Considerations of critical microorganisms and indicator enzymes in connection with the pasteurization of meat products

The first part of the work gives a general survey on critical microorganisms with regard to the pasteurization of meat products. Comparison of heat resistance of two microorganisms, under isothermal conditions, is not problematic when both survivor curves follow first-order or nth order inactivation kinetics provided that reaction orders are the same. If not so or, when survivor curves follow different types of inactivation kinetics, a more complex situation arises. It is obvious that, when z-values of the microrganisms to be compared differ considerably, z A≠ z B, the order of size of their heat resistance may be temperature dependent. The equivalent pasteurization time (EPT) is analogous with the sterilizing (F) value, but the chosen reference temperature is below 100°C. In the present work, z and D values of various non-sporeforming microorganisms were collected from the literature, 12D values were calculated for 60, 70 (= T ref) and 80°C and compared with those of `Str. faecalis-D' selected for basis of comparison. Results demonstrated that, depending on temperature, Lb. viridescens, Moraxella-Acinetobacter and some members of Lancefield D group of streptococci appear somewhat more heat resistant than ` Str. faecalis-D'. Problems of applicability of the acid phosphatase in meat as a potential indicator enzyme when its z-value is not identical with the z value of the critical (`target') microorganism, are also discussed. The EPT value of the entire heat processing curve, measured in the centre of the product, was calculated by the well known Bigelow's `general method' and the above-mentioned considerations were extended to non-isothermal heating conditions.