Enzymatic Hydrolyzing Characteristics Of Buckwheat Starch

In order to get the Hydrolytic characteristics of buckwheat starch, merchandise buckwheat starch was selected as the materials of this research. The enzymatic hydrolysis conditions and kinetics characteristics of buckwheat hydrolysis reaction was studied based on the systematic analysis of particle shape, crystal configuration, paste property. The results were as follow:The hydrolysis conversion ratios of buckwheat starch were both above 99.5% with mesothermal-α-amylase and fungal-α-amylase. It shows that the hydrolysis conversion ratios were more effective when two kinds of enzyme mixed with different proportions. Taking DE value as an evaluation index, fungal-α-amylase had higher catalysis ability. The regress equation of buckwheat starch hydrolysis between hydrolysis degree and temperature(X₁), pH value(X₂), substrate concentration(X₃) and added amount of fungal-α-amylase was: Y=63.31^-1.80X₁+2.55X₂+0.79X₄^-1.44X₁2+1.95 X₁X₂^-1.41X₂2-0.27X₃². The optimal conditions of the hydrolysis were: pH 6.0, temperature 54℃, substrate concentration 5% and enzyme dose 130U·g^-1. The DE value of 65.80% was achieved. The initial period of fungal-α-amylase hydrolysis is a first order reaction, coinciding with Michaelis-Menten equation. The kinetics parameters Vm and Km were 1.587mg(·mL·min)^-1and 5.470mg·mL^-1 respectively. The optimal temperature of kinetics model is 303.15-333.15K, namely 30-60℃。Mesothermal-α-amylase and glucoamylase have significant synergistic effect on buckwheat starch hydrolysis. The suitable pH value was 5.2, and suitable temperature was 55℃. Hydrolysis catalyzed by above two kinds of enzymes accorded with Michaelis-Menten equation. The reaction Michaelis constant (Km) and the maximum rate (Vm) of Mesothermal-α-amylase were 21.200 mg·mL^-1 and 1.482 mg·(mL·min)^-1 respectively; those of glucoamylase were 3.131mg·mL^-1 and 0.600mg(·mL·min)^-1 respectively, and the inhibition constant (Ki ) was 0.283mg·mL^-1. The regress equation between hydrolysis degree and the amount of mesothermal-α-amylase before gelatinization(X₁), the amount of mesothermal-α-amylase after gelatinization (X₂), glucoamylase dose(X₃) and saccharification temperature( X₄) was Y = 93.2567+0.9146X₁+3.4612X₃+2.3846X₄^-1.1851X₁2-0.6738X₂2- 2.0413X₃2-2.9951X₄2+0.9694X₂X₄-0.9744X₃X₄. On the optimal conditions, namely, the amount of mesothermal-α-amylase before gelatinization 61.87-66.26U·g^-1, the amount of mesothermal-α-amylase after gelatinization 20.89-24.64U·g^-1, glucoamylase dose 30.98-37.14U·g^-1 and saccharification temperature 60.85-62.28℃, the hydrolysis degree could be over 90%.Buckwheat starch hydrolysis with high-temperature resistantα-amylase obey Michaelis-Menten equation, whose Michaelis constant(Km) and the maximum rate(Vm) were 4.967mg·mL^-1 and 0.345mg·(mL·min)^-1 respectively. The optimum liquefaction conditions were: substrate concentration 25%, temperature 83℃, pH 6.5,α-amylase dose 40U/g and liquefy time 15 minutes. On above optimized conditions, the DE value of liquefaction solution could be up to 89.87%. The optimum technology conditions of saccharification were: temperature 60℃, pH 4.5 and glucoamylase dose100U·g^-1. On these conditions, the DE value of hydrolysis could be up to 96.52%.