Modification of the Functionality of Micellar Casein Concentrates by Changing the Structure of Casein Micelles Using High Pressure Processing
Growing interest in food products with high protein content has led to an increased demand for protein ingredients. Micellar casein concentrate (MCC) is an emerging dairy ingredient obtained by membrane filtration. MCC is characterized by a bland, clean taste and has potential for use in applications ranging from beverage fortification to manufacturing of soft gel products. High pressure processing (HPP) is a physical process that can be used to induce controlled changes in the structure of casein micelles and thus, modify the properties and functionality of MCC.
In this study, MCC suspensions with 2.5, 5, 7.5, and 10% protein content were processed at 150, 250, 350 and 450 MPa for 15 min, at cold (4-24 °C) and warm (53-60 °C) temperatures. Particle size, turbidity, and viscosity were assessed directly after HPP and during refrigerated storage. The study was replicated and data analyzed statistically.
Under cold HPP conditions, casein micelle size decreased significantly with increasing pressure (P<0.05), due to disruption of the casein micelle structure. The average micelle diameters ranged from 192 to 81 nm for 2.5% MCC and from 216 to 173 nm for 10% MCC, after treatment at 150 and 450 MPa, respectively. These effects were concentration dependent, indicated by increased micelle size and turbidity in samples with higher casein concentration (P<0.05). By contrast, HPP under warm conditions led to an increase in particle size, indicating a re-association of caseins. The increase in particle size was concentration dependent: for 2.5% MCC treated under warm conditions particle sizes ranged between 175 and 216 nm while for 10% MCC they ranged between 192 and 778 nm, when treating the samples at 150 and 350 MPa, respectively. Particle size and turbidity did not change significantly during storage at 4 °C of cold HPP treated samples, whereas samples treated under warm HPP conditions were less stable. Interestingly, cold HPP treated 10% MCC formed a weak gel above 250 MPa.
The present study suggests that HPP is effective for modifying MCC functionality, by inducing structural changes of the casein micelles. Most notably, cold HPP can induce shelf-stable size reduction of casein micelles and improved transparency at low casein concentrations, and gel-like structure at high casein concentrations. This data can be used as a basis for developing new food applications involving HPP treatment of MCC.
Keywords: micellar casein concentrate (MCC), high pressure processing (HPP), nonthermal processing