Effect of Critical Melting and Freeze-Thawing Pretreatment Assisted with Enzymatic Hydrolysis on Physicochemical and Structure Properties of Porous Starch

In this study, normal maize starch (NMS) and waxy maize starch (WMS) were utilized as raw materials, while enzymatic hydrolysis (EN) and a combination of critical melting and freeze-thawing with EN (CMFT+EN) as the main treatments used for porous starch preparation. The study aimed to provide a combined treatment that stabilize the porous starch granule structure, reduce enzyme dosage, and enhance enzymatic hydrolysis efficiency for porous starch preparation. Based on yield, water and oil absorption capacities of porous starch, the optimal conditions for EN preparation were 120 U/g of enzyme addition, 12 h hydrolysis at pH6.0, while for CMFT+EN were 80 U/g, 8 h at pH6.0. Scanning electron microscopy and confocal laser scanning microscopy showed that CMFT+EN prepared porous starch had denser pores and larger pore size while maintaining intact granular structure compared to native. Both maize starches displayed similar trends. After CMFT+EN treatment, water solubility index of starch increased while swelling power and water-holding capacity decreased (at 70 ℃ and 90 ℃). Compared with native and EN, the relative crystallinity (RC%) and short-range order of CMFT+EN prepared porous starch increased significantly. The RC% of NMS increased from 25.42% (native) and 24.58% (EN) to 29.52%, while WMS increased from 28.37% (native) and 27.54% (EN) to 32.98%. CMFT+EN significantly improved (P<0.05) thermal stability of starch, with melting onset temperature increases of 5.11 ℃ for NMS and 3.59 ℃ for WMS compared to EN. Furthermore, the vitamin C adsorption capacity of CMFT+EN increased significantly (P<0.05) from 29.85 mg/g (EN) to 34.99 mg/g for NMS and from 30.26 mg/g (EN) to 38.65 mg/g for WMS. This study provides a practical strategy for porous starch preparation.