# High-Pressure Technologies for the Recovery of Bioactive Molecules from Agro-Industrial Waste
## 4 Combined Extractions
At the optimized operating conditions, which for SFE are a temperature of 40 \({}^{\circ}\)C, a pressure of 350 bar (for phytosterols) and 400 bar (for tocopherol), and 5 wt% ethanol as cosolvent, SFE resulted in efficiencies that were three times higher than the ones obtained with the modified Soxhlet extraction technique. Considering that a cosolvent is needed, the benefit of using scCO\({}_{2}\) is reduced. For this reason, PLE is preferred for the extraction of these compounds. Indeed, because sc-CO\({}_{2}\) preferentially extracts non-polar compounds, the residue from supercritical fluid extraction (SFE) can be used as feedstock for a second extraction stage based on PLE (or other pressurized-assisted extraction processes) to complete the extraction of polar molecules. Furthermore, the future direction of food waste valorization is directed towards the combination of these innovative processes in a sequential stage extraction [16; 180]. This approach was evaluated by [PERSON] et al. [76], who, from an economical point of view, investigated the possibility of coupling PLE and SFE for the recovery of phytonutrients from biquinho pepper, using supercritical carbon dioxide and ethanol 75% aqueous solution. They estimated that producing biquinho pepper-derived products was economically viable and a combined and sequential process led to a lower manufacturing cost than the commercialization price of the extracts. Similarly, [PERSON] et al. [181] compared two process alternatives to obtain four extract fractions from passion fruit bagasse. The first, which showed economic promise, involved a sequential multi-stage process comprising three steps of supercritical fluid extraction (SFE) and one step of pressurized liquid extraction (PLE), while the second option included the production of one extract from passion fruit finds by single-stage PLE process. The efficiency of the biorefining process, based on consecutive supercritical carbon dioxide and pressurized liquid extractions, was also proposed in the work of [PERSON] et al. [182]. The authors used cranberry pomace as a raw material for the recovery linelonic, linoleic acids, andtocopherol rich extract by SFE and ethanol-soluble and water-soluble antioxidants from a sequential PLE extraction using ethanol and water, respectively. The feasibility and efficiency of using a sequential process with green extraction methods based on GRAS solvents from the Amazonian munguba seed was also investigated, showing a free-solvent oil mainly composed of palmitic acid can be firstly recovered by SFE, followed by a phenolic-rich fraction obtained from the defatted cake using ethanol by PLE [101]. The same approach was evaluated for several biomasses [173; 184; 173], indicating the increasing research interest towards these integrated green-based processes. Nevertheless, different combinations of these high-pressure-assisted processes can be taken into account, to exploit the advantages of supercritical carbon dioxide-based processes to provide solvent-free extracts. This was proposed in the work of [PERSON] al. [185], where extract obtained by PLE with ethyl lactate was further processed by supercritical carbon dioxide antisolvent technique for the solvent removal, or extract fractionation [140]. Although PLE and SFE are considered \"green extraction technologies\", a technology needs to be evaluated economically and be environmentally friendly before it can be industrialized. A tentative economic evaluation and comparison of supercritical fluid and pressurized liquid extraction analyzing single-stage and continuous-stage processes for phytonutrient extraction from red pepper is reported by [PERSON] et al. [76]. It was observed that PLE is more economical for the same yield of target compound. Similarly, this result is consistent with the economic evaluation of the extraction of paclitaxel from passion fruit bagasse by [PERSON] et al. [186]. The SFE process produces greater economical consumption.