Abstract

Introduction: Whitebait (“shirasu” in Japanese) is the collective name for immature fry of sardines, herring, mackerel, and various other fish of ~30 mm in length. Kamakura coast is blessed with a temperate climate, where much whitebait is caught. However, no studies of whitebait-derived fish sauce from Kamakura have been reported. Fish sauce is liquid seasoning made by adding salt to fish and allowing it to ferment via bacterial activity. It has a rich umami taste because of abundant peptides and amino acids, the products of protein digestion by enzymes from internal organs. Method: We used shirasu collected in March 2018 along Kamakura coast. To prepare fish soy sauce, 100 g shirasu and 300 g salt were aged for 2 months at 25°C and then centrifuged at 4,000 rpm for 10 min. Fish sauce composition was then analyzed, including total nitrogen, formol nitrogen, amino acids, carbohydrate, acidity, and pH. Additionally, the molecular weight distribution of proteins was examined by electrophoresis. β-Amylase and protease activity were also measured periodically during aging. Results: The composition of shiitake fish soy sauce was as follows: total nitrogen 4.37%, formol nitrogen 0.28%, acidity 2.6%, pH 4.8, total sugars 4.87%, reducing sugars 3.60%, and glutamic acid 290 mg/100 g. From these results, fish soy sauce aged for 2 months consists of decomposed protein and carbohydrate created by the digestive enzymes of shirasu, muscle enzymes, etc. The final composition included amino acids, peptides, and low-molecular-weight sugars. The umami component glutamic acid is produced, and organic acid levels are raised. This sauce is especially rich in minerals, especially iron, copper, magnesium, and zinc, and has high nutritional value. Significance: Shirasu fish sauce was confirmed to have high total nitrogen and strong umami compared with soy sauce. Using this seasoning for cooking confirmed its high food functionalities such as minerals.

Keywords

shirasu (whitebait), fish sauce production, general food ingredient analysis, food functionality, kamakura food