Impact of genetic modifications in starch biosynthesis on 3D printing performance of rice starches

Starch gels with favorable rheological properties are promising for 3D printing, but native starch often requires modification, and traditional physical or chemical methods may pose safety and food applicability concerns. In this study, we investigated the effects of gene modification in starch biosynthesis on gel microstructure, rheological behavior, and 3D printing performance of rice starch. Six rice starch samples with varying genotypes and molecular structures were selected to prepare starch gels retrograded for 1 h, 1 day, and 7 days. Knockout of starch branching enzyme IIb (BEIIb) increased amylose content (>30%), resulting in starch gels with smaller pore area/fraction, and correlation length (∼20-40 Å) and structural radii of the semicrystalline units, and faster recrystallization, but lower yield stress (<20 Pa) and shear recovery (∼30%-60%) during extended retrogradation, yielding optimal mid-term but limited long-term printability compared to the other three starch samples. In samples with intact BEIIb, the SSIIa^TT genotype increased fa chain content (27%-28%), thereby improving pore fraction, correlation length (∼35-55 Å) and structural radii, delaying B-type crystallization, and presenting the best initial and long-term printability. In contrast, the SSIIa^GC genotype had higher fb1 chain content (52%), yield stress (∼60-120 Pa), and consistency index (∼40-85 Pa·sn), but low pore area/fraction values, supporting good mid-term printability. These results indicate that both amylose content and amylopectin fine structure significantly affect starch printability. This genetic approach offers a sustainable, precise, and cost-effective solution for optimizing starch materials for 3D printing.