Food-Waste Valorisation: Synergistic Effects of Enabling Technologies and Eutectic Solvents on the Recovery of Bioactives from Violet Potato Peels

Abstract

The recovery of valuable bioactive compounds from the main underutilised by-products of the food industry is one of the greatest challenges to be addressed in circular economy. Potato peels are the largest waste generated during potato processing. However, they could be a potential source of valuable bioactive compounds, such as polyphenols, that can be reused as natural antioxidants. Currently, environmentally benign enabling technologies and new types of non-toxic organic solvents for the extraction of bioactive compounds may dramatically improve the sustainability of these processes. This paper focuses on the potential inherent in the valorisation of violet potato peels (VPPs) by recovering antioxidants using natural deep eutectic solvents (NaDES) under ultrasound (US)- and microwave (MW)-assisted extraction. Both the enabling technologies provided performances that were superior to those of conventional extractions in terms of antioxidant activity determined by the DPPH· (2,2-diphenyl-1-picrylhydrazyl) assay. In particular, the most promising approach using NaDES is proven to be the acoustic cavitation with a Trolox eq. of 1874.0 mmol_TE/g_Extr (40 °C, 500 W, 30 min), vs. the 510.1 mmol_TE/g_Extr of hydroalcoholic extraction (80 °C, 4 h). The shelf-life of both hydroalcoholic and NaDES-VPPs extracts have been assessed over a period of 24 months, and found that NaDES granted a 5.6-fold shelf-life extension. Finally, the antiproliferative activity of both hydroalcoholic and NaDES-VPPs extracts was evaluated in vitro using the MTS assay on human tumour Caco-2 cells and normal human keratinocyte cells (HaCaT). In particular, NaDES-VPPs extracts exhibited a significantly more pronounced antiproliferative activity compared to the ethanolic extracts without a noteworthy difference between effects on the two cell lines.

Keywords: Solanum tuberosum; antioxidant activity; green extraction; microwave-assisted extraction; phenolic compounds; potato peel valorisation; shelf life; ultrasound-assisted extraction.

Figure A1

DAD chromatogram of VPP extract (ChLa/US), 280 and 335 nm. Peaks matched with mass spectra are signalled with a red wildcard character.

Figure A2

DAD chromatogram of VPP extract (ChLa/US), 515 nm. Peaks matched with mass spectra are signalled with a purple wildcard character.

Figure A3

ESI+ Mass Spectra Scan, 355.3 [M+] → Chlorogenic acid isomers.

Figure A4

ESI+ Mass Spectra Scan, 742.22 [M+] → pelargonidin 3-rutinoside-5-glucoside; 918.27 [M+] → pelargonidin 3-feruloylrutinoside-5-glucoside; 934.27 [M+] → petunidin 3-p-coumaroylrutinoside-5-glucoside.

Figure 1

Monitoring antioxidant activity of EtOH/H₂O vs. ChLA systems over 24 months (degradation). Dashed lines represent confidence intervals resulting from SD.

Figure 2

Antioxidant activity reported as Pareto charts, monitored over 24 months; Purple line reports cumulative degradation; (A): hydroalcoholic solution; (B): ChLA.

Figure 3

Effect of VPP extracts in the final volume ratios of 0.5, 2.5, and 5% (v/v) on Caco-2 and HaCaT cell viability. Results are expressed as average values ± SD. Statistically different data (p < 0.05) are designated by lower-case letters (a–d or a*–d*, Caco-2 and HaCaT, respectively), according to volume ratios for each cell line.

Figure 4

VPP extracts’ effect on intracellular ROS formation in Caco-2 and HaCaT cells during H₂O₂-induced oxidative stress. Results are expressed as % of control cells. Results are expressed as average values ± SD. Statistically different data (p < 0.05) are designated by lower-case letters (a–d or a*–c*, Caco-2 and HaCaT, respectively).

Figure 5

Flowchart of the extraction strategy adopted in this work for the sustainable valorisation of VPP: technologies and solvent screening enabling the best-performing antioxidant activity. Highlighted squares represent the best performing samples.