Recovery of caseins at the electroactivation of whey

Abstract

The recovery of whey proteins in protein mineral concentrates (PMCs) depends on the regimes of electroactivation of whey, in particular, the density of the electric current and the specific energy consumption applied per unit volume [1]. The extraction of caseins in PMC is due to the presence of colloidal calcium phosphate, which forms aggregates with caseinate in the form of calcium phosphate-caseinate. Part of the calcium phosphate can be found in the form of a pure solution, and most of it - in the form of a colloidal solution. At the increase of active acidity upon electroactivation, calcium phosphate passes from the colloidal state to the ion-dispersed one, and during ionic flotation it separates in the form of calcium phosphate, or hydro- or dihydrocalcium phosphate, which is "captured" in the PMC at a mechanical level induced by ionic flotation. The same mechanism occurs in the formation of calcium phosphate-caseinate at the interaction of calcium ions with the carboxyl and serine phosphate groups of casein. In this case, calcium reacts with two groups -СООН and -ОН- located at small distances, forming intermolecular bridges of calcium: -R-Ca-R-. At the formation of structural bridges (between two phosphoserine radicals) can also participate hydrofosfates -R-Ca-HPO4-Ca-R- or dihydrophosphates -R-Ca-HPO4-Ca-HPO4-Ca-R-. Whey processing involves separation from casein powder, but this procedure still does not allow the complete separation of caseins from the initial whey (IW). Electrophoretic investigation (SDS-PAGE 15%) of the protein fractions of different types of whey with different protein content (supplied by the "JLC" Joint Stock Company, Chisinau, RM): (1) - whey obtained after the manufacture of granulated cheese "Grăuncior" ; (2) - whey obtained after the manufacture of cow's cheese, with a fat content of 5%; (3) - whey obtained after the manufacture of the cheese product, with a fat content of 18% identifies the presence of CSN. The content of caseins (CSN) is about 18% for IW (1), 12% - IW (2) and 10% for IW (3). The electroactivation of different types of whey in different electrolyzers allows the fractionation of whey proteins and their recovery in PMC with predetermined protein content depending on the processing regimes and the constructive and technical parameters of the electrolyzers [1]. CSNs are extracted in higher amounts in the EDP-2 electrolyser with a parallelepiped casing when processing whey (1) and varies from 16 -21% at current density j=10mA/cm2 increasing slightly to 26% at j=20mA/cm2; for whey (2) CSN are extracted unevenly at both electric current densities and vary 10-21%, and for whey (3) CSN are intensively extracted at j=10mA/cm2, constituting 22-27% and are extracted in insignificant amounts at at j=20mA/cm2 – 7-9%. At the processing of different types of whey in the EDC-3 electrolyzer with a semi-cylindrical casing, CSN is insignificantly extracted during processing, for whey (1) at j=10 -20 mA/cm2 and constitutes 3-5% in the first 10 min of treatment. Their extraction is not registred during further processing. For whey (2) CSN extraction constitutes 2-10% at j=10mA/cm2 and 2-8% at j=20mA/cm2. The uneven and reduced extraction in the semi-cylindrical casing electrolyser confirms the involvement of CSNs in the formation of high molecular weight proteins (of about 150-240 kDa) that could not be identified by 15% SDS-PAGE electrophoretic analysis. In IW, 2-3 fractions of CSN ‒α-CSN, β CSN and κ-CSN with the respective molecular mass of 37, 33 and 46 kDa were identified, which contribute to the separation of PMCs from different types of whey in different electrolyzers. The recovery of protein fractions occurs simultaneously with the isomerization of lactose into lactulose.