Extraction and Concentration of Bioactive Compounds of Cola nitida Using Membrane Processes: Analysis of Operating Parameters and Membrane Fouling

Abstract

Aims: Kola nut is a natural product that is rich in biological active compounds. This work was aimed at evaluating the potential of an integrated system based on the combination of membrane processes for the purification and concentration of kola extract bioactive compounds. Place and Duration of Study: Mature kola seeds were collected in October 2014-February 2015 in South of Côte d’Ivoire and the membranes performances were carried out from May to November 2016 at the European Institute of Membranes, France. Methodology: Kola extract obtained by ethanol-water mixture were clarified by Microfiltration (0.2 µm) and Ultrafiltration (5, 15 and 50 kDa). The choice of ultrafiltration membrane was carried out on a pseudo-tangential pilot and membranes chosen are characterized and validated on a tangential filtration pilot before the concentration of the extracts by nanofiltration (200-400 Da). The effect of crossflow velocity and transmembrane pressure was performed in recycle mode for each membrane. Fractions coming from the membrane processes were analyzed for their content in total polyphenols, proteins, caffeine, catechin and epicatechin. Results: Microfiltration (0.2 µm) coupled with ultrafiltration (50 kDa) produced the purified extract and was submitted to a nanofiltration process to produce a concentrated fraction enriched in active compounds such as polyphenols and caffeine. Permeate flux significantly decreased with time until a steady-state was established due to the membrane fouling. The high retention of proteins in microfiltration (35.71%) and ultrafiltration (35.29%) favors a purity gain of the compounds of interest suh as total polyphenols, caffeine and catechin. However, there is a loss of total polyphenols during ultrafiltration step due to its high retention (29.17%). This result in a low concentration factor in the final retentate (2.56) during the coupling of microfiltration/ ultrafiltration/nanofiltration compared to that observed during the direct concentration of the crude extract (4.27). The opposite is observed for caffeine, catechin and epicatechin. Conclusion: The membrane processes favor the purification and concentration of the bioactive compounds of Cola nitida nuts. However, the ultrafiltration step has the disadvantage of retaining a high proportion of polyphenols and therefore of reducing the antioxidant capacity of the final product.