Some aspects of the microbial ecology of poultry processing and storage with particular reference to microbiological/histological relationships of broiler carcass skin

Scanning and transmission electron microscopy were used in conjunction with standard microbiological procedures to examine some aspects of contamination of broiler carcass skin by bacteria during processing as well as the subsequent growth of these microorganisms during storage. The autochthonous skin microflora of the skin of poultry prior to processing, was mainly Micrococcus spp. which were located in accumulations of sebum-like substances on the surface of the stratum corneum. During scalding and plucking, the skin epidermis was removed and the exposed dermal tissue was contaminated by microorganisms from the mechanical plucker and subsequent stages of processing. The major sources of contamination of psychrotrophic bacteria were immersion washer and chiller water. Microorganisms contaminating the skin were mainly found within a fluid film covering this surface, but also deep inside skin channels. The fluid film contained serum proteins and some amino acids and the quantity of fluid and concentration of the components increased during storage of broiler carcasses. Skin microtopography and the presence of the liquid film were implicated as major factors controlling contamination of carcasses during processing. Fixation of skin in osmium tetroxide vapour allowed preservation of the liquid film components in situ, whereas fixation by immersion in solutions of glutaraldehyde or osmium tetroxide rinsed these materials from the skin and allowed unobstructed observation of the surface. Addition of alcian blue 8GX to glutaraldehyde solutions improved preservation of the fluid film components ,especially when high numbers of spoilage bacteria were present. During storage of carcasses under humid conditions, bacteria grew within the fluid film but were also found in deep skin channels and in feather follicle shafts, whereas under drying conditions, microorganisms grew in discrete colonies. Spoilage bacteria were not attached by acidic mucopolysaccharide fibrils to the skin of carcasses stored at 20, 40, and 10°C, although bridging substances were associated with bacteria on carcasses stored at 15° and 22°C. Skin invasion or gross degradation of this substrate by the spoilage microflora was not observed for carcasses stored at 20C. However, bacteria did degrade proteinaceous material present within the liquid film even before onset of spoilage. Strains of Pseudomonas groups I and II were the predominant types producing off odour on the skin of carcasses stored at 2°C. Sulphide-like or fruity-type off odours were produced by pure cultures of these bacteria when grown on either leg muscle pieces or skin. The major sulphur volatile produced was methanethiol. This volatile was also produced by these isolates when grown in a methionine supplemented medium, although the presence of glucose inhibited production of methanethiol. The significance of the results is discussed in relation to the mechanisms of contamination of broiler carcasses during processing and the growth and metabolism of microorganisms during storage.