Combined effect of carbohydrate and thermal processing on antioxidant activity of galangal coconut-milk paste extract, Tom-Kha

Galangal coconut-milk soup or Tom-Kha is the sixth order of top ten Thai foods. The ingredients of Tom-Kha paste have been addressed in vitro system as natural antimicrobe and antioxidant. The effect of carbohydrate (glucose, sucrose and inulin) and thermal processing on antioxidant activities of gallic acid, p-hydroxycinnamic acid and Tom-Kha paste extract were determined to verify the antioxidant activities in food system. The results showed that antioxidant activity of gallic acid was decreased while that of Tom-kha paste extract was not changed by heat treatment. However, antioxidant activity of p-hydroxycinnamic acid was increased after heating. In term of mixture system, after heat treatment, glucose did not cause any negative effect on antioxidant activities of gallic acid, p-hydroxycinnamic acid and Tom-Kha paste extract, whereas sucrose caused a decrease on antioxidant activity of gallic acid. However, antioxidant activities of Tom-Kha paste extract and p-hydroxycinnamic acid were not reduced by the addition of carbohydrate.