Vol.:(0123456789) 1 3 Journal of Food Measurement and Characterization https://doi.org/10.1007/s11694-020-00522-0 ORIGINAL PAPER Optimization of high hydrostatic pressure assisted extraction of stinging nettle leaves using response surface methodology experimental design Sílvia A. Moreira 1,2  · Manuela E. Pintado 2  · Jorge A. Saraiva 1 Received: 20 January 2020 / Accepted: 19 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract High hydrostatic pressure assisted extraction (HPE) is a very promising extraction methodology since it can operate at room temperature and therefore can avoid heat-sensitive compounds changes. Furthermore, it is recognized as a fast technology (only a few minutes) and it is also an already proven environmentally friendly technology. This is the first work to study HPE effect as a new extraction method to obtain improved extracts from stinging nettle, a commonly known weed, traditionally used as folk medicine and with several biological properties proven scientifically. In this work, the HPE process was optimized by an experimental design via response surface methodology using a central composite face-centered design. The effect of pressure level, extraction time, and solvent concentration were evaluated, as also the impact of HPE on total phenolics (TPC), flavonoids, pigments, and antioxidant activity. Results showed that experimental data could be well fitted to second-order polynomial mathematical models, since lack-of-fit values were non-significant and the regression coefficients were above 75%. The optimal conditions for the overall maximization of extraction yield, TPC and antioxidant activity were 200 MPa, 10.2–15.6 min, and 0% ethanol (aqueous extracts), which were tested in a further experiment confirming the predictability of all models (difference by percentage between predicted and experimental optimum were all below 10%. When compared to extraction at atmospheric pressure, HPE allowed increasing the extraction yield about 50.5%; TPC about 84.4%; and antioxidant activity about 77.7%. All the models fitted well the experimental data, being the observed values close to the predicted ones by the model equation. Keywords Extraction optimization · Response surface methodology · Bioactive compounds · Antioxidant activity · High- pressure extraction Introduction Food components such as bioactive compounds are increas- ingly used in pharmaceutical and food industries. Medicinal plants are very rich in bioactive compounds being used as natural sources of functional ingredients [1]. Stinging nettle (Urtica dioica L., Urticaceae) is an annual perennial herb, considered by many as a weed, but with great usage in tra- ditional medicine to treat several ailments, such as allergic rhinitis, hypertension, anaemia, gout, and benign prostatic hyperplasia [2]. These beneficial properties are related to nettle chemical composition in bioactive compounds, includ- ing phenolic acids, flavonoids, chlorophylls, and carotenoids [3–6]. Extraction is the first step for the recovery of impor- tant bioactive components present in herbal natural mate- rials, and it can be briefly described as a mass transport phenomenon where solids present in a matrix are transferred into the solvent [7]. There are several conventional extrac- tion methods, such as Soxhlet, maceration, extraction at room temperature, and hydrodistillation. Nevertheless, these methods have low efficiency and final-extract quality, need mild/high temperatures (60–90 ºC), and use a large volume of organic solvents to increase the solubility of materials * Manuela E. Pintado mpintado@porto.ucp.pt * Jorge A. Saraiva jorgesaraiva@ua.pt 1 LAQV-REQUIMTE, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal 2 CBQF - Centro de Biotecnologia e Química Fina – Laboratório Associado, Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Porto, Portugal