Recovery and liquefaction of nitrogen-containing component and minerals from food processing wastes of vinegar using subcritical water

In recent years, environmental problems such as production of industrial waste are getting worse in Japan. In particular, food processing residues are typically disposed of by spending a large amount of money. This paper studied the treatment of two by-products from vinegar production (rice bran and sake lees) using subcritical water and analyzing the extracted solution for functional ingredients. The results from sake lees showed that an operating temperature of 180 °C and a reaction time of 30 min solubilized 85% of the nitrogen-containing component (mainly protein) from the raw material into water-soluble peptides. When rice bran was used as the raw material the solubilization rate of the nitrogen-containing components was greatly decreased at a reaction temperature of 190 °C or higher. It was shown that calcium in the raw material caused the formation of water-insoluble complexes with amino acids and ammonia such as CaCN2. Subcritical water treatment was shown to be a useful technique to recover useful water-soluble components from residual solid biomass.