Nowadays, the food industry is heavily involved in searching for green sources of valuable compounds, to be employed as potential food ingredients, to cater to the evolving consumers’ requirements for health-beneficial food ingredients. In this frame, agri-food by-products represent a low-cost source of natural bioactive compounds, including antioxidants. However, to effectively recover these intracellular compounds, it is necessary to reduce the mass transfer resistances represented by the cellular envelope, within which they are localized, to enhance their extractability. To this purpose, emerging extraction technologies, have been proposed, including Supercritical Fluid Extraction, Microwave-Assisted Extraction, Ultrasound-Assisted Extraction, High-Pressure Homogenization, Pulsed Electric Fields, High Voltage Electrical Discharges. These technologies demonstrated to be a sustainable alternative to conventional extraction, showing the potential to increase the extraction yield, decrease the extraction time and solvent consumption. Additionally, in green extraction processes, also the contribution of solvent selection, as well as environmental and economic aspects, represent a key factor. Therefore, this review focused on critically analyzing the main findings on the synergistic effect of low environmental impact technologies and green solvents towards the green extraction of antioxidants from food by-products, by discussing the main associated advantages and drawbacks, and the criteria of selection for process sustainability.
This study was focused on the optimization of the pulsed electric fields (PEF)-assisted extraction process using central composite design for response surface methodology from response surface methodology (RSM) with the aim to sustainably intensify the extractability of phenolic compounds from white grape pomace. The cell disintegration index (Zp) was used as response variable to identify the optimal PEF pre-treatment conditions of grape pomace in terms of field strength (E = 0.5–5 kV/cm) and energy input (WT = 1–20 kJ/kg), to be applied prior to the subsequent solid-liquid extraction (SLE) process. for both untreated and PEF-treated samples SLE process was optimized to determine the most effective combination of extraction temperature (20–50°C), extraction time (30–300 min), and solvent concentration (0–100% ethanol in water). Total phenolic content (TPC), flavonoid content (FC), and antioxidant activity (FRAP) of the obtained extracts were determined. The extracted compounds from untreated and PEF-treated samples at the optimal conditions were analyzed via HPLC-PDA analysis. Results revealed that, at a fixed extraction temperature (50°C), the application of PEF at optimal processing conditions (E = 3.8 kV/cm, WT = 10 kJ/kg) prior to SLE has the potential to reduce the solvent consumption (3–12%) and shorten the extraction time (23–103 min) to obtain the same recovery yield of phenolic compounds. Under optimized conditions, the extracts derived from PEF-treated samples showed significantly higher TPC (8%), FC (31%), and FRAP (36%) values, as compared to the control extraction. HPLC analyses revealed that epicatechin, p-coumaric acid, and quercetin were among the main phenolic compounds extracted, and no degradation phenomena occurred due to PEF application.
This work compared the effects of pulsed electric fields (PEF) and ultrasound (US) technologies on the extent of cell disintegration of two Mediterranean herb tissues (Origanum vulgare L., Thymus serpyllum L.), as well as on the extractability of phenolic compounds during the subsequent hydroalcoholic extraction (0-50% ethanol in water, v/v) for up to 4h. The rate of phenolic compounds extraction decreased with time and was predicted rather satisfactorily (R 2 =0.898-0.989) by the Peleg's model. The application of either PEF or US treatment prior to solid-liquid extraction (SLE) has the potential to reduce duration and concentration of ethanol to achieve the same recovery yield of phenolic compounds. Under optimized PEF (3 kV/cm, 10 kJ/kg) and US (400 W, 20 min) treatment conditions, the extracts obtained from either PEF or US pre-treated herb samples showed higher total phenolic yield (36% on average) and antioxidant activity (FRAP) (36% on average) as compared to the control extraction, especially when 25% ethanol was used as a solvent. GC/MS analyses revealed no evidence of degradation of individual phenolics due to either PEF or US application.
In this work, the effect of pulsed electric field (PEF) pre-treatment on the extractability in green solvents (i. e., ethanol–water mixture and propylene glycol) of target aroma and bioactive compounds, such as vanillin from vanilla pods, theobromine and caffeine from cocoa bean shells, linalool from vermouth mixture, and limonene from orange peels, was investigated. The effectiveness of PEF as a cell disintegration technique in a wide range of field strength (1–5 kV/cm) and energy input (1–40 kJ/kg) was confirmed using impedance measurements, and results were used to define the optimal PEF conditions for the pre-treatment of each plant tissue before the subsequent solid–liquid extraction process. The extracted compounds from untreated and PEF-treated samples were analyzed via GC-MS and HPLC-PDA analysis. Results revealed that the maximum cell disintegration index was detected for cocoa bean shells and vanilla pods (Zp = 0.82), followed by vermouth mixture (Zp = 0.77), and orange peels (Zp = 0.55). As a result, PEF pre-treatment significantly enhanced the extraction yield of the target compounds in both solvents, but especially in ethanolic extracts of vanillin (+14%), theobromine (+25%), caffeine (+34%), linalool (+114%), and limonene (+33%), as compared with untreated samples. Moreover, GC-MS and HPLC-PDA analyses revealed no evidence of degradation of individual compounds due to PEF application. The results obtained in this work suggest that the application of PEF treatment before solid–liquid extraction with green solvents could represent a sustainable approach for the recovery of clean labels and natural compounds from aromatic plants and food by-products.
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