Food Microbiology, 1995, 12, 189-197 Microbial and physicochemical attributes of minced lamb: sources of contamination with pseudomonads E. H. Drosinos* and R. G. Board Minced lamb from butchers' shops was surveyed to establish the composition, and physico- chemical changes (pH, titrimetric acidity, extract release volume, glucose, L-lactate and ammonia) during the development of microbial associations. Pseudomonads or Brochothrix thermosphacta were dominant at the outset. Lactic acid bacteria, Enterobacteri- aceae and yeasts were minor components of the microbial association. Glucose and lactate were catabolized sequentially by the population. Dominance of B. thermosphacta declined after exhaustion of glucose. Pseudomonas fragi was dominant in the climax population at which time there was a marked production of ammonia. The incidence of fluorescent pseu- domonads in mince on the day of purchase was erratic. A survey in three meat factories and experiments with meat trays suggested that this may be associated with the presence of free water on meat preparation equipment. Introduction Spoilage of fresh meat is evident by the changes caused in its physicochemical attributes by microbial growth. Low molecular weight compounds such as glucose and lactic acid are used initially by the microbial associ- ations. Amino acids and amino acid-related compounds are catabolized in a latter stage with production of malodorous substances when the microbial population reaches a size of >108 cfu g-~ (Ayres 1960, Ingram and Dainty 1971, Gill and Newton 1978). Lamb differs from the other red meats (e.g. beef) in *Corresponding author: E. H. Drosinos, 23 Capa- neus Street, Colonus, 104 44 Athens, Hellas. pH, a key determinant for the selection and succession of a microbial association. Minced lamb is a commodity for which there is a little information. In this study a survey of mince sold by traditional outlets (butcher's shops) was made (i) to define the spoilage associa- tion of the commodity and its development under aerobic conditions and (ii) to identify physicochemical attributes associated with microbial growth, and the quality of the prod- uct. Moreover to find the role of substrates such as glucose for the succession of major groups of the microbial association. A survey in meat preparation areas had the objective of identifying possible sources of pseudo- monads in minced lamb and factors that influence the relative incidence of fluorescent and non-fluorescent pseudomonads. Received : 22 June 1994 University of Bath, School of Biology and Biochemistry, Claverton Down, Bath BA2 7AY, UK 1074-0020/95/030189+09508.00/0 © 1995 Academic Press Limited