Date of Graduation

8-2019

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Ya-Jane Wang

Committee Member

Andy Mauromoustakos

Second Committee Member

Han-Seok Seo

Keywords

amylases, brown rice, germination, gluten-free, long-grain rice, protease, short-grain rice

Abstract

Gluten-free products from rice are gaining popularity among consumers because of its hypoallergenic characteristic. The absence of gluten results in inferior bread qualities such as hard texture, reduced volume and shorter shelf-life, which can be improved by the addition of external hydrolytic enzymes. Hydrolytic enzymes are activated during germination to stimulate plant growth, and hence these enzymes may function similarly to the external enzymes to improve gluten-free bread from brown rice. Therefore, the objective of this work was to investigate the activities of amylases and protease in germinated brown rice (GBR) from long-grain and short-grain rices under different germination conditions and their impacts on flour properties and bread qualities. Brown rice (BR) was germinated aerobically and anaerobically for 2 and 4 days, and then assayed for alpha-amylase, beta-amylase, alpha-glucosidase, and protease activities, chemical composition, physiochemical properties and starch size distribution. GBR from long-grain rices displayed greater enzyme activities, resulting in more changes in chemical composition, physiochemical properties and starch size distribution. Breads were prepared from GBR along with BR (control) of long-grain rice and evaluated for specific volume, texture, retrogradation, color and starch characteristics. The results showed that breads prepared from GBR flour showed a greater specific volume (4-10%), a reduced hardness (34-90%), and a lower starch retrogradation (66-90%) compared with the control. After stored for 5 days, breads prepared from GBR flour exhibited no change in specific volume and less hardness and retrogradation than the control bread, which was supported by the significant reduction of starch molecular size. In conclusion, the hydrolytic enzymes activated from germination significantly improved physicochemical properties of BR flour and consequently bread qualities. Furthermore, rice germinated under aerobic condition for 4 days exhibited better properties.

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