The Effect of Traditional Thermal Cooking Processes on Anthocyanin, Total Phenolic Content, Antioxidant Activity and Glycemic Index in Purple Waxy Corn
Keywords:Purple waxy corn, Traditional cooking, Anthocyanin, Antioxidant activities, Glycemic index
Purple corn (Zea mays L.) appears as dark purple in the husk, cob and kernel, which contain primarily anthocyanin. The traditional thermal cooking method of purple corn may probably affect the content of anthocyanin and antioxidant activities, as well as the glycemic index. Purple waxy corn fancy 111, both with and without ears, were boiled at 80, 90 and 100°C for 30 min. The proximate composition, total monomeric anthocyanin (TMA) content, total phenolic content, antioxidant activities as well as the glycemic index were all measured and determined. The results indicated there is no significant effect on proximate composition e.g. moisture content, ash, dietary fibre and protein for corn both with and without ears in any thermal process temperature. The carbohydrate content might be lesser than raw purple waxy corn due to leaching during the thermal process. The TMA content of the raw purple waxy corn contain 698.72±34.41
µg CGE/g DW. The TMA content of corn cooked with ears and without ears dropped to 321.43–371.12 and 245.10–278.54 µg CGE/g DW, respectively. Total phenolic content further decreased in 90°C cooked purple corn without ears (201.83±8.94 mg GAE/100 g DW). The higher temperature was able to cause the loss of anthocyanin content and total phenolic content which are related to DPPH assay and FRAP assay. Neither traditional thermal processing methods of purple corn with or without ears would have any effect on the glycemic index. The glycemic index for both traditional thermal processes of corn with or without ears is 95.8–97.2.
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