Recovery of Bioactive Compounds from Hazelnuts and Walnuts Shells: Quantitative–Qualitative Analysis and Chromatographic Purification

Abstract

Hazelnut (HS) and walnut (WS) shells, an abundant by-product of the processing industries of these edible nuts, are traditionally considered as a low-value waste. However, they are a source of valuable compounds with an interesting chemical profile for the chemical and pharmaceutical sectors. In this study, the lipophilic and hydrophilic extracts present in HS and WS were quantified and identified, then the polar fractions were chromatographically separated, and their antioxidant capacity was studied. The experimental work includes the isolation of crude lipophilic and hydrophilic extracts by an accelerated extraction process, chromatographic analysis (gas chromatography-flame ionization (GC-FID), GC-mass spectroscopy (GC-MS), high-performance size-exclusion chromatography (HPSEC), thin-layer chromatography (TLC)), and quantification of the components. In addition, a thorough compositional characterization of the subgroups obtained by flash chromatography and their antioxidant capacity was carried out. The gravimetric concentrations showed different lipophilic/hydrophilic ratios (0.70 for HS and 0.23 for WS), indicating a higher proportion of polar compounds in WS than in HS. Moreover, the lipophilic extracts were principally composed of short-chain fatty acids (stearic, palmitic, and oleic acid), triglycerides, and sterols. The polar fractions were screened by thin-layer chromatography and then separated by flash chromatography, obtaining fractions free of fatty acids and sugar derivatives (97:3 in HS and 95:5 in WS), and mixtures richer in phenolic compounds and flavonoids such as guaiacyl derivatives, quercetin, pinobanksin, and catechin. The most polar fractions presented a higher antioxidant capacity than that of the crude extracts.

Valorization of Agri-Food Waste from Pistachio Hard Shells: Extraction of Polyphenols as Natural Antioxidants

“…The pertinent fragmentation pattern is shown in Figure S6. This identification was corroborated by 1 H NMR signals at 5.70 ppm (H-8), 5.80 ppm (H-6), assigned to the aromatic protons of ring A, and at 6.75 ppm (H-5 ), 7.27 ppm (H-6 ) and at 7.33 ppm (H-2 ), due to the aromatic protons of ring B [37].…”

“…at m/z 285, which could be assigned to kaempferol or luteolin. 1 H NMR analysis allowed one to discriminate between the two isomers in favour of kaempferol (24) based on the presence of two signals at 8.04 ppm (H−2′/H−6′) and 6.92 ppm (H-3′/H-5′), two singlets at 6.43 ppm (H−8) and 6.18 ppm (H−6), in agreement with literature data [37]. Of note, flavonol 24 has previously been identified in pistachio hulls extract [24] and its antioxidant activity is well documented [55,56].…”

“…Agricultural and forestry wastes are considered by-products with low economic value, generally used as feed for livestock or fuel for domestic heating [1,2]. Nevertheless, there is a growing interest in giving a second life to different types of food waste, thus reducing their environmental impact and providing added value to the entire food's production process.…”

An Integrated Approach for the Valorization of Sea Bass (Dicentrarchus labrax) Side Streams: Evaluation of Contaminants and Development of Antioxidant Protein Extracts by Pressurized Liquid Extraction

“…However, with regard to the skin sample, the extraction method applied at 60 °C negatively affected the antioxidant capacity of the extract components regardless of pH and extraction time. There is a great variety of phytochemicals with in vitro antioxidant capacity extracted by PLE from plant products and by-products [ 21 , 44 , 45 ]. However, as far as we know, there are no examples in the literature on the application of PLE to recover food compounds from food of animal origin and related side streams.…”

Biomolecules from Plant Residues

“…For instance, Herrera et al [10] analyzed qualitatively and quantitatively different extracts of hazelnut and walnut shells. These shells are a plentiful by-product of the edible nut processing industries and have traditionally been considered as a low-value waste.…”