Optimization of fast maceration extraction of polished yellow konjac (Amorphophallus muelleri Blume) flour by Box-Behnken response surface methodology

Abstract

Polished yellow konjac (Amorphophallus muelleri Blume) flour (PYKF) from the centrifugal milling process still contains a relatively high level of impurities that may be harmful to health, especially calcium oxalate. The extraction process using ethanol is needed to reduce the amount of impurities surrounding the glucomannan granules and hence to improve the purity of the latter. This study was aimed at determining the effects of process conditions including ethanol concentration, solvent to flour ratio and extraction time on the physicochemical properties of purified yellow konjac flour (PrYKF) using Response Surface Methodology. The desired characteristics of PrYKF were low calcium oxalate content and a high degree of whiteness (DoW), viscosity, and glucomannan content. The calcium oxalate content, viscosity, and glucomannan content of PrYKF were affected by ethanol concentration, solvent to flour ratio, and extraction time. In contrast, the DoW was only affected by ethanol concentration. The prediction of the optimum condition by Design-Expert was found at 46.36% of ethanol concentration, 8.33 mL/g of solvent to flour ratio, and 63.01 mins. Under these conditions, the characteristics were as follows: 0.12±0.00%w.b. calcium oxalate, 68.76±0.00 DoW, 29012±0.00 cP viscosity, and 84.59±0.00% d.b. glucomannan content. The actual verification was closely related (p > 0.05) compared to the Design-Expert software prediction by paired t-test. The fast maceration is a successful method to improve the characteristics of PYKF to PrYKF in a shorter time.