Glucose

Glucose (Glc), a Monosaccharide (or simple Sugar ), is one of the most important Carbohydrate s. The cell uses it as a source of energy and metabolic intermediate. Glucose is one of the main products of Photosynthesis and starts Cellular Respiration . The natural form (D-glucose) is also referred to as '''dextrose''', especially in the food industry. This article deals with the D-form of glucose (The mirror-image of the molecule is called L-glucose. See also '''''Isomers'''''-section below)

STRUCTURE

Glucose contains six Carbon Atom s and an Aldehyde group and is therefore referred to as an aldo Hexose . The glucose molecule can exist in an open-chain (acyclic) and ring (cyclic) form, the latter being the result of an intramolecular reaction between the aldehyde C atom and the C-5 Hydroxyl group to form an intramolecular Hemiacetal . In water solution both forms are in equilibrium, and at PH 7 the cyclic one is the predominant. As the ring contains 5 carbon and one oxygen atoms, which resembles the structure of Pyran , the cyclic form of glucose is also referred to as glucopyranose. In this ring, each carbon is linked to an hydroxyl side group with the exception of the fifth atom, which links to a sixth carbon atom outside the ring, forming a CH₂OH group.

Isomers

Glucose has 4 optic centers which means that in theory glucose can have 15 Optical Stereoisomers . Only 7 of these are found in living organisms, and of these Galactose (Gal) and Mannose (Man) are the most important. These eight isomers (including glucose itself) are all Diastereoisomer s in relation to each other and all belong to the D-series .

An additional asymmetric center at C-1 (called ''the anomeric carbon atom'') is created when glucose cyclizes and two ring structures, called ''. to Haworth Projection .]]

PRODUCTION

Natural

#Glucose is one of the products of Photosynthesis in Plants and some Prokaryote s.
#In animals and fungi, glucose is the result of the breakdown of Glycogen , a process known as Glycogenolysis . In plants - the breakdown substrate is Starch .
#In animals, glucose is synthesized in the Liver and Kidney s from non-carbohydrate intermediates, such as Pyruvate and Glycerol , by a process known as Gluconeogenesis .

Commercial

Glucose is produced commercially via the Enzymatic Hydrolysis of Starch . Many crops can be used as the source of starch. Maize , Rice , Wheat , Potato , Cassava , Arrowroot , and Sago are all used in various parts of the world. In the United States , Cornstarch (from maize) is used almost exclusively.

This enzymatic process has two stages. Over the course of 1-2 hours near 100 °C, these enzymes hydrolyze starch into smaller carbohydrates containing on average 5-10 glucose units each. Some variations on this process briefly heat the starch mixture to 130 °C or hotter one or more times. This heat treatment improves the solubility of starch in water, but deactivates the enzyme, and fresh enzyme must be added to the mixture after each heating.

In the second step, known as ''saccharification'', the partially hydrolyzed starch is completely hydrolyzed to glucose using the Glucoamylase enzyme from the Fungus '' Aspergillus Niger ''. Typical reaction conditions are PH 4.0–4.5, 60 °C, and a carbohydrate concentration of 30–35% by weight. Under these conditions, starch can be converted to glucose at 96% yield after 1–4 days. Still higher yields can be obtained using more dilute solutions, but this approach requires larger reactors and processing a greater volume of water, and is not generally economical. The resulting glucose solution is then purified by Filtration and concentrated in a Multiple-effect Evaporator . Solid D-glucose is then produced by repeated Crystallization s.

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Glucose