Cereal Chem. 70:385-391   |  VIEW ARTICLE

Swelling and Gelatinization of Cereal Starches. IV. Some Effects of Lipid-Complexed Amylose and Free Amylose in Waxy and Normal Barley Starches. W. R. Morrison, R. F. Tester, C. E. Snape, R. Law, and M. J. Gidley.

Cereal Chem. 70:385-391. Amylose (AM) and lysophospholipid (LPL) contents were directly correlated in barley starches, but the linear regressions that described the relationships in waxy and nonwaxy starches were quite different. The data indicated that AM exists partially as lipid-complexed amylose (L.AM), with an LPL-to-L.AM ratio of 1:7 and partially as lipid-free amylose (F.AM). The [13]C-cross polarization/magic angle spinning-nuclear magnetic resonance (CP/MAS-NMR) spectra of the nonwaxy starches had a broad resonance with a chemical shift of 31.2 +/- 0.4 ppm, which is characteristic of midchain methylene carbons of fatty acids in the solid state 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 discernible 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 complexed with L.AM existed in the native starches and was not an artifact formed subsequently from free LPL and F.AM. The intensity of the resonance was consistent with the LPL content of the starches. Independent supporting evidence was obtained by differential scanning calorimetry that 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. Twelve 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, as show by the chain lengths of debranched starches fractionated by gel-permeation chromatography and high-performance liquid chromatography. L.AM and F.AM appeared to have quite different effects on starch gelatinization behavior. Peak gelatinization temperature (Tp) of the waxy starches was p ositively correlated with L.AM content; because the Tp of the nonwaxy starches was much lower than predicted from the regression equation for the waxy starches, we concluded that F.AM lowered Tp. Swelling of starches at 80 C is essentially a property of AP content that is inhibited by LPL, but the relationship is not strictly linear. An improved equation to describe swelling properties assumed that 80% of the F.AM swelled with the AP fraction, although swelling was inhibited by L.AM0.485.