Shaping of Food Microstructures

Sammanfattning: Shape, the shaping process and the functionality of shape for food microstructure are the focus of this thesis. Shape is one of the parameters that influences the microstructure functionality; hence microstructure shape optimisation is an interesting task in the development of new functional materials and processes, especially for food, in which structure-related texture is an essential part of the product.

By the combination of a deforming flow and a simultaneous temperature-triggered gel formation of a biopolymer to fix the achieved deformation, shaped microstructures are formed. With this process, model food systems of: 1) simple-shaped i.e. ellipsoidal gel particles of gelatine and k-carrageenan, 2) particular aggregates of whey protein isolates with shear thinning rheological behaviour determined by the process and 3) complex-shaped gelled k-carrageenan particles with a high shape consistency can be produced. When shaping of gelled k-carrageenan particles was shifted from an experimental batch-process into a continuous process with totally food grade materials, this high shape consistency was preserved.

By combining time series of micrographs and image analysis it was possible to study and measure structure formation under dynamic conditions. By acquiring the micrographs with a confocal laser scanning microscope, detailed analysis of aggregation of whey-coated particles under shear was achieved. It was revealed that aggregation started at lower temperatures than expected. For gelatine and k-carrageenan drops in emulsions, the shape and shaping were investigated in micrographs from light microscopy and the effect of size, viscosity, temperature, flow, gelling kinetics and cooling was analysed. Their impact on small drop shaping was found to be in according to existing deformations theories. For larger drops the parameters temperature, viscosity and flow interacted and their influence on the shaping was different at different places and times in the process.

Shape characterisations by both classical shape analysis and Fourier-based method were performed on shaped gel particles and on time series of macrographs on the shaping. With shape characterisations based on the Fourier description technique it was possible to quantify and sort even very complex microstructure shapes of particle aggregates according to shape and to present a typical aggregate. This resulted in that shape could be used as parameter similar to the more usual size for complex shapes.

Finally, the shape-induced functionality of gelled drops was investigated and it was concluded that even relatively simply shaped particles altered rheology in a suspension containing shaped drops compared with a suspension containing spherical drops. As the gel formation was triggered by temperature changes, this type of shaping could be applied to several existing products because temperature changes in combination of flow are common in food process lines.