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

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.