Effect of Power Ultrasound on the Activity and Structure of Food-Grade Papain

Ultrasound (US) is an adaptable and innovative nonthermal technology that has received considerable attention since the application of ultrasonic energy can inactivate or activate many food-related enzymes by means of cavitation effects. Papain is a proteolytic enzyme widely used in the food industry. This research studied the effect of different US parameters on the activity of food-grade papain. The treatments included temperatures from 10 to 50 °C, amplitudes of 40 and 100%, and process times of 1, 5, 9, 13, and 17 min. Maximal inactivation (78.7%) was obtained after 17 min of ultrasound processing with an amplitude of 100% and 10 °C. Kinetic data showed that a thermal treatment at 72.1 °C and a nonthermal US treatment at 20 °C and an amplitude of 100% are equivalent in inactivating power for papain. The decrease in papain activity was accompanied by a significant decrease (5.6%) in protein solubility and a significant reduction (22.3%) in the sulfhydryl group content. The three US process factors (amplitude, time, and temperature) were important for the exposure of hydrophobic groups in papain and the decrease in the -SH group content to generate changes in structure and activity. The changes in the secondary structure of papain generated by the US treatment could be observed through fluorescence and infrared spectroscopy. This study showed that power US treatment, when operated at certain processing values, is an adequate method to modify papain activity and structure at room temperature.