*1.3. Recovery of Antioxidants from Agro-Wastes*

The recovery of antioxidants from agro-wastes is a facile and scalable method in the manufacturing of a broad array of lignin-containing compounds for industrial and biological applications. Martinez-Avila et al. [23] noted that the fermentation of fruit peel waste generated high-quality phenolic antioxidants for industrial application. However, the recovery of antioxidants from agro-wastes is impacted by production-related constraints traditional processes are associated with significant hazards to human health, low yields,

and negative ecological effects; this explains why solid-state fermentation and solid-state shear pulverization have become the techniques of choice in the recovery of polyphenols from agro-wastes [23,24]. From a manufacturing perspective, the technical constraints are offset by the cost advantage. The cost of agro-waste is about USD (United stated dollars) 0.05–0.10, which is significantly low compared to synthetic antioxidants, which cost > USD 6 per kg (Table 3) [24]. Future advances in technology might resolve the low yields, hazards to human health, and negative ecological effects associated with toxic products.


**Table 3.** Cost of recovering antioxidants from selected agro-wastes and the phenol content [24].

In theory, it is feasible to extract antioxidants from nearly all commonly available agricultural wastes. Nonetheless, there is a strong preference for antioxidant-rich precursors such as orange peel, coffee grounds, turmeric shavings, and waste and grape pomace wastes, which exhibit superior performance in the reinforcement of plastic properties.

The antioxidants are incorporated into polyolefins to enhance their material properties, primarily recyclability, weathering resistance, and high-temperature processability [23,24], which vary in line with the chemical properties of the precursors/agro-waste materials. The presence of hydrogen-donating hindered phenols in the agro-waste materials is integral to the capture of alkyl peroxide radicals, a process that impedes the propagation of free radical reactions [24]. The precursor-specific chemical behavior underscores the need to select appropriate natural antioxidant molecules for antimicrobial treatment, biodegradation of polymers, tumor-targeted drug delivery, and food fortification.
