Change in the composition of the microflora on vacuum-packaged beef during chiller storage

Abstract

Five fresh beef cut samples were divided into 10 pieces, respectively, vacuum-packaged and stored at 2 °C for up to 6 weeks. The average pH values of five pieces from five beef samples were 5.62±0.04 at the start of storage and 5.12±0.07 after 6 weeks of storage. The pieces were homogenized, diluted and cultivated at weekly intervals on glucose–blood–liver (BL), de Man Rogosa and Sharpe (MRS) and trypticase soya (TS) agars at 7 °C for 10–14 days. From plates with 30–300 colonies, or the highest number if below 30, 15 colonies were randomly picked from each of the three media used for each beef sample. Based on morphologies, SDS-PAGE whole-cell protein profiles and physio-chemical characteristics, a total of 1493 strains isolated were identified as Brochothrix thermosphacta (64), Carnobacterium divergens (79), Carnobacterium piscicola (27), Lactobacillus algidus (637), Lactobacillus sp. (4), Lactococcus piscium (270), Leuconostoc gelidum (375), Acinetobacter (3), Aeromonas (1), Bacillus (10), Corynebacterium (3), Enterobacteriaceae (1), Pseudomonas (13) or Psychrobacter (6). A wider range of organisms was isolated from TS (13 organisms) and BL (7) agars than from MRS agar (3). Leuc. gelidum, Lc. piscium and L. algidus increased in numbers during the first 3 weeks of storage from about 5×10 3 cfu/g to the level of about 10 8 cfu/g and persisted at this level thereafter. C. divergens and C. piscicola were inconsistently detected, but seemed to persist at the relatively low level of about 5×10 7 cfu/g during the last 3 weeks of storage. B. thermosphacta increased to the level of about 7×10 5 cfu/g during the first 2 weeks of storage, but was not detected thereafter. Remaining organisms were detected sporadically at levels of <3.5×10 2 cfu/g during the first 2 weeks of storage.