Editing Sugar (section)

== Chemistry ==

[[File:Saccharose2.svg|frame|[[Sucrose]]: a disaccharide of [[glucose]] (left) and [[fructose]] (right)]]

Scientifically, ''sugar'' loosely refers to a number of [[carbohydrate]]s, such as [[monosaccharide]]s, [[disaccharide]]s, or [[oligosaccharide]]s. Monosaccharides are also called "simple sugars", the most important being glucose. Most monosaccharides have a formula that conforms to {{chem|C|n|H|2n|O|n}} with n between 3 and 7 ([[deoxyribose]] being an exception). [[Glucose]] has the [[molecular formula]] {{chem|C|6|H|12|O|6}}. The names of typical sugars end with -''ose'', as in "glucose" and "[[fructose]]". Sometimes such words may also refer to any types of [[carbohydrate]]s soluble in water. The [[Open-chain compound|acyclic]] mono- and disaccharides contain either [[aldehyde]] groups or [[ketone]] groups. These [[carbonyl|carbon-oxygen]] double bonds (C=O) are the reactive centers. All [[saccharide]]s with more than one ring in their structure result from two or more monosaccharides joined by [[glycosidic bond]]s with the resultant loss of a molecule of water ({{chem|H|2|O}}) per bond.<ref name=Pigman>{{cite book |last=Pigman |first=Ward |author2=Horton, D. |title=The Carbohydrates: Chemistry and Biochemistry Vol 1A |editor=Pigman and Horton |edition=2nd |year=1972 |publisher=Academic Press |location=San Diego |isbn=978-0-12-556352-9 |pages=1–67}}</ref>

[[Monosaccharide]]s in a closed-chain form can form glycosidic bonds with other monosaccharides, creating disaccharides (such as [[sucrose]]) and [[polysaccharide]]s (such as [[starch]] or [[cellulose]]). [[Enzymes]] must hydrolyze or otherwise break these glycosidic bonds before such compounds become [[metabolism|metabolized]]. After digestion and absorption the principal monosaccharides present in the blood and internal tissues include glucose, fructose, and galactose. Many [[pentose]]s and [[hexose]]s can form [[Heterocyclic compound|ring structures]]. In these closed-chain forms, the aldehyde or ketone group remains non-free, so many of the reactions typical of these groups cannot occur. Glucose in solution exists mostly in the ring form at [[chemical equilibrium|equilibrium]], with less than 0.1% of the molecules in the open-chain form.<ref name=Pigman/>

=== Natural polymers ===

[[Biopolymer]]s of sugars are common in nature. Through photosynthesis, plants produce [[glyceraldehyde-3-phosphate]] (G3P), a phosphated 3-carbon sugar that is used by the cell to make monosaccharides such as glucose ({{chem|C|6|H|12|O|6}}) or (as in cane and beet) sucrose ({{chem|C|12|H|22|O|11}}). Monosaccharides may be further converted into [[polysaccharides#Structural polysaccharides|structural polysaccharides]] such as [[cellulose]] and [[pectin]] for [[cell wall]] construction or into energy reserves in the form of [[polysaccharides#Storage polysaccharides|storage polysaccharides]] such as starch or [[inulin]]. Starch, consisting of two different polymers of glucose, is a readily degradable form of chemical [[potential energy|energy]] stored by [[cell (biology)|cells]], and can be converted to other types of energy.<ref name=Pigman/> Another polymer of glucose is cellulose, which is a linear chain composed of several hundred or thousand glucose units. It is used by plants as a structural component in their cell walls. Humans can digest cellulose only to a very limited extent, though [[ruminant]]s can do so with the help of [[Symbiosis|symbiotic]] bacteria in their gut.<ref>{{cite journal |doi=10.1007/BF01089198 |last1=Joshi |first1=S |last2=Agte |first2=V |title=Digestibility of dietary fiber components in vegetarian men |journal=Plant Foods for Human Nutrition (Dordrecht, Netherlands) |volume=48 |issue=1 |pages=39–44 |year=1995 |pmid=8719737|s2cid=25995873 }}</ref> [[DNA]] and [[RNA]] are built up of the monosaccharides [[deoxyribose]] and [[ribose]], respectively. Deoxyribose has the formula {{chem|C|5|H|10|O|4}} and ribose the formula {{chem|C|5|H|10|O|5}}.<ref>{{Merck11th|8205}}.</ref>

=== Flammability and heat response ===

[[File:Sugar 2xmacro.jpg|thumb|Magnification of grains of refined [[sucrose]], the most common [[free sugar]]]]

Because sugars burn easily when exposed to flame, the handling of sugars risks [[dust explosion]]. The risk of explosion is higher when the sugar has been milled to superfine texture, such as for use in [[chewing gum]].<ref>{{Cite book|url=https://books.google.com/books?id=vmsoDwAAQBAJ&pg=PT120|title=The Science of Sugar Confectionery|last=Edwards|first=William P.|date=9 November 2015|publisher=Royal Society of Chemistry|isbn=978-1-78262-609-1|page=120|language=en}}</ref> The [[2008 Georgia sugar refinery explosion]], which killed 14 people and injured 36, and destroyed most of the refinery, was caused by the ignition of sugar dust.<ref>{{cite news|title=CSB Releases New Safety Video, "Inferno: Dust Explosion at Imperial Sugar"|date=7 October 2009|work=[[U.S. Chemical Safety and Hazard Investigation Board]]|location=Washington, D.C.|access-date=17 May 2021|url=https://www.csb.gov/csb-releases-new-safety-video-inferno-dust-explosion-at-imperial-sugar/|archive-date=24 April 2020|archive-url=https://web.archive.org/web/20200424011424/https://www.csb.gov/csb-releases-new-safety-video-inferno-dust-explosion-at-imperial-sugar/|url-status=live}}</ref>

In its culinary use, exposing sugar to heat causes [[caramelization]]. As the process occurs, [[Volatility (chemistry)|volatile]] chemicals such as [[diacetyl]] are released, producing the characteristic [[caramel]] flavor.<ref>{{cite journal |title=Characteristics of the Thermal Degradation of Glucose and Maltose Solutions |journal=Prev Nutr Food Sci |date=2015 |pmid=26175997 |pmc=4500512 |last1=Woo |first1=K. S. |last2=Kim |first2=H. Y. |last3=Hwang |first3=I. G. |last4=Lee |first4=S. H. |last5=Jeong |first5=H. S. |volume=20 |issue=2 |pages=102–9 |doi=10.3746/pnf.2015.20.2.102 }}</ref>