Sub-critical Water Hydrolysis Treatment for Waste Squid Entrails and Production of Amino Acids, Organic Acids, and Fatty Acids

The study presented in this paper is focused on processing squid wastes by using sub-critical water extraction and hydrolysis to produce valuable substances. Using a small-scale batch reactor (9.0 cm3), squid entrails were treated with sub- and supercritical water without oxidants. Reaction conditions involved temperatures of 443–673 K, pressures 0.792–30.0 MPa, and reaction times 1–50 minutes. Fat and oil were extracted into sub-critical water very efficiently, and soluble proteins, organic acids, and amino acids were produced in the aqueous phase by a hydrolysis reaction. Even in the short reaction time of 5 min, more than 99% of solid were converted to those products in the temperature, which was higher than 550 K. Results showed a maximum total yield of sixteen amino acids of 0.1031 kg/kg dry entrails at 473 K (5 min), and a maximum total yield of seven organic acids of 0.055 kg/kg dry entrails at 553 K (40 min). Also the oil extracted with hexane included useful fatty acids. Our experimental results indicated that the sub-critical water treatment method is very efficient for converting waste squid entrails to valuable materials as resources for many other industries.