Targeted Modification of Dietary Fiber for Increasing Soluble Dietary Fiber and Its Application in Foods

The high proportion of insoluble dietary fiber (IDF) in natural plant materials critically limits the solubility, functionality, and processing performance of dietary fiber (DF), making the conversion of IDF to soluble dietary fiber (SDF) a key focus in current research. Although numerous physical, chemical, and biological modification technologies have been developed, most studies focus on treatment outcomes but fail to adequately address two key determinants: the intrinsic properties of DF, specifically the typical composition of DFs from different sources, cellulose crystalline regions, and the inherent structural recalcitrance resulting from lignocellulosic network cross-linking; and the synergistic effects of parameters, referring to the impact of processing variables (such as power, pressure, and enzyme type) on DFs from various sources. This review provides a systematic comparison of mainstream and emerging modification strategies, highlighting their mechanisms, advantages, and limitations across diverse DF matrices. Based on this, lignocellulose is utilized as a representative IDF model to explain how its dense, multilayered architecture acts as the primary barrier to efficient SDF generation. Furthermore, this review synthesizes advances in the targeted disruption of lignocellulosic components, including targeted lignin degradation and the depolymerization of cellulose and hemicellulose, to propose strategies for overcoming IDF recalcitrance. Finally, the application potential of these modification pathways in improving DF utilization in foods is evaluated, enabling innovative formats such as personalized nutrition, 3D-printed products, and biodegradable materials. Overall, this review integrates technique-level insights with structure-guided strategies, offering a mechanistic framework and practical roadmap for achieving efficient, directional IDF modification and SDF enhancement.