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Name: Hannah B.
Status: Student
Age: 17
Location: N/A
Country: N/A
Date: April 2003

I am doing my A2 human biology course work- I have done a test on the pH level changes of the yolk and albumen of hens eggs as they get older (in this I tested the pH of the yolk and albumen of eggs over a period of 2 weeks). In the results, the pH of the yolk decreased and the albumen increased. I know that this is partly to do with the increased number of bacteria, but how does the bacteria affect the pH?

In general, bacteria can change the pH of their environment by producing acid or basic metabolites. For instance,lactic acid bacteria produce lactic acid when feeding on lactose in milk, and thus produce the typical taste of yoghurt or buttermilk.

Whether bacterial growth has produced the change in pH in your eggs experiment I can not say. Other factors, such as general decay (decomposition of proteins) can also influence pH.

Trudy Wassenaar

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