Structure, physicochemical characteristics, and functional properties of starches isolated from yellow (Curcuma longa) and black (Curcuma caesia) turmeric rhizomes

Starch, a dominant component of the turmeric rhizomes, has been traditionally used as a food coloring and functional foods. The objective of this study is to investigate the structure and physicochemical characteristics and functional properties of the yellow (Curcuma longa) and black (Curcuma caesia) turmeric starches. The C. longa and C. caesia starches contained the triangular to oval shaped granules, which exhibited similar B-type crystalline structure and amylose content. However, the C. longa starch had higher chain length of amylose and more short branching chains of amylopectin resulting in lower gelatinization temperature but higher transition enthalpy as compared to the C. caesia starch. Both C. longa and C. caesia starches showed broad peak viscosities with no breakdown indicating greater stability of these starches under heat and shear conditions, in which the C. longa had significantly higher viscosity than did the C. caesia starch. The resistant starch contents of the C. longa and C. caesia starches were 24 and 20%, respectively. Moreover, the C. longa starch contained higher amounts of total phenolics and curcumin resulting in stronger antioxidant capacity as compared to the C. caesia starch. As a result, the C. longa and C. caesia starches could be used as a functional food in both food and pharmaceutical industries.