Microwave-assisted acid hydrolysis of konjac products for determining the konjac powder content

The complete hydrolysis of konjac glucomannan (KGM) with an acid or enzyme generally takes a long time. To accelerate KGM hydrolysis without diminishing the conventional quality, a diluted acid hydrolysis of KGM with sulfuric acid was conducted using a microwave digestion system. The optimum conditions of microwave-assisted acid hydrolysis for KGM were: 10 mL of 0.25 M sulfuric acid, hydrolysis temperature of 135°C (microwave power of 600 W), and total microwave-irradiation time of 45 min. The yields of the component sugars, mannose and glucose, from two konjac powders were similar to those by conventional acid hydrolysis with 1 M sulfuric acid in a boiling water bath for 5 h. Furthermore, a pretest for microwave-assisted acid hydrolysis using mixtures of konjac powder and starch at different ratios proved that their konjac content can be calculated by determining the mannose generated by the new rapid hydrolysis method, if the raw materials are provided.