Effects of alkali concentration and conching temperature on antioxidant activity and physical properties of chocolate

The effects of alkalization on antioxidant activity and physical properties of chocolate were studied during conching using a chocolate recipe of the Indonesian Coffee and Cocoa Research Institute. The study was designed according to Response Surface Methodology in two variables. Alkali concentration and conching temperature were plotted in the range of 1 − 15 g kg-1 and 40 – 80°C, respectively. Parameters of the study were antioxidant activity, total polyphenol, chocolate hardness and fat melting point. The results of the study showed that antioxidant activity and polyphenol concentration were reduced as alkali concentration and temperature of conching were increased. Improvement of conching temperature from 40°C to 80°C with 1 g of sodium bicarbonate reduced antioxidant activity from 84% to 67%, and with 15 g of sodium bicarbonate the activity was reduced from 78% to 55%. Reduction of the antioxidant activity due to alkali improvement from 1 g to 15 g at conching temperature of 40°C and 80°C was calculated to be 7% and 18%, respectively. Reduction of the polyphenol antioxidant activity was suggested to be triggered by heat and alkali synergistically. However, a better chocolate quality in terms of hardness and significant antioxidant activity was obtained through application of alkalization with alkali concentrations between 5 to 12 g kg-1 and conching with temperatures up to 68°C.