Shelf-life stability, emulsions

Centrifuge tests are used to evaluate the settling stabUiQ of the polymer emulsions. Experiments are made either at cortstant rotational speed (1 h at 6000 ipm) or at variable speeds and times [13]. The wt% of the compacted material is subsequently determined. This method provides an estimation of the shelf-life stability of a given emulsion an emulsion unaffected by 2000 rpm centrifugation fm 2 h is assumed to remain stable from six months to one year. 

Stability is important for cosmetic skin care products from the points of view of function and also shelf-life. Stability against aggregation is important but fairly easily dealt with because most of these products are formulated to have a yield stress [33]. Stability against coalescence is very important but less straightforward (see Chapter 5 for the factors involved). In the cosmetics industry, standardized tests have been developed to yield the net effect of all aspects of emulsion stability. 

In many cases the creaming or sedimentation occurs simultaneously with coalescence and is related to emul sion stability. In the next section, we will briefly con sider the assessment of emulsion shelf-life by NMR. 

IX. DETERMINATION OF THE EMULSION SHELF-LIFE AND EMULSION STABILITY... 

Many products in the chemical and agrochemical, cosmetic, pharmaceutical, and food industries are emulsion-based. Their internal structure is composed of one or more fluids, with one being flnely dispersed as droplets within the other one. The size distribution of the droplets mainly influences characteristic product properties as color, texture, flow- and spreadability, viscosity, mouth-feel, shelf-life stability, and release of active ingredients. It therefore has to be maintained for the life-time of a product. Due to the extremely high interfacial area in these systems, this microstructure is thermodynamically unstable. By applying emulsiflers and thickeners, emulsions are kinetically stabilized for a certain amount of time. Elowever, shelf-life stability always is a big chal-... 

Slow release rates and remarkable long shelf-life (months) were obtained compared to typical multiple emulsions stabilized by two short surfactants (SMO and polyoxyethylene (20) sorbitan monolaurate). Finally, the long lifetime of the emulsions allowed study via diffusing wave spectroscopy (DWS) of the interactions between the droplets and the globule surface [37],... 

Vinyl substituted cyclic hemlamidals 2 and their Interconvertible acetal precursors (eg. acrylamldo-butyraldehyde dimethyl acetal 1) were Incorporated as latent crosslinkers and substrate reactive functional comonomers In solution and emulsion copolymers. Some use and applications data for copolymers prepared with these new monomers are presented. They show low energy cure potential, long shelf life and high catalyzed pot stability In solvent and aqueous media, good substrate reactivity and adhesion, and good product water and solvent resistance. They lack volatile or extractable aldehyde (eg. formaldehyde) components and show enhanced reactivity and hydrolytic stability with amines and diol functional substrates. 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

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. 

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. 

All samples were evaluated at time zero for total oil, surface oil, moisture, emulsion stability and sensory properties to provide background information for subsequent shelf life testing. Most of the methods were selected based on previous findings (, . 52.) Th results of the total oil, surface oil,... 

The so-called storage stability test is a standard test that is used across many different fields—e.g., the pharmaceutical, cosmetic, and food industries. The test is popular because it yields precise information about the long-term shelf life of emulsions. In this test, emulsions are stored under conditions that are applicable to those encountered in the actual production/consumption situation. It should be noted that the presented test protocol is time consuming and requires sampling over an extended period of time. In the... 

This example demonstrates that storage stability tests are extremely useful as they allow emulsion manufacturers to accurately follow even small changes in emulsion properties. Plots of droplet size distribution and concentration as a function of time can be used to determine the kinetics of the instability process and to determine the shelf life of the product by setting upper and lower limits for both mean droplet size and concentration at each port. 

The higher, long-chain dimers as well as the tetramer dehydroacetic acid are far more stable and can be handled safely. The alkylketene dimers (AKDs) are shipped to the paper industry in tank trucks in the form of ready-to-use aqueous emulsions with a total solids content of 12—25% and a guaranteed shelf life of 30 days, as they have good hydrolytic stability. In this form they are not combustible liquids, and are listed in the Canadian Domestic Substances List. 

Non-dairy creams (cream alternatives) are O/W emulsions stabilized by milk proteins. A relatively thick adsorption layer provides stability, mostly by steric stabilization and partly by electrostatic stabilization [829]. Figure 13.3 shows an example of a soybean-oil and milk-protein emulsion stabilized by fat globules and protein membranes. Stabilizers, such as hydrocolloid polysaccharides, are added to increase the continuous phase viscosity and reduce the extent of creaming. They must be stable enough to have a useful shelf-life but de-stabilize in a specific way when they are... 

The size of the droplets in an emulsion has a strong influence on many of its physicochemical and sensory properties, e.g., shelf life, appearance, texture, and flavor (1,2, 4). For example, the stability of an emulsion to gravitational separation or droplet aggregation can be greatly improved by decreasing the droplet size. This is because the velocity of sedimentation is proportional to the square of the droplet size. The size of the droplets in an emulsion is largely determined by the emulsifier type and concentration, the physicochemical properties of the component phases, and the homogenization conditions (4). A food manufacturer normally specifies a preestablished desirable droplet size distribution for a particular product. If the product does not meet this specification, it typically must be reprocessed or even discarded. 

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