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. 2022 Sep 10;11(18):2362.
doi: 10.3390/plants11182362.

Combined Pulsed Electric Field and Microwave-Assisted Extraction as a Green Method for the Recovery of Antioxidant Compounds with Electroactive Potential from Coffee Agro-Waste

Rodrigo Macías-Garbett  1 , Juan Eduardo Sosa-Hernández  1   2 , Hafiz M N Iqbal  1   2 , Juan Carlos Contreras-Esquivel  3 , Wei Ning Chen  4 , Elda M Melchor-Martínez  1   2 , Roberto Parra-Saldívar  1   2
Affiliations

Combined Pulsed Electric Field and Microwave-Assisted Extraction as a Green Method for the Recovery of Antioxidant Compounds with Electroactive Potential from Coffee Agro-Waste

Rodrigo Macías-Garbett et al. Plants (Basel). .

Abstract

Coffee agro-waste is a potential source of polyphenols with antioxidant activity and application in the food and cosmetic trades. The usage of these byproducts persists as a challenge in the industrial landscape due to their high content of purported toxic substances hindering management. This study presents a green extractive process using pulsed electric field (PEF) and microwave assisted extraction (MAE) to recover polyphenols from coffee parchment and two varieties of pulp, posing quick processing times and the use of water as the only solvent. The performance of this process with regard to the bioactivity was assessed through the Folin-Ciocalteu assay, total flavonoid content, DPPH, ABTS and FRAP antioxidant tests. The phenolic composition of the extracts was also determined through HPLC-MS and quantified through HPLC-DAD. When compared to treatment controls, PEF + MAE treated samples presented enhanced yields of total phenolic content and radical scavenging activity in all analyzed residues (Tukey test significance: 95%). The chromatographic studies reveal the presence of caffeic acid on the three analyzed by-products. The HPLC-DAD caffeic acid quantification validated that a combination of MAE + PEF treatment in yellow coffee pulp had the highest caffeic acid concentration of all studied extraction methods.

Keywords: coffee agrowaste; microwave-assisted extraction; polyphenols; pulsed electric fields; solvent-free extraction.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Total phenolic content of coffee agro-waste extracts. Values are represented as mean ± standard deviation (n = 3). GAE: gallic acid equivalents. (a) Extraction results for parchment waste. (b) Extraction results for yellow and red pulp waste MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 2
Figure 2
Total flavonoid content of coffee agro-waste extracts. Values are represented as mean ± standard deviation (n = 3). (a) Extraction results for parchment waste. (b) Extraction results for yellow and red pulp waste MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 3
Figure 3
DPPH antioxidant assay of coffee agro-waste extracts. Values are represented as mean ± standard deviation (n = 3). TE: Trolox equivalents. (a) Assay results for parchment waste. (b) Assay results for yellow and red pulp waste. MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 4
Figure 4
ABTS antioxidant assay of coffee agro-waste extracts. Values are represented as mean ± standard deviation (n = 3). TE: Trolox equivalents. (a) Assay results for parchment waste. (b) Assay results for yellow and red pulp waste. MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 5
Figure 5
FRAP antioxidant assay of coffee agro-waste extracts. Values are represented as mean ± standard deviation (n = 3). (a) Assay results for parchment waste. (b) Assay results for yellow and red pulp waste. MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 6
Figure 6
HPLC-DAD chromatographic profile of MAE + PEF treated residues. MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 7
Figure 7
Effect of MAE + PEF treatment on the peaks of yellow coffee pulp. MAE: Microwave assisted extraction; PEF: Pulsed Electric Field pretreatment.
Figure 8
Figure 8
Pulsed-electric field (PEF) pretreatment and microwave-assisted extraction (MAE) methodology flow diagram.
Figure 9
Figure 9
Pulsed-electric field (PEF) experimental setup. (a) PEF device layout, (b) treated coffee agrowaste on electrode detail. PEF: Pulsed Electric Field pretreatment.
Figure 10
Figure 10
Heating and pressure profile of the microwave-assisted extraction procedure.
See this image and copyright information in PMC

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