黄原胶发酵液纯化精制研究

溶剂法直接提取的黄原胶产品含有大量菌体蛋白和色素杂质,总氮含量高、透明度差、色泽暗深。通过中性蛋白酶处理发酵液,使成品含氮量下降５６．５％;通过Ｎａ２ＳＯ３漂白液,使产品色泽大为改善。实验得出最佳酶解条件：发酵液稀释１倍,温度４４℃、ｐＨ７,加酶量１００ｕ／ｇ发酵液,作用时间２．５ｈ;最佳Ｎａ２ＳＯ３漂白条件：温度２０￣３０℃,ｐＨ５￣６,Ｎａ２ＳＯ３用量为１％（ｗ／ｗ）,作用时间１￣１．５ｈ。     

槐豆胶与黄原胶的协效性研究

对槐豆胶与黄原胶的协效性进行了研究,结果表明,槐豆胶和黄原胶有较高的协效性,其最佳配比（重量比）为2：8;当混合液浓度达到0.5%-0.6%时形成凝胶,因此槐豆胶可作为黄原胶的增稠剂和凝胶剂。     

Synergistic interaction between xanthan and guar gum

The non-Newtonian behavior and dynamic viscoelasticity of a series of aqueous mixtures of xanthan and guar gum were measured with a rheogoniometer. At a concentration of 0.2% of total gums, gelation did not occur at room temperature but occurred at a low temperature (0°). A much stronger interaction was observed with a mixture of deacetylated xanthan than that with native xanthan. The maximum dynamic modulus was obtained when the ratio of xanthan to guar gum was 2:1. The transition temperatures of dynamic viscoelasticity for mixtures with native and deacetylated xanthan were observed at 25 and 30°, respectively. It was concluded that the side chains of the guar gum molecular prevent an intermolecular interaction with the side chains of the xanthan molecule. An intermolecular interaction between xanthan and guar gum at low temperature might be promoted between the periphery of the side chains of the xanthan molecule and the backbone of the guar gum molecule and dissociation takes place at the transition temperature.     

Hybrid modeling of xanthan gum bioproduction in batch bioreactor

This work is focused on hybrid modeling of xanthan gum bioproduction process by Xanthomonas campestris pv. mangiferaeindicae. Experiments were carried out to evaluate the effects of stirred speed and superficial gas velocity on the kinetics of cell growth, lactose consumption and xanthan gum production in a batch bioreactor using cheese whey as substrate. A hybrid model was employed to simulate the bio-process making use of an artificial neural network (ANN) as a kinetic parameter estimator for the phenomenological model. The hybrid modeling of the process provided a satisfactory fitting quality of the experimental data, since this approach makes possible the incorporation of the effects of operational variables on model parameters. The applicability of the validated model was investigated, using the model as a process simulator to evaluate the effects of initial cell and lactose concentration in the xanthan gum production.     

Kinetic analysis of growth and xanthan gum production with Xanthomonas campestris on sucrose, using sequentially consumed nitrogen sources

A batch fermentation strategy using Xanthomonas campestris ATCC 13951 for xanthan gum production has been established in which all essential medium components are supplied at the onset. This has been achieved using sucrose as sole sugar feedstock. Sequential consumption of nitrogen sources (soybean hydrolysates, ammonium and nitrate salts) was observed to facilitate the further optimisation of the medium. Biomass accumulation was limited by phosphate availability. Xanthan yields of more than 60% (grams of xanthan per gram of sugar) have been obtained with constant acetyl content. However, pyruvyl substitution decreased as the growth rate declined, due to the metabolic constraints specific to phosphate depletion. High rates of carbon conversion into xanthan were observed throughout the culture and the ATP/ADP ratio was not affected by the decline in the specific growth rate.     

Oligosaccharides produced by partial acetolysis of xanthan gum

Partial acetolysis of the extracellular polysaccharide from Xanthomonas campestris gives the constituent monosaccharides, cellobiose, and three mannose-containing neutral oligosaccharides thought to be derived from the branch points of the polysaccharide. The structural analyses of these oligosaccharides provide further evidence for the presence of β-D-glucopyranosyl and α-D-mannopyranosyl linkages in the polymer.     

pH-Dependent interaction between sodium caseinate and xanthan gum

Xanthan gum and sodium caseinate are used to improve stability and texture of food. To investigate interactions between them, the effects of pH on structure of sodium caseinate–xanthan gum complex were analyzed. HCl titration showed that the absorbance of the mixture was different from that of sodium caseinate alone throughout the acidification, and that syneresis in the mixture was delayed in acidic pH. Rennet digestion clarified that xanthan gum retarded degradation of κ-casein at pH 2.7. Atomic force microscopy revealed that xanthan gum interaction with sodium caseinate was pH-dependent. Sodium caseinate particles were individually bound with xanthan gum at pH 6.6, and a side-by-side aggregation of sodium caseinate along xanthan gum was observed at pH 4.2. The mixture formed a network composed of rod-like fibers at pH 2.7. These results indicate that hydrophobic and electrostatic interactions play a role in the complex formation at neutral and acidic pH, respectively.     

Mechanistic analysis of xanthan gum production in a stirred tank

The overall effect of agitation on xanthan gum production by Xanthomonas campestris ATCC13951 in a stirred vessel was mechanistically analyzed considering local variation of the specific production rate due to variation of shear stress in the vessel. The whole liquid volume in a fermentor was roughly divided into three regions; the micromixing region around the impeller with high shear stress, the macromixing region dominated by a circulating flow and the stagnant region. The value of the shear rate was first ascertained by experiments in order to obtain a picture of shear rate variation in a radial direction from the impeller, and the equivalence between the volumes of the high shear stress region and micromixing region was confirmed. The shear stress obtained using a correlation between the shear rate at the impeller tip and Reynolds number of Wichterle et al. was used as a representative of the shear stress in the micromixing region, and the shear stress estimated by use of an empirical correlation between the average shear rate in a fermentor and agitation speed derived by Metzner et al. was adopted as a representative of the shear stress in the macromixing region. The information about the circulation time distribution was also used to take into account oxygen deficiency during circulation of liquid elements in the macromixing region, considering that oxygen from the gas phase was supplied mainly in the high shear region. The calculated values of xanthan gum concentrations which were obtained by the proposed simulation method agreed well with the experimental data in the time course of xanthan gum production at various agitation speeds. Experimental results of the relationship between the overall specific production rate and ND (N, agitation speed, and D, impeller diameter) was also verified by the proposed method.     

Chemical modification of xanthan gum to increase dissolution rate

Xanthan gum is modified with formaldehyde to improve the dissolution rate. The FT-IR spectra and the X-ray diffraction spectra both show that chemical modification reduces intermolecular interactions and crystallinity. Viscosity measurements show that the chemically modified gum dissolves more rapidly than before.     

AFM studies on gelation mechanism of xanthan gum hydrogels

The effect of annealing on xanthan gum molecules was investigated using atomic force microscopy (AFM). The values of height and width of xanthan gum molecules in AFM images are ca. 1 nm, which strongly indicates that xanthan gum molecules extended on the mica surface are in mono- or double layers. When xanthan gum aqueous solution was annealed, a network structure was observed. In contrast, a network structure was not observed for non-annealed solution. AFM images provide direct information concerning oscillational change of the network structure. It is concluded that xanthan gum molecular chains in aqueous solution aggregate and dissociate in an oscillational manner with increasing annealing time and that a homogeneous network structure was formed by annealing at 40 °C for 24 h.     

Impact of the extrusion process on xanthan gum behaviour

Processing xanthan gum by extrusion and subsequent drying produces a biopolymer showing particulate, rather than molecular behaviour in aqueous solution. This form of xanthan disperses very readily to give a viscosity that is strongly dependent on salt concentration. On heating above the temperature of the order-disorder transition as determined by calorimetry, there is a viscosity transition that is indicative of the irreversible loss of the particulate structure. It is suggested that the extrusion process melts and aligns xanthan macromolecules. On cooling reordering will occur but in the highly concentrated environment in the extruder ( approximately 45% water w/w), inter-molecular association between neighbouring macromolecules cannot proceed to completion due to kinetic trapping. As a consequence a network structure is created maintained by associations involving ordered regions. A xanthan solution can be prepared from this particulate material by dispersing and subsequent heating far more readily than can be achieved with non-processed xanthan.     

Productivity improvement in xanthan gum fermentation using multiple substrate optimization

A novel and more comprehensive formulation of the optimal control problem that reflects the operational requirements of a typical industrial fermentation has been proposed in this work. This formulation has been applied to a fed-batch bioreactor with three control variables, i.e., feed rates of carbon source, nitrogen source, and an oxygen source, to result in a 148.7% increase in product formation. Xanthan gum production using Xanthomonas campestris has been used as the model system for this optimization study, and the liquid-phase oxygen supply strategy has been used to supply oxygen to the fermentation. The formulated optimization problem has several constraints associated with it due to the nature of the system. A robust stochastic technique, differential evolution, has been used to solve this challenging optimization problem. The infinite dimensional optimization problem has been approximated to a finite dimensional one by control vector parametrization. The state constraints that are path constraints have been addressed by using penalty functions and by integrating them over the total duration to ensure a feasible solution. End point constraints on final working volume of the reactor and on the final residual concentrations of carbon and nitrogen sources have been included in the problem formulation. Further, the toxicity of the oxygen source, H(2)O(2), has been addressed by imposing a constraint on its maximum usable concentration. In addition, the initial volume of the bioreactor contents and feed concentrations have been handled as decision variables, which has enabled a well-grounded choice for their values from the optimization procedure; adhoc values are normally used in the industry. All results obtained by simulation have been validated experimentally with good agreements between experimental and simulated values.     

The characterization of a viscoelasticity parameter and other rheological properties of various xanthan gum fermentation broths and solutions

Viscoelasticity has important implications in mass transfer and mixing processes. Previous studies regarding to the viscoelastic behaviour of xanthan solutions have been carried out with diluted solutions or they have not covered a wide range of polymer concentrations. In this study, it was shown that the first normal stress difference measured in fermentation broths is highly dependent on shear rate, and this viscoelastic level is modified by the heat treatment to which the broths are subjected as a postfermentative procedure. The viscoelasticity level is different for xanthan solutions prepared with products arising from different sources and for fermentation broths before the heat treatment, if compared with that measured in end-products. In general, the higher the polymer concentration, the higher the viscoelasticity (expressed as first normal stress difference or Weissenberg number). The addition of a biocide, the change in ionic strength and the addition of sucrose to the xanthan solutions, lead to significant changes in the first normal stress difference.List of Symbols A Pa.S^b constant in first normal stress difference power law (N ₁= ) - b constant in first normal stress difference power law (N ₁= ) - c kg m^–3 polymer concentration - K Nsⁿ m^–2 consistency index - N ₁ Pa first normal stress difference - n flow behaviour index - Wi Weissenberg number,N ₁/ - s^–1 shear rate - Pa shear stress - _y Pa Yield stress     

黄原胶发酵培养基优化研究

分别用单因素法和正交试验法对野油菜黄单胞菌J-12的发酵培养基成分进行研究。得到的最优培养基配方为:4％玉米淀粉、0.3％鱼粉、0.3％豆饼粉、0.3％CaCO_3、0.5％KH_2PO_4、0.25％MgSO_4、0.025％FeSO_4、0.025％柠檬酸,接种量5％。在消前pH7.2～7.5,发酵温度28℃,摇床转速180r/min,发酵时间72h的实验条件下,发酵液粘度为8740mPa·s,采用酒精直接沉淀法提取黄原胶的产率达2.91％,产品的丙酮酸含量3.32％。     

微波诱变提高黄原胶的主要理化性能

用微波诱变黄原胶产生菌－野油采黄单孢菌,得到产胶量,胶粘度,抗盐性,pH稳定性及温度稳定性都高于出发株的P402－21突变株,P402－21的产胶浓度为3．484％,1％胶粘度为1673cp,能耐受1％－11％,NaCl,在pH4-14范围内稳定,25－100摄氏度胶粘度没有明显的改变。     

Study of the reaction of grafting acrylamide onto xanthan gum

The present study aimed to study the reaction conditions of grafting of acrylamide on xanthan gum. It was analyzed the influence of reaction conditions, mainly type of initiator activation, initiator concentration and initiator/acrylamide ratio, on graft parameters and copolymer properties. Potassium persulfate was employed as an initiator and heating or N,N,N',N'-tetramethylethylenediamine was used to activate the initiator. Reaction time and initiator concentration were varied and final values for grafting percentage and grafting efficiency were the same for both methods, whereas speed in reaching these values differs from one technique to another. We found that reaction time was inversely proportional to intrinsic viscosity, likely due to main chain degradation promoted by potassium persulfate (KPS); furthermore, the increasing in the KPS concentration lowers grafting percentage, acrylamide conversion and chain degradation, possibly as a result of O(2) formation at high KPS concentrations.     

黄原胶生产菌株XCCNAU—92的选育

从野生型甘蓝黑腐黄单胞菌中筛选出XCCNAU—01作为育种的出发菌株。用硫酸二乙酯和氯化锂复合诱变得系列突变体,经平板、摇瓶发酵必传代试验筛选出黄原胶生产菌株XCCNAU－92。对蔗糖、玉米淀粉等碳源皆有较强的利用能力,当以蔗糖为碳源时,30℃,102r／m发酵72h,产胶量达36．25g／kg,提高12．9％,粘度达17200cp,增加43．3％,碳源转化率达72．5％。