Study On Antioxidant Activity Of Free Phenolic Acids In Beer

Phenolic compounds are the main important endogenous antioxidant substances in the beer. Although content is low, but they have a great influence on the production process of beer and the quality of the finished beer. Phenolic acid is one of the phenolic compounds. Phenolic acids in beer mainly from the malt. Phenolic acids presence in free form or in the form of esters and glycosides in beer. With the strong reducibility, phenolic acids play an important role on the beer flavor stability. Phenolic acids can delay and even prevent the oxidation process as a kind of antioxidant effect material. This paper established a RP-HPLC method of free phenolic acids in beer; investigated the change of free phenolic acids contents and antioxidant activity from process of brewing(saccharification, fermentation) and aging; research phenolic acids’ contribution in beer brewing and aging process and to analyse the antioxidant capacity and oxidation products of catechin.By extracting free phenolic acids in beer, after LC-MS determination, analysis is contained of 4-hydroxyphenylacetic acid, caffeic acid, p-hydroxycinnamic acid, ferulic acid, ainapic acid, epicatechin, catechin, vanillic acid and syringic acid in beer. Optimization of chromatographic conditions, determined the mobile phase A:water+acetic acid (0.1%), mobile phase B: methanol+acetic acid (0.1%), a flow rate of 0.8 mL/min, phenolic acids were separated completely, and the peak shape is better. Using optimized chromatographic conditions to determine retention time,9 kinds of phenolic acids within 42 min were well separated. External standard method for quantitative, establish a standard curve for each phenolic acids, phenolic each peak area and concentration showed a good linear relationship, the correlation coefficients were greater than 0.9993. Nine phenolic acids have lower limit of detection, can reach 1.11 mg/L. Precision of HPLC method and phenolic acids extraction method are within 5%, the repeatability is good; beer samples of each acid recoveries are more than 84%, recovery rate is high, can meet the testing requirements.By sampling analysis of whole wheat wort saccharification process, found that the content of nine kinds of free phenolic acids have different degrees of increase, the antioxidant power increases, especially the content of catechin change is most obvious, and the antioxidant activity of beer saccharification process is closely related, there was a significant negative correlation with the TBA value. The fermentation process of beer tracking sampling, the study found that the fermentation process is a process of oxidation resistance enhancement, in which the temperature in the process of fermentation process is good for the increase of catechin content, also provide the antioxidant capacity of phenolic acid is gradually strengthen. Catechin and RP value, TBA value were significantly correlated during the fermentation process. Test Description that catechin has an important role in the beer brewing process, properly adjust the content of catechin can enhance the flavor stability of beer.Through to the finished beer at 60 ℃ forced aging six days, the study found that in addition to the syringic acid and caffeic acid, other 7 kinds of phenolic acids contents have varying degree in the aging.9 kinds of phenolic acids and total phenolic content, antioxidant indicators correlation analysis, catechin and RP value, TPC was significantly positively correlated, suggests that contributed to the delay the ageing of the beer. Meanwhile the aging process catechin oxidation products were analyzed and found catechin in free radical scavenging oxidized after dihydro-dacatechin A. Compare exogenous antioxidants to delay the effects of aging beer, the greater the concentration of catechin as an antioxidant, inhibiting the ability of the stronger beer aging of carbonyl compounds inhibit class has produced. Test shows increase in the concentration of endogenous catechin beer will be for storage and flavor stability of beer has an important role.