Proteins are organic compounds present in both animal and vegetal organisms and are made up of long chains of amino acids linked together by amide bonds, called peptide bonds, that form between the amine and carboxyl group of the amino acids with the release of a molecule of water:
Amino acids differ from each other in the presence of a specific side chain that can have a nonpolar, polar, acid or basic nature and gives every single amino acids particular chemical properties.
Proteins differ from each other in the different presence, frequency and sequence in which the various amino acids can link together; the side chains can form bonds with each other making the polypeptide chain assume a particular spatial conformation or can associate with other side chains of another polypeptide chain. The spatial structural characteristics of the proteins amino acids chains and also of the respective hydrolysates in general depend on the physicochemical conditions of the aqueous solution in which they are (pH, presence of ions, temperature, concentration, presence of certain organic compounds) and a variation of the equilibrium conditions can easily denature them (e.g. loss of solubility).
Proteins solubility is mainly influenced by the molecular weight: at the same physicochemical conditions generally the decrease of the molecular weight causes an increase of protein solubility.
For native proteins we mean proteins isolated from vegetal or animal sources that maintain their original molecular weight and chemical characteristics of the amino acids. Hydrolysed proteins derive from native proteins and are composed of peptides with a lower molecular weight but a higher solubility.
The hydrolysis of proteins can be carried out by adding strong basic or acid substances or via enzymatic means; chemical hydrolysis can be mild or strong and causes destruction of the amino acids chains, denaturation of some amino acids side chains and destruction of some amino acids. Enzymatic hydrolysis makes use of specific proteases capable of breaking up the amino acids chains in specific sites; this kind of hydrolysis doesn’t cause amino acids side chains denaturation and amino acids destruction.
Therefore we can refer to a protein hydrolysate ONLY as amino acids chains with different molecular weight that can be in aqueous solution or in a powder form; on the market there may be found substances formed by molecules of proteinic origin condensed with other molecules such as of cationic nature or fatty acids chains. This kind of substances are obtained through synthesis processes and form surfactant molecules with loss of the peculiarity of proteins from which they originate.
During detergency the outermost layer of the skin comes in contact with surfactants substances capable of removing dirty but also part of the natural hydrolipidic component of the stratum corneum and causing a partial denaturation and depauperation of lipidic and proteinic substances with alteration of the normal cutaneus equilibrium; this can lead to an impairment of the skin barrier function with consequences that can range from the decrease of hydration of the stratum corneum to dermatitis in sensitive skins.
The use of proteins combined with tensides has proven to be an effective protection against the aggressive action of these substances without compromising their cleansing and foaming efficacy; the protective action performs both through the formation of interactions between the proteins and the tensides monomers (picture 1) which are those mostly capable of penetrating cutaneous membranes and through the formations of weak but numerous bonds with the epidermic proteins which get covered by a colloidal protective film.
Proteins applied on the skin form weak but numerous bonds with epidermic proteins creating a non-occlusive thin colloidal protective film: the higher the molecular weight of proteins the more the film-forming effect is on the skin; lower molecular weight hydrolysates rich in small peptides and free amino acids can have a buffering and humectant effect and be of useful application in products for skins that present deficient conditions in these compounds.
Some proteins exhibit an antiradical activity and can help to preserve other cutaneous components integrity (for example after UV exposure).
Hair cuticle is the first coming in contact with aggressive agents and its degradation can expose the outermost layers of the cortex condition that occurs when hair are brittle and damaged.
Low molecular weight hydrolysed proteins rich in small peptides and free amino acids exhibit a high affinity (substantivity) for hair especially for damaged hair: this substantivity performs in the ability of forming weak but numerous bonds with cuticle keratin proteins filling the cavities, restructuring and strengthening the hair shaft; higher molecular weight peptides have a film-forming effect compared to those with lower molecular weight.
Some native proteins with very high molecular weight made soluble through the complexation with some tensides exhibit a conditioning effect thanks to their ability to form a colloidal film on hair during rinsing and to form at the same time bonds with the tenside monomers; compared to the conditioning agents commonly used in shampoos the native proteins are significantly less irritating on skin and can be used in sensitive skin products.
The choice of the hydrolysate depends on the application for which is intended.
All ours protein-based preparations are water-soluble and may be divided into different categories: native proteins with very high molecular weight complexed with tensides, hydrolysates with high, medium and low molecular weight. Native protein use is suggested in all cleansing products for their protective and film-forming properties; some native proteins on account of their characteristic amino acid composition can be used in shampoos for their conditioning and protective effect on hair.
All the other hydrolysates with lower molecular weight may be used in cleansing products thanks to their protective effect against tensides but also in topical-use products for their affinity for epidermic proteins and binding-water ability (especially those with high molecular weigh); low molecular weigh hydrolysates are suggested for damaged hair care products thanks to their restructuring properties.
Some hydrolysates are obtained not only from isolated native proteins but also from seed flours rich in carbohydrates that are expressly solubilized via enzymatic means together with the protein fraction they contain; these carbohydrates may be of different kind such as starch, galactomannans, beta-glucans, mucilages as in case of millet, fenugreek, oat and mallow and be used in sensitive skin products for their lenitive effect.
Some substances can irritate skin because of a denaturing effect on stratum corneum cells and in more severe cases on epidermic underlying layers or in case these substances can penetrate the cutaneous barrier can provoke an allergic reaction.
The penetration of a substance may be influenced by different factors related to exposure, skin conditions and to the substance physicochemical characteristics such as molecular weight, pH (and consequently its ionization), polarity; generally substances with low molecular weight, not ionized, and not much polar have a great penetration capacity and may reach the deeper layers of the skin.
High molecular weight proteins don’t have functional groups capable of denaturing the hydrolipidic component of stratum corneum and are not able to penetrate it so they can considered safe; lower molecular weight hydrolysates, speaking about the component composed of very small peptides and free amino acids, may have a greater penetration without having caused any irritative event known so far.
Cytotoxicity and skin sensitization in vitro tests conducted on gluten hydrolysates we produce were negative.
Furthermore there are currently no proven scientific evidence regarding a correlation between allergenicity in celiac patients and wheat gluten derivatives contained in cosmetic products.