrolysis. 

Figure 5. Process combinations investigated for production of highly functional enzymatically modified soy proteins...

Soya Proteins. Early attempts to make albumen substitutes from soya protein also ran into problems. A bean flavour tended to appear in the finished product. A solution to these problems has been found. Whipping agents based on enzyme modified soy proteins are now available. The advantage of enzymatic modification is that by appropriate choice of enzymes the protein can be modified in a very controlled way. Chemical treatment would be far less specific. In making these materials the manufacturer has control of the substrate and the enzyme, allowing the final product to be almost made to order. The substrates used are oil-free soy flakes or flour or soy protein concentrate or isolate. The enzymes to use are chosen from a combination of pepsin, papain, ficin, trypsin or bacterial proteases. The substrate will be treated with one or more enzymes under carefully controlled conditions. The finished product is then spray dried. 

While the determination of total lysine is rather straightforward, the determination of free or available lysine is more problematic. In this situation, the term free is meant to imply that the e-amine of the lysine side chain has not reacted with various components of the sample matrix (most commonly carbohydrates via Maillard browning). This is important because reaction of the e-amine can render lysine nutritionally unavailable and the nutritive value for that protein is then diminished if lysine is the limiting amino acid (which is often the situation with soy proteins). While enzymatic digestion in the human gut may not release the modified lysine in a nutritionally available state, often these lysine adducts are labile to the standard acid hydrolysis in 6N HC1 at 110°C. This results in total lysine values that overestimate the amount of nutritionally available lysine. 

Hitherto, enzymatic modification of ultrafiltered soy proteins has not been described. The present investigation shows that protein products with better properties than enzymatically modified acid precipitated proteins can be produced by a suitable combination of the involved unit operations. 

It is beyond the scope of this chapter to analyze in detail the various surface interactions and forces that proteins can provide. The number of amphiphilic proteins in the world of proteins is limited, which means that the proteins in use are mainly caseins, whey proteins, P-lactoglobulins (BLGs), egg albumin, bovine semm albumin (BSA), lysozyme, and soy proteins. All other plant proteins have very limited ability to strongly adsorb onto interfaces and reduce interfacial tension to only a minor extent. However, chemical and enzymatic modifications will improve the performance of these proteins (pea, cotton, and cereal proteins), and as a result a few modified proteins can be found in the marketplace that have relatively improved performance. 

Watanabe and Arai wrote an excellent review on the properties of enzymatically modified proteins and compared the chemical and enzymatic processes of various proteins [135]. Enzymatic processes can normally be carried out under milder and therefore safer experimental conditions than conventional chemical processes. Proteolytic enzymes have been used on proteins to improve their solubility soy protein, leaf protein concentrates, fish protein concentrates, meat proteins, egg proteins, milk proteins, and blood proteins. Special attention was given to caseins, gelatins, egg proteins, and cereals. Partial hydrolysis of these proteins under well-controlled conditions can produce emulsifying and whipping agents... 

Figure 1. Difference spectra for soy 7S protein modified by enzymatic hydrolysis (----------------) by trypsin at pH 7.1 and (---) by rennin at pH 5.8...

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