Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Ramu M. Rao

Second Advisor

Marlene Windhauser

Abstract

Freshly milled raw rice bran was stabilized with microwave heat for 3 min. Half of raw and treated bran were packed in Ziplock(c) bags and the other half vacuum packed. Half of the samples were stored at 4--5°C and the other half at 25°C for 16 weeks. The free fatty acid (FFA) content increased rapidly in raw rice bran samples vacuum packed and samples packed in Ziplock(c) bags store at 25°C from an initial amount of 2.5% to 54.3% and 48.1%, respectively. FFA level increased significantly in raw samples vacuum packed and packed in Ziplock (c) bags stored 4--5°C from an initial amount of 2.5% to 25.4% and 19.5%, respectively. Microwave heat stabilized samples stored at 25°C had a significant increase in FFA level from an initial amount of 2.8% to 11.6% and 10.9% respectively, for vacuum packed and samples stored in the Ziplock(c) bags. FFA in microwave heat stabilized samples stored 4--5°C did not increase during 16 weeks of storage. Rice bran lipoxygenase had optimum pH of 8.5 and optimum temperature of 25--30°C. Michaelis constant and maximum velocity were 0.097 mM and 0.847 dA/min, respectively. Lipoxygenase activity in microwave heat stabilized samples in Ziplock (c) bags or under vacuum and stored at 25°C showed a significant increase from an initial amount of 0.18 dA/min to 0.54 and 0.26 dA/min, respectively. Lipoxygenase activity for microwave heat stabilized samples packed in both packing methods did not change significantly from the initial amount of 0.18 dA/min to 0.15 dA/min and 0.14 dA/min when stored at 4--5°C at 12 weeks. A significant decrease to 0.08 dA/min and 0.07 dA/min was observed at week 16. Fatty acid composition, especially linoleic acid, did not show any significant changes for the microwave heat stabilized samples stored at 4--5°C. Proximate composition did not change except for moisture content which decreased significantly from an initial amount of 8.4% to 6.3%. No advantage was found to vacuum packing the samples. The combination of 4--5°C storage temperature and Ziplock(c) bags provided the best shelf-life for microwave heat stabilized rice bran during 16 weeks of storage, under the conditions employed in this study.

ISBN

9780599213142

Pages

146

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