Structural Characterization of the Milled-Wood Lignin Isolated from Sweet Orange Tree (Citrus sinensis) Pruning Residue

Structural features of dioxane lignin: A comparative study with milled wood and formaldehyde-stabilized lignins

Dioxane lignin (DL) is isolated from plant material under mild acidolysis conditions and is widely used in many studies as a representative sample of protolignin, an alternative to milled wood lignin (MWL). However, the structural changes caused by hydrolytic degradation reactions during DL extraction are still poorly understood. In this work, an integrated approach based on 2D NMR and high-resolution mass spectrometry was used to establish the features of the lignin structure on the example of pine lignin isolated using dioxane under various conditions: MWL, DL and "formaldehyde stabilized" lignin (LSF). In this context, we sought to gain a deeper understanding of the chemical structure of DL, focusing on the least studied fragments. Cross-peaks related to the degradation products of 1,2-diarylpropane were uniquely identified for the first time by a combination of HSQC-HMBC spectra. In addition, the 1,3-dioxane structure of β-aryl ether, the presence of which in DL has not been previously observed and originates from elements of the native structure and formaldehyde (product of lignin destruction), was unambiguously shown and confirmed by NMR and mass spectrometry analysis. Additionally, signals related to the 1,3-dioxane structure of 1,2-diarylpropane were also detected for the first time in the HSQC spectrum of LSF.

Lignin from Plant-Based Agro-Industrial Biowastes: From Extraction to Sustainable Applications

Lignin, the most abundant aromatic polymer in nature, plays a critical role in lignocellulosic biomasses by providing structural support. However, its presence complicates the industrial exploitation of these materials for biofuels, paper production and other high-value compounds. Annually, the industrial extraction of lignin reaches an estimated 225 million tons, yet only a fraction is recovered for reuse, with most incinerated as low-value fuel. The growing interest in lignin potential has sparked research into sustainable recovery methods from lignocellulosic agro-industrial wastes. This review examines the chemical, physical and physicochemical processes for isolating lignin, focusing on innovative, sustainable technologies that align with the principles of a circular economy. Key challenges include lignin structural complexity and heterogeneity, which hinder its efficient extraction and application. Nonetheless, its properties such as high thermal stability, biodegradability and abundant carbon content place lignin as a promising material for diverse industrial applications, including chemical synthesis and energy generation. A structured analysis of advancements in lignin extraction, characterization and valorization offers insights into transforming this undervalued by-product into a vital resource, reducing reliance on non-renewable materials while addressing environmental sustainability.

Citrus Pruning in the Mediterranean Climate: A Review

Pruning is a common practice in citrus for various reasons. These include controlling and shaping the canopy; improving phytosanitary health, productivity, and fruit quality; and facilitating operations such as harvesting and phytosanitary treatments. Because pruning is an expensive operation, its need is sometimes questioned. However, it has been proven to be particularly important in Mediterranean citriculture, which is oriented towards producing fruits for a high-quality demanding fresh market. Herein, we summarize and explain the pruning techniques used in Mediterranean citriculture and refer to the main purposes of each pruning type, considering citrus morphology and physiology.

Lignins as Promising Renewable Biopolymers and Bioactive Compounds for High-Performance Materials

The recycling of biomass into high-value-added materials requires important developments in research and technology to create a sustainable circular economy. Lignin, as a component of biomass, is a multipurpose aromatic polymer with a significant potential to be used as a renewable bioresource in many fields in which it acts both as promising biopolymer and bioactive compound. This comprehensive review gives brief insights into the recent research and technological trends on the potential of lignin development and utilization. It is divided into ten main sections, starting with an outlook on its diversity; main properties and possibilities to be used as a raw material for fuels, aromatic chemicals, plastics, or thermoset substitutes; and new developments in the use of lignin as a bioactive compound and in nanoparticles, hydrogels, 3D-printing-based lignin biomaterials, new sustainable biomaterials, and energy production and storage. In each section are presented recent developments in the preparation of lignin-based biomaterials, especially the green approaches to obtaining nanoparticles, hydrogels, and multifunctional materials as blends and bio(nano)composites; most suitable lignin type for each category of the envisaged products; main properties of the obtained lignin-based materials, etc. Different application categories of lignin within various sectors, which could provide completely sustainable energy conversion, such as in agriculture and environment protection, food packaging, biomedicine, and cosmetics, are also described. The medical and therapeutic potential of lignin-derived materials is evidenced in applications such as antimicrobial, antiviral, and antitumor agents; carriers for drug delivery systems with controlled/targeting drug release; tissue engineering and wound healing; and coatings, natural sunscreen, and surfactants. Lignin is mainly used for fuel, and, recently, studies highlighted more sustainable bioenergy production technologies, such as the supercapacitor electrode, photocatalysts, and photovoltaics.