Purification and Structural Characterization of Protein Z4 from Malt

Abstract

In beer quality, the interactions of proteins with hop acids are understood to be the basis of beer foam stability. Among beer proteins, one barley malt albumin, protein Z4, has an important role in stabilizing beer foam. In this study, protein Z4 was purified from AC Metcalfe barley malt for further study. The secondary structure of protein Z4 was investigated via Fourier transform infrared spectroscopy and circular dichroism spectroscopy. The results showed that protein Z4 had high structural stability. These structural features of protein Z4 were proposed to explain its observed high tolerance and stability of high temperatures and pH during the brewing process. Relatively high beer ethanol concentrations and yeast-induced modifications during the fermentation process can only partially influence in the structure of protein Z4. Modification by carbohydrates was observed as a result of the malting process. Meanwhile, modifications could increase the stability of the structure of protein Z4. Furthermore, modifications to protein Z4 were also conducive to improving its contribution to beer foam stability. Finally, these results confirmed the positive relationship between protein Z4 and beer foam stability.