March 25, 2019 – Scientists from NIZO, in close collaboration with Abbott, bioMérieux, FrieslandCampina, Nestlé and U.S. Dairy Export Council, have identified a practical and reliable microbial method to enumerate heat-resistant bacterial spores in milk powders. Presence and survival of such spores in dairy powders can cause spoilage of UHT-treated reconstituted liquid products. The study provides tools to standardise tests and enables improved interpretation of spore count test results, in relation to spoilage risks in UHT dairy products.
Many different 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. That is why the scientists evaluated various methods that are 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 a special apparatus that is 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: “This study presents practical tools for the detection and enumeration of highly heat-resistant spores. This allows for harmonisation 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.
In the published article, efficiency of various enumeration methods was established for a wide range of spore-forming species that are commonly encountered in dairy. The comparison between the Consortium method and the ISO method is described in detail. The study sheds light on the performance of the various methods, highlights the importance of understanding and modelling spore heat resistance, and offers advice on the most practical and efficient way to predict spoilage in reconstituted UHT-treated liquid dairy products. NIZO Principal Scientist Food Safety Dr. Marjon Wells-Bennik will present this work at the American Dairy Science Association (ADSA) Annual Meeting (June 23 – 26, Cincinnati, Ohio, USA).