In the last decade, research strongly supports a role for polyphenols in the prevention of degenerative diseases, particularly cardiovascular diseases. Proposed mechanisms include inhibition of the oxidation of low-density lipoproteins (LDL), an important step in the aetiology of atherosclerosis and coronary heart disease (CHD) and effects on cell signaling or gene expression. Polyphenols are the most abundant antioxidants in the diet, with intakes as high as 1 g/day, principally from fruits, vegetables, cereals, chocolate, tea, coffee, and red wine. One source that is often overlooked is beer, which is polyphenol-rich, and is regularly consumed. Studies have shown that beer increases plasma antioxidant capacity in humans1, and in patients suffering from hyper-cholesterolemia and CHD, short-term moderate beer consumption was cardioprotective2. There are however, vast differences in composition between beers, and some evidence that darker beers have higher antioxidant activity in vitro resulting from interactions between sugars, amino acids and phenolic acids3.
The overall aim of this study is to investigate the bioavailability and metabolism of beer phenolics and their ability to protect LDL against oxidation. Initially, an investigation of the compounds present in beer, their relative antioxidant activity and how this differs between lager, ale and stout was performed. Ethyl acetate extracts and aqueous extracts were prepared from three commercial beer samples. Separation and identification of polyphenols and other potential compounds of interest was performed using reverse phase high performance liquid chromatography (RP-HPLC). Antioxidant activity was determined using the ferric-reducing antioxidant power (FRAP) assay. Preliminary results indicated that ale extracts possessed the most compounds of interest with highest antioxidant activity; therefore these extracts were subjected to further analyses. Centrifugal partition chromatography (CPC) was used to separate ale extracts into 17 fractions of differing composition.
RP-HPLC was used for the separation of CPC fractions, and subsequent identification and quantification of compounds belonging to different classes of polyphenols (hydroxycinammates, hydroxybenzoates, flavonoids; including one not previously reported in beer, but known to inhibit LDL oxidation), and also other compounds of interest (furans). Concentrations of compounds contained within CPC fractions have been correlated with antioxidant activity as measured using the trolox equivalent antioxidant capacity (TEAC) and FRAP assays. CPC fractions have been analysed by LC-(ESI)-MS, confirming detection of several phenolic compounds by mass.
Absorption across caco-2 monolayers is currently being studied, and the absorption of beer phenolics including the little studied prenylated flavonoids, which have been shown to protect LDL from oxidation4, will be described.
|Conference||Nutrition Society Summer Meeting|
|Period||16/07/07 → 19/07/07|