Studies On The Relationship Between Phenolic Compounds And Beer Flavor Stability

Achievement of both good haze and flavor stability of beer is a key problem that brewing researchers have been trying to address for years. Polyphenols were the compounds which their hydroxy groups were connected directly with phenyls. Phenolic compounds in beers including phenolic acids, flavonoids, proanthocyans and anthocyans, they take important role in beer non-biological stability, flavor stability, color and soluble oxygen, and so on. In practice, flavor stability can be improved by the choice of barley and malt, a low lipoxygenase activity, low temperature and high pH can be applied. In fact, oxygen is an important element that present at all times, so the role of endogenous antioxidants was shown. Polyphenols have been considered the main natural antioxidants in brewing raw materials and beer.In this article, Polyphenols were determined by RP-HPLC. The column was Zorbax Eclipse XDB-C18(4.6×250mm, 5μm),Waters 2487 detection. In the concentration of 6.4~68 μg/ml, they have the regressions which were greater than 0.9993. The RSD were within 6.4%. the percentage of recoveries were 84.8~108.5%. So it may be to apply estabilished HPLC analytical method to confirm the kinds of polyphenols in beers. The LC/MS analysis was also applied.An analysis method of thiobarbituric acid (TBA) value was improved, which has been brought forward by Palamand and Grigsby. The analysis condition was as follows: absorb wave-length was 530 nm; the TBA concentration was 0.28%, resolved in 60% acetic acid liquid; the reaction temperature was 60℃ and the reaction time was 60 minutes; The 60% acetic acid aqua was taken as the blank. At the same time, we studied the relationship between TBA value with aldehydes and other carbonyl compounds were discussed primarily.The antioxidative activity of polyphenol in wort and beer was determined by TRAP assay, The TRAP value responded well to the antioxygenic property of wort and beer. Furthermore, a well relativity was found between TRAP value and the content of polyphenols, the correlation coefficient was greater than 0.9000, RSD was 2.06%. It was found that ferulic acid and (+)-catechin showed high antioxidant ability, and anthocyan also demonstrated good antioxidant ability. Moreover, most of phenolic compounds had higher antioxidant ability than that of other antioxidant additive, such as ascorbate. In addition, the TRAP value was a good indicator of antioxidative activity principally derived from polyphenols. It's useful for monitoring the oxidative changes during the brewing process.The relationship between polyphenols and beer flavor stability was also studied. It was found that polyphenols can effect TBA value. A GC method was applied to detect aldehydes, it was shown that polyphenols can reduce the content of some aldehydes in beer. We also found that there were more polyphenols in Hops than in malts. PVPP and formaldehyde have negative effects on flavor stability, PVPP is likely to absorb some carbonyl compounds. In addition, a cooperativity of (+)-catechin and Vc was found.