Swelling of food powders: Comparative study of methods to quantify swelling of plant-based proteins

Material swelling during food powder reconstitution is a key mechanism involved in undesirable lump formation. The choice of food material often defines the extent of powder swelling and associated problems but the swelling itself is seldom characterized. Quantitative data on swelling kinetics of biopolymers relevant for food systems can help improve product and process design. However, such data is scarce due to the complexity of food powder composition and a lack of reliable measurement methods. This study employs three measurement methods (measurement of displaced volume in a normal force rheometer, image analysis of light microscopy data, particle size measurement) to measure volume changes of gelatin, pea protein concentrate, soy protein isolate and skim milk powder. Data is compared with NMR relaxometry data of a previous study and assessment of the methods regarding their ability to quantify swelling is conducted. For gelatin, data obtained by NMR relaxometry, displaced volume measurement and image analysis were comparable. While no swelling could be measured with the chosen methods for skim milk powder, swelling was clearly observable with all methods for plant-based proteins. However, resulting maximum volume increase ranged from 4 to 15 m3/m3 depending on material, water availability and dispersion conditions.