Compatibility of NADES and ABS with CE-SDS analysis of bovine milk proteins

• Milk proteins are analyzed by CE-SDS with laboratory-made gel-buffer in 6 min. • CE-SDS analysis is compatible with proteins dissolved in betaine:urea:water NADES. • Casein and whey protein partition in the NADES phase of the ABS with > 93 % extraction efficiency. • Back recovery from NADES phase in water is achieved with centrifugal filter devices. • Back recoveries measured by UV and by CE-SDS are in the 30 % level. The rising interest in studying milk proteins is due to several factors such as the food supplement consumption based on them and the circular economy of the whey obtained as a byproduct in the dairy industry. Modifications of the milk proteins, such as fragmentation, aggregation and denaturation happening during manufacturing need to be tightly controlled. In this work the use of an aqueous biphasic system (ABS) consisting of a natural deep eutectic solvent (NADES) and a salt to recover proteins from milk that could be applied to the extraction of milk proteins from byproducts in the dairy industry, was evaluated. As NADES betaine:urea:water (1:2:1 molar ratio) was employed. Back-extraction of milk proteins into water was evaluated by UV spectroscopy and by capillary electrophoresis with sodium dodecyl sulfate (CE-SDS). This study included the prior assessment of the usefulness of non-reducing CE-SDS method with laboratory-made gel-buffers for analyzing bovine caseins and whey proteins. Afterwards the compatibility of this CE method with the use of this NADES as protein solvent was established. The study allowed demonstrating that caseins as well as whey proteins mainly partition in the NADES-rich phase of the ABS, with recovery yield values higher than 77 %, extraction efficiencies higher than 97 % and back-extraction into water using centrifugal filter devices higher than 28 %. This work supports a procedure for recovering milk proteins from dairy industry byproducts using chemicals considered environmentally friendly. Sustainability of the ABS and back-extraction method was assessed using the AGREEprep tool. Besides the green characteristics of the sample preparation, the CE-SDS method established consumes a very low volume of sample and reagents and allows analyzing the individual caseins and whey proteins in less than 6 min as well as measuring the back-extraction recovery in water.