Physicochemical, thermal and structural properties of heat moisture treated common buckwheat starches.

Abstract

Common buckwheat starch modified by heat moisture treatment at different temperatures was analysed for functional, pasting, structural, thermal, gel textural and morphological properties. Heat moisture treatment decreased swelling power, solubility and oil absorption capacity while amplified water absorption capacity of buckwheat starch. Lower whiteness index with higher a* and b* values were observed for treated starches. Modified starches showed increased paste clarity and reduced syneresis. A declining order of paste clarity and freeze-thaw stability of native and treated starches was noticed during storage period. RVA analysis showed reduced viscosities (peak, trough, breakdown, final and setback viscosity) for hydrothermally treated starches. Increased gel hardness was observed for modified starches and starch sample treated at 85°C produced the hardest gel. FTIR spectrums of native and treated starch samples showed peaks at similar wavenumbers. Micrographs revealed the polygonal shape of native starch granules with flat areas on surface. Increased agglomeration in heat moisture treated starch samples was noticed in scanned images of starches. X-ray diffraction analysis showed 'A' type crystalline pattern in native starch of common buckwheat and no alteration in crystalline pattern due to hydrothermal treatment was observed. Relative crystallinity of native buckwheat starch decreased during heat moisture treatment and the minimum value was recorded for starches treated at 85°C. Differential scanning calorimetry showed raised gelatinisation temperatures (TO, TP and TC) and reduced ΔH values for hydrothermal treated starches.