Glycoalkaloids, potato

Removal of bitter-tasting compounds (glycoalkaloids) Potatoes (119)... 

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Wszelaki AL, Delwiche JF, Walker SD, Liggett RE, Scheerens JC and Kleinhenz MD (2005) Sensory quality and mineral and glycoalkaloid concentrations in organically and conventionally grown redskin potatoes (Solanum tuberosum). Journal of the Science of Food and Agriculture, 85, 720-726. 

Friedman M and McDonald G M (1997), Potato glycoalkaloids chemistry, analysis, safety and plant physiology , Crit Rev Plant Sci, 16, 55-132. 

Sanford L L, Deahl K L, Sinde S L and Ladd Jr T L (1992), Glycoalkaloid content in tubers from Solanum tuberosum populations selected for potato leafhopper resistance , Am Potato J, 69, 693-703. 

The fruit of a number of solanaceous plants, including tomato Lycopersicon esculentum), potato Solanum tuberosum) and eggplant Solarium melongena esculentum), have cholinesterase-inhibiting effects (Krasowski et al. 1997). They contain solanaceous glycoalkaloids o-solanine and o-chaconine, which are triglycosides of solanidine, a steroidal alkaloid derived from cholesterol. They are the only plant chemicals known to inhibit both acetlycholinesterase and butyrylcholinesterase, both in vitro and in vivo. 

Levels of solanaceous glycoalkaloids can be significant, occasionally causing toxicity in humans and livestock. Symptoms of potato poisoning include gastrointestinal disturbances, apathy, drowsiness, mental confusion, visual disturbances, dizziness, hallucinations, and trembling. Symptoms may perist 2-24 hours after consumption, and one recent outbreak showed reduced butyrylcholinesterase levels six days later, which then returned to normal in 4 to 5 weeks. 

Glycosides of compounds with a triterpenoid origin include saponins, cardiac glycosides, and glycoalkaloids such as solanine (in potatoes). 

The Indians of the Peruvian Altiplano eat potatoes with a dip of clay and a mustard-like herb. They say the clay removes the bitter taste and prevents stomach pains or vomiting after eating large amounts of potatoes. The people who eat clay intend detoxication. This may explain how Indians started to utilize and domesticate wild potatoes. Indeed, experiments have shown that four different types of edible clay adsorb the glycoalkaloid tomatine under simulated... 

Clay eating probably was extremely important in human evolution it enabled hominids who did not use fire to eat plants with toxic antifeedants. However, the glycoalkaloids of the potato are heat stable and insoluble in water. Domestication of tomatoes and potatoes probably went hand in hand with clay eating. Johns (1986) suggested that geophagy is the most basic human detoxification technique with behavior antecedents that are prehominid. ... 

Renwick, J. H., Glaring, W. B., Earthy, M. E., etal. (1984). Neural-tube defects produced in Syrian hamsters by potato glycoalkaloids. Teratology 30,371-381. 

Johns, T., Alonso, J. G. (1990). Glycoalkaloid change during the domestication of the potato, Solanum Section Petota. Euphytica, 50, 203-210. 

Friedman, M. (2006). Potato glycoalkaloids and metabolites Roles in the plant and in the diet. Journal of Agricultural and Food Chemistry, 54, 8655-8681. 

Sorensen, K. K., Kirk, H. G., Olsson, K, Labouriau, R., Christiansen, J. (2008). A major QTL and an SSR marker associated with glycoalkaloid content in potato tubers from Solanum tuberosum x S. sparsipilum located on chromosome I. Theoretical and Applied Genetics, 117, 1-9. 

Yencho, G. C., Kowalski, S. R, Kobayashi, R. S., Sinden, S. L., Bonierbale, M. W., Deahl, K. L. (1998). QTL mapping of foliar glycoalkaloid aglycones in Solanum tuberosum x S. berthaultii potato progenies quantitative variation and plant secondary metabolism. Theoretical and Applied Genetics, 97, 563-574. 

Arnqvist, L., Dutta, P. C., Jonsson, L., Sitbon, F. (2003). Reduction of cholesterol and glycoalkaloid levels in transgenic potato plants by overexpression of a type 1 sterol methyltransferase cDNA. Plant Physiol., 131, 1792-1799. 

Bergenstrahle, A., Borga, P, Jonsson, L. (1996). Sterol composition and synthesis in potato tuber discs in relation to glycoalkaloid synthesis. Phytochemistry, 41, 155-161. 

Krits, R, Fogelman, E., Ginzberg, I. (2007). Potato steroidal glycoalkaloid levels and the expression of key isoprenoid metabolic genes. Planta, 227, 143-150. 

Refstie, S, Tiekstra, H. A. J. (2003). Potato protein concentrate with low content of solanidine glycoalkaloids in diets for Atlantic salmon. Aquaculture, 216,283-298. 

This limited overview on the analysis of four classes of the following secondary potato metabolites is, except for anthocyanins, largely limited to our own studies of glycoalkaloids, calystegine alkaloids, and phenolic compounds. Because interest in these potato constituents arises from potential health benefits and occasional toxicity, we also include in this overview a brief discussion of these aspects that relate to composition and a description of experimental methods. The interested reader should consult the cited references for an entry into the extensive worldwide literature on the diverse analytical and biological aspects for these metabolites. 

In commercial potatoes (Solanum tuberosum) there are two major glycoalkaloids, a-chaconine and a-solanine, both trisaccharides of the common aglycone solanidine. These two compounds comprise about 95% of the glycoalkaloids in potato tubers. Their hydrolysis products, the p and 7 forms and solanidine, may also be present in relatively insignificant concentrations. The structures of these glycoalkaloids and their hydrolysis products are presented in Figure 6.1. 

Figure 6.1 Structures of potato glycoalkaloids a-chaconine and a-solanine, and hydrolysis products (metabolites).

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