Molecular Structure and Some Properties of Starches from Rhizome and Fusiform Root of Wild Turmeric (Curcuma aromatica Salisb .)

Abstract

Abstract: The molecular structure and some properties of starches from rhizomes and fusiform roots of wild turmeric (Curcuma aromatica Salisb.) have been examined . Starch content of the rhizomes and fusiform roots was 9.2 and 6.5% with actual amylose content of 25 and 20%, respectively . Both starches showed a B-type Xray diffraction pattern. RVA viscograms for both starches showed small breakdown, and the rhizome starch showed two-fold higher maximum and minimum viscosities and setback . Thermal properties indicated that crystallites in the starch granules were similar in content but different in structure . The amyloses had numberaverage degree of polymerization (DP_n ) of?`900 and the amyloses with DP_n 400-500 were predominant on a molar basis. Branched molecules of amylose consisted of 13 and 17% by mole and had an average number of chains of branched molecule (NCB) of 4.8 and 3.4. The amylopectins had DP_n of 3250 and 6040, and three molecular species with different size were observed. Number-average chain length (CL) of the amylopectins was 25 and molar ratio of unit chains, (A + B₁)/(B₂ + B₃), was 3.8 and 5.3, respectively. The size-distribution of C chains of the wild turmeric amylopectins showed a peak at DP35 . The phosphorus content was 2200 ppm for the rhizome and 600 ppm for the fusiform-root amylopectin, and the amount of phosphorus linked to C-6 position of glucosyl residues was exceptionally low, 14 and 17 %, respectively . The esterified phosphates were found to be linked mainly to long chains (B2 and B3), and DPn of phosphorylated unit-chains was 42 and 49, respectively.