Science Buddies: "Ask an Expert"

Hello, my name is Omkar and I am in the 7th grade. I have been working on the experiment “What is in this Water? -Experiments with a Homemade Turbidity Meter.” I have built the light sensing circuit in what I feel is a fairly accurate set up. I tested it by measuring the turbidity of different concentrations of 1:10, 1:20, 1:40, 1:100, 1:1000 and no milk. I have graphed the results (see attachment). Unfortunately I have run into trouble with the biology portion of the experiment. When I add 10ml pineapple juice to 200 ml of 1:10 milk dilution, the milk coagulates after some time. However I am wondering if this is because the protease in the pineapple is denaturing the proteins in the milk or if the acids in the pineapple are simply causing the milk to curdle. I added 5 ml of lemon juice to the 1:10 solution and a similar effect occurred except much faster. I wanted to know how to tell between the protease and curdling so I put some pineapple juice in the microwave in order to denature the protease but not take away the acid. Over 50 min, measuring every 5 min, I compared live pineapple juice to the micro-waved one. After 20 min, the live juice solution decreased in turbidity from 8.73V to 8.72V, and after 30 min the micro waved solution decreased in Turbidity from 8.74V to 8.73V. This gave me another concern: the change registered in turbidity is very small; can I increase the change or the accuracy in measuring in it? I plan to measure the effect of salt on the enzyme efficiency- is this a bad idea? Also, I was thinking of using commercially bought bromelain (which I think is the enzyme in question) instead of pineapple juice. Any help is appreciated, thank you.

Hello,

I think that measuring the effect that salt has on protease activity is a great project. I did some research on bromelain, and it is one of the proteases present in pineapples, but I think that you should stick with the procedure mentioned on the science buddies website - using pineapple extract - because the bromelain that is commercially available is not pure (it contains additional ingredients) and it could be difficult to determine the proper concentration of the enzyme for your experiment.

To address your concern about the acidity of pineapple juice, I found this article online which says store bought pineapples that are ripe generally have a very low to zero acidic level, so this should not be a problem for your experiment. http://www.pineapplejuice.com/why-is-pi ... cidic.html

Hope this helps, Good Luck
Nithin T.