Bitter enzymatic protein hydrolysis

Molecular and enzymatic properties of serine carboxypeptidase (EC.3.4.1.6.1, CPase Top), isolated and refined from the common squid (Todarodes pacificus) liver, were studied. It was found that this enzyme reacts well at the C-terminal position of peptides having hydrophobic amino acids. Because of this property, it was anticipated that this enzyme would have the effect of eliminating bitterness of some peptides. This enzyme was used on bitter peptides prepared by hydrolysis of proteins with pepsin and trypsin. It was found that this CPase Top can eliminate bitter peptides prepared from soy protein and com gluten. 

The three available industrial methods for the production of HVPs are (i) enzymatic a slow process that may result in the formation of bitter peptides and typically lacks the desired aroma/taste profile [20,21,39] (ii) alkaline hydrolysis which typically results in unacceptable flavor profile and an unbalanced amino acid content, and (iii) acid hydrolysis the most preferred method that is cost effective and yields a range of good flavors (see Chapter 11, section 11.4.1.2 Hydrolyzed Vegetable Proteins). 

Methods for eliminating bitter peptides in partial protein hydrolysates are known, but they cause a significant loss of essential amino acids. These procedures usually include additional enzymatic hydrolysis under controlled conditions (a shorter time for the hydrolysis leads to higher peptides that are not bitter) and a selection of suitable proteases, such as aminopeptidases, carboxypeptidases and some other proteases. Enzymes of plant and microbial origin have been successfully used for this purpose. For example, the intracellular peptidases from Lactococcus lactis ssp. cremoris and Brevibacterium linens, which have high proteolytic activity, successfully hydrolyse bitter peptides in cheeses. 

Hops or hops-derived products are usually boiled for 0.5 to 2.5 hours with wort. Wort is an aqueous solution of fermentable sugars (glucose, maltose, maltotriose) obtained by enzymatic hydrolysis of starch derived from malt extraction or from other sources (wheat, maize, rice). The hop boiling takes place in copper or stainless steel tanks and aims to precipitate wort proteins, to sterilize the wort, to remove volatile off-odours by steam distillation and most importantly, to transform the alpha acids into beer-soluble and bitter iso-alpha acids. 

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