Establishment of Critical Hygiene Indices for Meat Cooling Processes Evaluated by a Temperature Function Integration Method

Abstract

A temperature function integration technique that involves the calculation of the potential growth of Escherichia coli to obtain a process hygiene index (PHI) is the New Zealand industry standard method for assessing the potential for growth of enteric bacteria during meat cooling processes. The existing criteria to determine the acceptability of a cooling process with PHI values take no account of the differences between meat products and thus limit processing flexibility. A methodology was developed to set criteria for processing acceptability, based on the frequency distribution of the indicator organism E. coli number on meat carcasses immediately after slaughter (in log2 CFU per square centimeter) and a requirement that the E. coli numbers at the end of the cooling process be less than or equal to some maximum acceptable level. This methodology was used, along with accepted guidelines for maximum acceptable levels of E. coli in the meat and measured initial E. coli numbers for the whole New Zealand meat industry, to develop a set of PHI criteria that would be satisfied by a good-practice meat processing operation. A Monte Carlo modeling approach was used to illustrate the implications of these criteria if they had been applied to cooling processes for beef and lamb previously evaluated by the authors. If the proposed criteria were adopted, the maximum allowable PHI for beef cooling could be higher than that for lamb cooling because of the lower initial E. coli numbers found on beef than on lamb carcasses.