くさや汁におけるpH変化の機構について

抄録

The experiments were carried out to elucidate the reasons why marked increase in the pH of kusaya gravy after fish immersion occurred only in a beaker and did not in a manufacturer's large tank.
Changes in chemical components such as organic acids, volatile basic nitrogen and polyamines were analysed during storage of kusaya gravy in vitro. Acetic acid showed the most significant decrease by about 0.8% in the gravy of which pH increased from 7.0 to 8.8 after 8 days' storage at 20°C. When acetic acid was added into this gravy to give the concentration of 1%, the high pH recovered to below 7. Spiral bacteria isolated from kusaya gravy consumed acetic acid.
Drastic increase of pH value, accompaninig the growth of spiral bacteria, was observed in the gravy kept in an open beaker and was not observed in a screw-capped bottle. A great increase in the pH value was not observed in the bottom layer of the gravy infused in a long tube during 3 months' storage.
These results suggest that a reason why the pH of the gravy kept in a large tank in situ did not greatly increase is that spiral bacteria can hardly grow to consume organic acids like acetic acid in the inner part of the gravy.