Improving food sustainability by converting orange peel waste products into hydrogels using stirred media milling

There is a need for natural gelling ingredients within the food industry. We have shown that orange peel suspensions (OPS) form hydrogels when treated with a stirred media mill. Gels were formed when an aqueous 3% OPS was milled for longer than 60 min. Their gel strength increased with milling time, which was attributed to progressive disruption of the plant cell tissues and release of pectin and other polysaccharides. The water holding capacity and amount of bound water in the orange peel gels increased with milling time. Shear rheology experiments showed that the gels exhibited shear thinning and were predominantly elastic-like materials. FTIR analysis and addition of bond disruptive agents suggested that hydrophobic interactions between methoxy groups on the pectin were mainly responsible for crosslinking and gelation. Overall, our results suggest that stirred media milling may improve the utilization of orange peel as a functional ingredient in the food industry.