Technological optimization of enzymatic hydrolysis of dead pork and ultrasonic pretreatment

Abstract: The utilization of the dead livestock and poultry resources is an important way to solve the pollution of livestock and poultry mortality. To study enzymatic hydrolysis conditions of dead pork, in this paper, the pork as experimental raw material, the trypsin as experiment enzyme, the effects of several operating parameters, namely enzyme concentration, substrate concentration, initial hydrolysis pH value and hydrolysis temperature, were studied taking the degree of hydrolysis as criterion by single-factor method. The conditions for trypsin hydrolysis of pork were preliminarily determined by 4 main factors of pork enzymatic hydrolysis tests. The influence law of the 4 main factors on the enzymatic hydrolysis was analyzed. Subsequently, response surface methodology (RSM) based on a three-level, four-variable Box-Behnken experimental design was employed to evaluate the interactive effects. A mathematical model was established, in which the degree of hydrolysis was as a function of 4 variables. The best enzymatic hydrolysis conditions were determined finally. By analysis on the surface plot of response surface model, the interactions of various factors were analyzed intuitively. On this basis, the effect of pork ultrasonic pretreatment on the enzymatic hydrolysis was studied, and the ultrasonic pretreatment conditions were as follows: ultrasonic frequency 20 kHz; ultrasonic power 500 W; ultrasonic time 20 min. The effect of ultrasonic pretreatment on the degree of hydrolysis was analyzed by scanning electron microscopy (SEM), and the microstructure change could be observed. The final test results showed that the order of the effect of 4 factors on the degree of hydrolysis was as follows: Enzyme dosage>hydrolysis temperature>initial hydrolysis pH value>substrate concentration. The optimum conditions for trypsin hydrolysis of pork in the selected experimental ranges were determined as follows: enzyme dosage of 1.15% (by mass), substrate concentration of 80.5 g/L, initial hydrolysis pH value of 7.96, and hydrolysis temperature of 40.6 ℃. The predicted degree of hydrolysis under these conditions was 16.74%, and the actual degree of hydrolysis was 16.77%, which showed that the experimental results were in agreement with the results of the software analysis. The optimal hydrolysis time was 6 h, and the degree of hydrolysis reached 28.91% at this point. After ultrasonic pretreatment, the optimal hydrolysis time was 4 h, and the degree of hydrolysis could reach up to 32.86% at this time. It could shorten the hydrolysis test cycle by 2 h, and improve the degree of hydrolysis by 4 percentage points under the condition of ultrasonic pretreatment. The reason that ultrasonic pretreatment enhanced the hydrolysis reaction was that protein chemical bond of pork was broken apart and the cell membrane was damaged by ultrasonic cavitation and mechanical action, then the contact probability between the enzyme and substrate was proved, and the enzymatic reaction was promoted finally. This study demonstrates that ultrasonic pretreatment can increase the hydrolysis efficiency of trypsin hydrolysis of pork and shorten hydrolysis time.