Potato genotype differences in nutritionally distinct starch fractions after cooking, and cooking plus storing cool

Rapidly digestible (RDS), slowly digestible (SDS) and resistant starch (RS) were measured in 9 New Zealand supermarket potatoes and in 37 lines from a potato breeding program by in vitro digestion immediately after cooking, and after storing at 4 °C for 44 h post-cooking. The aim was to measure the range in the tendency to form SDS and RS in the potato gene pool in New Zealand. Immediately after cooking, the potatoes contained (mean and across-cultivar range, dry matter basis) 68% RDS (range 62–73%), 3% SDS (range 0–8.5%), and 3.9% RS (range 3–6.4%). Cool storage after cooking altered the distribution and ranges to 44% RDS (range 33–53%), 23% SDS (range 15–34%) and 7% RS (range 4.7–15.8%). There was no significant relationship between RS and SDS in the cooked-cooled potatoes. In the 37 potato lines, SDS ranged from 7 to 37% of total starch, RS from 12 to 27% of total starch after the post-cooking cool treatment. The results suggest that the glycaemic impact of some potatoes may be substantially reduced by cool-storing after cooking, and that the differences between cultivars in the tendency to form cold-induced SDS and RS are sufficient for these traits to be used in conventional plant breeding.