Antibacterial and antioxidant capacity of egg white hydrolysates screened from proteolysis-­assisted high intensity ultrasound treatment

Abstract

The main purpose of this research was to investigate the effect of high-intensity ultrasound treatment on one-step proteolysis of egg white proteins (EWPs) using commercial food-grade protease Alcalase as well as evaluating antioxidant and antibacterial capacity of sonicated hydrolysates rich in bioactive peptides. Prior to the Alcalase proteolysis, a series of 10 % (w/w) egg white (EW) solution samples were exposed to ultrasonic waves in ultrasonic water bath with a frequency of 40 kHz during 15 min and ultrasound probe high-intensity with a frequency 20 kHz during 15 min. The sonicated EWP solutions were intensively hydrolysed by the addition the bacterial endopeptidase from Bacillus licheniformis, namely Alcalase in the amount of 2 % (w/w). The proteolysis was performed in a glass batch reactor with mechanical stirring at 240 rpm at optimum condition for Alcalase (50 °C and pH 8.0). Upon completion of the hydrolysis, the reaction mixture was cooled down to room temperature and centrifuged at 12,000×g for 10 min. The bioactive hydrolysate was finally collected by decantation and stored at 4 °C. The antioxidant capacity of bioactive hydrolysates was evaluated by measurements the oxidation of β-carotene linoleic acid emulsion and scavenging of hydroxyl radicals. The antibacterial capacity was estimated against Gram-positive bacteria (Staphylococcus aureus ATCC 25923) and Gram-negative bacteria (Escherichia coli ATCC 25922) by hydrolysates' susceptibility of agar diffusion. The hydrolysate derived by proteolysis-assited ultrasound probe (UPH) has shown to be most effective in oxidation of β-carotene linoleic acid emulsion compared to hydrolysate acquired by proteolysis-assited ultrasound bath (UBH). The values of inhibition of lipid peroxidation were 85.4±0.42 and 73.9±0.49% for UPH and UBH respectively. The both hydrolysates were found to be potent scavengers of hydroxyl radicals compared to the untreated EW and its hydrolysate. Namely, UPH and UBH hydroxyl radical scavenging activities were 61.6±0.18 and 62.3±0.22 %, respectively. The results acquired from this research pointed that EWP hydrolysates have an intense inhibitory activity on Gram-positive bacteria, poor on Gram-negative bacteria, especially UPH. The inhibition zone both sonicated hydrolysates were significantly greater that control. Minimal inhibitor concentration against S. aureus and E. coli of UPH was significantly higher than UBH (63.3±0.83 μg/mL and 79.1±1.04 μg/mL, respectively). This research emphasized that by proteolysis-assisted high intensity ultrasound treatment, received hydrolysate with improved antimicrobial and antioxidant activities can be promoted enhancing utilization of EWPs as bioactive component of dietary supplements. Likewise, the results have been indicated that the producing bioactive hydrolysates from intact EWPs were affected by the ultrasound treatment type.