In vitro evaluation of the antioxidant activities of carbohydrates

•The antioxidant activities in vitro of different carbohydrates were studied by different manners.•The antioxidant activities of monosaccharide and oligosaccharide had not been found.•The antioxidant activities of complex carbohydrate were mainly attributed to the phenolic and protein components, rather than carbohydrate moiety.

In the current study, we evaluated the antioxidant activities of highly purified monosaccharides, oligosaccharides and complex carbohydrates using six in vitro antioxidant assays, including oxygen radical absorbance capacity (ORAC), ferric reducing antioxidant power (FRAP), β-carotene bleaching assay, 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, hydroxyl radical scavenging and superoxide radicals scavenging methods. The results suggested that monosaccharides and oligosaccharides scarcely exhibited antioxidant activities in vitro. For example in the β-carotene bleaching assay the inhibitory effects of monosaccharides at 1 mg/mL were between 0.24% to 2.25% although galacturonic acid demonstrated some inhibitory effects (8.59%). Significant lower antioxidant activities were observed for complex carbohydrates compared to ascorbic acid and BHT (e.g. ferric reducing antioxidant power by the FRAP assay), >1800 μmol Fe (Ⅱ)/g were observed for ascorbic acid and BHT compared to only 10–60 μmol Fe (Ⅱ)/g for complex carbohydrates, and 1.60 and 6.43 μmol Fe (Ⅱ)/g for mono and oligosaccharides. The observed antioxidant activities for complex carbohydrates are correlated with the presence of phenolic and/or protein components. The findings from the current study indicate that it is necessary to re-evaluate the antioxidant activities claimed for complex carbohydrates in the literature as many of them did not consider the contribution of other minor components such as phenolics and proteins.

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