Production of koji-catalyzed hydrolysates from dried bonito (KHDB) at low salt concentration and some cooking effects of them

Abstract

The production of koji-catalyzed hydrolysates from dried bonito (KHDB) was investigated. The sixty % ethanol treated dried bonito was hydrolyzed by soy sauce koji in 10% NaCl and 5% ethanol. After 3 months hydrolysis at 30°C, total nitrogen, formol nitrogen, and pH of mash reached 1.53%, 0.73%, and 5.32, respectively. No increase of yeast and lactic acid bacteria during hydrolysis was observed. The respective concentration of NaCl, and ethanol was 11.8%, and 6.1 %, respectively. The average peptide length of KHDB was 4.7, and longer than 3.5 of soy sauce. HPLC-GPC showed that KHDB contained much peptides having molecular weights between 1,000 and 3,000. KHDB had ID50 value of 1.52 mg protein/ml for angiotensin I converting enzyme (ACE), and contained 35.1 mg/100 ml of γ-aminobutyric acid, which is equivalent to 135.0 mg/100 g dry wt. KHDB is thought to have potential as an anti-hypertensive seasoning. For evaluation of usefulness of KHDB as a seasoning, sensory analysis of KHDB was done in comparison with soy sauce. Although "clear soup", "Tempura soup", and "Nimono" were made with the same concentration of sodium chloride, KHDB showed lower salty taste (p<0.1) than soy sauce. At the cocking with rice vinegar, KHDB suppressed sour taste more clearly (p<5) than soy sauce.