Phases Dispersion and Oxygen Transfer in a Simulated Fermentation Broth Containing Castor Oil and Proteins (original) (raw)
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Oil and Air Dispersion in a Simulated Fermentation Broth as a Function of Mycelial Morphology
Biotechnology Progress, 2003
The culture conditions of a multiphase fermentation involving morphologically complex mycelia were simulated in order to investigate the influence of mycelial morphology (Trichoderma harzianum) on castor oil and air dispersion. Measurements of oil drops and air bubbles were obtained using an image analysis system coupled to a mixing tank. Complex interactions of the phases involved could be clearly observed. The Sauter diameter and the size distributions of drops and bubbles were affected by the morphological type of biomass (pellets or dispersed mycelia) added to the system. Larger oil drop sizes were obtained with dispersed mycelia than with pellets, as a result of the high apparent viscosity of the broth, which caused a drop in the power drawn, reducing oil drop break-up. Unexpectedly, bubble sizes observed with dispersed mycelia were smaller than with pellets, a phenomenon which can be explained by the segregation occurring at high biomass concentrations with the dispersed mycelia. Very complex oil drops were produced, containing air bubbles and a high number of structures likely consisting of small water droplets. Bubble location was influenced by biomass morphology. The percentage (in volume) of oil-trapped bubbles increased (from 32 to 80%) as dispersed mycelia concentration increased. A practically constant (32%) percentage of oil-trapped bubbles was observed with pelleted morphology at all biomass concentrations. The results evidenced the high complexity of phases interactions and the importance of mycelial morphology in such processes.
Morphology of Soy Protein Isolate at Oil/Water and Oil/Air Interfaces
Journal of the Brazilian Chemical Society, 2013
Neste artigo, as propriedades emulsificantes da proteína isolada de soja (SPI) foram evidenciadas mostrando que estas macromoléculas sofrem mudanças conformacionais quando adsorvidas em interfaces. Investigou-se a conformação das cadeias proteicas ancoradas nas regiões interfaciais de emulsões de óleo em água (o/a) através de técnicas de espalhamento de raios X (SAXS) e de imagem (microscopia eletrônica de varredura (SEM)). O valor médio do raio de giro (R g) da SPI (aq) é 20 nm e aumenta para 30 nm em emulsões o/a; as proteínas atuam como moléculas anfifílicas expondo seus núcleos hidrofóbicos ao óleo e os resíduos hidrofílicos à fase aquosa. Este valor ainda é maior após o spray drying das emulsões, na interface o/ar das respectivas microcápsulas. As paredes das microcápsulas são fractais de objetos agregados com superfícies rugosas, que são alisadas pela presença de um agente de reticulação. Herein, the emulsifying properties of soy protein isolate (SPI) were highlighted by showing that the macromolecules undergo conformational changes when adsorbed at interfaces. The conformation of protein chains nested at the interfacial region of oil in water (o/w) emulsions by means of X-ray scattering (SAXS) and direct imaging (scanning electron microscopy (SEM)) techniques was investigated. The mean radius of gyration (R g) for SPI (aq) is 20 nm and increases up to 30 nm in o/w emulsions; the proteins act as amphiphilic molecules by exposing their hydrophobic core to the oil and their hydrophilic amino acid residues to the water phase. By spray drying the emulsions, it was also possible to measure the size (R g = 40 nm) and to evaluate the morphology of these proteins at the oil/air interface of the respective microcapsules. The walls of microcapsules are fractals of clustered objects with rough surfaces, which are smoothed by the presence of a cross-linking agent.
The destabilization of a hexadecane, water, and baker’s yeast (O/W/Y mixture) emulsion by aeration and formation of a clear oil layer was investigated. The role of the air bubbles to destabilize the emulsion and form a clear oil layer was observed on previous research, but not investigated further until the current research. Initial hypotheses stated that the air bubbles were assisting the mechanism by rupturing the protein film and inducing coalescence by direct contact between droplet/droplet or droplet/oil layer, and by surface aided contact, using the bubble as a mediator for coalescence. A sensitivity analysis of the 4 phase mixture (O/W/Y/A) system to yield a clear oil layer by changing operational parameters was used to determine and explain the existing interaction of the air bubbles with the oil droplets to induce their coalescence according to the results obtained and phenomena observed. Preliminary experiments were performed to identify the factors influencing the aeration process and understand the requirements to compare the parameters individually. The dynamics of the separation process were studied using a setup consisting of 4 custom made glass columns, custom made steel plate spargers and air flow mass controllers. The value to compare the different series of experiments was the percentage of oil recovered in each column. The results revealed an influence in the four parameters changed, superficial gas velocity, height, bubble size and yeast concentration. The increase of the superficial gas velocity resulted in a higher percentage recovery but without the presence of a clear oil layer (large droplets accumulated at the top instead). The increase of height in the mixture aerated resulted in a lower percentage recovery and large droplets accumulated at the top. In contrast, the reduction of the height resulted in a very positive recovery and the formation of a clear oil layer, almost immediately. The increase of the air superficial area by reducing the bubble size produced a higher recovery but with a large variation for the results obtained with the smallest bubble size. The increase of yeast concentration affected negatively the percentage of oil recovered as expected. Taking these results into account the hypothesized mechanism was adapted to consider the multilayer protein adsorption at the oil and bubbles to explain the phenomena observed. In general, the experimental setup lacked reproducibility and the analytics to measure the oil concentration in the cream, formed after settling of the emulsion, using GC equipment were not accurate and this aspects should be improved for further research in future projects
Journal of Colloid and Interface Science, 2002
The rate of shrinkage of air bubbles of initial radii, r, from 50 to 150 µm injected beneath a planar air-water interface has been measured. Bubbles were stabilized by 0.05 wt% protein in approximately 0.1 mol dm −3 ionic strength buffer at pH 7.0 and at room temperature. Four proteins were studied: commercial whey protein isolate (WPI), sodium caseinate, gelatin, and pure β-lactoglobulin. Bubbles in all systems showed shrinkage due to diffusion of gas from the bubbles, which accelerated as the bubbles got smaller. Within approximately 1 h all bubbles had disappeared, having shrunk to below approximately 1 µm, so that in no cases was there evidence of stabilization via a surface rheological mechanism. The rates of shrinkage with the different proteins were not significantly different except in the case of gelatin, which at any given bubble size appeared to give a slightly higher rate, probably because the surface tension is higher for this system. A new theoretical analysis of the dissolution kinetics for the case of a bubble close to a planar interface has been developed. For caseinate and WPI a simple model incorporating a constant surface tension and a constant bubble-interface separation appears to account for the kinetics. Interestingly, the model predicts a linear dependence of r n versus time when n is closest to 3, in contrast to n = 2 expected from previous work. For gelatin and pure β-lactoglobulin, the introduction of modest dilatational elasticities of approximately 2.3 and 7 mN m −1 , respectively, gives good agreement between theory and experiment. This is particularly the case for β-lactoglobulin, where there is a noticeable slowing, but not cessation, of the shrinkage as the bubbles get smaller. In the light of these findings the practical significance of surface rheology with respect to stability to disproportionation is discussed. Finally, we present experimental evidence that a bubble stabilized by βlactoglobulin shrinks to a nonspherical protein particle consisting of the completely collapsed protein film. C 2002 Elsevier Science (USA)
The influence of oil droplets on the phase separation of protein–polysaccharide mixtures
Food Hydrocolloids, 2014
A model system consisting of sodium caseinate (SC) þ xanthan AE a low volume fraction of oil-in-water emulsion droplets was studied. The phase separation behaviour of xanthan þ sodium caseinate was investigated as function of these two variables, followed by experiments on the same systems where oil droplets were introduced. More than 20 mM [Ca 2þ ] was needed to induce phase separation at pH 6.4 and 5.9, but at pH 5.4, phase separation occurred at as low as 5 mM [Ca 2þ ] and a lower concentration of SC or xanthan was required to induce phase separation. An increase in size of sodium caseinate aggregates is proposed as the main factor promoting phase separation. When oil droplets stabilized by sodium caseinate were added to systems containing 0.05e0.1 wt.% xanthan at pH 6.4 this appeared to inhibit significantly the phase separation of the mixtures at [Ca 2þ ] ¼ 22 mM. Simple calculations showed that this effect cannot reasonably be due to excessive accumulation of protein at the droplet surfaces, which is then carried away by the droplets due to creaming. Consequently, a possible mechanism of the inhibition is accumulation of droplets at and strengthening of, the waterewater interface of the caseinateexanthan phase separating entities.
Journal of the Science of Food and Agriculture, 1982
The adsorption behaviour of three food proteins-a soya protein isolate, a sodium caseinate and a whey protein concentrate-at a soya bean oil-water interface has been studied by the drop volume method. The interfacial behaviour has been compared with that at an air-water interface. The kinetics of surface tension decay were evaluated in terms of different rate-determining steps at different ionic strengths and concentrations of the proteins. The ranking order with respect to the surface activity of the proteins adsorbed at an air-water interface was the same as that at a soya bean oil-water interface. In the high concentration range the surface activity of the proteins was higher at an air-water interface than at a soya bean oil-water interface, whereasthereversewasfound in the low concentration range. In general, the adsorption of the proteins was more diffusion controlled at an air-water interface than at a soya bean oil-water interface; this suggested that proteins were less folded at the soya bean oil-water interface. A comparison of the rates of the diffusion controlled steps for the proteins at air-water and soya bean oil-water interfaces indicated that the solvation energy gained when caseinates adsorb at the soya bean oil interface was enhanced compared with the other two proteins. This indicated an enhanced loop formation of the caseinate molecules in the oil phase when adsorbing at this interface, as compared with the air-water interface.
Stability of the oil-in-water emulsions composed of 30% (w/w) rapeseed oil and emulsifying mixtures containing dried egg yolk and Tween 65 were investigated. It has been shown that, stability of emulsions was in range from 37.5% to 58.2% and increased in most cases with the addition of emulsifiers, particularly Tween 65. It was found that surface protein concentration in emulsions decreased as concentration of Tween 65 increased, as the result of competitive adsorption. Changes in interfacial protein concentration probably caused instability of emulsions, observed as oiling off effect, especially in samples heated at 80°C and containing 2.0% (w/w) dried egg yolk and 0.8 or 1.0% (w/w) Tween 65. Furthermore, increase of synthetic emulsifier concentration decreased average droplet diameters D [3,2] from 1.42 mm to 0.28 mm, considerable increasing interfacial areas. Composition of the emulsifying mixtures affected modal diameter of oil droplets especially in the emulsions containing: 0.2; 0.6 and 1.0% (w/w) of dried egg yolk, what may be explained by the fact that the mixtures exhibited different emulsifying properties in the studied range of concentrations. Visual inspection of the investigated emulsions in the microscope showed that all emulsions had individual oil droplets with no signs of flocculation.
Bioprocess and Biosystems Engineering, 1999
A water-in-oil (W/O) cultivation technology has the potential of overcoming the problems related with high broth viscosity in xanthan fermentations. The aqueous broth is dispersed in a continuous oil phase. Consequently, the broth thickening mechanisms are confined within the aqueous droplets without significantly increasing the overall viscosity. To better characterize the mixing and oxygen transfer in the complex multiple-phase (G-O-W) systems involved, the W/O dispersions of xanthan solutions in either n-hexadecane or vegetable oil were examined in this study. The experiments with n-hexadecane indicated that the coefficient for oxygen transfer from gas bubbles to the oil, i.e., (k L a)g/o, was much smaller than that for transfer from the bulk oil phase to the droplet surface, i.e., (k L a)o/w. The oxygen partial pressure at the surface of aqueous droplets, p R , was therefore close to that in the bulk oil phase. The experiments with vegetable oil were conducted under various combinations of operating conditions: agitation speed (N) – 400, 600, and 775 rpm; aeration rate (G/V) – 0.25, 0.5, and 0.875 vvm; aqueous-phase volume fraction (φw) – 0.2, 0.3, 0.4 and 0.5; and aqueous-phase xanthan concentration (Xn) – 10, 20, and 40 kg/m3. The correlations developed for the power input of agitation (P g, in W), droplet diameter (d p , in μm), and (k L a)g/oHo (in kg mol/m3 s atm) are: where Ho is the Henry's law solubility for oxygen in the oil phase (kg mol/m3 atm) and v s is the superficial gas velocity. The dependencies associated with P g, d p , and N are consistent with those reported in the literature for simpler systems although no previous correlations exist for complex G-L-L systems. The dependencies associated with Xn are intuitively plausible while the responsible mechanisms for the observed dependencies on φw are less clear.
The Effect of Proteinase A on Foam-Active Polypeptides During High and Low Gravity Fermentation
Journal of the Institute of Brewing, 2003
The ability of beer to produce good foam is influenced by the level of foam-active polypeptides. Specific polypeptides with hydrophobic domains, such as Lipid Transfer Protein (LTP1), are important components of beer foam. Although, high gravity brewing is a commercially viable technique, it has the disadvantage of producing beer with less foam stability compared to lower gravity brewed counterparts. It is thought that proteinase A plays a key role in the degradation of these hydrophobic polypeptides responsible the beer foam stability. The object of this study was to compare and quantify the loss of hydrophobic polypeptides and specifically foam-LTP1 during high gravity (20°Plato) and low gravity (12°Plato) wort fermentations and to evaluate the effect of proteinase A on these polypeptides. The losses of hydrophobic polypeptides and foam-LTP1 were generally greater in high gravity brews. Furthermore, the results obtained suggest that proteinase A alters the hydrophobicity of these polypeptides rather than their molecular size. Approximately 20% of hydrophobic polypeptides and approximately 57% of foam-LTP1 appeared to be proteinase A resistant. These differential losses of hydrophobic polypeptide and foam-LTP1 could have implications for the foam stability of the finished product.