Gel emulsions

What are they like to eat Humans are particular about the organoleptic properties of their food. Microbial cells may have little taste or smell, or even smell or taste unpleasantly to some people. The texture may not be the same as in conventional foods, particularly with unicellular organisms. These draw-backs can be overcome by adding a proportion of SCP to manufactured foods. However, even when SCP is incorporated into manufactured foods it may not have suitable characteristics such as stability, ability to bind water or fats, or ability to form gels, emulsions or foams. SCP for feed does not have to meet such strict requirements. 

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

Figure 1.7. Process of emulsification of a very concentrated W/O emulsion. An oU-in-water microemulsion at 7°C (a) is rapidly heated to 40°C, the gel emulsion is formed after less than 40 s (b), the emulsion does not flow if the tube is turned upside down (c). (From [133], with permission.)...

Figure 1.8. Microphotograph of the obtained gel emulsion. (From [133], with permission.)...

H. Kunieda, Y. Fukui, H. Uchiyama, and C. Solans Spontaneous Formation of Highly Concentrated Water-in-Oil Emulsions (Gel-Emulsions). Langmuir 12,2136 (1996). 

C. Solans, R. Pons, and H. Kunieda Gel Emulsions - Relationship between Phase Behaviour and Formation. In B. P. Binks (ed), ModemAspects of Emulsion Science. The Royal Society of Chemistry, Cambridge (1998). 

Various types of PFC-based gels and gel-emulsions have been reported [5,66,67]. They may find applications in topical drug delivery, wound healing, and implantable drug depots and as low-friction, gas-permeant, repellent protective-barrier creams against toxic or aggressive media, and in cosmetics. 

These concentrated emulsions have been referred to by a number of different names in the literature, including high internal phase ratio emulsions (HIPREs) [1,3-7], gel-emulsions [8-14] and hydrocarbon gels [15,16], In this review, the term HIPE will be used throughout. 

A considerable amount of experimental work has been carried out on the so-called gel emulsions of water/nonionic surfactant/oil systems [9-14, 80, 106, 107]. These form in either the water-rich or oil-rich regions of the ternary phase diagrams, depending on the surfactant and system temperature. The latter parameter is important as a result of the property of nonionic surfactants known as the HLB temperature, or phase inversion temperature (PIT). Below the PIT, nonionic surfactants are water-soluble (hydrophilic form o/w emulsions) whereas above the PIT they are oil-soluble (hydrophobic form w/o emulsions). The systems studied were all of very high phase volume fraction, and were stabilised by nonionic polyether surfactants. 

Non-Newtonian Systems. Although the determination of the required properties is straightforward for liquids, the situation is much more complex for non-Newtonian systems such as gels, emulsions, and slurries. As indicated earlier, there is a significant effort under way to prepare slurries of solids in liquid fuels to increase the volumetric energy of such fuels. These slurries must be stabilized as gels or emulsions to prevent solid separation. It therefore seems worthwhile to discuss the preparation of such slurries as well as the techniques used to measure some of the properties required to characterize these systems. 

Soderman et al. [8] gave an overview of NMR self diffusion studies of emulsion systems. They stated that a log-normal distribution function gives a better fit than a normal distribution. Several examples are given including margarine and hydrocarbon gel emulsions. 

Another carotenoid, lycopene, when applied topically at 0.03% in a gel-emulsion followed by UV irradiation reduced erythematous reactions significantly more than vehicle alone in human volunteers. The topical application of 0.5% vitamin E and 1% vitamin C in the same base also reduced erythematous reactions, but not significantly. None of these topical formulations showed a marked difference for hydration or skin barrier function.108... 

We have developed new reaction systems based on colloidal dispersions [23, 24], namely highly concentrated water-in-oil (gel) emulsions, which could overcome most of the disadvantages of the aqueoussolvent mixtures such as inactivation of the aldolase and incomplete aldehyde solubilization in the medium. These emulsions are characterized by volume fractions of dispersed phase higher than 0.73 [25] therefore, the droplets are deformed and/or polydisperse, separated by a thin film of continuous phase. Water-in-oil gel emulsions of water/Ci4E4/oil 90/4/6 wt%, where C14E4 is a technical grade poly(oxyethylene) tetradecyl ether surfactant, with an average of four moles of ethylene oxide per surfactant molecule and oil can be octane, decane, dodecane, tetradecane, hexadecane, or squalane, were typically chosen as reaction media [23, 26]. 

Gel emulsions were applied successfully for the first time in aldol additions of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde as model aldehydes catalyzed by RAMA [24]. The first interesting observation was that the stability of RAMA in water-in-oil gel emulsions improved by 25-fold compared to that in dimethylformamide/water l/4v/v co-solvent mixture. The reported experimental data concluded that both the highest enzymatic activities and equilibrium yields were observed in water-in-oil gel emulsion systems with the lowest water-oil interfacial tension attained with the most hydrophobic oil component (i.e. tetradecane, hexadecane, and squalane). 

Water-in-oil gel emulsions were tested in enzymatic aldolization of selected N-Cbz-amino aldehydes (Figure 19.3), N-Cbz-3-amino propanal (4), N-Cbz-glycinal, (5), (S)-N-Cbz-alaninal (6), and (R)-N-Cbz-alaninal (7) catalyzed by RAMA and L-rham-nulose-1-phosphate aldolase (RhuA) and L-fuculose-1-phosphate aldolase (FucA) from Escherichia coU [27,28]. The largest differences between conventional dimethyl formamide (DMF)/water co-solvent systems and gel emulsions were observed with RAMA and FucA catalysts (Figure 19.3). The emulsion media enhanced the catalytic efficiency of RAMA towards the N-Cbz amino aldehydes tested three, five. 

Figure 19.3 DHAP-aldolase catalyzed aldol addition of DHAP to N-Cbz-aminoaldehydes. Reaction conversion to aldol adduct in gel emulsion (black bars) and dimethylformamide/ water 1 4 system (gray bars) for reactions catalyzed by (a) RAMA, (b) RhuA and (c) FucA.

Many foods may be categorised as either a gel, emulsion, dispersion or foam. However, many more foods are actually a combination of these four types. For example, one may consider bread as being a gel in which air is dispersed, that is, a foam where the liquid around the droplets is a gel instead of a fluid. In order to... 

Analyses of in situ DNA synthesis of Euglena gracilis identify zinc-dependent steps in the eukaryotic cell cycle and show that the derangements in RNA metabolism are critical determinants of the growth arrest associated with zinc deficiency. Combined use of microwave-induced emission spectrometry and micro gel emulsion chromatography shows the presence of stoichiometric amounts of zinc essential to the function of E. gracilis and yeast RNA polymerases, the reverse transcriptases" from avian myeloblastosis, murine leukemic and woolly type C viruses, and E. coli methionyl tRNA synthetase. These results stress the importance of zinc to both nucleic acid and protein metabolism. Transient-state kinetic studies of carboxypeptidase A show that zinc functions in the catalytic step of peptide hydrolysis and in the binding step of ester hydrolysis. 

An important common feature of macroion solutions is that they are characterized by at least two distinct length scales determined by the size of macroions (an order up to lOnm in the case of ionic micellar solutions) and size of the species of primary solvent (water molecules and salt ions, i.e. few Angstroms). Considering practical colloidal macro-dispersions, like foams, gels, emulsions, etc., usually we are dealing with as many as four distinct length scales molecular scale (up to lnm) that characterizes the species of the primary solvent (water or simple electrolytes) submicroscopic or nano scale (up to lOOnm) that characterizes nanoparticles or surfactant aggregates called micelles microscopic or mesoscopic scale (up to lOO m) that encompasses liquid droplets or bubbles in emulsion and foam systems as well as other colloidal suspensions, and macroscopic scale (the walls of container etc). 

A general approach for preparing hollow spheres of mesoporous materials was based on sol-gel/emulsion technologies or the use of organic polymer beads as the templates that control the void formation and its volume. 

Twelve patients with peptic ulcers treated with aloe gel emulsion and "as needed" Pro-Banthine showed a clinical recovery and no relapse 1 yr later (Blitz et al., 1963). The results of this study are controversial, as researchers did not... 

Kunieda H, John AC, Pons R, Solans C. Highly concentrated emulsions (gel emulsions) macro self-organizing structures. In Esumi K, Ueno M, eds. Structure-Performance Relationships in Surfactants. Vol. 70. Surfactant Science Series. New York Marcel Dekker, 1997 359-393. 

Pons R, Solans C, Stebe MJ, Erra P, Ravey JC. Stability and rheological properties of gel emulsions. Progr Colloid Polym Sci 1992 89 110-113. 

Kunieda H, Yano N, Solans C. The stability of gel-emulsions in a water/ nonionic surfactant/oil system. Colloids and Surf 1989 36 313-322. 

H. Kunieda, A.C. Johns, R. Pons and C. Solans, Highly Concentrated Emulsions -Gel Emulsions Macro-Self-Organizing Structures, in [41], pp. 359. 

Fig. 6.5.8 Influence of the water-oil interfacial tension (-y) on the equilibrium product yield and initial reaction rate (v°) for the RAMA-catalyzed aldol addition of DHAP (30 mM) to phenylac-etaldehyde (50 mM) in water/CiaEa/oU 90/4/6w/w gel emulsion systems at 25 °C...

On the light of the experimental data reported and although the precise mechanism of the reaction in W/O gel emulsion media is not known yet, it is likely that the reaction takes place either at the oil/water interface or into the dispersed phase that contains the enzyme and the donor DHAP (Fig. 6.5.10). 

These systems were tested in the enzymatic aldolization of a variety of A/-Cbz-aminoaldehydes catalyzed by D-fructose-l,6-bisphosphate aldolase from rabbit muscle (RAMA) and L-rhamnulose-1-phosphate aldolase and L-fuculose-1-phosphate aldolase from E. coli (Espelt et al. 2003 a,b, 2005). The largest differences between conventional DMF/water cosolvent systems and gel emulsions were observed with RAMA catalyst (Fig. 6.5.11). 

Fig. 6.5.10 Schematic representation of a possible reaction model for aldolase-catalyzed carbon-carbon bond formation in W/0 gel emulsions. A aldehyde acceptor B donor...

Pinsach J, de Mas C, Lopez-Santm J (2006) A simple feedback control of Escherichia coli growth for recombinant aldolase production in fed-batch mode. Biochem Eng J 29 235-242 Pons R, Erra P, Solans C et al. (1993) Viscoelastic properties of gel-emulsions their relationship with structure and equilibrium properties. J Phys Chem 97 12320-12324 Princen HM (1979) Highly concentrated emulsions. 1. CyUndtical systems. J Colloid Interface Sd 71 55-66... 

Solans C, Pons R, Kunieda H (1998) Gel emulsions - relationship between phase behavior and formation. In Binks BP (ed). Modern aspects of emulsion science. The Royal Society of... 

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