Potential Valorization of Hazelnut Shells through Extraction, Purification and Structural Characterization of Prebiotic Compounds: A Critical Review

Abstract

Hazelnuts are one of the most widely consumed nuts, but their production creates large quantities of by-products, especially shells, that could be upcycled into much more valuable products. Recent studies have shown that hazelnut shell hemicellulose is particularly rich in compounds that are potential precursors of xylooligosaccharides and arabino-xylooligosaccharides ((A)XOS), previously defined as emerging prebiotics very beneficial for human health. The production of these compounds on an industrial scale-up could have big consequences on the functional foods market. However, to produce (A)XOS from a lignocellulosic biomass, such as hazelnut shell, is not easy. Many methods for the extraction and the purification of these prebiotics have been developed, but they all have different efficiencies and consequences, including on the chemical structure of the obtained (A)XOS. The latter, in turn, is strongly correlated to the nutritional effects they have on health, which is why the optimization of the structural characterization process is also necessary. Therefore, this review aims to summarize the progress made by research in this field, so as to contribute to the exploitation of hazelnut waste streams through a circular economy approach, increasing the value of this biomass through the production of new functional ingredients.

Circular Hazelnut Protection by Lignocellulosic Waste Valorization for Nanopesticides Development

“…The solvent-antisolvent method is based on the use of water and ethanol allowed to synthesize LNP without using heavy chemical reagents, with acceptable yields. The one concerning HS is much lower than HP since the starting matrix is composed of waxes and other lipid fractions that lower the efficacy of the proposed treatments [75,76]. In this sense, a much more effective dewaxing pretreatment is required in order to be able to exploit all the ligninic fraction in shells.…”

“…On the contrary, HS LNP showed a growing TPC: in fact, the LNP produced by the last extraction step had a higher content in polyphenols. Unlike the pruning residues, hazelnut shells present a much more complex structure, due to the high presence of waxes and other lipid components [75,76]. Such components, as it was assumed for CNC extraction, could play an important role in hampering the access of chemical reagents to the lignin fraction.…”

Hazelnut (Corylus avellana L.) shells as a potential source of dietary fibre: impact of hydrothermal treatment temperature on fibre structure and degradation compounds

“…Corylus avellana L., the European hazelnut, is the second most popular nut worldwide, just after almonds, and its crop added up to over 528 000 t (kernel basis) in 2019-2020. 13 One of the main drawbacks of hazelnut production is the large amount of by-products. The residual biomass resulting from the cracking process, the HS, represents approximately 50-55% of the weight of the in-shell product.…”

Valorization of Hazelnut Shells as Growing Substrate for Edible and Medicinal Mushrooms

“…Several studies have been conducted in order to enhance and valorize this waste by-product with the aim to obtain new materials, chemical compounds, and bioactive ingredients. In particular, HS were found to be suitable for the production of particleboard and Medium Density Fiberboard (MDF) [12,13], activated carbons capable of adsorbing and removing different heavy metals and CO 2 [14][15][16][17][18][19][20][21][22], antioxidant phenolics [6,[23][24][25][26], fermentable sugars and xylooligosaccharides [11,27], hydrogen production [28,29], ethanol [30] and some prebiotic compounds [31].…”