Isolation and characterization of water-soluble fractions of black sesame pigment and its antioxidant activities in vitro

Abstract

ObjectiveBlack sesame pigment (BSP) was a natural pigment with a variety of bioactivities, including antioxidant, antimutagenic, and neuroprotective properties. However, the high molecular weight and heterogeneous structure of BSP necessitate further investigation. The study's goal is to develop a theoretical foundation for water-soluble BSP as a potential functional food supplement. MethodsFirst, crude black sesame pigment (rBSP) was extracted from black sesame by sodium hydroxide-hydrochloric acid method, furtherly two water-soluble components (BSP-1, BSP-2) were prepared from rBSP by the separation methods of macroporous adsorption resin. In the dynamic test, 40% ethanol (v/v) was applied to five different macroporous resins (AB-8, D101, XAD-1600, D201, and HPD-600) for static adsorption/desorption of rBSP separation. The structure of the components was investigated using ultraviolet (UV) spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and 1H and 13C nuclear magnetic resonance (NMR). Oxygen radical absorption capacity (ORAC) and cellular antioxidation activities (CAA) were used to assess the antioxidant activity of the components. ResultsA macroporous polymeric adsorbent method was developed to obtain water-soluble fractions of rBSP. For the static adsorption/desorption characteristics of rBSP, five types of macroporous resins (AB-8, D101, XAD-1600, D201, and HPD-600) were evaluated, and two fractions (BSP-1 and BSP-2) were isolated from rBSP by 40% ethanol (v/v) on D101 resin in the dynamic test. Furthermore, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, 1H and 13C NMR revealed that BSP-1 and BSP-2 were macromolecule conjugate structures, with BSP-2 having higher aromaticity than BSP-1. ORAC and CAA results showed that rBSP, BSP-1, and BSP-2 had comparable antioxidant activities. The BSP-2 exhibited the highest CAA value of 1121.92 ± 54.45 µmol QE/100 g, DW. ConclusionThis study suggests that water-soluble BSP fractions could be used as functional food supplements that benefit human health.