Abstract
Zymomonas mobilis was immobilized using a cell suspension fixed to 8.6 x 107 CFU mL-1 by spectrophotometry. This biomass was suspended in sodium alginate solution (3%) that was dropped with a hypodermic syringe into 0.2 M calcium chloride solution. Was test two initial pH of fermentation medium (4 and 5) and different sucrose concentrations 15, 20, 25, 30 and 35% at 30˚C, without stirring for 24, 48, 72 and 96 hours. The levan production to pH 4 was high in sucrose 25% for 24 (16.51 g L-1) and 48 (15.31 g L-1) hours. The best values obtained to pH 5 was in sucrose 35% during 48 (22.39 g L-1) and 96 (23.5 g L-1) hours, respectively. The maximum levan yield was 40.8% and 22.47% in sucrose 15% to pH 4 and 5, respectively. Substrate consumption to pH 4 was bigger in sucrose 15 (56.4%) and 20% (59.4%) and to pH 5 was in 25 (68.85%) and 35% (64.64%). In relation to immobilization efficiency, Zymomonas mobilis showed high adhesion and colonization in support, indicated by cell growth increased from 107 to 109 CFU mL-1 during fermentation time.
Highlights
Levan biopolymer is composed by fructose units linked in (2-6), linear or branched form
In front of the necessity to develop technologies that allow increasing levan production and availability levan for commercial level, using raw materials of easy manipulation, this study aimed to evaluate pH effect in levan production by Zymomonas mobilis cells CCT4494 immobilized in alginate spheres and monitor cell growth in alginate beads
The higher production was observed with initial pH adjusted to 5 in sucrose concentration of 35% with 22.39 and 23.5 g L-1 of levan in 48 and 96 hours of fermentation, respectively
Summary
Levan biopolymer is composed by fructose units linked in (2-6), linear or branched form. It is synthesized by various microorganisms, Zymomonas mobilis, in culture medium with sucrose, yeast extract and mineral salts (ERNANDES; GARCIA-CRUZ, 2010; SWINGS; DE LEY, 1977). In food industry this polysaccharide has applications as stabilizer, thickener, flavor and color fixative, fat substitute, sweetening power, when hydrolyzed to fructose. Industrial scale for levan production is an alternative to replace xanthan and dextran gums, used widely in food that have high production cost (ERNANDES; GARCIA-CRUZ, 2005)
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