DISPERSION STATE OF PROTEIN-STABILIZED EMULSIONS Dependence of Globule Size and Size Distribution upon pH in Concentrated Oil-in-Water Systems

Concentrated benzene-in-water emulsions were prepared with various proteins such as lysozyme, bovine serum albumin, ovalbumin, casein and gluten. The emulsions consisted of coarse globules whose size distribution could be approximated to the log-normal distribution function, while the adsorbed film of protein molecules seemed to contribute to the stabilization of the globules. These properties were influenced by the pH of the aqueous phase. The mean globule size increased progressively up to the isoelectric point of the proteins. Both the interfacial tension and the rate of coalescence between the globules were minimized as the isoelectric point of the proteins was approached.     

COLD GELATION OF WHEY PROTEIN EMULSIONS

Stable and homogeneous emulsion‐filled gels were prepared by cold gelation of whey protein isolate (WPI) emulsions. A suspension of heat‐denatured WPI (soluble WPI aggregates) was mixed with a 40% (w/w) oil‐in‐water emulsion to obtain gels with varying concentrations of WPI aggregates and oil. For emulsions stabilized with native WPI, creaming was observed upon mixing of the emulsion with a suspension of WPI aggregates, likely as a result of depletion flocculation induced by the differences in size between the droplets and aggregates. For emulsions stabilized with soluble WPI aggregates, the obtained filled suspension was stable against creaming, and homogeneous emulsion‐filled gels with varying protein and oil concentrations were obtained. Large deformation properties of the emulsion‐filled cold‐set WPI gels were determined by uniaxial compression. With increasing oil concentration, the fracture stress increases slightly, whereas the fracture strain decreases slightly. Small deformation properties were determined by oscillatory rheology. The storage modulus after 16 h of acidification was taken as a measure of the gel stiffness. Experimental results were in good agreement with predictions according to van der Poel's theory for the effect of oil concentration on the stiffness of filled gels. Especially, the influence of the modulus of the matrix on the effect of the oil droplets was in good agreement with van der Poel's theory.     

STABILITY OF AQUEOUS EMULSIONS OF THE ESSENTIAL OIL OF HOPS

Hop oil emulsions prepared from different varieties of hops have been found to exhibit enhanced physical stability on the addition of blends of the emulsifiers Span 20/Tween 80 or Span 60/Tween 60. Examination of the particle size and volume distributions of an emulsion by use of a Coulter Counter was found to be an excellent method of monitoring its stability. An indication as to the relative efficiency of emulsifiers can be obtained from Coulter Counter measurements on hop oil emulsions after storage for 4 days. The use of an ultracentrifuge provies a rapid means of testing emulsion stability and hence the effectiveness of emulsion stabilizers.     

RELATIONSHIP BETWEEN COMPOSITION AND STABILITY OF SAUSAGE-TYPE EMULSIONS

SUMMARY— A laboratory technique for the preparation of small batches of sausage emulsion was developed for a comparative study of the effectiveness of fresh and frozen beef in achieving emulsion stability. The technique consisted of three basic steps: (1) low speed chopping and blending of ingredients at −2° to +2°C; (2) low speed blending with the gradual addition of soybean oil at 2°−8°C; and (3) high speed chopping to a temperature of 15°-16°C. The preparation and evaluation of emulsions with widely varying compositions revealed that the lean and fat percentages could be varied over wide ranges without significantly affecting emulsion stability, but the range for percentage of water was narrow and critical to stability. The relative stability for fresh and frozen lean was influenced by the amount of added water. For example, at 30% fat level, there was a sharp drop in stability as the added water was reduced below 16% for fresh beef; whereas, an equivalent drop in stability was found as the added water was reduced below 21 % for frozen beef. The theory is proposed that emulsion instability is highly dependent upon the level of added water based on results of this investigation.     

VOLATILES RETENTION DURING FREEZE DRYING OF SYNTHETIC EMULSIONS

Experimental results are presented for the retention of d-limonene during freeze drying of sucrose solutions, for 10% and 25% solution concentrations, for fast and slow freezing, and for various levels of d-limonene addition ranging from below to considerably above the solubility limit. The results show decreasing percentage retentions with increasing initial levels of d-limonene, reaching an asymptotic value at high initial d-limonene contents. These results are interpreted quantitatively in terms of both microscopic observations and a simple model which allows for the collection of emulsion droplets at the ice-concentrate interface during the freezing step, with subsequent loss of those droplets during freeze drying. Retention experiments with n-hexyl acetate and acetone lend additional support to this interpretation and demonstrate the importance of the ratio of emulsion droplet size to the thickness of the interstitial webs of concentrate.     

INFLUENCE OF EGG YOLK LIPOPROTEINS ON THE RHEOLOGY AND STABILITY OF O/W EMULSIONS AND MAYONNAISE 1. VISCOELASTICITY OF GROUNDNUT OIL-IN-WATER EMULSIONS AND MAYONNAISE

Viscoelastic properties of groundnut oil-in-water emulsions stabilized by egg yolk and of mayonnaise have been deduced from their creep compliance-time response to a constant low shear stress. The viscoelastic parameter values, emulsion stability and initial mean drop size were influenced by pH and NaCl, due to disruption of the egg yolk components. When carboxymethylcellulose was incorporated in the continuous phase of the O/W emulsions an egg yolk-carboxymethylcellulose complex was formed and this affected the rheological properties of the emulsions and also their stability. Mayonnaises exhibited more pronounced viscoelasticity and greater stability than the O/W emulsions. At elevated temperature the micelles adsorbed around oil drops degrade. Their lipoprotein structure unfolds so that more segments on adjacent drops are then available for interlinking and network formation.     

RHEOLOGICAL PROPERTIES OF OIL-IN-WATER EMULSIONS FORMED WITH MILK PROTEIN CONCENTRATE

The rheology and the microstructure of emulsions stabilized with milk protein concentrate (MPC) were investigated using different MPC and oil concentrations. Steady‐shear tests showed that the emulsions were Newtonian at low oil concentrations (<20 wt%), whereas they were pseudoplastic and thixotropic at high oil concentrations (>20 wt%). Dynamic rheological measurements demonstrated that these emulsions behaved as weak gels, as indicated by relatively high values of G′ to G″. The rheological behavior of these emulsions was consistent with bridging flocculation mechanisms, whereby more than one droplet is shared by adsorbed casein aggregates/micelles. This was confirmed by confocal microscopy, which showed that these emulsions were aggregated.     

AQUEOUS DISPERSION RHEOLOGY OF EXTRUSION COOKED MAIZE

The effects of twin screw extrusion cooking of maize grits at different high moisture contents are described. Starch granules survive in the extrudate at high extrusion moisture or with a low shear screw configuration. The aqueous dispersion rheology of the milled extrudate and its dependence on shear rate and heat treatment is explained in terms of the starch swelling behaviour and solubility. These data resemble that of raw maize most closely for the low shear screw configuration. For the high shear configuration under similar conditions of moisture, temperature and mechanical energy dissipation, starch granules are not seen and the dispersion rheology is markedly different from that of raw maize.     

碳纤维发展状况

叙述了国内外碳纤维的发展近况，介绍了碳纤维的种类、性能及用途．详细分析了我国碳纤维发展中存在的问题，并就此提出了一些建议．     

STABILITY OF MILK FAT-WATER EMULSIONS CONTAINING SINGLE AND BINARY EMULSIFIERS

SUMMARY —The stability of 25% milk fat-water emulsions containing sorbitan-fatty acid emulsifiers were compared to determine the influence of single vs. binary emulsifier systems, and saturated vs. unsaturated emulsifier side chains. These variables were compared at emulsifier HLB values of 9.5–10.0 and at usage levels of 0.5–2.0% of the fat. There were no statistical differences (P > 0.05) between single and binary emulsifier mixtures or between emulsifiers with saturated or unsaturated side chains. There also was no significant difference (P > 0.05) between emulsifier HLB numbers of 9.5 and 10.0. However, as the amount of emulsifier in the system was increased the stability of the emulsion increased (P < 0.01).     

MASKING OF THE BITTER TASTE OF SALT SUBSTITUTES WITH LACTOSE IN FOOD EMULSIONS

The forced-choice triangle test was used in the sensory evaluation of two emulsions containing salt mixtures similar to Morton Lite Salt or Mineral Salt against the same emulsions containing NaCl with an equal level of saltiness. 1%–2% wt/wt of lactose either in combination with sucrose or glucose and galactose produced a flavor which was not distinguished from that of 1.00% of NaCl. Sucrose alone was not able to mask the bitter taste of the mixtures in mayonnaise, nor were the other sugars in combination with 0.3% of lactose and 3.0% of vinegar in a simple emulsion. Doubling the vinegar concentration produced a complicated masking behavior with increasing concentration of lactose.