The influence of headspace and dissolved oxygen level on growth and haemolytic BL enterotoxin production of a psychrotolerant Bacillus weihenstephanensis isolate on potato based ready-to-eat food products Original Research Article

The major objective of this study was to determine the influence of the initial headspace and dissolved O2 level and vacuum packaging on growth and diarrhoeal enterotoxin production by Bacillus weihenstephanensis on potato based ready-to-eat food products. In general, the lower the initial headspace or dissolved O2 level the slower the maximum growth rate (μmax, log10 CFU g−1 d−1), the longer the lag phase duration (λ, d) and the smaller the maximum population density (Nmax, log10 CFU g−1) became. The slowest μmax, the longest λ and the smallest Nmax were generally found for growth under vacuum packaging. This implies shorter shelf-lives will occur at higher initial headspace or dissolved O2 levels as the growth of B. weihenstephanensis to the infective dose of 105 CFU g−1 in such atmospheres takes a shorter time. Significant consumption of dissolved O2 only occurred when growth shifted from the lag to the exponential phase and growth generally transitioned from the exponential to the stationary phase when the dissolved O2 levels fell below ca. 75 ppb. Diarrhoeal enterotoxin production (determined via detection of the L2 component of haemolytic BL) was similar for growth under initial headspace O2 levels of 1–20.9%, and was only reduced when growth took place under vacuum packaging. The reduction in L2 production when growth took place under vacuum was most probably related to the low final cell densities observed under this condition. Both growth and L2 production were inhibited over a 32-day incubation period at 7 °C by 40% CO2 irrespective of the headspace or dissolved O2 levels. The results illustrate the importance of residual O2 and CO2 on the shelf-stability and safety of modified atmosphere packaged potato based ready-to-eat food products with regards to B. weihenstephanensis.