Resistance to acid hydrolysis of lipid-complexed amylose and lipid-free amylose in lintnerised waxy and non-waxy barley starches

Waxy barley starches (0.8-4.0% lipid-complexed amylose = L-AM, 0.9-3.4% lipid-free amylose = F-AM) and non-waxy barley starches (6.1-7.2% L-AM, 23.1-25.9% F-AM) were lintnerised by steeping in 2 M HCl at 35 degrees C for 140 h. Material solubilised from the waxy starches was estimated to be 70.7% of their amylopectin (AP) plus 3.7% of their L-AM and F-AM, and material solubilised from the non-waxy starches was estimated to be 70.7% of their AP plus 28.9% of their L-AM and F-AM. The polysaccharide components of the insoluble residue were characterised by HPLC, GPC, and lambda(max) of the polyiodide complex. It was concluded that short chain-length (CL 16) material was from external chains of AP, intermediate material (modal CL 46) was from retrograded F-AM, and longer chain residues (CL 77, 120-130) were from lipid-complexed segments of L-AM. The starch lysophospholipids were completely hydrolysed to free fatty acids which remained complexed with L-AM residues. This was shown by the 13C CP/MAS-NMR spectrum which had a clear resonance at 31 ppm from mid-chain methylene carbons of fatty acids in complexes. The C-1 signal of the L-AM residues also included a feature at 104 ppm indicative of single V6 AM helices. The wide-angle X-ray diffraction patterns of the residues of non-waxy starches were Cc-type (= mixed A + B types), whereas the spectra of the original starches were A-type. It is suggested that, during the early stages of lintnerisation, amorphous F-AM was partially hydrolysed into material (CL < 120) that retrograded into double helices (with B-type crystallinity) that were resistant to hydrolysis. Evidence for some B-crystalline polymorph was also obtained from the 13C CP/MAS-NMR spectra, which were consistent with a mixture of double helices and V-type glycosidic conformations, with only a small proportion of non-ordered regions. Broad DSC endotherms were found for both waxy (50-110 degrees C) and non-waxy (50-110 degrees C) lintner residues, which were assigned to disordering of double helices from short chains (modal CL 16) for waxy residues, together with disordering of longer chains (modal CL 46) in double-helix residues of F-AM and also V-helix residues of L-AM for non-waxy starch residues.