I thought I would pass this on. I relayed this post to a family friend who works as some sort of microbiologist. This was his longish response. Not sure if you care, but he's generally positive on your methodology.
"It's a nice amount of data and props to the guy for actually getting up and doing it. But there is some confusion here, in his original text it appears he seems to be concerned with protein content meaning total protein content of the various powders. However, all he tested for was soluble protein content which can be a tremendous difference. Based on his method so far (using a colorimetric assay) I'd say he definitely needs to follow up with better methodology which, to his defense, he admitted to. The fitness crowd looks for protein that is soluble as they believe it absorbs more quickly into the bloodstream. But how much quicker would your body process free soluble proteins vs. ones that are in nano scale insoluble aggregates? I'm not sure... I haven't found any research done on that topic. The assay he used is dependent on solubility and protein amino acid composition. His solubility scoring was subjective and I'm not clear how he did it, by eye? I've dealt with a few synthesized dry protein powders I've used for assays and can tell you that solubility is tricky. Formation of clear gel aggregates and really small aggregate sizes do occur and have fooled others and myself in the past even after heating and sonication. These out of solution aggregates won't show up in a colorimetric assay (which gives you the protein content readout). Without to much more investment in resources he should have also done a very simple denaturing gel electrophoresis experiment, which would show, not very accurately, total protein content (soluble and insoluble). If after this he found that there still was very little protein, then I'd call foul on the manufacturer. But most of the labels state product Y contains X amount of protein, but do not specify if it is soluble or insoluble. It's true there is no standard in preparing whey protein as there are a few different ways to commercially prepare it. In order to get the convenient powder, we all know, you need combinations of spraying, pressure and heat. As you can imagine, that can change the natural shape of a protein considerably (they all have unique three dimensional shapes). It's been published that the various forms of commercial preparation can change the shape, among other properties, that in the end can influence the solubility of proteins. To the common person this data can be misleading. He should have labeled his spreadsheet as "Measurement of soluble protein content of various protein supplements."
