Pro-Cote soy protein polymers have complicated chemistry. The manufacturing process relies on precise input control, maintained over many complex operations including raw material selection, protein extraction, hydrolysis, refining, sterilizing, drying and packaging. Each processing step is monitored and the final product is subject to a variety of quality tests before approved for shipment.

Amino Acid Profile


The term "protein" itself does not refer to one specific compound, but rather to a set of compounds built up from individual amino acids (protein’s "building blocks").

Soy proteins are amide-linked polymers composed of amino acids. They are produced in soybeans as a storage protein to nourish the growth of the germinated seed. The amino acid distribution is shown in the table. The protein molecule is the condensation product (with subsequent release of water) of many individual amino acids joined together in a repeating bond called the peptide linkage.

Aside from the predominant elements of carbon, nitrogen, oxygen and hydrogen in the peptide linkage and the various amino acids, a few contain sulfur and phosphorous.












Grades of Soy Polymers
Unhydrolyzed Grades (Native Soy Proteins). Certain grades of soy polymers maintain a near native protein superstructure. The globular rigid structure has a relatively equal number of cationic and anionic sites that are reactive. The combination of hydrophobic and charged regions helps maintain the globular protein subunits and makes them self associating, resulting in higher solution viscosities. The large number of cationic sites makes the product reactive to positively charged surfaces, such as kaolin pigment, and are interactive with one another.

Hydrolyzed Grades (Alkaline Treated Soy Proteins). Other, more modified grades of soy polymer are composed of soy proteins that have been chemo-thermally modified to alter the protein structure and functionality. The chemical processing has allowed the native protein globular structures to unfold and reassociate by hydrophobic/hydrophilic regions. This exposes more hydrophilic anionic groups, thus reducing the self-association tendency and reducing solution viscosity. Since more anionic groups are available on the protein surface, the effect of the remaining cationic groups is reduced. These products are less attracted to the particle surface and allow more uniform reaction.

Carboxylated Soy Protein Polymers. The majority of DuPont soy polymer products have been chemically modified to give them higher anionic charge. By making the protein more anionic we are increasing the dispersant properties of the protein and reducing the attraction to anionic dispersed-phase components. Since this product remains in the solution phase to a greater degree, it helps the distribution of components through their dispersant action. The result is greater adhesive strength, controlled structuring, higher water retention and lower viscosities than non-carboxylated soy products.

Proteinates. Some soy polymers are finished as the neutralized form of the protein, to improve solubility and eliminate the need for addition of alkali by the user. Sodium proteinates are available at pH values of about 9.5, and ammonium proteinates are available at pH values of about 6.0.

Additional product lines are available in forms that contain the alkali required to dissolve the soy polymer, not based on sodium or ammonium protein.

Soy polymers are also available in the acid form of the protein, which is insoluble until the pH value is adjusted by the user from about 4.5 as-supplied to about 8.0-10.0.

Molecular Weight/Degree of Hydrolysis

DuPont Soy Polymer’s processing technology generates a variety of Pro-CoteŽ grades varying in molecular weight and degree of hydrolysis. Careful control of the hydrolysis process during manufacturing permits the production of hydrolyzed proteins of various molecular weights. Solutions prepared from unhydrolyzed soy polymers exhibit high viscosity, whereas fully hydrolyzed soy proteins produce low viscosity solutions. Soy proteins are associative polymers. Their molecular weight depends on the aggregated, associative structure formed by the protein, which in turn depends on the dissociating nature of the system into which it is dissolved. The molecular weight (Mw) of soy protein ranges from about 30,000 to over 1,000,000 Daltons. An estimate of the Mw of the associated form in a typical solution or formulation is about 150,000-300,000. The following graph shows examples of commercially available products and the respective molecular weights.

Charge Chemistry
The soy protein polymer is amphoteric in solution. The net charge of the polymer is anionic, ensuring good stability in the anionically-stabilized systems common in most aqueous coatings and emulsions. The cationic character of the soy polymer promotes interaction with colloidally-dispersed materials like pigments or synthetic emulsions. The charge characteristics of the soy polymer are modified during manufacturing to control the interaction of the charged polymer with dispersed phase components.

Colloid Chemistry
Soy protein in water does not exist as a true solution, but more accurately as a colloidal solution called a sol. These sols consist of aggregates of several protein molecules, or micelles. These protein micelles are tightly wrapped in an envelope of water and carry an electric charge. Proteins in sols tend to concentrate at interfaces and can be considered as natural wetting agents, surface tension reducers and/or protective colloids. Despite their relatively large size, proteins spread into extremely thin films at interfaces, exposing the reactive sites of their amino acid side chains.

Soy proteins tend to orient and fix their positively charged (cationic) sites to negative sites on the opposing surface. The anionic side-chains orient themselves to face the water phase.

Soy protein, having been peptized in a water system and oriented in a thin film over a substrate, or inert portion of the mixture, will dry to an exceedingly rigid structure upon removal of free water. Such protein, dried as a film, is more difficult to re-disperse in water than the original material. The degree of insolubilization (or denaturation) imparted is a function of the total drying energy input; i.e., water x temperature. Insolubization of soy protein films may be expedited or enhanced by reaction with aldehydes or di- and tri-valent cations.

Although it is necessary to employ special techniques to directly peptize soy protein in non-aqueous solvents, standardly-prepared aqueous protein sols are reasonably tolerant of many water-miscible solvents such as alcohols and can even serve to emulsify water/lipid mixtures.

Pro-Cote soy polymers are supplied in dry powder form and can be added directly into slurries during makedown or made into a separate solution for blending into the formula.



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