Green Ultrasound Assisted Extraction of trans Rosmarinic Acid from Plectranthus scutellarioides (L.) R.Br. Leaves

Abstract

Painted nettle (Plectranthus scutellarioides (L.) R.Br.) is an ornamental plant belonging to Lamiaceae family, native of Asia. Its leaves constitute one of the richest sources of trans-rosmarinic acid, a well-known antioxidant and antimicrobial phenolic compound. These biological activities attract interest from the cosmetic industry and the demand for the development of green sustainable extraction processes. Here, we report on the optimization and validation of an ultrasound-assisted extraction (USAE) method using ethanol as solvent. Following preliminary single factor experiments, the identified limiting extraction parameters (i.e., ultrasound frequency, extraction duration, and ethanol concentration) were further optimized using a full factorial design approach. The method was then validated following the recommendations of the association of analytical communities (AOAC) to ensure the precision and accuracy of the method used to quantify trans-rosmarinic acid. Highest trans-rosmarinic acid content was obtained using pure ethanol as extraction solvent following a 45-minute extraction in an ultrasound bath operating at an ultrasound frequency of 30 kHz. The antioxidant (in vitro radical scavenging activity) and antimicrobial (directed toward Staphylococcus aureus ACTT6538) activities were significantly correlated with the trans-rosmarinic acid concentration of the extract evidencing that these key biological activities were retained following the extraction using this validated method. Under these conditions, 110.8 mg/g DW of trans-rosmarinic acid were extracted from lyophilized P. scutellarioides leaves as starting material evidencing the great potential of this renewable material for cosmetic applications. Comparison to other classical extraction methods evidenced a clear benefit of the present USAE method both in terms of yield and extraction duration.

A Quick, Green and Simple Ultrasound-Assisted Extraction for the Valorization of Antioxidant Phenolic Acids from Moroccan Almond (<em>Prunus dulcis</em> (Mill.) D.A.Webb) Cold-Pressed Oil Residues

“…In addition, increasing US frequency can also lead to a drastic reduction in extraction time, thereby reducing energy consumption, which is in accordance with the green chemistry principles [27]. However, depending on the compound and the plant matrix subjected to the extraction, application of high US frequency can alter or even destroy the native structure of the compound, which not only decreases the extraction yield, but also considerably reduces its biological activity, thus negating any valuation interest [14]. Therefore, during the development of an USAE method, US frequency must be optimized very carefully depending on the compound, and the plant matrix subjected to the extraction.…”

“…The Behnken Box matrix is a spherical and rotating design, which, view on a cube, consists of the central point and the middle of the edges [22,23]. Many parameters can influence the extraction of phenolic compounds from plant matrices [24], but 3 parameters are very widely distinguished when developing an ultrasound-assisted extraction method: the type of solvent used, the frequency of ultrasound applied and the extraction time [13][14][15].…”

“…In addition, its extraction capacity can easily be modulated by the addition of water, making it an ideal solvent for the extraction of a wide range of polyphenols of low to high polarity. Last, these two universal solvents (namely EtOH and water) have been commonly used for various food and / or cosmetic applications [11,14,15,24,26].…”

“…Finally, regarding the extraction time, it is important to consider that its increase does not necessarily lead to a gain in terms of extraction yield, since, on the contrary, a prolonged exposure to US can lead to the increased degradation of the compound [14]. In addition, in order to reduce the impact of energy consumption in the green chemistry context, optimizing the extraction time also appears to be essential [27].…”

“…By the past, there were many methods developed for the extraction of natural antioxidants from various natural matrices based on conventional methods such as maceration or Soxhlet extraction. More recently, green extraction methods including microwave-assisted extraction or ultrasonic-assisted extraction (USAE) have been found to be particularly effective [11][12][13][14][15]. These green extraction technologies have also aroused great interest for industrial applications, and USAE is now considered as one of the most efficient energy saving processes in terms of duration, selectivity and reproducibility, operating under mid-extraction conditions [11].…”