Abstract:
The objectives of this research were 1) to determine the optimum condition for the production of Beta-limit dextrin having various average molecular weights from mung bean starch by using Alpha- and Beta-amylase, 2) to study the chemical and physical properties fo the Beta-limit dextrin and 3) to study the relationship between the flow behavior and average molecular weight of Beta-limit dextrin. The results showed that the optimum condition of mung bean starch hydrolysis by Alpha-amylase in liquefaction stage was pH of 5.0 and temparature of 90 C and that by Beta-amylase in saccharification stage was pH of 5.5, temparature of 60 C and the ratio of Beta-amylase to dry starch of 12.86 KU/100 grams for 48 hours. These conditions were used for Beta-limit dextrin production. To produce Beta-limit dextrin, 20 g/dl mung bean starch suspension was liquefied with Alpha-amylase and for 30 minutes using the ratio of Alpha-amylase to dry starch of 3.32, 6.64, 9.96, 13.28 and 16.60 KNU to 100 grams. Then, the liquefied starch was saccharified with Beta-amylase resulting in dextrin mixture. To obtain Beta-limit dextrin, the dextrin mixture was dialyzed at molecular weight cut off of 12,000. The Beta-limit dextrin had the number average molecular weight of 277363,23588,22645,17784 and 17738, the dextrose equivalent of 11.50, 11.90,11.80,13.90 and 13.40, and the intrinsic viscosity of 11.39, 9.70, 8.89, 7.62 and 7.33 ml/g, respectively. The yield of Beta-limit dextrin was 20-30 % on dry basis. At 25 C, the 10 g/dl B-limit dextrin solution was found to be Bingham plastic fluid having the yield stress of 703.28, 316.87, 216.91, 165.77 and 143.59 mPa., and the viscosity index of 6.69, 3.50, 3.41, 2.79 and 2.53 mPa.s for the number average molecular weight of 277363, 23588, 22645, 17783 and 17738, respectively.