Use of new methodologies to study phenolic compounds implicated in beer staling

The goal of our thesis was to better understand the fate of polyphenols through beer storage. First, new methodologies were needed to assess what happens to polyphenols in the bottled beer. They were optimized on fresh beer samples. NP-HPLC-ESI(-)-MS/MS with addition of ammonium salt revealed efficient to quantify monomers to trimers in a Sephadex LH20 acetone/water (70/30, v/v) beer extract: up to 3 ppm P1-P3 were measured in PVPP-treated beers vs. 10 ppm in silica gel-filtered beers. Thiolysis of such extracts indicated that most beer dimers are procyanidins whilst most trimers are prodelphinidins. Detailed structures of each oligomer were determined by reversed phase. As expected according to thioacidolysis data, most beer proanthocyanidins carry a catechin as terminal unit. The analysis of higher oligomers extracted by dialysis and thiolyzed lead us to conclude that natural beer oligomers exhibit a relatively low DP whilst transformed oligomers probably account for most of the heavy flavanoid content. The optimized methods were then applied on aged beers. Three lager beers differently stabilized before bottling in glass or PET bottles were monitored over a one-year period of storage at 20°C. In parallel, beer color was measured. Structural rearrangements of polyphenols revealed to be the main source of color changes. The evolution of color was the same in the silica gel-filtered beer as in identically bottled PVPP-treated samples, despite the high flavanoid dimers content of the former. This suggests that only monomers must be considered. Model media were also investigated by the same method. (+)-Catechin emerged as the precursor of less polar products characterized by a yellow-brown color. Similar structures were found in aged beers spiked with (+)-catechin. None of the usual global assays revealed efficient to predict the extent of beer polyphenol degradation.Doctorat en sciences agronomiques et ingénierie biologique (AGRO 3)--UCL, 200

Structure, Organoleptic Properties, Quantification Methods, and Stability of Phenolic Compounds in Beer-A Review

Beer composition changes through storage, altering the quality of the product. In the past decade, many papers have been devoted to the compounds responsible for aged-beer off-flavors, mainly trans-2-nonenal, methional, and dimethyltrisulfide. Due to their huge antioxidant activity, polyphenols have often been described as key compounds for limiting beer staling. Yet phenolic structures also evolve through storage. Low-molecular-weight phenols like 4-vinylsyringol can impart off-flavors in aged beer, whilst flavonoids strongly influence astringency, haze, and color. The instability of stilbenes, prenylchalcones, and derived flavanones could also modify their health potential through storage. After reviewing the structures and properties of all phenolic compounds found in beer, this paper will try to assess the impact of their degradation through aging. Extraction procedures for their quantification and treatments for their removal are also described

Involvement of flavanoids in beer color instability during storage.

Besides Maillard reactions, structural rearrangements of flavan-3-ol monomers cause color changes in beer during storage. Acetone/water-soluble fractions (70/30, v/v) of three lager beers of the same batch, differently stabilized before bottling in glass or poly(ethylene terephthalate) (PET) bottles, were monitored by normal-phase HPLC-ESI(-)-MS/MS over a 1-year period of storage at 20 degrees C. In parallel, beer color was monitored by the European Brewery Convention assay. The evolution of color was similar in the silica gel-filtered beer to that in identically bottled and stored poly(vinylpolypyrrolidone)-treated samples, despite the high flavanoid dimers content of the former. On the other hand, color evolved more rapidly in the PET bottle, suggesting a key role of oxygen. The kinetics was still increased in model media containing (+)-catechin, while no color was detected when normal-phase HPLC-fractionated dimers or trimers were investigated. (+)-Catechin emerged as the precursor of less polar products, characterized by a yellow-brown color. MS/MS enabled us to identify these products as issued from the oxidation and intramolecular additions of dehydrodicatechin B4. Similar structures were found in aged beers spiked with (+)-catechin. Beer storage in the absence of oxygen and at low temperature is recommended so as to minimize the synthesis of such pigments

Use of RP-HPLC-ESI(-)-MS/MS to differentiate various proanthocyanidin isomers in lager beer extracts

Normal-phase high-performance liquid chromatography electrospray ionization(-) tandem mass spectrometry (NP-HPLC-ESI(-)-MS/MS) and thioacidolysis analyses recently have revealed the presence of (+)-catechin, (-)-epicatechin, procyanidin dimers, and prodelphinidin trimers in acetone/water (70/30, vol/vol) LH-20 extracts of lager beers. In this study, detailed structures were determined by reversed-phase (RP) HPLC-ESI(-)MS/MS. Four dimers were identified: three procyanidins (B1, B3, and 134) and one prodelphinidin (133). Previously detected in hop or malt, three trimers; (the procyanidin C-4 alpha-8-C-4 alpha-8-C and two prodelphinidins, GC-4 alpha-8-C-4 alpha-8-C and GC-4 alpha-8-GC-4 alpha-8-C) were distinguished for the first time in beer. As expected based on previous thioacidolysis data, most beer proanthocyanidins carried a catechin as the terminal unit

Chocolate and cocoa: New sources of trans-resveratrol and trans-piceid

trans-Resveratrol and trans-piceid were found for the first time in dark chocolate (at least 0.4 ppm trans-resveratrol and 1 ppm trans-piceid) and cocoa liquor (at least 0.5 ppm trans-resveratrol and 1.2 ppm trans-piceid). Because these compounds are highly sensitive to light, a specific extraction procedure was required to recover them, involving delipidation with toluene and cyclohexane and ethanol/water (80/20, v/v) solid-liquid extraction at 60 degrees C before reverse-phase HPLC-MS/MS analysis (atmospheric pressure chemical ionization [APCI] in the positive mode). Thanks to an exceptionally high procyanidin content, chocolate products displayed higher antioxidant activity than much more concentrated commercial stilbene extracts. (c) 2005 Elsevier Ltd. All rights reserved