Haze activity of different barley trypsin inhibitors of the chloroform/methanol type (BTI-CMe)

Our previous study found that the critical protein in SE (silica eluted) proteins is BTI-CMe, and assumed that SE−ve malt for brewing may improve the haze stability in beer. In this study, we investigated the difference in gene sequence and corresponding amino acid sequence of BTI-CMe between SE+ve and SE−ve types. The results showed that there were 7 amino acid differences between Yerong (SE−ve) and Franklin (SE+ve). Two types BTI-CMe were expressed in vitro and purified successfully. By adding the purified BTI-CMe into commercial beer, we found that both original turbidity and alcohol chill haze degree of beer were increased. BTI-CMe of SE−ve haplotype showed a lower level of haze formation in beer than SE+ve haplotype. Response surface methodology (RSM) was conducted to determine the relationship between BTI-CMe and tannic acid, and their effects on haze formation. It was found that (1) higher content of BTI-CMe and/or tannic acid in beer would give rise to higher turbidity; (2) there was a significant interaction between BTI-CMe and tannic acid; (3) haze activity disparity of BTI-CMe between two types was significantly and positively correlated with the tannic acid concentration.