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The purpose of this paper is to evaluate the prevalence of Bacillus sporothermodurans in UHT milk brands in South Africa and to analyse the level of proteolysis in UHT milk due to the growth of B. sporothermodurans during short-term and long-term storage.

Different brands and batches of commercially available retail UHT milk packages were bought from different supermarkets, during different seasons and tested for the presence of B. sporothermodurans. Sterile UHT milk was spiked with B. sporothermodurans vegetative cells and incubated at 37°C for up to 172 hours. Total plate counts, pH, spore counts, UHT milk proteolysis and the headspace volatiles dynamics were analysed at different intervals.

The contamination of retail UHT milk packages by B. sporothermodurans was found to be prevalent. The growth of B. sporothermodurans in spiked UHT milk reached a maximum of 1.9×105 cfu/ml; however, the significant proteolytic activity in UHT milk due to B. sporothermodurans only occurred long after the exponential growth phase had been attained. Furthermore, the growth of B. sporothermodurans in UHT milk did not lead to significant changes in the headspace volatile profiles of spiked UHT milk samples. Proteolytic activity in retail UHT milk packages, contaminated with B. sporothermodurans, was significantly higher when the use-by dates were reached.

Significant proteolysis in UHT milk means the assurance of high-quality UHT milk with extended storage stability for up to 10-12 months is compromised. Proteolysis of casein may lead to rapid sedimentation in UHT milk compared to UHT milk without sedimentation.

This paper is of interest to manufacturers because it raises the awareness that UHT milk containing B. sporothermodurans may not have the same storage stability when compared those without B. sporothermodurans. The presence of B. sporothermodurans in commercial UHT milk packages may lead to international and national trade restrictions for manufacturers.

The presence of Bacillus sporothermodurans in retail UHT milk along with milk from different points of a processing line was determined. This paper aims to investigate the effect of chilling, pre‐heating, UHT, reprocessing and H₂O₂ individually and in combination on the survival of B. sporothermodurans in broth.

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.

B. sporothermodurans was detected in retail UHT milk packs from only one processor. UHT treatment at 140°C for 4s eliminated B. sporothermodurans in broth. The combination of chilling and UHT was more effective in eliminating B. 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.

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.