Fermentative Process Optimization Of Gellan Gum And Its Application In Food

The gellan gum is a multifunctional gelling agent produced by the non-pathogenic strainSphingomonas paucimobilis. Gellan gum is a linear anionic exopolysaccharides (EPS) basedon a tetrasaccharide repeat unit composed of two molecules of D-glucose, one of L-rhamnoseand one of D-glucuronic acid. Gellan gum has unique characteristics and has manyapplications, particularly in the food, pharmaceutical, and biomedical fields. In this paper,according to the principles of fermentation optimization, a series of feasible approaches orstrategies were achieved to maximize gellan gum production during the processes ofoptimization of S. paucimobilis ATCC31461cultivation. Moreover, the rheological and gelproperties of different proportion of gellan gum-xanthan gum and gellan gum-carrageenanwere investigated to provide theoretical guidance for the application in the food. Finally, thecharacterization of carboxymethyl-gellan (CMGe) films, and CMGe and pullulan blends filmswere investigated to enlarge the application of gellan gum.The effect of H2O2-induced oxidative stress on gellan gum production and cell growthwere investigated. Gellan gum production was improved and cell growth was inhibited byH2O2. A multiple H2O2stresses with different concentrations were developed to optimizegellan gum production. A maximal gellan gum yield (22.52g/L), which was35.58%higherthan the control, was observed with2,2,3,4mmol/L H2O2added at6,12,18,24h,respectively. Moreover, the carbon flow diverted toward gellan synthesis with H2O2stresses.UDP-glucose pyrophosphorylase activity and glucosyltransferase activity were increased withH2O2stresses. This new strategy of multiple H2O2-induced oxidative stresses would be furtherapplied to gellan gum production in future study.The effects of different initial sucrose concentrations and temperatures on gellan gumbiosynthesis by S. paucimobilis ATCC31461were investigated. Lower sucrose concentrationsand higher temperatures were favorable for cell growth. Higher sucrose concentrations andlower temperatures promoted gellan gum production but retarded cell growth. Based on theseresults, a two-stage culture strategy was developed to improve gellan gum production. Duringthe first24h, S. paucimobilis was cultured in a pulse fed-batch mode with an initial sucroseconcentration10g/L. Ten grams per liter of sucrose were added at12h and24h, and thetemperature was controlled at33°C. Batch culture was performed, and the temperature wasreduced to28°C to achieve a high gellan accumulation. The two-stage culture strategyachieved the highest gellan production (22.61g/L) at60h that was35.71%higher than theresult of the best conventional batch operation (16.66g/L). Meanwhile, high gellan gum yieldwas related to high the content of unsaturated fatty acids, in the proportion of unsaturated andsaturated fatty acids in the cell membrane, UDPG-pyrophosphorylase activity andglucosyltransferase activity. Lastly, the purification of gellan gum was studied, and thepurified gellan gum was as well as the commercial samples.The rheological and gel properties of different proportion of gellan gum-xanthan gumand gellan gum-carrageenan mixtures were studied, and the interaction mechanism wasdiscussed. The results shown that the viscoelastic, the storage modulus G’ and loss modulusG" increased with increasing the proportion of xanthan gum. The addition of xanthan gum would improve the gellan gum-xanthan gum mixed system of gel elasticity, cohessiveness andwater holding capacity. These results shown that the two polymers might remain intimatelymixed and formed two separate gels permeating through one another, to give aninterpenetrating network structure. Meanwhile, G’ and G" enhanced with increasingcarrageenan in gellan gum-carrageenan mixed system. When the ratio of carrageenan andgellan gum was7:3, G’ and G" value reached the maximum, indicating that the system have acomplex interaction in the process of lower the temperature. G’ and G" increased withdecreasing temperature. The results suggested the initial complex system was athree-dimensional network structure formed by gellan gum, and gellan gum formed acontinuous network and carrageenan formed a discontinuous phase.In order to develop a water solubility material possessing transparent film,carboxymethyl gellan (CMGe) was prepared by the reaction of gellan gum (GG) with sodiumchloroacetate. The products were characterized by Fourier transform infrared (FTIR), Nuclearmagnetic resonance (NMR) spectroscopy and X-ray diffraction (XRD). The results showedthat the introduction of carboxymethyl groups improved the solubility of GG. The CMGefilms were prepared by using the casting solvent evaporation method. The properties ofCMGe film were investigated compared to GG films by thermogravimetric analysis (TGA),mechanical properties, water barrier properties, transparency and moisture sorption isotherm.CMGe film had well thermal stability, the lower tensile strength (TS) and higher elongation atbreak (EAB), water vapor permeability (WVP), and transparency in contrast to GG films. Theresults suggested that CMGe was good use in film application as food package.This manuscript described the detailed characterization of edible films made from twodifferent polysaccharides—CMGe and pullulan (Pu), added with glycerol. CMGe/Pu blendfilms with different ratios were developed, and their effects on films’physical properties wereassessed. FTIR spectroscopy techniques, TGA, XRD, and Scanning electron microscope(SEM) were used to highlight the interaction between the two polysaccharides. The resultssuggested that the interactions between CMGe and Pu existed, indicating that this twopolymers had excellent blend miscibility. Moisture sorption isotherms were also studied andGuggenheim-Anderson-de Boer (GAB) sorption models were tested to fit the experimentaldata. Changes in the sorption parameters, particularly such as the decrease in monolayermoisture content (Mo), reflected the trend of reduced hydration capacity with increasedaddition of Pu. The addition of Pu to CMGe improved the EAB, decreased the TS, decreasedvalues of WVP leading to an improvement of barrier properties of the films. Therefore,different CMGe/Pu ratios could be used to tailor edible films with enhanced barrier andmechanical properties.