Impact of Bacterial Fermentation on Phytochemical Profile and Bioactivity of Calendula officinalis and Echinacea purpurea Extracts

The increasing consumer attention toward plant-based products having health-promoting benefits has drawn attention to medicinal herbs such as Calendula officinalis and Echinacea purpurea, that are abundant in bioactive compounds exhibiting anti-inflammatory, antimicrobial and antioxidant properties. In this work, four bacterial strains, Lactiplantibacillus plantarum 299 V, Pediococcus acidilactici IRZ12B, Lacticaseibacillus rhamnosus GG, and Bacillus subtilis natto, were used to ferment aqueous extracts of C. officinalis and E. purpurea. All tested strains exhibited robust growth in the herbal substrates, resulting in a marked drop in pH and increased microbial counts. Fermentation enhanced sugar utilization, stimulated organic acid synthesis, and reduced antinutritional compounds such as tannins, while improving the availability of certain minerals. After fermentation, extracts showed an increased total phenolic level, stronger antioxidant activity, and increased antimicrobial effects relative to unfermented controls. These findings indicate that bacterial fermentation, especially performed by lactic acid bacteria, can substantially augment the functional and phytochemical characteristics of C. officinalis and E. purpurea extracts. This approach supports the development of innovative plant-based fermented nutraceuticals with therapeutic potential. Moreover, the optimized fermentation process offers a strategy for incorporating fermented C. officinalis and E. purpurea extracts into plant-based food products, satisfying the increasing interest of consumers for nutrient-rich, health-oriented foods.