Lactic acid fermentation of food waste using integrated glucoamylase production

Commercial enzyme is usually needed for the bioconversion of organic waste or biomass. The overall cost could be reduced very significantly if enzyme production could be integrated with its application, avoiding unnecessary steps in enzyme production (such as concentration, recovery and transportation). This investigation attempted to integrate crude glucoamylase production with lactic acid fermentation of food waste. A maximum glucoamylase activity of 1850 U g^?1 was obtained with Aspergillus nigerduring solid‐state fermentation (SSF) of food waste, 14.8 times more than that obtained during submerged fermentation (SmF). The optimum pH for producing glucoamylase was 4.6, and glucoamylase retained 83.5% of peak activity at pH 3.0. Without any recovery treatment, the glucoamylase produced by SSF could be used directly for lactic acid fermentation of food waste. Lactic acid concentration reached 45.5 g L^?1 with the addition of the crude enzyme, 72% higher than the control. No side‐effects were caused by the viable A. niger in the crude enzyme. This work successfully integrated glucoamylase production with lactic acid fermentation. The enzyme produced by SSF of food waste had sufficient activity to be used directly without any treatment. The integrated process proposed in this study was very economical and may be helpful to other bioconversions. Copyright © 2008 Society of Chemical Industry