Shelf life extending of probiotic beef patties with polylactic acid-ajwain essential oil films and stress effects on Bacillus coagulans

Meat and meat products are prone to the microbial and chemical spoilage, due to the high nutritional content. This study investigated the effect of polylactic acid (PLA) films incorporated with ajwain essential oil (AEO) on microbial (total viable count [TVC], psychrotrophic bacterial count [PTC], Enterobacteriaceae, Pseudomonas spp., yeast and mold (Y&M), and also Bacillus coagulans [BCG]), chemical (pH, peroxide value [PV], thiobarbituric acid-reactive substance [TBARS], and TVN values), and sensorial properties of beef patties, as well as survivability of BCG during refrigerated storage. Results showed that all microbial counts of samples were significantly increased, except BCG, during storage but the lowest TVC of samples was achieved in samples wrapped with PLA-1% AEO (8 log colony forming units per gram [CFU/g]) at 12th of storage, which is significantly lower than control treatments (10.66 log CFU/g). The best results in all treatments are those wrapped by PLA-1% AEO in all evaluated characteristics. At the final day of storage, PTC (8.82 log CFU/g), Enterobacteriaceae (5.05 log CFU/g), Pseudomonas spp. (9.08 log CFU/g), Y&M (4.69 log CFU/g), and also pH (4.5), PV (5.12 meq/kg), TBARS (2.92 MDA/kg), and TVN (14.43 mgN/100 g) values of PLA-1% AEO treatments were significantly lower than control samples. AEO-PLA films reduce the survival of BCG in raw patties, which reached 6.19 log CFU/g in PLA-1% AEO treatments, although increasing the concentration of AEO in packaging PLA films led to the maintenance of BCG viability during the cooking process by increasing the AEO in PLA films. Overall, results showed shelf life of beef patties is extended 3 days more (150%) by wrapping with PLA films incorporated with 1% AEO.