Effect of immersion time of dried scallop on amino acids, antioxidant and ACE inhibitory activities in Japanese traditional Dashi

The dried adductor muscle of scallop (Mizuhopecten yessoensis) has been used as a material for "dashi." To prepare dashi, the dried scallop must be soaked in water before boiling. Although dashi recipes using dried scallops have been passed down for many generations as a local food, the optimum immersion time prior to cooking has not been elucidated. Thus, the objective of the present study was to determine the optimum immersion time of dried scallops for the preparation of dashi from the viewpoint of components and biological activities. Immersion of dried scallops changed the L * (lightness), a* (redness), and b* (yellowness) of dashi, and subsequent heat treatment led to evident changes in these values. Glycine (Gly), taurine (Tau), and arginine (Arg) are the major components of dashi, accounting for approximately 62%, 15%, and 11% of the total free amino acids, respectively. When the immersion time was 8 h and more, these major amino acids were significantly increased in dashi with or without heating compared to that after 1 h of immersion without heating. Heat treatment significantly decreased maltose in dashi prepared after 8 h of immersion. Dashi prepared following 4 h or more of immersion had significantly enhanced peroxyl radical scavenging and angiotensin converting enzyme (ACE) inhibitory activities compared to those prepared following 1 h of immersion. A minimum of 8 h of immersion appears to be necessary for preparing dashi rich in umami, sweetness, and antioxidant and ACE inhibitory activities. An extended immersion time (12 h) caused evident progress in the Maillard reaction. The soluble and aromatic compounds of the reaction products may affect the taste and functionality of dashi.