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SECTION I: MOLECULAR GENETIC ENGINEERING AND BIOCHEMICAL TECHNOLOGY 2674. STRUCTURE-ACTIVITY RELATIONSHIP OF UMAMI PEPTIDE4.1. The relationship between the arrangement order of amino acids and the umami effectThe arrangement order of amino acids is closely related to the umami effect. Umami peptide%u2019 umami taste results from the interaction of acidic and basic groups. Umami is produced only when the positions of these two groups are suitable. Yamasaki et al. extracted and isolated beef octapeptide from beef. Its peptide chain structure is identified as Lys-Gly-Asp-Glu-Glu-Ser-Leu-Ala [14]. The negatively charged acidic group -Asp-Glu-Glu-Glu- is in the middle position. The positively charged basic group Lys-Gly is in its N-terminal adjacent position. Their synergistic effect makes the beef octapeptide produce umami. Arai et al. synthesized 12 kinds of dipeptides containing Glu [9]. The results showed that only the C-terminal structure with weakly hydrophobic groups could reflect the unique umami characteristics of broth. The above research indicates that a peptide must contain a positive group, a negative group, and a hydrophobic group simultaneously. Also, the positive group should be located at the N-terminal of the negative group to produce umami.4.2. Relationship between peptide tandem and umami effectPeptide tandem can improve the expression amount and enhance the umami effect. However, simply increasing the number of single peptide tandem may not double the umami effect. The complex tandem of multiple peptides often plays a role in enhancing freshness. Gao Yingrui et al. conducted a flavor comparison experiment of expressing flavor peptides with different copy numbers in Pichia pastoris. They tandem genes that can produce umami to form groups of 4BMP, 8BMP, 12BMP, and 16BMP, and then introduced them into Pichia pastoris for