D- and Z-values of microflora in tuna mince during moist- and dry-heating

Fish and seafood are prone to rapid microbial spoilage, thus adequate care must be taken in drying of fish. The microbial load and its changes during drying and storage are important information in establishing a standard that will ensure food safety. In order to develop drying procedures leading to low safety risk, it is relevant to determine the decimal reduction time (D-value) and the thermal resistance constant (Z-value) during a heating process to identify the effect of temperature on lethality. In the case of drying, microbial changes occurred due to the effects of heat and concentration process. This study was conducted to investigate the changes of endogenous bacterial counts in minced tuna during dry-heating (convection air-drying) and moist-heating (heating in a closed chamber) as a function of temperature. The D-values for total viable counts decreased from 2.52 to 0.26 h for moist-heating and 2.57 to 0.34 h for dry-heating, respectively, when temperature was maintained constant within 60-140°C. In both cases, increasing temperature caused significant decrease in D- values (P < 0.05), whereas the effect of heating methods was not significant (P > 0.05). Thus the heat resistance characteristics of microorganisms in fresh tuna mince was not depended on the changing medium moisture content.