Phytonutrients TH E WOR LD OF T he European Association for Potato Research, the EAPR, every three years organizes its triennial conference. At its latest held in Romania in 2008 dr Chuck Brown from Prosser, Washington USA was invited to deliver a speech on his work on the variability of phytonutrient content of potato in relation to variety, growing location and cooking method. The work was also reported in Potato Research (51:259-270) and deals with carotenoids and anthocyanins. Carotenoids are a group of about 600 different plant pigments which give fruits and vegetables – potato – a yellow or orange colour. Carrots are best known for containing carotenoids. Well known examples are beta-carotene and lycopene. Some carotenoids function as anti-oxidants others as precursors of vitamin A. Anti oxidants neutralize free radicals in body tissue and cells and prevent them from ageing. Vitamin A – retinol – helps eyes to adjust to varying light and dark conditions. The main source of vitamin A is meat but is supplemented with vitamin A from converted carotenoids. All potatoes contain carotenoids in the flesh and the concentration increases with yellow or orange intensity: white fleshed varieties may have less than 100 micrograms per 100 g fresh potato weight, moderately yellow flesh varieties between 100 and 350 whereas orange colored varieties contain over 1000 micrograms per 100 g fresh weight. The highest level published is 2,600 micrograms per 100 g in a Papa Amarilla clone growing in the Andes mountains in South America. A cross made of two orange colored genotypes with a carotenoids concentration of around 850 micrograms per 100 g fresh weight yielded a progeny with a very wide range of tubers containing as little as 82 up to as much as 2,686 micrograms. Anthocyanins from the Greek anthos (flower) and kyanos (blue) are pigments that at low pH (acid) are colored red and at high pH (basic conditions) are colored blue. They appear in all plant parts and may accumulate in red beet and cabbage. They are healthy as they have anti-inflammatory properties and they protect blood vessels from oxidative damage. There is a straight correlation between anthocyanins concentrations and antioxidant level. Anthocyanins are present in the red skin and flesh of red fleshed potatoes. Levels may vary from zero to about 50 milligrams (dark purple) per 100 g fresh tuber weight. Besides making crosses to study heritability of carotenoids and anthocyanins concentrations dr. Brown and his team also tested different red fleshed genotypes at different altitudes in the United States of America: sea level, 960 and 1,250 meter above POTATO R ESEARCH sea level. Tubers grown at t he sea level location contained only about 50 tot 60 per cent of the anthocyanins compared to the tubers grown at the high elevation. This is in line with what I observed in Rwanda in the nineteen eighties when we produced potato of a red skinned variety at 1,350, 2,000 and 2,400 meter above sea level and that those from the lower altitudes had a much lighter color. We attributed this to the higher temperature level prevailing at the low altitude. Brown and colleagues did not find an effect of location (altitude) on the concentration of carotenoids but found anti-oxidant levels of yellowish potatoes sometimes to be quite high. This means that also colorless compounds may have anti-oxidant properties. Finally the researchers wanted to find out if the method of preparing potatoes influences the concentration of anthocyanins and if there is a varietal specific reaction to cooking method. It appeared that boiling did not diminish the anthocyanins concentration and that a microwave treatment diminished it slightly. Frying potatoes in oil to produce chips or French fries, however, almost halved the concentration. There was no different reaction pattern to means of preparation in high or low level containing genotypes. The authors conclude that attaining (genotype, altitude) and preserving (boiling rather than frying) high levels of phytonutrient “deserve more testing and extension of this knowledge to the food processing industry. ● Dr. Ir. Anton Haverkort Anton.haverkort@wur.nl Potato World 2009 • number 2 29 Pagina 28
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