In Vitro Bioactivities of Food Grade Extracts from Yarrow (Achillea millefolium L) and Stinging Nettle (Urtica dioica L) Leaves

Abstract

<p>Yarrow (<em>Achillea millefolium</em> L., AM) and nettle (<em>Urtica dioica </em>L., UD) are bioactive plants used commercially in functional food and supplement applications and traditionally to alleviate gastric disorders. In this work, the effects of food-grade optimized extracts of Finnish early-season AM and UD were tested on bacterial growth including potential beneficial and foodborne pathogens, as well as murine norovirus (MNV). The anti-inflammatory properties of the extracts were also tested <em>in vitro</em> by NF-κB reporter cells. The food-grade extraction was optimized with the response surface modelling in terms of total carotenoid, chlorophyll, and phenolic compounds contents and antioxidant capacities. The optimal food-grade extraction parameters were a 1-h extraction in 70% ethanol at 45 °C for AM, and at 49 °C for UD. There were no significant effects on the beneficial bacteria (<em>Lacticaseibacillus</em> and <em>Bifidobacterium</em> strains), and the extracts were more effective against gram-positive than gram-negative foodborne bacteria and potential pathogens. <em>Listeria innocua</em> was the most susceptible strain in the optimized extracts with a growth rate of 0.059 ± 0.004 for AM and 0.067 ± 0.006 for UD, <em>p</em> < 0.05 compared to control. The optimized extracts showed a logarithmic growth reduction of 0.67 compared to MNV. The hydroethanolic extracts were cytotoxic to both cell lines, whereas aqueous AM and UD extracts induced and reduced TLR4 signalling in a reporter cell line, respectively. The results provide novel food-grade extraction parameters and support the bioactive effects of AM and UD in functional food applications, but more research is needed to elucidate the precise biological activity<em> in vivo</em> for gastric health.</p>