Effects of microwave treatment on the oxidative stability of peanut (Arachis hypogaea) oils and the molecular species of their triacylglycerolsPeanut seeds (Arachis hypogaea) were roasted for 6, 12, 20, or 30 min at a frequency of 2450 MHz using a microwave oven. The quality characteristics and the compositions of the oils, i.e. their tocopherol distributions and the molecular species of the triacylglycerols (TAGs) were investigated. These results were compared with those of an unroasted oil sample. Only minor increases (p <0.05) in chemical and physical properties of the oils, such as the carbonyl value, the p-anisidine value and the color development occurred after a prolonged roasting period. Compared to the original level, more than 92 wt-% tocopherols remained after 30 min of roasting. A modified thin-layer chromatography argentation procedure provided 12 different groups of TAGs, based on both the degrees of unsaturation and the total fatty acid chain-length. Although significant increases (p <0.05) generated in these chemical and physical changes of the oils after 20 min of roasting, no significant loss (p >0.05) was observed in the molecular species of the TAGs during microwave roasting. These results indicate that phospholipids may be attributed to the quality characteristics of peanut oils during microwave roasting.

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Sesame seeds were roasted at different temperatures (180±220°C) using a domestic electric oven. The positional distribution of fatty acids in triacylglycerols (TAGs) and phosphatidylcholine (PC) isolated from total lipids in these seeds was investigated as well as the naturally occurring antioxidants that are present. Major lipid components were TAGs and phospholipids (PLs), while steryl esters (SEs), free fatty acids (FFAs) and sn-1,3-and sn-1,2-diacylglycerols (DAGs) were minor ones. Following roasting, a signi®cant increase (P < 0.05) was observed in FFAs and in both forms of DAG (primarily sn-1,3-DAG). The greatest PL losses (P < 0.05) were observed in phosphatidylethanolamine (PE), followed by PC and phosphatidylinositol (PI). On the other hand, the amounts of g-tocopherol and sesamin remained at over 80 and 90% respectively of the original levels after roasting at 220°C. The principal characteristics of the positional distribution of fatty acids were still retained after 25 min of roasting: unsaturated fatty acids, especially linoleic and/or oleic, were predominantly concentrated in the sn-2-position, and saturated fatty acids, especially stearic and/or palmitic, primarily occupied the sn-1-or sn-3-position. The results suggest that unsaturated fatty acids located in the sn-2-position are signi®cantly protected from oxidation during roasting at elevated temperatures.

Tea catechins inhibited TBARS accumulation in HepG2 cells, the order of effectiveness being (-)-epigallocatechin gallate (EGCG) > (-)-epigallocatechin (EGC) > or = (-)-epicatechin gallate (ECG) > (-)-epicatechin (EC). EGCG and EGC protected the depletion of alpha-tocopherol in the cells, and the glutathione content was enhanced by all four catechins. Moreover, all four catechins suppressed the formation of glutathione disulfide and the activation of glutathione peroxidase induced by tert-butylated hydroperoxide.

The content of tocopherols and oxidative quality of oils prepared from sunflower (Helianthus annuus L.) seeds roasted in a microwave ovenSunflower seeds (Helianthus annuus L.) were roasted for 6, 12, 20 or 30 min at a frequency of 2450 MHz using a domestic microwave oven. After the kernels were separated from the sunflower seeds, the quality characteristics and the compositions of the oils were investigated in relation to their tocopherol distributions, and they were further evaluated as compared with an unroasted oil sample. Only minor increases (p < 0.05) in chemical and physical changes of the oils, such as the carbonyl value, the p-anisidine value and the color development, occurred at a prolonged roasting period. Significant decrease (p < 0.05) was observed in the amounts of phospholipids in the oils after microwave roasting. Nevertheless, compared to the original level, more than 92 wt-% tocopherols still remained after 30 min of roasting. With a few exceptions, these results indicate that the exposure of sunflower seeds to microwaves for 12 min caused no significant (p < 0.05) loss or change in the content of tocopherols and polyunsaturated fatty acids in the kernels.