Separation and HPLC-MS Identification of Phenolic Antioxidants from Agricultural Residues: Almond Hulls and Grape Pomace

Abstract

Almond hulls and grape pomace are residues abundantly generated by agricultural industries, which could be processed to obtain bioactive products. To this purpose, crude ethanol extracts from both agricultural byproducts were attained and subsequently fractionated in order to obtain an organic/water fraction (FOW). Extracts and fractions were analyzed for antioxidant power and their phenolic components tentatively identified by HPLC-MS. Chromatographic peaks of almond hull extracts showed the occurrence of hydroxybenzoic and cinnamic acid derivatives, with minor presence of flavan-3-ols (ECG, EGCG), whereas the FOW fraction offered the additional presence of epicatechin (EC) and glycosylated flavonols. In the composition for extracts of white and red grape pomace several of these compounds were also detected but basically consisted of glycosylated flavonols (quercetin, kaempferol). As a difference between both grape pomaces, myricetin glycosyde was found in that from the red variety, whereas flavan-3-ols (EC, afzelechin) were only identified in white pomace. When their FOW fractions were analyzed, gallic acid and some hydroxybenzoic acids were additionally detected. Antioxidant activity was assessed by DPPH and TBARS assays. Almond hulls showed inhibition percentages lower than 50% in both assays, while the inhibition percentage ranged from 80% to 90% in pomace extracts. Red grape pomace extract was the most efficient antioxidant, with an EC50 value of 0.91 g/L for TBARS and 0.20 g/L for DPPH. Even appearing as two quite different vegetal matrixes, the composition of phenolics in grape pomace and almond hulls is quite similar, the main difference being the major occurrence of flavonols in grape pomace. This fact could presumably explain the lower antiradical activity of hull extracts.

In vitro physicochemical, phytochemical and functional properties of fiber rich fractions derived from by-products of six fruits

“…Perez-Jimenez and Saura-Calixto (2008) reported that polyphenols concentration in grape antioxidant dietary fiber was 19,740 mg/100 g dry weight. Rubilar et al (2007) found glycosylated flavonols (quercetin, kaempferol) in extracts of white and red grape pomace. Likewise, Schieber et al (2001) mentioned the presence of hesperidin and eriocitrin in peel and solid residue of lemon waste.…”

Phenolic Compounds and Antioxidant Activity in Grape Juices: A Chemical and Sensory View

“…The glucose part of the anthocyanins can both be unsubstituted or acylated as esters of acetic acid, p-coumaric acid, or caffeic acid, Figure 4 (Mazza, 1995). In the species Vitis labrusca, Vitis riparia and Vitis rupestrise hybrids, the glucose molecule appears in positions 3 and 5 of the carbon, forming the 3,5-O-diglucoside anthocyanins, this being an important factor in the differentiation of grapes [45,46]. Grape anthocyanins are flavonoids, and the monomeric anthocyanins are six in total: cyanidin, peonidin, pelargonidin, delphinidin, petunidin and malvidin, the latter being the main found in red grape juices [47].…”

Influence of Temperature and Drying Time on Extraction Yield of Phenolic Compounds from Grape Pomace Variety “Portogizac”

“…Rubilar et al 48 reported for WGP as well as Lu and Foo 49 for freeze-dried grape pomace that phenolic acid, flavan-3-ols, flavonoids were dominant compounds among others. Lafka et al 50 testified that gallic acid, catechin and epicatechin were the major phenolic compounds in ethanol extract of winery waste (grape skin and seeds) from red winemaking.…”