Effect of thermal treatments on antioxidative activity of selected vegetables
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Date
2014
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Punjab Agricultural University, Ludhiana
Abstract
The present study was undertaken to assess the effect of thermal treatments on the proximate composition and antioxidative compounds of selected vegetables namely: spinach beet, mustard leaves, cauliflower, peas, carrot and potato. The vegetables were subjected to five different thermal treatments i.e, boiling, steaming, pressure cooking, microwaving and sautéing. Raw and thermally treated vegetables were analyzed for proximate composition, total phenolic content (TPC), total flavonoid content (TFC), total carotenoids, β- carotene, ascorbic acid and antioxidant activity. Crude protein and fibre content of the vegetables cooked by the different cooking methods were slightly lower than that of the raw. In spinach beet, mustard leaves and potato the crude fat content was found to increase slightly by all the thermal treatments, but significantly (p<0.05) in case of spinach beet. All the thermally treated vegetables drastically lowered the vitamin C content. Among all the vegetables (raw and thermally treated), spinach beet (113.04) had exceptionally high total phenolic content, expressed as mg GAE/100g FW. TFC of the selected vegetables as expressed in mg QE/100g FW ranged from 0.12 to 33.9. TFC of spinach beet was found to be the highest among all the raw and thermally treated vegetables followed by mustard leaves and cauliflower. Total carotenoids content of the raw vegetables analyzed ranged from 0.18 to 12.13 mg/100g FW, with the lowest in potato and the highest in carrot. Thermal treatments of the vegetables significantly reduced the total carotenoids of all the vegetables except for carrot, in which the total carotenoids content was found to increase significantly (p<0.05). Among all the vegetables tested, mustard leaves showed the highest radical scavenging activity with an inhibition of 69.44 per cent whereas carrot had lowest activity with 11.20 per cent. Total antioxidant activity of spinach beet, mustard leaves, carrot and potato increased significantly (p<0.05) by all the thermal treatments compared to the raw counterparts. The study concluded that processing can enhance antioxidant potential of vegetables. Pressure cooking and boiling of vegetables are recommended for domestic cooking owing to the higher antioxidant activity retention.
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