Aujourd'hui je vous présente la solanine et ses cousines.

Quand Augustin Parmentier explora la pomme de terre, voulant la faire consommer aux Français qui mouraient alors parfois être faim, juste avant la Révolution de 1789, il l'explora du point de vue physico-chimique et publia  le résultat des travaux dans un ouvrage scientifique. Dans ce livre, naturaliste au sens d'une chimie naturaliste,  il signale que les  décoctions de peaux de pomme de terre ont un goût brûlant.

Ce que Parmentier ne savais pas, c'est que ce goût brûlant et dû notamment à des composés qui ont pour nom solanine, solanidine, chaconine. Ces composé sont naturellement présents dans les peaux de pommes de terre, et ils sont toxiques.

Bien sûr, on dira que c'est la dose qui fait le poison, de sorte que la question est de savoir si ces composés sont, ou non,  en quantités excessives dans l'alimentation.

Mais restons d'abord sur les composés eux-mêmes. je vais pas rentrer dans le détail de la constitution moléculaire de chacun, mais je commence par observer que le nom "solanine" (ou solanidine) est bien apparenté au nom de la famille botanique à laquelle appartiennent les pommes de terre : les "solanacées".
Et cela est juste, car c'est bien dans les pommes de terre que l'on a découvert ces composés.

D'autre part, j'ajoute que les solanines et leurs cousines sont des "alcaloïdes", à savoir que leurs molécules ont notamment un  atome d'azote, et, comme la strychnine, la nicotine, etc., elles ont une action  pharmacologique ou toxique.

Le risque que font courir solanine et consorts ? Il dépend à la fois du danger, c'est-à-dire la toxicité intrinsèque, et de l'exposition.

Dès lors, il faut se demander combien on consomme de ces composés et savoir si l'on dépasse de la dose journalière admissible.

Observons tout d'abord que certains d'entre nous mangent très souvent des pommes de terre, et notamment dans des pays où les frites sont vendues dans les rues, comme ils le sont dans des enseignes françaises de restauration rapide.

Dans une étude assez récente, il a été montré que pour un pays où la restauration de rue laissait la peau des pommes de terre, alors la population dépassait la dose journalière admissible.

Et pour la France ? Cette fois, l'Agence nationale de sécurité des aliments a été récemment saisie,  car la solanine n'est pas présente seulement dans les pommes de terre, mais aussi dans les aubergines, par exemple, qui est de la même famille végétale que les pommes de terre. Il a aussi, il faut faire un peu attention et ne pas multiplier les consommations.
J'ai juste pour terminer  : la solanine, la solanidine, la chaconine ne doivent rien, absolument rien à l'intervention de l'être humain. Ce sont les plantes qui les produisent naturellement, quelles que soient les conditions de culture. La nature n'est pas bonne, et il y a du génie humain chaque fois que notre espèce parvient à prendre dans la nature ce qui lui faut sans s'exposer à tous ses dangers.

PS. Voici le résumé d'un avis de l'Agence européenne de sécurité des aliments  :
The European Commission asked EFSA for a scientic opinion on the risks for animal and human health related to the presence of glycoalkaloids (GAs) in feed and food. This risk assessment covers edible parts of potato plants and other food plants containing GAs, in particular, tomato and aubergine. In humans, acute toxic effects of potato GAs (a-solanine and a-chaconine) include gastrointestinal symptoms such as nausea, vomiting and diarrhoea. For these effects, the CONTAM Panel identifed a lowest-observed-adverse-effect level of 1 mg total potato GAs/kg body weight (bw) per day as a reference point for the risk characterisation following acute exposure. In humans, no
evidence of health problems associated with repeated or lon g-term intake of GAs via potatoes has been identifed. No reference point for chronic exposure could be identifed from the experimental animal studies. Occurrence data were available only for a-solanine and a-chaconine, mostly for potatoes. The acute dietary exposure to potato GAs was estimated using a probabilistic approach and applying processing factors for food. Due to the limited data available, a margin of exposure (MOE) approach was applied. The MOEs for the younger age groups indicate a health concern for the food consumption surveys with the highest mean exposure, as well as for the P95 exposure in all surveys. For adult age groups, the MOEs indicate a health concern only for the food consumption surveys with
the highest P95 exposures. For tomato and aubergine GAs, the risk to human health could not be characterised due to the lack of occurrence data and the limited toxicity data.

About the toxicity of potato peels, I was asked to give references, and here are some, with abstracts :


Regulatory Toxicology and Pharmacology 41 (2005) 66–72Potato glycoalkaloids and adverse eVects in humans: an ascending dose study, par Tjeert T. Mensinga et al. :

Glycoalkaloids in potatoes may induce gastro-intestinal and systemic eVects, by cell membrane disruption and acetylcholinesterase inhibition, respectively. The present single dose study was designed to evaluate the toxicity and pharmacokinetics of orally administered potato glycoalkaloids ( -chaconine and -solanine). It is the Wrst published human volunteer study were pharmacokinetic data were obtained for more than 24 h post-dose. Subjects (2–3 per treatment) received one of the following six treatments: (1–3) solutions with total glycoalkaloid (TGA) doses of 0.30, 0.50 or 0.70 mg/kg body weight (BW), or (4–6) mashed potatoes with TGA doses of 0.95, 1.10 or 1.25 mg/kg BW. The mashed potatoes had a TGA concentration of nearly 200 mg/kg fresh weight (the presently recognised upper limit of safety). None of these treatments induced acute systemic eVects. One subject who received the highest dose of TGA (1.25 mg/kg BW) became nauseous and started vomiting about 4 h post dose, possibly due to local glycoalkaloid toxicity (although the dosis is lower than generally reported in the literature to cause gastro-intestinal disturbances). Most relevant, the clearance of glycoalkaloids usually takes more than 24 h, which implicates that the toxicants may accumulate in case of daily consumption.


Perishables Handling Newsletter Issue No. 87, August 06,
A Review of Important Facts about Potato Glycoalkaloids
by Marita Cantwell
I give only the conclusion :
To avoid toxic levels of glycoalkaloids, potato cultivar selection is very important. However, improper postharvest handling conditions are the main cause of toxic levels in potatoes. To keep glycoalkaloid content low, store potatoes at lower temperatures, such as 7°C(45°F), keep potatoes away from light, market in opaque plastics films and paper bags, and rotate frequently on retail displays.


And also :
Current Research in Nutrition and Food Science   
A Review of Occurrence of Glycoalkaloids in Potato and Potato Products
DUKE GEKONGE OMAYIO et al

There has been increasing consumption of potato products such as French fries and crisps in most countries as a result of lifestyle change in both developed and developing countries. Due to their generally pleasurable taste and texture, they are appreciated by a high number of consumers  across the world, with the younger members of the population mostly those in the urban areas having
a higher preference. The hard economic situations have also driven many people to their consumption as they are affordable. Moreover, these products are convenient for the younger generation who do not prepare their own food. However, there have been food safety concerns that have been linked
in the past to glycoalkaloids in the raw potatoes that are used for processing. Potatoes are known to accumulate glycoalkaloids (GAs) during growth and postharvest storage. Some potato varieties have been shown to have high glycoalkaloids. These toxicants have been found to bioaccumulate
in the body especially if daily consumption of foods containing the glycoalkaloids are consumed. Glycoalkaloids lead to intestinal discomfort, vomiting, fever, diarrhea and neurological problems and can lead to human or animal deaths in cases of acute toxicity. Transportation, handling, poor
storage and exposure to sunlight during marketing of potatoes exposes consumers to potential risk of glycoalkaloids due to injury and greening which lead to increased levels of glycoalkaloids. Glycoalkaloids are quite stable and therefore, freeze-drying, boiling, dehydration or microwaving have got limited effect and thus persist through the processing conditions into the final products with the levels being proportional to the concentrations in the raw materials used. This current review focuses on the occurrence of glycoalkakloids in potato and potato products that are commonly consumed.

And there are hundreds of others saying the same !