Comparative analysis of the effect of protein Z4 from barley malt and recombinant Pichia pastoris on beer foam stability: Role of N-glycosylation and glycation

Abstract

This study aimed to elaborate the effect of N-glycosylation and glycation of protein Z₄ from barley malt and recombinant Pichia pastoris on beer foam stability. The malt protein Z₄ and recombinant protein Z₄ showed similar N-glycosylation patterns while recombinant protein Z₄ was glycosylated at a higher degree. In the simulated mashing and boiling, malt protein Z₄ and deglycosylated malt protein Z₄ preferred to glycate with glucose and maltose while recombinant protein Z₄ and deglycosylated recombinant protein Z₄ showed preference towards fructose. The addition of protein Z₄ and protein Z₄-saccharide complexes in finished beer showed that the addition of glycosylated protein Z₄ only slightly enhanced the beer foam stability while the addition of glycated protein Z₄ and protein Z₄ with both glycation and glycosylation could significantly increase the beer foam stability. Therefore, glycation instead of N-glycosylation of protein Z₄ played important roles in maintaining beer foam stability.

Keywords: Beer foam stability; Glycation and N-glycosylation; Protein Z(4).