ULTRASOUND-ASSISTED TARO STARCH (Colocasia esculenta) ESTERIFICATION: OPTIMIZATION BY RESPONSE SURFACE METHODOLOGY TO ENHANCE ITS RESISTANT STARCH CONTENT

In the Peruvian Amazon, there is a high diversity of potential starchy sources (tubers, corms, and tuberous roots) that grow wild and are primarily consumed directly by indigenous communities. One of the most consumed is the taro (Colocasia esculenta) cultivar. The objective of this research was to optimize the ultrasound-assisted citric acid esterification conditions for taro starch to increase its resistant starch (RS) content. Taro was provided by the Nuevo Progreso community of Balsapuerto (Alto Amazonas, Loreto region, Peru), and starch was extracted in a pilot plant. The design variables for optimizing the esterification were: citric acid concentration (40, 50, and 60%, w/v), starch:acid ratio (0.5, 0.75, and 1), and sonication time (0, 10, and 20 min). A Box-Behnken design was used, consisting of 15 runs with one replicate and three replicates around the center point. The degree of substitution (DS) and RS (%) were evaluated as response variables. Native starch was characterized by proximate analysis and phosphorus content. Starch purity (%), amylose (%), and resistant starch (%) were determined by enzymatic methods. Additionally, paste clarity, color parameters, thermal properties, and rheological properties (flow behavior and viscoelasticity) were evaluated. Native starch had 90.54% of purity (dry basis), 16.47% amylose, and a low resistant starch content (5.38% dry basis) after gelatinization. The DS and RS content ranged from 0.029–0.071% and 8.16–23.87% (dry basis), respectively, across 15 treatments in the optimization design. A p-value > 0.1656 was obtained for the lack of fit of the quadratic model to the observed data (R² = 92.6% and adjusted R² = 88.7%). Finally, the optimal parameters for obtaining a modified taro starch with a higher RS content were a 45.3% acid concentration, a starch:acid ratio of 0.72, and 11.3 min of sonication, which predicts an RS response of 24.02%. These results indicate that the ultrasound-assisted citric acid esterification method effectively increases the RS content in taro starch by nearly 5-fold.