Milk Plastic project, compare the weight of the casein plastic

[reneeshih]

Hi my name is Emma and I am doing an experiment by comparing whole, 2% and skim milk adding vinegar. I used 100g for each milk and 30g vinegar. I molded them into same shape and let them. The final dry milk plastic weight differently (7.3g, 6.5g and 3.5g).My question is this: if all milks have about 3.3% protein, and within the protein there is about 8o% of casein protein. The math goes like this: 100x3.3%x80%=2.64. Why did I get much heavier casein protein? I weight my plastic everyday until the weight stay the same -so I know it is dry. Does my math wrong? or there is something in the milk that I do not know? Thank you!

[SciB]

Hi and welcome to Scibuddies.

No your math is not wrong. Are you sure that each of the three types of milk had the same amount of protein per 100 g? I checked online and the website I consulted (https://www.healthline.com/nutrition/wh ... k#section1) said that whole milk has less protein per cup (237 g) than skim or 2%. You reported more protein extracted from whole milk, however.

I can think of a couple of possibilities for the protein differences. Since your percentages increased with increasing fat content in the milk, there may be a connection there. Maybe the coagulated protein somehow traps fat and the more fat in the milk, the greater the amount that comes down with the protein.

The only other explanation I can think of is that the extracted protein was not absolutely dry when you weighed it so the weight appeared to be greater because you were weighing trapped water along with the protein. Here again, the weight increased with increasing fat content, so maybe there is some connection there.

You could try doing a search to find some information about this, but I really don't know what search terms you would use. I think it is a very interesting observation, however, and I am hoping some other expert with more knowledge of milk chemistry can tell us why this happened. Unexpected results often lead to especially interesting findings so try to figure this out by doing some online reading and please post again with what you have found. You have made me curious!

All the best,

Sybee

[reneeshih]

Hi Sybee,

Thank you for your reply! It is encouraging!

One of possible reasons that could interfere the weight of the plastic is the liquid that draped inside. So I have weighted each of the plastics after day4, and I recorded the weight everyday until the weight stayed the same for at least 3 days. For this method, I can be sure that there is no liquid trap inside.

Because of this, I can only conclude that the fat as the reason that whole milk weight the heaviest than the 2% than the skim. Right?

If according to the website info you posted about the protein percentage in each of the milk, skim milk contains hight protein percentage, so it should yield the heaviest plastic.

I did not mentioned that I made 3 trials of this experiment. They all have same result; whole milk weight heaviest, then the 2% then the skim.

If fat is trapped in the whole milk and 2%'s plastics, can I safely said that skim milk's plastic is purer?

Any feedback is welcome!
Emma

[SciB]

Hi Emma,

I'm glad my information was helpful so that you understand the problem better.

With regard to the water, I suspect that if it is 'trapped' somehow within the blob of proteins, just allowing the blob to stand is not going to drive the water out. You would probably have to do something to really dry it like heating or putting it into a vacuum. If your kitchen range has a convection oven, you could try putting the plastic proteins into the oven on a low setting, 100-150 F for a couple of hours and then weigh them again. This might reduce the water content, but I can't say for sure, so you would just have to try it.

The milk fat is not an impurity--it's what gives milk and other dairy products that rich, creamy taste. To me, skim milk tastes like water. I prefer whole milk but usually have 2% just to limit my fat intake.

You cannot say for sure that the difference in weight is due to difference in fat content. You would have to do a test for fat (not easy) to prove this. You can say that the extra fat might be the cause of the weight difference.

If you haven't already done so, take photos of the labels on the milk containers that show the amounts and percentages of fat, protein and other ingredients. You can post those on your board so people can compare the contents.

Hope this helps! Post again if you have more questions.

Sybee

[reneeshih]

Hi again! I did some research and found that the butterfat (the fat that is in milk) is put with the curds (the casein plastic). My mom and I did some math. We combined the amount of casein with the amount of fat in 100g. Skim milk’s casein should weigh 3.075 g. Whole milk’s casein should weigh 6.48g. 2% milk’s casein should weigh 5.5g. In our experiment, Skim milk’s plastic weighs an average of 3.5g, which is close to 3.075g. However, in our experiment, whole milk and 2% milk weigh a little more than our calculations. In our experiment, whole milk’s plastic weighs an average of 7.33g while our calculations say it should weigh 6.48. In our experiment, 2% milk’s plastic weighs 6.5g while our calculations say it should weigh 5.5g. By the time my mom and I found this, we already sand papered the plastic so we could test it with a durometer. Sand papering it would had reduced the plastics’ weight. So if I try to dry them in the oven and reweigh the plastic, the weight would be inaccurate. Any suggestion what to do?
BTW the website I researched is facstaff.bloomu.edu/mpugh/Experiment%2011.pdf
Thank you!
Emma

[SciB]

Hi Emma,

You found the answer! The butterfat was the cause of the apparently increased weight of the whole-milk plastic and 2% milk plastic compared to skim. I don't think you need do anything more. I suspect that there may be some water trapped in the plastics, but it would probably be about the same for each type of plastic and can be ignored. As you have altered the plastic by sanding, you could not dry it accurately anyway.

I am curious about your 'durometer' measurement. What is it and how did you find out about it? Are you planning to include the durometer data with your project? It would add another interesting dimension to it, especially if you can report the durometer readings of some other forms of plastic from hydrocarbons to compare to your milk protein plastic.

Sybee

[reneeshih]

Hi! Sorry, I was away visiting relatives overseas so there was no internet connection.

My initial hypothesis was that milk with a different fat content will produce a different plastic in its appearance and texture. I was planing to compare in weight, color and maybe hardness. So my mom found the Durometer device, which tests the hardness of plastic and rubber. So we bought a cheap one on Amazon.
Thank you for your replies! It helped me to finalize my conclusion. My Hypothesis got tested and the results was, the more fat content in milk (whole milk) will produce a heavier plastic, a brighter colored plastic and a plastic with a lesser hardness value.
Thank you again! It is amazing to get help from Science Buddies.
-Emma

[SciB]

You are welcome, Emma! We aim to please and provide the best science and project info and ideas around.

I'll be waiting to hear about your next project. Feel free to ask questions at any time. There are many new interesting areas of research now and you should be able to find some cool questions to ask that have not been explored yet.

Good luck!

Sybee