Incidence and survival of Bacillus sporothermodurans during processing of UHT milk

Abstract

The presence of Bacillus sporothermodurans in retail UHT milk along with milk from different points of a processing line was determined. The effect of chilling, preheating, UHT, reprocessing and H2O2 individually and in combination on the survival of B. sporothermodurans was also investigated in broth. Design/methodology/approach - Standard plate counts were conducted for all milk samples and isolates from UHT milk were characterised using PCR. BS vegetative cells and spores in broth were subjected to various stresses encountered during UHT processing of milk. Survival counts were conducted after all treatments. Findings - B. sporothermodurans was detected in retail UHT milk packs from only one processor. UHT treatment at 140 oC for 4s eliminated B. sporothermodurans in broth. The combination of chilling and UHT was more effective in eliminating sporothermodurans spores than UHT treatment alone. H2O2 was also effective in eliminating B. sporothermodurans spores after 15 min of exposure. The adopted real time (RT) PCR with SYBR Green method was effective for the confirmation of B. sporothermodurans. Originality/Value - This research is the first to be conducted with regards to the detection of B. sporothermodurans in UHT milk in South Africa and determining the effect of UHT processing stresses on their survival. These results can be used to design processing parameters so as to effectively eliminate B. sporothermodurans spores during UHT processing. This research is the first in which RT PCR with SYBR Green has been used to characterise B. sporothermodurans.