Effects of storage temperatures and annealing conditions on the structure and properties of potato (Solanum tuberosum) starch

Starches were extracted from freshly harvested potatoes (12 cultivars, grown in Perthshire) and the properties of the starches of six cultivars were compared with starches extracted from the same samples but stored at 5, 25 or 55 °C for 7 days before extraction. The amylose (total) content of the freshly extracted starches from tubers stored at 5, 25 or 55 °C was on average 27.9 ± 2.3, 28.3 ± 1.7, 29.2 ± 2.2 and 28.8 ± 1.5%, respectively, with corresponding phosphorus representing 60 ± 16, 64 ± 9, 61 ± 5 and 63 ± 9 mg 100 g−1. The unit chain distribution by chromatography of the amylopectin molecules from the starches extracted from the different conditions was very similar with an average degree of polymerisation (DP) of 26 ± 2 where the two major fractions (F1 and F2) represented 54 ± 2 and 19 ± 1, respectively. Peak gelatinisation temperatures (Tp) and enthalpies (ΔH) for the freshly extracted starches and from tubers stored at 5 or 25 °C were very similar (63.3 ± 1.5 °C and 18.6 ± 0.8 J g−1; 63.1 ± 1.0 °C and 17.7 ± 1.5 J g−1 and; 62.9 ± 0.7 °C and 18.7 ± 1.1 J g−1, respectively) although starches stored at 55 °C were annealed, where Tp represented 71.1 ± 1.1 °C and ΔH 18.1 ± 1.4 J g−1. These in situ-annealed starches were comparable in terms of gelatinisation characteristics to annealed freshly extracted starches where on average, Tp represented 72.7 ± 1.0 °C and ΔH 20.8 ± 1.0 J g−1. Annealing of tubers in situ prior to processing might be beneficial with respect to developing new potato-based products.