Green subcritical water extraction of Mentha x rotundifolia leaves collected in different annuities

Abstract

Aim: In this work, the development for the first time of a green and efficient method to obtain bioactive extracts from Mentha x rotundifolia leaves has been investigated. Methods: The efficiency of three techniques [microwave-assisted extraction (MAE), subcritical water extraction (SWE), and ultrasound-assisted extraction (UAE)] was compared in terms of total phenolic content (TPC) and antioxidant activity [1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzthioazoline-6-sulfonic acid) (ABTS) assays]. Results: Under similar operating conditions, SWE outperformed MAE and UAE for providing M. rotundifolia extracts with improved antioxidant activity. Further in-depth optimization of the SWE method by means of a Box-Behnken experimental design showed 120°C, 5 min, 0.08 g dry sample: 1 mL water and 2 extraction cycles as optimal experimental parameters to provide the maximum yield of phenolics and the highest bioactivity. The application of the developed SWE method to M. rotundifolia leaves collected in different annuities (2014–2017) showed, in general, no significant differences regarding both composition and antioxidant capacity, as expected from plant samples grown in field under drip irrigation conditions. Conclusions: The SWE method here optimized is shown as a sustainable and efficient alternative for providing bioactive M. rotundifolia extracts with application as functional ingredients, natural preservatives, etc. in the food industry, among others.