Effect of Microwave Irradiation on Acid-Catalyzed Hydrolysis of Starch

Recently, there has been growing interest in applying microwave heating to rapid thermal digestion prior to elemental and chemical analysis of inorganic and biological samples.1 Microwave heating involves direct absorption of energy by functional groups that bear ionic conductivity or a dipole rotational effect, and this energy is then released into the surrounding solution. This absorption of energy causes the functional groups involved to have higher reactivity with surrounding reactants than when they are simply incubated with the reactants at the same temperature. Because much debate still remains with regard to the contribution of the nonthermal effects of microwaves on hydrolysis, the present study examined the effects of isothermal microwave irradiation on the hydrolysis of starch.2 Starch (10%) suspended in dilute hydrochloric acid (0.5 M) was hydrolyzed using either microwave irradiation (a household microwave, 2.45-GHz microwaves, 10-μs pulses, 20-40% full power, temperature setting at 95 °C)3 or a traditional heating block (100 °C). The hydrolysis of starch to glucose was monitored using HPLC and gel filtration columns (see figure legends for details). For reactions under heated conditions, the starch suspension