Heat-Induced Changes in κ-Carrageenan-Containing Chocolate-Flavoured Milk Protein Concentrate Suspensions under Controlled Shearing

Milk protein dispersions containing added cocoa powder (1.5% (w/w)) and sucrose (7% (w/w)) and varying levels of κ-carrageenan (0.01, 0.03, or 0.05% w/w) were subjected to combined heat treatment (90 °C/5 min or 121 °C/2.6 min) and shear (100 or 1000 s−1) to investigate the heat stability of milk proteins. The application of shear led to a notable reduction in non-sedimentable proteins, resulting in an increase in the average particle size and apparent viscosity of the dispersions, particularly at high concentrations of k-carrageenan and elevated temperatures. This indicates that shear forces induced prominent protein aggregation, especially at higher κ-carrageenan concentrations. This aggregation was primarily attributed to the destabilisation of micelles and presence of loosely bound caseins within the κ-carrageenan network, which exhibited increased susceptibility to aggregation as collision frequencies increased due to shear

Impact of Heating and Shearing on Native Milk Proteins in Raw Milk

Processed foods are less susceptible to various biological contaminants as well as to enzymes causing spoilage as the risks associated with food borne illnesses are reduced while the shelf life is extended. In the dairy industry, thermal processing is one of the most common method used for this purpose. Treatments such as pasteurisation, strerilisation, and UHT treatment are some of the key methods that are widely applied. The complexity of these treatments impacts mainly on physico-chemical, nutritional and functional properties of the milk whereas Maillard reaction, κ-casein/β-lactoglobulin association, decrease in pH and whey protein denaturation are some of the common physico-chemical changes occurring during heating process. In addition to heating, milk is also subjected to shear forces during diverse processing methods including pumping, homogenisation, stirring and in flow-through equipment such as heating, holding and cooling. Large velocity gradients generated by shear forces along the shear flow promote structural modifications of the milk proteins leading to unfolding via denaturation and subsequent interactions. Thus, the both heating and shearing in combination would have a relatively greater impact on milk proteins. The simultaneous application of both heating and shearing are so common however, the concomitant effect of both heat and shear on milk proteins is less studied specially on native milk protein in raw milk. Therefore, the present study aimed at evaluating behaviour and structural modifications of native milk proteins in raw milk under various temperature and shear combinations that mimic common industrial applications

Effect of pH and Shear on Heat-Induced Changes in Milk Protein Concentrate Suspensions

The effect of shear on heat-induced changes in milk protein concentrate suspensions was examined at different pH levels, revealing novel insights into micellar dissociation and protein aggregation dynamics. Milk protein concentrate suspensions, adjusted to pH of 6.1, 6.4, 6.8, or 7.5, underwent combined heat (90 °C for 5 min or 121 °C for 2.6 min) and shear (0, 100, or 1000 s−1) treatment. The fragmentation of protein aggregates induced by shear was evident in the control MPC suspensions at pH 6.8, irrespective of the temperature. At pH 7.5, shear increased the heat-induced micellar dissociation. This effect was particularly pronounced at 121 °C and 1000 s−1, resulting in reduced particle size and an elevated concentration of κ-casein (κ-CN) in the non-sedimentable phase. At pH 6.1 or 6.4, shear effects were dependent on sample pH, thereby modifying electrostatic interactions and the extent of whey protein association with the micelles. At pH 6.1, shear promoted heat-induced aggregation, evidenced by an increase in particle size and a significant decline in both whey proteins and caseins in the non-sedimentable phase. At pH 6.4, shear-induced fragmentation of aggregates was observed, prominently due to comparatively higher electrostatic repulsions and fewer protein interactions. The influence of shear on heat-induced changes was considerably impacted by initial pH

Structural changes of native milk proteins subjected to controlled shearing and heating

Processing of milk results in structural modifications of proteins creating a foundation for various interactions. The present study aimed at identifying the effects of simulated processing conditions, the combination of temperature and shear, on native proteins in raw skim milk. The temperatures chosen (72 and 140 °C) were combined with selected shear rates (0, 500, or 1000 s-1) during processing. Impact of shear appeared temperature dependent, but it induced either reversible or irreversible changes in the secondary structure of milk proteins at all temperatures. Increase in shear may result in reversible structural modifications at 20 °C, while it could contribute to fragmentation of hydrophobically-linked protein aggregates at 500 s-1 and also reformation at 1000 s-1 during heating at 72 °C. The shearing at 140 °C appeared to enhance the formation of protein aggregates primarily by hydrophobic interactions, as well possibly thiol/disulphide interactions to a lesser extent