酸水解对DNS法测定甜高粱中总糖的影响分析

Influence of Acid Hydrolysis on Total Sugar Determination in Sweet Sorghum by DNS Method

分析了酸水解对DNS法(3,5-dinitrosalicylicacid method)测定甜高粱中总糖产生影响的原因。通过对甜高粱浸提液水解后的糖组分检测发现:6 mol/L盐酸与糖液按体积比2∶1混合,沸水浴30 min会造成果糖完全分解。在这种条件下,利用DNS法测定葡萄糖、果糖和蔗糖时,测量值分别为理论值的100%、2.5%和52.2%。同时,果糖水解后的溶液会在高压液相图谱上出现葡萄糖伪峰,造成葡萄糖测定值偏高。酸浓度、水解时间以及水解温度均会对果糖与蔗糖的测定产生影响。实验结果表明:果糖在酸水解过程中发生分解是造成DNS法测定甜高粱中总糖产生误差的原因。采用DNS法测定含有果糖与蔗糖的原料总糖时,需要在保证蔗糖完全水解的情况下果糖不被破坏,否则会造成测定的不准确。

The reason of the influence of acid hydrolysis on total sugar determination in sweet sorghum by 3,5-dinitrosalicylicacid method was analyzed. Fructose could completely degrade when the ratio of 6 mol/L hydrochloric acid to sugar liquid was 2：1 in a boiling water bath for 30 rain. Under such conditions, the measured values of glucose, fructose and sucrose by DNS method were 100% , 2.5% and 52.2% of the corresponding theoretical values. Meanwhile, the fructose solution after hydrolysis appeared a pseudo- peak of glucose in the HPLCchromatogram, which caused glucose value higher than the real value. The determination of fructose and sucrose was impacted by the acid concentration, hydrolysis time and hydrolysis temperature. Fructose degradation during the acid hydrolysis caused the measurement error in the total sugar determination in sweet sorghum by DNS method. When determinate total sugar content in raw material contained fructose and sucrose by DNS method, it should ensure the complete hydrolysis of sucrose, and no degradation of fructose, otherwise it would result in inaccurate measurement