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Skim Milk Powder

Overview

Nonfat dry milk is a product that is created when water is removed from pasteurized nonfat milk. By depriving microorganisms of the water which they require in order to develop, drying allows skim milk powder to have a shelf life of up to 3 years if stored properly. It contains lactose, milk proteins and minerals in the same relative proportions as the fresh milk from which it was made. Skim milk powder is by far the most common type of milk powder available.

The powder should be stored under cool, dry conditions and should be protected from contact with water during storage. With its low moisture content, chemical reactions in skim milk powder stored at room temperature take place so slowly that the nutritive value is not affected, even after years of storage.


Composition

Skim milk powder (SMP) must contain no less than 95 percent milk solids and must not exceed 4 percent moisture or 1.5 percent of fat, unless otherwise indicated. In the case of instantized SMP, Vitamins A and D are added. Regular and instantized SMP may also contain an anti-foaming agent.

Typical Composition for Skim Milk Powder 

Lactose

49.5 - 52.0%

Protein

34.0-37.0%

Ash

8.2-8.6%

Moisture

3.0-4.0%

Fat

0.6-1.25%

Minerals (mg/100 g)

Calcium

1248.00

Sodium

494.00

Potassium

1674.00

Phosphorus

993.00

Iron

0.40

Magnesium

110.00

Zinc

4.08

Essential Amino Acids (g/100 g Protein)

Isoleucine

2.19

Leucine

3.54

Lysine

2.87

Methionine

0.91

Phenylalanine

1.75



Whey Protein Nitrogen Index (WPNI) 

High-Heat, Heat Stability (HHHS) = Not more than 1.5 mg/gm
 

High-Heat (HH) = Not more than 1.5 mg/g

Medium-Heat (MH) = Between 4.00 - 5.99 mg/gm
 

Low-Heat (LH) = Not less than 6.0 mg/gm 


Strict microbiological requirements are placed on the quality of the raw milk that is used in the manufacture of milk powders. Consequently, SMP should be free from bacteria of the genus Salmonella. One gram of powder must not contain more than 50 000 mesophilic bacteria, 10 coliforms and 100 Staphylococcus aureus. These counts correspond respectively to about 5000, 1 and 10 per litre of reconstituted product, provided that contamination does not occur after manufacture.


Characteristics

  • Appearance: Dry milk powder must be reasonably uniform in composition, white- or cream-coloured, free from the brown or yellow colour (typical of overheated product) or any other unnatural colour and must also be substantially free from brown specks. Its flavour and odour must be sweet, clean and free from rancid, thallowy, fishy, cheesy, soapy or other objectionable flavours and odours.
  • Spray-drying: is the principal method used for drying milk in the dairy industry. Most skim milk powders used as ingredients are spray dried and are manufactured in two basic varieties: instant (agglomerated) and non-instant (regular). The instantized spray-drying process gives the powder a larger grain size than regular spray dried powder and renders it instantly soluble when reconstituted in cold water. Furthermore, the heat treatment applied during the manufacture of specific spray dried skim milk powders will, to a certain extent, affect the denaturation of the milk proteins, and consequently, their solubility and functionality as milk ingredients. The degree of denaturation is normally expressed by the Whey Protein Nitrogen Index (WPNI) as milligrams of undenatured whey protein (u.w.p.) per gram of powder. (See Whey Protein Nitrogen Index Table.)


Various Uses


Dried milk is used widely as a food ingredient. For the past several years, the largest markets for skim milk powder (SMP) have been dairy, prepared dry mixes, confectionery and bakery. SMP can be reconstituted by adding water to obtain liquid milk, recombined by adding water and fat in such a quantity to achieve the desired fat content, or simply used as an ingredient.  Its high nutritional quality combined with its versatile and multi-functional properties make it attractive for many applications such as the following:

Reconstituted Skim Milk Powder

  • As a result of the long stable shelf life, the reduced storage space needed and nutritive value of SMP as compared to fluid milk, it is desirable in many regions with unfavourable climatic conditions and also in certain unusual conditions (e.g. war, earthquakes, epidemics etc.)  In these situations, SMP can be reconstituted to provide a substitute for fluid milk. 
  • SMP is used in the food industry as a replacement for fluid milk.
Recombined Skim Milk Powder 
  • When recombined with water and fat, SMP can be used as a dairy component in place of fluid milk or cream in a number of applications where fluid milk and cream would ordinarily be used.
Confections
  • Used in aerated confections such as malted milk and nougat centers.  Addition of SMP stabilizes foam structure by preventing air bubbles from collapsing.  SMP also lends a desirable light dairy flavour, helps control sucrose crystallization (due to its lactose content), and binds water to produce the firm, chewy texture of confectionary centers.  The firm structure and increased stability from SMP also allows the confectionery centers to withstand high temperatures and enrobing process conditions. 
  • In caramel confections, the SMP is key in the colour formation due to both the caramelization of the lactose present and the Maillard reaction of the lactose and amino acids (protein) in SMP.
  • SMP is used to produce milk chocolate for its distinct flavour and smooth milky texture characteristics.
  • Also used frequently in soft sweets and various confection coatings.
Sports and Nutrition Foods
  • The highly nutritional value of SMP makes it an excellent ingredient for many athletic foods such as nutrition bars and beverages.  SMP provides the protein, vitamin (except for fat soluble vitamins) and mineral content (such as calcium) required as well as functional properties such as water binding, thickening, emulsification and flavour. 
  • Many new beverage applications include SMP as a natural source of calcium to fortify the beverage.  Mouthfeel, flavour and colour are also notable contributions from SMP in beverage products.

Infant Formulas

  • The nutritive value of SMP is the key consideration when formulating food for infants.  These infant formulas containing SMP are used as a nutritious substitute for mother’s milk. 
Bakery Products
  • Commonly used in many bakery products such as breads, cakes, doughnuts, rolls etc. to add nutritive value (flour lacks some essential amino acids and minerals), improve flavour, enhance browning (presence of lactose), and improve water binding capacity allowing the bakery product to remain fresh longer. 
  • In cakes, SMP has also been shown to stabilize the batter and improve tenderness.

 Dry Mixes

  • Found in cocoa mixes and other hot beverage mixes to impart a smooth creamy mouthfeel and enhance the flavour.
  • In dry mixes where whipping or foaming is required, SMP provides essential proteins to act as emulsifiers to stabilize and ensure proper whipping and foaming.
  • SMP adds mouthfeel, emulsification, colour, and flavour to dairy-based dry mixes such as sauces, soups and salad dressings.

 Fermented Milk Products

  • Improves the taste and mouthfeel of fermented dairy products such as sour cream. 
  • Source of dairy solids in products such as low-fat yogurts, cheeses and cultured skim milk.

Ice Cream and Frozen Dairy Desserts

  • Important source of non-fat milk solids in ice cream, sherbets, frozen yogurts and other dairy desserts.  Standardization is commonly practiced in dairy products to adjust the protein-to-fat ratio. 
  • Proteins in SMP aid to stabilize the ice cream by forming a stable film around the air bubbles produced during manufacture.

 Cheese Analogues/Processed Cheese

  • Due to its casein protein content, SMP can be used.  Rennet, acidification, heat treatment or other factors can be used to coagulate the casein present in SMP, producing the characteristic semi-firm gel of cheese-type products.
Meat Products
  • SMP improves the overall flavour and colour of meat products such as processed deli meats, sausages, smoked meats, etc. 
  • The water-binding capacity of SMP allows the meat products to retain moisture, giving them a plump appearance and leads to less shrinkage and leaking, improved slicing qualities and increased yield.

Other

  • The list of SMP applications is almost endless.  New uses are continually discovered and research with SMP and other milk proteins is prevalent.  Other applications include:

    • coffee whiteners and cream liqueurs (SMP emulsifies and provides smooth texture)
    • some cereal products
    • substitute for eggs in various products (SMP acts as the emulsifier)
    • battered and breaded products for flavour, adhesion and browning
    • frostings and puddings
    • animal feed for nutritive content
    • reconstituted as a medium for producing cultures and starters

 
Skim Milk Powder and Whey Protein Powder

Skim milk powder and whey protein powder are often used in similar applications as they share similar functionalities due to the protein content in both.  However, there are some differences which should be considered when choosing which powder to use in a particular application.

Whey protein powder typically has less protein unless concentrated, and the concentrated form is typically more expensive.  SMP contains natural milk proteins, namely the caseins and whey proteins, whereas whey protein powder contains only the whey protein component.  Caseins and whey proteins have unique functional properties that can be utilized by SMP.  High levels of whey protein can impart an undesirable whey flavour and off-colour that may not be suitable in some applications.

SMP is often used rather than whey powder in applications where rennetability or coagulation is required (such as in cheese and fermented dairy products) due to the presence in SMP of casein proteins which are not present in whey protein powder.  SMP is also used in cases where lactose crystallization may be an issue, such as in ice cream and frozen desserts, since SMP typically has less lactose than standard whey powder. 

One of the key differences is the nutritional profile of skim milk powder versus whey protein powder.  SMP has relatively the same proportion of nutrients as fluid milk (except for fat and fat-soluble vitamins), however whey powder contains less of some vitamins and minerals than SMP or fluid milk and contains other nutrients in different proportions.  This can be important in applications where nutritive value is critical such as in sports beverages and other dietetic foods. 


Functional Properties


Dairy ingredients perform a wide range of key functions in prepared foods, including emulsification, thickening, gelling and foaming. In addition, they provide nutrition and desirable sensory characteristics to the manufactured foods. Extensive worldwide food research has focused on understanding milk protein interaction in these products in order to optimize the manufacturing process and to control product functionality in food applications.

There is a variety of desirable benefits that can be obtained by introducing SMP to a food formulation since it contains approximately 35 percent of milk proteins and 50 percent lactose. Some of the more notable benefits are:

Functional Property

Mode of Action

Product Use

Emulsification

Formation and stabilization of fat emulsions (proteins acting as oil/water interfaces)

• Salad dressings
• Sausages (meat emulsions)
• Soups, sauces
• Dairy beverages
• Baked goods

Foaming/
Whipping*

Formation of a stable film of surrounding air bubbles (proteins acting as air-water interfaces)

• Ice creams (Soft-serve and hard frozen)
• Cakes, mousses

*Choose a powder that is free of anti-foaming agents

Browning/
Color/ Flavour

Lactose and proteins undergo Maillard caramelization

• Baked goods (doughs, cakes, muffins)

Thickening/
Waterbinding/
Gelling

Addition of milk solids to increase viscosity and gel strength by trapping water (lactose and proteins show high water-holding capacities)

• Puddings
• Yogurts (set types)
• Sauces
• Baked goods
• Dairy beverages

Solubility

High-Heat (HH) = Low solubility

• Prevents loaf volume depression in bakery products
• High moisture-absorbing quality desirable in meat, confectionary and bakery products

Medium-Heat (MH) = Medium solubility

• Used in ice cream, dry mixes and others products like confections and frozen desserts in which water absorption and flavour are important

Low-Heat (LH) =
High solubility

 

• Possesses optimum sensory qualities
• Ideal for use in dairy products and beverages
• Most common source of instant skim milk powder

 
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