Science Buddies: "Ask an Expert"

In early stages of researching project.
The topic: To prove whether or not silver will have an effect on the length of time unrefrigerated milk will stay fresh.

The teacher likes my plan in general, but says I need to be able to measure something.

I could measure the % of curdles, or something like that. I also looked at online catalog to try and find if there was some kind of a test kit for measuring the levels of bacteria each day. I could not really find one.

I need 1. suggestions of what I could measure and evaluate
2. IS there something like a test kit I can order from an online catalog that will help me collect information also?

THANK YOU!!!

Miller

Hi!
This sounds like a cool project! Since sour milk contains lactic acid, perhaps you could measure the relative concentration of lactic acid by measuring the pH. You can measure pH by using litmus paper or some other simple type of pH test. Here are some links that might help-
http://en.allexperts.com/q/Chemistry-in ... milk-1.htm
http://answers.google.com/answers/threadview?id=144545
Hope this helps, good luck!

Hi Miller,

Stary has made a good suggestion for your project. The normal pH of milk is 6.7, so is very close to neutral. Milk contains lactose, which can be fermented to form lactic acid, which will lower the pH. It also contains proteins, which can be metabolized to form basic molecules and this will raise the pH. So you would be looking for any change in the pH of the milk to confirm spoilage.

Here is an article on milk spoilage that includes several methods for detecting spoilage in milk. The authors evaluated the spoilage of milk using the traditional microbial counts using agar in Petri dishes. The science buddies website includes information on this technique. The authors also looked at proteolytic (protein breakdown) and lipolytic activity (fat, or lipid breakdown) to monitor the spoilage of milk. Using any of these 3 techniques would give you a quantitative number that you could use to make a graph for your project board. A quantitative technique would require more time and materials, and would be more challenging, but you would learn a lot also. So, let us know if you are interested in more information on any of these techniques.

http://www.insinet.net/jasr/2007/1383-1387.pdf

The authors of the paper also included a sensory evaluation (color, odor, taste) as part of the evaluation. You could include the sensory evaluation to complement the quantitative results.

Here is a website that includes information on milk chemistry and milk spoilage. You should read this article and also do more background research on your topic. It is very important to do lots of background reading on your topic as this will help you plan a better experiment.

http://www.ilri.org/InfoServ/Webpub/Ful ... mistry.htm

Now, why were you planning to test silver on milk spoilage? This sounds like an expensive way to preserve milk, but the idea is very intriguing. What gave you this idea? What form of silver are you planning to use?

Donna Hardy