Notes phytochemist. Potatoes. Part two. The story about potato fat or "Day of the Syroyid"

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I think the regular readers of my notes have already noticed my rather skeptical attitude to all kinds of food and nutritional deviations, such as raw food, mono-art, and prano-studies (“thousands of them”). But today I want to talk about such "nutrients" of potatoes, which in most cases are available only to those who use raw potatoes (or make potato juice) and will not bring special benefit to "cookers and cookers of all stripes" (to whom by the way, and the author of these lines). There should be a holiday on the street Syroeda. This day has come ...

In general, to find out how to cure arthritis with potatoes and lower blood pressure, what size the potato genome has and where potato kvass is produced now - you need to look under the cut.

- Biochemistry! Biochemistry! - shouted the pioneers and got notebooks.
paraphrased from a famous joke

Bulbyan tlushch, he's Fat of the ... potato

Speaking frankly, to introduce such a thing as “potato fat” even somehow and not comme il faut , because the fat content (they are lipids) in tubers is very low - only about 0.2 - 2 grams / kg wet weight (or an average of 1.2 g / kg). My favorite base of USDA speaks about the same thing., attributing 100 grams of boiled potatoes to 0.1 grams of lipids, of which 0.03 grams comes from saturated fatty acids, 0.002 to monounsaturated fatty acids, and 0.043 grams of polyunsaturated fatty acids. And this is despite the fact that for a healthy adult organism, up to about 17 grams of omega-6 and up to 2 grams of omega-3 polyunsaturated fatty acids are required per day. In general, it can be said for sure that it will not be possible to make a profit from potatoes ... But in general, not everything is so simple, we are looking for quality, not quantity.

To begin with, surprisingly, all lipids are synthesized in potato tubers from sucrose. Under the spoiler for advanced readers - biosynthesis scheme

Synthesis of starch and fats in potatoes
Сахароза превращается в UDP-глюкозу и фруктозу в клетках клубня с помощью сахароза синтетазы. Большая часть углеводов попадает в растительный амилопласт и используется для производства АДФ-глюкозы, предшественника в синтезе крахмала. Незначительное количество углеводов метаболизируется посредством гликолиза или превращается в ацетил-КоА и малонил-КоА для синтеза жирных кислот в том же амилопласте. Жирные ацильные группы переносятся специализированными белками в эндоплазматическую сеть, где в дальнейшем идут для биосинтеза липидов.

Обозначения: ACCase — Ацетил-СоА карбоксилаза, AGP — АДФ-глюкоза пирофосфорилаза, ACP — белок-носитель для ацильных групп, AATP — пластидный АТФ/АДФ-переносчик, bP — бисфосфат, CoA — коэнзим A, DAG — диацилглицерин, DGAT acyl-CoA — диацилглицерин ацилтрансфераза, Frc — фруктоза, Glc — глюкоза, P — фосфат, PGM — пластидная фосфоглюкомутаза, TAG — триглицериды

Free fatty acids and triglycerides in potatoes are trace amounts, but there are phospholipids (phosphatidylcholine - 30.7 mol.%, Phosphatidyl ethanolamine - 19.6%, phosphatidyl inositol - 9.3%, phosphatidyl acid - 3.2%, phosphatidylserine - 1 , 5%, phosphatidylglycerol - 1.2% and diphosphatidylglycerol ( cardiolipin ) - 0.7%) and galactolipids. If I already told about phospholipids and their properties in the section Fat of the ... bananahis latest “banana” article (which means that everything said there applies to potatoes), I will briefly tell you about galactolipids now. In fact, it is a type of glycolipids, substances containing in its composition a non-polar “tail” - a lipid residue (fatty acid), linked by a covalent (glycosidic) bond with a polar carbohydrate residue (literally sugar “head”). In the case of galactolipids, galactose acts as a carbohydrate residue.

In general, glycolipids are responsible for the stability of the cell membrane and for the recognition of “friend-foe”, both the underlying immune response and allowing cells to grow together, forming tissues. In addition, glycolipids are located on the surface of the membranes of eukaryotic cells, extending from the double lipid layer into the "open space" of the extracellular environment. Returning to the galactolipids, we can say that most often they are directly involved in the processes of photosynthesis and act as a backup "analog" of phospholipids, in case of a lack of phosphorus in the body. In addition to the fact that galactolipids have greater bioavailability than free fatty acids, they are also able to show good anti-inflammatory activity. An example is wild rose, containing galactolipids andhaving a pronounced anti-inflammatory action (anti-arthritis, in particular).

An interesting fact is that galactolipids can also act as a scaring agent (anti-fidget) for marine plants (as well as all sorts of tannins for terrestrial). An example is the Fucus algae that is widespread on the shores of the Atlantic and Pacific Ocean , which the cutest sea ​​hedgehog cannot eat because of the presence of galactolipids . Altogether, according to fats, about fat-related compounds present in tubers: Firstly , these are phytosterols already familiar to us (see the article Phytochemist Notes. Sunset of the Habr-banana era

to refresh knowledge of phytosterols / sterols). In fresh potato tubers, you can find a lot of free sterols. Fresh potato tubers contain about 43.1–43.7% β-sitosterol (of the total number of plant sterols), campesterol (26%), Δ5-avenasterin (20%), and 10% of the residue is approximately equally divided between the brassicasterin, Δ7-avenasterin and stigmasterister and their esters. So what? So subj is wrong ( why - see the banana article already mentioned above ):

But why do you eat this meat with a bull and go to bed?
А затем, что фитостерины бульбы снижают всасывание холестерина мяса, не с бананом же это мясо многострадальное, ей богу, жрать…

Secondly , the lipophilic biopolymer suberin , which is the main component of the inner part of the potato skins. Suberin consists of the so-called. suberic acids (cork acids) and glycerin. The acids themselves are sometimes used to synthesize drugs ( such as these , according to the Russian Wikipedia) and biodegradable plastics. And suberin - suberin, friends, this, roughly speaking, is the same cork, absolutely the same in the wine bottle, which is in the form of a finishing material on the kitchen wall. “Roughly speaking” because a cork is a mixture of suberin, fiber, lignin and various plant waxes.

And thirdlyIt is the fats that are responsible for the same potato smell. It is important that raw potatoes have almost no odor, because they contain very small amounts of volatile substances. As soon as the oxidation of lipids has gone - odors have gone as well (by the way, it is with the processes of lipid oxidation that all antioxidants fight). The pleasant smells of freshly-boiled potatoes, as well as roasted and baked, are formed due to the fact that oxidation of unsaturated fatty acids occurs (which contain only a small amount) - mainly linoleic and linolenic. As a result , a number of volatile aldehydes, ketones, alcohols and alkyl furanes are formed. According to the authors of the work , the difference in tastes of boiled potatoes of different varieties is related to the content of linoleic acid, and the compound cis-4-heptenalwhich is formed as a result of oxidation (the compound is, by the way, used as a food fragrance). As a fly in the ointment, you can add that unpleasant odors (“rancidity”, etc.) also owe their appearance to unsaturated fatty acids, which are easily oxidized during storage (especially dehydrated potatoes and products from it). In this paper, the authors showed that the unpleasant odor that is formed during long-term storage of potato flakes, the latter is due to the decomposition products of linoleic acid (formed during the splitting of linoleic acid peroxo-complexes), in particular, hexanal (which gives the smell of "freshly cut grass").

I suspect that commentators necessarily at the mention of the smell of thermally processed potatoes can recall all sorts of pyrazines, which give the potato "the very taste familiar from childhood." Therefore made adjustments for "smell-better suited to fats, but for a taste - everything else is the result of" known to every cook " Maillard reaction .

Maillard reaction (sugar-condensation reaction) is a chemical reaction between amino acids and sugars that occurs when heated. An example of such a reaction is roasting meat or baking bread, during which a typical smell, color and taste of cooked food arises in the process of heating a food product. These changes are caused by the formation of Maillard reaction products. Named in honor of the French chemist and physician Louis Camille Maillard, who was one of the first to investigate the reaction in the 1910s.
It may be necessary later to stop separately on the process of heat treatment of potatoes and consider its chemistry. In the meantime, I’ll just say that mainly alkyl alkyl alloys (pyrazines there), formed in the same Maillard reaction, take part in the formation of the taste of cooked / fried potatoes (and its inherent aroma).

To the note : an interesting fact is that the decay products of RNA - some ribonucleotides formed in the process of baking / frying potatoes act as precursors (precursors) of “glutamate-like” flavor enhancers, stimulators of the “ umami ” class receptors . So, if “the language does not go to glutamate, glutamate goes to the language,” and you,% USERNAME%, cannot guess about it :)

Potato protein

Fat - little, protein - a little more (in potatoes, of course). But all the same, even with a great desire to reach out to animal products will not work. On average, one potato tuber contains about 20 grams of protein (6.9-46.3) per kilogram of green weight. And according to the USDA, the pulp of a single uncooked potato contains approximately 1.87 grams of protein per 100 g of product. Thus, the protein that can enter the body with potatoes is a tiny part of the total daily protein intake for the body. But, nevertheless, it is necessary to recognize that even with such a low content, root vegetables (such as potatoes and sweet potatoes) are a valuable non-grain source of protein on a global scale. In addition, potato protein is of particular value due to the high content of essential acids such as lysine, methionine, threonine and tryptophan. Yet, so to speak, endogenous proteins that can be found in potatoes can be divided into three classes: patatins, protease inhibitors and high-molecular proteins. About each detail below.

The main protein found in potatoes is patatin , also known as tuberin (as it will turn out in Russian, “potatoes” or something ...). It is mainly found in tubers or plant stolons (in vacuoles of the parenchyma). On patatins about 40–60% of all potato proteins account for. Patatins are reserve-type glycoproteins (ie, proteins accumulated during the growth and development of the fetus as nutrients necessary for plant development in the initial stages of germination), having lipidacyl hydrolase enzymatic activity ( L AH, capable of cleaving fatty acids from membrane lipids, but this, by the way, is the main cause of potato allergy) and having a molecular weight of 40 to 45 kDa.

Patatin consists of about 366 amino acids, is present in potatoes as a dimer with a molecular weight of about 88 kDa. The tertiary structure of a protein is stable up to 45 ° C, with an increase in temperature, the secondary structure begins to unfold and at 55 ° C denatures the α-helix. So, rejoice, O admirers and fans of the current fashionable SU-KID flow , even it can save you from potato protein.

Interestingly, compared to other common plant protein sources, patatin has the same nutritional efficiency as egg white, and at the same time has emulsifying properties better than soy proteins ( manufacturers of various vegetarian surrogates should stop here and think ).

The second group of proteinspotato, are protease inhibitors (so-called tuberinin), which have a molecular weight in the range from 5 to 25 kDa. Like patatin, protease inhibitors account for 30–40% of total tuber protein. And yes, this is if someone has already forgotten, as much as anti-nutrients. Protease inhibitors block the work of serine, cysteine ​​(inhibits papain = do not eat raw potatoes with papaya), aspartic protease (can inhibit trypsin, chymotrypsin and elastase of human leukocytes, aha), some invertases and metal-containing carboxypepsida (PCI). In general, today there are five families of these inhibitors (A - with a mass of up to 8.1 kDa, B - with a mass of up to 12.3 kDa, C - with a mass of 22–25 kDa, K, M), which differ in their amino acid sequence , chain length and composition of the subunit (from monomer to pentamer). 70% of potato protease inhibitors belong to the so-called. " Domains marten"(accent on the first syllable), which, by the way, are actively used as a basis for the development of new pharmaceutical products. Compared with patatin, protease inhibitors are usually more hydrophilic, but both protein fractions have the same tendency to coagulate under the influence of heat treatment (t they are also vulnerable to sous-vide .) Once again I remind you that protease inhibitors received the status of anti-nutritional substances for reducing the digestibility and biological value of protein, which, however, takes place only in the case of Beating raw or improperly cooked products from potatoes.

And finally, the third, “NONAME”, a group of potato proteins (20–30% of the total potato protein). This includes mainly high-molecular proteins involved in the synthesis of starch, such as phosphorylase L-1 with a molecular mass of 80 kDa (4%). You can also recall lipoxygenase (10%), defensin (5%), annexin, glyoxylase I, enolase, catalase, UDP pyrophosphorylase, etc. Nobody has really studied this family yet . So there are still white spots (Belarusian potato experts, ay! Work for you) .

So, the description is given and worth telling, and what is all this interesting. And it is interesting that during the enzymatic degradation of many of the mentioned polypeptides, short-chain proteins are formed, which may have hormone-like (antithrombotic, antihypertensive, immunomodulating, etc.) activity. Peptides with 3–20 amino acid residues that are able to penetrate the intestinal epithelium or bind to specific receptors of the intestinal epithelial cells usually have bioactivity.

Today, it is necessary to recognize that neither the physiological role nor the biological activity of potato proteins has been sufficiently studied (read, waiting for its researchers). Based on the amino acid sequences of potato proteins, the researchers suggest the presence of several potential “precursor proteins” (precursors) that form peptides with different activity in the human body.

Lyrics about potato genome and potato kvass from Belarus
Не знаю, многие ли в курсе, но геном картофеля уже расшифровали. И его даже можно скачать, записать на DVD-R и подарить бабушке, от которой осенью повезем пару-тройку мешков… Благо занимает он всего-то 844 Мб (это вам не геном пшеницы , размером около 15 Гб, причем всякие геномы гороха, земляники, какао, огурца, сои и т.д. и т.п. тоже не маленького размера). Наглядно это выглядит примерно так:

Картинка, кстати, из той самой, легендарной статьи в не менее легендарном Nature. Геном картофеля был отсеквенирован в 2011 году силами Международного консорциума по секвенированию картофеля. В состав этого коллектива входили 16 научных групп из разных стран, из России специалисты были, а вот были ли из «картофельной» Беларуси — не знаю, если комментаторы подскажут — поправлю статью.

Но скорее всего, пока международное комьюнити секвенировано секвенировало, да не высеквенировало, наш брат «мытьем и катаньем» (=как завещал нам дедушка Мичурин) выводил себе селекционными методами "картофель с розовой, синей и фиолетовой мякотью". Не столь важно, что уже в 2003 году исследователи из Корнеллского университета США встречали Новый год с фиолетовой картошкой сорта Adirondack Blue, сколь то, что из «Белорусского цветного» можно делать картофельный квас Miкола (Miкола — это Николай на русском, если что) (для Европейских игр 2019, ага).

As an example of biological activity, one can cite the work in which the effect of a “potato” is shown that leads to enhanced inhibition of the angiotensin - converting enzyme (ACE) responsible for controlling blood pressure (and a bunch of other consequences of various diseases). Moreover, the proteins of the so-called most active in this field. "Vascular bundle" and internal tubers. The age of these tubers also affected (lovers of young potatoes, whatever one may say, but they are right in their taste preferences).

Although, if we talk about lowering blood pressure, then it is worth mentioning such a thing as cucoamines (in the picture - cucoamine A)

In 2005, British researchers discovered these compounds in potatoes. Chemically, cucoamines are catechins (i.e., belong to a subset of antioxidants), as well as derivatives of the dihydro cofeic acid diamines. Previously, such compounds were found in a single plant Lycium chinense (Solanaceae) aka Dereza Chinese

If anything, Dereza ordinary belongs to the same family , the fruits of which are also called “wolf berries” in our country. But there is no system here, so do not even think about grabbing wolfberry at your leisure, the pressure will not drop, despite the external similarity (find ten differences with Lycium chinense)

Chinese dereza has traditionally been used in phytomedicine, as a means of effectively reducing blood pressure. Similar properties and have cokeamine potatoes. True, it is worth noting that in the same work in 2005 there are references to studies showing the presence of cucoamines in forest tobacco (Nicotiana sylvestris) and tomato (Lycopersicon esculentum). While the role of cucoamines in potatoes has not been sufficiently studied, there are articles where the authors attribute to them the regulation of starch biosynthesis , the formation of resistance to diseases and the stimulation of germination . With regard to the biological activity in the human body, there is still to assess the thermal stability of potato amines (and today there are about 30 of them) and their bioavailability.

Another interesting fact of the nature of the protein can serve as a work ( amb , two ). The researchers found that potato proteins, in particular, aspartic protease inhibitors, stimulate the release of cholestystokinin (CCK) in mice and stimulate cells that produce CCKAR (English Cholecystokinin A receptor), which, interacting with food proteins, contributes to the saturation effect.

Considering all the above, potato proteins can act as an excellent component for creating functional food (I mentioned it repeatedly in my “banana” articles).

In addition, potatoes, due to the huge amount of virtually free polypeptides, can act as an excellent in vitro nanoreactor of many necessary biological compounds. Researchers at work, for example, found that small potato peptides obtained by alkaline enzymatic hydrolysis had a positive effect on lipid metabolism in rats. As a result of this work, the high molecular weight proteins of the potato were able to be “crushed” into peptides with a molecular weight from 700 to 1840 Da, and the basic molecular weight (90% of the total) was 850 Da. As a result, it was concluded that such a method of obtaining low molecular weight peptides is the most economically available from existing, with excellent opportunities for industrial scaling (not to mention the fact that low molecular weight peptides have a wider range of functional properties than their high-molecular "colleagues").

What is it all about? And the fact that today potato protein is most often tried to be removed during the production of starch and is not even always used for animal feed (due to the bitter taste that some compounds can produce, the same solanine), potato proteins are also not used for emulsification and foaming, although, I think, everyone who has cooked potatoes at least once knows how stable the foam produced during boiling can be. And the thing comes out is an interesting and not sufficiently studied. Their only drawback is that all the most interesting properties appear only when using as is, i.e. in the raw form ... Chemists, raw foodists, your turn!

To be continued...

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