The Effect of Lactic Acid Fermentation on Extraction of Phenolics and Flavonoids from Sage Leaves

This work analysed the effect of spontaneous fermentation of sage leaves on the release and extraction of flavonoid and phenolic compounds. Chemical profiling based on thin-layer chromatography was used to compare different extracts from two sage species, common sage (Salvia officinalis) and white sage (Salvia apiana). Non-fermented Salvia apiana extracts are richer in antioxidants, phenolics, and terpenoids. Fermentation significantly enhances extraction of total phenolics, flavonoids, and antioxidants only from Salvia officinalis leaves, while it does not affect extraction from Salvia apiana leaves. In each 20 µL of extract, extraction of polyphenolics increases from 6.55 to 21.01 µg gallic acid equivalents (GAE), anti-oxidants from 0.68 to 2.12 µg GAE, and flavonoid content from 48.01 to 65.33 µg RE (rutin equivalents). Higher antioxidant activity in fermented Salvia apiana ethyl acetate extracts is associated with an increased concentration of phenolics and phenolic terpenoids. However, in Salvia officinalis, the higher antioxidant activity of fermented extract is a result of the release and improved extraction of flavonoids, as there is no increase in the extraction of phenolics. Lactic acid produced via fermentation and proline from Salvia officinalis leaves forms a natural deep eutectic solvent (NADES), which significantly increases the solubility of flavonoids.