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. 2022 Aug 20;12(8):806.
doi: 10.3390/membranes12080806.

Extraction and Characterization of Antioxidant Compounds in Almond (Prunus amygdalus) Shell Residues for Food Packaging Applications

Arantzazu Valdés  1 , María Carmen Garrigós  1 , Alfonso Jiménez  1
Affiliations

Extraction and Characterization of Antioxidant Compounds in Almond (Prunus amygdalus) Shell Residues for Food Packaging Applications

Arantzazu Valdés et al. Membranes (Basel). .

Abstract

This work proposes the revalorization of almond shell (AS) wastes as an active additive for food packaging applications. A new microwave-assisted extraction (MAE) method to obtain extracts rich in polyphenolic compounds with high antioxidant capacity was optimized. An experimental design to optimize the MAE procedure through response surface methodology (RSM) using a Box-Behnken design was proposed. The effects of extraction temperature, irradiation time, ethanol:water concentration, and solvent pH at three levels were evaluated in terms of total phenolic content (TPC) and antioxidant activity (DPPH (2,2-diphenyl-1-picrylhydrazyl) and ferric reducing antioxidant power (FRAP) assays). The optimal conditions found were 57 min, 80 °C, pH 8, and 70% (v/v) ethanol. Optimized MAE extracts showed low soluble protein content (0.43 mg BSA g-1) and were rich in TPC (5.64 mg GAE g-1), flavonoids (1.42 mg CE g-1), and polysaccharides (1.59 mg glucose g-1), with good antioxidant capacity (2.82 mg AAE acid g-1). These results suggest the potential application of these extracts in the food industry as active additives. This strategy opens new pathways to valorize almond shell residues, contributing to the circular economy.

Keywords: Prunus amygdalus; almond; antioxidant compounds; food packaging; microwave-assisted extraction; response surface methodology; shell residues.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Scheme of (a) AS powder preparation and (b) MAE process to obtain ASE.
Figure 2
Figure 2
Pareto charts obtained for (a) DPPH (mg TE g−1), (b) FRAP (mg AAE g−1), and (c) TPC (mg GAE g−1) values of ASE by MAE. The vertical line indicates the statistical significance at 5% of the effects.
Figure 3
Figure 3
Response surface and contour plots showing interactions on DPPH ((a): temperature vs. pH) and TPC ((b): temperature vs. time; (c): ethanol concentration vs. pH) values of ASE by MAE.
Figure 4
Figure 4
Chemical structures of main polyphenolic compounds reported in AS residues.
Figure 5
Figure 5
SEM micrographs of AS before (a) and after MAE under optimal conditions (b) at 1000×.
See this image and copyright information in PMC

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