Abstract
Meat stored under aerobic conditions and chilled temperatures has a very limited shelf life. Its deterioration is further influenced by the level of hygiene during slaughtering, processing and handling, where contamination by microorganisms such as bacteria, yeast and moulds will affect its shelf life. Several scientific reports have suggested venison has better bacterial stability than other commercial meats such as beef and lamb. However, there have yet to be in-depth investigations on the antibacterial properties and the mechanism of action in venison. The current study investigated the antibacterial activity of venison and the changes in bacterial numbers during aerobic storage of fresh venison.
The microbiological (total bacterial count, Pseudomonads, Enterobacteriaceae, and lactic acid bacteria) and biochemical changes (pH, TBARS, glucose, glycogen, myoglobin derivatives) of 24 hour post-mortem venison and beef minced loins were compared during aerobic storage at 4 °C. The length of the bacterial lag phase (BLP) was used as an indicator of the bacterial inhibitory activity. Fresh venison had a significantly (P < 0.05) longer bacterial shelf life (time to 6 log CFU g-1) than beef (14 and 5 days respectively). The lower pH value (P < 0.05), and higher glucose and glycogen concentrations (P < 0.05), higher TBARS (P < 0.05), and higher iron concentration (P < 0.05) in venison than beef suggested a potential involvement of reactive oxygen species (ROS) in the observed phenomena.
An evaluation of various ROS generation systems on bacterial growth indicated antibacterial activity arising from H2O2 rather than superoxide and hydroxyl radicals. Further evaluation of a glucose-glucose oxidase H2O2 generating system indicated that the extension of the bacterial lag phase was dependent on the concentration and maintenance of H2O2 during storage. An increase in glucose concentration increased the antibacterial activity (P < 0.05).
Due to technical limitations to observe and quantify H2O2 directly in fresh venison during storage, a series of cause and effect experiments were used to evaluate the association of H2O2 in fresh meat with bacterial numbers. Altering the concentration of H2O2 via manipulation of catalase and SOD activities had no effect (P > 0.05) on bacterial growth. The use of tyrosine, tryptophan, SDS and EDTA to inhibit either SOD or Catalase, showed that only tyrosine had an effect on bacterial growth. A low tyrosine concentration (5 mg/g) treatment of both venison and beef resulted in a longer bacterial lag phase (P < 0.05). Since the generation of H2O2 in situ is largely dependent on the activity of several enzymatic systems involved in superoxide generation (a precursor for H2O2), various inhibitors (DPI, Antimycin, Oxypurinol, Rotenone, and L-name) associated with the superoxide production pathway were used to identify the possible relationship of superoxide with the length of the bacterial growth lag phase. A decrease (P < 0.05) in the bacterial lag phase in venison was observed in Oxypurinol treated samples, while an increase (P < 0.05) in the bacterial lag phase was observed with Rotenone, Antimycin and L-name treated samples. The effect of these inhibitors on ROS associated pathways indicated the potential relationship of oxidative activities with the bacterial growth lag phase and suggested that ROS may play a role in exerting antibacterial activities.
Overall, circumstantial evidence suggests a potential role of ROS in increasing the shelf life of venison associated with the increased length of the bacterial lag phase.