Effects of Amylose Level and Cooking Method on Type V Resistant Starch Formation in Coconut‐Milk‐Cooked White Rice

Abstract

Type V resistant starch (RS5), produced through amylose–lipid complexation, provides important functional and nutritional benefits. However, its formation in rice cooked with coconut milk, a key component of Malaysia's nasi lemak, remains poorly understood. This study examined RS5 formation in three rice varieties of differing amylose levels (Commercial variety, UPM Putra 2, and NMR 152) cooked with and without coconut milk using steaming and boiling. The most significant findings show that amylose level and cooking method strongly influenced complex formation. Although Commercial variety contained 26.38 ± 1.52 a highest amylose content, the medium‐amylose UPM Putra 2 with amylose 21.50 ± 0.62 b unexpectedly exhibited the highest complexing index under both steaming (30.39% ± 0.45%) and boiling (26.01% ± 0.19%). Steaming consistently produced higher complexing indices than boiling across all rice types, demonstrating its superior efficiency in promoting amylose–lipid interactions. Thermal analysis showed that samples cooked with coconut milk displayed a characteristic high‐temperature dissociation peak (118°C–131°C), demonstrating amylose–lipid complex presence. Commercial variety exhibited the highest enthalpy values during complex dissociation in both steaming (104.05 ± 1.87 J/g) and boiling (38.20 ± 1.39 J/g), indicating greater thermal stability and suggesting that, despite its lower complexing index, it formed more stable complexes structurally. Notably, steamed samples with lipid consistently showed higher enthalpy changes than boiled samples. X‐ray diffraction data revealed increased intensity at the 19.8° peak in all rice samples cooked with coconut milk, suggesting RS5 formation. Commercial variety demonstrated the sharpest and most defined peak, reflecting higher crystallinity and a more ordered starch–lipid structure. Overall, the study demonstrates that coconut milk enhances RS5 formation in white rice, with steaming outperforming boiling in promoting amylose–lipid complex development. While medium‐amylose rice showed the highest complexing index, high‐amylose rice produced the most thermally and structurally stable complexes. These findings offer practical implications for optimizing rice preparation to improve functional and nutritional qualities in traditional and modern food applications.