Technological influence on sensory stability and antioxidant activity of beers measured by ORAC and FRAP.

BACKGROUND: Many studies have confirmed a wide variation in the phenolic content and antioxidant activity of beers. However, when commercial beers are studied, there is usually no information available on the brewing technology applied. In this study, technological parameters were varied systematically to influence the antioxidant content of beer with a view to improving its flavor stability. High-throughput assays, ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) were investigated as fast analytical methods to evaluate the influence of brewing technology on antioxidant activity. RESULTS: Beers (n = 12) were brewed with systematic technological variations (malt modification, hopping regime) to influence the antioxidant potential. A late hop addition resulted in significantly higher phenolic content (high-performance liquid chromatography with diode-array detection - HPLC-DAD) and antioxidant activity. Raw protein content and malt modification significantly influenced phenolic content and the antioxidant activity of beers hopped at the beginning of wort boiling. Samples were stored under forced and natural conditions and were evaluated by a sensory panel. The decline of bitter iso-α-acids as an analytical marker for oxidative aging was significantly lower in beers brewed from malts with high raw protein content. These samples also had higher antioxidant activity values. Panelists gave higher ratings for beer quality to aged beers with a late hop addition. However, late hopping resulted in enhanced hoppy aroma attributes and therefore an altered aroma profile. CONCLUSIONS: Both antioxidant capacity methods were well suited as fast methods to evaluate brewing raw material and technological influence on antioxidant activity. The appropriate choice of barley malt and the malting regime could be promising tools to enhance the antioxidant activity of traditionally hopped beers. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phenolic Substances in Beer: Structural Diversity, Reactive Potential and Relevance for Brewing Process and Beer Quality.

For the past 100 years, polyphenol research has played a central role in brewing science. The class of phenolic substances comprises simple compounds built of 1 phenolic group as well as monomeric and oligomeric flavonoid compounds. As potential anti- or prooxidants, flavor precursors, flavoring agents and as interaction partners with other beer constituents, they influence important beer quality characteristics: flavor, color, colloidal, and flavor stability. The reactive potential of polyphenols is defined by their basic chemical structure, hydroxylation and substitution patterns and degree of polymerization. The quantitative and qualitative profile of phenolic substances in beer is determined by raw material choice. During the malting and brewing process, phenolic compounds undergo changes as they are extracted or enzymatically released, are subjected to heat-induced chemical reactions or are precipitated with or adsorbed to hot and cold trub, yeast cells and stabilization agents. This review presents the current state of knowledge of the composition of phenolic compounds in beer and brewing raw materials with a special focus on their fate from raw materials throughout the malting and brewing process to the final beer. Due to high-performance analytical techniques, new insights have been gained on the structure and function of phenolic substance groups, which have hitherto received little attention. This paper presents important information and current studies on the potential of phenolics to interact with other beer constituents and thus influence quality parameters. The structural features which determine the reactive potential of phenolic substances are discussed.

Quantitative Antioxidant Profiling Throughout Beer Brewing Followed by Discovery and Isolation of Precursors from Barley (Hordeum vulgare L.).

The application of high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) revealed the origin and evolution of antioxidants during the brewing process of hopped and unhopped reference beer. As tachioside (3-methoxy-4-hydroxyphenyl-ß-d-glucopyranoside), arbutin (4-hydroxyphenyl-ß-d-glucopyranoside), and hordatines clearly increased during the fermentation step, the raw material barley was investigated as a source of the corresponding precursors. Therefore, 4-hydroxyphenyl-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranoside, 4-hydroxy-3-methoxyphenyl-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranoside, 4-hydroxy-3-methoxyphenyl-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranoside, and 4-hydroxy-2-methoxyphenyl-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranoside were isolated from barley for the first time, and identified using liquid chromatography-mass spectrometry (LC-MS) and one-dimensional/two-dimensional-nuclear magnetic resonance (1D/2D-NMR) experiments. Moreover, hordatine glucosides A, B, and C were isolated and identified from barley, and hordatine C glucoside was characterized for the first time. A fermentation model followed by HPLC-MS/MS analysis substantiated the release of tachioside from 4-hydroxy-3-methoxyphenyl-ß-d-glucopyranosyl-(1 → 6)-ß-d-glucopyranoside by Saccharomyces cerevisiae. Quantitation experiments monitoring the content in wheat, barley, and different barley malt types demonstrated a wide range of concentrations, providing a basis for further comprehensive investigations to optimize the antioxidant yield in beer to contribute to improved flavor stability.

Ultrathin-layer chromatography on SiO(2), Al(2)O(3), TiO(2), and ZrO(2) nanostructured thin films.

We explored four different inorganic oxides and determined their merits in miniaturized planar chromatography. Despite progression of chromatographic techniques over several decades, such alternatives to traditional planar silica gel stationary phases have not been fully evaluated. Glancing angle deposition(GLAD) provided an excellent platform for engineering nanostructured thin films in these materials for ultrathin-layer chromatography (UTLC). Separations of carotenoids and synthetic food dyes were used to investigate the attributes of SiO(2), Al(2)O(3), TiO(2), and ZrO(2)GLAD UTLC media. These anisotropic high surface area thin films possessed similar channel-like features but different chromatographic properties.TiO(2)and ZrO(2)media were especially interesting since analyte retention could be modified through sim-ple oxidation heat treatments and UV irradiation. Generally, oxidation reduced analyte retention while UV exposure increased retention. Changes in retention factor as large as ΔhRF∼ 40 (for Acid Red 14 on titanium oxide) were achieved. Food dye mixtures were applied using consumer inkjet printers as per the Office Chromatography concept and separation performance was quantified using advanced video instrumentation designed for miniaturized plates. Enhanced time-resolved UTLC methods were used to calculate figures of merit from recorded dye separation videos. Small theoretical plate heights (<4 µm)and low limits of detection (<2 ng per zone for the food dye tartrazine) were measured. The combination of engineered GLAD UTLC plates, inkjet application of analyte spots, time-resolved UTLC, and custom analysis algorithms enabled some of the best performance achieved on GLAD UTLC layers. Separations on the inorganic oxide thin films were also successfully hyphenated with electrospray ionization mass spectrometry for the first time. This investigation demonstrates the utility of alternative inorganic oxide GLADUTLC media and probes avenues of expanding the capabilities of miniaturized planar chromatography.