PACKAGING OF DAIRY PRODUCTS

Module 5. Packaging of milk and milk products

Lesson 18
UHT STERILIZED MILK

18.1 Introduction

High heat treatment of milk is not enough to give long shelf life of UHT milks if packaging is not proper. So packaging plays an important role in UHT products.
UHT milks, like pasteurized and sterilized milks, can be packed in plastic bottles and pouches. The bottles may be blow-moulded at the point of packing, or pre-moulded on either unsterilized or sterilized form. Because of the shelf-life requirements of UHT milks, multiple laminates, for example a triple layer of high density polyethylene are used. An intermediate light barrier may be incorporated, according to the manufacturer’s preference. Oxygen penetration during storage is not usually a problem. Whatever the source of bottles, aseptic techniques are used in filling and sealing to prevent contamination, and milk can be expected to have a shelf-life of 6 months at ambient temperatures.
For short shelf-life (10-15 days) products, pouches are usually made of white polyethylene and paper.

18.1.1 Cans

Aseptic canning is expensive, particularly for a low cost product like milk. Cans are not preferred for packaging of UHT processed products as the processors and marketers of the product generally want to emphasise the newness of the process whereas cans are identified with conventionally retorted products. The cans may be of tinplate or drawn aluminium. The solder in tinplate cans must be of higher melting point than normal to withstand the in-can sterilization temperatures. The cans pass along a conveyor belt within a continuous tunnel. Tunnel temperature (200-220°C) for sterilization of cans is attained by steam (at atmospheric pressure), superheated with gas flames-sterilization time being 40s, normally. The cans having passed through the sterilizing tunnel continue through the filling chamber where they are filled with the product. The can lids are sterilized, again by superheated steam, in a separate unit. The lids are applied and seamed in a chamber kept sterile by super heated steam and flue gas.

18.1.2 Paper board cartons

This kind of packaging materials are commonly used in aseptic filling systems for milk, cream, fruit juices, soups etc. The filling systems could be either of the following two types: those in which the carton is formed within the filler from a continuous reel of material; and those in which the cartons are supplied as preformed blanks, folded flat, which are assembled into cartons in the filler. The packaging material is mainly composed of printed-
paper coated with aluminium foil and several plastic layers (Polyethylene-paper board-polyethylene-aluminium foil polyethylene). The inner material side of the finished package is coated with a special layer facilitating the sealing process. Each layer has a specific function:

Fig. 18.1 Multi layered Packaging

• The outer polyethylene layer protects the ink and enables the sealing process of the package flaps.

• The paperboard serves as a carrier of the décor and printing gives the package required mechanical strength.

• The laminated polyethylene binds the aluminium to the paper.

• The aluminium foil acts as a gas and light barrier.

• The inner polyethylene layer provides liquid barrier and sealing

18.2 Flavored Milk

Flavoured milk drinks are generally skimmed or partly-skimmed and contain less than 1.5% fat. The package should be leak and tamper proof, should have sufficient wet strength and should not pass on any odour or taint to the product packed inside. The plastic based material used for sachets is octane LLDPE (O-LLDPE). OLLDPE when blended with 50% LDPE provides excellent puncture resistance, excellent seal strength. Co-extended multiple layers low-density films with an outer opaque film and an inner black film for reducing the transmission of light are also used.

In India, flavoured milk drinks are available in sterilizable crown cork glass bottles, glass bottles with aluminium foil lid or snap-on plastic lid, plastic sachets and aseptic packs (Tetra bricks). Recently 200ml, translucent bottles of HDPE with an aluminium foil cap have also been introduced. Poly carbonate bottles with the leak proof screw cap are also used in place of glass bottles as these are unbreakable and are much lower in weight (1/6th the weight of glass bottle). PET containers are in use as they are light in weight, have good sales appeal and are strong.