Combination of Different Methods, Including Image Analysis, to Define the Fibrous Structure of High-Moisture Extrusion-Cooking Extrudates

Abstract

Several methods are available to characterize the extrudates produced by High Moisture Extrusion-Cooking, including the Anisotropy Index, spectroscopy and scattering measurements, and microscopy measurements. In this study, a new image analysis method of the fibrous structure of extrudates at the macroscale, divided into two tests: the lamellarity and the aspect of the fibration, has been developed and applied to extrudates made from soy concentrate and wheat gluten in various proportions. The combination of these tests with anisotropy index measurements, light microscopy, Confocal Scanning Laser Microscopy, and X-Ray Micro-computed Tomography has firstly made it possible to suggest a definition of the “fibration”, that is, visible fibers. These fibers, quantified with the aspect of the fibration test, might come from the pore walls inside the extrudates, on conditions for which the latter are strong enough to persist when the extrudate is torn. Second, this new image analysis method enabled us to check, as long as the anisotropy index is already greater than 1, if the extrudate can be considered as fibred, depending on whether it breaks or not during the lamellarity test. Lastly, the method has contributed to show that, when wheat gluten is incorporated up to 75% (db), it resulted in a more compact extrudate, harder to delaminate, with less visible fibers than with soy alone. Nevertheless, the heterogeneity of the fibration has led to large standard deviations, and the repeatability of the method varied from 10.6% for lamellarity to 35.3% for difficulty in delaminating when a same extrudate was analyzed from 1 day to the next. In forthcoming work, this method could be tested on extrudate samples produced under the same operating conditions, but for which production day and operator would vary.