Kokumi Substances from Garlic; Discovery of Glutathione (GSH; γ-Glu-Cys-Gly) as a Kokumi Substance

Garlic has been used in various cuisines worldwide. The unique sensory characteristics of garlic include not only its aroma, but also its flavor, designated as the thickness of taste, complexity, continuity of flavor, and mouthfulness. The present chapter describes the fractionation and identification of the compounds responsible for enhancing the thickness of taste, mouthfulness, and continuity of flavor. The results of fractionation and sensory evaluations revealed that S-allyl-l-cysteine sulfoxide (alliin), cycloalliin, S-methyl-l-cysteine sulfoxide, γ-glutamyl-S-allyl-cysteine, γ-glutamyl-S-allyl-cysteine sulfoxide, cysteine, and glutathione were the compounds responsible for enhancing the flavor characteristics described above. Among these compounds, glutathione has been detected in animals, plants, and microorganisms. Therefore, it is expected to be present in various foods. High-performance liquid chromatography was performed to quantify glutathione in various foods, such as meat and meat products, chicken, seafood, vegetables, and alcoholic beverages. A sensory evaluation of glutathione revealed a lower threshold in an umami solution than in water. Furthermore, the addition of glutathione at a concentration below the threshold in water to reconstituted model extract enhanced the thickness of taste (complexity), mouthfulness, and continuity of flavor. These results suggest that glutathione acts as a kokumi substance in foods.