Investigation into Antimicrobial Activity and Its Stability of Protein Hydrolysate Derived from Earthworms

Abstract

This study utilized the earthworm (Perionyx excavatus) to generate antimicrobial protein hydrolysate. Alcalase hydrolysis was carried out under the condition including the earthworm:phosphate buffer ratio of 1:6 (w/v), 50 °C, pH 7.5, enzyme:substrate (E:S) ratio of 500 U/g protein, and 3 h of hydrolysis so that the earthworm protein hydrolysate exhibited the highest antimicrobial capacity against Escherichia coli and Bacillus subtilis. The inhibition zone diameter (IZD) against E. coli and B. subtilis were 11.33 ± 0.58 mm and 10.67 ± 0.58 mm, in order; and their minimum inhibitory concentration (MIC) was 0.5 mg/mL for both bacteria. The hydrolysate was further fractionated using ultrafiltration to recover 5 fractions of > 30 kDa, 10-30 kDa, 3-10 kDa, 1-3 kDa and < 1 kDa for testing their antimicrobial activity. The greatest antimicrobial activity was found at the 1-3 kDa fraction, with its IZD against the E. coli and B. subtilis 2.25 and 1.46 folds lower than that of Ciprofloxacin, in that order. The hydrolysate's antimicrobial activity remained over 55 % after pH treatment in the range from 1 to 11, or after being heated at 100 (C for 180 min. The findings indicate that the earthworm-derived hydrolysate and/or its peptide fractions could be employed as natural versatile antimicrobial agents for different purposes.