Effect of physical pretreatment of mixed food waste on protein hydrolysis and optimization of process conditions through response surface methodology

Physical pretreatment methods can improve the protein hydrolysis of food waste. This paper investigates the effects of three physical pretreatment methods of mixed food waste on the variance of soluble protein concentration. A higher thermal pretreatment temperature (95 ℃) can shorten the protein hydrolysis time to 12 h. A longer microwave pretreatment time (90 s) can shorten the protein hydrolysis time by 50%. Compared with these pretreatment methods, ultrasonic pretreatment (20 min) is more effective because the protein hydrolysis time is further shortened by 36 h and the protein hydrolysis rate is higher (ultrasonic: 82.4%, microwave: 77.8%, thermal: 78.8%). This paper also studies the effects of three ultrasonic factors by using the response surface methodology (RSM). The protein hydrolysis rate is 86.96% under optimal ultrasonic conditions: an acoustic energy density of 102 W/L, an ultrasonic time of 23 min, and an initial ultrasonic temperature of 33 ℃. The R² value and predicted R² of the RSM model are 0.9925 and 0.9162, respectively. The relative error between the actual value and the predicted value obtained from the RSM model is 1.24%. That means the protein hydrolysis rate of mixed food waste can be predicted by the proposed RSM model.