Coriander Straw and Press Cake from Seeds

Abstract

The coriander press cake is the co-product obtained during the mechanical pressing of the seeds through twin-screw extrusion, a continuous operation that produces a fragrant vegetable oil now used in cosmetics and nutraceuticals. Due to its high protein content (27%), thermoplastic and adhesive properties, and high lignocellulose content (36%), it can be used to produce self-bonded particleboards through hot pressing. Optimized molding conditions (21.6 MPa, 300 s, 205°C) result in a board with a flexural strength of 23 MPa and a thickness swelling of 31% after 24 h immersion in water. This is even reduced to 20% after heat post-treatment at 200°C. An improvement in the board’s use properties is seen with the addition of coriander straw to the cake. Representing up to 85% of the plant’s aerial part, straw is the co-product of its cultivation. It is a fibrous material, with a lignocellulose content of around 65%. The cake acts as a mechanical reinforcement and as a natural binder in fiberboards and straw fibers. The straw could be refined through twin-screw extrusion to enhance this ability, which improves fiber morphology. The best fiberboard is composed of extrusion-refined straw in the presence of water (0.4 for the liquid-to-solid ratio) and cake, added at 40%. It has a flexural strength of 29 MPa and a thickness swelling of 24% after heat post-treatment. It is a viable and sustainable alternative to wood-based materials (plywood, MDF, chipboard, OSB, particleboard, etc.), with high cost-effectiveness. The formaldehyde emission of this board (<0.2 μg/m2.h) is 300–600 times lower than that of commercial boards, making it a much more environmentally and human health-friendly building material. The study of volatile organic compounds (VOC) emissions also revealed the presence of linalool. This terpene alcohol is the main component of the essential oil of coriander seeds, which was also found in the cake. This volatile oil in the fiberboard could significantly improve indoor air quality. Other uses for straw are also possible. It could be used as loose insulation in the attics of houses. The best insulating performance (47 mW/m.K for thermal conductivity) is obtained after the extrusion-refining of straw with water (1.0 for the liquid-to-solid ratio). Low-density insulating blocks, combining straw and a starchy binder, can also be produced. With a thermal conductivity of 56 mW/m.K, these blocks are machinable and could be used for thermal insulation in buildings. Finally, dry-crushed and sieved straw can be used to reinforce polypropylene and biopolyethylene. The reinforcement effect is significant, resulting in a 50% increase in flexural and tensile strengths compared to neat polypropylene, at a 40% filling rate. This reinforcement effect is comparable to that of wood flours. Straw-based biocomposites also have excellent durability in prolonged exposure to UV radiation, hygrothermal aging, and high recycling potential. They could be used in the automotive or construction industry as non-structural materials (e.g., door and window frames) or sports equipment.