Study On Endogenous Antioxidant Capacity Of Craft Beer

The flavor stability of beer is one of the most important indexes of beer,and the research in recent years indicates that the endogenous antioxidant capacity of beer plays a major role in the flavor stability of beer.In recent years,the global beer market in craft beer shows a significant growth trend,and a large number of research work focuses on the development of new beer products in craft beer.However,there are few studies on the source of endogenous antioxidant capacity of craft beer and the comparison of endogenous antioxidant capacity between craft beer and industrialized beer.In this study,the non-heat-sterilized beer in craft beer and industrialized beer were taken as the research objects,and the comprehensive evaluation index of antioxidant capacity was constructed.The difference of endogenous antioxidant capacity between the craft beer and industrialized beer was clarified,and the key compounds affecting the endogenous antioxidant capacity of the beer in craft beer were further studied.Finally,six grains（quinoa,buckwheat,coix seed,brown rice,highland barley and sorghum）were applied in the brewing of craft beer to investigate their effects on endogenous antioxidant capacity and brew high antioxidant capacity beer.The main research contents and results are as follows:（1）The total reactive antioxidant potential（TRAP）,DPPH radical–scavenging activity（DSA）,ABTS radical–scavenging activity（ASA）,reducing power（RP）and metal chelating activity（MCA）were used to determine the antioxidant activities of twenty-one industrialized beer samples and nine craft beer samples.The principal component analysis was used to construct an antioxidant comprehensive evaluation index（ACEI）.The results showed that ACEI was significantly correlated with the other five measures and the antioxidant activity of craft beer was much higher than that of industrialized beer.Taking the ACEI as the standard,the average antioxidant activity of craft beer was 96.0%higher than that of industrialized beer.（2）Multiple linear stepwise regression analysis was used to determine the extent of contribution of antioxidant substances in beer to antioxidant indicators.Polyphenols were the most important antioxidant substances in beer.The total polyphenol content played a major contribution to TRAP,DSA,ASA and RP,with the contribution degree reaching81.5%,80.6%,75.5%and 64.4%.The content of melanoidin played a major contribution to MCA,with the contribution degree reaching 38.3%.The largest contribution to the establishment of ACEI in this study was the total polyphenol content,with the contribution degree reaching 80.8%.（3）Guided by DPPH radical scavenging activity,the key antioxidant substances in craft beer（yellow beer,white beer and IPA）were separated by alcohol precipitation,ethyl acetate extraction,macroporous resin separation and semi-preparative high performance liquid chromatography.The separated antioxidant substances were identified by ultra-high phase liquid chromatography-four-stage time-of-flight mass spectrometer.Fifteen compounds were identified,of which four phenolic acids and one flavonoid had much higher antioxidant activities than the other components.The phenolic acid compound are N-feruloyl tyramine（N-FT）,verbascoside（VBC）,4-hydroxy cinnamamide（4-HC）and alpha-sorin（AS）,the flavonoid compound is epicatechin（EC）.N-FT,VBC and EC were identified in the yellow beer sample;N-FT,EC and 4-HC have been identified in white beer samples;N-FT,EC,4-HC,and AS were identified in the IPA sample.The antioxidant activities of these substances accounted for 75.9%,79.7%and 67.9%of the total antioxidant activities in the three craft beer samples.Phenolic acids were derivatives of ferulic acid,p-coumaric acid and gallic acid,indicating that these 3 phenolic acids and epicatechin were the key substances affecting the antioxidant activity of craft beer.The antioxidant capacity of the four monomer compounds was in the order of gallic acid>epicatechin>ferulic acid>p-coumaric acid.The total content of monomer compounds in craft beer was 57.0%higher than that in industrialized beer.（4）In this study,quinoa,buckwheat,coix seed,brown rice,naked barley and kaoliang were used respectively as adjuncts for above fermentation technique brewing with the addition level of 20%.The antioxidant activity and monophenols composition of beer with different grain adjuncts were measured,and supplemented by flavor substance content and sensory evaluation,the effects of different grains on antioxidant activity of craft beer and the possibility of brewing high antioxidant beer were analyzed.The results showed that according to the ACEI established in this study,the antioxidant activities of buckwheat beer and quinoa beer were 31.2%and 15.5%higher than those of the control group.The total contents of monophenols in the two kinds of adjunt beer were 3.62 and 3.67 mg·L^-1,and those in the control group were 2.11 mg·L^-1,71.6%and 73.9%higher than those in the control group,respectively,The alcohol-ester ratio of that two adjunt beer was lower than that of the control group and the sensory score was high than that of the control group.In conclusion,buckwheat beer and quinoa beer had strong antioxidant activity,high content of monophenols,high sensory score and relatively harmonious flavor,indicating that buckwheat and quinoa are suitable for brewing craft beer with high antioxidant capacity as auxiliary adjuncts.