Comparison of direct steam injection and steam-jacketed heating in squid protein hydrolysis for energy consumption and hydrolysis performance

Direct steam injection (DSI) and conventional steam-jacketed (SJ) heating systems were compared for energy consumption and hydrolysis performance in producing squid hydrolysates (SH). Hydrolysis was carried out with endogenous enzymes at 55 °C for 90 min and native pH (6.5 ± 0.2), followed by pasteurization at 75 °C for 30 min. Hydrolysis performance was evaluated by monitoring the changes in viscosity, degree of hydrolysis (DH), and protein profile during the course of hydrolysis. The DSI heating process was more energy efficient than SJ heating with significantly less energy usage (∼30% energy reduction), shorter come-up times, and total processing time. While considerable fouling was evident with SJ heating, no fouling was observed with DSI heating. No appreciable differences in hydrolysis performance were observed between DSI and SJ heating, although the DSI-treated hydrolysate exhibited slightly lower values in viscosity and DH, as well as weaker protein band intensities due to dilution caused by steam condensation. The use of a steam filtration unit in DSI not only filtered the incoming steam, but also reduced condensation. Results suggest that DSI heating with steam filtration is an energy efficient and fouling-free process for preparing SH and potentially for other type of enzymatic protein hydrolysates.