Microwave roasting effects on the oxidative stability of oils and molecular species of triacylglycerols in the kernels of pumpkin (Cucurbita spp.) seeds

Pumpkin (Cucurbita spp.) seeds of the two cultivars were exposed to microwaves for 6, 12, 20 or 30 min at a frequency of 2450 MHz using a microwave oven. After the kernels were separated from the whole pumpkin seeds, the quality characteristics and composition 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 for the two cultivars. Only minor increases (P<0.05)(P<0.05) in chemical changes of the oils, such as peroxide value, carbonyl value, p-anisidine value and thiobarbituric acid reactive substances (TBARS), occurred after a prolonged roasting period. Compared to the original level, more than 85% tocopherols remained after 20 min of roasting. Therefore, significant differences (P<0.05)(P<0.05) in fatty acid distributions were observed in the pumpkin seeds roasted for 20 min or more. A modified AgNO3-TLC procedure provided 11 different groups of TAG, based on both the degrees of unsaturation and the total fatty acid chain-length. With a few exceptions, microwave roasting for 12 min caused no significant (P>0.05)(P>0.05) loss or changes in the content of tocopherols and polyunsaturated fatty acids (PUFAs) in the kernels. These results contribute to further investigation of the functional properties of pumpkin seed products.