*5.1. Thermal Extraction*

Thermal extraction includes decoction, reflux, Soxhlet, hydro, and steam distillation techniques [126]. Incorporating bioactive compounds such as flavonoids, phenolic acids, and polysaccharides into polymer materials improves both the antioxidant and antibacterial activity [127]. Temperature increases the solubility and diffusivity in solid–liquid extraction, resulting in high yields of extracted compounds. Thermal degradation of enzymes and desired bioactive compounds occurs during prolonged extraction at high temperatures [128]. Regarding the extraction of FVW and FVB for industrial applications, various methods are used, such as fermentation and separation (lactic acid extraction from potato peels), hot dilute acid treatment and alcohol precipitation (pectin extraction from citrus peels), and steam distillation and alkali treatment (D-limonene extraction from citrus peels) [129]. These methods are appropriate for batch and large-scale processing. Meanwhile, emerging thermal processes, such as microwave-assisted extraction (MAE), pressurized liquid extraction (PLE), and subcritical water extraction (SWE), offer additional benefits and have the potential to replace conventional methods due to being efficient, economical, and environmentally friendly [17].
