title: Comparison of different peptidase substrates for evaluation of microbial quality of aerobically stored meats.
abstract: Different aminopeptidase and endopeptidase substrates were assessed for the detection of enzymatic activity of microorganisms collected from the surface of aerobically cold-stored pork and beef. The most sensitive substrates were fluorogenic Ala-7-amino-4-methylcoumarin (Ala-AMC) or Leu-AMC and colorogenic Ala-p-nitroanilide (Ala-pNA). Activity on natural oligopeptides, e.g., bradykinin or alpha(s1) casein fragment 1 to 23, was very low. The correlation coefficient (r) between log surface counts of 66 meat samples and log fluorescence or absorbance after incubation of surface microbial cells for 2 h with Ala-AMC, Leu-AMC, and Ala-pNA was 0.89, 0.83, and 0.82, respectively. A distinct yellow color was obtained with Ala-pNA when the surface count was approximately 10(6) CFU/cm2. Although correlation and sensitivity was better, no clear advantage is obtained with the use of the fluorogenic Ala-AMC or Leu-AMC instead of Ala-pNA, a substrate proposed by Alvarado et al. (J. Food Sci. 57:1330, 1992) for rapidly assessing the microbial quality of refrigerated meat. The correlation coefficient (r) between time of cold storage and surface count was 0.69.
authors.affiliation: Department of Food Science, Agricultural University of Norway. leszek.stepaniak@inf.nlh.no
authors.forename: L
authors.initials: L
authors.lastname: Stepaniak
mesh_terms: D000332:Aerobiosis; D000818:Animals; D002417:Cattle; D003080:Cold Temperature; D015169:Colony Count, Microbial; D003116:Color; D005456:Fluorescent Dyes / Q000378:metabolism*; D005519:Food Preservation; D008460:Meat / Q000382:microbiology*; D010447:Peptide Hydrolases / Q000378:metabolism*; D013223:Statistics as Topic; D013379:Substrate Specificity; D013552:Swine
chemical_list: D005456:Fluorescent Dyes; D010447:Peptide Hydrolases