Granule-associated surface and channel lipids (GALs) were extracted and identified from four small-granule (rice, oat, quinoa and amaranth) starches. All small-granule starches had apparent bimodal granule size distribution, which was due to the aggregation of granules. The bimodal pattern disappeared after extraction of GALs, and the starches showed typical monomodal distributions, indicating that the presence of GALs has a profound effect on granule aggregation. GALs were effectively extracted from small-granule starches, indicated by CLSM coupled with Pro-Q Diamond-staining. GALs content of starches ranged from 0.347 to 0.631%. The GALs of starches were mainly neutral lipids, others were glycolipids or phospholipids, and the fatty acid composition was mainly palmitic acid, stearic acid, myristic acid, oleic acid and linoleic acid. Removing GALs increased the peak, breakdown and setback viscosities of rice, oat and amaranth starches, while quinoa starch after GALs removal exhibited a weaker granular structure and a greater tendency to decrease in viscosity under shear. Removing GALs contributed to amylose leaching, accelerated the recrystallization and rearrangement of starch molecules, and facilitated retrogradation, thereby leading to a higher gel hardness. Even though GALs content is very low, it may be of value for manipulation of starch properties.
- Granule-associated surface and channel lipids
- Small-granule starch
- Fatty acid composition
- Pasting behaviour