Analysis of volatile compounds and headspace oxygen and carbon dioxide in full fat soy flour

초록

Soy flour can be a good protein source and used to improve the color, texture and water binding capacity in baked products. The flavor quality of soy flour very often determine the quality of final products. A sensitive and reproducible method is thus necessary to monitor the off-odor in soy flour. The objective of this study was to analyze the changes of headspace oxygen and carbon dioxide and headspace volatile compounds from full fat soy flour stored at -20C dark, 60C dark and light. Seven g of full fat soy flour were put into serul bottles and sealed air-tightly with Teflon-coated septa and aluminum caps. Samples were kept at -20C dark, 60C dark or 60C light for 10 days. Volatile compounds were isolated by solid phase microextraction(SPME)-gas chromatigraphy(GC) and SPME-GC-mass selective detector(MS). The headspace oxygen and carbon dioxide were determined every other day for 10 days by GC with a thermal conductivity detector. The coefficient of variation for the headspace volatile compounds from soy flour by SPME was 4.8% in total peak area. As storage time increased from 0 to 10 days, total volatile compounds of sample stored at 60C under dark or light increased by 2.2 and 2.5 times, erspectively. Headspace oxygen of samples at 60C under dark or light for 10 days decreased by 4 and 5%, respectively, due to lipid oxidation and headspace carbon increased by 1.7 and 2.2%, respectively, due to the non-enzymatic browning reaction. Forty eight volatile compounds including 9 furan and pyrazine compounds were identified and detected in 60C dark and light samples. However, these compounds were not detected in the samples stored at -20C. Lipid oxidation and non-enzymatic browning reaction are responsible for the formation of volatile compounds and the changes of headspace oxygen and carbon dioxide in soy flour.