Editing Propionic acid (section)

===Biotechnological <span class="anchor" id="Propionic acid fermentation"></span> ===
Biotechnological production of propionic acid mainly uses ''[[Propionibacterium]]'' strains.<ref>{{cite journal |doi=10.1007/s00253-017-8616-7 |title=Propionibacterium SPP.—source of propionic acid, vitamin B12, and other metabolites important for the industry |year=2018 |last1=Piwowarek |first1=Kamil |last2=Lipińska |first2=Edyta |last3=Hać-Szymańczuk |first3=Elżbieta |last4=Kieliszek |first4=Marek |last5=Ścibisz |first5=Iwona |journal=Applied Microbiology and Biotechnology |volume=102 |issue=2 |pages=515–538 |pmid=29167919 |pmc=5756557 |s2cid=23599974 }}</ref> However, large scale production of propionic acid by ''Propionibacteria'' faces challenges such as severe inhibition of end-products during cell growth and the formation of by-products (acetic acid and [[succinic acid]]).<ref>{{Cite journal|doi = 10.3109/07388551.2011.651428|pmid = 22299651|title = Microbial production of propionic acid from propionibacteria: Current state, challenges and perspectives|journal = Critical Reviews in Biotechnology|volume = 32|issue = 4|pages = 374–381|year = 2012|last1 = Liu|first1 = Long|last2 = Zhu|first2 = Yunfeng|last3 = Li|first3 = Jianghua|last4 = Wang|first4 = Miao|last5 = Lee|first5 = Pengsoon|last6 = Du|first6 = Guocheng|last7 = Chen|first7 = Jian|s2cid = 25823025}}</ref> One approach to improve productivity and yield during fermentation is through the use of cell immobilization techniques, which also promotes easy recovery, reuse of the cell biomass and enhances microorganisms' stress tolerance.<ref>{{cite journal | doi = 10.1007/s00253-015-6517-1| pmid = 25776062| title = A novel approach to monitor stress-induced physiological responses in immobilized microorganisms| journal = Applied Microbiology and Biotechnology| volume = 99| issue = 8| pages = 3573–3583| year = 2015| last1 = Alonso| first1 = Saúl| last2 = Rendueles| first2 = Manuel| last3 = Díaz| first3 = Mario| s2cid = 860853}}</ref> In 2018, 3D printing technology was used for the first time to create a matrix for cell immobilization in fermentation. Propionic acid production by ''Propionibacterium acidipropionici'' immobilized on 3D-printed nylon beads was chosen as a model study. It was shown that those 3D-printed beads were able to promote high density cell attachment and propionic acid production, which could be adapted to other fermentation bioprocesses.<ref>{{cite journal | doi = 10.1016/j.biortech.2017.10.087| pmid = 29136932| title = Cell immobilization on 3D-printed matrices: A model study on propionic acid fermentation| journal = Bioresource Technology| volume = 249| pages = 777–782| year = 2018| last1 = Belgrano| first1 = Fabricio dos Santos| last2 = Diegel| first2 = Olaf| last3 = Pereira| first3 = Nei| last4 = Hatti-Kaul| first4 = Rajni| bibcode = 2018BiTec.249..777B}}</ref> Other cell immobilization matrices have been tested, such as recycled-glass Poraver and fibrous-bed bioreactor.<ref>{{cite journal | doi = 10.1016/j.biortech.2012.05.079| pmid = 22728152| title = Batch- and continuous propionic acid production from glycerol using free and immobilized cells of Propionibacterium acidipropionici| journal = Bioresource Technology| volume = 118| pages = 553–562| year = 2012| last1 = Dishisha| first1 = Tarek| last2 = Alvarez| first2 = Maria Teresa| last3 = Hatti-Kaul| first3 = Rajni| bibcode = 2012BiTec.118..553D| s2cid = 29658955| url = http://lup.lub.lu.se/search/ws/files/4073436/4937831.pdf}}</ref><ref>{{cite journal | doi = 10.1002/bit.20473| pmid = 15977254| title = Enhanced propionic acid fermentation by ''Propionibacterium'' acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor| journal = Biotechnology and Bioengineering| volume = 91| issue = 3| pages = 325–337| year = 2005| last1 = Suwannakham| first1 = Supaporn| last2 = Yang| first2 = Shang-Tian}}</ref>

Alternative methods of production have been trialled, by genetically engineering strains of ''[[Escherichia coli]]'' to incorporate the necessary pathway, the Wood-Werkman cycle.<ref>{{cite journal |doi=10.1002/bit.27182 |title=Engineering Escherichia coli for propionic acid production through the Wood–Werkman cycle |year=2020 |last1=Gonzalez-Garcia |first1=Ricardo A. |last2=McCubbin |first2=Timothy |last3=Turner |first3=Mark S. |last4=Nielsen |first4=Lars K. |last5=Marcellin |first5=Esteban |journal=Biotechnology and Bioengineering |volume=117 |issue=1 |pages=167–183 |pmid=31556457 |s2cid=203438727 |doi-access=free }}</ref>