SWELLING AND GELATINIZATION OF CEREAL STARCHES .4. SOME EFFECTS OF LIPID-COMPLEXED AMYLOSE AND FREE AMYLOSE IN WAXY AND NORMAL BARLEY STARCHES

Amylose (AM) and lysophospholipid (LPL) contents were directly correla ted in barley starches, but the linear regressions that described the relationships in waxy and nonwaxy starches were quite different. The d ata indicated that AM exists partially as lipid-complexed amylose (L.A M), with an LPL-to-L.AM ratio of 1:7 and partially as lipid-free amylo se(F.AM). The C-13-crosspolarization/magic angle spinning-nuclear magn etic resonance (CP/MAS-NMR) spectra of the nonwaxy starches had a broa d resonance with a chemical shift of 31.2 +/- 0.4 ppm, which is charac teristic of midchain methylene carbons of fatty acids in the solid sta te or in V-amylose (V-AM) complexes. The extracted lipid was a viscous liquid that, when mixed with seven parts AM, did not give a discernib le peak under the conditions used to acquire the solid-state spectra. However, when the lipid was complexed with AM, it gave a typical V-AM spectrum and a broad resonance at 31.8 ppm. This proves lipid complexe d with L.AM existed in the native starches and was not an artifact for med subsequently from free LPL and F.AM. The intensity of the resonanc e was consistent with the LPL content of the starches. Independent sup porting evidence was obtained by differential scanning calorimetry tha t showed a constant enthalpy for disordering of amylopectin, DELTAH(AP ), for all waxy and nonwaxy starches, regardless of L.AM content and, hence, no exothermic formation of L-AM during starch gelatinization. T welve waxy barley starches used in this study contained 0.8-4.0% L.AM and 0.9-6.4% F.AM; six nonwaxy starches contained 6.1-7.2% L.AM and 23 .1-25.0% F-AM. All starches had essentially identical AP structures, a s shown by the chain lengths of debranched starches fractionated by ge l-permeation chromatography and high-performance liquid chromatography . L.AM and F-AM appeared to have quite different effects on starch gel atinization behavior. Peak gelatinization temperature (T(p)) of the wa xy starches was positively correlated with L-AM content; because the T (p) of the nonwaxy starches was much lower than predicted from the reg ression equation for the waxy starches, we concluded that F.AM lowered T(p). Swelling of starches at 80-degrees-C is essentially a property of AP content that is inhibited by LPL, but the relationship is not st rictly linear. An improved equation to describe swelling properties as sumed that 80% of the F.AM swelled with the AP fraction, although swel ling was inhibited by L-AM0.485.