V-type crystal formation in starch by aqueous ethanol treatment: The effect of amylose degree of polymerization

Maize, rice, cassava, potato and pea granular starches, representing the different starch polymorphs (A-,B- and C-types) and covering a broad range in amylose (AM) content and degree of polymerization (DP), were converted to V-H-type granular starch by aqueous ethanol treatment at 95 degrees C in a 68 to 48% ethanol (v/v) range. Microscopy, X-ray diffraction and calorimetric analyses showed that loss of native molecular order already occurred at the highest ethanol concentrations for starches containing the intrinsically less stable B- type crystals, whereas lower ethanol concentrations were necessary to induce native crystal melting in A- type starches. C-type starch, containing a mixture of A- and B- type crystals, exhibited features characteristic of both A- and B- type starches. No native crystals remained and granular products containing only V-H-type crystals were formed for all starches when using 48% (v/v) ethanol. However, the relative kinetics of V-H-type crystal formation depended on AM DP. For low DP AM starches (maize and rice), V-H-type crystal formation started during heating up to 95 degrees C once the native crystals were melting. The V-H-type crystallization went up to completion during the isothermal stay at 95 degrees C. For mid (pea) and high DP (potato and cassava) AM starches, V-H-type crystallization was initiated during holding at 95 degrees C and progressed further during subsequent cooling. The V-H-type crystallinity in the final product decreased with increasing DP of the AM fraction, likely as a result of progressively more disturbing entanglements. Surprisingly, there was no quantitative relation between V-H-type crystallinity and AM content. (C) 2016 Elsevier Ltd. All rights reserved.