STRUCTURE AND FUNCTIONALITY OF BARLEY STARCHES

Amylose contents of prime starches from nonwaxy and high-amylose barle y, determined by colorimetric method, were 24.6 and 48.7%, respectivel y, whereas waxy starch contained only a trace (0.04%) of amylose. Ther e was little difference in isoamylase-debranched amylopectin between n onwaxy and high-amylose barley, whereas amylopectin from waxy barley h ad a significantly higher percentage of fraction with degree of polyme rization <15 (45%). The X-ray diffraction pattern of waxy starch diffe red from nonwaxy and high-amylose starches. Waxy starch had sharper pe aks at 0.58, 0.51, 0.49, and 0.38 nm than nonwaxy and high-amylose sta rches. The d-spacing at 0.44 nm, characterizing the amylose-lipids com plex, was most evident for high-amylose starch and was not observed in waxy starch. Differential scanning calorimetry (DSC) thermograms of p rime starch from nonwaxy and high-amylose barley exhibited two promine nt transition peaks: the first was >60 degrees C and corresponded to s tarch gelatinization; the second was >100 degrees C and corresponded t o the amylose-lipid complex. Starch from waxy barley had only one endo thermic gelatinization peak of amylopectin with an enthalpy value of 1 6.0 J/g. The retrogradation of gelatinized starch of three types of ba rley stored at 4 degrees C showed that amylopectin recrystallization r ates of nonwaxy and high-amylose barley were comparable when recrystal lization enthalpy was calculated based on the percentage of amylopecti n. No amylopectin recrystallization peak was observed in waxy barley. Storage time had a strong influence on recrystallization of amylopecti n. The enthalpy value for nonwaxy barley increased from 1.93 J/g after 24 hr of storage to 3.74 J/g after 120 hr. When gel was rescanned eve ry 24 hr, a significant decrease in enthalpy was recorded. A highly st atistically significant correlation (r = 0.991) between DSC values of retrograded starch of nonwaxy barley and gel hardness was obtained. Th e correlation between starch enthalpy value and gel hardness of starch concentrate indicates that gel texture is due mainly to its starch st ructure and functionality. The relationship between the properties of starch and starch concentrate may favor the application of barley star ch concentrate without the necessity of using the wet fractionation pr ocess.