Surface Microenvironment and Penetration of Bacteria into Meat

Abstract

Surface contamination in the form of discrete colony-forming units is the main source of bacteria associated with meat spoilage. The fate of these bacteria is determined by the microenvironment at the meat-atmosphere interface, where the constraints determine the nature of a developing microflora. Nutrients, water availability and nutrient diffusion are prominent factors influencing microbial activity. While surface growth is most commonly recognized through enumeration studies based on removal of microorganisms, the less-studied phenomenon of movement of bacteria may be of considerable significance. In model systems, Serratia marcescens moves rapidly in intact meat as well as in compacted comminuted meat. The invasion process may depend on specific enzymes rather than the general class of collagenases. Need for more knowledge about factors that control surface microenviron-ment of meat is apparent. Microorganisms as surface contaminants of meat are the basis of problems of protecting meat quality and public health. The nature of these contaminants, microenvironment at the meat-atmosphere interface and time span for action determine their fate. Factors that control these microorganisms are basic to protection of quality and healthfulness of meats. A summation of some of the current thinking and work on microbial activity at meat surfaces and penetration of the surface by microorganisms therefore will be presented. SURFACE MICROENVIRONMENT Factors affecting the microenvironment at a meat· atmosphere interface The microenvironment involves both meat and atmosphere as well as the unique physicochemical forces at the interface. The degree of influence of either air or meat depends on location of the microorganisms from the absolute surface to being embedded in the meat tissue. One of the most critical factors is available water, expressed as aw, in the microenvironment. Evaporation occurs at the meat surface, where the moisture content is lowest of any intact unit of meat.