Antioxidant and Physico-Structural Insights of Walnut ( Juglans regia ) and Hazelnut ( Corylus avellana L.) Shells: Implications for Southern Chile By-Product Valorization

Carlos Manterola-Barroso, Karina Godoy Sanchez, Erick Scheuermann, Daniela Padilla-Contreras, Filis Morina and Cristian Meriño-Gergichevich ()
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Carlos Manterola-Barroso: Doctoral Program in Science of Natural Resources, Universidad de La Frontera, Temuco 4811230, Chile
Karina Godoy Sanchez: Scientific and Technological Bioresources Nucleus (BIOREN-UFRO), Universidad de La Frontera, Temuco 4811230, Chile
Erick Scheuermann: Scientific and Technological Bioresources Nucleus (BIOREN-UFRO), Universidad de La Frontera, Temuco 4811230, Chile
Daniela Padilla-Contreras: Scientific and Technological Bioresources Nucleus (BIOREN-UFRO), Universidad de La Frontera, Temuco 4811230, Chile
Filis Morina: Department of Plant Biophysics and Biochemistry, Institute of Plant Molecular Biology, Biology Centre of the Czech Academy of Sciences in Budweis, CZ-370 05 Ceske Budejovice, Czech Republic
Cristian Meriño-Gergichevich: Scientific and Technological Bioresources Nucleus (BIOREN-UFRO), Universidad de La Frontera, Temuco 4811230, Chile

Resources, 2025, vol. 14, issue 5, 1-19

Abstract: Considerable amounts of agro-industrial by-products are discarded every year. Moreover, these represent an interesting source of phenolics, cellulose and lignin, in addition to useful compounds such as antioxidants. However, these compounds may be affected by external factors such as genotype, locality and productive season, increasing or decreasing the antioxidant potential of by-products. In this study, hazelnut ( Corylus avellana L.) and walnut ( Juglans regia L.) nutshells were investigated for their fiber content and antioxidant capacity as valorized by-products in this industry. The determination of oxygen radical absorbance capacity (ORAC), total phenolic content (TPC) and color difference was performed using hazelnut and walnut shells collected from orchards located in Southern Chile during three consecutive seasons (2020/21, 2021/22 and 2022/23). The ORAC in nutshells showed the highest values in both species for the season 2020/21 (3217 and 4663 µmol TE g DW −1 for hazelnut and walnut), whereas the variability in consecutive seasons was lower for hazelnut than for walnut. The TPC in hazelnut shells was positively correlated with L* (R: 0.883) and ΔE (r = 0.924) during the 2020/21 season and with L* for 2022/23 (r = 0.907). On the other hand, the ORAC was negatively correlated with L* (r = 0.922) in 2021/22. In addition, the morphological and structural features of both nutshells examined by scavenging electron microscopy (VP-SEM) and confocal scavenging laser microscopy (CSLM) revealed differential tissue distribution and accumulation patterns of both cellulose and lignin. In addition, photo-colorimetric values were determined for both shells and corresponding seasons, and non-significant differences were found for both shells and among seasons. Finally, our results provide new insights into the physicochemical characteristics of these two types of nutshells as valorized by-products, considering their antioxidant properties as residual materials derived from this agroindustry.

Keywords: hard-shelled seeds; nutshells; shell features; valued material; waste material (search for similar items in EconPapers)
JEL-codes: Q1 Q2 Q3 Q4 Q5 (search for similar items in EconPapers)
Date: 2025
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