Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

Marie K. Walsh

Abstract

The effects of thermosonication (high intensity ultrasound coupled with thermal treatment), on the reduction of thermophilic spore-forming microorganisms and its effects on the solubility index in reconstituted skim milk powder (RSMP) were evaluated. Thermosonication was applied to RSMP at various solids concentrations, temperatures, and lengths of time based on commercial milk powder processing conditions. Microbial counts were determined prior to and after treatments to determine the log reduction of Geobacillus stearothermophilusvegetative cells and spores. Log reductions were recorded, and data were analyzed by response surface analysis. The log reductions induced by temperature and time without high intensity ultrasound (HIU) were compared to reductions observed with HIU. Thermosonication was also applied to RSMP to determine effects on solubility using a continuous flow cell system. Thermosonication yielded a significantly higher level of microbial destruction for both vegetative cells and spores than heat treatment alone. For experiments involving vegetative cells, the interaction of treatment time and temperature proved to have the greatest influence on microbial inactivation. In comparison, the interaction of total solids content and length of HIU treatment demonstrated the greatest effect on the increased log reductions for spores. The solubility of RSMP treated with HIU did not significantly differ from the solubility of RSMP not treated with HIU. Further data showed the implementation of HIU, or thermosonication, during milk powder processing would be most effective before and after the evaporation stage when the total solids content of product is 9.2% and 50% at 75°C and 60°C, respectively. Based on preliminary data, it is assumed HIU applied for 10 s at these two locations would produce an additive effect, thereby reducing overall microbial counts by 5.76 log and 0.51 log for G. stearothermophilus vegetative cells and spores, respectively, in the product prior to entering the drying stage. All research findings and observations suggest HIU, or thermosonication, to be a successful method for reducing microbial populations during milk powder processing without sacrificing skim milk powder solubility

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