Role of free amino acids and peptides

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

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

Kato, H., Rhue, M.R., and Nishimura, T., Role of free amino acids and peptides in food taste, in Flavor Chemistry Trends and Developments, Teranishi, R., Buttery, R.G., and Shahidi, F., Eds., ACS Symposium Series 388, American Chemical Society, Washington, DC, 1989, pp. 158-174. 

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). 

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

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. 

There are at least two answers to question (i). First, abnormal proteins can arise in cells due to spontaneous denaturation, errors in protein synthesis, errors in post-translational processing, failure of the correct folding of the protein or damage by free radicals. They are then degraded and replaced by newly synthesised proteins. Secondly, turnover helps to maintain concentrations of free amino acids both within cells and in the blood. This is important to satisfy the requirements for synthesis of essential proteins and peptides (e.g. hormones) and some small nitrogen-containing compounds that play key roles in metabolism (see Table 8.4). 

As already known, amino acids are the building units of peptides and proteins and they play an important plastic, energetic, and regulatory role in all living organisms. Almost all foods contain amino acids, either in the bound (partially hydrolyzed or intact proteins) or in the free form. High amounts of free amino acids can be found in some fermented foodstuffs as a consequence of proteolytic processes. 

Final degradation of substrates to oligopeptides and free amino acids may involve gastro-dermal exopeptidases such as a cathepsin C (Caffrey et al., 2004), which removes dipeptides from the N-terminus of proteins, and a leucine aminopeptidase (LAP McCarthy et al., 2004), which is capable of releasing free amino acids from peptides and dipeptides. However, it is notable that cathepsin B also exhibits carboxydipeptidase activity and, therefore, may well play a dual role (Tort et al., 1999 Caffrey et al., 2004). 

Amino Acids. Chloroformates play a most important role for the protection of the amino group of amino acids (qv) during peptide synthesis (32). The protective carbamate formed by the reaction of benzyl chloroformate and amino acid (33) can be cleaved by hydrogenolysis to free the amine after the carboxyl group has reacted further. The selectivity of the amino groups toward chloroformates results in amino-protected amino acids with the other reactive groups unprotected (34,35). Methods for the preparation of protected amino acids on an industrial scale have been developed (36,37). A wide variety of chloroformates have been used that give various carbamates that are stable or cleaved under different conditions. 

Other neurotransmitters. The abundant glutamate, GABA, and glycine are major neurotransmitters. Do other amino acids also function in the brain Roles for L-aspartate and D-serine (p. 1785) have been identified, but it is very difficult either to discover or to disprove a neurotransmitter function for other amino acids. It is even more difficult for small amounts of various amines and small peptides that are present in the brain. Taurine (Fig. 24-25) is one of the most abundant free amino acids in animals and meets several criteria for consideration as both an inhibitory and an excitatory transmitter.797 798 However, its function is still uncertain (see Chapter 24). Homocysteic acid, formed by oxidation of homocysteine, is a powerful neuroexcitatory substance, but its concentration in the brain is very low.149 d-Aspartate is also present... 

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