Optimization of Pregelatinization Temperature and Time of Black Potato (Coleus tuberosus) Flour Using Response Surface Methodology

Pregelatinization can improve functional properties of underutilized black potato (Coleus tuberosus) flour. Pregelatinization temperature and time were optimized using response surface methodology (central composite design, 13 runs) to maximize water absorption capacity (WAC) and solubility index (SI). Quadratic models were significant (WAC R² 92.83%; SI R² 95.57%; p < 0.05; lack of fit non-significant). Optimal conditions (62 °C, 8.44 min; desirability 0.91) gave validated WAC 2.70 g/g and SI 8.83% (1.42% and 6.83% from predicted), 1.41-fold and 3.57-fold above native flour (WAC 1.92 g/g; SI 2.47%). Pregelatinization lowered pasting temperature (86.25 to 83.90 °C), peak viscosity (4495 to 2792 cP), breakdown (564 to 82 cP), peak time (5.27 to 5.13 min), and paste hardness (63.88 to 28.85 g). SEM showed irregular, rough granules with sheet-like structures; XRD showed fewer peaks (reduced crystallinity). Results suggest potential for instant foods and neglected-tuber valorization, pending food-product evaluation.