Emulsion size

Rosin sizing usually involves the addition of dilute aqueous solutions or dispersions of rosin soap size and alum to a pulp slurry (44—46). Although beater addition of either coreactant is permissable, addition of both before final pulp refining is unwise because subsequently exposed ceUulose surfaces may not be properly sized. The size and alum should be added sufficiendy eady to provide uniform distribution in the slurry, and adequate time for the formation and retention of aluminum resinates, commonly referred to as size precipitate. Free rosin emulsion sizes, however, do not react to a significant degree with alum in the pulp slurry, and addition of a cationic starch or resin is recommended to maximize retention of size to fiber. Subsequent reaction with aluminum occurs principally in the machine drier sections (47). 

Alkylketene—dimer emulsion sizes can be appHed to the surface of paper and provide very efficient sizing. Used by themselves, these sizing agents can provide a sHppery surface consequendy, they often are used in conjunction with starch or some filler which reduces sHppetiness without detracting from sizing efficiency. 

No data are as yet available on the effect of length of tail on the emulsion size. As has already been noted (p. 46) fatty acids with short hydrocarbon tails are very water soluble and the sodium soaps soluble to a greater degree, interfacial adsorption is consequently small. Thus the concentration required to produce a saturated film at the oil-water interface will be correspondingly greater. This necessitates a high sodium ion concentration in the... 

Effect of Emulsion Size on Fiavor Retention and Sheif Stability... 

The effect of emulsion size on the retention and shelf-life of spray dried orange oil were investigated. 

The samples (ca. 2500 g for each sample) were spray dried in a Niro Utility drier with the inlet temperature at 200 C and outlet at 100 C. The drier temperatures were allowed to stabilize before samples were collected for analysis. The dried samples were analyzed for total oil, surface oil, moisture, emulsion size and emulsion stability. Samples were also stored at an elevated temperature for shelf-life determination. Sensory analysis of rehydrated powder from the coarse and Microfluidized emulsions was performed to determine if differences in emulsion size affects the perceived flavor intensity. 

A 1% solution of spray dried powder in water was prepared and gently stirred with a magnetic stir bar until the powder was completely dispersed. The absence of any clumps when the solution was viewed under a microscope was used as an indicator of complete dispersion. A few mL of solution were placed in the chamber of the Microtrac. In the instrument, the solution flows past a laser beam in an optically clear cell. The angle of diffraction of the laser beam is measured and the size of the emulsion calculated. The calculation is based on the principle that the smaller the emulsion size, the larger the angle of diffraction. The instrument gives results on emulsion size and size distribution as well as calculating the surface area of the emulsion. The entire analysis is computerized. 

The test for emulsion size in the finished powders was run to confirm that different oil droplet sizes were created by the different processing conditions. The average particle sizes are listed in Table I. An important point to note is that as particle size decreased, the range of particle sizes also decreased. The smaller the emulsion, the more uniform the particle size. 

Table I. Emulsion Size of Spray Dried Orange Powders...

Emulsion sizes determined only on first and third trials Microfluidized sample not prepared for first trial... 

Table II. Influence of Emulsion Size on the Retention of Orange Oil During Spray Drying...

Figure 2. Influence of emulsion size on shelf life (45 C) of spray dried orange oil with gum arabic as carrier.

Table III. The Influence of Emulsion Size on the Shelf-life of Encapsulated Orange Oil...

The extractable surface oil results of the spray dried powders are listed in Table IV. The extractable surface oil decreased as the emulsion size decreased. Based on previous knowledge, one would anticipate that less surface oil would result in a better shelf-life. The results of this study do not support that theory especially when you consider the third set of samples in which the coarse emulsion had the greatest amount of extractable surface oil yet also had the longest shelf-life. 

There may be competing factors between emulsion size and extractable surface oil that produce these results. While the finer emulsions have less extractable surface oil which should improve shelf-stability, the total surface area of the oil droplets in these powders is greater (Table V). The lower amount of surface oil provides less oil that is openly exposed to oxidation but the greater surface area of the droplets in the carrier matrix provides greater possibility for oxidation once oxygen has permeated the spray dried particles. 

Moisture content of the samples is listed in Table VI. The percent moisture in the samples ranged from an average of 4.7 to 5.8. While the moisture content tended to drop as the emulsion size decreased, there was not a significant difference (a =. 05) between any two samples. 

This is particularly important in beverage applications where viscosity cannot be increased to help stabilize the flavor emulsion. These are the three disinct advantages of creating finer emulsions for spray drying citrus oils. While the emulsion size is only one factor which can influence the stability of spray-dried citrus oils, it may be possible to use this information in conjunction with other data and information to manufacture a product with an extended shelf-life, better emulsion stablity, and higher flavor load. 

Recently,it was reported that when maltodextrins were used as the encapsulating agent, increasing the dextrose equivalent by 10 could result in a three to six fold enhancement in shelf life (5). The reduction in emulsion size of feed emulsion also improved the shelf stability (Risch, S. J., University of Minnesota, personal communication, 1986). However, the influence of particle size distribution on the stability of encapsulated flavors has not been clearly addressed in the literature. 

Uses Preparation of emulsions, sizing paper, adhesives, light filters. 

Dickinson, E., Murray, B.S., Stainsby, G. 1988. Coalescence stability of emulsion-sized droplets at a planar oil-water interface and the relationship to protein film surface rheology. J. Chem. Soc., Faraday Trans. I, 84, 871-883. 

The high-resolution line-start technique can be used, but this is not amenable to scanning since the low concentrations necessarily employed generate a noisy baseline. An additional benefit of the new software is that it allows for particles whose density is lower than that of the surrounding liquid, thus making it suitable for emulsion sizing. 

Microscopy is often the last word in the determination of the size distribution of dispersed systems (98-101), Throughout the literature, distributions obtained by various particle and emulsion sizing techniques are compared to the values determined by microscopy (13, 102—107), Establishing a representative sample is a concern for all of the techniques discussed and is not necessarily a particular problem for microscopic observation, although this criticism is often given for the microscopic methods. Indeed, many of the sample handling concerns discussed in this section apply equally to samples prepared for other techniques. 

The practical lower limit of emulsion sizing with optical microscopy is on the order of 0.5 (xm. This limit is much lower with electron microscopy, on the order of 0.1 (xm or less with direct observation of frozen samples in a scanning electron microscope, and 0.01 xm or less with replicas and transmission electron microscopy. Sizes smaller than these lower limits can be recognized with each of these techniques, but quantification of the size distribution becomes difficult. Furthermore, at levels of about 0.01 xm, it is extremely difficult to avoid artifacts and subsequent misinterpretations. As mentioned earlier, sample preparation is an extremely important consideration in both optical and electron microscopic techniques. With optical... 

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