X-ray scattering study on potato (Solanum tuberosum L.) cultivars during winter storage

The nanometer range structure of potato (Solanum tuberosum L.) tubers was examined by wide-angle, small-angle and ultra small-angle X-ray scattering methods. The crystallinity of starch, the lattice constants of the hexagonal lattice of amylopectin, the average crystallite size in the direction [100], the lamellar distance and the thickness of lamella stacks were determined from the data. A new achievement presented in this paper is that reasonable results for these parameters of potato starch were obtained by carrying out experiments on slices and mashes of raw potato tubers. The effects of sample preparation were also investigated by doing experiments on air-dried and re-hydrated potato samples, and on isolated potato starch as well. Changes in the structure of three different cultivars grown in Finland (S. tuberosum cv. Satu, Saturna and Lady Rosetta) were studied monthly from August to May. The physiological ageing caused changes in the crystallinity and in the crystal structure. The mean values (±SD) were determined from the data measured between September and January (30 samples). The lattice constants a=18.4±0.06 and c=10.4±0.04 Å, the crystallinity of starch 24±2% and the crystallite size 118±10 Å were obtained. The lamellar distance was 97±3 Å and the thickness of lamella stacks 513±6 Å. The structural parameters did not vary significantly between Satu, Saturna and Lady Rosetta. For comparison, two cultivars grown in the Netherlands were studied in December. The Dutch cultivars showed the same structural parameters as the Finnish cultivars.