Alkaline extraction-isoelectric precipitation has been the most used method to extract protein from plant foods. The sample preparation will depend on the features of the starting material. For instance, in solid samples, the method starts with homogenization until producing a powder with a certain particle size distribution. It is recommended to homogenize the particle size of the starting material to increase reproducibility of the extraction. Subsequently, the proteins are extracted using an alkaline pH far from the isoelectric point of the proteins. The isoelectric point is the pH at which the proteins¿ net charge is zero. Afterwards, the pH is adjusted to the isoelectric point to promote protein precipitation and isolation. As discussed in this chapter, this method has some advantages and disadvantages that need to be addressed to optimize the extraction. Compared to other methods, it is inexpensive, it has a relatively easy protocol, however, it does not represent an environment-friendly option because of the solvents, wastewater, and toxic reactive species such as lysinoalanine that can form at high pH. Resulting proteins can also be denatured and have poor functional properties. In this chapter, the principles, relevance, and technological implications of this extraction method are discussed.
