Abstract
The competitiveness of the dairy industry is increasingly shaped by the adoption of innovative food processing technologies that enhance functionality and create unique properties in dairy products. Extrusion, particularly for casein-based products, offers a promising alternative to traditional cheese-making by enabling continuous production and better control over process, texture, and functionality. This is particularly relevant in response to the growing demand for nutrient-dense, high-protein products, where milk proteins are recognized for their essential amino acids and health benefits. Despite their nutritional advantages, high-protein dairy products remain under-consumed globally, making exploring extrusion technology necessary to meet this demand and unlock new opportunities in dairy product development.
This PhD thesis aims to generate new knowledge supporting the development of innovative dairy products produced from extruded renneted skimmed milk curd. More specifically, the work investigated the effect of modifying milk fat concentrations in casein emulsion gels and their extrudates on the process and product properties. Furthermore, a novel extrusion process for foaming mozzarella-like products through nitrogen injection was developed to create new cheeses with modified functional and structural properties.
In addition to the state-of-the-art review, this thesis focuses on four key studies, each detailed in its own chapter. The first part (Chapter 3) focuses on skimmed milk curd's emulsifying capabilities and how milk fat concentrations ranging from 0.1 to 18% w/w influence its rheological and structural properties. The results showed that milk fat can be naturally emulsified into the casein gel network, enhancing viscoelastic properties and altering the microstructure. The incorporation of fat led to more rigid gels but weaker structures, as indicated by an increase in G' from 12.30 to 28.86 kPa with fat concentrations ranging from 0.1 to 18% w/w. Confocal laser scanning microscopy revealed a more open protein network with larger fat droplets and serum pocket formation in higher fat gels (> 11% w/w). Similarly, low-field nuclear magnetic resonance showed increased water mobility in higher-fat gels due to the more open protein structure.
The second part (Chapter 4) explores the impact of milk fat concentrations (1 to 18% w/w) on the extrusion process and extrudate properties using a twin-screw extruder. Increasing the fat content from 1 to 18% w/w resulted in micro-fat separation and a reduction in specific mechanical energy from 70.4 to 61.4 kJ kg-1 and promoted the formation of a fibrous gel matrix at > 17% w/w fat. This study demonstrated that skimmed milk curd effectively retains fat globules even under thermal and shear forces during extrusion given by the similar G’ values between feed and extrudates. Texture profile analysis revealed lower force values with increasing fat content, indicating a softening behavior at the macroscopic level. This study shows that milk fat concentration in emulsion gels before extrusion distinctly impacts the micro- and macroscopic properties of extruded casein gels, with the most significant effects observed at fat contents above 17% w/w.
The third part (Chapter 5) introduces a novel extrusion method to produce micro-foamed cheese curd infused with nitrogen (0 to 0.015% w/w). This micro-foaming process resulted in a spongy, foam-like structure, reducing extensibility (from 36.9 to 10.9 mm), tensile strength (from 1.3 to 0.6 N), and hardness (from 8.7 to 3.4 N) while increasing porosity (from 8.5 to 43.3%). These findings present new opportunities for producing cheese with customized textures, such as improved mouthfeel and lower density.
The last part (Chapter 6) reviews recent research on the extrusion of whey proteins and milk protein concentrates, focusing on their structural changes, functionality, and potential applications. Whey proteins, derived from cheese production, offer excellent solubility and versatility. Extrusion processes, including those under varying pH conditions, can enhance whey proteins' functional properties by inducing denaturation and creating microparticulate structures for improved mouthfeel. Additionally, combining milk proteins with carbohydrates in extrusion has enhanced the nutrient density and texture of products like snacks. This chapter highlights the opportunities and challenges of utilizing milk proteins to develop innovative dairy products with tailored properties.
The results, methodologies, and insights presented in this PhD thesis highlight the potential to guide the development of next-generation extruded and texturized dairy products, offering opportunities to tailor their properties.
This PhD thesis aims to generate new knowledge supporting the development of innovative dairy products produced from extruded renneted skimmed milk curd. More specifically, the work investigated the effect of modifying milk fat concentrations in casein emulsion gels and their extrudates on the process and product properties. Furthermore, a novel extrusion process for foaming mozzarella-like products through nitrogen injection was developed to create new cheeses with modified functional and structural properties.
In addition to the state-of-the-art review, this thesis focuses on four key studies, each detailed in its own chapter. The first part (Chapter 3) focuses on skimmed milk curd's emulsifying capabilities and how milk fat concentrations ranging from 0.1 to 18% w/w influence its rheological and structural properties. The results showed that milk fat can be naturally emulsified into the casein gel network, enhancing viscoelastic properties and altering the microstructure. The incorporation of fat led to more rigid gels but weaker structures, as indicated by an increase in G' from 12.30 to 28.86 kPa with fat concentrations ranging from 0.1 to 18% w/w. Confocal laser scanning microscopy revealed a more open protein network with larger fat droplets and serum pocket formation in higher fat gels (> 11% w/w). Similarly, low-field nuclear magnetic resonance showed increased water mobility in higher-fat gels due to the more open protein structure.
The second part (Chapter 4) explores the impact of milk fat concentrations (1 to 18% w/w) on the extrusion process and extrudate properties using a twin-screw extruder. Increasing the fat content from 1 to 18% w/w resulted in micro-fat separation and a reduction in specific mechanical energy from 70.4 to 61.4 kJ kg-1 and promoted the formation of a fibrous gel matrix at > 17% w/w fat. This study demonstrated that skimmed milk curd effectively retains fat globules even under thermal and shear forces during extrusion given by the similar G’ values between feed and extrudates. Texture profile analysis revealed lower force values with increasing fat content, indicating a softening behavior at the macroscopic level. This study shows that milk fat concentration in emulsion gels before extrusion distinctly impacts the micro- and macroscopic properties of extruded casein gels, with the most significant effects observed at fat contents above 17% w/w.
The third part (Chapter 5) introduces a novel extrusion method to produce micro-foamed cheese curd infused with nitrogen (0 to 0.015% w/w). This micro-foaming process resulted in a spongy, foam-like structure, reducing extensibility (from 36.9 to 10.9 mm), tensile strength (from 1.3 to 0.6 N), and hardness (from 8.7 to 3.4 N) while increasing porosity (from 8.5 to 43.3%). These findings present new opportunities for producing cheese with customized textures, such as improved mouthfeel and lower density.
The last part (Chapter 6) reviews recent research on the extrusion of whey proteins and milk protein concentrates, focusing on their structural changes, functionality, and potential applications. Whey proteins, derived from cheese production, offer excellent solubility and versatility. Extrusion processes, including those under varying pH conditions, can enhance whey proteins' functional properties by inducing denaturation and creating microparticulate structures for improved mouthfeel. Additionally, combining milk proteins with carbohydrates in extrusion has enhanced the nutrient density and texture of products like snacks. This chapter highlights the opportunities and challenges of utilizing milk proteins to develop innovative dairy products with tailored properties.
The results, methodologies, and insights presented in this PhD thesis highlight the potential to guide the development of next-generation extruded and texturized dairy products, offering opportunities to tailor their properties.
| Original language | English |
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| Publisher | Department of Food Science, Faculty of Science, University of Copenhagen |
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| Number of pages | 191 |
| Publication status | Published - 2025 |