Xanthine Oxidase
Cheese MoleculeAn enzyme found in milk; used for preservation purposes in some cases
Xanthine Oxidase is an enzyme naturally produced by cows. Some of this enzyme ends up in their milk and therefore cheese. This enzyme is an important part of a cow’s normal metabolic processes and is crucial for their health. However, this isn’t a dairy nutrition blog, so let’s park that discussion for now. (It involves the breakdown of purines into uric acid)
The structure of xanthine oxidase. This structure is from the enzyme derived from bovine milk. (1FO4)
Visualized using 3Dmol.js.
Some cheesemakers can take advantage of this enzyme and use it to help preserve their cheese! Specifically, this enzyme when combined with sodium nitrate can help inhibit Clostridia species of microbes. Why does this matter? The “late blowing” defect in cheese can be caused by Clostridia microbes like Clostridium tyrobutyricum. This baddie can produce gas and butyric acid, which cause unsightly openings, cracks, etc. (Not to mention an awful aroma/flavor)
Late blowing is a common defect in many semihard and alpine-style cheeses.
Sodium nitrate, when added to milk, will react with xanthine oxidase and transform into sodium nitrite. Nitrites can inhibit Clostridia, thereby alleviating one source of late blowing. Most of you reading this are probably wondering why you’ve never seen “sodium nitrate” as an ingredient in cheese if it’s so effective at preventing such a common problem? Here’s the thing: the FDA allows sodium nitrate in meat* as a preservative, but not cheese!
Xanthine oxidase catalyzes the conversion of nitrate to nitrite.
*Meat doesn’t rely on xanthine oxidase to convert nitrate to nitrite. Instead, native cultures and “cure accelerators” like sodium erythorbate are used.
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