Multi-scale characterisation of pasta - Effects of raw materials on water absorption, water distribution, and microstructure

Doctoral thesis, 2015

Pasta is a product with a long history, but is also still being developed today. Producers want to use new raw materials to make pasta more nutritious, less allergenic, and less dependent on durum wheat. All have in common that new raw materials shall not compromise the desired texture properties of cooked pasta such as the “al dente” feeling. To facilitate the development of new pasta products, understanding the microstructure of pasta can be a tool. Water transforms and interacts with the microstructure during cooking and the outcome determines the texture. The main objective of this work was to analyse the interplay of microstructure and water, and how this is affected by the choice of raw materials. We combined light microscopy and Magnetic resonance imaging (MRI) to study the microstructure and water distribution of pasta. We improved the resolution of MRI to yield data in 3D and were able to link MRI data to microstructure components such as fibre particles and the extent of starch gelatinisation. Monitoring microstructure transformations during cooking and warm-holding of pasta revealed that some transformations are not dependent on the raw materials used. Water ingress towards the core is regulated by starch gelatinisation, which holds true both during cooking and warm-holding. The extent of the continuous starch and protein transformation from core to surface in cooked pasta is mainly governed by the product geometry. Also, texture changes during warm-holding depended mainly on the amount of available water within and around the pasta after cooking. Nevertheless, raw materials are of importance: A higher protein content limited the degree of starch swelling within the gelatinised region in cooked pasta. Fibre particles can hinder water migration locally due to their perpendicular alignment against the direction of water ingress. Bran particles in particular do not absorb water during cooking, but redistribute it around the particles and create a strong variation in the degree of starch swelling. The severity of this effect correlated with bran particle size. This thesis provides a comprehensive overview over how local microstructure and raw material choice affect water distribution at different scales in the cooked product.