Starch granules of different crops have definite and characteristic shape and size and show a large range. In fact the granule size has considerable influence on the functional properties and applications.
The shape of the granules has been varyingly reported as oval, truncated, and rounded as observed by various microscopic techniques (e.g., scanning electron microscopy and light microscopy). The granule surface has been probed by atomic force microscopy (AFM) to reveal the structural details. Blocklets, depressions, and protrusions on the surface of starch granules have been observed as illustrated in Figure 1. In general, cassava starch possessed smoother surface compared with that of potato (Juszczak et al., 2003).
The granules exhibit wide variation in size range (5-40 mm) (Table 1), and variation in granular size distribution among varieties and during growth period has been documented. The size of 7-20 mm was the most frequent (Rolland-Sabate et al., 2012). The average size of granules from normal genotypes differed greatly between different studies (10-18 mm) (Juszczak et al., 2003; Waterschoot et al., 2015; Wikramsinghe et al., 2009).
| No. | Pattern | Crystallinity (%) | Granule Size (μm) | Shape |
| 4a | Ca | 15.3-17.8 | 2.4-31.1 | |
| 6 | 6.96-11.21 | |||
| 1b | Ca | Round, cylindrical, and polygonal | ||
| 1 | A | |||
| 3X2c | Ca | 15.4-17.8 | 2.4-31.1 | |
| 1 | A | |||
| 1 | A | 15 (average) | ||
| 5 | 3-32 | |||
| 4X2X5d | A | 3-32 | ||
| 4X4e | 8-22 | Irregular, oval, round, truncated | ||
| 11 | 9-20 | Oval, truncated, rounded | ||
| 5 | 12.9-17.2 | |||
| 40 | 12.5-23.8 | |||
| 1 | 16 | |||
| 4 | 5.8-18.73 | |||
| 39 | 12.5-22.5 | |||
| 1 | 2.81-14.03 | |||
| 17 | 7.3-9.7 | |||
| 2 | A | 40-49 | 16.9-18 | Oval to round |
| 12 | A | 4.6-22.8 | Round and truncated | |
| 8 | Ca | 25-40 | 8-17 | Spherical, polyhedral, truncated |
| 8 | Ca | 35-40 | 12.1-16.1 | |
| 1 | 7.1-25 | Spherical, truncated |
No., number of genotypes/samples.
a 3-4 different harvesting months.
b Two extraction methods.
c With/without pruning aerial growth.
d Five different harvesting months, and two different planting seasons.
e Four different harvesting months; peak and average in the parenthesis denote the peak and average size of the granules, respectively.
Peroni-Okita et al. (2006) has studied the particle size distribution in different starches using image analyzer and the data is given in Table 2.
| Starch | Size (μm) | Average size (μm) | Size Distribution (μm) | Size Distribution (%) | Shape |
| Cassava | 7.6-23.5 | 15.9 | 5-10 10-20 >20 | 8.6 71.4 20 | Round |
| Arrowroot | 8.6-42 | 21.1 | 5-20 20-30 >30 | 42.7 50.5 6.8 | Round, oval |
| Sweet potato | 7.5-28.5 | 13.9 | 5-10 10-20 >20 | 21 70.5 8.5 | Polygonal |
| Yam | 6.8-47 | 25.3 | 5-15 15-35 >35 | 19.3 67.2 13.5 | Elliptical |
| Ginger | 5-33.6 | 15.8 | 5-10 10-20 >20 | 6.6 82.7 10.7 | Polygonal |