This study aimed to investigate the effects of soymilk ingredients on the inactivation of Lactobacillus plantarum subsp. plantarum and Lactobacillus pentosus. Pretreated bacteria were inoculated in MRS broth or soymilk and incubated at 30°C for 48 h. The cells were suspended in 0.85% NaCl or soymilk and incubated at 65°C for 60-120 s at high-pressure in the 300–450 MPa range. The logarithmic survival ratios of the lactobacilli cultured in MRS or soymilk decreased with heating time. The inactivation rate constant, k, did not change between MRS and soymilk medium by heat treatment. The difference in composition of cell membranes was also small. The survival behavior of each sample subjected to high-pressure was described by first-order kinetics. A gradual increase in k was observed at 300–450 MPa. It is found that pre-exponential factor and activation volume of the lactobacilli subjected to high-pressure treatment were related linearly. These indices did not have clear relationship with membrane composition of the lactobacilli. Thus, the different effects of heat and high-pressure stresses on cell resistance are possibly due to the incubation conditions. The results of this study indicate that the mechanism of inactivation may be essentially similar to numerous chemical processes in many microorganisms though factors for the acquisition of heat and pressure tolerance are diverse.

Salt restriction is important in the treatment of hypertension. Therefore, we investigated a method for producing dried fish utilizing used tea leaves that retain most of the components that exhibit antibacterial and antioxidant effects. When treated with a mixture of used tea leaf extract and salt, water content, salt concentration and the number of bacteria were lower than that found for the single substance solution. A synergistic effect was particularly observed for bacterial count reductions when using a 2% salt and used tea leaf mixture. Sensory evaluation showed there was a highly positive evaluation of the dried fish produced with a mixture of 2% salt and used tea leaf extract as compared to commercially available dried fish. Current results suggest that application of used tea leaves during dried fish production can reduce salt while retaining the antibacterial effect, with utilization of used tea leaves thereby expected to reduce food waste.

The objective of this study was to elucidate the effect of coexisting components in the filler, sterilization time, and solid-to-filler ratio of prepackaged food on the amount of seasoning sorbed on solid food. To evaluate the mass transfer of seasonings in food, konjac or mackerel with either a sodium chloride solution or a model solution as a filler were prepackaged. The distribution coefficient of sodium chloride (i.e., the ratio of the amount of sodium chloride sorbed on the solid food to the concentration of sodium chloride in the solution) for konjac was approximately 0.76 × 10^-3 m³/kg and that for mackerel was approximately 0.40 × 10^-3 m³/kg. These values are similar to those obtained when the model solution is used. Changes in sterilization time and solid-to-filler ratio did not significantly affect the distribution coefficients. The values of the distribution coefficients for commercial canned fish were similar to those obtained experimentally.