Dairy-Substitutes.pdf

DAIRY SUBSTITUTES

1. Introduction

Dairy products have been an important component of the human diet for thou-

sands of years. The popularity of dairy products is due to the wide range of

diverse products (in both texture and ﬂavor) that can be made from milk, and

to the high nutritional value of milk and milk products. In part, this popularity

has led to the emergence of a market for dairy substitute products, which offer a

similar texture and taste to traditional dairy products, but may have differen-

tiated properties, eg, low or no lactose, reduced fat, or may be completely dairy

free. The market for these products has been driven at least in part by the nega-

tive health image of saturated animal fats, and the increasing demand for vege-

tarian and vegan products. In addition to this, a number of consumers will have

allergies or intolerance to certain dairy foods–ingredients. Dairy substitutes

allow them to enjoy dairy-like foods without the negative health implications.

There are no universally accepted deﬁnitions of substitute dairy foods,

which are referred to as imitations, simulates, substitutes, analogues, and

mimics, and are associated with terms, such as ﬁlled, nondairy, vegetable non-

dairy, and artiﬁcial milk, cheese. The term nondairy has been used indiscrimi-

nately to describe both imitation dairy products and products legally deﬁned

as not being imitation dairy products. Dairy substitutes can be divided into

three types: those in which an animal or vegetable fat has been substituted for

milk fat; those that contain a milk component, eg, casein or whey protein, and

those that contain no milk components. The ﬁrst two types make up most of

the substitute dairy products.

The International Dairy Federation (IDF) has deﬁned the following terms

(1,2).

1. Substitute dairy foods. A substitute dairy product is a food stuff where the

intended use is to substitute for milk or dairy foods that have legal stan-

dards of identity. In some countries, the term substitute requires that

the food be nutritionally equivalent to the product for which it substitutes.

2. Imitation dairy foods. An imitation dairy food is a substitute dairy product

in which the general composition, appearance, characteristics, and in-

tended use is similar to milk or to a dairy food that has a legal standard

of identity. Filled milk products are included under this deﬁnition.

3. Synthetic products. These are made in semblance of a dairy product and do

not contain a milk component, although some include sodium caseinate.

Sodium caseinate is classiﬁed as nondairy because of its industrial usage.

4. Filled. Filled imitation dairy products are made in semblance of a dairy

product. A vegetable or animal fat is used to substitute for milk fat.

5. Nondairy. Milk–protein-based imitation dairy products are made to resem-

ble a dairy product and contain one or more proteins derived from milk.

Nondairy in this case has previously referred to imitation dairy products

that contain proteins derived from casein because the FDA has ruled

that such proteins are chemicals and cannot be considered dairy products.

2 DAIRY SUBSTITUTES

More recently, the term nondairy has been used for products that contain

whey proteins derived from milk, using the same rationale as for casein.

2. Ingredients

To reproduce the texture and properties of dairy products, manufacturers of sub-

stitute and imitation dairy foods make use of a range of functional ingredients.

The major ingredients are fats–oils, emulsiﬁers, proteins, polysaccharides and

sugars, and salts. Careful selection of ingredients is an essential part of the for-

mulation of imitation products, as the properties of the product are controlled by

these. Each component of a formulation is added for a speciﬁc function, but often

there is a synergistic interaction between different ingredients that contribute to

product texture. The major ingredients of dairy substitutes are discused below.

2.1. Fats and Oils. Fats and oils play a large role in determining the

texture of imitation dairy products. For example, the creamy mouthfeel of ﬂuid

milks and substitute milks comes from the properties of the fat emulsion (3). The

distinction between fats and oils is one of physical state. Fats are solid at room

temperature, while oils are liquid. At the molecular level, fats have a higher

melting temperature than oils due to differences in the fatty acid composition

of the constituent triglycerides. Fats have a higher proportion of unsaturated

fatty acids, while oils are rich in polysunsaturated fatty acids. In general, fat

are derived from animal sources, eg, bovine milk fat, while oils are plant derived

(eg, soya bean oil, palm oil). The melting point of a fat is an important considera-

tion for its use in dairy substitutes. Fats with a melting point in the range 31–

368C are favored since these will melt in the mouth and contribute to ﬂavor and

mouthfeel of a product. It is common practice to modify the melting properties of

vegetable oils by hydrogenation, which converts unsaturated to saturated fatty

acids, thus turning an oil into a fat.

There are several properties that a fat or oil must possess if it is to be used

in an imitation dairy product. These are bland ﬂavor, low peroxide value and

good ﬂavor stability, low levels of free fatty acids, resistance to hydrolysis,

and a desired solid fat content over the use temperature range of the product.

Thecommonfatsusedinsubstitutedairyfoods are hydrogenated coconut, cot-

tonseed, soybean, groundnut, palm kernel, and various blends of these pro-

ducts. The solid fat content is particularly important in products, such as

whipped toppings and imitation whipped creams, where hardened oils are

used to give optimum whipping properties (4). For powdered coffee whitener,

a long shelf-life is desirable, and so good oxidative stability is a prerequisite

for the fat (4).

2.2. Emulsiﬁers. The term emulsiﬁer is usually taken to denote an

ingredient that helps in the formation of a dispersed fat emulsion. As such, the

term includes both low molecular weight emulsiﬁers and protein emulsiﬁers. In

many dairy substitutes, the fat is found in the form of discrete droplets dispersed

in an aqueous phase. This is termed an emulsion. In this state, the fat is only

kinetically stable, and there is a thermodynamic tendency for the fat to separate

out from the aqueous phase. To stabilize the fat droplets and to impart a satis-

factory shelf-life on ﬂuid emulsion products, emulsiﬁers are added that adsorb to

DAIRY SUBSTITUTES 3

the surface of the emulsion droplets and protect them from coalescence (5). In

other products, eg, margarine, the aqueous phase forms droplets, dispersed in

a continuous fat phase. To stabilise these so-called water-in-oil emulsion droplets

requires the use of a different type of emulsiﬁer compared to those needed to sta-

bilize oil-in-water emulsion droplets.

Food grade low molecular weight emulsiﬁers are usually amphiphilic esters

that contain a hydrophilic and hydrophobic region. The hydrophobic region is

usually a fatty acid (commonly stearic, palmitic, oleic, or lionoleic acids) while

the hydrophilic character often comes from hydroxyl or carboxyl groups. In

dairy substitutes, common emulsiﬁers are mono- and diglycerides, lactic acid

and fatty acid esters of glycerol, polyglycerol esters of fatty acids, sorbitan esters

of fatty acids, polyoxyethylene esters of fatty acids, and propylene esters of fatty

acids. Frequently, a combination of emulsiﬁers are used to achieve the desired

characteristics in the ﬁnal product.

Selection of emulsiﬁers for a particular function is often an empirical excer-

icse informed by the experience of the formulator. To aid in this exercise, a sys-

tem of classiﬁcation of emulsiﬁers has been devised called the HLB (Hydrophile–

Lipophile Balance) system (6). In simple terms, it is a measure of the relative

hydrophobicity or hydrophilicity of an emulsiﬁer, and it can be used to predict

whether an emulsiﬁer will stablize oil-in-water or water-in-oil emulsions. The

HLB number for a particular emulsiﬁer is estimated from the molecular formula

by using the group contribution method proposed by Davis (7). The HLB values

for emulsiﬁers range from 1 to 20, with higher values denoting a more hydrophi-

lic character. Emulsiﬁers that promote oil-in-water emulsions typically have

HLB values in the range 8–28, and those that form water-in-oil emulsions 3–

8. The HLB numbers for a range of emulsiﬁers are shown in Table 1.

In addition to the role of emulsiﬁers in aiding formation of emulsion dro-

plets, there are several other functions attributed to emulsiﬁers. In whipped top-

ping, imitation cream and ice cream the emulsiﬁers are required to destabilize

the fat emulsion so that when it is whipped the fat droplets are able to adsorb

to the surface of the air bubble and to stabilize them (8). In ﬂuid milks and

milk substitutes emulsiﬁers aid in the heat stability of the fat emulsion (9).

While in powdered formulations emulsifers are used both to give heat stability

during drying, and to act as wetting agents to aid redispersion of the powder

in water (10). In coffee whitener formulations, emulsiﬁer blends of sodium stear-

oyl lactylate and and monoglycerides are used as a replacer for sodium caseinate

(11). The emulsiﬁer here forms a complex with the remaining caseinate (12),

which gives improved fat encapsulation in the dried powder state, thus allowing

a cost saving through the reduction in caseinate concentration.

2.3. Proteins. Proteins play a role as both functional ingredients in sub-

stitute dairy products. In addition to emulsiﬁcation, proteins are also used as gel-

ling agents, thickeners, for water binding, to improve melting properties, and for

foaming–whipping properties.

Protein from a wide range of sources can be used in dairy substitutes. These

include: animal proteins, ie, skim milk in liquid, condensed, or dry form (ﬁlled

products); casein, caseinates, and coprecipitates; whey proteins; oil-seed pro-

teins, ﬁsh proteins; and blood proteins. Oil-seed protein sources include soybean

protein concentrates and isolates, groundnut protein, cottonseed protein, and

4 DAIRY SUBSTITUTES

sunﬂower seed, rapeseed, coconut, and sesame seed proteins. Other sources are

leaf and single-cell proteins. Of these protein sources, milk and soybean

proteins are most widely used. Protein usage is based on economics, ﬂavor, func-

tionality, and availability.

Milk Proteins. Many dairy substitutes still contain a considerable propor-

tion of dairy derived protein ingredients. Of these, the various casein and whey

protein products, and skim milk powder (SMP) are the most important, although

newer milk protein products that contain both casein and whey, but at a higher

protein content than SMP, are ﬁnding increasing use in the food industry.

Skim Milk Powder (Non-fat Dried Milk). To prepare skimmed milk

powder (SMP), whole milk is ﬁrst separated in a centrifugal separator to produce

a skim milk stream with a fat content of 0.1%. The skim milk is then concen-

trated to 45–50%, and then dried to a powder. Three forms of SMP (high heat

SMP, medium heat SMP, and low heat SMP) are manufactured depending on

the severity of the heat treatment given during processing. The three types of

product ﬁnd different applications. Low heat SMP is favored for dairy and imita-

tion dairy products. A preheat treatment is usualy given to the skim milk before

concentration as this is believed to protect the casein micelles against extensive

heat damage (13).

Casein and Caseinates. The caseins in milk are found in the form of the

a supramolecular association structure, the casein micelle. Casein micelles are

stabilized in milk by a hydrophilic layer of k-casein at the surface. This is highly

charged and provides both electrostatic and steric stabilization. To separate the

casein protein from milk, one can either remove the charge from the stabilizing

layer, or remove the layer itself. Both charge neutralization with acid, or hydro-

lysis of k-casein with rennet enzyme will precipitate the casein micelles, and

allow separation from the whey stream of the milk.

In the prepartion of casein, the ﬁrst stage is defatting (skimming) of the

milk. This stage is followed by precipition with either a mineral acid to give sul-

furic or hydrochloric casein, with lactic acid to give lactic casein or with rennet to

give a rennet casein. The precipitate formed is either pressed and dried to form a

casein powder, or it is further processed by heating with a food grade alkali

(sodium, calcium ammonium, or potassium hydroxide) to form a caseinate.

Sodium caseinate has a higher solubility than casein and makes an excellent

emulsifying agent. It is used in many product for this function (14). Calcium

caseinate has a highly aggregated structure, due to interactions between calcium

and phosphoserine. This reduces its solubility, making it a less potent emulsify-

ing agent. It is, however, favored in imitation cheese applications. Typical com-

positions for the various casein types are given in Table 2.

Whey Protein Concentrates and Isolates. Whey is the name given to

the liquid left over after the precipitation of casein from milk. Two general

types of whey are formed: sweet whey from cheese manufacture, and acid

whey from casein manufacture. The composition of whey can be variable as it

depends on the conditions used to separate the casein. For sweet whey, the com-

position depends on the type of cheese that is being made since this determines

the coagulation pH, and thus the structure of the curd (15). Similarly, acid whey

composition depends on the acid type used for coagulation (16). Different curd

structures retain differing amounts of whey and thus inﬂuence the ﬁnal whey

DAIRY SUBSTITUTES 5

compositon. The way in which the curd is handled after precipitation also affects

whey composition, eg, the inclusion of washng steps, and the method of separa-

tion of coagulum from the whey.

Dried acid whey contains 12.5 wt% protein, 11.0 wt% ash, and 59 wt% lac-

tose, whereas sweet whey contains 13.5 wt% protein, 1.2 wt% fat, 8.4 wt% ash,

and 74 wt% lactose.

Whey proteins have been used in dairy substitutes only since the develop-

ment of technology to remove nonprotein components of whey, which allows the

production of high protein dried powders. Two types of high protein whey powder

are available, whey protein concentrate and whey protein isolate. Concentrates

are made by concentrating the whey using ultraﬁltration. This is a membrane-

ﬁltration process where the membranes are selected so as to retain protein, but

allow water, lactose, and minerals to pass through and be removed. After drying,

protein content up to 80 wt% protein can be achieved. Whey protein isolates use

a different processing technique, whereby the protein components of the whey

are selectively removed using ion-exchange onto specially selected resins to

achieve high purity and proten content. This process is expensive, and means

that isolates are only used in high value-added products where their cost can

be justiﬁed.

An increasing number of WPI products are now being manufacturerd using

membrane process, eg, microﬁltration and a combination of ultraﬁltration and

diaﬁltration.

Whey proteins have a functionality that is signiﬁcantly different from that

of the caseins. Being globular proteins, they denature, aggregate, and gel when

heated, and so can be used as thickeners and gelling agents. Unlike the caseins,

whey proteins are stable at acid pH and can be used as emulsiﬁers in acidic

environments. Whey protein concentrates are utilized in a limited number of

substitute dairy products; ice cream and other frozen desserts, fermented pro-

ducts, coffee whiteners, whipped toppings, and infant and enteral formulations.

In infant and enteral formulations the whey proteins are often hydrolyzed to aid

digestion, and to reduce the intolerance that some infants have to the protein b-

lactoglobulin. A range of hydrolysate powders have been produced to service this

application.

Whey proteins that have been heat precipitated under very high shear have

a particle size between 1 and 3 mm, and give the impression of fat in some pro-

ducts. These microparticulated whey proteins are being used as fat replacers in

frozen desserts and processed cheese substitutes.

Milk Protein Concentrates. Milk protein concentrates (MPC) have been

developed over the last few decades as a way of utlizing both the casein and whey

protein fractions in a single product without the need for a two-stage preparation

of casein and whey powders. Their production uses ultraﬁltration to remove lac-

tose and minerals from skimmed milk. The resultant high solids concentrate is

dried to produce MPC powder Depending on the degree of concentration by ultra-

ﬁltration, the protein content in the powder can typically be in the range 56–

85%. The processing conditions are relatively mild compared to casein manufac-

ture, and therefore the casein in MPC retains much of its micellar structure. The

highly aggregated state of the casein protein means that MPC is a relatively poor

emulsifer compared to sodium caseinate, although it is comparable to SMP (17).

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