Abstract
Willowherb (Epilobium angustifolium L., family Onagraceae) is a well-known food and medicinal plant used after fermentation as a source of beverages with high antioxidant potential. Despite this long history of use, only a few papers have described the chemical profile and bioactivity of fermented willowherb tea in general. To understand the basic metabolic differences of non-fermented and fermented E. angustifolium leaves, we used general chemical analysis, high-performance liquid chromatography with photodiode array detection and electrospray ionization triple quadrupole mass spectrometric detection assay, and an isolation technique. As a result, the content of 14 chemical groups of compounds was compared in the two plant materials; 59 compounds were detected, including 36 new metabolites; and a new water-soluble phenolic polymer of melanoidin nature was isolated and characterized. The fundamental chemical shifts in fermented E. angustifolium leaves relate mainly to the decrease of ellagitannin content, while there is an increase of melanoidin percentage and saving of the antioxidant potential, despite the significant changes detected. The strong antioxidative properties of the new melanoidin were revealed in a series of in vitro bioassays, and a simulated gastrointestinal and colonic digestion model demonstrated the stability of melanoidin and its antioxidant activity. Finally, we concluded that the new melanoidin is a basic antioxidant of the fermented leaves of E. angustifolium, and it can be recommended for additional study as a promising food and medicinal antioxidant agent.
Highlights
Fermentation, as a biotechnological process, is widely used in the food industry to modify various organoleptic and physicochemical properties of plant materials, including the colour, odour, taste, and extractability [1]
Using literature data to construct the Van Krevelen diagram, we found that plant melanoidins were similar to fungal melanoidins; there were certain differences (Figure 4a)
The results indicated that E. angustifolium angustifolium melanoidin melanoidin (EAM) is a polymer with an irregular and complex structure similar to that of known pigments from other fermented foods, such as black tea and Java tea
Summary
Fermentation, as a biotechnological process, is widely used in the food industry to modify various organoleptic and physicochemical properties of plant materials, including the colour, odour, taste, and extractability [1]. Used functional products are functional beverages, namely herbal teas, which have pleasant organoleptic properties and a positive biological effect [7]. The application of fermentation to create plant-based beverages is the most commonly used process. Among the functional drinks obtained from fermented plants, the most famous are those using Camellia sinensis (L.) Kuntze (Theaceae) to create teas with a wide range of fermentation [8,9]. The most fermented product, black tea, is the most popular functional drink along with green tea. The chemical feature of such beverages is the presence of lowmolecular-weight metabolites of the unfermented plant and a specific group of phenolic
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