Maximizing the Recovery of Phenolic Antioxidants from Wild Strawberry (Fragaria vesca) Leaves Using Microwave-Assisted Extraction and Accelerated Solvent Extraction

Abstract

Due to the presence of diverse phenolic classes in wild strawberry (Fragaria vesca L.) leaves, there is an ever-growing effort to find new, efficient methods for their recovery and detailed characterization. Microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) were evaluated to understand the impact of the extraction temperature, extraction time, and solvent-to-sample ratio (SSR) on the quantitative and qualitative properties of the obtained extracts. The highest total phenolic content (8027 mg GA/100 g DW), as well as the highest DPPH• antiradical activity (903 μmol TE/g DW), was obtained with ASE at 150 °C with a static time of 5 min and an SSR of 40:1, while the highest ABTS•+ antiradical activity (681 μmol TE/g DW) and FRAP (2389 μmol TE/g DW) were obtained with MAE after 5 min at 80 °C and an SSR of 40:1. A total of 54 different phenolics were identified by UPLC/MS-MS, some for the first time. The MAE extract had a higher content of phenolic acids (40%; esp. p-hydroxybenzoic acid, gallic acid) and myricetin, while the ASE extract was richer in proanthocyanidins (88%; esp. procyanidin B1, procyanidin trimer), flavonols (29%; esp. quercetin, quercetin-3-glucuronide, rutin), flavan-3-ols (50%; esp. epicatechin), and flavones (39%; esp. luteolin). The results indicated that for optimal extraction conditions, the target phenolics and the desired antioxidant properties of the obtained extracts should be considered.

Green Approach to Enhance the Recovery of Polyphenols from Blackcurrant and Bilberry Leaves: Evaluation of Microwave-Assisted and Pressurized Liquid Extraction

“…Moreover, the pressure application decreases the tension between the sample and the solvent, and compounds with more hydroxyl substituents increase the amount of hydrogen bonds with the solvent, which enhances their solubility [ 45 , 46 ]. These results are in accordance with those reported by Terpinc et al [ 10 ] for the comparison of MAE and PLE effects on individual polyphenols in strawberry leaves, where PLE was shown to be more effective than MAE for the isolation of flavonols, flavan-3-ols, flavones and procyanidins. Similarly, PLE provided a 2-fold higher polyphenolic yield from Moringa oleifera leaves than MAE and was proven to be a more effective technique for the isolation of phenolic compounds with a higher number of hydroxyl-type substituents and those sensitive to high temperatures [ 47 ].…”

“…PLE provided significantly higher amounts of both hydroxycinnamic and hydroxybenzoic acids, while MAE was more effective only in the recovery of syringic acid. This observation is not in line with the results of Terpinc et al [10] for strawberry leaves, reporting that the syringic acid content was 63% higher in the PLE extract than in the MAE extract; however, it aligns with the phenolic acid stability principle during MAE, claiming a better stability of methoxyilates during exposure to microwaves [44]. Regarding flavonoids, PLE was more effective for the isolation of all identified compounds apart from myricetin arabinoside, catechin and procyanidin B1, which were better recovered by MAE.…”

“…On the other hand, the TPC in bilberry leaves was the highest at the highest applied SS ratio of 40 mL/g. When the same PLE study design was applied for the isolation of strawberry leaves’ phenols, a similar effect was observed [ 10 ].…”

“…Generally, temperature is considered the main factor in extraction processes, as it regulates the solubility of the target compounds in the extraction solvent through varying the molecular diffusivity and viscosity of the solvent [30,31]. Similar temperatures were found to be optimal for the PLE of polyphenols from strawberry leaves [10], Stevia rebaudiana leaves' phenolic acids [32] and L. nobilis leaves' polyphenols [8].…”

“…Nowadays, in compliance with the green technology concept, advanced extraction techniques have taken priority over the conventional methods, primarily in terms of time and energy savings. Among these, microwave-assisted extraction (MAE) and pressurized liquid extraction (PLE) have been widely applied for the isolation of polyphenols from plant matrices, including leaves [ 8 , 9 , 10 , 11 ]. The MAE extraction principle is based on the interaction of microwaves with polar compounds through ionic conduction and dipole rotation which cause heating of the sample by friction and consequently cell wall disruption, thus enabling a better solvent penetration into the matrix and a more efficient extraction of the target compounds [ 12 , 13 ].…”