Mechanisms and ways for improving heat stability of Micellar Casein Concentrates
Heat stability of proteins is the major hurdle in designing high protein containing heat stable foods and beverages with long shelf-life. Micellar Casein Concentrate (MCC) can be an ideal ingredient for such products. As MCC typically has > 90%w/w casein and is devoid of whey proteins, the mechanism of it’s heat stability is expected to be different compared to milk powders and MPC. However, little is known about heat stability of MCC solutions, particularly at higher protein concentrates. The objective of the present study was to explore the mechanisms of heat stability of MCC and also investigate the effects of different additives on heat stability of MCC.
Aliquot of MCC (12, 14 and 16%w/w protein) were prepared by diluting concentrated MCC retentate with glass distilled water. Experiments were designed with following treatments: (i) no treatment (control) (ii) addition of Sodium Phosphate (SP) at 1, 5, 10, 25, 50 mML-1 (iii) addition of Sodium Citrate (SC) at 1, 5, 10, 25 and 50mML-1. The time required for visual precipitation or aggregation (generally referred as heat coagulation time (HCT) was measured using oil-bath at 140°C and 120°C. The visual observations, calcium-ion activity and particle size were also measured.
The HCT of control samples was 49 seconds. The colloidal state of casein micelle, calcium activity and voluminosity of casein micelles seemed responsible for poor heat stability of MCC. Addition of SP and SC at low level (1 mM) improved HCT by 15s compared to control samples., whereas their addition at 5, 10 and 25 mM exhibited significant improvement (P<0.05) in heat stability at all protein concentration showing no aggregation when heated for more than 3 min at 140°C or 120°C. The color was also changed from opaque to translucent. However, increasing level of SP and SC to 50 mM decreased both HCT and turbidity of samples. The addition of SP and SC shifted the casein-mineral equilibria leading to decrease in free Ca-ion concentration as well as dissociation of colloidal calcium phosphate from casein micelle and increased negative charges of the casein micelle and hence increased repulsion, which contributed to increase in heat stability of MCC.
The results of this study showed significant (P<0.05) improvement in the heat stability of micellar casein concentrate using additives such as SP and SC, which show promise to make shelf-stable MCC with higher protein content.
Keywords: Micellar casein concentrate, Heat stability, Calcium chelators