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 HCI at 35-d egrees-C for 140 h. Material solubilised from the waxy starches was es timated 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 esti mated to be 70.7% of their AP plus 28.9% of their L.AM and F.AM. The p olysaccharide components of the insoluble residue were characterised b y HPLC, GPC, and lambda(max) of the polyiodide complex. It was conclud ed that short chain-length (CL 16) material was from external chains o f AP, intermediate material (modal CL 46) was from retrograded F.AM, a nd longer chain residues (CL 77, 120-130) were from lipid-complexed se gments of L - AM. The starch lysophospholipids were completely hydroly sed to free fatty acids which remained complexed with L.AM residues. T his was shown by the C-13 Cp/MAS-NMR spectrum which had a clear resona nce at 31 ppm from mid-chain methylene carbons of fatty acids in compl exes. The C-1 signal of the L.AM residues also included a feature at 1 04 ppm indicative of single V6 AM helices. The wide-angle X-ray diffra ction patterns of the residues of non-waxy starches were Cc-type ( = m ixed 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) tha t retrograded into double helices (with B-type crystallinity) that wer e resistant to hydrolysis. Evidence for some B-crystalline polymorph w as also obtained from the C-13 Cp/MAS-NMR spectra, which were consiste nt with a mixture of double helices and V-type glycosidic conformation s, with only a small proportion of non-ordered regions. Broad DSC endo therms were found for both waxy (50-110-degrees-C) and non-waxy (50-11 0-degrees-C) lintner residues, which were assigned to disordering of d ouble helices from short chains (modal CL 16) for waxy residues, toget her with disordering of longer chains (modal CL 46) in double-helix re sidues of F.AM and also V-helix residues of L.AM for non-waxy starch r esidues.