Use of non-invasive X-ray microtomography for characterizing microstructure of extruded biopolymer foams

Understanding foam microstructure formation is important for a priori design and engineering of new biopolymer-based products for both food and industrial applications. However, this has been hindered by unavailability of an imaging technology to characterize the cellular structure of foams accurately. This study investigated a non-invasive imaging technology, X-ray microtomography (XMT), for visualization and measurement of microstructural features of biopolymer foams. Brittle corn starch foams with two levels (5% and 15%) of whey protein concentrate (34% protein) factorialized with two moisture contents (26% or 34%) were produced using extrusion. XMT allowed non-invasive imaging of sample cross-sections at various depths, and facilitated accurate and hitherto impossible measurements of features like true cell size distribution (bi-modal), average diameter (0.58 to 2.27 mm), open wall area fraction (0.068 to 0.099), cell wall thickness (0.09 to 0.15 mm), and true void fraction (0.63 to 0.84). Results indicated XMT is superior to conventional imaging techniques for characterizing foam microstructure.