Novel Approaches on Cheese Feed Preparation: Towards Reducing Additives in Cheese Powder Production

Cheese feed is an emulsion-like system that is utilized as spray drying feed during cheese powder production. The basic formulation of cheese feed includes minced natural cheeses of various types, water, and emulsifying salts (ES). The colloidal stability and physicochemical properties of cheese feed are critical factors in achieving the desired characteristics of the resulting cheese powder. Currently, the cheese powder industry relies on the addition of citrate- or phosphate-based ES to produce stable and homogenous cheese feed. However, the growing consumer demand for clean label products and the desire to reduce sodium and phosphate in food products has created a need for new strategies to reduce or eliminate the use of ES in cheese powder production. Therefore, this Ph.D. project aimed to introduce new perspectives and novel approaches to the preparation of cheese feed with the desired characteristics in the absence of ES.

Understanding the interactions between ES and caseins is essential for reducing their use in cheese powder. Simplified milk protein systems, which avoid the complexities of cheese, such as pH variations, types, and proteolysis, provide a basis for comprehending and predicting ES behavior. This knowledge is critical for developing strategies to produce clean label cheese powder. Therefore, the first part of Chapter 3 (Paper I) explores the role and interaction of phosphate-based ES in casein systems. The results indicated that calcium, pH, temperature, casein concentration, and ES type and concentration are pivotal factors in these interactions. This complex interplay underscores the importance of using simplified model feed systems to understand the influence of individual factors on the resulting cheese feed. The second part of this chapter (Paper II) discusses the behavior of two different ES-free cheese feed systems prepared solely from Cheddar or Camembert cheeses. This study highlighted the importance of cheese type, insoluble calcium content, and extent of proteolysis on cheese feed stability and yield in the absence of ES. This chapter provides a good overview of the role of ES on casein systems, which is relevant to cheese feed preparation, and how cheese feeds made from different types of cheese respond to the absence of these salts.

Chapter 4 investigates the role of pH in the preparation of Cheddar-based cheese feeds. Besides their calcium-chelating ability, the addition of ES in cheese feed preparation increases the feed pH, aiding in protein solubilization. Therefore, the first part of this chapter (Paper III) evaluates the influence of increasing emulsification pH to different levels during cheese feed preparation without the addition of ES. This investigation aims to isolate the specific impact of increasing pH without the addition of ES, which is essential for distinguishing the individual effects of pH adjustment from those of ES in cheese feed preparation. The results indicated that increasing the emulsification pH during cheese feed production had a significant impact on the composition of the cheese feed, primarily due to shifts in mineral balance and protein interactions. These changes correlated with variations in particle size, feed viscosity, and colloidal stability. A noticeable change in trends was observed above emulsification pH of 6. Additionally, Raman spectroscopy detected alterations in protein structure with increased emulsification pH. In the second part of this chapter (Paper IV), a different approach was employed by acidification and re-neutralization of the cheese feed during its preparation to better understand the relationship of pH, calcium solubilization, its reversibility, and feed stability. It was concluded that re-neutralization treatments exhibited reversible calcium solubilization depending on the extent of pre-acidification. Additionally, feed viscosity was predominantly influenced by the final pH, regardless of the acidification history, with lower pH values resulting in increased viscosity, likely due to reduced electrostatic repulsion. The form of calcium upon re-neutralization possibly varied depending on the acidification history. By elucidating the independent effect of pH, Chapter 4 aims to provide a deeper understanding of its influence on mineral balance as well as protein interactions during cheese feed preparation.

Finally, Chapter 5 evaluates the potential of using novel processing techniques - namely ohmic heating, pulsed electric field (PEF) treatment, and ultrasonication - on cheese feed preparation to reduce the need for ES in cheese powder production. The first part of this chapter (Paper V) examines the influence of ohmic heating pre-treatment on Cheddar cheese before cheese feed preparation, aiming to alter the mineral equilibria in the cheese and thereby improve the emulsifying properties of the para-caseins. Ohmic heating increased mineral solubilization from the cheese matrix during the pre-treatment, with higher temperatures exhibiting a synergistic impact due to increased ion mobility. In addition, ohmic heating-treated cheese showed structural weakening, possibly due to colloidal calcium phosphate (CCP) solubilization, which was confirmed by increased porosity observed in confocal imaging. Despite these effects, the overall stability of the prepared cheese feed did not improve, indicating the need for further optimization of the ohmic treatment set-up or combining with other technologies. In the second part of this chapter (Paper VI), a stronger electric field was applied as pre-treatment on cheese by using PEF technology to further investigate the influence of electric field application under non-thermal (<40ºC) conditions. Again, the goal was to induce mineral solubilization through more effective electroporation, thereby improving para-casein functionality in cheese feed. PEF treatment effectively weakened the cheese structure, evidenced by reduced hardness and increased mineral solubilization from the cheese matrix. However, the stability of the cheese feed remained unaffected under the studied PEF parameters. This suggests that optimization through alternative settings, such as different pulse shapes or shorter durations, might enhance mineral solubilization and protein functionality. In conclusion, both methods of electric field application demonstrated potential in promoting mineral solubilization and inducing structural changes in cheese. However, further studies focusing on optimizing treatment methods and parameters are necessary. The final part of this chapter (Paper VII) explores the combined influence of ultrasonication and ohmic heating on Cheddar cheese. These technologies have shown promise in modifying milk protein structure and improving their solubility and emulsifying properties. Hence, the study aimed to incorporate this idea into cheese feed production by investigating their influence on para-casein functionality. The results demonstrated that ultrasonication improved protein-mediated fat stabilization, while subsequent ohmic heating had a less pronounced effect, showing only a slight increase in mineral solubilization compared to the control sample. The findings of this chapter suggest that these novel technologies have the potential to reduce or eliminate the need for ES in cheese powder production.

Overall, this thesis offers valuable insights for developing strategies to reduce or eliminate the use of ES in cheese powder manufacturing.