Whippable emulsions

H. D. Goff Instability and Partial Coalescence in Whippable Dairy Emulsions. J. Dairy Sci. 80, 2620 (1997). 

Methods for characterization of structure in whippable dairy-based emulsions... 

This chapter describes some methods to study physical characteristics and ingredient interactions in whippable dairy-based emulsions. The story of whippable emulsions begins with natural dairy cream. From this starting point a range of dairy-type whippable emulsions has been developed over the years. 

This chapter will deal with the following types of whippable emulsion ... 

Most studies have dealt with ice cream, because commercially this product is the most important whippable emulsion. Thus, methods for characterization of ice cream will be highlighted more than other types of whippable emulsions. 

There is a fundamental problem which must be solved when dealing with whippable emulsions. Before use the emulsion must be sufficiently stable. On the other hand, it must be possible to destabilize the emulsion by mechanical treatment combined with air incorporation (whipping, air pressure, cooling, freezing). The partly destabilized fat globules in the whipped emulsion are important for the stability of the foam structure. There is a... 

The ingredient composition and manufacturing process are important for the different types of whippable emulsions. In many industrially produced whippable emulsions, functional ingredients, such as food emulsifiers and hydrocolloids are used to improve functionality and product stability. 

The subject of this chapter is whippable emulsions, and some background theory on foams may be appropriate. 

In the food industry a range of practical or descriptive tests are used to evaluate product quality and the stability of whippable emulsions. Using such methods a number of reliable and commercially valuable whippable emulsions have been developed over the years. To develop new whippable emulsion systems which are more difficult to stabilize, i.e. primarily low-fat products, more advanced physical methods have been used to elucidate the fundamental mechanisms behind the behaviour of whippable emulsions. 

In this chapter the physical methods for analyzing whippable emulsions are divided into analyses of 1) the emulsified fat phase 2) the fat-water interface and air-water interface, and 3) the continuous water phase. The descriptive tests are mentioned at the end of the chapter as it is easier to explain the meaning of these tests after the fundamental mechanisms have been described. 

As already mentioned above, the functional properties of whippable emulsions depend largely on the properties of the fat globules they contain. The fat globules form the skeleton of the foam. The crystallization behaviour inside the fat globules of whippable emulsions is decisive for the stabilization of the foam structure after aeration. It is a well-known fact in the food industry that whippable emulsions made with liquid fats are totally devoid of functionality. 

The time scale of fat crystallization is much shorter for topping powders than for ice cream mix as presented in Figure 2. This is due to the much higher emulsifier content in topping powder. The induction of fat crystallization in whippable emulsion systems is due to interfacial protein desorption from the fat globules of the emulsion mediated by the emulsifiers. This phenomenon is described in section 3.1. 

Other methods to study fat crystallization in whippable emulsions may be used, e.g., a recently developed technique using ultrasonic velocity14. 

Various electron microscopy techniques have been used to study the structures of whippable emulsions such as normal and cryo-scanning electron microscopy or transmission electron microscopy using various preparation methods such as freeze fracturing, freeze etching, etc. The literature is quite extensive, and only a few important papers will be discussed in this chapter. 

The total fat content in whippable emulsions may be estimated by the Gerber method28 or by the gravimetric method29. 

During homogenization of whippable emulsions at high temperatures, emulsification is facilitated by emulsifiers, whereas protein binding to the fat globules acts as an emulsion... 

In whippable emulsions, such as ice cream mix, toppings and homogenized creams, weakening the protein-fat binding by emulsifiers results in an improvement of the whipping properties9 12-33,34. 

It is recommended that the temperature in these types of studies be strictly controlled, as protein-fat binding is highly dependent on temperature. The effect of temperature and whipping on three whippable emulsion systems is shown in Table 1. For further details and results, see references9121316. 

Protein-fat binding in three whippable emulsion systems ... 

The ageing at 5°C of whippable emulsions such as ice cream mix will enhance the hydration of milk proteins in the system. This is due to a property of casein micelles in milk. At low temperatures, the hydration or voluminosity of casein increases. The voluminosity is the volume of hydrated protein per gram of protein. This can be studied by analyzing the protein and water content in the sedimented casein pellet after centrifugation of skimmed milk. 

Interfacial tension analysis may be used to study the interaction of emulsifiers and milk protein at the oil-water interface of whippable emulsions. The interfacial activity of proteins is affected only slightly by temperature changes. In general, emulsifiers can reduce interfacial tension much more than protein, and this effect is especially pronounced at low temperatures. 

In whippable emulsions with a high fat content, the air-water interface of the foam after whipping is dominated by adsorbed deproteinated fat globules. In whippable emulsions with a low fat content other foam stabilizing mechanisms come into play, such as protein-hydrocolloid and protein-emulsifier interactions. The former subject may be studied by... 

The properties of the water phase in whippable emulsions are important for product stability. The water phase is influenced by the soluble components of the systems, i.e., sugars, proteins and hydrocolloids. Interfacial hydration may also influence the properties of the water phase, particularly in high-fat systems. 

Water crystallization in frozen whippable emulsions such as ice cream or aerated desserts, may be analysed by the NMR technique similar to that described for solid fat content analysis. Again, this technique is best used for only relative studies on the effects of ingredient composition on freezing/melting behaviour. 

A range of methods are used to test the textural quality of whippable emulsions. These methods are used to quantify the mechanical properties of the various products. 

The viscosity range varies, depending on the whippable emulsion system in question. In whipped toppings viscosity increases as soon as the topping powder is reconstituted in cold water. This is due to the formation and aggregation of hydrated fat crystals which will... 

After whipping whippable emulsions obtain more solid-like properties. This means that ordinary viscometry measurements are not useful. 

The solid-like properties may be measured by non-destructive dynamic rheology analysis or by destructive methods using a Penetrometer, Jelly Tester, Instron instruments, or other types of texture analyzers. The latter methods are the most useful due to their simplicity and speed. Texture analysis of whippable emulsion must always be compared with the amount of air incorporated into the foam, which is known as percentage overrun and is calculated as follows ... 

Where W, = Weight of a given volume of whippable emulsion before whipping W2 = Weight of the same volume of whippable emulsion after whipping... 

Krog, N., Barfod N.M. and Buchheim W., Protein-fat-surfactant interactions in whippable emulsions, in "Food Emulsions and Foams , E. Dickinson (Ed.), Royal Society of Chemistry, London (1987) 144. 

Barfod N.M., Krog, N. and Buchheim, W., Lipid-protein emulsifier-water interactions in whippable emulsions, in "Food Proteins", J.E. Kinsella and W.G. Soucie (Eds.), Am. Oil Chem. Soc., Champaign, Illinois (1989) 144. 

Buchheim, W., N.M. Barfod, and N. Krog, Relation Between Microstructure, Destabilization Phenomena and Rheological Properties of Whippable Emulsions, Food Microstruc. 4 221-232 (1985). 

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