Preparation, characterization, and application of soluble dietary fiber-rich kiwi peel pomace: Fiber-fortification of bread

Kiwifruit processing generates large amounts of peel pomace rich in dietary fibers and polyphenols, but these by-products are usually discarded or underutilized. In this study, an optimized cellulase/ β -glucosidase treatment was developed to valorize kiwifruit peel pomace. The treatment converted insoluble dietary fiber (IDF) into soluble dietary fiber (SDF), increasing SDF to 14.83%, and simultaneously enhanced total phenols, flavonoids, antioxidant activities, and volatile compounds. When assessed as a functional ingredient in bread, the treated pomace improved dough properties by elevating α-amylase activity, reducing free sulfhydryl groups, and increasing disulfide bonds, thereby promoting gluten cross-linking and the formation of a continuous gluten network with embedded starch granules. This mechanism was associated with improved farinograph parameters, dough extensibility, and viscoelasticity. In bread, the treated pomace improved loaf volume and texture, raised resistant starch to 54.61%, lowered the estimated glycemic index to 63.16, and prolonged gastric emptying, while antioxidant capacities and sensory scores were also improved. Overall, enzymatic conversion of IDF to SDF effectively enhanced dough processability and bread nutritional quality. These findings demonstrate that enzyme-assisted valorization of kiwifruit peel pomace is a sustainable strategy for producing a functional bread ingredient, with benefits mechanistically linked to gluten network reinforcement and modulated starch digestibility.