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排序方式: 共有64条查询结果,搜索用时 15 毫秒
1.
黄单胞杆菌XC—82,R5二步发酵工艺研究 总被引:2,自引:0,他引:2
通过对黄单胞杆菌XC-82,R5株的黄原胶二步发酵工艺研究,针对菌株在生长时期与产胶时期不同培养条件的需求,确定了两个阶段各自适宜的培养基组成,温度,pH值条件,实验表明,当流加稀释率为5时,二步发酵生产可达到了较高水平,其产胶量较传统的间歇发酵提高31%。 相似文献
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Seyed Mohammad Taghi GharibzahediSeyed Mohammad Mousavi Manouchehr HamediFaramarz Khodaiyan Seyed Hadi Razavi 《Carbohydrate polymers》2012,87(2):1611-1619
The susceptibility of lipids to oxidation is one of the most fundamental problems in oil-in-water emulsions. A response surface methodology 5-level-3-factor central-composite rotatable design was applied to study the effects of key formula ingredients including walnut oil (WO, 3-6%, w/w), gum arabic (GA, 5-10%, w/w) and xanthan gum (XG, 0.05-0.15%, w/w) on lipid oxidation in walnut-beverage emulsions. During 30 days’ storage, the oxidation process was monitored by evaluating the peroxide value, anisidine value and total oxidation (Totox) value in different emulsion formulations. Use of XG as a stabilizer at high concentrations considerably inhibited the oxidation of WO in the prepared emulsions. The experimental data were satisfactorily fitted to quadratic models using multiple regression analysis. The optimum conditions to obtain the minimum peroxide (0.923 mequiv. O2/kg oil), anisidine (0.500) and Totox (2.347) values are met when a walnut-beverage emulsion is formulated with 3% WO, 10% GA and 0.12% XG. 相似文献
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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. 相似文献
6.
Three different encapsulation systems were developed in the form of oil-in-water acidic emulsions (pH 3.0) with the oil phase in the form of microdroplets in which Pediococcus acidilactici cells were enclosed. The first emulsion contained corn oil microdroplets (mean diameter 1.5 μm) emulsified with peptides and stabilized with SDS. The other two, were food grade systems with microdroplets of corn or olive oil (m.d. 2.1 and 2.2 μm, respectively) emulsified with peptides and stabilized with xanthan. In all systems, meat peptone, a rich source of peptides and amino acids, was provided in aqueous solution in which the cultures were suspended. Peptone derived peptides acted as emulsifiers and at the same time as nutrient substrates and osmoprotectants for cells. Emulsions were stored for 30 days at 4 °C. During this period, samples were examined for physical stability and viability of the encapsulated and freely suspended microorganisms present in the emulsions. Examinations were made through phase contrast microscopy and subsequent image capture and analysis with an automatic image analysis system. Viable and non-viable cells were discriminated on the basis of color differences produced through staining with trypan blue. The method permitted extraction of a large amount of information and produced large amounts of data through automated measurements on images. Emulsion characteristics and cell viabilities were also examined under conditions simulating the gastro-intestinal environment. Encapsulation proved to be critical since, following successive treatments of samples with simulated gastric juice (pH 2.0) and intestinal juice (pH 7.4), it ensured viability rates of encapsulated cells as high as 85% and delivered as much as 92% of the initially encapsulated cells to the target point. The formulated emulsion systems may have a large number of applications in the food sector provided further studies on engineering properties and improvements of stability over a wide pH range are carried out. 相似文献
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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. 相似文献
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Carignatto CR Oliveira KS de Lima VM de Oliva Neto P 《Indian journal of microbiology》2011,51(3):283-288
Xanthan is a important biopolymer for commercial purpose and it is produced in two stages by Xanthomonas campestris. In the first one, the bacterium is cultivated in the complex medium enriched in nitrogen and the biomass produced is used
as inoculum for the next stage in which the gum is produced in another medium. In this work a new medium for the first stage
is proposed in place of currently used YM medium. Different formulated growth media were studied and the correspondent biomass
produced was analysed as inoculum for the second stage. The inoculum and gum were produced by batch process in shaker at 27°C
in pH 6.0 and at 30°C in pH 7.0, respectively. The gum was precipitated with ethanol (3:1 v/v). The dryed biomass and xathan
gum produced were determined by drying in oven at 105 and 40°C, respectively. The viscosity of the fermentation broth and
1% gum solution in water were determined in Brookfield viscometer. The formulated medium presented the increase in gum production
(30%), broth (136%) and 1% gum solution viscosity (60%) compared to YM, besides the inferior cost. The results showed the
importance of the quality of the inoculum from the first stage of the culture which influenced on the gum viscosity in the
second stage. 相似文献
9.
Arimura T Omagari Y Yamamoto K Kadokawa J 《International journal of biological macromolecules》2011,49(4):498-503
This paper reports the chemoenzymatic synthesis of an amylose-grafted xanthan gum. An amine-functionalized maltooligosaccharide was chemically introduced to xanthan gum by condensation with its carboxylates using a condensing agent to produce a maltooligosaccharide-grafted xanthan gum. Then, a phosphorylase-catalyzed enzymatic polymerization of glucose 1-phosphate from the graft chain ends on the xanthan gum derivative was performed, giving an amylose-grafted xanthan gum. Furthermore, the product formed a gel with an ionic liquid, which was converted into a hydrogel with high water content by replacement of the ionic liquid with water. The ionically cross-linked hydrogel was also provided by soaking the primary formed hydrogel in FeCl3 aqueous solution. The mechanical properties of the resulting hydrogels were evaluated by compressive testing. 相似文献
10.
Anne E. Osbourn Belinda R. Clarke Barry J.H. Stevens Michael J. Daniels 《Molecular & general genetics : MGG》1990,222(1):145-151
Summary Two-component regulatory systems comprising a sensor and a regulator protein, both with highly conserved amino acid domains, and commonly genetically linked, have been described in a range of bacterial species and are involved in sensing environmental stimuli. We used two oligonucleotide probes matching the postulated coding regions for domains of sensor and regulator proteins respectively in Xanthomonas campestris pathovar campestris (Xcc) to identify possible two-component regulatory systems in Xcc. Two different fragments of Xcc DNA with homology to both of these probes were cloned. The DNA sequence of part of one of these fragments encompassed a potential open reading frame (ORF), the predicted amino acid sequence of which had extensive homology with regulator proteins of two-component regulatory systems. Analysis of the predicted amino acid sequence for the 3 end of an adjacent ORF revealed a very high level of homology with the C-terminal end of sensor proteins. Strains of Xcc with Tn5-induced mutations in the regulator gene were affected in extracellular polysaccharide production, and also in resistance to salt and chloramphenicol. No effects of mutation in the second clone were observed. 相似文献