Characterization of Phenolic Compounds from Sunflower Hulls and their Application as Antioxidants in Oil-in-Water Emulsions.

Sunflower hulls are a significant byproduct of the oil industry that can be revalorized as a source of phenolic compounds with potential antioxidant capacity in food applications. The objective of this work was to evaluate phenolic extracts from sunflower hulls with different characteristics (black and striated hulls) and assess their performance in a model oil-in-water (O/W) emulsion system. The extracts were characterized according to phenolic compound type (free and bound), total phenol and flavonoid content, antioxidant activity, and phenolic acid profile by HPLC. In addition, the hulls were analyzed using FTIR and SEM. Antioxidant performance in the O/W model emulsions was evaluated by monitoring primary lipid oxidation through peroxide value measurements during 90 days of storage. The results showed a predominance of the free phenolic fraction (84-96%), exhibiting higher yields, phenolic content, and antioxidant activity than the bound fraction. Chlorogenic acid was the primary compound among the free phenolics, while the bound phenolic extract showed a greater contribution from gentisic and ferulic acids. FTIR and SEM analyses revealed structural modifications in the hulls associated with phenolic extraction. The incorporation of the phenolics into O/W emulsions significantly delayed the formation of primary oxidation products during storage, even at low concentrations, with extracts from black-hull hybrid being the most effective. These findings highlight the potential of sunflower hulls as a source of natural antioxidants and encourage further studies to validate their performance in more complex, food-grade emulsified formulations.