Enzymatic hydrolysis of hydroxypropyl distarch phosphate (HPDSP) by α-amylase and its effects on the rheological properties of pasteurized yogurt

Residual α-amylase activity in stored pasteurized yogurt hydrolyses hydroxypropyl distarch phosphate (HPDSP), threatening product quality and motivating this study to establish safe enzymatic thresholds for texture stability. Bacillus licheniformis α-amylase (HEa) demonstrated superior thermal stability with a static half-life 5-10 times longer than that of Aspergillus oryzae (ASa) at 85-100 °C. HEa effectively hydrolysed HPDSP, reducing starch residue to 77 % at ultra-trace concentrations of 1.0 × 10^-4 U/L, respectively. Conversely, ASa exhibited negligible hydrolysis even at a concentration of 1 U/L. Rheological analysis revealed that elevated α-amylase concentrations significantly decreased yogurt viscosity and yield stress. However, controlled enzyme levels (ASa ≤ 1.0 × 10^-1 U/L or HEa ≤ 1.0 × 10^-3 U/L) maintained optimal viscosity and shear-thinning behaviour throughout storage. These findings highlight the importance of stringent α-amylase level control to maintain consistent texture and quality in pasteurized yogurt products during storage.