Antioxidant polysaccharide-enriched fractions obtained from olive leaves by ultrasound-assisted extraction with α-amylase inhibition, and antiproliferative activities

Abstract

Polysaccharide-rich materials were extracted from the alcohol-insoluble solids of Olea europaea l. **leaves. Structural characteristics were determined by colorimetric techniques, FT-IR, GC-MS, SEC/MALS/VD/DRI, and NMR (¹H,¹³C). The extract and its main macromolecular components were characterized to assess their ability toward antioxidant, α-amylase inhibition, and antiproliferative activities. Results revealed that the ultrasound olive leave extract comprises polysaccharides with uronic acid, galactose, arabinose, and glucose in molar percentages of 11.7%, 11.3%, 7.5%, and 4.9% respectively, constituting 41% of the total mass. In addition, polyphenols (21%) and proteins (9%) are associated with these polysaccharides. Further, the extract showed noticeable ORAC and free radical scavenging abilities, in addition to high in vitro antiproliferative activity against Caco-2 colon carcinoma cell lines. Similarly, the extract exhibited a strong, uncompetitive inhibition of α-amylase by 75% in the presence of the extract with 0.75 µg/mL of concentration. This research concludes that ultrasound extraction method can be used for the extraction of polysaccharide-polyphenol-protein complexes. These conjugates exhibit the potential for combined biological activities resulting from a synergistic effect of its compounds, making them promising ingredients for the development of functional food.

Keywords: Caco-2 cell line; In vitro activities; Non-conventional method; Olea europaea l.,. Olive by-products; Polysaccharides–polyphenol–protein complex.

Fig. 1

Scheme for ultrasound-assisted extraction of polysaccharide-rich fractions from Olea europaea L. leaves

Fig. 2

Elution profiles obtained using SEC from the refractive index (solid line), light scattering at 90° (dashed line), and viscosity (dotted line) of UOLE obtained with ultrasound extraction using SEC/MALS/DRI/VS in a 0.1 molL⁻¹ LiNO₃ aqueous solution to determine the molar mass distribution

Fig. 3

FT-IR spectra of UOLE registered at the wavelength range (400–4000 cm⁻¹)

Fig. 4

The ¹H a (300 MHz) and ¹³C (75 MHz) b NMR spectra of UOLE

Fig. 5

Kinetics of a hydrolysis of potato starch by pork α-amylase and b Lineweaver–Burk representation of the Michaelian enzyme inhibited uncompetitively by olive leave extract. Starch and UOLE are dissolved in the same 20 mM phosphate buffer at pH 6 and 30 °C

Fig. 6

Antiproliferative activity of olive leaf extract obtained by ultrasound extraction (UOLE) was assessed using Caco-2 cells. Cells containing 4 × 10³ cells/well were exposed to three different concentrations (2.5, 5.0, and 10 mg/mL). Following 1 to 7 days of incubation