Date of Award:

5-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Committee

Marie Walsh

Committee

Donald McMahon

Committee

Karin Allen

Abstract

Thermosonication is the application of soundwaves at temperatures ≥50°C. It can be used to improve functional properties, overall quality, and shelf life of dairy products. Milk is concentrated before being spray dried and currently milk concentration is limited by increased viscosity. Decreasing the viscosity of concentrates prior to spray drying could be economically beneficial to dairy processors. Results from this study showed that that thermosonication significantly reduced the viscosity of concentrates such as reconstituted milk protein concentrate (rMPC) and reconstituted skim milk powder (rSMP). This would allow for spray drying of these concentrates at a higher total solids with a lower viscosity.

Currently, the shelf of pasteurized fluid milk stored at refrigeration temperatures is 2-3 weeks and is limited due to bacterial growth during refrigerated storage. Increasing milk shelf life would potentially minimize product loss and consumers can enjoy their refrigerated milk for longer time. Some thermophilic bacterial cells and spores can survive high temperatures involved in dairy processes and decrease milk product quality. Minimizing losses due to product quality loss could potentially minimize losses for dairy producers and It would be beneficial to improve dairy product shelf life and quality by eliminating these microorganisms using thermosonication.

The effect of thermosonication at pasteurization temperatures on survival of total and thermophilic bacteria such as Geobacillus stearothermophilus, Anoxybacillus flavithermus, and Bacillus subtilis in both batch and continuous systems was studied. Results showed that thermosonication successfully reduced thermophilic bacterial cells but not spores. Moreover, the cell reductions observed may not have an impact on milk product quality. Thermosonication along with pasteurization successfully improved the milk microbial quality along with other quality indicators such as pH and free fatty acid (FFA) content. Milk shelf life was extended by 2 weeks and minimal changes in consumer acceptance of milk were observed. Thus, thermosonication along with pasteurization could be used to improve milk quality and shelf life and decrease the viscosity of milk concentrates.

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