Hydrolysate bitterness

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. 

The enzymatic hydrolysates of milk casein and soy protein sometimes have a strong bitter taste. The bitter taste is frequently developed by pepsin [9001 -75-6] chymotrypsin [9004-07-3] and some neutral proteases and accounted for by the existence of peptides that have a hydrophobic amino acid in the carboxyhc terminal (226). The relation between bitter taste and amino acid constitution has been discussed (227). 

Bitter almonds contain amygdalin, which is the P-D-glucoside of prunasin, so it hydrolyses sequentially to the same products. Cassava, which is used in many parts of the world as a food plant, contains linamarin, which is the P-D-glucoside of acetone cyanohydrin. Preparation of the starchy tuberous roots of cassava for food involves prolonged hydrolysis and boiling to release and drive off the HCN before they are suitable for consumption. 

Cheung, I. W. Y. and Li-Chan, E. C. Y. (2010). Angiotensin-I-converting enzyme inhibitory activity and bitterness of enzymatically-produced hydrolysates of shrimp (Pandalopsis dispar) processing byproducts investigated by Taguchi design. Food Chem. 122,1003-1012. 

Amygdalin (the glucoside of bitter almonds) is a white crystalline compound, soluble in water, readily hydrolysed on heating with dilute sulphuric acid to benzaldehyde, hydrocyanic acid and glucose. 

Bitter peptides Casein hydrolysate Cheese, casein... 

Enzymatic hydrolysates of various proteins have a bitter taste, which may be one of the main drawbacks to their use in food. Arai el al. [90] showed that the bitterness of peptides from soybean protein hydrolysates was reduced by treatment of Aspergillus acid carboxypeptidase from A. saitoi. Significant amounts of free leucine and phenylalanine were liberated by Aspergillus carboxypeptidase from the tetracosapeptide of the peptic hydrolysate of soybean as a compound having a bitter taste. Furthermore, the bitter peptide fractions obtained from peptic hydrolysates of casein, fish protein, and soybean protein were treated with wheat carboxypeptidase W [91], The bitterness of the peptides lessened with an increase in free amino acids. Carboxypeptidase W can eliminate bitter tastes in enzymatic proteins and is commercially available for food processing. 

The earliest commercial milk protein enzymatic modification dates back to the 1940s, when the first formulas for allergenic infants were made. The aims of this process were to reduce allergenicity as well as to change the functional properties of proteins while preserving their nutritional value for clinical use. Unfortunately the hydrolysates thus obtained were characterized by bitter taste, and for mainly this reason proteolysis, as a technological process, enjoyed very little popularity. 

It seems that the negative charges can also be on a peptide chain. Fujimaki describes the bitter masking action of peptides rich in glutamyl residues (29 ) and the isolation and identification of acidic oligopeptides from a flavour-intensifying fraction from fish protein hydrolysate (30). 

Series of bitter peptides have been isolated from enzymatic hydrolysates of proteins, esp. casein and soybean protein. 

From soybean protein hydrolysates several series of bitter peptides have been isolated. As an example Table XIV shows bitter peptides isolated by Fujimaki (69., 70) As before the high Q-values are evident. 

Bitter peptides from peptic soya protein hydrolysates... 

From peptic Zein hydrolysates, Wieser and Belitz (71) isolated bitter peptides which are given in Table XV together with the corresponding high Q-values. 

Regarding the whole picture of enzymatic hydrolysates we came to the conclusion, that certain proteins are more prone to yield bitter peptides than others. Therefore we tried to transfer our method also to proteins as well. This would enable a prediction to be made as to whether in the... 

Bitter peptides fron peptic Zein hydrolysates... 

It is interesting to see that proteins with high Q-values above 1400 as e.g. soybean protein, casein wheat gluten, potato protein, Zein are the "parents" of bitter peptides, whereas no bitter peptides have been isolated from hydrolysates prepared from collagen or gelatin, proteins with Q-values below 1300. 

Fujimaki (77,78) condensed bitter soybean protein hydrolysates in a Plastein-Reaction (79) and obtained non-bitter protein-like products, unfortunately without determination of molecular weights. 

Parent Protein Q Molecular weight of hydrolysate in Dalton Tas bitter te non- bitter... 

Above this molecular weight, also peptides with a Q-value above 1400 will no longer exhibit bitter taste. It is clear therefore, that 2 ways exist to come to non-bitter protein hydrolysates. As demonstrated in Figure 4... 

Ney, K.H. and RezzlafF, G. 1986. A computer program predicting the bitterness of peptides, especially in protein hydrolysates, based on amino acid composition and chain length (computer Q) In Shelf Life of Foods and Beverages , Proceedings of the 4th International Flavour Conference (G. Charalambous ed.), pp. 543-550. Elsevier, The Netherlands. 

Slattery, H. and FitzGerald, R.J. 1998. Functional properties and bitterness of sodium caseinate hydrolysates prepared with a Bacillus proteinase. J. Food Sci. 63, 418-422. 

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