Effects of Ohmic Heating on Microbial Counts and Denaturation of Proteins in Milk

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The objective of this study was to compare the inactivation effects of ohmic heating (internal heating by electric current) and conventional heating (external heating by hot water) on viable aerobes and Streptococcus thermophilus 2646 in milk under identical temperature history conditions. The effects of the two treatments on quality of milk were also compared by assessing degrees of protein denaturation in raw milk and sterilized milk (raw milk being sterilized by ohmic heating or conventional heating). It was found that microbial counts and calculated decimal reduction time (D value) resulting from ohmic heating were significantly lower than those resulting from conventional heating. There was no difference in degrees of protein denaturation during the two treatments. The results suggested that ohmic heating had not only a lethal thermal effect but also a lethal nonthermal effect due to the electric current on microorganisms. Based on the results, we propose that ohmic heating can be effectively used to pasteurize milk with no additional protein deterioration.
2008-03-01