The removal of psychrotropic spores from milk protein isolate feeds using tubular ceramic microfilters

The application of microfiltration (MF) to remove spores from high solids content (5-15 wt %) Milk protein isolate (MPI) solutions are reported as a possible alternative process to pasteurization. MPI feeds were inoculated with Bacillus mycoides spores as a safer alternative to Bacillus cereus found in dairy feeds. The protocol used led to successful filtration outcomes for 5 and 10 wt % feeds, with the most encouraging result for 10 wt % found using a 12.0-m membrane and 1.4m/s cross-flow velocity. This produced a flux of 123L m2/hr (LMH), a 90% protein transmission and a 2.6 log spore reduction. The filtration of 15 wt % MPI solutions proved more challenging. The best set of results for this feed was also obtained using a 12.0-m membrane at 1.4m/s, producing a flux of 27 LMH, 96.5% protein transmission and a 2.1 log spore reduction. These results indicate that large pore ceramic MF may be a suitable technology to replace or augment pasteurization for high solids content dairy feeds. PRACTICAL APPLICATIONS: Milk and other dairy products are highly nutritious media, in which microorganisms can cause spoilage. The use of microfiltration (MF) as an alternative to pasteurization to reduce the microbial load of raw skim milk is a well-established technology being used to produce commercially available products such as Cravendale milk. However, its application in reducing bacteria from highly viscous dairy-based solutions has not become established because of issues of low flux and high fouling tendency. The novelty in this study is the filtration of high solids content (up to 15 wt %) MPI streams to reduce microbial load. MF represents an attractive alternative processing technique to pasteurization for the treatment of dairy products. Whereas pasteurization only destroys heat-sensitive spoilage and pathogenic bacteria, MF is capable of removing all types of microorganisms including thermoduric and spore-forming bacteria. Moreover, MF can be carried out using lower temperatures than those used during pasteurization.