Extraction, isolation of heat-resistance phenolic compounds, antioxidant properties, characterization and purification of 5-hydroxymaltol from Turkish apple pulps.

Apple pulps (AP) were obtained as a side product in fruit juice factories and contains valuable phenolic compounds. The dried AP was subjected to extraction with water, ethyl acetate (APEA) and n-butanol (APBU), respectively. 5-Hydroxymaltol (5-HM) was isolated and confirmed by NMR techniques. The HPLC-TOF/MS analysis revealed the presence of 16 components including major components of morine, gentisic, 4-hydroxybenzoic, vanillic and fumaric acid. The antioxidant activities were evaluated with total antioxidant activity, reducing power, inhibition of lipid peroxidation, metal chelating, free radical and H2O2 scavenging activities. 5-HM, APEA and APBU exhibited the in vitro antioxidant activities in a concentration-dependent and moderate manner. The IC50 values were effective for free radical scavenging activity of 5-HM (8.22 µg mL-1), H2O2 scavenging activity for APEA (8.12 µg mL-1) and inhibition of lipid peroxidation for APEA (0.93 µg mL-1). The 5-HM and APEA have antioxidant capacities and also feasible to apply variety in vivo tests.