A rapid sterility testing for UHT products

To produce beverages such as milk or fruit juices with long shelf lives at ambient temperatures without the use of preservatives products must be Ultra High Temperature (UHT) processed. This involves holding product for a short time at a high temperature and packing into sterile packaging to ensure commercial sterility. While the food standards code doesn’t dictate a UHT test (standard 4.2.4 Primary Production and Processing Standard for Dairy Products only cites a minimum pasteurisation of 72◦C for 15s) it is vital to ensure processing has been adequate to reach shelf life.

Before any product can be sold, testing for sterility has to be completed. While once this involved plating of samples and lengthy incubation, there is now a rapid sterility testing method available for faster release of the product.  

While still taking days to gain a result, ATP bioluminescence is still a faster method than traditional microbiological plating. All cells have adenosine triphosphate (ATP) present within them. The enzyme luciferase catalyses a reaction with ATP that emits light. UHT samples are incubated for several days at optimum growth temperatures to multiply bacterial colonies if they are present. Incubation is necessary as UHT will cause a significant reduction in microbiological counts even if sterility is not achieved. Samples are then dosed with luciferase and placed in an apparatus with a luminometer. Each sample is measured (as well as negative controls) to determine if the product is sterile. If there is luminescence measured than the product is not sterile and should not be released. 

Image source

"Federal Register Of Legislation - Australian Government". Legislation.gov.au. N.p., 2016. Web. 12 Sept. 2016.

Cunha, A. F., Lage, A. D., Pereira e Araújo, M. M., Abreu, C. F., Tassinari, A. R., Ferraz, M. A., … Cerqueira, M. M. O. P. (2014). ATP-Bioluminescence as a method to evaluated microbiological quality of UHT milk. Arquivo Brasileiro de Medicina Veterinária E Zootecnia, 66(6), 1909–1916.