Physicochemical and functional properties of Garcinia kola Heckel (bitter kola) protein fractions

The use of natural compounds as safer substitutes in/as functional foods, dietary supplements, therapeutics and pharmaceuticals is of great interest because of the secondary effects of synthetic compounds. This study investigated the physicochemical, functional and in vitro bioactivities of Garcinia kola seed protein fractions. G. kola seed albumin, globulin and prolamin were extracted with water, saline, and alcohol, respectively. Structural characterization was done by Fourier transform infrared spectroscopy (FTIR). Antioxidant activities (Fe²⁺-chelating activity and ferric reducing power) and functional properties (solubility, foaming and emulsification) were done using standard procedures. Zone of inhibition test was used to ascertain the antibacterial potentials of the fractions. Prolamin was the predominant protein component of Garcinia kola seeds. FTIR spectrum revealed that the fractions are characterized by Amide I and Amide II bands. The fractions showed significant antioxidant activity, with globulin having the highest activity. Globulin and prolamin fractions exhibited the highest solubility between pH 10–12 and were least soluble at pH 2, while albumin had its lowest solubility at pH 9. High emulsifying activity index was observed for all the fractions, with the highest emulsifying stability index of about 160 min. The fractions also showed no antimicrobial activity, except prolamin, which minimally inhibited Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis. Therefore, Garcinia kola proteins can be effectively used as health-beneficial foods and dietary supplements to improve food nutrition and product diversification.