Impact of continuous or cycle high hydrostatic pressure on the ultrastructure and digestibility of rice starch granules

• Starch structure and digestibility of single or cycle HHP-treated rice was studied.
• 600 MPa damaged the structure and lowered the RS over 200 MPa.
• Cycle HHP caused severer structure breakdown, lower RS and crystallinity of starch.
• Based on RS, cycle HHP at 200 MPa might improve the starch functionality.

The effects of continuous or 2-cycle high hydrostatic pressure (HHP) treatments (200 and 600 MPa) on the microstructure and digestibility of rice starches were investigated. The morphological and structural changes were characterized using polarized light microscopy, scanning electron microscopy, atomic force microscopy, X-ray scattering and 13C CP/MAS NMR, and the starch digestibility was examined by in vitro hydrolysis. Results showed that HHP at 600 MPa significantly alters the microstructure and lowers the resistant starch (RS) compared with HHP at 200 MPa. Under the same pressure level, the two 15-min cycle treatment induced more structural disruption, gelatinization, disappearance of surface protrusion, and lower RS of rice starches than that of the continuous HHP treatment (30 min). Based on the results on RS, the two 15-min cycle HHP treatment at 200 MPa could be beneficial for improving the functionality of the rice starch.