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. 2023 Sep 23;12(10):1796.
doi: 10.3390/antiox12101796.

Unlocking the Bioactive Potential of Pomegranate Peels: A Green Extraction Approach

Giorgio Grillo  1 , Giorgio Capaldi  1 , Kristina Radošević  2 , Željko Jakopović  3 , Ksenija Markov  3 , Mladen Brncic  4 , Lorenzo Gallina  1 , Emanuela Calcio Gaudino  1 , Giancarlo Cravotto  1
Affiliations

Unlocking the Bioactive Potential of Pomegranate Peels: A Green Extraction Approach

Giorgio Grillo et al. Antioxidants (Basel). .

Abstract

Pomegranate (Punica granatum L.) is well known for its high content of bioactives, including polyphenols, flavonoids, and tannins, which have been shown to exhibit a wide range of biological activities, such as antioxidant, antimicrobial, and anticancer effects. It is worth noting that the majority of these molecules are found in the peels, which are usually disposed of after processing, causing a significant amount of waste, amounting to more than 3.6 million t/y. This work investigates microwave-assisted extraction (MAE) in water for the recovery of antioxidants from pomegranate peels (PP), including the optimisation of temperature and extraction times. The total phenolic, anthocyanin, flavonoid, and tannin contents of the recovered extracts were determined, as well as their antioxidant activities, which were found to be 356.35 mgGAE/gExtr, 303.97 µgCy3G/gExtr, 37.28 mgQE/gExtr, 56.48 mgGAE/gExtr, and 5.72 mmolTE/gExtr, respectively (according to the adopted reference). All results were compared with those obtained using a conventional protocol. In addition, the potential for water recycling by means of downstream nanofiltration in optimised MAE was investigated, leading to overall water reuse of approx. 75%. Power consumption (20.92 W/mgGAE) and common green metrics, Reaction Mass Efficiency (RME), E-Factor, and the Process Mass Intensiti/efficiency (PMI, PME), were considered in evaluating the proposed PP valorisation strategy. Finally, the biological activities of the main products were assessed. The antimicrobial properties of the PP extracts against three Gram-positive and three Gram-negative bacteria and their antiproliferative activity towards human cancer cells were tested. S. aureus bacteria was the most susceptible to the PP extracts. All tested products displayed antiproliferative activity against HeLa cells when higher concentrations were tested, with D-PP/NF (obtained from dried PP and sequential nanofiltration) being the most effective. This result was also confirmed via clonogenic analysis, which generally indicated the possible anti-cancer activity of pomegranate peel extracts obtained using this green approach.

Keywords: anthocyanins; antioxidant activity; biological activity; energetic evaluation; flavonoids; food-waste valorisation; green extraction; green metrics; polyphenols; pomegranate peels.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure A1
Figure A1
Representative result of a disc diffusion assay on S. aureus treated with PP extract (50, 250, and 500 µg/mL) compared to negative and positive controls.
Figure 1
Figure 1
Dry extraction yields for MAE of F-PP and D-PP: time and temperature screening, with cumulative dry yield reported as stacked percentages for comparison.
Figure 2
Figure 2
TPC selectivity for MAE of F-PP and D-PP: time and temperature screening.
Figure 3
Figure 3
TPC yields for MAE of F-PP and D-PP at different temperatures: 100 °C, 125 °C, and 150 °C.
Figure 4
Figure 4
TAC seletcitivies for MAE of F-PP and D-PP: time and temperature dependence at 100 °C and 125 °C. 150 °C is not reported due to the absence of signal.
Figure 5
Figure 5
The main components of the quali-quantitative analysis for MAE scale-up of F-PP and D-PP. Yields are reported per gram of extracted matrix, reporting total weights of polyphenols, flavonoids, anthocyanins, tannins, and sugars according to the adopted reference. TPC: mgGAE; TFC: mgQE; TAC: µgCy3G; TTC: mgGAE; TSC mgGLU.
Figure 6
Figure 6
Comparison of TPC and TAC variations in scale-up transposition. Selectivities and yields are reported for D-PP and F-PP. Dashed lines: Lab-scale; Solid lines: Scaled-up.
Figure 7
Figure 7
Main components of quali-quantitative analysis for MAE scale-up of D-PP and its NF retentate. Selectivity is reported per gram of extract, reporting total weights of polyphenols, flavonoids, anthocyanins, tannins, and sugars according to the adopted reference. TPC: mgGAE; TFC: mgQE; TAC: µgCy3G; TTC: mgGAE; TSC mgGLU.
Figure 8
Figure 8
Comparison with hydroalcoholic benchmark extraction for D-PP scaled-up extraction and the related NF retentate. Percentage variations are calculated using the conventional benchmark as the reference (y-axis).
Figure 9
Figure 9
Antimicrobial activity of PP extracts against pathogens (mm). pc = positive control. Reported data are normalised against pc.
Figure 9
Figure 9
Antimicrobial activity of PP extracts against pathogens (mm). pc = positive control. Reported data are normalised against pc.
Figure 10
Figure 10
Viability of HeLa cells treated with four PP extracts for 72 h in the concentration range from 50 to 500 μg/mL, assessed using the CellTiter AQueous One Solution Cell Proliferation Assay. Cell viability (%) is expressed as percentage of treated cells versus control cells. Presented value followed by different lower-case letters (a–d) are significantly different from each other in each group (p < 0.05), as measured by Tukey’s HSD test.
Figure 11
Figure 11
Results of clonogenic analysis after treatment with PP extracts at a concentration of 500 µg/mL.
Figure 12
Figure 12
Power consumption and relative distribution. All data refer to scaled-up extractions.
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