The hard-shelled seed industry plays an important role in the global agricultural economy. In fact, only considering hazelnut and walnut, the global nut supply is over 5.6 tons. As a result considerable amounts are produced year by year, burnt or discarded as waste, bypassing a potential source of valuable compounds or features. This review deals with the recent scientific literature on their chemical composition as well as functional applications as an approach to sustain the utilization of the main byproduct derived from industry. Indeed, nutshells have received great interest due to their lignin, antioxidant, physical and mechanical features. It was found that these properties vary among cultivars and localities of plantation, influencing physical and structural features. The inconsistencies regarding the above-mentioned properties of nutshells lead to exploring the status of hazelnut and walnut shell applications in sustainable bio-economy chains. In fact, in terms of potential applications, the state of the art links their use to the construction industry and the manufacture of materials, such as resin or plastic composites, particleboards or construction panels, or vital infrastructure and as a filler in cement pavements. However, their current use continues bypassing their great antioxidant potential and their interesting chemical and mechanical features.

Hazelnut (Corylus avellana L.) is of great agroeconomic importance, prized for its nutritional value and antioxidant properties. Its yield and quality may differ due to factors such as season (S), locality (L) and cultivar (C). Our objective was to determine the adaptive behavior of morphological features and antioxidant properties in nuts of the Barcelona and Tonda di Giffoni (TDG) cultivars planted at two localities (Cunco and Perquenco) during three productive seasons (S1, S2 and S3). Barcelona grown in Perquenco in S1 and S3 (less precipitation, more solar radiation) performed better than in Cunco with respect to most morphological nut, kernel and shell features, and the same parameters generally had the same trends for TDG in S2 and S3. Among the seasons at the same localities, the differences between the predominant condition defects for both cultivars were in the decreasing order wrinkled/deformed kernels, double kernels, blank and mold kernels, with about 75% of hazelnuts without defects. In both cultivars, the shell had higher antioxidant properties that increased in S1 and S3 at both localities and were consistently higher than in the kernels. Lipid peroxidation was higher in the kernel than shell in both cultivars and localities for S1 and S3. The results of this study suggest that the different hazelnut cultivar features including physical and chemical components depend on season and locality, which offers important clues for all those interested in the hazelnut industry.

To determine the effects of pre-harvest calcium (Ca), magnesium (Mg) and potassium (K) spraying on the antioxidant activity and capacity of hazelnut (Corylus avellana L.) shells, as an approach to sustain the utilization of the main residue derived from this industry, four commercial hazelnut (Tonda di Giffoni) orchards located in Southern Chile (Cunco, Gorbea, Perquenco and Radal), during the 2018/19 season were sprayed three times with five combinations of Ca (300 and 600 mg L⁻¹), Mg (300 and 600 mg L⁻¹) and K (300 and 600 mg L⁻¹). Yield components were determined in harvested whole nuts, whereas Ca, Mg and K concentrations, as well as total phenolic compounds, free radical scavenging antioxidant activity, and oxygen radical absorbance capacity, were determined in shells. All spray treatments with both Ca, Mg and K combinations showed a significant interaction between locality and treatment (L × T) on increased stabilized nut yield (kg ha⁻¹) in comparison with the control treatments, whereas nut quality was differentially affected by treatment and orchard locality, thus confirming a significant L × T relationship regarding nut length and kernel yield. However, locality showed a major effect on kernels and shells. A significant relationship was determined between locality and the Ca, Mg and K spraying (L × T) concerning antioxidant compounds such as phenolics, whose amounts exceeded those of the control treatments by three times. Antioxidant capacity and activity in shells showed a significant L × T relationship, and nutshells collected from Cunco showed remarkably (3–4 times) higher levels of these factors than the other evaluated localities. Interactions between spray treatment and orchard location were responsible for the different values obtained in the experiments, confirming the influence of the environment on the efficacy of the treatments. Finally, these shells are worth further study as an interesting residue of the hazelnut industry due to their nutritional and antioxidant properties.

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.

Hazelnut (Corylus avellana L.) is of great agroeconomic importance, prized for its nutritional value and antioxidant properties. Its yield and quality may differ due to factors such as season (S), locality (L) and cultivar (C). Our objective was to determine the dynamics of morphological features and antioxidant properties in nuts of Barcelona and Tonda di Giffoni (TDG) cultivars planted at two localities (Cunco and Perquenco) during three productive seasons (S1, S2 and S3). Barcelona grown in Perquenco in S1 and S3 (less precipitation, more solar radiation), performed better than in Cunco with respect to most morphological nut, kernel and shell features, and the same parameters generally had the same trends for TDG in S2 and S3. Among the seasons at the same localities, the differences between the predominant condition defects for both cultivars were in the decreasing order wrinkled/deformed kernels, double kernels, blank and mold ker-nels, with about 75% of hazelnuts without defect. In both cultivars, the shell had higher antioxi-dant properties that increased in S1 and S3 at both localities, and were consistently higher than in the kernels. Lipid peroxidation was higher in the kernel than shell in both cultivars and local-ities for S1 and S3. The results of this study suggest that the different hazelnut cultivar features including physical and chemical components depend on season and locality, which offers im-portant clues for all those interested in the hazelnut industry.

Drought stress is one of the major constraints limiting crop productivity, primarily through oxidative damage, pigment degradation, and metabolic imbalance. Nanostructured selenium particles (SeNPs) have recently attracted attention for their potential to enhance plant tolerance to abiotic stress. In this study, green-synthesized SeNPs, with a main hydrodynamic size distribution in the range of 90–100 nm, were foliar applied to broccoli (Brassica oleracea var. italica) plants grown under well-watered (100% water holding capacity) and drought (50% water holding capacity) conditions at concentrations of 0, 10, 20 and 50 ppm. Drought stress significantly decreased chlorophyll a and b, total chlorophyll, and carotenoids, while increasing malondialdehyde (MDA) and proline levels, confirming oxidative stress and membrane damage. SeNPs treatments partially mitigated these effects by enhancing pigment stability, increasing carotenoid content, and reducing both MDA and proline accumulation. Phenolic and flavonoid responses exhibited a dose-dependent pattern with the highest stimulation at 50 ppm under drought and moderate enhancement at 10 ppm under optimal irrigation. Antioxidant capacity assays demonstrated that SeNPs modulate plant redox metabolism, in a context-dependent manner, particularly under water deficit. Peroxidase (POD) activity was also significantly induced under drought stress, mainly at 20 ppm. These results indicate that foliar-applied SeNPs can influence physiological and biochemical responses associated with drought tolerance in broccoli. The observed effects are consistent with nanoparticle–leaf surface interactions contributing to redox regulation and stress adaptation, rather than implying direct nanoparticle internalization.