# Advanced and Potential Methods for Extraction of Bioactive Compounds from Avocado Peel--A Review
## 4 Advanced Methods for Extraction of Bioactive Compounds from Avocado Peel
### Three-Phase Partitioning (TPP)
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**Extraction Method** & **Important Finding** & **Ref.** \\ \hline Microwave-assisted extraction & The extract showed high matrix metalloproteinases inhibitory capacity and antioxidant activity. The total phenolic content of the extract was & [7] \\  & 18.1–68.8 mg GAE/g peel DE, which was affected by time, temperature, and & \\  & solvents during extraction. & \\ \cline{2-3}  & The highest antioxidant capacity was obtained by 74.48 \({}^{\circ}\)C–4.13 min and & \\  & 66.37 \({}^{\circ}\)C–0.97 min extractions with 42.58\% ethanol. The extract showed a high & [16] \\  & polyphenic content (3.79.28 \(\pm\) 19.35 mg GAE/g dry extract) and high & \\  & antioxidant activity measured by DPPH, ABTS, and ORAC assay. & \\ \cline{2-3} Vacuum microwave-assisted aqueous extraction & The optimal extractions were temperature of 79.64 and 78.11 \({}^{\circ}\)C, time of & \\  & 11.89 and 11.75 min, ratio of water and avocado peel 16.45 and 10.02\%, and & \\  & microwave power of 5708.04 and 5699.10 W. The conditions showed the highest & [62] \\  & TPC (0.352 gallic acid equivalent-GAE/g fresh avocado peel/min) and DPPH & \\  & radical scavenging activity (0.104 L/min). & [63] \\ \hline Vacuum microwave-assisted aqueous extraction & - The avocado peel extract contained flavonoids that exhibited antioxidant, & [64] \\ \hline Ultrasound-assisted extraction & The extract by Sonotrode extraction had higher flavan-3-ols recovery (54\%) and & \\  & antioxidant activity (62–76\%) than ultrasound bath extraction. Sonotrode extraction was an alternative to non-thermal, low-time-consuming, and scalable & [64] \\  & methods for extracting the bioactive compounds as functional ingredients. & \\ \cline{2-3}  & The extract with acetone–water solvent showed higher total phenolic content & \\  & (208.5 \(\pm\) 19.8 mg GAE/g DE) than the extract with ethanol (183.4 \(\pm\) 6.0 mg GAE/g DE) and ethanol–water solvent (192.6 \(\pm\) 11.1 mg GAE/g DE). & [65] \\  & The optimal extraction obtained by response surface methodology was 50.9 \({}^{\circ}\)C & \\  & of temperature, 49.5\% of ethanol/water, and 61.8 min. The extract contained & [66] \\  & 124.050–125.187 mg GAE/g of phenolic content. & \\ \hline The ethanol concentration higher than 40\% decreased phenolic content. The & \\  & optimized extract was obtained with 38.46\% of ethanol, 44.06 min, and 50 \({}^{\circ}\)C. & \\  & The extract contained high phenolic and flavonoid compounds. It influenced the & \\  & metabolic activity of normal and cancer cells, but the extract had positive effects & [22] \\  & on metabolic activity and inhibited cancer (Caco-2, A549, and HeLa) cells. The & \\  & extract showed low cellular toxicity in normal cells but negatively affected & \\  & cancer cells, particularly HeLa cells. & \\ \cline{2-3}  & The avocado peel extract had higher phenolic content and antioxidant activity & \\  & but lower IC\({}_{50}\) value (59 ppm) than cocoa bean, coconut, and cactus pear extract. & [67] \\  & The avocado peel extract showed inhibitory activity against & \\  & _Staphylococcus aureus_, _Shigella dysenteriae_, and _Candidia albicans_. & \\ \hline Ultrasound–microwave combined extraction & The avocado extract had higher phenolic compounds and antioxidant activity & \\  & than the aqueous fraction and the acid-microwave hydrolyzed fraction. The & \\  & extract inhibited growth of _Pseudomonas aeruginosa_ and _Bacillus cereus_, _Staphylococcus aureus_, _Salmonella_ spp., and _Salmonella_ spp. & [68] \\ \hline Ultrasound-assisted deep eutectic solvent extraction & The optimal extraction conditions were a matrix/solvent ratio of 1:30 (\(w/v\)), an extraction time of 15 min, and a temperature of 25 \({}^{\circ}\)C. The phenolic compounds of 8.29 \(\pm\) 0.07 g GAE/100 g of dry avocado peel were extracted by the optimal extraction above. & [69] \\ \hline Ultrasound-assisted extraction and enzyme-assisted extraction & The major polyphenic compounds of the extract were benzoic acid, vanillic acid, syringic acid, and resveratrol. The ultrasound-assisted extraction yielded phenolic extraction equal to that of enzyme-assisted extraction. The extract of ultrasound-assisted extraction showed a solid-to-solvent ratio of 1:20 (\(w/v\)), 20\% ultrasonic intensity, 30 min showed the highest polyphenols (35.4 mg GAE/g of dried peel). & [21] \\ \hline \hline \end{tabular}
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