Influence of particle size fraction and bioactive compound contents on the biological activities of Solanum torvum L. leaf powder extracts

This study investigates the bioactive compound content and biological activities of raw powder extracts and particle size fractions from Solanum torvum leaves. The leaves, harvested from Douala, were processed into powders and subsequently divided into different fractions. Methanolic extracts of these powders were analyzed for their content of bioactive compounds (total polyphenols, total flavonoids, and condensed tannins), antioxidant (DPPH, ABTS, FRAP assays), and antimicrobial (bacterial and fungal) activities. The particle size fraction of 250-400 µm constitutes the largest proportion (33.41%) of the raw powder. The highest contents of bioactive compounds are found in the 200-250, 400-500, and < 125 µm fractions for total polyphenols (44.62 ± 0.19 mg GEA/100 ml extract), total flavonoids (14.47 ± 0.37 mg QE/100 ml extract), and condensed tannins (22.79 ± 0.12 mg CE/100 ml extract), respectively. The antioxidant activity of extracts from 500-800µm fraction improved their DPPH and ABTS assays by 31.50% and 40.44% compared to the raw powder. The same fraction (500-800 µm) and the raw powder extracts demonstrated bactericidal activities, while the 125-200, 200-250, and ≥ 800 µm fraction extracts exhibited moderate and significant antifungal activities against several bacterial and fungal strains, respectively. These biological activities are primarily attributed to the average flavonoid contents, which become more accessible in extracts after fractionation. This method of processing powder suggests that no plant powder should be disregarded or rejected due to its low content of bioactive compounds.