A new microbial method to enumerate heat-resistant bacterial spores in milk powders, thereby preventing spoilage, is being put forward by scientists from food and health research company NIZO, together with key players in the dairy industry. Abbott, BioMérieux, FrieslandCampina, Nestlé and the US Dairy Export Council have joined forces to work towards a harmonized method which provides tools to standardize tests and improve spore count test results, in relation to spoilage risks in UHT dairy products.

Known as “The Spores Consortium,” the partners offer a practical standardized method that can be applied by dairy powder producers and their customers worldwide.

The presence of bacterial spores in powdered ingredients, such as soy, milk or pea, may determine the microbiological safety and quality of finished products, as spores may not be inactivated by commonly applied processing conditions. Surviving spores can germinate, followed by outgrowth in products, subsequently leading to spoilage or even foodborne illness. However, methods to detect relevant spores in powders are not harmonized globally.

The presence and survival of such spores in dairy powders can cause spoilage of UHT-treated reconstituted liquid products, while the use of various enumeration methods and subsequent differences in results and interpretations can pose challenges in global trade. 

Currently, there are several methods used to detect heat-resistant bacterial spores in milk powders which can lead to different outcomes, which, in turn, can lead to disputes between producers of milk powder and their customers, such as, producers of UHT milk. 

By evaluating the various methods that are commonly used in the food industry to enumerate heat-resistant spores in milk powders, scientists compared the most efficient and practical approach with the current International Organization for Standardization (ISO) method for Enumeration of Specially Heat-Resistant Spores of thermophilic bacteria in Dried Milk (ISO/TS27265; 2009). 

Their study discovered that the application of the consortium’s 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’s approach and 100 cfu/g when using the ISO approach).

What is the advantage of the consortium method?
The consortium’s method includes heating the milk for 30 minutes at 100 degrees Celsius which, according to the researchers, is much more practical than heating at 106 degrees Celsius. This is in compliance with ISO TS27265; 2009, but is made much more challenging because it requires a special apparatus that is not commonly available.

“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,” says Robyn Eijlander, Senior Project Manager Microbiomics and Food Safety at NIZO.

“Furthermore, the results improve our insights into the prediction of spoilage of reconstituted UHT-treated liquid dairy products,” he notes. 

Why are spores such a concern for the food industry?
Due to their potential high heat-resistant properties, spores are a primary concern and are considered to be the number one cause of spoilage in processed foods. 

Initially launched in 2013, The Spores Consortium Initiative has now expanded to cocoa powders and plans to address similar issues in various other non-dairy powders, such as soy and pea protein concentrates.

The study sheds light on the performance of the various methods, highlights the importance of understanding and modeling spore heat resistance and offers advice on the most practical and efficient way to predict spoilage in reconstituted UHT-treated liquid dairy products. 

NIZO will present this work at the American Dairy Science Association in June.