Solvent-Free Microwave-Assisted Extraction of Polyphenols from Olive Tree Leaves: Antioxidant and Antimicrobial Properties

Abstract

Response surface methodology (RSM) and artificial neural networks (ANN) were evaluated and compared in order to decide which method was the most appropriate to predict and optimize total phenolic content (TPC) and oleuropein yields in olive tree leaf (Olea europaea) extracts, obtained after solvent-free microwave-assisted extraction (SFMAE). The SFMAE processing conditions were: microwave irradiation power 250–350 W, extraction time 2–3 min, and the amount of sample 5–10 g. Furthermore, the antioxidant and antimicrobial activities of the olive leaf extracts, obtained under optimal extraction conditions, were assessed by several in vitro assays. ANN had better prediction performance for TPC and oleuropein yields compared to RSM. The optimum extraction conditions to recover both TPC and oleuropein were: irradiation power 250 W, extraction time 2 min, and amount of sample 5 g, independent of the method used for prediction. Under these conditions, the maximal yield of oleuropein (0.060 ± 0.012 ppm) was obtained and the amount of TPC was 2.480 ± 0.060 ppm. Moreover, olive leaf extracts obtained under optimum SFMAE conditions showed antibacterial activity against S. aureus and S. epidermidis, with a minimum inhibitory concentration (MIC) value of 1.25 mg/mL.

Effect of drying method on oleuropein, total phenolic content, flavonoid content, and antioxidant activity of olive (Olea europaea ) leaf

“…Olive leaves, an agricultural waste obtained during harvesting or processing of olive fruits, contain significant amounts of valuable compounds such as phenolic compounds, which have attracted considerable interest due to their potential use as food additives and/or nutraceuticals in both food and pharmaceutical industries (Le Floch, Tena, Ríos, & Valcarcel, ; Moubarik et al, ; Roselló‐Soto, Barba, et al, ; Roselló‐Soto, Koubaa, et al, ; Şahin et al, ). The polyphenol profiles of olive leaves are different depend on their distribution in various regions (Özcan & Matthäus, ).…”

Effect of Methyl β-cyclodextrin on Radical Scavenging Kinetics of Olive Leaf Extracts and Interactions with Ascorbic Acid

“…In this study, however, it was shown that the maximum response in hesperetin/AA mixtures was achieved at a molar ratio of 5.2/1, which clearly indicated that the nature of polyphenolic antioxidant may define the molar ratio that could yield maximum antioxidant effect, in combination with AA. Furthermore, other authors supported that compounds that are co-extracted with polyphenols from OLL could also interfere [29], but such an effect remains to be elucidated. …”

Utilization of Response Surface Methodology in Optimization of Extraction of Plant Materials

“…(5) (5) where X 1 is the amount of sample, X 2 is the MW irradiation power, and X 3 is the extraction time [9].…”

“…(4) [9] Yield = 0.62767 − 0.029622 X 1 − 2.60 × 10 Where X 1 is the amount of sample, X 2 is the Microwave (MW) irradiation power, and X 3 is the extraction time. The researchers found that the second power of microwave intensity was the most significant parameter, followed by the amount of sample, quadratic time, and power for oleuropein yield [9].…”

“…Box-Behnken designs (BBD) and central composite design (CCD) are two main experimental designs used in response surface methodology [3]. Central composite rotatable design (CCRD) and face central composite design (FCCD) has also been applied to optimization studies in recent years [7][8][9].…”