Subcritical hydrolysis of ice-cream wastewater: Modeling and functional properties of hydrolysate

The hydrolysis kinetics of ice-cream wastewater was studied under subcritical conditions (130-230 °C and 20-60 bar) in a continuous stirred-tank reactor. The kinetic was monitored by measuring the degree of hydrolysis (DH, %) at different time intervals (up to 240 min). Samples of ice-cream wastewater were collected from the university dairy plant after a typical clean-in-place protocol. Overall, the reaction time and temperature significantly increased the DH, reaching a maximum value of 40.99 ± 0.81, 34.44 ± 0.47, 20.61 ± 0.42, and 5.74 ± 0.36% after 200-240 min at 130, 170, 200 and 230 °C, respectively. The experimental data were modeled using the Weibull distribution model showing a satisfactory correlation between experimental data and predicted values (R2 = 0.971). The apparent activation energy for subcritical hydrolysis was 37.53 ± 5.21 kJ mol−1. After 240 min of reaction, the hydrolyzates were recovered, and their antiradical ability was measured through free radical scavenging (2,2-diphenyl-1-picrylhydrazyl) method. Additionally, the angiotensin converting enzyme (ACE)-inhibitory ability was determined. The inhibition of a free radical was found to increase linearly with the DH (R2 = 0.991). The hydrolysate recovered at 230 °C showed the highest ACE-inhibitory ability (98.0 ± 1.6%). The study outcomes present an opportunity for utilizing subcritical hydrolysis to convert wastewater into valuable materials.