Characterization of a salt-tolerant aminopeptidase from marine Bacillus licheniformis SWJS33 that improves hydrolysis and debittering efficiency for soy protein isolate

An aminopeptidase was isolated from the marine Bacillus licheniformis SWJS33 (BLAP) and purified. According to the tandem mass spectrometry, the enzyme displayed 11% amino acid identity with the aminopeptidase from Bacillus (gi|496687392). BLAP exhibited maximum activity at 60 °C and pH 8.0-8.5 and had a molecular mass of 100 kDa. The presence of NaCl enabled 50% improvement of enzyme activity with 10-15% NaCl being the best. The observed inactivation by EDTA and bestatin and activation by Co2+ and Ag+ indicated that the obtained enzyme was a metalloaminopeptidase. Such an aminopeptidase could further improve the hydrolysis degree of soy protein isolate hydrolysates catalyzed by papain, Alcalase 2.4 L or Flavourzyme 500MG from 8.5%, 9.5% or 14.4-18.8%, 18.7% or 20.1%, respectively, while decreasing the bitter intensity score of the SPI hydrolysates catalyzed by Alcalase 2.4 L from 3.6 to 0.4.