Characterization of Commercial Olluco (Ullucus tuberosus) Tubers From La Plata, Argentina: Potential as a Source of Starch, Flour, and Soluble Dietary Fiber

Abstract

Ullucus tuberosus (olluco) is an underutilized Andean tuber known for its high soluble fiber and distinctive betalain pigments. This study aimed to characterize the morphological and compositional traits of commercially available olluco tubers in La Plata, Argentina, and evaluate their potential for flour and starch production, and the characteristics of its soluble fiber. The tubers exhibited spherical shape (mean weight 19 ± 3 g), yellow to green skin with magenta spots, and a succulent interior with no visible mucilage. Their high moisture and moderate starch content (45.3% dw) suggest limited suitability for starch extraction. Olluco flour retained the content of phenolic compounds found in the tubers, but degradation of betacyanins (41%) and betaxanthins (54%) occurred during drying. The flour demonstrated high solubility at 92.5 °C, which increased with smaller particle size, and exhibited moderate swelling capacity (5 ml/g). Slight color changes were observed upon cooking in excess water. The apparent viscosity of the flour paste at a shear rate of 50 s⁻¹ was also higher for flours with smaller particle sizes, and the paste exhibited pseudoplastic behavior, indicating its potential as a functional food ingredient. The soluble fiber fraction consisted of two molecular weight populations, one < 500 Da and the other around 48,000 Da. Solubility of this fraction was reduced after freeze-drying, likely due to interactions between polysaccharides and co-extracted proteins and phenolic compounds. FTIR analysis revealed the presence of pectic polysaccharides with strong similarity to citrus peel pectin, suggesting that these polar groups are exposed on the surface of the freeze-dried particles.