Drying effect on flavonoid composition and antioxidant activity of immature kumquat

A seven flavonoids in hot water extract of immature kumquat (Citrus japonica var. margarita) were identified and quantified (mg/100 g fresh fruit): 3',5'-di-C-beta-glucopyranosylphloretin (DGPP, 285.9 +/- 2.9 mg/100 g), acacetin 8-C-neohesperidoside (margaritene, 136.2 +/- 2.6 mg/100 g), acacetin 6-C-neohesperidoside (isomargaritene, 119.1 +/- 1.8 mg/100 g), fortunellin (acacetin 7-O-neohesperidoside, 28.5 +/- 0.7 mg/100 g), apigenin 8-C-neohesperidoside (16.9 +/- 0.1 mg/100 g), poncirin (isosakuranetin 7-O-neohesperidoside, 5.1 +/- 0.1 mg/100 g), and rhoifolin (apigenin 7-O-neohesperidoside, 2.0 +/- 0.1 mg/100 g). When immature kumquat was dried at 110 and 130 degrees C for 0.5 h (h), the antioxidant activity, total phenolic content and identified flavonoids increased. The UV absorbance of browning products of immature kumquat dried at 130 degrees C for 1.5 h increased dramatically, while the identified flavonoids decreased. Therefore, it was concluded that drying below 130 degrees C for 1.0 h, could release phenolic compounds, which resulted in the increasing antioxidant activity. Drying at 130 degrees C for 1.5 h, it might be due to the effect of formed browning products. (C) 2014 Elsevier Ltd. All rights reserved.