Fructose
IUPAC name	(2R,3S,4R,5R)-2,5-Bis(hydroxymethyl)oxolane-2,3,4-triol
Other names	D-arabino-Hexulose Fruit sugar beta-Levulose Levulose
Identifiers
CAS number	53188-23-1 (D-fructose)
SMILES	C(C1C(C(C(O1)(CO)O)O)O)O
Properties
Molecular formula	C6H12O6
Molar mass	180. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) 16 g mol−1
Melting point	β-D-fructose: 103°C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Fructose (also levulose or laevulose) is a simple reducing sugar (monosaccharide) found in many foods and is one of the three important dietary monosaccharides along with glucose and galactose. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. In Chemistry, the standard state of a material is its state at 1 bar (100 Kilopascals exactly A reducing sugar is any sugar that in basic solution forms some Aldehyde or Ketone. Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Monosaccharides (from Greek monos: single sacchar: sugar are the most basic unit of Carbohydrates They consist of one sugar and Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Galactose (Gal (also called brain sugar) is a type of Sugar which is less sweet than Glucose. Honey, tree fruits, berries, melons, and some root vegetables, such as beets, sweet potatoes, parsnips, and onions, contain fructose, usually in combination with sucrose and glucose. Honey is a sweet and Viscous fluid produced by Honey bees (and some other species and derived from the nectar of Flowers According to the The word berry has two meanings one based on a botanical definition the other on common identification Melon is a term used for various members of the Cucurbitaceae family with fleshy fruit The beet or beetroot is a Flowering plant species ( Beta vulgaris) in the family Chenopodiaceae. The sweet potato ( Ipomoea batatas) is a Dicotyledonous plant which belongs to the family Convolvulaceae The parsnip ( Pastinaca sativa) is a Root vegetable related to the Carrot. Organicsalsajpg||thumb|right|Onions used in salsa.]]Cooked onions in frying pan Solubility of Pure SucroseTemperature(Cg Fructose is also derived from the digestion of granulated table sugar (sucrose), a disaccharide consisting of glucose and fructose, and high-fructose corn syrup (HFCS). High-fructose corn syrup (HFCS is any of a group of Corn syrups that has undergone Enzymatic processing to increase its Fructose content and is then mixed

Crystalline fructose and high-fructose corn syrup are often mistakenly confused as the same product. The former is simply pure (100%) fructose. The latter is composed of nearly equal amounts of fructose and glucose. Crystalline fructose is held to offer many unique benefits such as improved product texture, taste and stability. Specifically, when combined with other sweeteners and starches, crystalline fructose is said to boost cake height (in baked goods) and mouth-feel of foods and beverages and to produce a pleasing brown surface color and pleasant aroma when baking. ^[1]

Fructose is often recommended for, and consumed by, people with diabetes mellitus or hyperglycemia, because it does not raise blood glucose or insulin concentrations since it is metabolized without the need of insulin. Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc Hyperglycemia, hyperglycaemia, or high blood sugar is a condition in which an excessive amount of Glucose circulates in the Blood plasma However, this benefit is tempered by concern that fructose may have an adverse effect on plasma lipid and uric acid levels. Uric acid (or urate) is an Organic compound of Carbon, Nitrogen, Oxygen and Hydrogen with the formula C5H4N4O3

Contents 1 Chemical Properties 1.1 Classification and Structure 1.2 Chemical Reactions 1.2.1 Fructose and Maillard Reaction 1.2.2 Fructose and Fermentation 2 Physical and Functional Properties 2.1 Relative Sweetness 2.2 Fructose Solubility and Crystallization 2.3 Fructose and Starch Functionality in Food Systems 3 Food Sources 3.1 Table 1 – Sugar Content of Selected Common Plant Foods (g/100g) 3.2 Commercial Sweeteners (% of Carbohydrate) 4 Digestion and Absorption 4.1 Capacity and rate of absorption 4.2 Malabsorption 5 Fructose Metabolism 5.1 Fructolysis 5.2 The Metabolism of Fructose to DHAP and Glyceraldehyde 5.3 Synthesis of glycogen from DHAP and Glyceraldehyde 3 Phosphate 5.4 Synthesis of Triglyceride from DHAP and Glyceraldehyde 3 Phosphate 6 Health effects 7 See also 8 References 9 External links

Chemical Properties

Classification and Structure

Fructose, also referred to as fruit sugar is a simple monosaccharide with a ketone functional group. Monosaccharides (from Greek monos: single sacchar: sugar are the most basic unit of Carbohydrates They consist of one sugar and A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or Fructose is an isomer of glucose with the same empirical formula (C₆H₁₂O₆) but with a different structure. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Fructose is a 6-carbon polyhydroxyketone. Like glucose, it forms ring structures when dissolved in solution. When fructose forms a 5-member ring, the OH group on the fifth carbon atom attaches to the carbonyl group that is on the second carbon atom (D-Fructofuranose). Alternatively, the OH group on the sixth carbon may attach to the carbonyl carbon to form a 6-member ring (D-Fructopuranose). Fructose may be found at equilibrium containing a mixture of 70% fructopuranose and 30% fructofuranose ^[2]

Figure 1 Isomeric Forms of Fructose

Chemical Reactions

Fructose and Maillard Reaction

Fructose undergoes the Maillard reaction, non-enzymatic browning, with amino acids. This article is about an automobile For the chemical reaction see Maillard reaction, named for Louis Camille Maillard. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Because of fructose exists to a greater extent in the open-chain form than does glucose, the initial stages of the Maillard reaction occurs more rapidly than with glucose. Therefore, fructose potentially may contribute to changes in food palatability, as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of mutagenic compounds. ^[3]

Fructose and Fermentation

Fructose may be fermented by yeast or bacteria. Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have ^[4] Yeast enzymes convert sugar (glucose, or fructose) to ethanol and carbon dioxide. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Fermentation is accompanied by the release of carbon dioxide that causes foaming. ^[5] Colonic bacterial fermentation of fructose may cause gas, cramps, and diarrhea problems in people with fructose malabsorption. Malabsorption is a state arising from abnormality in Digestion or Absorption of food nutrients across the gastrointestinal(GI tract. ^[6]

Physical and Functional Properties

Relative Sweetness

The primary reason that fructose is used commercially in foods and beverages is because of its relative sweetness. It is the sweetest of all naturally occurring carbohydrates. Fructose is 1. 73 times sweeter than sucrose^[7][8] .

Figure 2 Relative Sweetness of Sugars and Sweeteners

The Sweetness Intensity Profile of Fructose The sweetness of fructose is perceived earlier than that of sucrose or dextrose, and the taste sensation reaches a peak (higher than sucrose) and diminishes more quickly than sucrose. Fructose can also enhance other flavors in the system^[9].

Sweetness Synergy Fructose exhibits a sweetness synergy effect when used in combination with other sweeteners. The relative sweetness of fructose blended with sucrose, aspartame, or saccharin is perceived to be greater than the sweetness calculated from individual components^[10].

Fructose Solubility and Crystallization

Compared to other sugars and sugar alcohols, fructose has the highest solubility. As a result, fructose is difficult to crystallize from an aqueous solution ^[11]. Sugar mixes containing fructose, such as candies, are softer than those containing other sugars because of the greater solubility of fructose ^[12].

Fructose Hygroscopicity and Humectancy Fructose is quicker to absorb moisture and slower to release it to the environment than sucrose, dextrose, or other nutritive sweeteners ^[13]. Fructose is an excellent humectant and retains moisture for a long period of time even at low relative humidity (RH). Relative humidity is a measurement of the amount of Water vapor that exists in a gaseous mixture of air and water Therefore, fructose can contribute to improved quality, better texture, and longer shelf life to the food products in which it is used ^[14].

Freezing Point Fructose has a greater effect on freezing point depression than disaccharides or oligosaccharides, which may protect the integrity of cell walls of fruit by reducing ice crystal formation. However, this characteristic may be undesirable in soft-serve or hard-frozen dairy desserts^[15].

Fructose and Starch Functionality in Food Systems

Fructose increases starch viscosity more rapidly and achieves a higher final viscosity than sucrose because fructose lowers the temperature required during gelatinizing of starch, causing a greater final viscosity ^[16].

Food Sources

The primary food sources of fructose are fruits, vegetables, and honey ^[17]. The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. The term " vegetable " generally means the edible parts of Plants The definition of the word is traditional rather than Scientific, however Honey is a sweet and Viscous fluid produced by Honey bees (and some other species and derived from the nectar of Flowers According to the Fructose exists in foods either as a free monosaccharide or bound to glucose as the disaccharide, sucrose. Monosaccharides (from Greek monos: single sacchar: sugar are the most basic unit of Carbohydrates They consist of one sugar and A disaccharide is a Sugar (a Carbohydrate) composed of two Monosaccharides 'Disaccharide' is one of the four chemical groupings of carbohydrates ( Solubility of Pure SucroseTemperature(Cg Fructose, glucose, and sucrose can all be present in a food; however, different foods will have varying levels of each of these three sugars.

The sugar content of common fruits and vegetables are presented in Table 1. In general, foods that contain free fructose have equal amount of free glucose. In other words, the ratio of fructose to glucose roughly equals 1:1. A value that is above 1 indicates higher proportion of fructose to glucose and vice versa. Some of the fruits have larger proportions of fructose to glucose compared to others. For example, apples and pears contain more than twice as much free fructose as glucose, while apricots contain less than a half of fructose than glucose. The apple is the pomaceous Fruit of the apple tree Species Malus domestica in the Rose family Rosaceae. A pear is a pomaceous Fruit produced by a tree of Genus Pyrus. The Apricot ( Prunus armeniaca, "Armenian plum" in Latin syn

Apple and pear juices are of particular interest to pediatricians due to the juices’ high concentration of free fructose relative to glucose, which can cause diarrhea in children. Pediatrics (also spelled paediatrics) is the branch of Medicine that deals with the medical care of Infants Children and Adolescents In Medicine, diarrhea, also spelled diarrhoea (see spelling differences) is frequent loose or liquid Bowel movements Acute diarrhea The cells of the small intestine, enterocytes, have lower affinity for fructose absorption compared with that for glucose and sucrose ^[18]. In Biology the small Intestine is the part of the Gastrointestinal tract (gut between the Stomach and the Large intestine, and comprises Enterocytes, or intestinal absorptive cells, are Simple columnar Epithelial cells found in the Small intestines and Colon. Unabsorbed fructose creates higher osmolarity in the small intestine, which draws water into the gastrointestinal tract, resulting in osmotic diarrhea. Osmolarity is a measure of the osmoles of solute per Liter of solution while the osmolality is a measure of the osmoles of Solute per Kilogram This phenomenon is discussed in greater details in Health Effects section. Health effects, health impacts or health risks are changes in Health resulting from exposure to a source

Table 1 also shows the amount of sucrose found in common fruits and vegetables. Solubility of Pure SucroseTemperature(Cg Sugar cane and sugar beet have a high concentration of sucrose, and are used for commercial preparation of pure sucrose. Sugarcane ( Saccharum) is a genus of 6 to 37 species (depending on taxonomic interpretation of tall perennial grasses (family Poaceae tribe Andropogoneae Sugar beet ( Beta vulgaris L a member of the Chenopodiaceae family is a plant whose root contains a high concentration of Sucrose. Extracted cane or beet juices are clarified from the impurities and concentrated by removing excess of water. The end product is 99. 9% pure sucrose. Solubility of Pure SucroseTemperature(Cg Sucrose containing sugars include common white granulated sugar, powdered sugar, as well as brown sugar ^[19]. Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Powdered sugar, also known as confectioner's sugar or icing sugar, is a very finely ground form of Sugar. Brown sugar is a Sucrose Sugar product with a distinctive brown color due to the presence of Molasses.

Table 1 – Sugar Content of Selected Common Plant Foods (g/100g)

Food Item	Total Carbohydrate	Total Sugars	Free Fructose	Free Glucose	Sucrose	Fructose / Glucose Ratio	Sucrose as a % of Total Sugars
Fruit
Apple	13. 8	10. 4	5. 9	2. 4	2. 1	2. 4	19. 9
Apricot	11. 1	9. 2	0. 9	2. 4	5. 9	0. 4	63. 5
Banana	22. 8	12. 2	4. 9	5. 0	2. 4	1. 0	2. 0
Dates	75. 0	63. 4	19. 6	19. 9	23. 8	1. 0	37. 6
Grapes	18. 1	15. 5	8. 1	7. 2	0. 2	1. 1	1. 0
Peach	9. 5	8. 4	1. 5	2. 0	4. 8	0. 8	56. 7
Pear	15. 5	9. 8	6. 2	2. 8	0. 8	2. 3	8. 0
Vegetables
Beet, Red	9. 6	6. 8	0. 1	0. 1	6. 5	1. 0	96. 2
Carrot	9. 6	4. 7	0. 6	0. 6	3. 6	0. 9	70. 0
Corn, Sweet	19. 0	3. 2	0. 5	0. 5	2. 1	1. 0	64. 0
Red Pepper, Sweet	6. 0	4. 2	2. 3	1. 9	0. 0	1. 2	0. 0
Onion, Sweet	7. 6	5. 0	2. 0	2. 3	0. 7	0. 9	14. 3
Sweet Potato	20. 1	4. 2	0. 7	1. 0	2. 5	0. 7	60. 3
Yam	27. 9	0. 5	tr	tr	tr	na	tr
Sugar Cane		13 - 18	0. 2 – 1. 0	0. 2 – 1. 0	11 - 16	1. 0	100
Sugar Beet		17 - 18	0. 1 – 0. 5	0. 1 – 0. 5	16 - 17	1. 0	100

Data obtained at http://www.nal.usda.gov/fnic/foodcomp/search/ ^[20] All data with a unit of g (gram) are based on 100 g of a food item

Fructose is also found in the synthetically manufactured sweetener, high-fructose corn syrup (HFCS). A sweetener is a Food additive which adds the Basic taste of Sweetness to a food artificial sweeteners are Sugar substitutes High-fructose corn syrup (HFCS is any of a group of Corn syrups that has undergone Enzymatic processing to increase its Fructose content and is then mixed Hydrolyzed corn starch is used as the raw material for production of HFCS. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Cornstarch, or cornflour, is the Starch of the Maize grain commonly known as Corn. Through the enzymatic treatment, glucose molecules are converted into fructose ^[21]. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins There are three types of HFCS, each with a different proportion of fructose. The most common are HFCS-42, HFCS-55, and HFCS-90. The number for each HFCS corresponds to the percentage of synthesized fructose present in the syrup. HFCS-90 has the highest concentration of fructose, and is typically used to manufacture HFCS-55; HFCS 55 is used as sweetener in soft drinks, while HFCS-42 is used in many processed foods and baked goods.

Commercial Sweeteners (% of Carbohydrate)

Sugar	Fructose	Glucose	Sucrose	Other Sugars
Granulated Sugar	(50)	(50)	100	0
Brown Sugar	1	1	97	1
HFCS-42	42	53	0	5
HFCS-55	55	41	0	4
HFCS-90	90	5	0	5
Honey	50	44	1	5
Maple Syrup	1	4	95	0
Molasses	23	21	53	3
Corn Syrup	0	35	0	0

Data obtained from Kretchmer, N. & Hollenbeck, CB (1991). Sugars and Sweeteners, Boca Raton, FL: CRC Press, Inc. ^[22] for HFCS, and USDA for fruits and vegetables and the other refined sugars. ^[23]

Cane and beet sugars have been used as the major sweetener in food manufacturing for centuries. However, with the development of HFCS, a significant shift occurred in the type of sweetener consumption. As seen in Figure 3, this change happened in the 70’s. Contrary to the popular believe, however, with the increase of HFCS consumption, the total fructose intake has not dramatically changed. Granulated sugar is 99. 9% pure sucrose, which means that it has equal ratio of fructose to glucose. The most commonly used HFCS, 42 and 55, have relatively equal ratio of fructose to glucose, with minor differences. HFCS has simply replaced sucrose as a sweetener. Therefore, despite the changes in the sweetener consumption, the ratio of glucose to fructose intake has remained relatively constant ^[24].

Figure 3 Adjusted U. S. Per Capita Refined Sugar Consumption

Digestion and Absorption

Fructose exists in foods as either a monosaccharide (free fructose) or as a disaccharide (sucrose). Free fructose does not undergo digestion; however when fructose is consumed in the form of sucrose, digestion occurs entirely in the upper small intestine. As sucrose comes into contact with the membrane of the small intestine, the enzyme sucrase catalyzes the cleavage of sucrose to yield one glucose and fructose unit. Fructose, passes through the small intestine, virtually unchanged, then enters the portal vein and is directed toward the liver.

Figure 4 The Hydrolysis of Sucrose to Glucose and Fructose by Sucrase

The mechanism of fructose absorption in the small intestine is not completely understood. Some evidence suggests active transport, because fructose uptake has been shown to occur against a concentration gradient. Active transport is the mediated process of moving particles across Biological membrane against the concentration gradient ^[25] However, the majority of research supports the claim that fructose absorption occurs on the mucosal membrane via facilitated transport involving GLUT5 transport proteins. Facilitated diffusion (or facilitated transport) is a process of Diffusion, a form of Passive transport facilitated by Transport proteins The GLUT5 is a Fructose transporter Fructose malabsorption or Dietary Fructose Intolerance is a dietary disability of the Small intestine, where the amount Since the concentration of fructose is higher in the lumen, fructose is able to flow down a concentration gradient into the enterocytes, assisted by transport proteins. Enterocytes, or intestinal absorptive cells, are Simple columnar Epithelial cells found in the Small intestines and Colon. Fructose may be transported out of the enterocyte across the basolateral membrane by either GLUT2 or GLUT5, although the GLUT2 transporter has a greater capacity for transporting fructose and therefore the majority of fructose is transported out of the enterocyte through GLUT2. GLUT 2 is a transmembrane carrier Protein and gene which is involved in passive glucose transport, especially the Renal glucose reabsorption.

Figure 5 Intestinal Sugar Transport Proteins

Capacity and rate of absorption

The absorption capacity for fructose in monosaccharide form ranges from less than 5g to 50g and adapts with changes in dietary fructose intake. Studies show the greatest absorption rate occurs when glucose and fructose are administered in equal quantities ^[26]. When fructose is ingested as part of the disaccharide sucrose, absorption capacity is much higher because fructose exists in a 1:1 ratio with glucose. Solubility of Pure SucroseTemperature(Cg It appears that the GLUT5 transfer rate may be saturated at low levels and absorption is increased through joint absorption with glucose ^[27]. GLUT5 is a Fructose transporter Fructose malabsorption or Dietary Fructose Intolerance is a dietary disability of the Small intestine, where the amount One proposed mechanism for this phenomenon is a glucose-dependent cotransport of fructose. In addition, fructose transfer activity increases with dietary fructose intake. The presence of fructose in the lumen causes increased mRNA transcription of GLUT5, leading to increased transport proteins. GLUT5 is a Fructose transporter Fructose malabsorption or Dietary Fructose Intolerance is a dietary disability of the Small intestine, where the amount High fructose diets have been shown to increase abundance of transport proteins within 3 days of intake. ^[28]

Malabsorption

Several studies have measured the intestinal absorption of fructose using hydrogen breath test^{[29] [30] [31] [32]} . A hydrogen breath test (or HBT) is used as a clinical medical Diagnosis for people with Irritable bowel syndrome, and common Food intolerances These studies indicate that fructose is not completely absorbed in the small intestine. When fructose is not absorbed in the small intestine, it is transported into the large intestine, where it is fermented by the colonic flora. Hydrogen is produced during the fermentation process and dissolves into the blood of the portal vein. This hydrogen is transported to the lungs, where it exchanged across the lungs and measurable by the hydrogen breath test. The colonic flora also produces carbon dioxide, short chain fatty acids, organic acids, and trace gasses in the presence of unabsorbed fructose ^[33]. Short chain fatty acids are a sub-group of Fatty acids with Aliphatic tails of less than eight carbons The presence of gasses and organic acids in the large intestine causes gastrointestinal symptoms such as bloating, diarrhea, flatulence, and gastrointestial pain ^[34]. Exercise can exacerbate these symptoms by decreasing transit time in the small intestine, resulting in a greater amount of fructose being emptied into the large intestine^[35].

Fructose Metabolism

All three dietary monosaccharaides are transported into the liver by the GLUT 2 transporter ^[36]. Fructose and galactose are phosphorylated in the liver by fructokinase (km = 0. Galactose (Gal (also called brain sugar) is a type of Sugar which is less sweet than Glucose. Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule Fructokinase (/fruc•to•ki•nase/) also known as D-fructokinase or D-fructose (D-mannose kinase is an enzyme of the Liver, Intestine, and Kidney cortex 5 mM) and galactokinase (km = 0. 8 mM). By contrast, glucose tends to pass through the liver (km of hepatic glucokinase = 10 mM) and can be metabolised anywhere in the body. Uptake of fructose by the liver is not regulated by insulin.

Fructolysis

Fructolysis can be divided into two main phases: The first phase is the synthesis of the trioses, dihydroxyacetone(DHAP) and glyceraldehyde; the second phase is the subsequent metabolism of these trioses either in the gluconeogenic pathway for glycogen replenishment and/or complete metabolism in the fructolytic pathway to pyruvate, which enters the Krebs cycle, and is converted to citrate and subsequently directed toward ’’de novo’’ synthesis of the free fatty acid palmitate ^[37]. Fructolysis refers to the metabolism of fructose from dietary sources A triose is a Monosaccharide containing three Carbon Atoms There are only two trioses an aldotriose ( Glyceraldehyde) and a Dihydroxyacetone (also known as DHA) is a simple Carbohydrate that is primarily used as an ingredient in Sunless tanning products Glyceraldehyde is a Triose Monosaccharide with Chemical formula C 3 H 6 O 3 Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such Pyruvic acid (CH3COCO2H is an alpha-keto acid. The Carboxylate Anion of pyruvic acid is known as pyruvate. The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle Citric acid is a weak organic Acid. It is a natural Preservative and is also used to add an acidic or sour taste to foods and Soft drinks Palmitic acid,CH3(CH214COOH or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated Fatty acids found in animals

The Metabolism of Fructose to DHAP and Glyceraldehyde

The first step in the metabolism of fructose is the phosphorylation of fructose to fructose 1-phosphate by fructokinase, thus trapping fructose for metabolism in the liver. Fructose 1-phosphate then undergoes hydrolysis by aldolase B to form DHAP and glyceraldehydes; DHAP can either be isomerized to glyceraldehyde 3-phosphate by triosephosphate isomerase or undergo reduction to glycerol 3-phosphate by glycerol 3-phosphate dehydrogenase. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Aldolase B is an Isoenzyme of Fructose 16-bisphosphate Aldolase ( Aldolase A) which is also capable of cleaving Fructose 1-phosphate In Chemistry isomerisation is the process by which one Molecule is transformed into another molecule which has exactly the same atoms but the atoms are rearranged The glyceraldehyde produced may also be converted to glyceraldehyde 3-phosphate by glyceraldehyde kinase or converted to glycerol 3-phosphate by glyceraldehyde 3-phosphate dehydrogenase. The metabolism of fructose at this point yields intermediates in the gluconeogenic and fructolytic pathways leading to glycogen synthesis as well as fatty acid and triglyceride synthesis.

Synthesis of glycogen from DHAP and Glyceraldehyde 3 Phosphate

The resultant glyceraldehyde formed by aldolase B then undergoes phosphorylation to glyceraldehyde 3-phosphate. Increased concentrations of DHAP and glyceraldehyde 3-phosphate in the liver drive the gluconeogenic pathway toward glucose and subsequent glycogen synthesis. It appears that fructose is a better substrate for glycogen synthesis than glucose and that glycogen replenishment takes precedence over triglyceride formation ^[38]. Once liver glycogen is replenished, the intermediates of fructose metabolism are primarily directed toward triglyceride synthesis.

Figure 6 The Metabolic Conversion of Fructose to Glycogen in the Liver

Synthesis of Triglyceride from DHAP and Glyceraldehyde 3 Phosphate

Carbons from dietary fructose are found in both the free fatty acid and glycerol moieties of plasma triglycerides. In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which High fructose consumption can lead to excess pyruvate production, causing a buildup of Krebs cycle intermediates ^[39]. Accumulated citrate can be transported from the mitochondria into the cytosol of hepatocytes, converted to acetyl CoA by citrate lyase and directed toward fatty acid synthesis ^[40]; ^[41]. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. Hepatocytes make up 70-80% of the Cytoplasmic mass of the Liver. Acetyl-CoA is an important molecule in metabolism used in many biochemical reactions Additionally, DHAP can be converted to glycerol 3-phosphate as previously mentioned, providing the glycerol backbone for the triglyceride molecule ^[42]. Triglycerides are incorporated into very low density lipoproteins (VLDL), which are released from the liver destined toward peripheral tissues for storage in both fat and muscle cells.

Figure 7 The Metabolic Conversion of Fructose to Triglyceride (TG) in the Liver

Health effects

Fructose absorption occurs via the GLUT-5^[43] (fructose only) transporter, and the GLUT2 transporter, for which it competes with glucose and galactose. GLUT5 is a Fructose transporter Fructose malabsorption or Dietary Fructose Intolerance is a dietary disability of the Small intestine, where the amount Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Galactose (Gal (also called brain sugar) is a type of Sugar which is less sweet than Glucose. A deficiency of GLUT 5 may result in excess fructose carried into the lower intestine. There, it can provide nutrients for the existing gut flora, which produce gas. The gut flora are the Microorganisms that normally live in the Digestive tract and can perform a number of useful functions for their hosts It may also cause water retention in the intestine. These effects may lead to bloating, excessive flatulence, loose stools, and even diarrhea depending on the amounts eaten and other factors. Bloating is any abnormal general Swelling, or increase in diameter of the abdominal area Flatulence is the production of a mixture of gases in the digestive tract of Mammals that are byproducts of the digestion process In Medicine, diarrhea, also spelled diarrhoea (see spelling differences) is frequent loose or liquid Bowel movements Acute diarrhea

Excess fructose consumption has been hypothesized to possibly cause insulin resistance, obesity,^[44] elevated LDL cholesterol and triglycerides, leading to metabolic syndrome. Insulin resistance is the condition in which normal amounts of Insulin are inadequate to produce a normal Insulin response from Fat, Muscle Obesity is a condition in which excess Body fat has accumulated to such an extent that health may be negatively affected Low-density lipoprotein ( LDL) is a type of Lipoprotein that transports Cholesterol and Triglycerides from the Liver to peripheral (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the Metabolic syndrome is a combination of medical disorders that increase the risk of developing Cardiovascular disease and diabetes. Short term tests, lack of dietary control, and lack of a non-fructose consuming control group are all confounding factors in human experiments. However, there are now a number of reports showing correlation of fructose consumption to obesity,^[45][46] especially central obesity which is generally regarded as the most dangerous type.

There is a concern with Diabetic 1 patients and the apparent low GI of fructose. Fructose gives as high a blood sugar spike as that obtained with glucose. In fact, GI only applies to high starch foods. The basic GI definition is chemically incorrect. This is because the body blood glucose response is "standardized" with 50g of glucose, while the GI Researchers use 50g of digestible carbohydrate as a reference quantity. Although all simple sugars are isomers, each have separate chemical properties. This is illustrated with pure fructose. In a study from The American Journal of Clinical Nutrition, "fructose given alone increased the blood glucose almost as much as a similar amount of glucose (78% of the glucose-alone area)". ^{[47][48][49][49][50]}

A study in mice suggests that fructose increases obesity. Obesity is a condition in which excess Body fat has accumulated to such an extent that health may be negatively affected ^[51]

One study concluded that fructose "produced significantly higher fasting plasma triacylglycerol values than did the glucose diet in men" and "if plasma triacylglycerols are a risk factor for cardiovascular disease, then diets high in fructose may be undesirable". (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the Cardiovascular disease or cardiovascular diseases refers to the class of diseases that involve the Heart or Blood vessels ( arteries and ^[52] Bantle et al. "noted the same effects in a study of 14 healthy volunteers who sequentially ate a high-fructose diet and one almost devoid of the sugar. "^[53]

Studies that have compared high fructose corn syrup (an ingredient in soft drinks sold in the US) to sucrose (common cane sugar) find that they have essentially identical physiological effects. High-fructose corn syrup (HFCS is any of a group of Corn syrups that has undergone Enzymatic processing to increase its Fructose content and is then mixed Soft drink is a beverage that does not contain Alcohol. Carbonated soft drinks are commonly known as soda soda pop pop, or Solubility of Pure SucroseTemperature(Cg Sugarcane ( Saccharum) is a genus of 6 to 37 species (depending on taxonomic interpretation of tall perennial grasses (family Poaceae tribe Andropogoneae For instance, Melanson et al (2006), studied the effects of HFCS and sucrose sweetened drinks on blood glucose, insulin, leptin, and ghrelin levels. Blood sugar, used in a physiological context is a misnomer and misleading Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance Leptin (Greek leptos meaning thin is a 16 kDa Ghrelin is a Hormone produced mainly by P/D1 cells lining the fundus of the human Stomach and epsilon cells of the Pancreas that stimulates They found no significant differences in any of these parameters. ^[54] This is not surprising since sucrose is a disaccharide which digests to 50% glucose and 50% fructose; while the high fructose corn syrup most commonly used on soft drinks is 55% fructose.

Fructose also chelates minerals in the blood. Chelation is the binding or complexation of a bi- or multidentate Ligand. This effect is especially important with micronutrients such as copper, chromium and zinc. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Since these solutes are normally present in small quantities, chelation of small numbers of ions may lead to deficiency diseases, immune system impairment and even insulin resistance, a component of type II diabetes. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc ^[55]

Fructose is often recommended for diabetics due to its glycemic index being significantly lower than both glucose, sucrose and starches. The Glycemic index (also glycaemic index) or GI is a measure of the effects of Carbohydrates on Blood glucose levels

"The medical profession thinks fructose is better for diabetics than sugar," says Meira Field, Ph. D. , a research chemist associated with the questionable Weston A. Price Foundation ^[56], "but every cell in the body can metabolize glucose. However, all fructose must be metabolized in the liver. The livers of the rats on the high fructose diet looked like the livers of alcoholics, plugged with fat and cirrhotic. "^[57] This is not entirely true as certain other tissues do use fructose directly, notably the cells of the intestine, and sperm cells (for which fructose is the main energy source).

Fructose is a reducing sugar, as are all monosaccharides. A reducing sugar is any sugar that in basic solution forms some Aldehyde or Ketone. The spontaneous addition of single sugar molecules to proteins, known as glycation, is a significant cause of damage in diabetics. Glycation (sometimes called non-enzymatic Glycosylation) is the result of a sugar molecule such as Fructose or Glucose, bonding to a Protein Fructose appears to be as dangerous as glucose in this regard and so does not seem to be a better answer for diabetes for this reason alone. ^[58] This may be an important contribution to senescence and many age-related chronic diseases. Senescence refers to the biological processes of a living Organism approaching an advanced age (i ^[59]

Fructose is used as a substitute for sucrose (composed of one unit each of fructose and glucose linked together with a relatively weak glycosidic bond) because it is less expensive and has little effect on measured blood glucose levels. Solubility of Pure SucroseTemperature(Cg In Chemistry, a glycosidic bond is a certain type of Functional group that joins a Carbohydrate (sugar molecule to another which may be another carbohydrate Often, fructose is consumed as high fructose corn syrup, which is corn syrup (glucose) that has been enzymatically treated by the enzyme glucose isomerase. High-fructose corn syrup (HFCS is any of a group of Corn syrups that has undergone Enzymatic processing to increase its Fructose content and is then mixed Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Glucose-6-phosphate isomerase, or phosphoglucose isomerase, is an Enzyme ( that catalyzes the conversion of Glucose-6-phosphate into Fructose-6-phosphate This enzyme converts a portion of the glucose into fructose thus making it sweeter. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. This is done to such a degree as to yield corn syrup with an equivalent sweetness to sucrose by weight. Corn syrup is a Syrup, made using Cornstarch as a feedstock and composed mainly of Glucose. Solubility of Pure SucroseTemperature(Cg While most carbohydrates have around the same amount of calories, fructose is sweeter and manufacturers can use less of it to get the same result. Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. Manufacturing (from Latin manu factura, "making by hand" is the use of tools and labor to make things for use or sale The free fructose present in fruits, their juice, and honey is responsible for the greater sweetness of these natural sugar sources. The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. Honey is a sweet and Viscous fluid produced by Honey bees (and some other species and derived from the nectar of Flowers According to the

Some studies point to fructose as key factors in hyperactivity and tooth decay in children.

Unlike glucose, fructose is almost entirely metabolized in the liver. "When fructose reaches the liver," says Dr. William J. Whelan, a biochemist at the University of Miami School of Medicine, "the liver goes bananas and stops everything else to metabolize the fructose. " Eating fructose as compared to glucose results in lower circulating insulin and leptin levels, and attenuation in the suppresion of ghrelin postprandially. Leptin (Greek leptos meaning thin is a 16 kDa Ghrelin is a Hormone produced mainly by P/D1 cells lining the fundus of the human Stomach and epsilon cells of the Pancreas that stimulates ^[60] These hormones are implicated in the control of appetite and satiety, and it is hypothesized that eating lots of fructose could increase the likelihood of weight gain. ^[61]

It has been suggested in a recent British Medical Journal study that high consumption of fructose is linked to gout. Gout (also called metabolic arthritis) is a disease created by a buildup of Uric acid. Cases of gout have risen in recent years, despite commonly being thought of as a Victorian disease, and it is suspected that the fructose found in sweet drinks is the reason for this. Culture The Victorian fascination with novelty resulted in a deep interest in the relationship between modernity and cultural continuities ^[62]

See also

• DMF (potential fructose-based biofuel)
• Fructose intolerance
• Fructose malabsorption
• Fructan (fructose polymer)
• Galactose
• Glucose
• Glycation
• High fructose corn syrup
• Hyperuricemia
• Seliwanoff's test
• Sucrose

References

External links

• Fructose
• Carbohydrate metabolism
• [1] Hereditary Fructose Intolerance
• [2] Sugars4Kids

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