A novel potato that contains modified starch has been developed by researchers in plant breeding, and now, a study carried out by food scientists shows that the modification has resulted in a healthier starch.
Considering that we eat a lot of potato in Scandinavia, potato starch makes up a large part of the energy in many people’s daily diet. If a new potato with a more resistant starch would be commercially available in the future, it might have a positive impact on public health. Resistant starch is a dietary fiber with benefits for our bodies. As such, it lowers the glucose levels and the insulin responses, increases fecal output and reduces the fecal transit time. It decreases the calorie content in foods which is related to weight loss, and it promotes the growth of beneficial gut bacteria.
Such a new potato was successfully developed by plant researchers by down-regulating two starch branching enzymes. Potato starch usually consists of 25 percent amylose (linear molecules) and 75 percent amylopectin (highly branched molecules). The objective with this modification was to produce a potato with high amylose content.
In a study, PhD student Xue Zhao and her supervisors Roger Andersson and Mariette Andersson show that a high content of amylose gives a high content of resistant starch in this cooked potato. But they also found something else.
– The down regulation of the enzymes had an effect on amylopectin structure where the outer chain-length of amylopectin was much longer than in the unmodified potato cultivar, Xue Zhao explains.
This unique amylopectin has properties that are similar to amylose. After cooking, the modified amylopectin recrystallizes, and after that it is not split as easily as the ordinary potato starch, which means it is more resistant and takes longer time to digest.
– An additional analysis revealed that one extra day of cold storage gives a further increase of resistant starch content, since amylopectin needs some time to get recrystallized, says Xue Zhao.
The study showed that the resistant starch content was influenced both by the amylose/amylopectin ratio and by the amylopectin structure. These are important findings in order to design functional starch and healthier food.
The potato was developed using genetic modification. At the moment the researchers are working on a new similar “high amylose” potato using the genome editing technique Crispr/Cas9.
Zhao, X., Andersson, M. & Andersson, R. 2018. Resistant starch and other dietary fiber components in tubers from a high-amylose potato. Food Chemistry 251: 58-63
”It’s soft, not so stiff, and it has a high potential to become something important in the future.”
Researcher Mariette Andersson describes the material that she and her colleagues have made from the starch of a genetically modified potato. This plastics can be composted after using it. Furthermore, the starch has now been used as a part of a composite material. By tailoring mixtures of plant proteins and starch, molecularly and biochemically, one can design sustainable materials for various uses including packaging and plastic film.
In two studies Mariette Andersson and colleagues have tested how this particular potato starch works with proteins from wheat (gluten, gliadin and glutenin which are possible components of the new material). The idea is to develop a stretchable and strong material. They used either glycerol or glycerol + water as plasticizer and extruded the plastics at two different temperatures, 110 °C and 130 °C. In the analysis, they could see that the different proteins reacted in different ways in combination with the starch. In some cases, the material became relatively soft and flexible, and in other cases, stronger and less soft.
The higher temperature induced a higher degree of protein cross-links. With glycerol + water as plasticizer, the starch got improved gelatinous properties, and the material became stronger, more stretchable and easier to process (compared to using only glycerol).
They also tested what happened to the protein structure at the nanometer level (a level that is one millionth of a millimeter), the mechanical strength of the plastics, and if the material let oxygen molecules to pass through. Some of the gliadin molecules adopted an unusual hexagonal structure in mixtures with starch, and this structure made the material stronger. The combinations of protein + starch worked well as an oxygen barrier.
Ordinary potato starch, consists of molecules with both short and long chains of glucose. The starch molecule amylose has long linear chains of glucose while the amylopectin molecule has a highly branched structure. Native potato starch contains 20-30 percent amylose and 70-80 percent amylopectin.
Using biotechnology, the researchers decreased the levels of two enzymes regulating the branching of starch molecules in potato. This modification increased the glucose chain length of the amylopectin molecules. Thanks to this, the starch got the fiber-like properties that make it suitable as a component of a new environmentally friendly packaging material.
Researchers at the Swedish University of Agricultural Sciences, KTH Royal Institute of Technology, Innventia AB, MAX IV Laboratory in Lund and Institut Polytechnique in France did this study with funding from Mistra Biotech, TC4F, Lyckeby Starch AB, Formas and Partnerskap Alnarp.
Muneer, F., Andersson, M., Koch, K., Hedenqvist, M. S., Gällstedt, M., Plivelic, T. S., Menzel, C., Rhazi, L., & Kuktaite, R. (2016). Innovative Gliadin/Glutenin and Modified Potato Starch Green Composites: Chemistry, Structure, and Functionality Induced by Processing. ACS Sustainable Chemistry & Engineering.
Muneer, F., Andersson, M., Koch, K., Menzel, C., Hedenqvist, M. S., Gällstedt, M., Plivelic, T.S., & Kuktaite, R. (2015). Nanostructural morphology of plasticized wheat gluten and modified potato starch composites: relationship to mechanical and barrier properties.Biomacromolecules, 16: 695-705
Talking about potato, Sweden, Norway and Finland have a lot in common. We prefer the floury potato cultivars, while elsewhere in Europe people prefer the firmer potatoes. We have the cold northern climate in common, with long days in the short summer, and problems with the same kind of pathogens. On the other hand we have no major problems with drought. Therefore, drought tolerance is not a particularly prioritized potato trait in this region.
With this in mind, researchers at SLU suggest that the three countries join hands and cooperate to develop new better potato cultivars.
In a scientific paper, researcher Dennis Eriksson and his colleagues presented an overview of the potato cultivation, consumption and potato processing in Fennoscandia (Sweden, Norway and Finland). The development of new potato varieties have diminished in Norway and Sweden, and ceased altogether in Finland.
– This is a shame because potato is the highest yielding food crop here. At the same time, potato is an irreplaceable part of our food culture, and the potato breeding has a long and proud history in our countries, says Dennis Eriksson.
Having previously decreased for decades, potato consumption has remained steady at just above 40 kg per person and year in Sweden the last 20 years. Do we want to continue to eat potatoes in the future? Can we grow potatoes more sustainable than today? Yes, scientists believe so, but sustainability requires smart strategies.
We need potato varieties that do not need to be sprayed with fungicides. All the varieties we grow today are susceptible to late blight caused by the pathogen Phytophthora infestans. The spraying is bad for the environment and makes potato cultivation more expensive. Potato varieties also need to eventually be adapted to a future climate, predicted to become warmer and wetter in the north. And more pests are expected to find their way to this region as the climate changes.
– A high and stable potato production, under the particular conditions that we have in the north, is crucial. This requires an early tuber maturity due to the short summer season. And, in addition to late blight, there are other potato diseases that are common in this region, says Dennis Eriksson.
The researchers say that the Fennoscandian market is too small to motivate the profit-driven breeding companies to invest in potato breeding that matches the specific requirements of this region. Consequently we rely on public investment to develop new varieties, and such financial support must be maintained for a long time.
In their study, the researchers present seven reasons for public investment in potato breeding in the Fennoscandian region:
Once you have a new potato variety, and want to test and commercialize it, it might be a good idea to collaborate with an established plant breeding company.
– The advantage of this would be that the testing of cultivars can be done on a larger scale and more efficiently. This kind of collaborations could provide access to an infrastructure that would not be available otherwise. The payment for these services could take different forms. In Norway the plant breeders at Graminor have an agreement with the private partner Agrico, giving Graminor the right to market the cultivars at a national level while Agrico has gained the right to market the cultivars abroad, says Dennis Eriksson.
The plant breeding company Graminor is largely financed by the state but it also has private part-ownership.
Eriksson, D., Carlson-Nilsson, U., Ortíz, R., & Andreasson, E. (2016) Overview and breeding strategies of table potato production in Sweden and the Fennoscandian region. Potato Research, 1-16.
The classic science on plant nutrition states that plants acquire nitrogen from the soil as nitrate or ammonium, or as nitrogen gas if the plant forms symbiosis with nitrogen-fixing bacteria. Today we know that there are plants that also can make use of organic nitrogen, but the consensus has been that it only applies to certain mycorrhiza-forming plants growing in nutrient-poor soils. Together with colleagues from Austria and Australia the SLU researchers show that a plant that does not form mycorrhiza acquires organic nitrogen when grown in nutritious agricultural soil.
The findings show that the plant is dependent on a specific protein for this to work. The protein is an amino acid transporter, and the researchers have performed a number of experiments on genetically modified thale cress (Arabidopsis thaliana) that either lack the transporter or over produces it.
Torgny Näsholm is Professor in ecophysiology at the Swedish university of agricultural sciences in Umeå, and he led the study.
– We grew the plants in greenhouses in agricultural soil, and could follow the way of the amino acid glutamine from the soil into the plant by labelling the glutamine with carbon and nitrogen isotopes. It turned out that the uptake of the amino acid is much more efficient in plants that overproduce the amino acid transporter, and very low in plants lacking the transporter, he explains.
Additionally, the plants that were lacking the transporter had the lowest carbon/nitrogen ratios, and the plants overproducing the transporters had the highest ratios. Theoretically the amino acids should result in a higher carbon concentration, which indicates that the plants have been taking up organic nitrogen from the soil continuously.
– This study is a milestone in our research. With the use of genetically modified model plants we have been able to show that amino acids in soil are used as nitrogen sources by plants. We also aim to increase the plant capacity to take up nitrogen from the soil, and our results show that an optimization of organic nitrogen uptake is a possible way to achieve this, says Torgny Näsholm.
Thale cress is not an agricultural crop, but a model plant which is often used to predict the effects of genetic modifications in agricultural plant species. The research group now investigates how the uptake of organic nitrogen can be improved in potato.
– We are now testing if it is possible to use the same strategy to increase the uptake of organic nitrogen in an agricultural crop. We have propagated modified potato clones to see if we get the same increase in potato as in thale cress.
Ganeteg, U., Ahmad, I., Jämtgård, S., Aguetoni-Cambui, C., Inselsbacher, E., Svennerstam, H., Schmidt, S., and Näsholm, T. (2017) Amino acid transporter mutants of Arabidopsis provides evidence that a non-mycorrhizal plant acquires organic nitrogen from agricultural soil. Plant, Cell & Environment, 40: 413–423. doi: 10.1111/pce.12881.