AuthorsRodrigo Valenzuela B.Nutrition and also Dietetics School, Faculty that Medicine, university of Chile, Santiago, ChileAlfonso Valenzuela B.Lipid Center, Nutrition and Food technology Institute, college of Chile, Faculty of Medicine, college of Los Andes, Santiago, Chile
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From the Edited Volume
The ax lipid is provided to classify a huge number of substances having very different physical - chemical characteristics, gift its solubility in necessary non-polar solvents the typical property for their classification. Lipids space composed of carbon, hydrogen and oxygen atoms, and also in some situations contain phosphorus, nitrogen, sulfur and also other elements. In this context, fats and oils room the main exponents of lipids current in foods and also in nutritional procedures <1,2>, being diverse fatty acids and cholesterol the many representative molecules due their important metabolic and nutritional functions <3,4>. The structural, metabolic and nutritional prominence of lipids in the human body is supported by numerous investigations in different biological models (cellular, animals and also humans). Lipids have actually been crucial in the development of species, having important function in the growth, breakthrough and maintenance of tissues <5,6>. A clear instance of this importance is the elevated fatty mountain concentration current in nerve tissue, especially really long-chain polyunsaturated fatty acids <7,8>.
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Fatty mountain are, amongst lipids, of crucial relevance in the structure and also physiology the the body because: i) creates an integral component of phospholipids in cabinet membranes; ii) room the primary source of power (9 kcal /g or 37.62 kjoules/g); iii) in infants, provide an ext than 50% of the daily power requirements; iv) some fatty acids are of important character and are forced for the synthesis of eicosanoids and docosanoids (of 20 and also 22 carbon atoms, respectively), such together leukotrienes, prostaglandins, thromboxanes, prostacyclins, protectins and also resolvins), and; v) few of them might act as 2nd messengers and also regulators of gene expression <9,10>. As well as fatty acids, cholesterol is an additional lipid the has necessary functions in the body, among which are: i) together with phospholipids is essential in the formation of cell membranes; ii) constitutes the skeleton for the synthetic of steroid hormones (androgens and estrogens); iii) from its structure is derived the framework of vitamin D, and; iv) participates in the synthesis of the bile salts and also the composition of bile cheap <11>.
Lipids play a key role in the expansion and breakthrough of the organism, whereby the requirements of this molecules (mainly fat acids) will change depending top top the age and also physiological state of people <12>. Furthermore, lipids have an essential participation both, in the prevention and/or in the development of numerous diseases, specifically chronic non-communicable diseases <13>, affect the lipid requirements in people <14>. Together food components, lipids are also important because: i) are significant in giving organoleptic qualities (palatability, flavor, aroma and texture); ii) are automobile for fat soluble vitamins, colours or dyes and antioxidants, and; iii) might act as emulsifying agents and/or encourage the stability of suspensions and also emulsions <15>.
Fats and oils, the most common lipids in food, are triacylglyceride mixtures, i.e. Structures developed by the linking the three various or similar fatty acids to the tri-alcohol glycerol <16>. A fat is characterized as a mixture that triacylglycerides i m sorry is solid or pasty in ~ room temperature (usually 20 °C). Conversely, the ax oil corresponds to a mixture of triglycerides which is fluid at room temperature. In addition to triacylglycerides, which space the main components of fats and also oils (over 90%), these substances commonly contain, to a lesser extent, diacylglycerides, monoacylglycerides, phospholipids, sterols, terpenes, fat alcohols, carotenoids, fat soluble vitamins, and many various other minor chemical frameworks <17,18>. This chapter faces the general facets of lipids, especially those concerned the chemical framework and function of these molecules.
2. Fatty acids
Fatty acids space hydrocarbon frameworks (containing carbon and also hydrogen atoms) created by 4 or more carbons attached come an acidic practical group referred to as carboxyl group. The chemical and also physical nature of the various fatty acids, such as their solubility in non-polar solvents and the melt point, will count on the variety of carbon atom of the molecule. <19>. The higher the variety of carbon atom of the chain the greater will it is in melting allude of the fat acid. Follow to the chain length fatty acids are referred as short-chain fatty acids, those having 4 (C4) come ten (C10) carbons; as medium-chain fat acids those having actually twelve (C12) to fourteen (C14) carbons; long-chain fatty acids come those of 16 (C16) to eighteen carbons (C18); and really long-chain fat acids those having actually twenty (C20) or more carbon atoms. Molecules having less than 4 carbon atoms (C2; acetic acid and C3; propionic acid) space not considered fatty mountain due their high water solubility. Top top the other side, fatty acids the high number of carbon atoms space not frequent, but are existing in far-ranging amount in the mind of vertebrates, consisting of mammals and human. In the human mind have been figured out fatty mountain as long as 36 carbon atoms <20>.
The link between carbons in fatty acids, exchange mail to a covalent link which might be solitary (saturated bond) or dual (unsaturated bond). The variety of unsaturated bond in the very same molecules can variety from one come six double bonds. Thus, the much more simple classification of the fatty acids, divided them in those that have not twin bonds, named saturated fatty acids (SAFA), and fatty mountain that have actually one or more dual bonds, collectively named unsaturated fat acids. In turn, once the molecule has one unsaturation it is classified as monounsaturated fatty mountain (MUFA) and when has two to six unsaturations room classified as polyunsaturated fat acids (PUFAs) <21>. The visibility of unsaturation or twin bonds in fatty acids is represented by denoting the variety of carbons of the molecule followed by an indication that the number of double bonds, thus: C18:1 synchronizes to a fatty mountain of 18 carbons and also one unsaturation, it will be a MUFA. C20: 4 exchange mail to a molecule having 20 carbons and also four twin bonds, gift a PUFA. Now, the is crucial to recognize the place of the unsaturations in the hydrocarbon chain both in MUFAs and PUFAs <22>.
3. Nomenclature of fatty acids
According to the main chemical nomenclature created by IUPAC (International Union the Practical and also Applied Chemistry) carbons of fat acids should be numbered sequentially indigenous the carboxylic carbon (C1) come the most extreme methylene carbon (Cn), and the place of a double bond have to be shown by the price delta (Δ), with each other to the number of the carbon where twin bonds begins. According to this nomenclature: C18: 1, Δ9, suggests that the twin bond is in between carbon 9 and also 10 <23>. However, in the cabinet the metabolic utilization of fatty acids occurs by the successive scission of 2 carbon atom from the C1 to the Cn (mitochondrial or peroxisomal beta oxidation). This way that together the fatty acid is being metabolized (oxidized in beta position), the variety of each carbon atom will certainly change, creating a problem for the identification of the metabolic products formed as the oxidation progress. Therefore R. Holman, in 1958, proposed a new type of notation that is currently widely offered for the biochemical and nutritional to know of fatty acids <24>. This nomenclature lists the carbon enumeration from the other too much of the fatty acid molecule. Follow to this notation, the C1 is the carbon farthest from the carboxyl group (called as terminal or finish methylene carbon) i m sorry is designed together "n", "ω" or "omega". The last notation is the most regularly used in nutrition and refers to the last letter the the Greek alphabet <25>. Thus, C18: 1 Δ9 coincidentally is C18: 1 ω-9 in the “ω” notation, yet C18: 2 Δ9, Δ12, follow to this nomenclature ω would certainly be C18: 2 ω-6. What happens v fatty acids having an ext than a double bond? double bonds room not randomly i ordered it in the fatty acid structure. Nature has been "ordained" as largely incorporate lock in well-defined positions. Many frequently double bonds in PUFAs space separated through a methyl team (or many correctly methylene group) forming a -C=C-C-C=C- structure which is recognized as "unconjugated structure", i beg your pardon is the layout of double bonds in many naturally arising PUFAs <26>. However, although much less frequently, there are likewise present "conjugated structures" where twin bonds room not be separate by a methylene group, creating a -C=C-C=C- structure. This details structural disposition of twin bonds, i.e conjugated structures, is now obtaining much interest since some fat acids having actually these structures show special nutritional properties, castle are dubbed "conjugated fatty acids". Many of them are obtained from the unconjugated framework of linoleic acid (C18:2 ω-6) <27,28>.
For the application of the ”ω” nomenclature and also considering the "order" of twin bonds in unsaturated fatty acids having actually unconjugated stucture, it deserve to be observed that by pointing the ar of the first twin bond, it will immediately determined the place of the subsequent dual bonds <29>. Thus, C18: 1 ω-9, which has a single dual bond at C9 counted from the methyl end, exchange mail to oleic acid (OA), which is the main exponent of the ω-9 family. Oleic mountain is extremely abundant both in vegetable and also animal tissues. C18: 2 ω-6 coincides to a fatty mountain having twin bonds in ~ the C6 and C9 (for unconjugated fat acids it is not essential to indicate the position of the second or successive double bonds). This is linoleic acid (LA), the main exponent of the ω-6 family and which is an extremely abundant in vegetable oils and also to a lesser level in animal fats <30>. C18: 3, ω-3 corresponds to a fatty acid having double bonds in ~ C3, C6 and also C9. That is alpha-linolenic mountain (ALA), the leading exponent of the ω-3 family. ALA is a much less abundant fat acid, virtually exclusively present in the vegetables kingdom and also specifically in land-based plants <31>. Within (LCPUFAs), C20: 4, ω-6 or arachidonic mountain (AA); C20: 5, ω-3 or eicosapentaenoic acid (EPA) and; C22 : 6, ω-3 or docosahexaenoic acid (DHA), space of great nutritional importance and are only uncovered in ground pet tissues (AA) and also in aquatic animal tissues (AA, EPA and also DHA) and in plants of maritime origin (EPA and DHA) <32>.
The increase of dual bonds in fatty acids substantially reduces its melting point. Thus, because that a structure of the same number of carbon atoms, if that is saturation may give rise come a hard or semisolid product in ~ room temperature, yet if the very same structure is unsaturated, might originate a liquid or less solid product in ~ room temperature. Figure 1 mirrors the category of fat acids according to their level of saturation and unsaturation and considering the notation "ω", and also table 1 shows various fatty acids, reflecting the C nomenclature, their organized name, their usual name and the corresponding melting point.
Classification of fat acids according to their degree of saturation and also unsaturation and considering the notation " ω".
|Nomenclature||Systematic name||Common name||Melting suggest °C|
|Saturated fatty Acid|
|Unsaturated fat Acid|
Different fatty acids, showing the C nomenclature, their organized name, their common name and the corresponding melting point.
4. Mono-, di- and triacylglycerides
The structural company of fatty acids in food and in the human body is mainly identified by the binding come glycerol by ester linkages. The reaction of a hydroxyl team of glycerol, at any of its three groups, through a fatty acid offers rise come a monoacylglyceride. The linking that a second fatty acid, which might be comparable or different from the existing fatty acid, provides rise come a diacylglyceride. If all 3 hydroxyl teams of glycerol are connected by fat acids, then this will be a triacylglyceride <33>. Monoacylglycerides, by having totally free hydroxyl teams (two) are fairly polar and therefore partly soluble in water. Various monoacylglycerides attached to fatty acids of various lengths are offered as emulsifiers in the food and also pharmaceutical market <34>. The much less polar diacylglycerides which have only one complimentary hydroxyl team are much less polar than monoacylglycerides and also less dissolve in water. Finally, triacylglycerides, which lack of cost-free hydroxyl groups are totally non-polar, however highly soluble in non-polar solvents, i m sorry are generally used for their extraction from vegetables or animal tissues, due to the fact that constitutes the energy reserve in these tissues <35>. Diacylglycerides and monoacylglycerides are crucial intermediates in the digestive and also absorption procedure of fats and oils in animals. In turn, some of these molecules also perform various other metabolic functions, such as diacylglycerides which might act as "second messengers" in ~ the intracellular level and are also part of the composition of a new generation of oil nutritionally designed as "low calorie oils" <36>. When glycerol creates mono-, di-, or triacylglycerides, that carbon atoms are not chemically and also structurally equivalent. Thus, carbon 1 the the glycerol is referred together carbon (α), or sn-1 (from “stereochemical number”); carbon 2 is referred together carbon (β), or sn-2, and also carbon 3 together (γ), or sn-3. It is essential to note that the notation “sn” is currently the most frequently used <37>. This spatial structure (or conformation) the mono-, di- and also triacyglycerides is appropriate in the digestive process of fats and also oils (ref). Number 2 mirrors the structure of a monoacylglceride, a diacylglyceride and also a triacylglyceride, point out the "sn-" notation.
Structure the a monoacylglyceride, a diacylglyceride and also a triacylglyceride, specifying the "sn-" notation
5. Vital fatty acids
The capacity of an biology to metabolically introduce dual bonds in particular positions of a fatty mountain or the inability to execute this, determines the presence of the so-called non-essential or necessary fatty mountain (EFAs). Follow to this capability, mammals, consisting of primates and also humans, deserve to introduce a double bond just at the C9 place of a saturation fatty acid (according come "ω" nomenclature) and to other carbons nearest to the carboxyl group, however not in ~ carbons nearest the C1 place <38>. This is the factor why OA is not an EFA. In contrast, mammals can not introduce twin bonds at C6 and C3 positions, being the factor why AL and ALA are EFAs. By derivation, the AA is formed by the elongation and also desaturation that LA, and also EPA and also DHA, i beg your pardon are formed by elongation and desaturation of ALA, become also essential for mammals once their corresponding precursors (LA and ALA, respectively) room nutritionally deficient <39>. Number 3 reflects the chemical framework of a SAFA, such together the stearic acid (C18:0), AO, LA and also ALA, exemplifying the "ω" notation that each and also indicating the essential problem in relation to the place of their unsaturated bonds.
The chemical framework of a SAFA, such together the stearic acid (C18:0), AO, LA and also ALA, exemplifying the "ω" notation the each and indicating the essential problem in relation to the position of their unsaturated bonds
6. Isomerism of fat acids
According to the distribution of twin bonds in a fat acid and also to that is spatial structure, unsaturated fatty acids may have actually two varieties of isomerism: geometrical isomerism and positional isomerism. Through isomerism that is referred to the existence two or an ext molecules having the same structural elements (atoms), the very same chemical formula and merged in same proportions, yet having a different position or spatial circulation of part atoms in the molecule <40>.
6.1. Geometrical isomers of fat acids
Carbon atoms developing the structure of the fatty acids possess a three-dimensional spatial structure which forms a perfect tetrahedron. However, as soon as two carbons having tetrahedral structure space joined together through a twin bond, the spatial conformation of the twin bond is modified adopting a flat or aircraft structure <41>. Rotation around single bonds (C-C) is totally free, but when they are developing a dual bond (C=C), this rotation is impeded and the hydrogen atoms the are connected to every carbon associated in the bond might be at the exact same side or opposed in the plane forming the double bond. If hydrogen atoms remain at the same side, the structure formed is referred together cisisomer (denoted as “c”). As soon as hydrogen atoms continue to be at opposite political parties the structure developed is referred as transisomer (denoted as “t”, trans: way crossed) <42>. Figure 4 mirrors the cis– transgeometric isomerism of fat acids. The cisor transisomerism of fat acids confers them an extremely different physics properties, gift the melting suggest one of the most relevant <43>. Table 2 reflects the melting point of miscellaneous cis– transgeometric isomers of different fatty acids. It have the right to be observed considerable differences in the melting suggest of cis- or transisomers for the same fatty acid. Melting allude differences lug to the geometrical isomers of a fat acid very different biochemical and nutritional behavior. Fatty acids having transisomerism, specifically those of technological origin (such as generated throughout the partial hydrogenation of oils), have actually adverse effect on humans, an especially referred to the threat of cardiovascular diseases <44>. It is noteworthy that the majority of naturally arising fatty acids have cisisomerism, back thermodynamically is much more stable the transthan the cisisomerism, by which under details technological manipulations, such together the application of high temperature (frying process) or throughout the hydrogenation procedure applied because that the to produce of shortenings, cisisomers are conveniently transformed right into transisomers <45>.
6.2. Positional isomers of fatty acids
Positional isomerism describes the various positions that deserve to occupy one or more twin bonds in the framework of a fatty acid. Because that example, oleic mountain (C18:1 Δ9c), is a usual fatty mountain in vegetable oils, particularly in olive oil, yet vaccenic mountain (C18:1 Δ11t) is more common in animal fats. This is a dual example, due to the fact that both fatty acids space geometric isomers (oleic mountain cisand vaccenic acid trans) and also at the very same time positional isomers, because oleic acid has a double bond at the Δ9 position and also vaccenic mountain at the Δ11 position <46>.
|Fatty acid||Isomerism||Melting suggest (°C)|
|C18:3||cis, cis, cis||11.0|
|C20:3||trans, trans, trans||29.5|
Changes in the melting suggest of assorted cis – transgeometrical isomers of different fatty acids
In general, every fatty acids naturally existing positional isomerism that their more frequent molecule structure. However, these isomers occur in very low concentrations. Unequal the known biochemical and nutritional impacts of transgeometric isomers, over there is little information about the biological effects the positional isomers and also for the bulk of lock these impacts are considered as not relevant, other than for some conjugated structures, such together conjugated linoleic mountain (C18:2, Δ9, Δ11, CLA), a geometric and positional isomer the the most usual linoleic acid, because that which it has actually been deadline various wellness properties, especially those regarded anti-inflammatory and also lipolytic actions, however up to date the scientific evidence for this properties are considered insufficient <47>. Such together geometrical isomerism, the technological manipulation of fatty acids (i.e. Temperature and/or hydrogenation) rises the number and also complexity the the positional isomers <48>. Figure 5 summarizes the positional and geometric isomers the unsaturated fat acids.
Phospholipids room minor contents in ours diet due to the fact that less than 4-5% of our fat intake corresponds to phospholipids. However, this does not detract nutritionally important to this lipids, since they are crucial constituents the the cellular structure having likewise relevant metabolic attributes <49>. Life, in that is origin, would not have been feasible without the figure of phospholipids, together these structures space the basic components of all cellular membranes. Phospholipids have structural and also functional nature that identify them from your counterparts, triacylglycerides. In phospholipids location sn-1 and also sn-2 that the glycerol moiety are occupied by fatty acids, more frequently polyunsaturated fat acids, linked to glycerol through ester bonds. The sn-3 position of glycerol is connected to orthophosphoric acid <50>. The structure which is formed, live independence of the kind of fatty acid that binds at sn-1 and also sn-2, is called phosphatidic acid. The visibility of phosphate substituent at the sn-3 position of the glycerol gives a good polarity come this part of the molecule, being non-polar the remainder of the structure, such together in triacylglycerides. This dual feature, a polar extreme and a non-polar domain due the existence of the two fatty acids characterizes phospholipids as amphipathic molecule (amphi: both; pathos: sensation) <51>.
Positional and also geometric isomers the unsaturated fat acids
The structure of phospholipids is usually streamlined representing the polar end as a sphere and the fatty acids as 2 parallel rods. Figure 6 mirrors the chemical framework of phosphatidic mountain in its simplified representation. The amphipathic personality of phosphatidic acid can be boosted by joining to the phosphate different basic and polar molecule that rises the polarity come the excessive of the sn-3 position. As soon as the substituent of the phosphate team is the aminoacid serine it is developed phosphatidylserine; as soon as it is etanolamine that is created phosphatidylethanolamine (frequently recognized as cephalin); when choline is the substituent that is created phosphatidylcholine (well recognized as lecithin); and when the substituent is the polyalcohol inositol it is created phosphatidylinositol, a an extremely important molecule associated in cell signaling. <52>.
Chemical framework of phosphatidic acid and its streamlined representation
These more complex phospholipids space much much more common 보다 phosphatidic acid, because this is only the structure precursor that the over molecules. Number 7 reflects the structure of various phospholipids. A variety of other molecules are likewise classified as phospholipids, but are structurally different. Cardiolipin is a "double" phospholipid in which 2 phosphatidic mountain molecules are attached v their phosphates by a molecule the glycerol. Cardiolipin is a very important in the structure of the inside membrane of mitochondria and also due your molecular volume it is the only immunogenic phospholipid (which stimulates the formation of antibodies) <53>. Plasmalogens are various other lipid molecules related to phospholipids. In these molecules the substituent at sn-1 place of the glycerol is not a fatty acid, yet a fatty alcohol which is attached to glycerol by one ether linkage. Phosphatidalethanolamine (different than phosphatidylethanolamine) is an abundant plasmalogen in the nervous organization <54>. Phosphatidalcholine, the plasmalogen related to phosphatidylcholine, is numerous in the heart muscle. One more structures pertained to phospholipids are sphingolipids. In these frameworks glycerol is changed by the amino alcohol; sphingosine. As soon as the hydroxyl team (alcoholic group) that sphingosine is substituted by phosphocholine, the is created sphingomyelin, which is the just sphingolipid that is existing in far-reaching amount in human tissues as a constituent of myelin that creates nerve yarn . Platelet activating element (PAF) is an inexplicable glycerophospholipid structure. In this molecule position sn-1 of glycerol is attached to a saturated alcohol v an ether bond (such as in plasmalogens) and at the sn-2 binds an acetyl group instead that a fatty acid. PAF is exit by a variety of cells and by binding to membrane receptor produces aggregation and also degranulation the platelets, has actually potent thrombotic and inflammatory effects, and also is a mediator the anaphylactic reaction <55>.
Structure of assorted phospholipids
A fundamental aspect of phospholipids is their participation in the structure of organic membranes, and the structural characteristics of the fat acids are appropriate to recognize the behavior and also the organic properties that the membrane. As an example, a diet affluent in saturated fat acids result in rise in the level of this fatty acids right into cell membrane phospholipids, bring about a significant decrease in both, membrane fluidity and also in the ability of these structure to incorporate ion channels, receptors, enzymes, structure proteins, etc., result which is associated to an enhanced cardiovascular danger <56>. By contrast, a diet rich in monounsaturated and/or polyunsaturated fat acids create an inverse effect. At the nutritional and metabolic level this effect is highly relevant because as the fatty acid composition that the diet is directly reflected into the fatty acid composition that phospholipids, changes in the composition of the diet, i.e. Boosting the contents of polyunsaturated fatty acids, will avoid the development of several illness <57>. Number 8 reflects a simulation exactly how the structural differences of the fat acids which comprise phospholipids may affect the physical and chemical actions of a membrane.
Sterols are acquired from a usual structural precursor, the sterane or cyclopentanoperhydrophenanthrene, consist of in a main structure developed by four fragrant rings identified as A, B, C and D rings. All sterols have actually at carbon 3 of A ring a polar hydroxyl team being the remainder of the structure non-polar, which offers them particular amphipathic character, such as phospholipids. Sterols have also a double bound at carbons 5 and also 6 the ring B <58>. This dual bond can be saturation (reduced) which leader to the development of stanols, which along with plant sterols derivatives are right now used together hypocholesterolemic agents when integrated into some practical foods. In ~ carbon 17 (ring D) both sterols as stanols have attached one aliphatic group, consisting in a direct structure of 8, 9 or 10 carbon atoms, depending upon whether the sterol is from pet origin (8 carbon atoms) or indigenous vegetable origin (9 or 10 carbon atoms) <59>. Figure 9 shows the framework of cyclopentanoperhydrophenanthrene and cholesterol. Frequently sterols, and also less regular stanols, have esterified the hydroxyl team of carbon 3 (ring A) v a saturation fatty mountain (usually palmitic; C16:0) or unsaturated fatty mountain (most constant oleic; C18:1 and less regular linoleic acid; C18:2. The esterification of the hydroxyl group eliminates the anphipaticity the the molecule and converts it right into a structure fully non-polar. Undoubtedly amongst sterols cholesterol is the most important due to the fact that it is the precursor the important animal metabolic molecules, such as steroid hormones, bile salts, vitamin D, and also oxysterols, which are oxidized derivatives of cholesterol created by the thermal manipulation the cholesterol and also that have actually been identified as regulators that the metabolism and also homeostasis of cholesterol and sterols in basic <60>.
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Simulation how the structural differences of the fatty acids which make up phospholipids may impact the physical and chemical behavior of a membrane
Lipids are a huge and large group of molecules that are current in all living biology and additionally in foods and also characterized by specific physicochemical properties, such as their no polarity and their solubility in necessary solvents. Part lipids, in details fatty acids and also sterols, are essential for animal and plant life. Lipids are key elements in the structure, biochemistry, physiology, and nutritional condition of an individual, because are connected in: i) the to move structure; ii) the cellular energy reserve, iii) the development of regulation metabolites, and; iv) in the regulation and gene expression, which straight affects the functioning of the body. One more important facet related come lipids is their essential involvement, either in the treatment and/or the beginning of countless diseases which can affect humans. Structural and also functional features of lipids, questioned in this chapter, will permit you to integrate those metabolic aspects of these important and also essential molecule in close relationship of how foods items containing these molecules can have a relevant affect in the wellness or disease of an individual.