Effect of thermophilic lactic acid bacteria on the viability of Salmonella serovar Typhimurium PT8 during milk fermentation and preparation of buffalo's yogurt

Abstract

Viability of dairy‐borne Salmonella enterica ssp. enterica serovar Typhimurium PT8 was studied during the fermentation of skim milk by thermophilic lactic acid bacteria (LAB). Longer generation times of Salmonella were found in mixed cultures of skim milk containing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus or a mixture of them (1:1), as compared with single cultures of the pathogen. Salmonella was less able to survive in mixed cultures with these LAB during prolonged incubation at 41°C and also during cold storage of the fermented milk. Lactobacillus ssp. bulgaricus and its mixture with S. thermophilus were more inhibitory to the growth and survival of Salmonella than was S. thermophilus. This was associated with higher ability of L. ssp. bulgaricus and the mixture to develop acidity in milk than S. thermophilus. Examining the antibacterial activity of these LAB towards Salmonella showed that other factors including heat‐resistant and heat‐labile compounds were involved in inhibiting the pathogen by these cultures. The viability of the same Salmonella strain during the preparation and cold storage of buffalo's yogurt was also examined. Salmonella was found to survive longer in yogurt made with starter containing probiotic bacteria than in that prepared with the traditional starter. This was ascribed to the development of lower pH by the traditional starter.

Survival and detection of coliforms, Enterobacteriaceae, and gram-negative bacteria in Greek yogurt

“…Notably, the 3 isolates showing moderate die-off were classified as Salmonella. By comparison, a previous study evaluating the viability of Salmonella in yogurt prepared with probiotic starter cultures reported a slight numerical increase in Salmonella numbers over the first 24 h of storage at 4°C (Nassib et al, 2006); after the initial 24 h, Nassib et al (2006) observed a >1 log reduction in viable Salmonella over the next 48 h of cold storage. On the other hand, the 3 Yersinia isolates tested in this study showed the ability to survive in Greek yogurt over 12 h with numerical increases ranging from 0.05 to 0.18 log.…”

Microbiological Quality and Safety of Commercial Market Yogurt in Giza, Egypt

“…contamination before and after storage (Table 1). Massa et al, 1997;Ng et al, 2011 demonstrated that the decrease in the microbial load may be attributed to various environmental stresses during food production and storage condition, or/and may be due to accumulation of some inhibitory metabolites such as organic acids produced during lactic acid fermentation, as recorded from pH shift, that slows down or stops the growth as recommended by Nassib et al, (2006)); Beitane and Klava, (2013), which can be also the results of decrease in pathogenic counts in yogurt samples. The antagonistic action of produced organic acid is believed to be (i) interference with the maintenance of cell membrane potential, (ii) inhibition of active transport, (iii) reduction of intracellular pH, and (iv) inhibition of various metabolites functions (Sarkar, 2007).…”

Bio Controlling of Yoghurt Using Bifidobacterium Bifidum and Lactis

“…Salmonella typhimurium can survive for up to 5 days at 4 ° C in both TY and BY when the yoghurt pH is < 4.5, but up to 10 days if pH is 4.5 or higher Hal-Haddad (2003). Nassib et al, (2006) found that Salmonella typhimurium survived longer in BY than TY, and this was due to the development of lower pH by traditional starters. In Table (4) all yoghurt samples showed increase in titratable acidity during the storage and the yoghurt fortified with probiotic strains should higher increase in the acidity than the traditional yoghurt and that may be one of the antimicrobial mechanisms the probiotic could use against the pathogenic microorganisms.…”