Physicochemical and Functional Properties of Tropical Tuber Starches: A Review

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  1. Introduction
  2. Extraction Techniques
  3. Other components in Starch
  4. Colour and Appearance
  5. Granule Shape and Size
  6. Spectral Features
  7. X-Ray Diffraction Pattern
  8. Molecular Weight
  9. Amylose Content
  10. Thermal Characteristics
  11. Gelatinisation and Pasting Temperatures
  12. Viscosity
  13. Swelling Power
  14. Solubility
  15. Clarity
  16. Sol stability
  17. Digestibility
  18. Conclusions

14. Solubility

Solubility of starch depends on a number of factors such as source, inter-associative forces, swelling power, presence of other components etc.

  1. Cassava Starch

    Cassava starch has a higher solubility than the other tuber crop starches on the higher solubility can be attributed partly to the higher swelling cassava starch undergoes during Gelatinisation. The solubility values ranged from 25-48o (Tab.8)[33]. The solubility of starch of different cassava varieties varied from 17.2-27.2%. However, no direct correlation between swelling and solubility could be observed [5]. Solubility data of starch from different varieties during the growth periods also showed that the starch of varieties H.2304 and M4 had good stability in their solubility whereas the stability of the other varieties are medium or poor [62]. The solubility was enhanced by heat-moisture treatment [107]. Among a few non aqueous solvents studied for solubility of starch, maximum solubility was obtained in DMSO and formalin while in glycerol it was moderate. Starch was insoluble in anisole and methyl cellosolve (Tab.15). The solubility data indicate that starch is more soluble in polar solvents or solvents with affinity towards water [149].

    Table 15 : Solubility gelatinisation temperature and viscocity of starch solutions in different solvents

    Solubility [g/100mL] Gelatinisation Temperature [0C] Viscosity (2%) Redwood [s] Viscosity (2%) after cooling [s]
    Glycerol 10 130-145 175 1800
    Ethanediol 2 110-125 17.5 38
    DMSO 25 75-85 85 130
    Formalin 25 70-85 78 139
    DMF Nil
    Methyl cellulose Nil
    Anisole Nil
  2. Sweet potato starch

    The data on solubility of sweet potato starch is given in Tab.8 the solubility of starch extracted from seven sweet potato collections from peru indicated that solubility increased with temperature and reached nearly 10% while for commercial starch, it was 28% [26]. The authors found that selection indentity did not have noticeable effect, but location had significant influence but temperatures above 600C, Collado et al. [135] found that for 44 Philippine genotypes of sweet potato, the solubility varied in the range of 12-24%, mean being 16.9%. The high swelling volume of the starch was reflected in its solubility. It was presumed that the bonding forces might be tenuous but comparatively extensive, immobilizing the starch within the granules even at high levels of swelling.

  3. Other Starches

    The solubility of D.abyssinica starch was found to be enhanced with temperature and the values resembled those of the maize starch[39]. The solubility starch of yams and aroids pretreated with various chemicals was affected to different extent by the chemicals used and also the concentration [10]. The values were between 18-32%. Solubility of the other tuber starches varied from 10-30% and in general the aroid starches had usefully lower solubilities.

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