To study the factors and mechanisms involved in microorganisms' death or resistance to temperature in low-water-activity environments, a previous work dealt with the viability of dried microorganisms immobilized in thin-layer on glass beads. This work is intended to check the efficiency of a rapid heating-cooling treatment to destroy microorganisms that were dried after mixing with wheat flour or skim milk. The thermoresistance of the yeast Saccharomyces cerevisiae and the bacterium Lactobacillus plantarum were studied. Heat stress was applied at two temperatures (150 or 200 degrees C) for treatments of one of four durations (5, 10, 20, or 30 s) and at seven levels of initial water activity (a(w)) in the range 0.10 to 0.70. This new treatment achieved a microbial destruction of eight log reductions. A specific initial water activity was defined for each strain at which it was most resistant to heat treatments. On wheat flour, this initial a(w) value was in the range 0.30-0.50, with maximal viability value at a(w)=0.35 for L. plantarum, whatever the temperature studied, and 0.40 for S. cerevisiae. For skim milk, a variation in microbial viability was observed, with optimal resistance in the range 0.30-0.50 for S. cerevisiae and 0.20-0.50 for L. plantarum, with minimal destruction at a(w)=0.30 whatever the heating temperature is.

Rabbitfish, Siganus fuscescens 16.6 to 24.3cm in fork length caught off Tokushima Prefecture in the Pacific Ocean were used for these experiments. These fishes were reared by feeding fish only (experiment I) and both fish and seaweed (experiment II) under continuous flowing seawater conditions during November 2015 to February 2016 and the influence of low water temperature in winter on the survival and feeding was examined. The feeding on fishes stopped at 10.6-10.7 and on seaweed stopped at 12.9degC. Siganus fuscescens in experiment I started to die from 11.1degC (January 24) and one in experiment II from 10.4degC (February 11). These results show that low water temperature below 10.6-12.9degC led to exhaustion of Siganus fuscescens. The lower limiting water temperature for survival was estimated to be 10.4-11.1degC and feeding on both fish and seaweed enhanced the tolerance to low water temperature.