Kinetic Modeling of Amino Acid Production from Ice-Cream Wastewater in Subcritical Conditions

Wastewater derived from ice-cream manufacture contains high concentration of protein, making it a suitable feedstock for hydrolysis. In this study, ice-cream wastewater was hydrolyzed under subcritical conditions (170–230 °C and 40 bars) and different nominal pH (3, 6, and 9) to produce amino acids. The formation and subsequent degradation of amino acids were modeled using a two-consecutive reaction model. Apparent activation energy for the formation and degradation of amino acids varied from 41 to 83 and 33 to 59 kJ/mol, respectively, changing with the nominal pH. The amino acid profile showed 21 amino acids, whose concentration was strongly influenced by the reaction conditions. The maximum concentration of amino acids was found within the first 50 min at 170 °C and nominal pH 3. After 50 min, a mixture of amino acids was obtained mainly made of glutamic acid (20–30%), proline (9–12%), aspartic (3–10%), and leucine (9–12%), showing slight variation with the nominal pH. Subcritical hydrolysis of ice-cream wastewater showed to be an effective alternative to produce amino acids that can be used as platform chemicals.