Intensification of Shrimp Shell Deproteinization Using Subcritical Water: Comparison of Continuous Ultrafast Reactors with Microwave Treatment

Abstract

A green strategy employing only water as solvent has been adopted to obtain protein hydrolysates from residual shells of Litopenaeus vannamei generated as waste during the production of this species by aquaculture. The goal was to produce a protein hydrolysate through the fractionation of waste biomass, eliminating the need for conventional alkaline treatments and avoiding the environmental and operational issues associated with the use of strong bases. Subcritical water (sCW) refers to the water in the temperature range of 100–374℃ where high pressure (up to 220 bar) is applied to maintain water in the liquid state. At sCW conditions, the physico-chemical properties of water change significantly in comparison with water at ambient conditions; non-polar compounds can be extracted due to the changes of electrochemical properties, such as the decrease of dielectric constant and increase of ionic product of water. The ionic product of water increased from 10-14 at ambient temperature to 10-12 under subcritical conditions, increasing the concentrations of H+ and H3O- acting as an acid-like catalyst for hydrolysis reactions. Therefore, sCW can hydrolyze some compounds in matrices like shrimp shell, where proteins are released from the matrix and broken down into valuable peptides and free amino acids. A crustacean exoskeleton is constituted mostly by a three-layered cuticle of chitin (15-30%) with trapped minerals (40-60%), proteins (15-25%) and minor components like astaxanthin.