Fractionation of beta-lactoglobulin and alfa-lactalbumin from WPC/HPMC mixture driven by protein-polysaccharide thermodynamic incompatibility

JARA, FEDERICO L.; PILOSOF, ANA M. R.

Porto

Congreso; International Functional Foods Conference; 2008

PROGRAMA CYTED; ESCUELA SUPERIOR DE BIOTECNOLOGIA - UNIVERSIDAD CATOLICA PORTUGUESA

Blends of proteins and polysaccharides are usually not stable. After prepara­tion, they tend to demix into protein-rich and polysaccharide-rich phases. This phase separation is driven by a thermodynamic incompatibility phenomenon between these biopolymers. Thermodynamic incompatibility is the result of enthalpy and entropy barriers caused by the size and chemistry of different biopolymers, hydrophilicity/hydrophobicity, conformation and affinity for water. Whey proteins have many technological and functional applications. The main proteins are the  beta-lactoglobulin (beta-lg), the alpha-lactalbumin (alpha-lac) and the bovine serum albumin (BSA). They are responsible for the hydration capacity, gelling, foaming and emulsifying properties of whey protein concentrates (WPC). Hydroxypropylmethylcellulose (HPMC) is a cellulose ether in which some of the hydroxyl groups have been etherified. It is used in the food industry, printing technology, and has pharmaceutical applications because is nontoxic and possesses good mechanical properties. In the pharmaceutical industry, HPMC has acquired special interest for controlled drug release matrices. The objective of the present work was to assess the potential usage of the protein-polysaccharide thermodynamic incompatibility as a method for protein isolation and purification. For this pupose, incompatible blends with different proportion of HPMC and WPC were made. These blends were centrifuged to ensure the fully phase separation. Then, the protein concentration in both phases, was determined by the Kjeldhal method. The proportion of each protein was determinated by SDS-PAGE joined to an image analysis. The results show that it was possible to retain about 70 % of total protein of WPC in the HPMC rich-phase after phase separation. The low molecular weight whey proteins (beta-lg and alpha-lac) remains in high proportion in this polysaccharide rich-phase. Moreover, the most efficient condition to isolate beta-lg and alpha-lac (more than 85 % of total low molecular weight whey protein) was the phase separation of an imcompatible blend with a low concentration of HPMC and a high concentration of WPC (i.e., WPC 20% / HPMC 0,5 %). From these results, it can be concluded that the thermodynamic incompatibility which arise from mixing whey proteins with HPMC could be used as an alternative method of fractionation and purification instead of traditional membrane processes.