Relation between spores in milk powders and predictability of spoilage of UHT milk products

By Jim Cornall contact

- Last updated on GMT

Pic: ©Getty Images/Iuliia Morozova
Pic: ©Getty Images/Iuliia Morozova

Related tags: Uht milk

Scientists from Dutch company NIZO, in collaboration with Abbott, bioMérieux, FrieslandCampina, Nestlé and the U.S. Dairy Export Council, have identified a practical and reliable microbial method to enumerate heat-resistant bacterial spores in milk powders.

The presence and survival of such spores in dairy powders can cause spoilage of UHT-treated reconstituted liquid products. The study, published in the International Journal of Dairy Technology, provides tools to standardize tests and enables improved interpretation of spore count test results, in relation to spoilage risks in UHT dairy products.

Many methods are in use to detect heat-resistant bacterial spores in milk powders. Potentially different outcomes resulting from the application of different methods can lead to disputes between producers of milk powder and their customers, for instance, producers of UHT milk.

This is why scientists evaluated various methods commonly used in the food industry to enumerate heat-resistant spores in milk powders. They compared the most efficient and practical approach with the current ISO method for Enumeration of Specially Heat-Resistant Spores of thermophilic bacteria in Dried Milk (ISO/TS27265; 2009).

It was found that application of the Consortium method provides similar predictability of spoilage of reconstituted UHT-treated milk as the ISO approach, provided that specifications of spores in milk powders are 10-fold higher (e.g. 1000 cfu/g when using the Consortium approach and 100 cfu/g when using the ISO approach).

The major advantage is that the Consortium method includes heating for 30 minutes at 100°C. This is much more practical than heating at 106°C, which is in compliance with ISO TS27265; 2009, but requires special apparatus not commonly available.

The continued use of multiple enumeration methods, and subsequent differences in results and interpretations poses challenges in global trade. Robyn Eijlander, senior project manager Microbiomics and Food Safety at NIZO, said, “This study presents practical tools for the detection and enumeration of highly heat-resistant spores. This allows for harmonization of the interpretation of spore concentrations in dried milk within the entire dairy industry, which helps to avoid disputes between producers and customers. Furthermore, the results improve our insights into the prediction of spoilage of reconstituted UHT-treated liquid dairy products”.

The Spores Consortium Initiative

Spores are a primary concern for the food industry: due to their potential high heat-resistant properties, they are the number one cause of spoilage of a wide range of processed foods. In 2013, the Spores Consortium Initiative was launched to reach consensus on the use of the method mentioned above. Together with partners in the food industry, scientists from NIZO have now expanded the Consortium to cocoa powders and plan to address similar issues in various other non-dairy powders, such as soy and pea protein concentrates.

NIZO principal scientist food safety, Dr Marjon Wells-Bennik, will present the work at the American Dairy Science Association (ADSA) Annual Meeting (June 23-26, Cincinnati, Ohio).

An interview with Eijlander will be part of this week's Dairy Dialog podcast.


Source: Journal of Dairy Technology

Spores in dairy – new insights in detection, enumeration and risk assessment

Authors: Robyn T Eijlander, Rina van Hekezen, Annie Bienvenue, Victoria Girard, Erik Hoornstra, Nicholas B Johnson, Rolf Meyer, Arjen Wagendorp, Donald C Walker, Marjon H J Wells‐Bennik


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Re: Source country of anoxybacillus & geobacillus & projected country of sale of this UHT milk.

Posted by Robyn Eijlander,

Daar Mary. The study was not set up to define the quality of milk powders and resulting UHT milk, but rather to evaluate the methods that are generally used to detect spores in dried milk and provide leads on how to interpret and improve them. The powders used in this study were manufactured specifically for the project and are not in the nearest a reflection of commercially available powders used for UHT products. The powders were selected specifically to understand the efficiency of two different spore detection methods and correlate the findings to the chance of spoilage, for which the conditions were also artificial. The manuscript provides insights on variety in sporeformers that may occur in practice and provides leads on how to improve and reach agreement on most effective methods for risk assessment. I'm sure it will become clear once you read the paper.

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Source country of anoxybacillus & geobacillus & projected country of sale of this UHT milk.

Posted by Mary Krause,

What is the country/countries where these bacilli are found? And in what country/countries do you expect to sell these UHT milks? Are these bacilli found in a particular species of milk cow?
My personal experience with evaporated milk in the past few decades leads me to ask if the milk dehydrated for these products is very fresh milk or older milk which might be more problematic.

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Re: Please define terms

Posted by Robyn Eijlander,

Dear Mary, thank you for your comments.
Firstly, UHT stands for 'Ultra-High-Temperature' and 'cfu' for colony forming unit in per gram (which is indicated in the text above as 'cfu/g').
Concerning the counts and the interpretations as most suitable specifications, depending on the method (heat treatment) used, this does not necessarily mean different thermophilic organisms are begin recovered, but rather different strains of the same species. As we explain in detail in the published article (e.g. Table 6), similar spore forming species are recovered (mainly Bacillus, Anoxybacillus and Geobacillus species) when using 100C for 30 minutes or 106C. However, these species are known to display a great variety in spore heat resistance, even between strains. This is further discussed in the Discussion section of the manuscript, in which we show the bandt-width of heat resistance of spores of various strains of Geobacillus stearothermophilis; the only spoilage-causing organism observed in this study. Unfortunately, this variety in spore heat resistance will always remain a great complication in optimal prediction of spoilage based on spore counts only (cfu/g), and would require more sophisticated (molecular) methods. Nevertheless, the observed correlation (10-fold difference) between both heating methods tested does offer a suitable guideline for which specifications can be used in practice during risk assessments using a simple and practical method.
I hope this clarification helps!

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