Degradation of Soy Sauce Cake by Subcritical Water Treatment

The present study investigates the degradation of soy sauce cake, which is the waste obtained during soy sauce manufacturing, in subcritical water (170-300 degrees C, 10 MPa). In the experiments performed at a constant temperature, the yields of the identified saccharides were lower than the total sugar yield. This suggested that saccharides were recovered mainly as oligomers. We performed a two-step experiment in which the holding temperature was 200 degrees C and 260 degrees C in the first and second steps, respectively. Most of the hemicellulose-derived saccharides were detected in the fraction treated at 200 degrees C, while glucose was detected in the fraction treated at both of the abovementioned temperatures. The total sugar yield in the aforementioned experiment was higher than that obtained in other experiments performed at a constant holding temperature, suggesting that stepwise elevation of the holding temperature facilitates the recovery of valuable compounds from biomass.