|MadSci Network: Chemistry|
Measuring protein is hard to do without a good chemistry lab. Here are a number of methods used: 1. "Crude protein" is measured actually by finding out how much nitrogen is in a food. Only protein contains much nitrogen. So if you measure nitrogen, you can multiply by a factor (6.25 for meat) to find protein. This method requires high-temperature boiling in sulfuric acid, conversion to ammonia with sodium hydroxide, then distillation and titration. This method is dangerous even in a good lab, so it's not for you! 2. Digest the meat in dilute sodium hydroxide under heat, add Biuret reagent, and measure color change with a spectrophotometer. This requires equipment and supplies and has some danger from the hot lye. 3. Get the protein in solution and measure the absorption at the UV wavelength of 280 nm. This requires equipment and digestions again. 4. There is a simple method based on measuring moisture and then getting protein from models for different meats. You use of the microwave would complicate this. 5. Meat is composed almost entirely of moisture, fat and protein. If you measure the moisture and fat and subtract from 99.5% you will get a reasonably accurate protein for normal (not organ) meats. Unfortunately fat is just as hard as protein to do. I suggest you change your experiment, in any event! The reason is simple: protein is not broken down under microwave heat. The same weight of protein will be there before and after. What will happen is that the weight of the meat will go down as the moisture evaporates, so the percentage protein will increase, but not the mass. A more suitable experiment would be to measure the effects of "cooking" on protein. Although the protein is still there after cooking, it no longer has the same chemical properties, due to a change in conformation (shape of the molecule) called "denaturation". You can measure denaturation by a simple test: 1. Make up a 5% salt solution (5 g salt per 1 L water). 2. Extract a measured amount of solution (say 50 mL) and meat (say 5 g) in a blender jar for 60 seconds at low speed. 3. Filter the extract through cheese cloth to remove large pieces and then through a coffee filter to get the turbid extract without pieces. 4. Dry the extract and find the weight of the solids left. (You'll have to weigh the glass container first, then after drying and subtract the glass weight.) 5. Subtract out the salt weight found by drying an equivalent amount of liquid through the cheesecloth and paper. What you will find is that the amount of solids in the extract goes down with the time the meat is microwaved, as you cook more and more of the protein. Eventually the extraction process will become very simple, as the liquid will easily pass through the filter paper. That's because there's no protein in the liquid anymore!
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