Non-thermal plasma as a pretreatment for extraction of herbal tea by-products

Traditional extraction methods involve the use of polar solvents and/or high temperatures. Both are often energy or timeconsuming and require additional purification steps. This compromises the quality of the extracts obtained. Non-thermal plasma pretreatment for extraction is a promising technique that could increase the sustainability of the process while following the principles of hurdle technology. In this work, we investigated the effects of plasma treatment on the aqueous extraction of antioxidant compounds from herbal tea by-products. Stinging nettle, hoary willowherb, and St. John's Wort extracts were treated with plasma at different time intervals. The extracts obtained were analyzed for their antioxidant capacity and total phenolic content. Their potential use as growth media for Ligilactobacillus sp. was also investigated. Hoary willowherb extracts showed the highest total phenolic content and antioxidant activity. While plasma treatment slightly decreased the antioxidant capacity of these extracts, it improved microbial growth. In contrast to hoary willowherb, the antioxidant capacity of stinging nettle extracts' was not affected by plasma treatment. These extracts were also better for bacterial growth. When added to 25% v/v Mrs broth, stinging nettle extracts achieved a growth rate similar to that of pure Mrs broth (~10⁹ CFU/ml), demonstrating their potential for microbial biomass production and food and feed supplementation.