Peptide Affinity Extraction Of β-Lactoglobulin From Milk
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
A major challenge faced by dairy industries is the extraction of whey proteins from milk without pre-treatment, because of the presence of colloidal solids and the complex composition of milk. Various methods have been investigated to isolate whey proteins but other than the extraction of lactoferrin, none have been successful because of high processing costs and low product yield. To overcome some of these challenges, this thesis focused on the specific isolation of β-lactoglobulin, in particular without involving pre-treatment of the milk. Previous investigations showed β-lactoglobulin to be allergenic towards some infants and hence its removal from whey and milk was the main objective of this thesis. Isolating this protein from milk using a single-step extraction process has not been demonstrated previously. A Protein A Mimetic (PAM) ligand, originally designed for isolation of Immunoglobulin G from a variety of sources, was shown in previous unpublished work to have an unexpected affinity for β-lactoglobulin. In the current work, the equilibrium/static binding capacity of this PAM ligand immobilized on a chromatography resin was determined using varying concentrations of pure β-lactoglobulin in neutral aqueous solutions. An affinity chromatography resin was created by amine-coupling the ligand to an activated resin (N-hydroxysuccinimidyl-Sepharose 4 Fast Flow), and its equilibrium binding capacity was found to be 54.11+0.03 mg β-lactoglobulin/g wet, drained resin. PAM tetramer ligand showed some cross-reactivity with caseins and immunoglobulins, but the majority of these proteins were recovered in the regeneration step. The majority of the β-lactoglobulin was recovered during elution, with minor traces of α-lactalbumin and immunoglobulins. A novel, cost effective and scalable method was developed to isolate β-lactoglobulin from milk using an immobilized tetramer peptide ligand, which had previously shown high affinity towards β-lactoglobulin in the presence of other milk proteins. Previous research had shown that the peptide ligand maintained selectivity over a range of buffer pH values, but the optimum selectivity was found to be at pH 7. At buffer pH 7 and a conductivity of around 8 mS/cm, the affinity resin bound almost all β-lactoglobulin present in whey/milk, with only minor leakage in flowthrough fractions. An advantage to this process was the use of low salt during the elution process. Bound β-lactoglobulin was observed to elute at a buffer conductivity of 22 mS/cm. The results confirmed that β-lactoglobulin could be selectively removed from milk, thereby producing modified milk suitable for infant intake. In addition, β-lactoglobulin has uses in the confectionary and protein supplement industries and can be used as a gelling and foaming agent in functional foods. Suggestions for further work are expected to support development of this process and to provide a higher recovery of the bound protein, to minimize product loss.