Module 5. Packaging of milk and milk products

Lesson 22

22.1 Introduction

The shelf life of a dehydrated product is influenced to a large extent by the packaging, which must conform to certain special criteria.

These are:
  • Protection of the dehydrated product against moisture, light, air, dust microflora, foreign odour, rodents etc.
  • Strength and stability to maintain original container properties through storage, handling and marketing.
  • Size, shape, appearance to promote marketability of the product.
  • Composition of the container must be approved for use in contact with foods.
  • Lower cost.
22.2 Selection of Packaging Materials

Dehydrated dairy products are generally hygroscopic in nature and even slightest increase of the moisture content will decrease the shelf life considerably. Hence, the packaging material should be impervious towards water vapour and such property is to be considered important for packing such products. When retention of low moisture content is the limiting factor of the shelf life of the product, the tests required to be made for determining the shelf life are: determination of
  • The normal moisture content of the product
  • The moisture content of the product at which the product becomes unacceptable to the consumer and
  • The R.H. and temperature of the surrounding atmosphere at which the equilibrium moisture content is maintained in the product. Initial level to the level of unacceptability is calculated. From this data along with requirement for gas permeability etc. and utilizing the published data for different packaging material, the suitable packing material is selected.
22.3 Properties of Dried Milk Products Relevant to Packaging

1. Hygroscopicity is the principal requirement which is important in small packs size where ratio of pack surface area to product is high. In tropical countries because of the high humidity prevailing, this is the important factor.

2. Cohesivity or the Cohesion of product is the serious stickiness problem particularly in high speed packaging lines. In case of powder, observations made on cohesivity are

1. Cohesion increases with decreasing particle size.

2. It is independent of fat content in the range of 20-40% Fat.

3. A small amount of surface fat is sufficient to give cohesion to WMP.

4. Increasing the moisture from 2 to 4%, cohesion first decreases and beyond 4% cohesion increases very fast.

3. O2 Sensitivity: Preheating releases the -SH groups which protect against oxidization. However still there are chances of oxidation. Therefore for Fat containing products prevent the gas diffusion by employing either Vacuum or N2 flushing.

4. Light sensitivity: Powder exposed to light for long period bleaches the surface and thereafter it accelerate Fat oxidization.

5. Heat sensitivity: Affect Flavour and Solubility. Ideal storage conditions are 180-190˚C temperature and dry atmosphere.

6. Bulk Density is very important because Packaging size is affected. The Free flowing properties improves with increased Bulk Density.

7. Odour pick up: Product containing Fat is prone to pick up odour. High Fat powders pick up odour from packaging materials, surrounding atmosphere, stores, water and houses. The off flavour problem is encountered from kraft paper, PE film, CFB, fiber board cases and even from rubber sealing compositions.

8. Static electricity: The problem is difficult to resolve. The plastic packaging materials are also important where antistatic agents are added e.g. Glycol alkyl esters (prevent electrical charge accumulated on the film surface).

9. Bacterial aspects: Powders of normal moisture and RH do not give rise to bacterial problem.

22.4 Requirements of Package for Dried Milks
  • Adequate mechanical strength to withstand damage during packaging, handling, transportation and storage is necessary.
  • Resistance to climatic hazards: The material should be resistant to damage by exposure to high / low temperature and humid atmosphere. This is more important in tropical countries.
  • Convenient closure: Sealing is of supreme importance. Simple, effective re-closure is also desirable.
  • Bulk packages should be light in weight, easy to handle and stack during transport and storage. Empty packages should occupy minimum storage space before use.
  • Very low Water vapour and gas permeability: Dried milk absorbs moisture very easily. Powder with > 5 % moisture gets deteriorated during storage. The stale and gluey flavours result from Maillard reaction. It results in losses of solubility, colour change; lumping and free flowing properties are affected. For long storage, vacuum and N2 flushing is essential especially in hot climate. An impervious container is needed which should also be odour-proof.
  • Impermeability to light: To avoid surface bleaching and fat oxidation.
  • Inertness, durable, safe, utilizing minimum space, identification of product and directions for use, easy availability at reasonable cost are the other requirements.
22.4.1 Packaging materials available

1. Glass: Bottles, barrels, jars, etc.

2. Metal: Cans, barrels, drums, bins, etc.

3. Wood: Drums, bins, cask, barrels, etc.

4. Paper and paper derivatives

5. Metal foils

6. Thermoplastics and their derivatives

7. Composite films
  • Co-polymer film
  • Coated film
  • Co-extruded plastic film
  • Laminates
22.4.2 Flexibles for powder
  • Cartons lined with Al-foil-PE:
    • Bag-in-box: Coated Al-PE bag or plastic coated paper inside cartons.
    • Modified Atmosphere Packaging -80% N2 and 20% CO2 where O2 content is reduced to 3.0%.
  • Long storage: Lacquer/print/print pre-lacquer, Al-foil (10 gsm)/Adhesive coated paper (40 gsm)/PE (30 gsm).
  • Shorter Keeping quality: Al-foil may be omitted. Paper thickness increased to ~ 70 gsm and coated with PVDC (30 gsm).
  • Bulk Packaging: Sacks made of craft paper laminates, parchment, polyethylene, Al, Cellophane, bitumen, wax or paraffin. Even cast films now are used recently. Most common types:
    • WMP: Laminates of paper, PE, Foil, Metallized, BOPP/PE or PET.
    • SMP: HDPE or LDPE or Laminates of HD, LD, LLD, Nylon, Saran (coating), EVA. PE coating or wrinkling- Bag-in-box paper board/lined with paper, Al or Metallized/PE
  • Powder packaging materials:
    • Number of Kraft paper layers for strength required is 3-6 for 25 kg wt.
    • Outer Kraft paper bag strength 70 gsm, Second Kraft paper bag with paper alone. PE lined (95 gsm).
    • WMP: 4-6 ply kraft paper, 3 mm PE
    • SMP: 2-4 ply kraft paper 2 mm PE
    • Separate PE liner/inner bag – 0.04 mm for 25 kg & 0.05 mm for 50 kg.
    • PE varies in thickness from 0.02 to 0.08 mm as inside layer.
22.4.3 Retail packages
  • Thick laminated paper (45 gsm) – Al-foil (9 μ) – PE (25 μ) having Bursting strength 179 KPa (1.83 kg.f/ cm2) and very low WVTR & GTR.
  • PET (12.5 μ)/Al-foil (9 μ) / PE (64 μ), Bursting strength 290 KPa (2.95 kg.f/ cm2).
    • Form – Fill – Seal: 17 μ PET / 9 μ PE – 9 μ foil – 70 μ PE
    • Metallized film is also used. Lined cardboard – Adhesive / Coating of PVDC or RHC – Metallized PET / Al-foil / PE.
    • Metal/Plastic laminate – Retain O2 content of 0.5 % even after 13 numbers. Bulk: Heavy gauge PE used mainly for sea voyage (passing through tropics).
  • PE is used to much lesser extent as a separate bag within or as a liner for (a) Card board cartons, (b) Calico bags, (c) Jute bags with paper, (d) Liner between jute and PE.
  • Alternative material to PE
    • Multi walled paper sack may incorporate one layer of waxed paper which is more satisfactory than paper alone but is inadequate for long storage.
    • Multi wall sack may include a layer of bituminized paper, often the outer layer with 4-5 inner kraft layers. This is a good packaging material used even for export but is slightly inferior to PE.
  • Perfect closure is required
    • Metal is completely impervious but closure is a weak point.
    • Sack is sealed by sewing threads which makes holes and therefore it is covered by H2O proof tape.
    • Gas packaging by mixture of N2 + H2 + Palladium as a catalyst and if kept impervious can have up to 10 years of storage life.
22.5 Whole Milk Powder and Baby Food

Generally packed in Lacquered tins under N2 gas packaging. Whole milk powder is packed in 15 kg tins. For retail milk powder s packed in laminate bags made of PET /Al / PE.

22.6 Skim Milk Powder

Skim milk in bulk quantities of 25 kg is packed in kraft paper bags with inside polyethylene bag. Skim milk powder for retail is packed in HDPE bottles and HDPE bags.

22.7 Malted Milk Food

The malted food beverage industry is popularly known as the health beverage sector. Historically, malted beverage has a strong association with milk. The Indian health beverages market is divided into white and brown health drinks. White beverages contribute about 65% of the market.

Malted milk foods are highly sensitive to moisture and are prone to oxidative changes in the presence of light, heat and oxygen. Aroma retention of the product and prevention of moisture and oxygen ingress are important and therefore are very critical in protecting the product, and in selection of the right packaging material.

Malted milk foods are packed in quantities of 200 grams to 1 kilogram in a variety of packages. The types of packages used conventionally are glass jars, tinplate containers, which are now slowly being replaced by plastic containers and flexible laminated pouches. Though glass containers are hygienic and safe and offer the advantage of a long shelf-life, it has the disadvantage of being heavy, fragile and costly. Tinplate containers though provide good protection from gases and moisture, are likely to rust at body welding or at top and bottom seams. Tinplate containers are also expensive.

The plastic containers used are blow moulded HDPE or HM– HDPE or stretch blow moulded PET containers / jars, for brown and white malted milk food products for capacities ranging from 200 grams to 2.5 kilograms. The plastic containers are light weight, sturdy, unbreakable and hygienic, and have a good shelf appeal.

Besides the plastic containers, the trend is also to use flexible pouches, which may be with or without paperboard cartons. This type of pack has an advantage of low cost compared to plastic bottles. Moreover, the storage space requirement is low and the filling operation is comparatively faster.

Some of the typical structures of flexible materials used are:

1. 50 and 100 grams

a. 12μ PET/12μ metallised PET/38μ LDPE

2. 500 grams

a. 12μ PET/20μ metallised BOPP/50μ LDPE

b. 12μ PET/12μ metallised PET/50μ LDPE

3. 1000 grams

a. 12μ PET/12μ metallised PET/65μ LDPE

22.8 Precautions Before Packaging

Protection against moisture pick up: The low moisture products must be packaged as soon as possible after removal from the dehydrator. Each product has its individual need with regard to moisture uptake.

22.8.1 In-package desiccation

In-package desiccation has been used successfully for many dried products, particularly powders. The desiccant compound is placed in the container inside a small envelop made out of a moisture permeable material which does not allow the contamination of the product with desiccant, Calcium oxide or silica gel are usually used for this purpose. When in package desiccant is used, the dried product can be stored at higher moisture content without caking than in the absence of a desiccant. However, this is not used for milk powders.

22.8.2 Anticaking agents

Anticaking agents are mixed with the low moisture product usually during the milling operation. Calcium Stearate is the most commonly used Anticaking agent in dehydrated products. This is also not used in case of milk powders.

22.8.3 Packaging of condensed milk and evaporated milk

In the early days sweetened condensed milk in bulk is packed in barrels made of gumwood. Later white oak, paraffin lined barrels were used 50 to 300 kg.
For industrial purposes steel drum containers with removable lids are used which are suited for re-use.
For retail marketing, sweetened condensed milk is packed in lacquered hermitically sealed tin can (400 gm)/ FK can. Most tins used are open top tins, the top end of which is clinched on to the can after filling. The tins are filled in automatic filling machines. The tins should be filled as completely as possible to ensure that as much as less space remains in the head space. The temperature of filling room is maintained around 16°C. the tins and lids should be sterilized by super heated steam/ hot air or U.V radiation before use.
Aluminium cans filled with condensed milk will not be subsequently sterilized, strict sanitary conditions should be observed during filling by process sealing.

Evaporated milk is packed in cans before sterilization.

Last modified: Thursday, 8 November 2012, 10:02 AM