Subcritical hydrolysis of ice cream wastewater: Modeling and hydrolyzates properties.

Document Type


Publication Date



American Dairy Science Association


Journal of Dairy Science




Suppl. 2






ice cream wastewater, subcritical water, hydrolysis


Dairy industry generates large quantities of wastewater (WW) from their routine cleanup operations. During the manufacturing of ice cream, the amount of WW generated is estimated to be between 8 and 12 L per kg of product. Ice cream WW is a complex mixture of suspended solids, soluble material, dispersed particles of different size (proteins and emulsified fat), and residues of cleaning agents. Such WW have proved to be problematic for the receiving effluent treatment plant. A promising method for WW conversion involves the hydrolysis of the compounds forming the colloidal mixture under subcritical conditions, which results in compounds of a lower molecular size that can be separated and further convert into valuable chemicals. In this study, the hydrolysis of ice cream WW was studied under subcritical conditions. The subcritical hydrolysis of ice cream WW was studied at 130–230°C, 20–60 bar, and 0–240 min in a continuous stirred-tank reactor. The degree of hydrolysis (DH) at different time intervals was measured by spectrophotometric method. Samples of ice cream WW were collected from the university dairy plant after the first step of a typical clean-in-place. The total protein of the ice-cream WW were 7.79 ± 1.33 on dry basis. 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 = 0.981). After 240 min of reaction, the hydrolysates were recovered and their antiradical ability was measured through free radical scavenging (2,2-diphenyl-1-picrylhydrazyl) method. The inhibition of a free radical was found to increase linearly with the DH (R2 = 0.991). The study outcomes presents an opportunity for utilizing subcritical hydrolysis to convert wastewater into valuable materials.