Effects of starch nanoparticle-stabilized oleic acid emulsions and warm storage on the structural properties and starch digestibility of cooked rice.

Cooked white rice has a high glycemic index, which is associated with an increased risk of metabolic disorders, including obesity and type 2 diabetes. This study investigated the potential of starch nanoparticle (SNP, 2%)-stabilized oleic acid (OA, 5%) emulsions to reduce starch digestibility through amylose-lipid interactions. Rice grains were soaked in OA or SNP-OA emulsions, cooked in a rice cooker, and subsequently stored at 70 °C for up to 2 days. OA droplets stabilized by SNPs were significantly smaller (6.90 μm) and more uniform than those without SNP stabilization (29.38 μm). Structural analyses indicated the formation of V-type crystalline structures associated with amylose-lipid complexes, with higher crystallinity observed in the SNP-OA-treated samples during warm storage. Consequently, resistant starch content in the simulated gastro-intestinal digestion model increased from 26.04% in the OA treatment to 33.03% in the SNP-OA treatment after 2 days of storage, whereas rapidly and slowly digestible starch fractions decreased. OA-containing samples maintained lower hardness than the control and SNP treatments during warm storage. Overall, OA incorporation during warm storage was the primary factor responsible for reducing starch digestibility, while SNP-assisted emulsification provided additional benefits through improved OA dispersion and enhanced amylose-lipid complex formation. The combination of SNP-stabilized OA emulsions and controlled warm storage may provide a practical approach for promoting resistant starch formation and modulating starch digestibility in cooked rice.