Upcycling citrus peel residue into multifunctional nanofiber colloids via sustainable ball milling

In this study, the natural nanofiber-based colloids derived from citrus peel residue were facilely prepared through an eco-friendly wet ball milling method. The effects of milling time (0.5-3 h) on the structure, physicochemical properties, and emulsifying performance were investigated. Compared with unmilled citrus peel particles (D_4,3 = 253.00 μm), the D_4,3 of colloidal particles decreased to 78.78 μm after 3 h of ball milling, alongside remarkable increases in apparent viscosity and suspension-dispersion stability. Moderate ball-milling enhanced fiber nanofibrillation and accelerated the dissolution of soluble dietary fiber, thereby greatly improving water-holding, oil-holding and swelling capacities of the colloids, whereas further prolonging milling to 3 h induced a slight decline. Furthermore, the mild ball milling process retained the natural bioactive substances such as polyphenols and flavonoids, endowing the colloids with good antioxidant activity. Additionally, the colloids obtained after 2 h of ball milling showed favorable emulsifying performance and could stabilize low-to-medium internal phase emulsions as natural emulsifiers. This study effectively developed citrus byproducts into multifunctional food ingredients, especially as a food emulsifier in clean-label foods.