Soy Protein Isolate

Soy Protein Isolate (SPI) is the major proteinaceous fraction of soybeans prepared from de-hulled and de-oiled soybeans by removing the majority of non-protein components and must contain not less then 90% protein on a moisture-free base.  SPI is the most concentrated and sophisticated form of commercially available soybean protein products.  Soy isolates are processed to increase soy protein content and to decrease oligosaccharide content relative to other soybean materials. SPI is to contain at least 90% of soy protein and little or no water soluble oligosaccharide/carbohydrates or fiber.

The basic design principles of the SPI process followed by CCI use defatted soy flour or white flakes as the starting material.  The protein is first solubilized in water/alkali and extracted alongside with water soluble carbohydrates from soy flakes with an alkaline aqueous extractant.  The solution is then separated from the solid residue (insoluble in the extract, mainly fiber). The procedure for SPI production is based on protein solubilization at a slightly alkaline pH and precipitation by acidification to the iso-electric point, near a pH 4.5.  The resulting product is an “iso-electric” SPI.  It has low solubility in water and limited functional ability.  Different types of SPI as to functionality can be produced by re-suspending the isoelectric SPI in water and neutralizing it with a pH adjustment and different bases, and then spray-drying the resulting solution or suspension.  Different bases can be used for neutralization like sodium, potassium, ammonium or calcium, thus resulting in different functional properties of the final isolate. The first three are highly soluble in water, producing solutions with very high viscosities, foaming, emulsification and gel forming properties.  The SPI neutralized by calcium has low solubility and is used in products where high levels of protein incorporation, without excessive viscosity are needed.
Ultra-filtration (U/F) and reverse osmosis (R/O) should be used for the solution concentration and separation based on molecular size.  U/F is employed to retain or permeate molecules according to the size of membrane pores selected and R/O is used for dewatering and concentration. Dia-filtration to maintain a constant ratio of water to solids in the feedstock should be incorporated prior to U/F to minimize problems of retentate concentration and surface fouling during ultra-filtration. 

Since spray-drying is used as drying method, the SPI is produced in the form of a fine powder.  So an agglomerator is required to avoid losses and dusty conditions. Structured forms, such as granules, spun fibres or other fibrous forms are made by further processing.  Being almost pure protein, SPI can be made to be practically free of objectionable odor, flavor, color, anti-nutritional factors and flatulence.  The high protein concentration provides maximum formulation flexibility when SPI’s are incorporated into food products.

FACT SHEET
Plant Capacity Range – Up to 50 TPD