Dual modification of red rice starch: Combining hydrothermal pretreatment with acid hydrolysis for the production of nanomaterials

This study evaluated the combination of acid hydrolysis with hydrothermal pretreatment (HPT) for the production of nanomaterials using red rice starch. Native red rice starch (A0) was subjected to HPT in an autoclave at 121°C/10 min (A3) or cooked at 100°C/10 min (A4) and then hydrolyzed with 3.16M sulfuric acid at 25°C for a period of 5 days. The A3 treatment enhanced acid diffusion, leading to the efficient production of starch nanomaterials with a diameter of 106.97 nm. This process resulted in a crystallinity of 31.94%, a higher degree of polymerization of amylopectin (DP ≥ 37: 31.39–34.98%), and a yield of 33.48% on the third day, surpassing A0′s 10.12%. These characteristics classify A3 as starch nanocrystals (SNC). In contrast, A4 exhibited an increased diameter of 260.81 nm, and crystallinity remained in the range of 15%. It is classified as starch nanoparticles (SNP) and displayed higher gelatinization temperatures due to amorphous regions. DP was most affected by A4 with lower values DP ​​≥ 37 (25.68-30.16%) throughout acid hydrolysis, confirming the lower crystallinity. Finally, it was found that autoclaving was efficient as a pretreatment for native red rice starch to produce SNC through acid hydrolysis in a reduced time.