Bacillus and Paenibacillus species associated with extended shelf life milk during processing and storage

Abstract

Characterisation of spore formers associated with extended shelf life milk was performed by analysing the bacteriological quality of milk samples collected at various processing stages and during storage. Isolates were identified with MALDI‐TOF‐MS. Milk had spore counts <2 log10 cfu/mL and 4 log10 cfu/mL during processing and storage, respectively. Bacillus pumilus dominated the bacterial population. Bacterial species were inoculated into sterile milk for a shelf life study, and the population change was observed over 42 days at 7 °C. Although the extended shelf life milk process was effective in reducing bacterial counts and species diversity, the presence of Bacillus cereus shows a potential safety problem in extended shelf life milk.

Short communication: Source tracking Bacillus cereus in an extended-shelf-life milk processing plant using partial sequencing of rpoB and multilocus sequence typing

“…Despite advancement in preservation and processing technologies, Bacillus cereus remains a shelf-life and consumer safety challenge for the dairy industry (Ranieri et al, 2012;Aouadhi et al, 2014;Mugadza and Buys, 2017a). Bacillus cereus is a ubiquitous sporeforming bacterium (Ranieri et al, 2012;Aouadhi et al, 2014) that is reported to produce various toxins responsible for diarrheal and emetic food poisoning (Hansen and Hendriksen, 2001;Bartoszewicz et al, 2008;Stenfors Arnesen et al, 2008).…”

“…Bacillus cereus is a ubiquitous sporeforming bacterium (Ranieri et al, 2012;Aouadhi et al, 2014) that is reported to produce various toxins responsible for diarrheal and emetic food poisoning (Hansen and Hendriksen, 2001;Bartoszewicz et al, 2008;Stenfors Arnesen et al, 2008). Studies conducted at an extended shelf-life (ESL) milk processing plant revealed the presence of psychrotrophic B. cereus in milk during processing as well as during storage and in filler nozzles after cleaning in place (CIP; Khoza, 2016;Mugadza and Buys, 2017a). A follow-up study on these B. cereus strains then showed close relatedness between these strains using repetitive element palindromic (rep) and 16S partial sequencing (Mugadza and Buys, 2017b).…”

“…Seven B. cereus isolates obtained from various sampling points in an ESL milk processing plant: ESL milk during shelf life (BC7, BC8), pasteurized milk (BC23, BC26), raw milk (BC24), as well as filler nozzles after CIP (BC5, BC29) and described in previous studies (Khoza, 2016;Mugadza and Buys, 2017a), were selected for sequencing. The isolates were selected based on previously described (GTG) 5 fingerprints (Mugadza and Buys, 2017b), ensuring representation of each sampling point.…”

Molecular characterization and biofilm formation potential of Bacillus subtilis and Bacillus velezensis in extended shelf-life milk processing line

“…Extended shelf-life (ESL) milk has the inherent characteristic of a shelf-life longer than that of HTST milk, and lacks the burnt flavor commonly associated with UHT milk (Mugadza and Buys, 2018). A temperature regimen that bridges the gap between HTST and UHT processing is employed in the processing of ESL milk (Lorenzen et al, 2011).…”

Extended shelf life milk processing: Effect of simulated cleaning in place on the germination and attachment of Bacillus cereus spores

“…Regardless of bactofugation and microfiltration significantly reducing spore formers in ESL milk, an increased amount of spore formers in the final product may indicate post‐processing contamination most likely from filler nozzles (Eneroth et al . 2001; Mugadza and Buys, 2018). This could be problematic as we showed in the viability assay that B. cereus spores survived simulated CIP treatment and had the potential of growing under refrigerated conditions over a prolonged period, that is at least 28 days.…”