title: Structure of xanthan gum and cell ultrastructure at different times of alkali stress.
abstract: The effect of alkali stress on the yield, viscosity, gum structure, and cell ultrastructure of xanthan gum was evaluated at the end of fermentation process of xanthan production by Xanthomonas campestris pv. manihotis 280-95. Although greater xanthan production was observed after a 24h-alkali stress process, a lower viscosity was observed when compared to the alkali stress-free gum, regardless of the alkali stress time. However, this outcome is not conclusive as further studies on gum purification are required to remove excess sodium, verify the efficiency loss and the consequent increase in the polymer viscosity. Alkali stress altered the structure of xanthan gum from a polygon-like shape to a star-like form. At the end of the fermentation, early structural changes in the bacterium were observed. After alkali stress, marked structural differences were observed in the cells. A more vacuolated cytoplasm and discontinuities in the membrane cells evidenced the cell lysis. Xanthan was observed in the form of concentric circles instead of agglomerates as observed prior to the alkali stress.
authors.affiliation: School of Chemistry and Food, Federal University of Rio Grande, RS, Brazil. Electronic address: mmluvielmo@gmail.com.
authors.forename: Márcia de Mello
authors.initials: Mde M
authors.lastname: Luvielmo
authors.affiliation: Center of Chemical, Pharmaceutical and Food Sciences, Universidade Federal de Pelotas, RS, Brazil.
authors.forename: Caroline Dellinghausen
authors.initials: CD
authors.lastname: Borges
authors.affiliation: Department of Food Sciences, Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas, SP, Brazil.
authors.forename: Daniela de Oliveira
authors.initials: Dde O
authors.lastname: Toyama
authors.affiliation: Center of Technological Development, Biopolymeres, Universidade Federal de Pelotas, Pelotas, RS, Brazil.
authors.forename: Claire Tondo
authors.initials: CT
authors.lastname: Vendruscolo
authors.affiliation: Department of Food Sciences, Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas, SP, Brazil.
authors.forename: Adilma Regina Pippa
authors.initials: AR
authors.lastname: Scamparini
mesh_terms: D000468:Alkalies / Q000633:toxicity*; D002462:Cell Membrane / Q000648:ultrastructure; D003593:Cytoplasm / Q000648:ultrastructure; D015388:Organelles / Q000648:ultrastructure; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000378:metabolism*; D013312:Stress, Physiological; D016959:Xanthomonas campestris / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure*
chemical_list: D000468:Alkalies; D011135:Polysaccharides, Bacterial; C002563:xanthan gum
keywords: Alkali stress; Scanning electron microscopy; Transmission microscopy; Xanthan production; Xanthomonas campestris