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

Abstract

Objective: Black 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. Methods: First, 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. Results: A 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. Conclusion: This study suggests that water-soluble BSP fractions could be used as functional food supplements that benefit human health.

Keywords

• Black sesame pigment
• Isolation
• Characterization
• Antioxidant activity