Study Of Polyphenols In Beer

Proanthocyanidins oligomers are the most interesting antioxidant around the world, which could easily be found in hops. Hop proanthocyanidins have a great impact non-biological stability and oxidant resistance in beer brewing, and it is good for human health too.In this study, the commercial proanthocyanidins from grape seed extracts which were used as reference substance were analyzed by RP-HPLC and UPLC-MS. Target compounds were separated by Zorbax Eclipse XDB-C18(4.6×250 mm,5μm) using methanol-water (including 0.05% TFA) as mobile phase. The flow rate was 0.4 mL min-1, column temperature was 25℃, and injection volume was 10μL. 8 compounds were obtained at OD280, and they were identified using UPLC-MS. There were three monomers, three dimers, one trimer and one dimer-monoester. Afterwards, the proanthocyanidins from hop were purified and analyzed. The hops were processed by organic solvent extraction, macroporous resin adsorption, and sephadex LH-20 chromatography. The optimum organic solvents extraction conditions were established as follows:50% ethanol(v/v) was used as solvent, and the extraction was taken for 2 h at pH4.0-4.2 and 85℃with the ratio of solvent to material at 20:1(v/w). Then the crude proanthocyanidins from hop were purified by using column chromatography (φ10×200 mm). AB-8 resin was chosen in this study from 5 kinds of macroporous resins (ADS-8, ADS-17, ADS-21, AB-8, and D101) for its excellent adsorption and desorption properties. The parameters were set as follows: the column volume, 14.5 mL; sample concentration, 1.8 mg/mL; sample volume, 3 mL; sample flow velocity, 20 mL/h. The adsorbed hop proanthocyanidins could be well eluted by 70 mL 100% ethanol with a elution rate of 60 mL/h. This method also has a good applicability in purification of hop proanthocyanidins. Finally various chemicals were purified including (±)-catechin and prodelphinidin.Seven proanthocyanidins with different degree of polymerization were obtained by the classification of average degree of polymerization. At the same time, the antioxidative activities of these polymers were measured using (+)- catechin and Vitamin C(Vc) as control. The tests included reducing capability, ability of inhibiting lipid peroxidation, ability of antioxidant in linoleic acid system, ability of scavenging hydroxyl free radical, and impact on TBA changes during wort boiling. The results of reducing ability were as follows: proanthocyanidins of mDP=1.5-4 > (+)- catechin> Vc > proanthocyanidins of mDP=5.55. Hop proanthocyanidins with any mDPs could inhibit the peroxidation of lipid, and the strength of inhibition effect has nothing to do with mDP. Besides, the inhibition had a certain concentration effect. In the linoleic acid system, the oligomeric procyanidins and Vc had the same effect in terms of inhibiting the oxidation of linoleic acid, and the inhibiting effect enhanced with increased dosage. The ability of scavenging [HO·] gradually strengthened with concentration increased. During wort boiling there was an obvious relationship with TBA changes and the mDP of procyanidins. Proanthocyanidins of mDP=2 had the most powerful antioxidative ability, which could significantly inhibited the forming of precursors.