Phenols/polyphenols extraction from grapes

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

Retention times of the peaks are subject to the particular type of column. The acidic fraction from solid-phase extraction consists of phenolic acids such as cis-coutaric, trans-coutaric, and trans-caftaric acids. Isocratic elution is suitable because of the limited number of compounds found in the acidic fraction. Analysis of the acidic fraction is completed within 30 min. See Figure 11.3.1 for an HPLC chromatogram of the acidic polyphenolics isolated from Niagara grapes. 

Wine tannins are polyphenolic compounds extracted from the skins and seeds of grapes during the process of wine-making. These phenolic compounds exhibit a wide diversity of structures having a flavonoid skeleton (Figure 6.1). 

Souquet, J.-M., Veran, F, Mane, C., Cheynier, V. (2006). Optimization of extraction conditions on phenolic yields from the different parts of grape clusters - Quantitative distribution of their proanthocyanidins. XXlll International Conference on Polyphenols. Winnipeg, Manitoba, Canada. 

Grapes and berry fruits are rich sources of flavonoids and polyphenolics. Labor-intensive investigations over the years, initially from botanists and later from chemists and food scientists, provide a vast amount of knowledge about chemical structure, occurrence and stability of these compounds. As a consequence, food products, extracts, tinctures and dry powders are available with documented levels of flavonoids and other phenolics. 

Recently, Romani et al. [200] published a sophisticated solid phase extraction procedure for the qualitative analysis of grape skins. In a first extraction on Extrelut 20 (kieselguhr, Merck) polyphenols are separated from anthocyanins. The polyphenols are subsequently fractionated on a C-18 cartridge (Bond Elut , Varian) into phenolic acids and esters, procyanidins, flavonol glycosides and acylated anthocyanins. 

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