Effect of Alkaline Treatment on Color, Phenolic Composition and Antioxidant Property of Raisin

Alkaline treated raisin is one of the most important raisins produced from Bidaneh Sefid grape in large scale in Iran. In current research, effects of potassium carbonate on drying rate, antioxidant activity, total phenolics and color of raisin were investigated. Raisin was produced sun-dried (as control), cold and warm alkaline at four concentrations of 0.75, 1.5, 3 and 6 percent of potassium carbonate. Results indicated that by increasing concentration of potassium carbonate and using warm solution, drying time reduced. Furthermore, raisin pre-treatment highly affects on total phenolic content and antioxidant activity. The highest content of totol phenolic and antioxidant activity were observed in warm 6% potassium carbonate treated raisins. In addition, warm-alkaline treated raisin showed higher total phenolic and antioxidant activity in comparison to those of cold-alkaline treated raisins. Production method revealed a significant effect on color, drying rate and antioxidant properties of Bidaneh Sefid. It seems the higher speed of drying helped in marinating polyphenol content and higher antioxidant activity. Based on current result, pre-treatment of grape by warm potassium carbonate solutions at lower concentration is suggested for marinating phenolic compounds.