Date of Graduation

12-2016

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Ruben O. Morawicki

Committee Member

Ya-Jane Wang

Second Committee Member

Danielle J. Carrier

Third Committee Member

Thomas A. Costello

Abstract

Grain sorghum is an underutilized crop despite many advantages to its cultivation. A drought-tolerant plant with many pest-resistant cultivars, its applications are limited by problems with nutrient availability, particularly protein digestibility. Digestibility of grain sorghum protein is reduced by antinutritional compounds in the grain like tannins and phytates, and by moist-heat cooking. Some of these concerns can be mitigated by how the grain is processed. Fermentation is one processing method that can improve digestibility. Fermentation can also concentrate protein in a substrate. In this experiment, grain sorghum was subjected to different treatments and used as a substrate for yeast fermentation. Two species of yeast were tested; common baker’s yeast (Saccharomyces cerevisiae), and an amylolytic strain (Lipomyces kononenkoae). Effects of pasteurization or sterilization of the substrate, nitrogen supplementation, amyloglucosidase addition, and co-culture with an amylolytic lactic acid bacteria Lactobacillus amylovorous were examined. After 48 hours of incubation, baker’s yeast samples treated with enzyme increased in crude protein, from 9% in unfermented grain to approximately 27% after treatment. Nitrogen supplementation accelerates protein enrichment and is a significant factor at 24 hours of fermentation. Pepsin digestibility of fermented samples was improved compared to thermally processed controls. Phytates increased in concentrated high-protein samples, but the ratio of phytate to protein was reduced by both yeasts. Both types of yeast increased pepsin digestibility of sorghum protein compared to thermally processed control samples. L. kononenkoae reduced phytates in the substrate, but did not enrich protein content. The lactic co-culture had no significant effect on measured responses, but decreased incidence of spoilage and contamination of the fermentation samples. A fermentation with baker’s yeast can concentrate sorghum protein in a substrate if the grain starch is hydrolyzed first, and can increase digestibility as well.

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