Aminopeptidase Activity by Spoilage Bacteria and Its Relationship to Microbial Load and Sensory Attributes of Poultry Legs during Aerobic Cold Storage

The shelf life of poultry legs stored aerobically and the possible role of the aminopeptidase activity of gram-negative bacteria (p-nitroaniline test) as a predictor of poultry spoilage were evaluated on the basis of microbiological and sensory parameters. Chicken legs (n = 30) obtained immediately after evisceration in a local poultry processing plant were kept under aerobic refrigeration (4 ± 1°C) for 7 days. Microbiological (counts of aerobic bacteria and psychrotrophs) and sensory (odor, color, and general acceptability on a hedonic scale of 1 to 9) parameters and aminopeptidase activity (absorbance at 390 nm [A390]) determinations were performed after 0, 1, 3, 5, and 7 days of storage. Aerobic plate counts of 7 log CFU/g and a score of 6 for general acceptability were used as indicators of the end point of shelf life. Strong correlations (r ≥ 0.76; P < 0.001) were obtained between bacterial counts, hedonic scores, and A390 values. Samples were judged as unacceptable (shelf-life end point) after 2 and 4 days on the basis of sensory and microbiological analyses, respectively. A390 values of 0.52 and 0.89 (corresponding to p-nitroaniline concentrations of 6.25 and 10.7 μg/ml, respectively) are proposed as the upper limits for acceptability on the basis of sensory and microbiological determinations, respectively. However, these recommendations are based on a small set of samples, and their general application is yet to be verified.

Use of Time–Temperature Integrators and Predictive Modeling To Evaluate Microbiological Quality Loss in Poultry Products

The purpose of this study was to characterize the kinetics of the spoilage process of chicken drumsticks in order to evaluate the application of an enzyme process–based time–temperature integrator (TTI) as a continuous quality monitor of poultry products. Shelf life studies were conducted at several temperatures (3 to 20°C) to characterize (i) the poultry spoilage process as a function of total aerobic bacteria and Pseudomonas species populations and (ii) the TTI chroma response function. Two types of poultry products were examined: ice-packed and chill-packed drumsticks. An enzyme-based TTI with a color change response from green to yellow was used. Activation energies for each of the poultry products and each of the bacterial populations were as follows: 21.8 ± 1.6 kcal/mol (ca. 91.2 ± 6.7 kJ/mol) for ice-packed drumsticks and total aerobic population, 18.8 ± 4.5 kcal/mol ca. 78.7 ± 18.8 kJ/mol) for ice-packed drumsticks and Pseudomonas spp., 17.0 ± 2.3 kcal/mol (ca. 71.1 ± 9.6 kJ/mol) for chill-packed drumsticks and total aerobic population, and 14.1 ± 3.6 kcal/mol (ca. 59.0 ± 15.1 kJ/mol) for chill-packed drumsticks and Pseudomonas spp. The activation energy calculated for the TTI, 19.1 ± 1.8 kcal/mol (ca. 79.9 ± 7.5 kJ/mol), was determined to be adequately close to that of the poultry spoilage process to make effective quality predictions possible. Initial bacteria levels on the chicken drumsticks were uniform and not judged as important limiting factors in the application of TTIs to poultry products. Because the poultry spoilage process was reasonably characterized on the basis of Arrhenius kinetics, there is further need to conduct validation studies to determine the ability of TTIs to provide a continuous quality monitoring system.