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Importance of soluble, insoluble and bioavailable phenolics to antioxidant properties of readyto- eat breakfast cereals

In spite of the growing interest in this field, determination of antioxidant capacity of foods is limited by the antioxidant extraction technique since some antioxidants may remain associated in extraction residues. Therefore, the aim of this study was to compare in vitro physiological extraction with methanol/HCl/water extraction of soluble phenolics and to assess the contribution of bound phenolics to the total phenolic content in different types of breakfast cereals. Eight commercially available readyto- eat breakfast cereals were investigated regarding the content of soluble (methanol/HCl/water extraction), insoluble (alkaline hydrolysis of sample residue) and bioavailable phenolics (enzymatic digestion). Obtained phenolic fractions were subsequently extracted into the diethylether-ethylacetate, evaporated to dryness and diluted in methanol. Phenolic content was determined using Folin- Ciocalteu´s reagent and antioxidant activity of phenolic fractions was evaluated using Trolox equivalent antioxidant capacity and the ferric reducing power assay. Free phenolic content ranged from 12.4-473.3 mg/100g dry matter while the contribution of bound phenolics to the total phenolic content was significantly higher ranging from 35.2-937.2 mg/100g dry matter. The content of bioavailable phenolics obtained after enzymatic extraction was about equal or higher in comparison to soluble phenolic content thus indicating the importance of physiological approach in evaluating breakfast cereals as sources of these biologically active compounds. In majority of investigated samples the bound and bioavailable phenolic fraction demonstrated a significantly higher antioxidant capacity in comparison to free phenolics. Therefore, inclusion of bound phenolics and enzymatic approach in studies related to quantification and antioxidant activity evaluation of breakfast cereals is essential.

breakfast cereals; antioxidant properties; phenolics

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