Inhibitory activity of some functional cultures toward common microbial contaminants in soft cheese manufactured from raw milk

Abstract

The inhibitory activity of Lb. plantarum NRC AM10, Lb. curvatus NBIMCC 3452, Lb. paracasei NRRL B-4560 and Lb. gasseri NRRL B-14168 were investigated against the microbial contaminants in raw milk soft cheese. Cultures were added at the level of 5 % in T1, T2, T3 and T4 respectively, and the control treatment made without starters. Microbial counts in raw milk sample showed 10.25, 6.85, 5.89, 4.76, 4.42, 4.44, 3.77, 3.64 and 3.46 log cfu/ml for total viable count, total coliforms, Staphylococci, moulds and yeasts, Enterococci, fecal coliforms, spore forming bacteria, psychrotrophic and Salmonella respectively. Some of microbial groups in control cheese were increased in the first 5 days of storage and others were increased until 10 days then all microbial groups were gradually decreased with extending storage period. Staphylococci reached to the lowest counts 3.11 log cfu/ml after 20 days, on contrast moulds and yeasts reached to the highest count 5.22 log cfu/ml at the end of storage period. The inhibition rate % (IR) were influenced by the variety of strain added in cheese treatments and the highest IR 32.58 and 33.96 % against total coliforms and Enterococci were recorded in the treatment containing Lb. plantarum NRC AM10 while the highest IR 25.84 % against fecal coliforms was recorded in the treatment containing Lb. curvatus NBIMCC 3452. Meanwhile, the IR 35.19 and 15.84 % were recorded against Salmonella and spore forming bacteria with strain Lb. gasseri NRRL B-14168. The strain Lb. paracasei NRRL B-4560 showed IR 42.23 and 44.4 % against Staphylococci and psychrotrophic respectively. Moulds and yeasts talked a revers trend of IR because of increasing the counts by acidity development. In conclusion, the only addition of functional cultures to control the growth and survival of pathogens in raw milk products is not enough to produce safe product. Use of pasteurized milk, good hygienic and good manufacturing practices are essential to reduce the risk of microbial contamination and health hazards in dairy products.