Hydrolysis-induced sericin molecular states regulate citrus pectin-based emulsion fluid gels: Structure and swallowing-related properties

Controlled sericin hydrolysis generated fragments with distinct molecular and interaction characteristics. • Ser hydrolysates regulated the structure, rheology, and recovery of pectin soft and emulsion fluid gels. • Utensil tests and CFD linked bulk properties with IDDSI-relevant confined-flow behaviour. People with dysphagia often depend on texture-modified foods to maintain oral intake, yet achieving the required balance of flow, cohesion, and shape retention remains difficult in renewable citrus-peel-derived pectin matrices, even among products within similar consistency ranges. This study used graded alkaline-protease hydrolysis to generate sericin (Ser) populations with distinct molecular states that regulated citrus-pectin gels. Hydrolysis caused a rapid early decrease in apparent molecular size, with most of the decrease occurring within the first 15 min (Ser15), while the molecular-weight distribution subsequently narrowed. In oil-free Ser-pectin gels, limited hydrolysis increased resistance to sustained penetration, intermediate hydrolysis reduced large-deformation resistance while retaining small-strain elasticity, and extensive hydrolysis partially restored penetration work and low-shear viscosity. After oil incorporation, all emulsion fluid gels (FGs) maintained weak-gel-like behaviour, pronounced shear thinning, and final viscosity recovery of approximately 75-85%. Their performance shifted from the highly flowable Ser15-FG, through the more complete recovery and balanced storage behaviour of Ser60-FG, to the strongly shape-retaining and more thermally and freeze-thaw-stable Ser180-FG. Confined-flow simulations mapped IDDSI-relevant utensil responses onto outlet flow rate, mean velocity, and low-velocity volume fraction, partially quantifying spreading, dripping, and shape retention. Hydrolysis-generated Ser molecular states therefore provide a simple strategy for tuning pectin-based fluid gels with differentiated consistency and handling profiles, supporting formulation differentiation and optimization. As illustrated in the graphical abstract, controlled alkaline-protease hydrolysis was used to generate sericin (Ser) populations with distinct molecular states, characterised by differences in apparent molecular-weight distribution, fragment continuity, and molecular mobility. These hydrolysates were combined with citrus pectin to construct soft gels and emulsion fluid gels, allowing hydrolysis-dependent regulation to be evaluated in both oil-free and oil-containing structural contexts. In soft gels, hydrolysis drove a transition from a more connected network to a coarse intermediate structure and finally to a more dispersed open network. In emulsion fluid gels, the same molecular-state shift altered droplet–matrix coupling, spatial heterogeneity, and local reassociation around oil droplets. These structural changes produced distinct combinations of flowability, shape retention, recovery, and utensil-handling behaviour, which CFD further resolved into different confined-flow profiles. Controlled Ser hydrolysis therefore broadened the accessible handling range of Ser–pectin systems and provided a time-controllable strategy for tuning IDDSI-relevant material and handling properties. Download: Download high-res image (391KB) Download: Download full-size image