EFFECT OF SODIUM ALGINATE EDIBLE FILMS WITH OREGANO AND LIMONENE ESSENTIAL OILS ON THE MICROBIAL AND PHYSICOCHEMICAL PROPERTIES OF PORK STORED AEROBICALLY AND UNDER VACUUM

摘要

Edible films can serve as carriers of natural antimicrobial substances like essential oils, providing an alternative, low cost packaging method that can be used efficiently for and extending shelf life of products such as meat. The present study aimed to evaluate the effect of edible films with or without the incorporation of oregano and limonene essential oils, on the microbial, physicochemical and sensory profile of pork pieces, stored aerobically or under vacuum at 4°C. Pieces of pork (10 g) were immersed: (i) in sodium alginate gel (3% w/v); (ii) in sodium alginate gel with oregano essential oil (0.5,1.0, 2.5, 5.0% v/v) for 1 minute and then in a 2% w/v CaCl_2 solution for an extra minute. Pieces of pork meat without edible coating were considered as controls. All samples were packaged aerobically or under vacuum and stored at 4°C. Sampling was performed at specific time intervals for enumeration of the total viable counts (TVC, PCA), Pseudomonas spp. (CFC), yeasts and moulds (RBC), Brochothrix thermosphacta (STAA), lactic acid bacteria (MRS) and Enterobacteriaceae (VRBGA). The pH and colour (L*, a*, b* parameters), as well as the sensory properties of meat, such as odor and total appearance were also evaluated. The changes in glucose and organic acids (as potential biochemical spoilage indicators) of samples during storage were determined by HPLC (UV-RI) analysis. Under aerobic conditions Pseudomonas spp. was the dominant spoilage group, while lactic acid bacteria were the specific spoilage organisms in vacuum packaged meat. Vacuum packaging in combination with essential oil caused greater inhibition of spoilage microflora than aerobic storage. The 5% v/v concentration of oregano was the most efficient in delaying growth of specific spoilage microflora (2.5-3log cfu/g) compared to control samples, although it had negative impact on the sensory characteristics of the meat. Treatment with 1 and 2.5% oregano concentrations resulted in a satisfactory growth suppression of TVC (1 log cfu/g) compared to control samples, while maintaining a good visual appearance for the film and sensory quality of meat. Edible film alone showed no significant (p>0.05) antimicrobial activity. The colour was maintained stable during storage under vacuum, compared to air packaging where gradual decrease of redness (a* parameter) was observed. In addition, colour parameters (L*, a*, b*) were more stable during storage as the concentration of oregano increased, regardless of packaging type. Using edible films as a vessel for oregano essential oil can be an effective packaging method for delaying spoilage of pork under aerobic conditions, and can be more efficient in extending shelf life of meat, when combined with vacuum packaging. However, although increasing essential oil concentration (e.g., up to 5%) might maximize the antimicrobial effectiveness of edible coating, it may compromise the sensory properties of the coated meat.