Effect of lactic acid bacteria on the quality of beef hamburger under different storage conditions

Meat products and meat preparations are very sensitive to external factors such as temperature and are good substrates for microbial growth and biochemical processes that occur during storage. The aim of this work was to study the effect of a selected lactic acid bacteria formulation (LAB) on the microbiological characteristics and colour of beef hamburgers stored at different temperatures. Two batches of hamburgers (average weight of about 100g) were prepared: one with the addition of LAB (Lactococcus lactis ssp. lactis, strain 340; L. lactis ssp. lactis, strain 16; Lactobacillus casei ssp. casei, strain 208 and Enterococcus faecium strain 614 in a ratio lac- tococci:lactobacilli:enterococci of 2:1:1; level of inoculum 107 cfu g1) and one without (NO LAB), in three replicates done in three different days. For each batch, a subset of samples was stored under proper conditions (4C) and the other at 40C (temperature abuse conditions, to mimic inadequate storage conditions after purchase by consumer) both for 5 hours. After 5 hours, each subset was further divided into two subgroups: one maintained at 4 C and the other at 10 C. All hamburgers were evaluated on day-0, day-1, day-3, and day-5 for the following microbiological parameters (Staphylococcus spp., enterococci, Lactococcus spp., Lactobacillus spp., total mesophilic aerobes, Pseudomonas spp., total coliforms) according to standard methods; moreover colorimetric measurements were performed with Colorimeter - Digital Color Picker for iOS 10, under a 6500K light, with the CIELAB system, by taking three readings for each sample. The arithmetic means within each sampling was computed, subsequently all data (geometric mean for microbiological data) were elaborated with GraphPad InStat, 3.0b and GraphPad Prism 6.0d for Mac OS X. Two way analysis of vari- ance (ANOVA) followed by the Tukey's multiple comparisons test was performed. On day-5, all batches with LAB kept at abuse temperature and stored at 4 C had a higher blue-yel- low, green-red and lightness coordinates compared to the batches made without LAB maintained at the same condi- tions. On day-5 Pseudomonas spp. (PS103) counts were sig- nificant lower (p<.05) in all batches made with LAB; Staphylococcus spp. (BP) counts were significant lower (p<.05) in batches made with LAB in abuse conditions. In conclusion, the application of the proposed LAB formula- tion maintains hamburgers quality standards and can be a potential tool to increase their shelf-life.