Production of organic acids and amino acids from fish meat by sub-critical water hydrolysis

Fish meat was easily liquefied by hydrolysis under subcritical conditions without oxidants, and aqueous phase and water-insoluble phase containing oil and fat-like solid were formed. Lactic acid found in the raw fish meat (about 0.03 g/g-dry meat) was stable up to the reaction temperature 513 K (3.35 MPa). Pyroglutamic acid was produced with a yield of 0.095 kg/kg of dry meat by 30 min reaction at 553 K (6.42 MPa). Amino acids such as cystine, alanine, glycine, and leucine were produced in the temperature range 513-623 K with a maximum peak at 543 K. Amounts of cystine, alanine, glycine, and leucine produced in 5 min at 543 K (5.51 MPa) were 0.024, 0.013, 0. 009, and 0.004 kg/kg of dry meat, respectively. The oil extracted with hexane contained useful fatty acids such as eicosapentanoic acid (EPA) and docosahexianoic acid (DHA). Thus, subcritical water hydrolysis would be an efficient process for recovering useful substances from organic waste such as fish waste discarded from fish market.