Editing Mochi (section)

== Chemistry and structural composition of glutinous rice ==
[[File:Amylose4.svg|thumb|The structure of amylose with alpha 1-4 glycosidic bonds]]
[[File:Dextrin skeletal.svg|thumb|The structure of amylopectin with alpha 1-4 and alpha 1-6 glycosidic bonds]]
[[Amylose]] and [[amylopectin]] are both components of starch and polysaccharides made from D-[[glucose]] units. The big difference between the two is that amylose is linear because it only has αlpha-1,4-[[Glycosidic bond|glycosidic]] bonds. Amylopectin, though, is a branched polysaccharide because it has αlpha-1,4-glycosidic bonds with occasional αlpha-1,6-glycosidic bonds<ref name=":1">Fredriksson, H et al. (1997). ''The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches.'' Elsevier Publications, Carbohydrate Polymers. 35, 119-134.</ref> around every 22 D-glucose units.<ref>{{Cite journal | doi=10.1002/pat.3501|title = Electrosprayed maize starch and its constituents (amylose and amylopectin) nanoparticles| journal=Polymers for Advanced Technologies| volume=26| issue=8| pages=917–923|year = 2015|last1 = Ghaeb|first1 = Maryam| last2=Tavanai| first2=Hossein| last3=Kadivar| first3=Mehdi}}</ref> Glutinous rice is nearly 100%<ref name=":0">{{Cite book | url=https://books.google.com/books?id=Anbz_whRM2YC&q=glutinous&pg=PP1 | title=Starch: Chemistry and Technology| isbn=9780080926551| last1=Bemiller| first1=James N.| last2=Whistler| first2=Roy L.| date=April 6, 2009| publisher=Academic Press}}</ref> composed of amylopectin and almost completely lacks its counterpart, amylose, in its starch granules. A nonglutinous rice grain contains amylose at about 10–30% weight by weight and amylopectin at about 70–90% weight by weight.<ref name=":1"/>

Glutinous or waxy type of starches occur in maize, sorghum, wheat, and rice. An interesting characteristic of glutinous rice is that it stains red when iodine is added, whereas nonglutinous rice stains blue.<ref name=":0" /> This phenomenon occurs when [[iodine]] is mixed with iodide to form tri-iodide and penta-iodide. Penta-iodide intercalates between the starch molecules and stains amylose and amylopectin blue and red, respectively.<ref>{{Cite web|url=https://www.applichem.com/fileadmin/produktinfo/a3505_de.pdf|title=Iodine-Potassium iodide - Solution|access-date=March 23, 2016|archive-date=April 23, 2016|archive-url=https://web.archive.org/web/20160423024935/https://www.applichem.com/fileadmin/produktinfo/a3505_de.pdf|url-status=dead}}</ref> The gelation and viscous texture of glutinous rice is due to amylopectin being more hygroscopic<ref>{{Cite journal|last1=Svagan|first1=Anna. J.|last2=Berglund|first2=Lars A.|last3=Jensen|first3=Poul|date=April 26, 2011|title=Cellulose Nanocomposite Biopolymer Foam—Hierarchical Structure Effects on Energy Absorption|journal=ACS Applied Materials & Interfaces|volume=3|issue=5|pages=1411–1417|doi=10.1021/am200183u|pmid=21520887}}</ref> than amylose, thus water enters the starch granule, causing it to swell, while the amylose leaves the starch granule and becomes part of a colloidal solution.<ref>{{Cite journal|last1=Hermansson|first1=Anne-Marie|last2=Svegmark|first2=Karin|date=November 1, 1996|title=Developments in the understanding of starch functionality|journal=Trends in Food Science & Technology|volume=7|issue=11|pages=345–353|doi=10.1016/S0924-2244(96)10036-4}}</ref> In other words, the higher the amylopectin content, the higher the swelling of the starch granule.<ref>{{Cite journal|last1=Laovachirasuwan|first1=Pornpun|last2=Peerapattana|first2=Jomjai|last3=Srijesdaruk|first3=Voranuch|last4=Chitropas|first4=Padungkwan|last5=Otsuka|first5=Makoto|date=June 15, 2010|title=The physicochemical properties of a spray dried glutinous rice starch biopolymer|journal=Colloids and Surfaces B: Biointerfaces|volume=78|issue=1|pages=30–35|doi=10.1016/j.colsurfb.2010.02.004|pmid=20307959}}</ref>

Though the amylopectin content plays a major role in the defined characteristic of viscosity in glutinous rice, factors such as heat also play a very important role in the swelling since it enhances the uptake of water into the starch granule significantly.<ref>{{Cite web|url=http://www.fao.org/docrep/w8079e/w8079e0h.htm|title=Dietary carbohydrate composition|website=www.fao.org|access-date=March 11, 2016}}</ref>

The high amylopectin content of waxy or glutinous starches is genetically controlled by the waxy or wax gene. Its quality of greater viscosity and gelation is dependent on the distribution of the amylopectin unit chains.<ref name=":1" /> Grains that have this gene are considered mutants, which explains why most of them are selectively bred to create a grain that is close to having or has a 0% amylose content.<ref name=":0" /> The table below summarizes the amylose and amylopectin content of different starches, waxy and nonwaxy:

{| class="wikitable"
|+'''Proportion of amylose and amylopectin in various starch sources'''<ref>{{Cite web|url=https://online.science.psu.edu/chem005_wd/node/7882|title=07-2: Structure of Starches {{!}} CHEM 005|website=online.science.psu.edu|access-date=March 14, 2016}}{{Dead link|date=April 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> 
! Starch
! Amylose %
! Amylopectin %
|-
|Potato
|20
|80
|-
|Sweet potato
|18
|82
|-
|Arrowroot
|21
|79
|-
|Tapioca
|17
|83
|-
|Corn (maize)
|28
|72
|-
|Waxy maize
|0
|100
|-
|Wheat
|26
|74
|-
|Rice (long grain)
|22
|78
|}

The soaking of the glutinous rice is an elemental step in the preparation of mochi, either traditionally or industrially. During this process, glutinous rice decreases in protein content as it is soaked in water. The chemicals that make up the flavour of plain or "natural" mochi are [[ethyl acetate]], [[ethanol]], [[2-Butanol|2-butanol]], [[Isobutanol|2 methyl 1-propanol]], [[1-Butanol|1-butanol]], [[isoamyl alcohol]], [[1-Pentanol|1-pentanol]] and propane acid.<ref>{{Cite journal|last=Lee|first=Yong-Hwan|date=2001|title=Changes in Chemical Composition of glutinous rice during steeping and Quality Properties of Yukwa|url=https://www.researchgate.net/publication/264181544|journal=Korean Journal of Food Science and Technology|access-date=March 13, 2016|display-authors=etal}}</ref>

Mochi is usually composed solely of glutinous rice, however, some variations may include the additions of salt, spices and flavorings such as cinnamon ([[cinnamaldehyde]]).<ref>{{Cite book|url=https://books.google.com/books?id=VHRP5mMfWQUC|title=The Whole Food Bible: How to Select & Prepare Safe, Healthful Foods|last=Kilham|first=Christopher|date=October 1, 1996|publisher=Inner Traditions / Bear & Co|isbn=9780892816262}}</ref> Food additives such as [[sucrose]], [[sorbitol]] or [[glycerol]] may be added to increase viscosity and therefore increase gelatinization. Additives that slow down retrogradation are not usually added since amylopectin has a very stable shelf life due to its high amylopectin content.<ref>{{Cite journal|last1=Ploypetchara|first1=Thongkorn|last2=Suwannaporn|first2=Prisana|last3=Pechyen|first3=Chiravoot|last4=Gohtani|first4=Shoichi|date=October 22, 2014|title=Retrogradation of Rice Flour Gel and Dough: Plasticization Effects of Some Food Additives|journal=Cereal Chemistry|volume=92|issue=2|pages=198–203|doi=10.1094/CCHEM-07-14-0165-R|issn=0009-0352}}</ref>