ARS | Publication request: Apparent Amylose Determination in Wild and Cultivated Potatoes

Submitted to: Plant Breeding Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 2009
Publication Date: August 3, 2009
Citation: Fajardo, D., Jansky, S.H. 2009. Apparent Amylose Determination in Wild and Cultivated Potatoes [abstract]. Plant Breeding Conference Proceedings. p. 8.

Technical Abstract: As a storage organ, a potato tuber is mostly water and starch. Approximately 20% of fresh tuber weight is starch and the remainder is water. Most of the starch (around 70%) in the tuber is amylopectin; the remainder is amylose. The ratio between amylose and amylopectin is the most important property influencing the physical properties of starch. Starch is typically digested by amylases in the small intestine. Cooking increases the digestibility of standard potato starch. However, following cooking, a portion of high amylose starch recrystallizes to form resistant starch, which acts as dietary fiber. In humans, amylose is more slowly digested than amylopectin, so blood glucose and insulin levels are lower after a meal high in amylose, satiety is maintained longer, and the next meal is likely to be smaller. Starch with high amylose content has superior nutritional qualities, acting as a form of dietary fiber following cooking. An increase in the amylose content of potato starch could improve the nutritional quality of potato by increasing fiber content and reducing the glycemic index. It is important to identify wild Solanum species and accessions with higher amylose content than is found in cultivated potatoes. This germplasm may then be introduced into breeding programs as parents. It is also important to understand how environmental effects influence amylose content in the tuber. To approach these questions, we evaluated a mini core collection from the U.S. Potato Gene Bank (NRSP-6) plus additional wild potato species. In addition, we evaluated commercial cultivars grown at three locations in Wisconsin across two years. Preliminary evaluations showed high apparent amylose content (AAC) for the species S. commersonii (37.7%) and S. acaule (36.6%), and a high variability among and within species. Commercial cultivars showed significant differences of AAC between organic (Baraboo and Rosholt) and commercial (Hancock) fields. Across the three locations, ‘Kerr’s Pink’ and ‘Russet Norkotah’ showed significantly higher amylose content, while the variety with lowest AAC was ‘German Butterball’. Finally, it was relevant to find a feasible and practical high throughput technique for evaluating freeze dried materials in a fast, efficient and reproducible way. After comparing and applying different apparent amylose determination methods, a modified iodine binding protocol was selected since it allowed the use of 96-well plates, making it appropriate for numerous samples. Even though iodine binding methods overestimate amylose content, they are useful for the screening of potato accessions and germplasm from potato breeding programs.