Science Buddies: "Ask an Expert"

Hello scientists!
I am doing a project regarding the growth of milk into yogurt with the aid of certain active cultures!
During my experiment I found that the only brand of yogurt that did not affect the milk very much or at all was Fage. It seems as if most of the yogurts used the L. Acidophilus culture. I was wondering if anyone knew if any of the types of active cultures used in the Fage yogurt would have changed my outcome. Thanks in advance!

Fage: L. Bulgaricus, S. Thermophilus, L. Acidophilus, Bifidus, L. Casei
Yoplait: L. Acidophilus
Ralph's: L. Acidophilus, B. Bifidum
Dannon Oikos: Dannon's website lists the culture in Oikos as "the culture used" but I believe it's implied there is only one.

I would also like to ask: What similarities are there between active cultures in the yogurts and human's active cultures?

Hello,
There could be a couple of reasons why the Fage yogurt didn't grow. It could be that the cultures were old (did you check the expiration date?), or perhaps they need a longer period to grow, or maybe the concentration of them in that brand of yogurt is lower than in the other brands you tested. Since that brand contains some of the same cultures that are in the other brands that did work, my guess is that it is an issue with that particular sample of yogurt, not that the cultures wouldn't grow in milk. Does that make sense?

If you want to be extra thorough, you could set up a series of experiments on that one brand of yogurt to see if you can get it to grow by changing the conditions. Perhaps adding more yogurt to start with, or find one that has the newest expiration date, use more or less milk, change the temperature...these are all variables that you could play around with. Just make sure you only change one thing at a time so if the yogurt starts to grow, you know why.

To determine similarities between cultures in yogurt vs humans you may want to find out what strains exist in humans and go from there.

Hope this helps!
Katie