I do love the hydrolyzed proteins - they're humectants, emollients, and film formers, and they do this at really low usage levels, so they're fantastic additions to your products. We can choose from dozens of proteins - silk, wheat, oat, corn, soy, and so on - and what you choose really depends upon what you are seeking in your product.
Proteins have very poor water solublility, so they are hydrolyzed to increase this solubility. (How do they do it? They hydrolyze by cleaving the protein molecule to disrupt the peptide bonds. This cleavage can happen by chemical or biological means, or can be a combination of applying high temperatures and pressure.) They are usually vegetable proteins, and the hydrolyzation means they will be water soluble to offer conditioning, moisturizing, and film forming properties. They are amphoteric, and a positive charge makes them substantive.
Proteins can increase the substantivity (the adsorption of the product to your hair or skin) of your product by binding fatty alkyl groups to the proteins. The lower the molecular weight, the better they will penetrate your hair and skin. The higher the molecular weight, the better they will film form.
Proteins offer moisturizing, and will feel silky and soft in your creations. In surfactant blends, they will increase foam stability, add slipperiness, and offer creaminess and density. They can also reduce skin irritation caused by anionic surfactants, so they are good for combatting skin dryness. (Add a little crothix and you have an anti-irritation festival going on!)
If you've ever seen the hydrolyzed proteins, you'll notice some of them have a brownish colour and slightly weird odour (believe me, the kids in my craft group have noticed it!) This is due to the Maillard reaction between the proteins and carbohydrates (oligosaccharides) - you might recognize this from cooking, when meat browns! - and it is normal. (More complicated explanation here, if you're interested!)
So what does this all mean? Adding a hydrolyzed protein to your products can increase conditioning and moisturizing without the oils, make your products feel silkier and softer, and decrease irritation. Not bad for 2% of your recipe, eh? (You can go higher, but with the cost, you might not want to do so!)
Proteins should be added at 1 to 5% to your cool down phase, when your creation is less than 45C. Please preserve them well using the maximum level of your chosen preservative as they are protein based!
UPDATE NOTE: I've been contacted by Bonnie, who reminds me of the legendary LabRat's suggestion that adding a hydrolyzed protein to your cool down phase can result in contamination. Although all the materials I've read have suggested adding to the cool down phase, I'm going to side with LabRat on this one (after all, he's my guru!) Adding the hydrolyzed proteins to your water phase and heating and holding it will not result in the destruction of the goodness that is found therein, so add your percentage to your water phase while warm and avoid the pains and suffering of icky lotions and potions!
So when you're reading past posts, please put your proteins in the water phase, not the cool down phase. And yes, I've been doing it this way for years...which just goes to show we are always learning, eh? And no, I haven't had any visibly contaminated creations yet, but not all contamination is visible.
So let's take a look at some of my favourite proteins tomorrow!