How ingredient arrangement in food is important for texture and taste
Sanam Foroutanparsa defened her PhD thesis at the department of Chemical Engineering and Chemistry on November 24th.
Many foods are optimized and developed on a trial-and-error basis. The optimization process can be shortened if we know what role each ingredient plays and how it responds to changes in composition or processing conditions. One way to understand this is to observe the arrangement of food ingredients at the macro- and nanoscales. This would help food companies to optimize the taste and texture of foods with fewer or no additives. PhD researcher Sanam Foroutanparsa studied the microscopic arrangement of proteins in food. She used high-resolution microscopy techniques to visualize the distribution of proteins in dairy gels (such as yogurt) and emulsions (such as mayonnaise).
Foods are composed of macromolecules such as proteins and carbohydrates. The arrangement of these macromolecules at the micro- and nanoscales affects food quality.
For her Ph.D. thesis, Sanam Foroutanparsa and her collaborators wanted to look at the arrangement of these molecules in food, and to do so, she used so-called super-resolution optical microscopy. “To see the structures, we stained the molecules with appropriate dyes that would help with the identification of the molecules,” says the researcher.
Conventional optical microscopes cannot resolve finer details of the structures due to the natural diffraction limitation of light, which explains why Foroutanparsa turned to super-resolution optical microscopy. “We needed to stain the macromolecules of our interest to make them visible and distinguishable under the microscope. Among others, we used antibodies that are naturally raised to recognize and bind to certain proteins in yogurt.”
Yogurt is made by acidifying milk by lactic acid bacteria, which consume the sugars in the milk and produce acids. Milk comprises of two main families of proteins: caseins and whey proteins. Four types of casein proteins together form a complex particle carrier of calcium phosphate in milk. These structures, about 200 nm in size, are called casein micelles.
“During the acidification of milk, the casein micelles undergo changes in size and composition,” notes Foroutanparsa. “They form a network that causes the milk to thicken when the pH drops below 4.6.”
Using high-resolution microscopy techniques, Foroutanparsa and her collaborators observed individual casein micelles in the milk. Thereafter, they stained and imaged these caseins within the micelles using antibodies that were specific to two types of casein proteins.
“For the first time, we showed how different casein proteins are organized within the protein network and that their distribution depends on the processing conditions of the yogurt,” says Foroutanparsa.
Enhancing yogurt properties
Some lactic acid bacteria also produce exopolysaccharides, which can enhance yogurt sensory properties. Foroutanparsa observed that the caseins, that were distributed differently within the network of yogurts, fermented with bacterial cultures producing different types of exopolysaccharides in the process.
In addition, Foroutanparsa determined the relationships between the properties of this protein network, such as its pore size and connectivity, and its physical properties. A desired quality characteristic of yogurt is the lack of visible whey separation. Foroutanparsa observed that yogurt microstructure with highly-connected caseins, more small-sized pores, and thicker strands showed minimal whey separation.
“During my research, we gained insight into what the microstructure of yogurt with low whey separation looks like and how certain ingredients can promote such a microstructure,” says Foroutanparsa. “This demonstration of super-resolution microscopy in yogurt has broad implications as it can be applied to other food systems and help reveal the functional properties of many food ingredients. With this knowledge, food can be optimized with more precision and fewer artificial additives.”
Title of PhD-thesis: Foods inside out: super-resolved imaging of biomacromolecules in dairy gels and emulsions. Supervisors: Ilja. K. Voets (TU/e) and J.C. Hohlbein (Wageningen University). Other main parties involved: DSM Netherlands, Unilever Netherlands, Confocal.nl Netherlands, and Wageningen University.
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