Extraction and characterization of residue fibers from defatted date-pits after alkaline-acid digestion: effects of different pretreatments

Holo-cellulose fibers were prepared by pre-treatments (i.e., water, ethanol, microwave and pressure cooker) followed by alkaline-acid digestion of defatted date-pits. Ethanol pre-treated fibers showed the highest content of hollo-cellulose (i.e., 76.1 g 100 g⁻¹ sample⁻¹) and the lowest content of lignin (0.8 g 100 g⁻¹ sample⁻¹). Low lignin content in lignocellulosic fibers is required when it is used for biofuel production and food products. Thermal analysis of defatted date-pits showed a structural relaxation at 267.7 K followed by an onset glass transition at 403 K and solids melting-decomposition endothermic peak at 456 K with enthalpy of 125 kJ kg⁻¹. However, all treated defatted date-pits showed a cold crystallization as indicated by exothermic peak (i.e., 423–433 K). Ethanol pre-treated sample showed the highest specific heat change (i.e., 380 J kg⁻¹ K⁻¹) at their glass transition temperature (i.e., the highest fraction of amorphous component) and the highest solids melting-decomposition peak at 460 K and enthalpy of 239 kJ kg⁻¹ (i.e., more energy needed to decompose molecular networks). Microwave pre-treated sample showed the highest crystalline lignocellulosic fibers. High crystalline lignocellulose is required when it is used as fillers in bio-composites and as ingredients to form crust in food products, while amorphous lignocellulose is required in breads to make it more soft crumb and bioplastic films for their flexibility. Fourier Transform Infrared (FTIR) spectra of all treated date-pits showed higher absorptions, and this indicated more interlinking ability with other components.