How does Flourensia microphylla extract affect polyphenolic composition, antioxidant capacity, and antifungal activity?

Abstract

Tomato (Solanum lycopersicum L.) fruit is one of the most popular vegetables worldwide, as it is widely consumed due to its many nutrients and antioxidants. Fusarium oxysporum and Alternaria alternata are two phytopathogenic fungi that attack tomato in the field and postharvest. To control them, synthetic chemical fungicides are used; however, the fungi develop resistance to them, and they can cause damage to human health and the environment. Therefore, research on plant polyphenolic extracts with fungicidal potential has increased. Flourensia microphylla has shown antifungal activity in vitro against different phytopathogens; however, the extraction process is a main factor affecting this activity. Ultrasound-assisted extraction (UAE) has been reported to increase the bioactivity of plant extracts. Based on the above, the aims of the present study were to evaluate how F. microphylla extract affects polyphenolic composition, antioxidant capacity, and antifungal activity. A total of 9 F. microphylla extracts were obtained by UAE, and a control extract was obtained by conventional extraction. The yield, total phenolic and flavonoid contents (TPC and TFC, respectively), antioxidant activities by three methods, and polyphenol identification by high-performance liquid chromatography (UHPLC) of the extracts were evaluated. The antifungal activity of the extract was evaluated in vitro against F. oxysporum and A. alternata, for which an extract treatment was selected considering the treatment that obtained the highest TFC and antioxidant activity values as a criterion. As a result, three phenolic acids and six flavonoids were detected in the extract treatments: gallic, 4-hydroxybenzoic and ferulic acids, catechin, naringin, quercetin, kaempferol, isorhamentin and chrysin. In addition to reducing the extraction times, the treatment that was selected corresponded to a solvent-to-sample ratio of 40 mL/g and an extraction time of 20 min. The selected extract resulted in an extraction yield of 23.4 g/100 g dry weight (DW), TPC of 252.8 mg gallic acid equivalents (GAE)/g DW, and TFC of 435.9 mg quercetin equivalents (QE)/g DW. For antioxidant activities, the 2,2-diphenyl 1-picrylhydrazyl (DPPH), 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and reducing power values were 74.2, 740.4 mM Trolox/g DW and 33.0 mg ascorbic acid/g DW, respectively. Moreover, the F. microphylla treatment selected inhibited 87.72 % of the mycelial growth of F. oxysporum and 100 % of that of A. alternata, demonstrating fungistatic and fungicidal activity, respectively, in the fungi under study. Thus, the phenolic extract obtained by UAE increased the contents of phenolic compounds, mainly flavonoids, as well as antioxidants, which potentiated the bioactivity of F. microphylla against phytopathogenic fungi. In addition, the antifungal activity could be attributed to the presence of flavonoid compounds identified in the selected polyphenolic extract.