Physicochemical and Functional Properties of Tropical Tuber Starches: A Review

Prev Page | Next Page

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 25-48^o (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.