Extraction and Characterization of Starch Fractions of Five Phenotypes <i>Pachyrhizus tuberosus</i> (Lam.) Spreng

Abstract

Pachyrhizus tuberosus is a native plant of short life cycle found in South America riverside, which provides easy starch extraction from its tuberous roots. The aim of this study was to determine the physicochemical, rheological and functionality of the starch granules extracted from the roots of five phenotypes identified as V2, V3, V4, V6 and V7. Protein and ash content of all phenotypes were considerable high when compared to other root sources such as cassava varying from 4.35% to 7.43% and 1.58% to 2.49%, respectively, whereas lipid content was lower, between 0.29 and 0.49%. The starch granules were mostly circular and polygonal with varied sizes. The starch granules structural conformation showed cristallinity A type, normally for cereals. The maximum pasting viscosity at 95 ℃ ranged from 1644 cP (V7) to 2232 cP (V2). The initial temperature of pasting formation occurred at 69.4 ℃ for V2, 71.5 ℃ for V3, 87.9 ℃ for V4, 69.5 ℃ for V6 and 71.5 ℃ for V7. These values showed high variability within the phenotypes and generally high for roots and tubers starches. The maximum viscosity at 95 ℃ for V2, V3, V4, V6 and V7 were 2232, 2150, 1995, 2214 and 1644 cP, respectively. The viscosity curves showed low tendency to retrogradation. The thermal properties showed that the enthalpy of gelatinization varied from 8.91 J/g (V3) to 11.78 J/g (V2). The initial gelatinization temperature varied from 63.19 ℃ (V6) to 65.14 ℃ (V4). The swelling power at 90 ℃ ranged from 14.7% to 20.1% p/p and solubility from 10.3% (V2) to 27.2% (V7). It is concluded that Pachyrhizus tuberosus starch showed low retrogradation (1320 - 1560 cP) comparable to non-common native waxy starches, a feature which indicates the capability of using this natural and easy extraction starch source as gelling agent in certain manufactured food of undesirable retrogradation.