Characterization of local Canadian beer and brewers’ spent grain through the identification of phenolics and evaluation of their antioxidant activities
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Date
2019-12-18
Authors
Rahman, Md. Jiaur
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Abstract
Phenolic compounds are derived in beer from malts, hops and other ingredients during the brewing process. The first objective of the research work was to examine the profiles of major hydroxycinnamic acids (HCAs) and their derivatives of a laboratory-made, selected Canadian and foreign commercial beer extracts as well as evaluation of their antioxidant activities. Using the Folin Ciocalteu assay, the total phenolic content (TPC) of the beer extracts ranged from 3.72 ± 0.23 to 13.73 ± 0.49 mg GAE/ 100 mL beer. The total flavonoid content (TFC) was also found to vary from 0.82 ± 0.02 to 5.28 ± 0.04 mg CE/ 100 mL in the beer extracts. Major HCAs such as ferulic acid, p-Coumaric acid, sinapic acid and a key derivative of ferulic acid, 4-vinyl guaiacol (4-VG) were identified and quantified using high-performance liquid chromatography with diode array detection (HPLC-DAD). A significant variation of TPC, TFC, HCAs and 4-VG content were observed across different beer extracts tested. Antioxidant activities of beer extracts, determined by DPPH radical and ABTS radical cation scavenging as well as reducing power assays, significantly correlated (p < 0.05; p < 0.01) with TPC and TFC. 4-vinyl guaiacol showed a significant correlation with ABTS radical cation scavenging and reducing power assays. These findings suggest that beer phenolics and 4-VG, the key derivative of the ferulic acid, may have a protective role in the beer as an antioxidant.
Phenolics in food grains may exist as bound form with cell wall carbohydrates, especially with lignin and arabinoxylan. Effective processing e.g. heat treatment can breakdown cell walls by disrupting cell membranes and cleaving covalent bonds to release low molecular phenolics. The second objective of the research work was to examine the effect of various oven heat treatments (100, 140 & 1600C) on the extractability of bound phenolics from the brewers’ spent grains (BSG) and analyze their profiles by chemical and instrumental methods. BSG treated at 160oC showed a two-fold higher TPC (172.98 ± 7.3 mg GAE/100 g defatted meal) and TFC (16.15 ± 2.22 CE/100 g defatted meal), when compared to the untreated BSG extracts. Heating BSG at 160oC showed two-fold higher DRSC (22.67 ± 6.93 to 46.26 ± 2.17 µmole TE/g defatted meal) and FRAP (8.30 ± 0.49 to 17.27 ± 1.15 µmole/g defatted meal) values than the corresponding untreated BSG extracts. Eleven phenolic acids were identified and quantified by Ultra Performance Liquid Chromatography with Photodiode Array (UPLC-PDA) with their amounts varying significantly (p < 0.05) at 160°C. Chlorogenic acid was the predominant phenolic acid present in all fractions, however, its amount decreased from 107.18 ± 2.29 to 71.28 ± 4.74 µg/g in the defatted meal. This was attributed to its conversion to caffeic acid that was identified at 140°C and 160°C. This supports the ability of the higher temperature to cleave the esterified bonds. Therefore, the observed results indicate that heat processing releases bioactive phenolic acids except the chlorogenic acid, from their bound forms.
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Keywords
Beer, Hydroxycinnamic acids, 4-Viny guaiacol, Antioxidant properties, Brewers’ spent grain, Heat- treatments, Valorization, Bioactive phenolics