Emulsifiers in the Dairy Industry

Submitted by :-Vasudha Sharma

0608126

Emulsion :- Becher (1957)

An emulsion is a heterogenous system, consisting of atleast one immiscible liquid intimately dispersed in another in the form of droplets.

Types of emulsions :- Sharma & Shah(1985)

a. Macroemulsions:-These are defined as a mixture of two immiscible liquids, one of them being dispersed in the form of fine droplets, with diameter greater than 0.1micrometer in the other liquid.

b. Microemulsions:-These are defined as mixtures of two immiscible liquids, where the dispersed phase consists of small droplets, in the range of 100-1000 Angstrom.

Emulsions are systems which possess a minimal stability, which may be accentuated by additives such as surface active agents, or emulsifiers.Commonly, emulsifiers are materials that keep fat globules dispersed in water or water droplets dispersed in fat.

Emulsifiers in Dairy Industry :-

Introduction: Emulsifiers have recently been recognized in dairy industry due to the use of automatic and more rational, manufacturing processes, and partly due to the development of new types of dairy products and dairy substitutes. Emulsifiers are commonly used to facilitate greater production capacity or to modify the texture, rheological properties, or the shelf life of the finished product according to the consumer’s desires. Because of an increasing consumer demand for fabricated foods based on low fat, low calorie, and natural ingredients an attempt has been made to stimulate further innovation directed at increasing the quality and reducing the expense of processed dairy products and substitutes through the use of emulsifiers.

Mode of action:To understand the mode of action of emulsifiers let us consider the example of lecithin , a natural food emulsifier present in milk, blood, eggs.

Lecithin, has an electrically charged or polar end (the + and – at the bottom) and a non charged or non polar end at the top. The polar end is hydrophilic or water loving, gets easily dissolved in water and non polar end, that is hydrophobic or fat loving. The result is that, the emulsifier dissolves part of itself in water and the other part in oil. When oil is shaken in excess of water, oil forms small droplets, non polar ends of lecithin molecules orient themselves within fat droplets and polar ends stick out from the surface of the droplets with an electrically charged surface, thus repelling the droplets. So, the emulsion is stabilized.Thus, an emulsifier, basically acts by positioning itself at the air/water interface where it can act to lower the interfacial tension.

Milk fat as an Emulsion:Milk is an oil in water emulsion. The milk fat globules range in diameter from 0.1 to 20 micrometers with a mean of about 3.5 micrometers. Lipids are insoluble in water and an interfacial tension exists between the phases when the lipids are dispersed (emulsified) in water or vice versa. This interfacial tension is very large, due to which the oil and water phases would quickly coalesce. But, coalescence is prevented by a film around each fat globule and reduces the interfacial tension. This emulsifying film, is referred to as the milk fat globule membrane (MFGM).Analysis of the washed globules, have shown that the MFGM contained phospholipids and proteins. (Brunner, 1974)And, phospholipids consist mostly of lecithin.

Emulsifiers as Food Additives:-The term emulsifier strictly speaking covers only those chemical components which are capable of promoting emulsification or stabilization of emulsions or foams by interfacial action.Emulsifiers are prepared from food ingredients such as phospholipids and proteins, which are accepted as foods and often classified as food additives.

In the United States, food emulsifiers fall into two categories :-

a. Substances affirmed as GRAS b. Direct food additives

GRAS emulsifiers have less stringent regulations attached to their use, but direct food additives are allowed in certain specific foods at low maximum allowable levels.

Classification of Emulsifiers:-Emulsifiers have been classified according to whether they are:-

a. Anioinic, cationic or non ionicb. Natural or syntheticc. Surface active agents, viscosity enhancers, solid absorbents.d. Their hydrophilic or hydrophobic properties

Common Food Emulsifiers and their ApplicationsEmulsifier Typical ApplicationsEmulsifier affirmed as GRASLecithin Margarines, chocolate productsMonoglycerides Margarines, ice creamDiacetyl tartaric acid Baked foodsconfectionary,dairy Esters of monoglycerides product analoguesEmulsifiers as direct food additivesLactylated monoglycerides Baked products,whipped topping Acetylated monoglycerides PizzaSuccinylated monoglycerides Shortenings, breadEthoxylated monoglycerides Cakes,whipped toppings,frozen deserts Sorbitan monostearate Confectionary coatings, yeast Cakes,icingsPolysorbates Salad dressings,coffee whiteners Ice cream

Selection of Emulsifiers:-The common problem in food sector is the choice of suitable emulsifier to obtain the desired results. The selection of the proper type of emulsifier for a given product is normally based on experience and pilot plant tests by trial and error. A common practice is to use two or more component emulsifier blends to achieve multiple functionalities. A number of different methods have been introduced in emulsifier selection for a given purpose. The most common methods are discussed here.

1. Solubility Concept: Solubility of the emulsifier determines the type of emulsion that is formed. An oil soluble emulsifier will create an oil-continuous emulsion and a water soluble emulsifier will turn the emulsion into a water-continuous one.

2. Phase Inversion Concept: An emulsifier that tends to be preferentially soluble in water at relatively low temperatures may become preferentially soluble in oil at higher temperatures at which hydrophobic interactions are stronger. Determination of the temperature at which this inversion occurs provides a useful basis for emulsifier selection. A strong positive correlation has been observed between the Phase Inversion temperature of emulsifiers and emulsion stability.

3. Hydrophile-Lipophile Balance (HLB) Concept: The HLB is a semi-empirical scale for selecting an appropriate emulsifier based on the relative fraction of hydrophilic and hydrophobic groups in the emulsifier molecules. Water in oil emulsions are generally formed using emulsifiers with a low HLB number and oil in water emulsions from those with a high HLB number. Substances with extremely high or low HLB number are not functional as emulsifiers since almost all of the molecules will be solubilized in the continuous phase.

Emulsifier Funtionality:-The major function of emulsifiers in food systems are as follows:-

a. Modifying intermolecular forces which stabilize or destabilize the structure of food colloids and gels.

b. Lower the interfacial tension between liquid phases or liquid-air phases.c. Reduce the pressure gradients required to disrupt the droplets when forming a

dispersion.d. Reduce the tendency of the droplets, once created to coalesce.e. Alter the flow properties.f. Modification of the crystallization of fats and oils.g. Improve whipping quality of foam.h. Interaction with starch and protein components in foods which modify texture and

rheological properties.

Emulsifiers in Dairy Industry:-It is almost universally accepted that the naturally pure condition of milk should be maintained for all milk products. Only a small number of additives indispensable for the product quality or for the success of manufacturing are permitted. Utilization of emulsifiers is not allowed with the exceptions of a few. Since milk perse contains natural emulsifier system, the addition of emulsifiers are not claimed to be indispensable. Except for some cheese varieties, all commercial dairy products are made from heat treated milk.The condition and stability of the heat treated milk is, however of practical importance, especially for longlife products. It is now understood that the production of milk based products is a consequence of either stabilization or destabilization of the dispersed aqueous phase proteins. In a nutshell, emulsifiers play a vital role in the formation of structure in many dairy products.

Milk and Dairy CreamThe surface active system of milk has the ability to stabilize sufficiently fine dispersions of oil against coalescence. An adsorbed layer of protein and phospholipids called the milk fat globule membrane, which is distinct from the aqueous phase protein, stabilizes the fat droplets. The synergy of phospholipids and milk proteins is presumably an essential factor for the stability of milk products. In unhomogenized whole milk and cream, the fat globules are protected by their original membranes. In homogenized milk, the emulsion stability depends essentially on the condition of the protein micelles and phospholipids, which have the ability to enroll the unprotected fat globules. In general, emulsifiers are usually not added to milk and cream, as they are naturally stabilized. However, emulsifier and stabilizers are required only if the product is to be given a high heat treatment to protect the protein or emulsified fat from heat damage.

Recombined Milk and CreamIn the recombination process, anhydrous milk fat, skimmed milk powder and water or alternatively whole milk powder with water are recombined to give a product with the same fat and protein content as whole milk. Many manufacturers add low molecular weight emulsifiers to the formation, particularly mono- and di- glycerides. Emulsifiers in the form of phospholipids can also be added through the practice of replacing 20% of the SMP with butter milk powder to give an improved taste. It is suggested that emulsifiers aid in formation of milk fat emulsion during homogenization.

Commercial Emulsifiers and their ADI values

Emulsifier ADI(mg/kg body weight)*

Mono- and diglycerides Not limitedPropylene glycol monoesters 0-25Lactylated esters Not limitedPolyglycerol esters 0-25Sorbitan esters (SPANs) 0-25Ethoxylated esters(TWEENs) 0-25Diacetyl tartaric acid ester 0-50Fruit acid esters Not limitedAcetylated monoglycerides Not limitedPhosphated esters 0-30Sucrose esters 0-25Lecithin Not limited

*Assigned by FAO-WHO Codex Alimentarius Committee

Whipped Cream and Whipping CreamWhipping cream is an oil in water emulsion stabilized by adsorbed milk protein and low molecular weight emulsifiers. The fat content of whipping cream is about 35% by weight. Whipping cream can be made by concentration of milk fat found naturally in milk or by recombined anhydrous milk fat, milk proteins and emulsifiers. Whipped cream is formed from whipping cream when air is incorporated into the emulsion to form a foam. Non- homogenized cream contains fat globules stabilized by native MFGM may whip satisfactorily without use of emulsifiers. If the cream is homogenized prior to whipping, emulsifiers have to be added to aid destabilization. If the whipped cream bases were formulated with milk protein, as the only surface active material, these would encounter the same problems as homogenized cream. Hence, recombined whipping creams and homogenized natural creams contain added low molecular weight emulsifiers. Whipping cream emulsifiers are usually a blend of lipophillic emulsifiers (glycerol monostearate) or one of its derivatives and a hydrophilic Tween. Phospholipids are natural components of milk fat and produced as by-product Butter milk powder(BMP). This can suggest the increasing use of BMP as combined emulsifiers/protein systems in whipped emulsions.

Non-Dairy Whipping CreamThis emulsion is mainly stabilized by sodium caseinate. The fat levels of dairy whipping cream are 35 to 40%. When the fat content is reduced, whipping becomes difficult along with drastic effect on foam stiffness and problems of syneresis in the foam, whereas in emulsion made out of vegetable fat along with emulsifiers such as lactylated esters and propylene glycol esters, it is possible to reduce fat content considerably with good stiffness and stand up properties.

ButterButter is a water-oil emulsion. Growth of micro organisms is noticeably restricted in individual water or buttermilk droplets which are sufficiently small in size(<10micron). A very fine dispersion of the aqueous phase is of primary importance for an adequate keeping quality of butter. Surface-active substances present in butter, do not contribute to emulsion stability. However, they emulate a small proportion of the finest water droplets and form very stable true water oil emulsions. Hence, addition of low molecular weight emulsifiers is not required. In recombined butter, phospholipids are added as anti-spitting agents, to prevent fat spitting during heating and monoglycerides have been claimed to provide better “stand up” properties during storage.

Butter SpreadButter spreads are generally water-oil type emulsions. A satisfactory low fat spread can be produced from a dairy cream using a distilled monoglyceride with high iodine value (80-105) in the cream and thickener such as alginate. Other emulsifiers used in spreads include 0.5% lecithin and a combination of 0.2% lecithin with 0.5% monoglycerides.

Evaporated and Concentrated MilksEvaporated and concentrated milks are produced by removal of water from natural or recombined milks. On addition of surfactants, viz, sodium dodecyl sulphate(SDS), cetyl-trimethyl ammonium bromide(CTAB), the heat stability of concentrated milk increases. However, these surfactants cannot be added to milk products. In non-homogenized whole milk, the fat globules have little effect on heat stability. However, after homogenization, the heat coagulation decreases with increasing homogenization pressure. Lecithin can be used to increase heat stability of homogenized and concentrated milks.

Processed CheeseProcessed cheese manufacture was used as a way of increasing the shelf life of cheese and of fat globules in protein gel network and the stability of the emulsion is controlled by adsorbed caseins or hydrolyzed caseins. To control the structure of processed cheese, so called emulsifying salts, viz, polyphosphates are added. Some manufacturers also add mono- and di-glycerides as emulsifiers. The use of low molecular weight emulsifiers are not as good as emulsifying salts in promoting structure and formation in processed cheese and, in some cases they act to destabilize the fat emulsion by protein displacement from the surface.

Ice CreamEmulsifiers are very important for ice cream production, for the following reasons:-

- improve sensory quality, by aiding the whipping process,- improve air cell distribution,- enhance heat shock resistance of the product,- impart smooth body and texture, a dry appearance and stand up property,- higher over run and more stable foam structure

Common emulsifiers used in ice cream production are lecithin, mono- di-glycerides and polysorbates. Mono and di-glycerides sre better foaming agents, polysorbates are more efficient at efficient at displacing protein from oil/water interface. Sodium casienate is added to ice cream to improve whipping, stabilizing, and emulsifying properties at a level of 0.5-1.0%.

Coffee WhitenersIn recent years, coffee whiteners have gained increasing importance in the food industry from a consumer acceptance stand point due to economy, ease in handling and the preference of many consumers for a vegetarian product. The stability and functionality of these emulsions depend mainly on the degree of emulsification. FDA has allowed use of ethoxylated esters, blends of monoglycerides with the above at levels o 0.4-0.5%. Function of emulsifiers in coffee whiteners is to improve whitening ability and to aid powder dispensability in coffee.

Cream LiquersThese are dairy emulsions of high added value. The combination of milk protein (2.6-3.5%) and high alcohol content (14%) make cream liquers unique among dairy emulsions. But addition of high level of sodium caseinate during its manufacturing process makes cream liquer emulsions unstable in acid environments. This can be made stable in an acid environment by replacing sodium caseinate with GMS. In practice, legal limits set the level of GMS at not more than 0.4% and hence, total replacement of caseinate by GMS is not feasible. Cream liquers stored at ambient temperatures have shelf lives of many years , but are likely to be consumed before serum separation.

Whipped ToppingWhipped toppings, usually made with hydrogenated vegetable oils have been popular dairy analogs for several years. Emulsifiers used for whipped toppings are :- propylene glycol monostearate (PGMS), acetic acid esters, glycerol lacto palmitate(GLP).

Other Dairy Applications of Emulsifiers Emulsifiers like sucrose esters and monoglycerides are finding a wide range of novel applications. They are known to improve the mouthfeel in yoghurt, inhibit microbial growth, enhance the thermal death rate of bacteria and increase heat stability of bovine serum albumin.

Trends for the FutureEmulsifiers have an important role in the future. Saturated fats have been long associated with its ability to raise serum cholesterol notably LDL. Food processors have therefore, been making a substantial effort towards substitution of fats with liquid oils, by use of emulsifiers.Elimination of fats from products normally containing high fat levels creates enormous challenges to maintain texture and flavour. This trend towards replacement of fat functionality with emulsifiers shall continue.