Reducing Sugar Production in Sweet Potatoes Heated by Electromagnetic Radiation

The apparent reaction rate constant needed to generate reducing sugar was determined by heating a thin slice of sweet potato using thermal conductive heating. This value was used to predict reducing sugar production in sweet potatoes cooked by electromagnetic irradiation. The generation of reducing sugar in the thin slice was not observed at temperatures <65 degrees C or >85 degrees C, but it increased linearly during the early stage of heating. The Arrhenius plot had a peak of approximately 83 degrees C, allowing determination of the values for activation energy and frequency factor. Then, using the values obtained for apparent reaction rate constant, the yields of reducing sugar in sweet potatoes cooked by infrared (IR) and microwave (MW) heating were calculated and compared with experimental data. Although the calculated values exceeded the experimental values in the early stages of electromagnetic irradiative heating, the calculated amounts of reducing sugar generally agreed with the experimental values. Moreover, when the time needed to heat the sweet potato from 65 degrees C to 85 degrees C was longer than approximately 8 min, the yield of reducing sugar was maximized for both MW and IR heating. These results indicated that the yield of reducing sugar did not depend on the heat transfer mechanism and that the amount of reducing sugar produced in heat-treated sweet potatoes could be predicted.