Can we predict - how long we can store milk powders especially in elevated temperatures and humidities?


Fonterra Co-operative Group is the world's larger exporter of dairy products, owned by around 10,500 New Zealand dairy farmers and a leading multinational dairy company. The Fonterra Group's global supply chain stretches from Fonterra's shareholders' farms in New Zealand through to customers and consumers in more than 100 countries. Collecting around 15 billion litres of New Zealand milk each year along with around 6.5 billion litres sourced globally, Fonterra manufactures and markets over 2 million tonnes of product annually. This makes the Fonterra Group the world's leader in large scale milk procurement, processing and management, with some of the world's best known dairy brands.

Fonterra continue to focus on our quality and food safety infrastructure, ensuring that we identify and remain ahead of emerging food safety risks. One such risk is product deteriorating whilst in storage. In the case of milk powder the risks are minimised by nature of the drying process and appropriate packaging and handling of the finished goods, but there will always be some deterioration in storage and require a method for assessing what the commercial shelf-life really is.

Problem for MINZ: Milk powder is a very complex material whose sensory properties change with time and it is the possible development of taints corrupting the powder – either through chem/micro reactions within powder or coming through the packaging membrane from the storage environment. The kinetics of these reactions are not well known and as a result generic storage rules have developed such as store below 25C for now longer than x months have been developed and used, but increasingly there is desire to better define these rules and establish shelf-lives for product stored in less than ideal conditions

Factors that might influence the shelf life might include

  • Chemical (and microbiological) composition of the powder.
  • Levels and types of fortification (eg calcium, iron, zinc, vitamins)
  • Powder physical properties
  • Packing material properties
  • Packing configuration (arrangement of bags on pellet, pellets in shipping containers/warehouses etc)
  • Environmental conditions during storage/transit, including temperature, humidity
  • Seasonal effects
  • Cattle feed, including supplements

While there is some data from historic storage trials this data is often of limited use as often at only NZ ambient conditions and often using powder stored at laboratory scale (not 25kg or larger bags). Processing technologies have also developed significantly and both the gross and micronutrient nature of milk powders has changed so cannot be applied to commercially stored product, but may be possible to develop a crude “overall powder quality”

Some customer complaint data is also available, but this too is of limited value as often there is insufficient knowledge of how the powder was stored or transported to assess

From the workshop we would like a model to be produced, taking into account a number of the above factors, that will provide us with an estimate of the true shelf-life. This may include assessing if an overall powder quality parameter can create as a surrogate for each individual quality measurement and if a realistic worst case kinetic model for this can be constructed. Alternatively, taking a more statistical approach, to look at the type of experimental design that best suited for a shelf-life trial that can take into account many of the aspects and while this is very likely to be along the lines of a fractional factorial split-plot type design with repeated time measurements are there alternative experimental designs that more appropriate