Effect of repeated cycled crystallization on digestibility and molecular structure of glutinous Bora rice starch

- Repeated cycled crystallization slowed the digestion of waxy rice starch.
- Molecular weight distributions of amylopectin were altered.
- Loss of typical Maltese cross revealed reorientation of crystalline structures.
- V-type complex observed in the SDS product even in the absence of co-polymers.

The effects of repeated cycled crystallization on the digestibility and molecular structure of glutinous Bora rice starch were investigated. Temperature cycle 4/45 °C; cycle duration 5 d; time interval of cycles 24 h; and starch to water ratio 1:2 were found to be optimum for SDS (slow digestible starch) product development. The SDS content increased from 18.01 ± 2.11% to 82.81 ± 2.34%. An increase in the resistance to digestion, crystallinity, molecular weight, polydispersity and molecular order was observed in the optimal SDS product. Notably, the FT-IR peak at 947 cm−1 and XRD peaks at 2θ ≈ 13° and 20° in the optimal SDS product indicated the formation of V-type complexes even without the presence of co-polymers. Birefringence studies showed a loss of typical Maltese cross in the SDS product and revealed a reorientation of crystalline structures within starch granules, suggestive of imperfect crystallite development.