A propos des alcaloïdes des peaux de pomme de terre

J'ai fait la promesse publique de ne plus parler de toxicologie et de nutrition, parce que, d'une part, je ne suis pas spécialiste de ces disciplines (même si je suis attentivement les publications scientifiques, avec plusieurs alertes dans des journaux de bonne qualité), et, d'autre part, je crains que ce soit un peu inutile   : je ne suis pas sûr que mes interlocuteurs changent de comportement quand ils ont des données juste qui contrarient leurs opinions alimentaires personnelles.
Voici ce que j'avais écrit : https://hervethis.blogspot.com/2019/10/ni-nutrition-ni-toxicologie.html.

De ce fait je suis vraiment embarrassé quand on m'interroge sur des questions de toxicologie ou de nutrition, et la seule chose que je puisse faire est de donner des informations.
En l'occurrence, aujourd'hui, on m'interroge sur la solanine des pommes de terre et, chimiste, je peux commencer par observer que ce composé, cet alcaloïde, n'est pas le seul qui soit présent dans la peau des pommes de terre  : il y a également la chaconine et la solanidine,k notamment.
Ces composés ont des toxicités (comme tous les composés) qui sont  connues depuis longtemps, puisque déjà, Parmentier avait observé un goût brûlant quand il avait consommé une décoction de peau de pomme de terre (voir mon article sur Parmentier à l'Académie de Pharmacie).
À l'époque, on ignorait tout de ces alcaloïdes, mais on en sait plus aujourd'hui et je renvoie mes amis vers l'immense masse de publications scientifiques à ce propos : il suffit d'ouvrir Google Scholar et de taper "potatoes alcaloïds" : https://scholar.google.com/scholar?hl=fr&as_sdt=0%2C5&q=potatoes+alcaloids&btnG=.

Mais je veux quand même signaler plusieurs points que j'ai relevés dans les publications que j'ai lues.
Tout d'abord, les alcaloïdes de la pomme de terre se trouvent dans les trois premiers millimètres sous la peau.
Ensuite, ils résistent à des température de 285 degrés Celsius, de sortes qu'ils ne sont pas détruit par la cuisson.
Il y a, en ligne, une publication qui a considéré la quantité d'alcaloïdes des pommes de terre consommé dans les nourriture de rue au Pakistan  : les frites sont faites à partir de pommes de terre qui n'ont pas été pelées... et la "dose journalière admissible" est dépassée (Aziz et al., Journal of Food Science ! Vol. 77, Nr. 3, 2012).
Enfin l'Agence européenne de sécurité des aliments, l'Efsa, vient de publier un rapport que j'invite tous mes amis à consulter  : Risk assessment of glycoalkaloids in feed and food, in
particular in potatoes and potato-derived products, doi: 10.2903/j.efsa.2020.6222.
Et voici le résumé :

Abstract
The European Commission asked EFSA for a scientific 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 identified 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 long-term intake of GAs via potatoes has been identified. No reference point for chronic exposure could be identified 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. For horses, farm and companion animals, no risk characterisation for potato GAs could be performed due to insufficient data on occurrence in feed and on potential adverse effects of GAs in these species.

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 !