Abstract

CHARACTERIZATION OF A NOVEL TAYLOR-COUETTE ULTRAVIOLET REACTOR FOR NON-THERMAL PASTEURIZATION OF MILK

Rawa Abdul Redha Aziz* and Keith Warriner

Abstract

Disinfection of milk by a novel UV reactor based on Taylor-Couette vortex flow has been evaluated as part of an effort to develop nonthermal 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 flowpattern of the milk passing through the reactor. The highest level of microbial inactivation was achieved at the transition from laminar wavy vortices (WV) to laminar modulated wavy vortices (MWV). The stability of the generated Taylor-Couette vortices could be enhanced when 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 1 log cfu reduction in numbers could be achieved under optimal operating conditions. The poor stability of generated vortices coupled with UV absorption effects of milk constituents would limit the application of the reactor for nonthermal pasteurization of opaque fluids.

Keywords: Ultraviolet, Taylor-Couette reactor, MWV, pasteurization.