Emulsions emulsifying capacity

The presence of a thermodynamically incompatible polysaccharide in the aqueous phase can enhance the effective protein emulsifying capacity. The greater surface activity of the protein in the mixed biopolymer system facilitates the creation of smaller emulsion droplets, i.e., an increase in total surface area of the freshly prepared emulsion stabilized by the mixture of thermodynamically incompatible biopolymers (see Figure 3.4) (Dickinson and Semenova, 1992 Semenova el al., 1999a Tsapkina et al., 1992 Makri et al., 2005). It should be noted, however, that some hydrocolloids do cause a reduction in the protein emulsifying capacity by reducing the protein adsorption efficiency as a result of viscosity effects. 

Lin et al. ( 6) measured the emulsion capacity of defatted sunflower seed products. Data in Table VII show that sunflower flour was superior in emulsifying capacity to all other products tested. The emulsions were in the form of fine foams and were stable during subsequent heat treatments. The diffusion-extraction processes employed to remove phenolic compounds dramatically reduced emulsion capacity, although isolating the protein improved emulsion capacity to some extent. 

Kuehler and Stine (43) studied the functional properties of whey protein with respect to emulsifying capacity as affected by treatment with three proteolytic enzymes. Two microbial proteases and pepsin were examined. The emulsion capacity decreased as proteolysis continued, suggesting that there is an optimum mean molecular size of the whey proteins contributing to emulsification. 

Swift, C.E., Lockett, C.. and Fryer, P.J. 1961. Comminuted meat emulsions—The capacity of meat for emulsifying fat. Food Technology 15 468-472. 

Emulsifying capacity Maximum amount of oil that can be emulsified by a protein solution before emulsion breakdown Emulsifying capacity = volume of oil emulsilied/wl. of protein... 

A.N. Gurov, M.A. Mukhin, N.A. Larichev, N.V. Lozinskaya and V.B. Tolstoguzov, Emulsifying properties of proteins and polysaccharides, I, Methods of determination of emulsifying capacity and emulsion stability, Colloids Surfaces 6 (1983) 35-42. 

Tornberg and Ediriweera, 1987). Phase inversion temperature (Shinoda and Saito, 1969) and emulsifying capacity (Swift et al., 1961) have been used to evaluate the effects of low molecular weight and protein emulsifiers, respectively. Unfortunately, it is not possible to measure the size of the large droplets present in unhomogenized water-in-oil emulsions because the droplets coalesce very quickly. The phase inversion temperature is not a relevant test, as it may not be related directly to the stability to inversion at the emulsification temperature. Furthermore, it has been stated (Matsumoto and Sherman, 1970) that water-in-oil emulsions do not exhibit a true phase inversion temperature, unlike oil-in-water emulsions. 

Emulsion Capacity. Enzymatic digestion of proteins beyond 10 min, except the trypsin-treated sample for 30 min, destroyed emulsifying capacity of the flour (Figure 13). Apparently, hydrolysis substantially altered protein surface activity strengths and the ability of the protein to stabilize oil-in-water emulsions. This assumption agrees with earlier work showing decreased emulsion capacity of peanut flour fermented with fungi (27). 

Succinylation increased the emulsifying activity and emulsion stability of soy and cottonseed proteins (12,38). The pH emulsifying capacity profiles of succinylated protein paralleled those of the solubility curves and in all cases the succinylated protein had about double the emulsifying capacity of the unmodified... 

Alkali treatment has been used to improve the functional properties of the insoluble protein prepared by heat precipitation of an alkaline extract of broken yeast cells (63). Heating yeast protein at pH 11.8 followed by acid precipitation (pH 4.5) yielded a preparation composed of polypeptides with increased aqueous solubility. It also increased foaming capacity of the protein 20-fold. The emulsifying capacity of the modified protein was good whereas the original insoluble protein was incapable of forming an emulsion. Alkali treatment must be carefully controlled to avoid its possible deleterious effects (24,75), e.g. alkaline treatment of yeast protein resulted in a loss (60%) of cysteine (63). 

The emulsifying capacity of the yeast proteins was progressively improved with the extent of succinylation (Table IX) as measured by the turbidimetric technique (89). The modified yeast proteins had excellent emulsifying activities compared to several other common proteins. McElwain et al. (88) observed that succinylation of yeast protein increased emulsion viscosity but decreased emulsion stability. 

The emulsifying properties of proteins have been a subject of concern for those dealing with functional properties of proteins. The studies so far have been restricted to two main approaches emulsifying capacity and emulsion stability measurements. The former measures the maximum oil addition until inversion or phase separation of the emulsion occurs, whereas the latter measures the ability of the emulsion to remain unchanged. 

Oil-in-water emulsions lend themselves readily to the delivery of oils and oil-soluble bioactives. The surfactant or biopolymer provides a means of isolating and protecting the lipophihc cores. Many types of materials with emulsifying capacity have been used to encapsulate oils and oil-soluble bioactives in single and multiple emulsion systems. Multilayered interfaces have also been used to improve the robustness of microcapsules. 

The emulsifying capacity is represented by the volume of oil (cm3) that is emulsified in a model system by 1 g of protein when oil is added continuously to a stirred aliquot of solution or dispersion of the tested protein. It is determined by measuring the quantity of oil at the point of phase inversion. The latter can be detected by a change in color, viscosity, or electrical resistance of the emulsion, or the power taken by the stirrer engine. The emulsifying capacity decreases with an increasing concentration of protein in the aqueous volume. It is affected by the parameters of emulsification, depending on the equipment, as well as by the properties of the oil. 

Euston et al. (2001) found that whey protein concentrates with low degree of hydrolysis (4—10%) impaired the emulsifying capacity of whey protein concentrate but increasing the degree of hydrolysis to 10-27% improved emulsifying capacity. However, further increases in the degree of hydrolysis reduced emulsion stability and heat stability of emulsions. 

Grant (58), single-cell protein concentrates by McElwain et al. (59), and fish protein by Groninger and Miller (60) and Chen et al. (61). Succinylated fish myofibrillar protein had rapid rehydration and good dispersion characteristics at neutral pH (60). Succinylation of fish protein concentrate improved its emulsifying capacity and emulsion stability (61). 

Emulsifying capacity and emulsion stability —sausages, mayonnaise, soups, breads... 

The interphase is the phase between the aqueous and the lipophilic phase. For the integration of the aqueous phase and the lipophilic phase a surfactant is needed (see Sect. 18.4.3). Surfactants reduce the surface tension between both phases resulting in the formation of an emulsion, see Sect. 12.5.5. Surfactants are used in emulsions for cutaneous application such as creams and water emulsifying ointments. The emulsifying capacity of the surfactant is determined by the HLB value (see Sect. 18.4.3). These characteristic and to a certain degree the ratio water-fat determines whether an emulsion will be an oil in water (o/w) or a water in oil (w/o) emulsion. Surfactants are described in Sect. 23.6. In this section their function in cutaneous emulsions is summarised. 

The most important excipients in parenteral nutrition solutions are emulsifying agents. Lecithin and phosphatides are mostly used. The emulsifying capacity of phosphatides correlates with their ionisation rate and thereby the pH of the emulsion. The pH also influences the stability of the hpid droplets [58]. If the pH decreases below 3, the droplet surfaces are no longer negatively charged and the droplets coalesce (see Sect. 18.4.1). If necessary, the pH is adjusted with an aqueous solution of sodium hydroxide or hydrochloric acid. 

Sherman, P. (1995) A critique of some methods proposed for evaluating the emulsifying capacity and emulsion stabilizing performance of vegetable proteins. /. Food Sci., 1,3. 

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