Application of response surface methodology for obtaining fermented extract of Sanguisorba officinalis L. herb with high antioxidant activity, polyphenols, and lactic acid content: analysis of the content and skin permeation of selected phenolic acids.

Fermented plant extracts are becoming increasingly popular as active ingredients in cosmetics and pharmaceutical preparations applied topically to the skin. One of the most popular fermentation methods is fermentation using lactic acid bacteria. The aim of the research was to assess the impact and optimise the technological parameters of the fermentation process (using response surface methodology) of the Sanguisorba officinalis L. herb (i.e., fermentation time, plant material content, molasses content, and inoculum content) in terms of antioxidant activity (DPPH and FRAP techniques), total polyphenol content, and lactic acid content. Using optimal parameters - fermentation time: 10 days, plant material content: 1.3 g L-1, molasses content: 16%, and inoculum content: 19% - a fermented extract was obtained with antioxidant activity of 8.1 ± 0.3 mmol Trolox per L (DPPH method), 44.1 ± 0.1 mmol FeSO4 per L (FRAP method), polyphenol content of 3.2 ± 0.1 g GA per L and lactic acid (LA) content of 25.2 ± 1.1 g L-1. The obtained fermented extract is characterized by high hydrophilicity (log P = -0.8). HPLC analysis showed the presence of phenolic acids in the fermented extract, among which the highest concentrations were observed for chlorogenic acid (347 ± 7 mg L-1), 4-hydroxybenzoic acid (231 ± 8 mg L-1), 2,5-dihydroxybenzoic acid (210 ± 10 mg L-1), and gallic acid (205 ± 6 mg L-1). Among the identified acids, gallic acid permeated porcine skin the fastest and achieved the highest concentration, ranging from 11.62 ± 1.05 µg cm-2 at the 5th hour of penetration to 35.8 ± 1.6 µg cm-2 after 24 hours. The presence of 3,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 4-hydroxybenzoic acid, and vanillic acid was also noted in the acceptor fluid after 24 hours of permeation. The obtained results confirm the validity of using the fermentation process to obtain extracts with a high content of compounds with antioxidant potential, including polyphenols and lactic acid, which have a multifaceted positive effect on the skin. Optimisation of the fermentation process of the S. officinalis herb, which has so far had very limited use in cosmetic and pharmaceutical preparations (unlike the root of this plant), may contribute to the increased interest in and use of this plant raw material in the cosmetic and pharmaceutical industries.