Using Genome Analysis Methods to Screen Lactococcus Starter Cultures for Bitter‐Related Genes and Establish a Differentiation Method Using qPCR for Lactococcus lacits and Lactococcus cremoris Species in Cheddar Cheese
Date of Award:
Master of Science (MS)
Nutrition, Dietetics, and Food Sciences
Taylor S. Oberg
Taylor S. Oberg
Consumers of Cheddar cheese expect consistent flavor and texture in the cheese they eat. Cheese flavor and texture is highly influenced by the bacteria cheese makers add during cheese production. These bacteria are generally responsible for the flavors and textures consumers associate with Cheddar cheese and are referred to as starters.
Sometimes during cheese manufacture off-flavors and textures can arise that make the cheese unappealing to eat. One such flavor that is off putting is bitterness. The bitter taste in cheese arises while the cheese is aging and is largely due to the same flavor producing starters added to the cheese by manufacturers. The key determining factor between a starters tendency to produce bitter tasting cheese is the type of enzyme, or protein with a function, on the outside of the cell. Past studies have shown that this protein can be classified as bitter or non-bitter producing. Locating the gene for this protein in starters and comparing it to known bitter and non-bitter using genome comparison tools will help screen and classify these starters as bitter or non-bitter before they get used in cheese making.
These same starters contain more enzymes that help to reduce bitterness in cheese. A survey of the complete genome of the starter bacteria revealed that all of the starter strains contained versions of these enzymes whether they produce bitter cheese or not. This reinforces the idea that bitterness in cheddar cheese is due more to the type of enzyme on the outside of the cell than the cells production of de-bittering enzymes
Knowing that some starters produce bitterness while others do not, it becomes imperative to be able to track the growth of bitter and non-biter starters in the cheese as it ages. To this end, specific genes in the bacteria were targeted. A genome analysis tool that targets these specific genes, causes them to replicate, and tracks that replication was used to develop a relatively inexpensive time saving method to track the growth of the bacteria in the cheese overtime.
All of the above experiments lend a better understanding of how bacteria behave in the cheese especially when related to the development of bitter taste. Pre-screening bacteria for bitter enzyme should help cheese makers pick bacteria that won’t cause bitterness. This will save the manufacturer money and in return lower costs for the consumer. Additionally, using genome analysis tools to track the number of bacteria in cheese overtime can help resolve future problem that could arise from the starter bacteria in cheese making.
Wood, Brantzen R., "Using Genome Analysis Methods to Screen Lactococcus Starter Cultures for Bitter‐Related Genes and Establish a Differentiation Method Using qPCR for Lactococcus lacits and Lactococcus cremoris Species in Cheddar Cheese" (2023). All Graduate Theses and Dissertations. 8786.
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