Home > RESEARCH > Foundational > Polyphenols in plant foods higher than previously estimated

Polyphenols in plant foods higher than previously estimated   Researchers in this featured study make an important discovery regarding the total content of polyphenols in plant foods. In recent years investigators have compiled increasing data on these bioactive compounds and their potential health effects, including data on flavanols, proanthocyanidins, anthocyanidins, flavones, flavonols and tannins, among others. However, Arranz et al, note that most reports only include data on "extractable polyphenols (EPP);" food compounds extracted in aqueous organic solvents before undergoing high performance liquid chromatography (HPLC) analysis. Meanwhile, cite researchers, significant amounts of bioactive polyphenols may remain unaccounted for in the residues from such extractions. These "nonextractable polyphenols (NEPP)" require a different chemical or enzymatic treatment process in order to be extracted from the food matrixes before undergoing an HPLC analysis. Given the many potential antioxidant activities of nonextractable polyphenols (largely comprised of hydrolysable tannins and proanthocyanidins), together with the absence of data in the literature, Arranz et al sought to extract and quantify NEPP and compare the concentrations to EPP.   To determine total content of polyphenols in apple, peach and nectarine, researchers conducted a common analysis of EPP in aqueous-organic extracts together with a NEPP analysis in acidic hydrolysates of extraction residues using HPLC-MS and spectrophotometry. All fruits were purchased at optimal maturity from markets in Madrid, Spain. The results for EPP and NEPP were determined as mg per 100 g of fresh fruit. EPP determination included concentrations of chlorogenic acids, epicatechins, quercetin-3-glucosides and several other polyphenols. Arranz et al's data for EPPs is consistent with previous findings in the literature. Though there is no other data on HPLC quantification of NEPP in the literature, researchers note the concentrations of NEPP in this study (epicatechins, ellagic acid, gallocatechins and others) are "consistent with other reported data from spectrophotometric analyses."   The most significant findings of this study was that NEPP content of apples, peaches and nectarines were significantly higher that the EPP content of these fruits (112-126 mg/100g to 18.8-28 mg/100 g). Investigators elaborated on the significance of their findings, noting, for instance, that concentrations of proanthocynanidins may be very underestimated if nonextractable proanthocynanidins are not considered. Arranz et al cite previous research attributing "antimicrobial properties, antimutagenic activity, and cardioprotective effects" to proanthocynanidins. Given the absence of data of NEPP in the literature, the findings of this featured study contribute greatly to the growing knowledge base of bioactive compounds in fruits and plant foods, and in turn, their potential biological and clinical significance.   Study: Arranz, S., et al, J. Agric. Food Chem., 57: 7298-7303, (2009)

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