Volume 21 Issue 1

Starch hydrolysate from breadfruit was used as the sole carbon source for citric acid (CA) biosynthesis by the filamentous fungus Aspergillus niger under surface fermentation conditions. The process was modeled and optimized by examining the influence of four critical factors: Starch hydrolysate concentration ranging from 50 to 100 g/L, medium pH between 3 and 6, nitrogen source comprising of (NH₄)₂HPO₄​ or NaNO₃, and fermentation time from 1 to 7 days, on CA concentration. The results demonstrated that A. niger efficiently metabolized the hydrolysate, achieving a maximum CA concentration of 14.7 g/L after 7 days of fermentation. Statistical modeling predicted the optimal production conditions as a starch hydrolysate concentration of 50 g/L, pH of 5.4, (NH₄)₂HPO₄​ as the nitrogen source, and a fermentation duration of 7 days. Under these conditions, the predicted CA concentration was 14.7 g/L, which was validated experimentally. Additionally, the process yielded 2.02 g/L of biomass and 15.2 g/L of reducing sugars. This study underscores the potential of breadfruit as a low-cost and sustainable substrate for CA biosynthesis. Applying response surface methodology with D-Optimal design proved effective in optimizing process variables and enhancing production efficiency. These findings provide a framework for developing cost-efficient and scalable fermentation processes, particularly in regions with abundant breadfruit resources.

Enzyme inhibition activities, phenolic compounds, antioxidant activities, bioactive compounds, antimicrobial activities, and chemical components of essential oil and methanol extracts obtained from the aerial parts of S. cretica subsp. anatolica were investigated. The main phenolic compounds of aerial parts were catechin, oleuropein, and epicatechin. The determined enzyme inhibitor activities highlight the potential of S. cretica subsp. anatolica as a source of bioactive compounds, particularly for carbonic anhydrase and cholinesterase inhibition. The essential oil and methanol extract exhibited remarkable activities against CA-II, AChE, and BChE, although they were less potent than standard inhibitors. The essential oils generally showed stronger antimicrobial activity compared to the 30% methanol extracts across most bacterial and fungal strains, as evidenced by minimum lethal concentration (MLC) and lower minimum inhibitory concentration (MIC) values and larger inhibition zones. Chloramphenicol used alone exhibited the highest antimicrobial efficacy, with the lowest MIC and MLC values and the largest inhibition zones. The essential oils of S. cretica subsp. anatolica were determined as esters, oxygenated sesquiterpenes, and aldehydes in aerial parts. The main components were found to be hexahydrofarnesyl acetone in the aerial parts.

This study aimed to achieve the value-added utilization of waste Tetra Pak (WTP) and to alleviate the shortage of wood resources by partially replacing wood shavings with WTP and using phenol-formaldehyde resin (PF) to prepare composites. Flame-retardant modification was conducted by introducing single additives-boric acid/borax (BA/Brx), ammonium polyphosphate (APP), and disodium octaborate tetrahydrate (DOT)-as well as the combined systems (BA/Brx/APP, BA/Brx/DOT, and BA/Brx/APP/DOT). Their effects on flame retardancy, mechanical properties, and thermal stability were investigated. It was found that all six systems improved flame retardancy, among which the DOT-modified composite specimen (Z3) achieved a limiting oxygen index (LOI) of 34.3%, representing a 25.6% increase compared with the control composite specimen (Z0), reaching the flame-retardant grade. The mechanical properties of Z3 met the requirements of GB/T 4897 (2015) for general particleboard. Fourier transform infrared spectroscopy (FTIR) indicated that the flame retardants interacted with the matrix through hydrogen bonding and functional composite specimen reactions. Thermogravimetric analysis (TG) showed that the char yield of Z3 reached 32.0%, which was 4.16 times higher than that of the control composite specimen, indicating a significant improvement in thermal stability. This study provides a feasible pathway for WTP recycling and the preparation of flame-retardant composites.

Due to the societal appeal in carbon emission reduction and neutralization, chemical recycling of waste polyester for valuable chemicals has attracted attention in an increasing number of applications. Research on chemical recycling of polyester wastes is currently rising sharply and becoming a hot spot gradually. Many technical and fundamental questions still need to be addressed, such as harsh depolymerization conditions (high temperature, long reaction time, low yields, etc.) and techno-economy and environmental sustainability matters. The chemical recycling protocol and optimization of degradable polyester wastes are systemically investigated along with short discussions on non-degradable ones. The thermoset polyurethane and epoxy adhesives derived from depolymerized waste polyesters for contributing to wood-based structural composite materials (e.g., laminated plywood, fire retarded wood coating, and transparent wood composites) along with life-cycle assessment and techno-economic analysis are also critically evaluated and analyzed. These novel insights are expect to open a new avenue to develop wood-based structural materials via value-added chemicals from polyester waste recycling, which contribute to the sustainable society along with prompting further research and extension in forestry biomaterials and renewable natural resources.

This study focused on mechanical and physicochemical characterization of wood materials produced from Larix decidua and P. sylvestris L. species. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and scanning electron microscopy (SEM) analyses were employed to examine the structure, chemical bonding, and surface morphology. Mechanical properties, such as tensile strength and elasticity, were evaluated to assess durability and potential applications. The results revealed considerable differences in the chemical composition and mechanical properties of the two species, underscoring their distinct suitability for specific industrial applications. L. decidua exhibited superior mechanical performance compared to P. sylvestris L., with higher bending strength (90.5 N/mm²), compressive strength parallel to the grain (42.1 N/mm²), and density (0.62 g/cm³). Moreover, L. decidua showed greater resistance to decay under outdoor weather conditions compared to P. sylvestris L. These findings provide valuable insights into the potential uses of these wood species in construction, furniture production, and other industries requiring durable and versatile natural materials.

The objective of the study was to investigate the influence of heat treatment on air-dried density, equilibrium moisture content (EMC), porosity, average surface roughness (R_a), sound transmission loss, and sound absorption coefficient of poplar (Populus nigra L.) and beech (Fagus orientalis Lipsky) woods. Specimens were exposed to four different temperature levels, namely 150 °C, 170 °C, 190 °C, and 210 °C, for 3 h. The sound absorption coefficient and sound transmission loss of test samples were determined in the frequency range of 63 Hz to 6300 Hz using an impedance tube. It was found that the density, EMC, and average surface roughness values of samples decreased with the heat treatment temperature. In contrast, as the heat treatment temperature increased, porosity of samples increased. The sound absorption coefficient and sound transmission loss of both wood species increased with the heat treatment temperature. The average sound absorption coefficients of untreated and heat-treated poplar samples were approximately 0.16 and 0.18; whereas for beech wood the corresponding values were approximately 0.15 and 0.16. The average sound transmission losses of untreated and treated poplar were approximately 22.7 and 24.0 dB, for the untreated and treated beech samples were 17.3 and 20.7 dB respectively.

Olive tree pruning waste represents a significant agricultural byproduct in Mediterranean regions. It can be regarded as a sustainable and cost-effective alternative resource to other traditional materials for buildings. It is necessary to evaluate the flammability of these materials, according to building regulations. In this preliminary study, several fire-retardant coatings were applied to the materials obtained from olive leaves mixed with a natural adhesive. The coatings included cement-based layers, hydraulic lime, gypsum plaster, intumescent varnishes containing phosphate-based compounds, and graphene-based paints. Treated samples were subjected to flame spread tests to determine their fire resistance properties according to Standard EN ISO 11925-2. The potential of using olive leaves waste as a building material when combined with appropriate fire-retardant coatings is highlighted. The findings suggest that such treatments contribute to mitigating fires and promote the sustainable use of agricultural byproducts in buildings. By applying the coatings, the fire resistance increases significantly compared to untreated samples. The ceramic coatings provided the highest level of protection by reducing the flame spread rate and increasing the time to ignition. Additionally, the treated samples exhibited increased char formation, reducing heat transfer, and delaying combustion. Further research is recommended to optimize the formulations and application methods for large-scale implementation.

Tensile, edgewise, and flatwise bending behaviors of visually graded fir (Abies nordmanniana subsp. bornmuelleriana) boards were investigated through destructive and non-destructive testing to evaluate their mechanical performance and grading accuracy. A total of 724 specimens were prepared and tested in accordance with EN 408 standards. Knot diameter ratios (narrow, mean, and parallel) were used to establish three visual grading methods. Vibration-based (PLG, Hitman) and time of flight (ToF) (Microsecond Timer, Ultrasonic Timer, and Sylvatest Duo) techniques were used for non-destructive evaluation (NDE), along with screw withdrawal tests. The results showed that although the vibration method had lower dynamic modulus of elasticity (MOEd) values ​​than the ToF method, it provided stronger correlations with tensile and bending properties. The mean and parallel knot diameter ratios provided more reliable grading results than the narrow ratio. Tensile strength was more affected by defects than bending strength, and the flatwise bending method consistently produced the highest strength values. The adjustment from global to local MOE reduced modulus values below 9000 MPa, resulting in lower strength class assignments. Overall, the vibration-based NDE method proved the most effective for predicting lumber quality, and the flatwise bending test emerged as a viable alternative to tension and edge bending methods for structural grading.

To address the loosening of mortise and tenon joints in solid wood chairs caused by prolonged use and wood expansion and contraction, this study proposes a reinforcement method using 3D-printed connectors based on polyethylene terephthalate-1,4-cyclohexanedimethanol (PETG) filament. First, the influence of key process parameters (extrusion extent, nozzle travel speed, and nozzle temperature) on the mechanical properties of PETG models was analyzed. Subsequently, based on the optimized process parameters, reinforcement connectors with rib structures were designed and 3D printed. The reinforcement effectiveness was evaluated by comparing the ultimate load of mortise and tenon joints with and without the reinforcement connectors. Results indicated that with the increase of extrusion extent and nozzle temperature, and the decrease of nozzle travel speed, the ultimate strength and Young’s modulus of PETG models increased, improving their mechanical properties. The optimal process parameters were determined as follows: extrusion extent of 105%, nozzle travel speed of 70 mm/s, and nozzle temperature of 250 °C. After installing the reinforcement connectors, the average ultimate load of the mortise and tenon joints reached 445.7 N, which was 34.9% higher than that of joints without reinforcement, demonstrating that the 3D-printed connectors effectively reinforced and protected the mortise and tenon joints.

Graphical Abstract

Chitin is the second most abundant natural polysaccharide after cellulose and consists of N-acetyl-D-glucosamine units linked by β-1,4-glycosidic bonds. In nature, chitin does not accumulate due to the synergistic action of chitinolytic enzymes. Based on their catalytic domains, chitinases are classified into glycosyl hydrolase families GH18 and GH19. They are widely produced by bacteria and filamentous fungi. Different types of chitinolytic enzymes, including endochitinases, exo-acting enzymes, and N-acetylglucosaminidases, have been reported to exhibit antimicrobial and insecticidal activities, making them valuable tools for controlling phytopathogenic fungi and insect pests. Chitin degradation generates chitooligosaccharides (COS), which possess diverse biological properties such as antimicrobial, antioxidant, anti-inflammatory, and antitumor activities, contributing to improved human health. Microbial chitinases are also applied in several industrial and environmental processes, including protoplast formation, single-cell protein production, and dye removal. Advances in recombinant expression and genetic engineering have enhanced chitinase production, stability, and catalytic efficiency. Moreover, recombinant chitinases have been successfully utilized in biocontrol strategies and in developing transgenic plants with increased resistance to phytopathogens. This review highlights the broad agricultural, industrial, and biomedical applications of chitinases and their crucial role in promoting environmental sustainability and advancing bio-based industrial processes.