MARKET MILK

Module 9. Packaging of milk

Lesson 40
PACKAGING - MATERIALS AND PROCESS

40.1 Introduction

Milk being extremely perishable product requires suitable packaging to preserve its initial quality for a predetermined length of time. Milk has been packaged in different types of containers throughout the world. Milk is sold in flexible packages like cartons, bags, pouches, plastic bottles, jars etc. The unique advantages offered by the plastic packages are that they have good barrier properties, permit visibility of the contents, are light in weight, can be used for single service, are easy to carry home, are more economical and can be made more attractive. The use of plastic containers eliminates noise normally encountered in the milk bottling plants and during delivery, and also reduces water pollution caused by milk residues and detergents used in the bottle washing process.

At present, only 15% of all milk produced is packaged by the commercial dairy industry and the flexible pouch accounts for approximately 92% of total marketing. Marketing of liquid milk in India is quite difficult, keeping in view the agro-climatic conditions (high ambient temperature) and poor infrastructure for transportation. Concerted efforts are needed to improve overall quality of packaged fluid milk in India, which will prevent colossal wastage of milk due to inferior packaging. In the light of technological advances in India and abroad in the dairy sector, the success of dairy business is deeply anchored in the packaging system. Inadequate packaging leads to rapid degradation of product's quality.

40.2 Definition

Packaging may be defined as a means for protection and prolongation of shelf-life of a particular food item, so that it may be transported without any hassle.

40.3 Purpose

Packaging serves the following purposes:

1. to contain and protect the product during handling and storage thereby increasing shelf life

2. to inform consumers about product quality and facilitate transportation

3. to attract the attention of consumers and increase sale

4. to prevent scope of adulteration (tamper proof system)

The name, trade name, description of food contained in the package, the name and business address of the manufacturer etc. are printed on the package. A statement about the addition of preservative and its class, permitted colouring agent/antioxidant/vitamins, anticaking agent/stabilizing agent/emulsifying agent/minerals, chemical composition of product and the amount of energy supplied by the product, the net weight or number or volume of contents, batch number or code number are also mentioned on the package.

40.4 Different Packaging Materials

Common packaging materials for market milk industry are:

(i) Glass (ii) Plastics (iii) Coextruded and multilayered packaging materials

40.4.1 Glass

Earlier market milk was distributed in glass bottles. The bottles could be reused after adequate cleaning in a mechanized bottle washing machine. Glasses are generally of two types: (a) transparent and (b) opaque. Glass does not react chemically with the product contained in it. It has excellent barrier property. Besides this, the transparent bottles provide clear visibility of the product inside it. But glasses are brittle in nature, prone to breakage during transportation, handling and even mechanized cleaning. Moreover, they are heavier than plastics/paper packs. Sterilized flavoured milk drinks are still being packaged in heat-resistant glass bottles in India. Presently, flexible polymeric containers have replaced glass bottles for packaging of milk.

40.4.2 Plastics

It has made a revival in the packaging industry and is the most popular material for packaging of market milk. Plastic packaging materials include polyolefins, LDPE (Low density polyethylene), LLDPE (Linear low density polyethylene), HDPE (High density polyethylene), HMHD (High molecular high density) polyethylene, BOPP (Biaxially oriented polypropylene) films, PET (Polyethylene Terephthalate) films, MPET (Metallized Polyester) films, MPP (Metallized Polypropylene) films etc.

These are flexible in nature and are mostly used as wrapper or sachets, bags or pouches. It protects the food from microorganisms, insects, etc. It controls humidity of the dairy products. Some of these packaging materials are discussed below:

40.4.2.1 LDPE

Earlier, single layer LDPE film was used. However, there was a lot of wastage of milk and film, due to pin-holes and poor puncture resistance of the film. Later, coextruded double layer LDPE films with lower incidence of pin-holes was adopted that helped to reduce the wastage.

40.4.2.2 Butane LLDPE

In 1970, Butane LLDPE was introduced to the packaging industry. Eventually, it earned popularity over LDPE because of its puncture resistance, better sealing characteristics and mechanical properties. It has four carbon atoms, of which two align themselves to the backbone, while the other two impart improved physical, mechanical and sealing properties.

40.4.2.3 Octane LLDPE

When blended with 50% LDPE, octane LLDPE provides excellent puncture resistance, superior seal strength and is also amenable to low temperature storage. It has eight carbon atoms, of which two align themselves to the backbone and six carbon atoms introduce long and tightly packed branching. The higher the heat seal strength (HSS) of octane LLDPE, lower is the chance for leakage after packaging and during transportation. Octane LLDPE with excellent hot tack can withstand the load and handle high speed packing with minimal or zero leakage. Hot tack is the strength of a heat seal immediately after sealing while still in a hot condition, i.e. before it has cooled down to ambient temperature and achieved its final strength. It saves the cost of packaging.

40.4.3 Coextruded and multilayered packaging materials (Laminates)

It is a combination of two or more different films. Laminations are done for strengthening the film material, to improve grease-resistance and to increase barrier properties. Some of the laminates are polyethylene/paper, polyethylene/aluminium foil/polyethylene etc.

40.5 Different Packaging Forms

Of the different forms used for milk packaging, flexible pouches dominate with 92% market share and are the easiest, safest and most cost-effective option. The remaining comprises of glass bottle (7%) and Tetra-paks for UHT products (1%).

40.6 Aseptic Packaging

Aseptic packaging refers to a technique in which previously sterilized food is aseptically packaged in a sterile package and hermetically sealed to have prolonged shelf life even under ambient conditions.

Fig. 40.1 Basic flow of an aseptic process

Aseptic package started in Sweden nearly 50 years ago. Tetra Pak was the first company to introduce the aseptic packaging to the market. Now, more than 80% of the aseptically packed products are from Tetra Pak. The food items remain safe upto 6 months in aseptic package without refrigeration. The Tetra Pak packaging materials comprise of six layers in the following order from the outside: (i) polyethylene (ii) paper (iii) polyethylene (iv) aluminium foil (v) adhesive polymers and (vi) polyethylene, all of which work together to keep the product fresh. The innermost polyethylene layer forms the seal that makes the package liquid tight, while the exterior layer keeps the package dry. The adhesive polymer acts as glue between the aluminium foil and inner polyethylene layer. Aluminium foil (6% of the package) forms a barrier against light and oxygen.

40.7 Fino (Fibre Pillow) Package

One of the important packages for market milk industry is Fino-aseptic package. Fino is tailored to provide cost-effective alternative packaging to dairy industry by bringing revolutionary improvement in the efficiency and economy of milk distribution.

Fig. 40.2 Different alternatives in fluid milk packaging

Fino package is a multilayered fibre based tamper¬-proof aseptic pack with its shape similar to a plastic pouch. This package has six protective layers to extend the shelf-¬life of UHT milk, which allows transportation and distribution of milk at ambient temperature.

40.7.1 Fino packaging material

The packaging material for Fino pouch is laminate of paper, aluminium foil and polyethylene. All three components form the six-layer laminate, to provide an effective barrier to microorganisms and external hazards such as sunlight and oxygen. Fino packaging concept is presented in Fig. 40.3.

Fig. 40.3. Fino packaging concept

40.7.2 Process of filling

There are four sections of filling used in Fino packaging:

1. feeding of the packaging material into the filler

2. application of hydrogen peroxide (H2O2) – concentration and means to evaporate the same to have no residual traces

3. forming the packaging material tube

4. evaporation of hydrogen peroxide and filling under aseptic environment

Fig. 40.4 Fino filling machine

40.7.2.1 Feeding of the packaging material into the filler

The packaging material is supplied in roll form to the filling machine and travels up to the backside of the machine. A strip is applied to one edge of the packaging material. This strip has two functions: (i) to reinforce the longitudinal seam and (ii) to prevent the product from coming into contact with paper layer.

40.7.2.2 Application of hydrogen peroxide

After the initial section, a film of H₂O₂ is applied on the interior side of packaging material (six ply) by a transfer roller system. For this purpose, 35% H₂O₂ is used along with a wetting agent. The purpose of this H₂O₂ bath is to sterilize the packaging film.

40.7.2.3 Forming the packaging material tube

The packaging material tube now passes the top of the filling equipment and is formed into a tube on its way down to the tube heater and to the transversal sealing area. During production, sterile air is constantly blown into packaging material tube, creating a sterile air curtain in front of the food contact surface of the packaging material.

40.7.2.4 Evaporation of hydrogen peroxide and filling under aseptic environment

Generally, a pair of pressure rollers removes the surplus hydrogen peroxide. While working down, the remaining H2O2 is evaporated by heat through tube heater. After the packaging material passes the tube heater element, its surface becomes dry and sterile.

40.8 PET (Polyethylene Teraphthalate) Packaging

PET bottles give a perfect finish, making the bottles re-closable without leakage. They neither contribute to off-flavour nor impart plastic taste. They are clear, transparent, recyclable, eco-friendly and are available in various design or forms. They have excellent oxygen barrier property. In monolayer PET bottles, the shelf-life of milk may be extended upto 30-90 days. These can be either clear bottles, or for some sensitive flavours, colour may be added for light protection. For UHT milk, shelf-life up to six months can be achieved with PET bottles stored at ambient temperature. However, a light barrier is a must to prevent degradation of milk. For pure white milk, multilayer PET bottles or monolayer bottles with full light barrier are used. Milk fortified with vitamins can be kept safe in multilayered PET bottles, having light and oxygen barrier.

40.9 Retort Packaging

It is oldest process and is still used by major dairies to package flavoured milks, which involve filling milk into heat resistant glass/polyethylene bottles and then sealing them with air-tight and pressure resistant caps.