46C-29 |
Free fatty acid development and lipid oxidation on milled rice |
H. S. LAM, Food Science, University of Arkansas, 2650 N. Young Ave., Fayetteville, AR 72704 and A. Proctor. Milled rice surface free fatty acid (FFA) levels are used commercially as a predictor of rancidity. The FFA is derived from hydrolysis of acylglycerides in residual surface bran lipids and are more readily oxidized than acylglycerides. This is of particular importance in the brewing industry where FFA levels (> 0.1%) significantly affect product flavor quality. The objective of this study was to understand the formation of FFA on milled rice at different temperatures and its relationship to lipid oxidation using wet chemistry and FTIR spectroscopic methods. Commercially milled long-grain rice was stored at 24°C, 37°C, and 50°C at 70% relative humidity for 50 days and sampled regularly to determine FFA and conjugated diene hydroperoxide (CD) content spectrophotometrically. Diffuse reflectance infrared spectroscopy (DRIFTS) was used to measure ester, FFA, and aldehyde carbonyls and spectral changes on milled rice surface. FFA initially increased rapidly and reached 0.1% with little changes in CD at 24°C, 37°C, and 50°C after 15, 3, and 10 days, respectively. FFA reached a level of 0.1% more quickly at 37°C as compared to 50°C and 24°C. Increasing FFA levels were accompanied by a corresponding increase in CD. FFA levels remained stable until around day 31, 20, and 18 at 24°C, 37°C, and 50°C, respectively, before increasing again rapidly. The rice DRIFTS spectra showed a decrease in the ester carbonyl stretch, increase in FFA carbonyl and increase in DRIFTS aldehyde carbonyl stretch as rancidity development progressed corresponding with FFA as determined by wet chemistry. At each temperature, there was an initial rapid increase in FFA followed by a slower but greater increase. CD formation followed FFA development showing the importance of storage and transport condition of milled rice on end product quality. Furthermore, the potential of FTIR as rapid means of evaluating rice quality was also demonstrated.
Session 46C, Food Chemistry: Lipids, antioxidants and emulsifiers
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