PACKAGING OF DAIRY PRODUCTS

Module 5. Packaging of milk and milk products

Lesson 19
ASEPTIC PACKAGING

19.1 Introduction

Aseptic packaging is a packaging concept where product is packed under aseptic conditions.The history of aseptic packaging goes back to the early 20th century. A patent was filed for a process, termed as aseptic conservation process in Denmark, prior to 1913 by J. Nielson-following Orla Jensen which was obtained in 1921. In 1950 another major advancement in aseptic packaging took place when first aseptic filling plant was commercialised in the market by Dole which used superheated steam at 210ºC for sterilization. The most significant development in this field is the development of a commercially viable packaging plant for milk, i.e. the Tetra Pak system, following the development of UHT process for milk. The system remains till today the most widely used aseptic processing concept.

The production of a commercially sterile product by continuous UHT processing requires a means of packing which will ensure continued product sterility with the attainment of expected shelf-life. Such a requirement is fulfilled by aseptic packing. Aseptic processing and packaging denotes the filling commercially sterilized and cooled product into pre-sterilized containers under aseptic conditions and sealing in an atmosphere free of micro-organisms.

The basic operation in aseptic packaging consists of:

• Heating the product to sterilization temperatures (140-150°C for 0-few seconds).

• Maintaining the sterility of the products till they are cooled/packed.

• Filling into sterile containers and sealing aseptically.

The main characteristics of aseptic packing which are essential from basic functional point of view are as following.

• Low water-vapour transmission rate.

• Low gas transmission rates, especially to oxygen. This is important to preserve the colour, flavour and nutritional constituents in the products.

• Good physical or mechanical strength, sufficient to resist any physical damage during manufacture, handling and distribution.

• Good sealing characteristics to prevent entrance of external contaminants.

• Capability to fit into automatic fabricating and filling equipment.

• Resistance to withstand the temperatures encountered during filling of the product as well as during storage and distribution.

• Chemically resistant to the product packed and ability to withstand sterilisation packing material with gas, liquid radiation.

• Resistance to microbes, insects and other types of bio¬logical hazards.

• Compatibility with the milk packed. The constituents and additives etc. of the package material should be inert with low migration levels in accordance with the appropriate codes of practice and standards of the country.

• Economical in cost in comparison to the packaged product and readily available in the market.

19.2 Packaging Materials used in Aseptic Packaging

a. 1^st generation material: Paper board/plastic /foil/plastic laminates.

b. 2^nd generation: plastic containers.

19.2.1 Properties sought in laminate for aseptic packaging

The packaging material or container is sterilized prior to filling and sealing in a sterile environment. Both the packaging material and seal are of sufficient strength and function to prevent recontamination of the product during storage and transport.

Various packaging materials are used for milk, from paper-based laminates or carton board, to bottles made from polyethylene or polypropylene. The common packing is typically a combination of polyethylene, paper and aluminium foil. The polyethylene forms a mono-layer protective coat on the outer surface of the carton, and a co-extruded double layer on the inner food-contact surface which aids in sealing. Between the polyethylene layers is a paper layer which provides strength, rigidity and printability and the aluminium foil layer serves as an oxygen barrier.

The general principle of a common aseptic packaging system is that cartons are formed from a roll of packaging material which passes through a sterilizing bath containing a 35% solution of hydrogen peroxide (H₂O₂) at 70-80°C. The packaging material then passes through rollers and a curtain of air at 125°C which evaporates the solution and also serves to increase the rate of sterilization. The film is formed into a continuous tube sealed along the longitudinal edge and the base of carton is then formed by a transverse seal. Milk from aseptic storage tank is filled into the carton, under aseptic conditions maintained by a heater and the carton is sealed by another transverse seal which also forms the base of the next carton. An appropriate cut along the transverse seal separates the cartons.

The complete carton forming, filling and sealing operation is carried out in a closed room, sterilized prior to use. This Aseptic packaging room is separate from other plant and supplied with a positive pressure sterilized air atmosphere.

Figure 19.1 shows the principle of aseptically forming and filling UHT milk cartons. Pre-formed cartons may be used for UHT milk, in which case the packaging is usually pre-sterilized, for example with ethylene oxide gas, and once again with a combination of H₂O₂ and sterile air at around 180°C, just prior to filling and sealing.
Pipelines valves and fittings that are coming in contact with sterile milk are pre-sterilized before use.

Fig. 19.1 Aseptic packaging of UHT milk

There are various packaging forms in which the UHT milk is packed.

19.2.1 Tetra pack cartons

Tetra Pak group of Sweden had launched various types of cartons and 'Tetra Hedron' cartons were the first type introduced in fifties, which required the development of heavy weight paper board/aluminium/polyethylene and have proved to be quite successful for UHT milk packaging. The Tetra Pak Company had gradually replaced these Tetra Hedron cartons with Tetra Brick cartons as the former posed problems of col¬lating and stacking and short shelf life