The Western Dairy Center at Utah State University funded this project as part of its BUILD Dairy program with support from the dairy farmers of Idaho, to investigate the problem of splits that form in cheese during storage. The bacteria, Lactobacillus wasatchensis had previously been identified as a cause of unwanted gas production in cheese and the defects then make the cheese unsuitable for cutting into slices. The project team proposed a two-year, $150,912 project to investigate methods for determining the presence of this bacterium in cheese by extracting DNA from the cheese and looking for DNA that was specific to Lactobacillus wasatchensis. The project identified a suitable method for extracting DNA and demonstrated that methods that extract DNA directly from the cheese are not as repeatable or reliable as a method that first separates and collects the bacteria from the cheese and then extracts the DNA. While the detection limit for identifying Lactobacillus wasatchensis in cheese of 100,000 cells per gram, was not any lower than that which can be achieved using plating methods, this work provides the benefit of laying groundwork for selection of a NDA extraction method for use with cheese. Further research can now be applied to lower this detection limit so this bacterium can be identified in cheese earlier and thus reduce the problem of slits and cracks and provide a higher value of the cheese to the manufacturer.

There are numerous challenges encountered during the manufacturing and storage of cheese by both the large-scale and artesian producers. One such challenge has been the formation of late gassy defect, which occurs when gas is produced by certain lactic acid bacteria found in the cheese block during storage and aging over a three month time period. Negative consequences of late gas production are slits and cracks in the cheese block and puffy cheese packaging, which cause significant financial losses for manufacturers along with poor consumer acceptance. Lactobacillus wasatchensis is one such lactic acid bacterium shown to produce gas during cheese storage. This bacterium has now been found in cheese samples exhibiting late gas defect in the Midwest and Western states. The goal of this study was to further characterize and understand the growth attributes of Lb. wasatchensis, and thereby gain some understanding on how it enters the cheese vats and if there are possible ways to limit or inhibit its subsequent growth. An additional goal was to determine if we could effectively extract Lb. wasatchensis DNA from cheese samples and visualize using the qPCR molecular technique. If possible, this detection method would allow a faster and more sensitive approach to determining if Lb. wasatchensis is present in cheese blocks, which would help manufacturers know how long they should age their cheeses. It was discovered that Lb. wasatchensis does not survive processing through an industrial heat exchanger and therefore must be entering the cheese vats by other means such as: cross-contamination, biofilm formation or aerosolizing. We also showed growth of Lb. wasatchensis is limited at an increased salt-in-moisture ratio in cheese. Additionally, we found that Lb. wasatchensis DNA can be extracted from cheese and visualized using qPCR, although further experimentation is needed to optimize this method.