Masters Theses

Hongyu Wu

Date of Award

12-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Greg Hulbert

Committee Members

John Mount, Luther Wilhelm

Abstract

Yogurt production was selected to study the effects of ultrasound on milk homogenization and fermentation. A microscope was used to check the size distribution of fat globules to evaluate ultrasound homogenization. The pH change during fermentation and the water holding capacity, viscosity and syneresis for finished yogurt were evaluated. It was found that ultrasound has a very good homogenization effect at high amplitude levels compared with conventional homogenization. Longer exposure times improved the ultrasound homogenization effect. If enough exposure time and amplitude level are provided, extremely small fat globules can be produced. The fermentation results showed that the method of sonicating bacteria had a significant effect on the pH change. Sonication after inoculation could reduce the total fermentation time by 0.5 hours. Ultrasound also significantly affected the water holding capacity, viscosity and syneresis. In general, increasing the ultrasound amplitude level improved the water holding capacity, and viscosity and reduced syneresis. However, sonication after inoculation did not decrease the syneresis effect. This may have been due to the lower pH of those samples.

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