29B-21 |
Free fatty acid formation and subsequent development of lipid oxidation products in stored milled rice |
H. S. LAM, Food Science, University of Arkansas, 2650 N. Young Ave., Fayetteville, AR 72704 and A. Proctor, Food Science, Univ. of Arkansas, 2650 Young Ave., Fayetteville, 72704. Rice is an important adjunct for brewing. However, rice lipid from residual rice bran can impart off flavors by undergoing lipid hydrolysis and subsequent oxidation during storage. Therefore, free fatty acid levels are used as indicator of off-flavor volatile development. Understanding the changes in free fatty acids (FFA) and volatile oxidation products of milled rice is important in identifying the sources of off flavors and correlation with sensory quality. The objective of this study was to observe the changes in the total FFA and FFA profiles of milled rice with storage and relate FFA breakdown volatile oxidation product development to aroma. Milled rice was stored at 37oC and 70% relative humidity for 50 days and sampled 12 times on a regular basis. Rice surface lipid was extracted in propan-2-ol and fractionated in an SPE column. The fatty acid fraction was analyzed on a reverse phase HPLC. Rice volatiles were extracted from headspace with SPME fiber for 30 minutes at 30oC with agitation and analyzed by GC-MS. Aroma values of the main volatiles identified were calculated based on the published flavor threshold values. Oleic, linoleic and palmitic FFA levels increased much more than stearic and linolenic acids and contributed most significantly to the total rice FFA. More than twenty volatiles, including aldehydes, ketones, alcohols, furans, acids and alkanes were identified from headspace analysis. Nonenal, hexanal and octanal were the most significant volatile formed and showed the highest aroma values of the volatiles measured. Oleic and linoleic acid oxidation products, nonenal, hexanal and octanal contributed most significantly towards milled rice rancidity. Identification of flavor volatiles and their aroma values allows important volatile components to be used as sensory and chemical markers and to establish baseline data for stored rice quality control.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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