Structural determinants of gelation kinetics in rambutan seed starches: Implications for enhanced precision in 3D food printing

Precise modulation of starch gelation kinetics is essential for achieving high-fidelity 3D printing of functional foods; however, the narrow processing window of conventional starches remains a primary bottleneck. Since native starch molecular structures are source-dependent and difficult to tailor through modification, the discovery of novel starch sources is pivotal for developing high-performance starch-based inks. This study posits that structurally-diverse starches from underutilized sources offer a fundamental strategy to address this challenge. We characterized three rambutan seed starch varieties (BR-4, BR-5, and BR-7) across multiple structural scales and assessed their 3D food printing performance. The extracted starches featured small, monodisperse spherical granules (7.28–8.26 μm), high molecular weight (9.99 × 10⁴–1.29 × 10⁵ kDa), moderate amylose content (21.59–25.70%), rapid room-temperature gelation (2–10 min), and high slowly digestible starch content (69.71–73.45%). All resulting gels satisfied the IDDSI Level 5 (minced & moist) criteria. Remarkably, BR-7, with its higher amylose content and abundant short-chain amylopectin, formed a dense gel network. This unique structural configuration conferred excellent properties including gelation rate (2 min, 11× faster than pea starch), gel strength, printing accuracy (99.14%), and digestion resistance. This study offers insights into the valorization of tropical fruit processing by-products for precision 3D food printing applications.