Effect of thermal processing and protein nutrients on antioxidant activity of Tom-kha paste extract

Tom-kha or galangal coconut soup is the sixth order of top ten Thai foods. An ingredient of Tomkha paste has been addressed as natural antimicrobial and antioxidant activities. In order to verify the antioxidant activities in food system, the effect of thermal processing and protein, beef extract on antioxidant activities of ascorbic acid, gallic acid, Trolox, ρ-hydroxycinnamic acid and Tom-kha paste extract were determined. It was found that antioxidant activities of ascorbic acid were decreased while gallic acid and Tom-kha paste extract were not changed by heat treatment. Heating at 121 o C for 15 min, however, antioxidant activities of ρ-hydroxycinnamic acid were increased. After heat treatment, mixture of beef extract-Tom-kha paste extract, beef extract-ascorbic acid and beef extract-Trolox pronounced more antioxidant activity in term of DPPH assay. However, mixture of beef extract-gallic acid and beef extract-ρ-hydroxycinnamic acid had no change in DPPH activity after heating. Moreover, there was not change in ABTS assay in any mixtures after thermal process. FRAP activity, the mixture of beef extract-gallic acid, beef extract-ascorbic acid and beef extract-Trolox was decreased while beef extract-Tom-kha and beef extract-ρhydroxycinnamic acid were increased by heating 121 o C for 15 min. To sum up, thermal processing and protein nutrient did not reduce antioxidant activity of the Tom-kha paste extract. Therefore, in consuming Tom-kha soup may promote healthy benefit.