Study On Effect Of Endogenous Proteins On Oxidative Stability Of Beer

The oxidative stability of beer plays an important role in the quality and shelf life of beer.How to improve the endogenous antioxidant activity to delay the flavor aging and improve the oxidative stability of beer has always been one of the focus issues in brewery industry.Proteins,as one of the most compositions of beer,have important influence on the quality of beer,such as the foam and the turbidity of beer.Furthermore,lipid transfer protein 1(LTP1)as a thiol-rich protein has been confirmed to be closely related to the antioxidant capacity of beer.In this paper,the changes of protein(including LTP1)content,molecular structure and antioxidant activity during forced-aging in beer were systematically studied.And then the effects of dissolved oxygen content on the structure and antioxidant activity of beer protein were discussed.Moreover,the effect of beer brewing process on protein and its oxidative stability was clarified,especially in mashing process.The mechanism of beer endogenous protein on beer oxidative stability was revealed,which provided a theoretical basis for improving the oxidative stability of beer by regulating protein components.The main research results are as follows:(1)The changes of protein and its molecular structure and antioxidant activity in beer were studied during forced-aging.The results showed that with the extension of forced-aging time,the protein content in beer decreased continuously,and the macromolecular protein gradually degraded.The conversion of free thiol group to disulfide group increased,increasing the degree of oxidation of the protein,indicating that the protein played an important role during forcedaging in beer.The LTP1 which isolated and purified from beer showed strong ABTS free radical scavenging ability,but its secondary structure was destroyed during forced-aging,and the tertiary structure was changed drastically,thus losing the ability of free radical scavenging and delaying beer oxidation.(2)The mechanism of the effect of dissolved oxygen content on protein in beer was discussed.The results showed that during forced-aging,the increase of dissolved oxygen content aggravated the loss of beer protein,accelerated the oxidation of LTP1,and caused more damage to its secondary structure and tertiary structure.The increase of dissolved oxygen content could significantly increase the aging degree of beer and accelerated the deterioration of beer flavor during forced-aging.(3)The changes of protein and free thiol groups in the brewing process and their relationship with the antioxidant capacity of wort were revealed.The results showed that the mashing step was the most intense phase of protein and free thiol groups content in wort.At the appropriate mashing temperature,appropriately extension of the mashing time was beneficial to the dissolution and accumulation of protein in wort,which significantly improved the ABTS free radical scavenging activity of wort.Therefore,the protein in wort,especially LTP1 with antioxidant activity,was closely related to the oxidative stability of wort.