Enhancing antioxidant activity of olive pomace with reinforcing its phenolic compounds by fermentation

Background and objective Valorization of olive pomace (OP) by solid-state fermentation of the generally regarded as safe yeast, Kluyveromyces marxianus was reported to enhance its antioxidant activity. However, a detailed identification of bioactive compounds present in unfermented OP and fermented OP was not clarified. The aim of the present study was to identify the major classes of bioactive compounds, and alteration in the phenolic profile after fermentation to explain the enhanced therapeutic activity of OP after fermentation. Materials and methods Methanolic extracts of unfermented OP and fermented OP were subjected to qualitative preliminary phytochemical analysis. Moreover, both extracts were subjected to high-performance liquid chromatography analysis using different phenolic compounds' standards. Also, total antioxidant capacity of both extracts was evaluated. Results Simple phenols, tannin, phlobatannins, flavonoids, steroids, terpenoids, cardiac glycosides, reducing sugars, alkaloids, carbohydrates, sterols, and triterpenes are the major phytochemical classes present in both extracts. While both extracts lack saponin, anthraquinones, free amino acids, free cholesterol, and polyuronides. High-performance liquid chromatography analysis confirmed that fermentation of OP by K. marxianus led to a sharp increase in rutin, vanillin, and cinnamic acid contents by 69.22, 39.35, and 31.40%, respectively. This was accompanied with 22.78, 7.07, and 5.81% increase in quercetin, catechin, and syringic acid contents, respectively. While gallic, caffeic, and coumaric acid contents were decreased after fermentation by 59.24, 55.25, and 53.96%, respectively. Methanolic extracts of unfermented OP and fermented OP showed a maximum total antioxidant capacity of 144.81 & PLUSMN;1.47 and 187.57 & PLUSMN;4.00 mgVCE/l at a concentration of 10 and 6 mg/ml, respectively. Conclusion Solid-state fermentation of OP with K. marxianus strongly affected its total antioxidant capacity by increasing its content of several bioactive compounds.