Green tea polyphenols improve the texture and storage stability of starch matrices with reduced digestibility

The impact of complexation with green tea polyphenols (GTE) and rice starch on digestibility, multi-scale structure and storage stability of normal (NRS) and waxy rice starch systems (15% w/v) was investigated. Normal and waxy starch gels and starch–GTE composites (2%, 5% w/v) were gelatinised (90 °C, 20 min), cooled and stored at 4 °C for up to 14 days or subjected to three freeze–thaw cycles. Multi-scale characterisation was performed using FTIR, XRD, texture analysis profile, light microscopy and rheology. Additionally, the in vitro digestibility and syneresis of these samples were evaluated. FTIR and XRD data confirmed complexation via both inclusion (V6-type) and non-inclusion intermolecular hydrogen bonds between rice starch and green tea polyphenols. Non-inclusion interactions between amylose and polyphenols appeared to predominantly modulate the digestibility, texture and storage stability of rice starch. NRS–GTE (5% w/v) composites exhibited significantly modulated digestibility (C∞~64 mg∙100g-1, RDS~49%, SDS~18%, RSF~34%), increased viscoelasticity (G’~28 kPa, G’’~7 kPa) and hardness (109 g), decreased adhesiveness (67 g∙s-1) (p<0.05) and improved storage stability, with reduced changes in texture and syneresis after 14 days at 4 °C and freeze-thaw conditions (p<0.05). These effects were attributed to starch-GTE interactions reinforcing the gel network while partially disrupting amylose reassociation and appeared strongly influenced by amylose content and the miscibility of the extract within the composite matrix. Our findings provide new insight into the complexation-digestibility-structure relationship of rice starch that could pave the way for the reformulation of palatable ready-to-eat rice-based foods with tuned digestibility and improved storage stability.