Potatoes and Diabetics
By Treena Hein
Feb. 26, 2013 - Worldwide, more people are gobbling up potatoes, but in Canada, concerns over eating too much simple starch in our diets – and perhaps eating potato chips and french fries a little too often – has resulted in decreased consumption. Agriculture and Agri-Food Canada stats show that globally, annual potato production increased by almost 25 per cent from the mid-1980s to 2008, but Canadian consumption declined by about the same amount from 1996 to 2005.
What can the industry do to entice more Canucks to eat more spuds?
Offer new cultivars with more health benefits.
"Developing potato varieties with more slowly digested starch – having a low glycemic index or GI – is now a goal of our breeding program," says Dr. Benoit Bizimungu, a scientist with Agriculture and Agri-Food Canada (AAFC) in Fredericton, New Brunswick. "We've incorporated a number of low GI varieties and selections in our crossing program and we're in the process of evaluating advanced selections for starch properties and potential glycemic effect for eventual release to the industry." Bizimungu says it's too soon to tell how many cultivar selections will come from this process, but that they are also developing the use of tools such as molecular markers and near-infrared spectrometry to more rapidly and efficiently identify suitable selections early in the breeding process.
However, one "advanced selection" called AR2012-04 was released to industry for evaluation in February 2012 as part of the AAFC "Accelerated Release" program (see www.agr.gc.ca/potato-cultivars). "If its performance is satisfactory, it should make it to the market within the next five years," Bizimungu says. "More low-glycemic selections will be released for evaluation in the near future."
Agriculture and Agri-Food Canada creates about 350 new potato hybrid combinations a year and grows about 120,000 new seedlings annually, offering industry an opportunity to annually evaluate between 10 and 20 advanced selections of interest for evaluation and eventual licensing. These selections have undergone at least six years of rigorous field and laboratory testing.
The glycemic index of foods also relates to their fibre content (the more fibre, the lower the GI). Although potatoes are not commonly seen as a dietary source of fibre, research has found that they are a "good" source. Potatoes on average contain 8.5 per cent fibre, with the skin containing 22.5 per cent. Most of the skin fibre is insoluble fibre – also called neutral detergent fibre (NDF) – which is important to human health for removing toxic waste within the colon and promoting regularity. However, soluble fibre (SF) is also important in the diet, and achieving an equal NDF and SF ratio in fibre content is ideal.
At this point, there is limited knowledge of the physiology behind fibre production in potatoes. "We do know that biochemical pathways for both starch granule production and fibre synthesis are under strong genetic control, but the influence of the growing environment plays a huge role," says Bizimungu. "There are multiple biochemical pathways and enzymes driving the production of fibre components, and each genetic combination of enzymes responds in a unique way to environmental conditions." Previous research has found correlations between stress and fibre content, particularly in NDF content. This means the more stress a potato plant is subjected to in terms of temperature and moisture levels, the more NDF will be present – although this increase needs to be considered relative to potential impact of stress on yield and other quality traits.
Bizimungu, along with University of Guelph colleagues Stephanie Bach, J. Alan Sullivan and Rickey Yada, just published a study that examined the fibre profiles of selected potato genotypes in Ontario, and determined how stable the fibre profiles were under different growing conditions. "We used six environments – three locations over two years – with the same soil types, but involving a range of temperature and moisture levels," he notes. "We grew 12 types of potatoes in all – eight elite potato clones and four commercial cultivars (serving as checks), which were Atlantic, Russet Burbank, Goldrush and Norland." The team measured total dietary fibre (TDF), neutral detergent fibre (NDF) and soluble fibre (SF) content.
As expected, most of the fibre profiles of the 12 genotypes were strongly affected by environmental conditions, but some were not (they had high levels of stability for fibre content). "Two of the elite clones (CV96044-3, also called AR2012-04, and F05081) were identified as high fibre sources (13.3 and 14.4 percent, respectively) compared to the other elite clones and the commercial cultivars (for example, Russet Burbank had a fibre content of 11.7 percent). "These lines may be suitable as parents to use in crosses involving other desirable qualities," Bizimungu says. "F05081 and CV96044-3, or AR2012-04, were able to outperform the commercial genotypes with improved overall fibre content and the amount of NDF and SF available."
However, only F05081 was stable. "We need to do further testing for fibre content profile over more years and locations," Bizimungu says.
Bizimungu and others at AAFC are also looking into breeding potatoes with other added health benefits, such as higher antioxidant levels. Several purple-fleshed and yellow-fleshed selections from the AAFC potato breeding programs at Fredericton and Lethbridge, Alberta, are now being evaluated by industry.
"Getting value-added cultivars to become a commercial success means making sure they are segregated through the processing chain and that they are marketed well to consumers," Bizimungu says. "This means preserving and promoting their identity and their value."