Microwave-assisted extraction of cellulose nanocrystals from almond (Prunus amygdalus) shell waste

Arantzazu Valdés; Gurutz Mondragon; María Carmen Garrigós; Arantxa Eceiza; Alfonso Jiménez

doi:10.3389/fnut.2022.1071754

Microwave-assisted extraction of cellulose nanocrystals from almond (Prunus amygdalus) shell waste

Front Nutr. 2023 Jan 24:9:1071754. doi: 10.3389/fnut.2022.1071754. eCollection 2022.

Authors

Arantzazu Valdés¹, Gurutz Mondragon², María Carmen Garrigós¹, Arantxa Eceiza², Alfonso Jiménez¹

Affiliations

¹ Department of Analytical Chemistry, Nutrition and Food Science, University of Alicante, San Vicente del Raspeig, Spain.
² Materials Technologies Group, Chemical and Environmental Engineering Department, University of the Basque Country - UPV/EHU, Donostia-San Sebastián, Spain.

Abstract

Almond (Prunus amygdalus) is one of the most common tree nuts on a worldwide basis. This nut is highly regarded in the food and cosmetic industries. However, for all these applications, almonds are used without their shell protection, which is industrially removed contributing approximately 35-75% of the total fruit weight. This residue is normally incinerated or dumped, causing several environmental problems. In this study, a novel cellulose nanocrystal (CNCs) extraction procedure from almond shell (AS) waste by using microwave-assisted extraction was developed and compared with the conventional approach. A three-factor, three-level Box-Behnken design with five central points was used to evaluate the influence of extraction temperature, irradiation time, and NaOH concentration during the alkalization stage in crystallinity index (CI) values. A similar CI value (55.9 ± 0.7%) was obtained for the MAE process, comprising only three stages, compared with the conventional optimized procedure (55.5 ± 1.0%) with five stages. As a result, a greener and more environmentally friendly CNC extraction protocol was developed with a reduction in time, solvent, and energy consumption. Fourier transform infrared (FTIR) spectra, X-ray diffractogram (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) images, and thermal stability studies of samples confirmed the removal of non-cellulosic components after the chemical treatments. TEM images revealed a spherical shape of CNCs with an average size of 21 ± 6 nm, showing great potential to be used in food packaging, biological, medical, and photoelectric materials. This study successfully applied MAE for the extraction of spherical-shaped CNCs from AS with several advantages compared with the conventional procedure, reducing costs for industry.

Keywords: Prunus amygdalus; almond shell waste; cellulose nanocrystals; experimental design; microwave-assisted extraction; valorization.

Grants and funding

This work was supported by Conselleria de Educación (Spain) (APOSTD/2016/093 Postdoctoral Research Training Grant), the Spanish Ministry of Economy, Industry and Competitiveness (MAT2017-84909-C2-1-R), and the University of the Basque Country (UPV/EHU) (GIU18-216).