What are protein hydrolysates?
Proteins that have been treated with enzymes to break them down into amino acids or shorter peptides are referred to as protein hydrolysates. Protein hydrolysates are valued for their superior nutritional qualities, including increased bioavailability and reduced antigenecity. Several enzymatic modifications of proteins / enzymes are known to occur in biological systems. Such modifications of proteins in vitro can be used to improve their functional properties. Only few of the enzymatic modifications of proteins are practical for modifying proteins for food use. Hydrolysis of food proteins using proteases (trypsin, chymootrypsin, papain and thermolysin) alters their functional properties. Extensive hydrolysis by nonspecific proteases, such as papain, cause stabilization of even poorly soluble proteins. Such hydrolysates usually contain low molecular weight epties of the order 2-4 amino acids residues. Extensive hydrolysis damages several functional properties, such as gelation, foaming and emulsifying properties. These modified proteins are useful in liquid-type foods, such as soups and sauces, where solubility is a primary criterion and feeding a person who might not be able to digest solid foods.
Partial hydrolysis of proteins either by using site-specific enzymes (such as trypsin or chymotrypsin) or by control of hydrolysis time, often improves foaming and emulsification properties, but not gelling properties. With some proteins, partial hydrolysis may cause a transient decrease in solubility, because of exposure of the buried hydrophobic regions. The drawback of many protein hydrolysates, is that when hydrolysed, most of the food proteins liberate bitter tasting peptides, which affect their acceptability in certain applications. The bitterness is associated with their mean hydrophobicity. The intensity of bitterness depends on the amino acid composition and sequence and the type of protease used. Hydrolysates of hydrophilic proteins, such as gelatin; are less bitter than the hydrolysates of hydrophobic proteins, such as casein and soya proteins. Protease that show specificity for cleavage at hydrophobic residues, produce hydrolysates that are less bitter than those enzymes which have a broader specificity. Thus, thermolysin, which specifically attacks the amino side of hydrophobic residues, produces hydrolysates that are less bitter than those produced by low specificity trypsin, pepsin and chymotrypsin.