Abstract
The effect of spontaneous fermentation by lactic acid bacteria on the extraction yield of bioactive compounds and antioxidant activity from rosemary leaf extracts was investigated using high-performance thin-layer chromatography (HPTLC). Brining and spontaneous fermentation with lactic acid bacteria more than doubled extraction of polyphenolics and antioxidants from the rosemary leaves. The results show that lactic acid fermentation enhances antioxidant activity in extracts by increasing the total phenolic content but does not increase extraction of phytosterols. Increased extraction of phenolic oxidants during fermentation assisted extraction, results from the in situ generated natural eutectic solvent from the plant sample. ATR-FTIR spectra from the bioactive bands suggests that this increased antioxidant activity is associated with increased extraction of rosmarinic acid, depolymerised lignin, abietane diterpenoids and 15-hydroxy-7-oxodehydroabietic acid.
Highlights
The aim of this study was to investigate the effect of spontaneous fermentation by lactic acid bacteria on the extraction yield of bioactive compounds and antioxidant activity from rosemary leaf (Rosmarinus officinalis L., Lamiaceae) extracts, using high-performance thin-layer chromatography (HPTLC) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to provide chemical characterisation of detected major antioxidants
The effect of spontaneous lacto-fermentation on the extraction efficiency of antioxidants and natural products from rosemary leaves was studied via HPTLC profile comparison
Low pH prevents other pathogenic bacteria to grow, while different cell wall degrading enzymes from lactic acid bacteria (LAB) helped in the maceration of the plant matrix and promoted the release of the plant secondary metabolites. This biotransformation of complex constituents into extractable components during fermentation is similar to the metabolic activity of the gut microbiota in the human intestine, with its microbiome being composed of a wide range of different LAB [15]
Summary
The most abundant secondary metabolites, are the main source of dietary antioxidants and have many health benefits [1]. Rosemary and other members from the Lamiaceae family are a rich source of natural antioxidants. The European Union has recently approved rosemary extracts as a safe and effective natural antioxidant for food preservation [2]. Different extraction methods were found to recover quite different groups of polyphenols. Their use in foods is limited because of their odour, colour and taste. Various methods have been developed for the preparation of odourless and colourless antioxidant compounds from rosemary. The principal antioxidant components in these extracts are phenolic diterpenes carnosol and carnosic acid, and phenolic acids such as rosmarinic acid (the caffeoyl derivative) [3,4]
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