Characterization of a novel Taylor-Couette ultraviolet reactor for non-thermal pasteurization of milk

Disinfection of milk by a novel UV reactor based on Taylor-Couette vortex flow was evaluated as part of an effort to develop non-thermal processing technology for pasteurizing milk. By using Bacillus subtilis endospores and bacteriophages as model microbes, it was demonstrated that level of inactivation was dependent on the flow-pattern of the milk passing through the reactor. The transition from laminar wavy vortices (WV) to laminar modulated wavy vortices (MWV) achieved 4.5log pfu reduction of Salmonella phages. Turbulent wavy vortices (TWV) achieved 5.8log cfu reduction of Bacillus subtilis endospores PS346. The stability of the generated Taylor-Couette vortices could be enhanced by increasing the viscosity of the milk although this did not translate to higher levels of microbial UV inactivation. Tryptophan and cysteine provided protection to the microbes by absorbing UV photons. Although the actual UV dose required to inactive Escherichia coli in milk was comparable to the efficacy of other reactors, only a l log cfu reduction in numbers could be achieved under optimal operating conditions. The results from this study would suggest to re-design Taylor Couette reactor to decrease the force of the flow rate and to generate stable vortices that could support efficient mixing, hence higher level of microbial inactivation.