Barley α-amylase/subtilisin inhibitor shows inhibitory activity against endogenous xylanase isozyme I of malted barley: A novel protein function.

Mashing process had little influence on the arabinoxylan content in the finished wort. In this paper, a protein with inhibitory activity against the endogenous xylanase isozyme I (X-I) of malted barley was extracted and purified using a combination of ion-exchange and size-exclusion chromatography. The protein was identified as barley α-amylase/subtilisin inhibitor (BASI). According to the amino acid sequence analysis, BASI was completely different from the previous reported xylanase inhibitors. BASI showed dosage-dependent inhibitory activity. BASI exhibited a maximum inhibitory activity at 50°C and pH 6.0. BASI inhibited X-I as a competitive manner. PRACTICAL APPLICATIONS: A protein with inhibitory activity against the major endogenous xylanase isozyme I (X-I) of malted barley was extracted, purified, and characterized, which was identified as barley α-amylase/subtilisin inhibitor (BASI). The results help brewers to achieve a better understanding of the mechanism of arabinoxylan degradation during mashing. BASI can be used as an indicator to screen microbial xylanases. The microbial xylanases insensitive to BASI would have obvious advantages in the degradation of arabinoxylan polymers and filterability improvement during mashing.