Free amino acids, taste

Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. 

The results found in the literature and from these experiments enabled us to select parameters which may give an indication of the degree of integration. These are resistance to diseases and pests, overall taste, phenols, ratio of proteins to free amino acids (physiological amino acid status), integration score on crystallisation pictures and species-typical colour ratio in spectral-range luminescence. 

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. 

Looking at compounds with direct taste effects, the significance of amino acids and nucleotides in the formation of potato taste has been described in several papers (3,4,5). The free amino acids and 5 -nucleotides are certainly an important fraction they contribute to taste due to their content of glutamic acid, aspartic acid, 5 -AMP, 5 -IMP and other compounds. From the vast literature two analytical examples which have also been tested in taste tests are presented in Table II. 

Potato taste is not characterized by one of the primary taste sensations. Especially sweet, sour or bitter notes are considered off-flavors. However, free amino acids and 5 -nucleotides are important compounds that convey an agreeable basic taste to potato products. The amino acids occur naturally in free form the 5 -nucleotides are liberated during the heat preparation of potatoes by a specific enzymatic degradation of RNA. Starch forms a matrix for all potato preparations. Although it is tasteless, is has an influence on taste quality due to textural characteristics, and due to its pronounced capability to form stable complexes with flavor compounds either in a thermal gradient or under isothermal conditions. 

Taurine and arginine, which account for an important part of the free amino acids, made little contribution to the taste. 

From these results and from the free amino acid compositions of the extracts, they regarded amino acids, chiefly glutamic acid and glycine, as the main contributors to the taste of these crustaceans. 

An excess of proteolysis must be avoided as it can impair the sensory characteristics for the following reasons (Toldra 2002) (i) Development of a bitter and metallic taste as a consequence of the accumulation of an excess of peptides and free amino acids (ii) formation and random distribution of white crystals of tyrosine... 

Role of Free Amino Acids and Peptides in Food Taste... 

Free amino acids and/or some peptides have some sweetness, bitterness, sourness, saltiness and umami, and are very important as taste substances in foods. 

In this paper, we discuss 1)some tastes of free amino acids and some peptides, 2)the role of free amino acids in the characteristic tastes of vegetables and marine foods, 3)the role of the bitter peptides in cheese and the traditional Japanese foods "miso" and "natto", and 4.)the contribution of free amino acids and peptides to the improvement of the meat taste during storage of meats (beef, pork and chicken). 

Free amino acids and peptides are very important as taste substances. The importance of amino acids to food taste was first recognized by Ikeda in 1908 ( ] ), He discovered that monosodium... 

This paper deals with the tastes of free amino acids and peptides, and their roles in the taste of foods. 

Though amino acids can elicit any one of the primary tastes, the threshold value of taste of each amino acid is high. As the levels of some free amino acids in natural foods are lower than their threshold values, it may be thought that they may not contribute directly to food taste. However, they may have an Important role in making the food savory because of the synergistic effect. 

ROLE OF FREE AMINO ACIDS AND PEPTIDES IN FOOD TASTES Vegetable Foods... 

Free amino acids play an Important role in the taste of vegetables. There are large amounts of Glu, Asp, Ser, Val, Ala, Pro and Gin in vegetables as shown in Table 7 ( ). The detailed research on the taste of green tea, onion and potato reveals the presence of umami substances. The most important umami substances of green tea are Glu and L-theanine, which is an ethylamide derivative of Glu (39-41). It has been shown that the most Important umami substance of onion ( ) is Glu. Buri al. ( ) examined the role of free amino acids in the flavor of boiled potatoes. Analytical data has shown that the taste of boiled potato soup stock was similar to that of synthetic potato soup composed of free amino acids and nucleotides. This indicated that free amino acids are very important in potato taste. Although they contain large amounts of Glu and Asp, there are... 

The free amino acid content in natto was very small and corresponded to only about 10 % of the total nitrogen compounds. Most of the other nitrogen compounds were peptides. These peptides have been shown to contribute to the bitterness of the characteristic taste of natto ( ). One of these peptides was Isolated and its amino acid sequence was investigated. The amino acid composition of this peptide was Asp 1, Thr 1, Glu 1, Ala 1, Pro 2, Val 3, He 3 and Leu 5. The amino acid at N-terminus of this peptide was Leu and the G-termlnal structure was -Ala-Val-Ile-Leu. 

Taste components of a number of sea food products have been examined for each sea food product has its individual characteristic taste. In studies on the free amino acids analysis (Table 9), it was shown that the major amino acid is His in red meat of fish, Gly and Pro in cuttlefish, Gly and Arg in prawns, and Tau and Arg in abalone ( ). The major amino acids in sea urchin are Gly, Ala and Leu (50). However, the components contributing to their individual characteristic tastes were not elucidated because the relationship between the taste components and the taste was not thoroughly correlated and Investigated in most of these studies. 

The contribution of Gly and Ala to sweetness, Val to bitterness, and Glu, IMP and GMP to umami taste was found. Met was shown to be responsible for the characteristic taste of sea urchin. The characteristic taste of shrimp is sweet taste which is attributed to Gly, the largest component of all the free amino acids in shrimp... 

Free amino acids and peptides released by such proteolytic enzymes as chymosin and lactic acid bacterial proteases in cheeses contribute to the formation of cheese taste. Biede and Hammond (54) reported that free amino acids and small peptides played an Important... 

Sensory evaluation of the relative strengths of each taste (sweet, sour, umami, salty, bitter and brothy) among beef, pork and chicken soups prepared after storage showed that the intensity of umami and brothy tastes was weakest in beef soup (Fig. 5) (Rhue, M.R., University of Tokyo, unpublished data.). There was less Glu in beef than in pork and chicken. The addition of Glu into beef soup to bring up the Glu concentration equal to those in pork and chicken soups made the umami and brothy tastes in the beef soup similar to those in pork and chicken soups. From this observation, Glu seemes to play a very important role in the umami and brothy tastes of meats. This experiment showed that other free amino acids also contribute somewhat to the meaty taste. 

Each food has a characteristic taste which is determined by the balance of the primary and/or secondary tastes. Free amino acids and peptides play an important role in the elicitation of each food taste. 

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