Application of Ultrasound as Clean Technology for Extraction of Specialized Metabolites From Stinging Nettle (Urtica dioica L.)

Abstract

Nettle is a highly valued medicinal plant that is still largely neglected, both in terms of nutrition and use for pharmacological purposes. Tinctures, i.e., alcoholic extracts, are becoming increasingly popular nettle products, mainly because they allow better availability of phytochemicals and their stability over a longer period of time. The production of alcoholic extracts is a chemically demanding process that is still usually carried out using conventional techniques, which have numerous drawbacks. The use of green technologies such as ultrasound-assisted extraction (UAE), which is characterized by high efficiency of phytochemical extraction, shorter treatment time, and a much lower environmental footprint, is a suitable and sustainable solution. Therefore, the aim of this study is to determine the influence of the extraction method, conventional and ultrasound (by varying two ultrasound equipment systems), time and ethanol concentration on the extraction of specialized metabolites from nettle powder. Ultrasonic extraction using a probe system significantly contributed to increase the ascorbic acid yield, polyphenolic compounds, and antioxidant capacity of nettle extracts compared to conventional extraction. In addition, when a probe system was used during UAE, significantly less time was required for isolation of individual specialized metabolites compared to ultrasonic extraction in the bath. Ethanol concentration (50 and 80% v/v) also proved to be an important factor in the efficiency of extraction of specialized metabolites, with 80% ethanol being more effective for the isolation of ascorbic acid and pigment compounds (chlorophyll and carotenoids), while 50% v/v for the extraction of polyphenolic compounds. It can be concluded that extraction with the ultrasonic probe system is much more efficient in obtaining higher yields of specialized metabolites from nettle powder in a shorter time (average process duration 5–10 min) both compared to UAE in the bath and classical extraction. However, optimization of the key factors of time, solvent type, and ultrasonic power is necessary to maintain the nutritional quality of the nettle extract in order to obtain a final product with a high specialized metabolites content, antioxidant capacity, and functional value. The future application of alcoholic nettle extracts is based on the fact that these products have significant potential as functional foods and pharmacological preparations for the treatment of a number of but also to strengthen the immune system, mainly due to the rich nutritional composition and high content of various specialized metabolites. The prepared extracts can be safely taken orally by diluting the tinctures with water immediately before ingestion.

Ultrasonic-Assisted Extraction and Antioxidant Potential of Valuable Protein from Ulva rigida Macroalgae

“…using a high-voltage pulse electric field (PEF) and mechanical press [ 14 ]. Ultrasonic-assisted extraction was used for bio substances or phytochemical extraction as a green technology [ 15 ]. Ultrasonic pretreatment was applied for protein extraction from Ascophyllum nodosum using probe-type ultrasound equipment with 750 W capacity and 20 kHz frequency.…”

Recent advances in ultrasound application in fermented and non‐fermented dairy products: antibacterial and bioactive properties

“…Moreover, several new technologies have been reported for improvement of protein digestion efficiency and production of bioactive compounds including high‐pressure, infrared, microwave, and ultrasound (Switzar et al ., 2013). Among them, ultrasound has been widely used for the extraction of bioactive compounds in many studies (Surin et al ., 2020; Šic Žlabur et al ., 2022) and recently, its positive and promising effects on physicochemical and bioactive properties of food compounds, have greatly increased the interest and attention of food science researchers for more ultrasound applications in the food industry. It has been revealed that the extraction of proteins and bioactive peptides using ultrasound caused an increment in the rate and yield of extraction (Kadam et al ., 2015).…”

How to Increase the Nutritional Quality of Stinging Nettle Through Controlled Plant Nutrition

“…Stinging nettle ( Urtica dioica L.) is a plant species that has been known for its nutritional and medicinal properties since ancient times ( 5 ). Nettle has a great potential in food processing for the production of food supplements, tinctures and capsules ( 6 ) and as a source of green pigments for food colouring ( 7 ). It is also used in the pharmaceutical, cosmetic and textile industries.…”

“…It is also used in the pharmaceutical, cosmetic and textile industries. All parts of the plant contain large amounts of different bioactive compounds, but leaves are the richest source, which is why they are intended for consumption as a green leafy vegetable ( 6 ). Nettle leaves contain: carbohydrates, dietary fibre, protein, fatty acids (mostly palmitic and linoleic acids), vitamins (A, B group vitamins, C, D, E and K), minerals (especially P, Ca, Mg and Fe), photosynthetic pigments (chlorophyll a and b, carotenoids), amino acids, organic acids, tannins, terpenoids and phenols ( 8 , 9 ).…”