Physicochemical properties, antioxidant activity and in vitro gastrointestinal digestion of purified proteins from black cumin seeds.

The main purpose of this work was to investigate some physiochemical and antioxidant properties of purified proteins of 18 kDa from black cumin seeds. The structural properties of purified proteins were characterized using Fourier Transform-Infrared spectroscopy (FT-IR) and Circular dichroism (CD) spectroscopy analysis. The Tunisian purified protein exhibited a α-helix structure and the Turkish purified protein adopted a ß-sheet conformation. The thermal properties were also evaluated by differential scanning calorimetry (DSC). The Tunisian purified protein presented two endothermic peaks, the first one was at 76.71 °C and the second one was at 131.32 °C. However, only one endothermic peak was found for the Turkish purified protein at 157.63 °C. Both Tunisian and Turkish purified proteins were very stable towards heat-induced denaturation. In addition, the effect of pH, salt (NaCl and Na2SO4) and temperature on functional properties was investigated. The Tunisian black cumin seeds pure protein exhibited better antioxidant activity than that of the Turkish one at all tested concentrations (0.2 to 1 mg/mL) and temperatures (50 °C, 75 °C and 100 °C), as well as after gastrointestinal digestion simulation.

Physicochemical properties of water-soluble polysaccharides from black cumin seeds.

In the present work, water-soluble polysaccharides were isolated from black cumin seeds. Polysaccharides were characterized by their carbohydrate composition, molecular weight, thermal stability and by FTIR, NMR spectroscopy and X-ray diffraction. The surface, the functional and the antioxidant properties of black cumin water-soluble polysaccharides (BCWSP) were also investigated. BCWSP consisted mainly of galacturonic acid (30.20%), glucuronic acid (17.66%) and neutral sugar (22.99%). BCWSP was composed of high peak molecular weight. The FTIR spectrum obtained for BCWSP showed two most important absorptions, at 1659 and 1085 cm-1, which corresponded to COO- of uronic acids and pyranose form, respectively. NMR spectroscopy data suggested that the BCWSP is probably a rhamnogalacturonan backbone with galactan and arabinan side chains. X-ray pattern revealed the semi-crystalline behavior of BCWSP. WHC and OHC of BCWSP were relatively high and varied with temperatures. The polysaccharide zeta potential was greatly affected by pH. Results indicated that the decrease of surface tension has influenced foaming and emulsifying capacities. The DPPH radical scavenging activity of the BCWSP was 63.25% at 1 mg/mL. The BCWSP displayed moderate reductive, ß carotene bleaching and chelating abilities. Overall, our results suggested that BCWSP could be used as alternative additives in food and non-food products.