# High-Pressure Technologies for the Recovery of Bioactive Molecules from Agro-Industrial Waste
## 4 Combined Extractions  
Pressurized Liquid Extraction (PLE) and Supercritical Fluid Extraction (SFE) are environmentally friendly advanced techniques enabling the use of non-toxic and/or GRAS solvents such as water, ethanol, or carbon dioxide for the extraction and enhancement of target compounds yield [173; 174]. These green technologies are now highly encouraged due to recent increased attention to the environmental impact of processes. The supercritical fluid extraction of polar compounds, in general, is conducted using an organic solvent as the modifier (frequently ethanol). For example, bioactive compounds are extracted from mandarin peel [175] using scCO2+ 5 and 10% ethanol, from papaya [176] seeds using scCO2+ 2-8% ethanol, from walnut husk [177] using scCO2+ 20% ethanol, or from olive residues [178] (leaves, pomace and prunings) using scCO2+ 60% ethanol. The results in terms of total phenolic compounds and antioxidant activity were, in some cases, compared to the ones obtained through conventional extraction: when phenolic antioxidants were extracted from papaya agro-industrial waste, the yield in the ethanolic extract was slightly higher than the one in the scCO2+ ethanol extract, but the latter had \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Carotenoid**} & \multirow{2}{*}{**Source**} & \multicolumn{2}{c}{**Sample Weight**} & \multirow{2}{*}{**EtOH \%**} & \multirow{2}{*}{**P Bar**} & \multirow{2}{*}{**T** \({}^{\circ}\)**C**} & \multirow{2}{*}{**t min**} & \multirow{2}{*}{**Recovery**} & \multirow{2}{*}{**Ref**} \\  & & **Treated** & & & & & & \\ \hline \(\alpha\)-carotene & Apricot peels & 5 g & 15.5 & 350 & 59 & 30 & 97.9 & [167] \\ \(\beta\)-carotene & Tomato paste waste & 60 g & 5 & 300 & 65 & 120 & 50 & [168] \\ \(\beta\)-carotene & Tomato processing waste & 40–50 g & / & 300 & 80 & / & 88 & [169] \\ \(\beta\)-carotene & Sweet potato peels & 5 g & 15.5 & 350 & 59 & 30 & 99.8 & [167] \\ \(\beta\)-carotene & Tomato peels & 5 g & 15.5 & 350 & 59 & 30 & 96.9 & [167] \\ \(\beta\)-carotene & Apricot peels & 5 g & 15.5 & 350 & 59 & 30 & 99 & [167] \\ \(\beta\)-carotene & Pumpkin peels & 5 g & 15.5 & 350 & 59 & 30 & 88.2 & [167] \\ \(\beta\)-carotene & Peach peels & 5 g & 15.5 & 350 & 59 & 30 & 99.2 & [167] \\ lycopene & Tomato paste waste & 60 g & 5 & 300 & 55 & 120 & 54 & [168] \\ lycopene & Tomato processing waste & 40–50 g & / & 300 & 80 & / & 80 & [169] \\ lycopene & Tomato processing waste & 2 kg & / & 450 & 70 & 420 & 75 & [170] \\ lycopene & Tomato peels & 5 g & 15.5 & 350 & 59 & 30 & 92.5 & [167] \\ lycopene & Apricot peels & 5 g & 15.5 & 350 & 59 & 30 & 83.2 & [167] \\ lutein & Spinach by-products & 25 g & 10 & 390 & 56 & 215 & 72 & [171] \\ lutein & Sweet potato peels & 5 g & 15.5 & 350 & 59 & 30 & 99.8 & [167] \\ lutein & Peach peels & 5 g & 15.5 & 350 & 59 & 30 & 75.3 & [167] \\ chlorophyll & Spinach by-products & 25 g & 10 & 390 & 56 & 215 & 50 & [171] \\astaxanthin & Crustacean waste & 25 g & 13 & 200 & 40 & 180 & 62 & [50] \\astaxanthin & Shrimp waste & 60 g & / & 250 & 45 & 120 & 47 & [51] \\ fucoxanthin & Brown seaweed waste & 56 g & / & 400 & 40 & 180 & 80 & [172] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Extraction of carotenoids by supercritical carbon dioxide. EtOH = ethanol; P = operating pressure; T = operating temperature; t = extraction time. higher antioxidant activity in vegetable edible oil [176]. In the case of walnut green husk, SFE gave far more encouraging yields than those obtained using water, ethanol, or methanol as an extracting solvent [177]. [PERSON] et al. [179] compared the extraction of phytosterols and tocopherols from rapeseed oil waste by using scCO\({}^{2+}\) ethanol and conventional Soxhlet extraction.