STARCH AND ENZYME-RESISTANT STARCH FROM HIGH-AMYLOSE BARLEY

A Glacier variety selection with a 43% amylose content was used for isolation and purification of barley starch. The starch was separated into two fractions that varied in granule size, and the two fractions were assayed using chemical, microscopic (scanning electron microscopy), and thermoanalytical methods. Large and small barley starch granules were different in both chemical composition and endothermic properties; the small starch granules were higher in amylose than the large granules. Heat-moisture treatment (autoclaving at 121-degrees-C) with subsequent cooling was used to produce amylase-resistant starch (RS) from purified high-amylose starch samples. The formation of RS in barley starch was strongly affected by the number of autoclaving-cooling cycles; increasing the number of cycles from one to 20 raised the RS yield from 6 to 26%. Differential scanning calorimetry thermograms showed that all isolated RS preparations exhibited an endothermic transition over a similar temperature range (116-177-degrees-C), with a mean peak temperature at 158-degrees-C, which could apparently be attributed to the melting of RS amylose crystallites. The maximum melting enthalpy for RS from barley, 37 J/g, was achieved by 12 repeated autoclaving-cooling cycles. The thermodynamic data indicated that changes in the quality of RS occurred during autoclaving-cooling cycles.