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.

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.

Influence of microwave roasting on positional distribution of fatty acids of triacylglycerols and phospholipids in sunflower seeds (Helianthus annuus L.)Whole sunflower seeds were exposed to microwave roasting for 6, 12, 20 or 30 min at a frequency of 2450 MHz. The kernels were then separated from the sunflower seeds, and the lipid components and the positional distribution of fatty acids in triacylglycerols (TAGs) and phospholipids (PLs) were investigated. Major lipid components were TAGs and PLs, while steryl esters, free fatty acids and diacylglycerols were also present in minor proportions. The greatest PL losses (p < 0.05) were observed in phosphatidyl ethanolamine, followed by phosphatidyl choline or phosphatidyl inositol. Significant differences (p < 0.05) in fatty acid distributions occurred (with few exceptions) when sunflower seeds were microwaved for 20 min or more. Nevertheless, the principal characteristics for the positional distribution of fatty acids still remained after 20 min of microwave roasting; unsaturated fatty acids, especially linoleic, were predominantly concentrated in the sn-2-position and saturated fatty acids, especially stearic and palmitic acids, primarily occupied the sn-1-or sn-3-position. These results indicate that no significant changes in fatty acid distribution of TAGs and PLs would occur within 12 min of microwave roasting, ensuring that a good-quality product would be attained.

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