Purification of α-lactalbumin from a prepurified acid whey: Ultrafiltration or precipitation

Abstract

Acid casein whey is a co-product of casein manufacture that contains a protein, α-lactalbumin, with high nutritional and biological properties. The target protein can be purified using a two-step cascade. The previously reported first step consists of ultrafiltration, which aims at producing a tailor-made permeate with a decreased content of contaminants (bovine serum albumin, immunoglobulins) down to zero and enhanced α-lactalbumin/β-lactoglobulin ratio. The second step is described in the present work. Two routes were investigated. The ultrafiltration route consisted of a second ultrafiltration step with an appropriate membrane, transmembrane pressure, ionic strength and protein concentration. As expected, the purity of α-lactalbumin was satisfactory (0.65) but the yield was poor (0.15) due to the low transmission of α-lactalbumin (<0.2). The precipitation route (reversible precipitation of α-lactalbumin) was more promising, provided proper conditions (initial protein concentration, precipitation pH, length of precipitation time and number of precipitate washings) were maintained. The purity was in the range 0.77-0.99 depending on the feed generated by the first step of the operation (microfiltration and ultrafiltration). The yield of the insoluble route was satisfactory (0.46-0.83). The role of operating parameters for both routes was investigated.