Protein isolates are rich in amino acids; note the word “acid”. Isolated proteins are acid-forming (systemically acidic), regardless of whether the whole plant may be alkaline-forming. Hence, brown rice protein isolate is a product isolated from brown rice; hence, it is no longer whole brown rice since the germ and fiber are removed, and is now rich in acid-forming protein. It is no longer an alkaline whole grain as the name, and product marketing, may imply. The same logic would apply to other protein isolates. If only whole grain powders are used, without protein concentration or isolation, the alkaline-forming claim would still be reasonable; otherwise not so.
Raw proteins are typically harder to digest than cooked ones, but that depends on how much the heat denatures the proteins. Denaturing = digestion and is normally necessary to make the amino acids bioavailable and to reduce the likelihood of developing food sensitivities due to incomplete digestion triggering immune (IgG) reactions. There is nothing wrong with denaturing proteins, unless you are trying to preserve certain structures like immunoglobulins in whey protein. But the nature of whole plant foods is to lock up nutrients by binding them in a food matrix, requiring a process of digestion, or denaturing, to separate them from their food matrices for optimal absorption from the gut. It is also questionable exactly how “raw” these proteins are. Some companies ferment so-called raw materials and only count the presence or absence of heat after fermentation when labeling them as “raw”. This may be as inaccurate as labeling yogurt with live cultures as “raw” even if pasteurized milk was used as a sterile culturing medium.
There is some evidence that animal proteins can better promote cancer growth (The China Study) than plant-based proteins, but otherwise are considered excellent protein sources.
Plant proteins each have their own issues: Rice protein tends to have heavy metal contamination. Chia protein is very gummy and thus hard to use in a liquid mixture intended for drinking. Hemp protein doesn’t taste very good. Etc.
Protein digestion is obtained by actions of stomach acid (low pH) and enzymes both in the stomach & intestines (pancreatic protease). In the acidic environment of the stomach, the negatively charged side chains are removed by pepsin. In the stomach, Pepsin helps to "unwind" the proteins and breaks the bonds between the amino acids in certain places. In the more alkaline environment of the intestine, the positively charged side chains are removed by trypsin. In the small intestine, other enzymes break the bonds between different amino acids that pepsin can’t break. Because proteins are such complicated molecules, it takes a long time and more than one enzyme to completely digest them (break them down into amino acids). Digestion results in about 60% small peptides (or peptide-bound), which are chains of amino acids, and 40% free amino acids (or free form). Peptides can be further broken down by hydrolysis in enterocytes (intestinal absorptive cells, simple columnar epithelial cells found in the small intestines and colon).
Plant enzymes (proteases) can also digest protein in a wider range of pH, to help compensate for low stomach acid. But plant enzymes don’t compensate for other functions of stomach acid:
- Acidic immune barrier
- Environment to promote Acidophilus (literally: ”acid loving”)
- Digestion (liberation) of minerals from food, water, and non-chelated supplements
- Digestion (liberation) of vitamins from food matrices