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°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 λmax of the polyiodide complex. I was concluded that short chain-length (CL 16) material was from external chains of AP, intermediate material (modal CL 46) was from retrogated 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-chin 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 retrogated 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°C) and non-waxy (50–110°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.