Mechanical-acoustic and sensory evaluations of cornstarch-whey protein isolate extrudates

The mechanism relating sensory perception of brittle food foams to their mechanical and acoustic properties during crushing was investigated. Cornstarch was extruded with four levels of whey protein isolate (0, 6, 12 and 18%) and two levels of in-barrel moisture (23 and 27%). Hardness, fracturability and roughness of mass were three main sensory attributes that varied substantially between products. High correlations (r = 0.841-0.998) were observed between sensory attributes and instrumentally determined mechanical properties, including crushing force (11.2-57.9 N) and crispness work (4.6-75.8 N·mm). Based on acoustic data obtained during instrumental crushing, time-domain signal processing and a novel voice recognition technique utilizing frequency spectrograms were successfully employed for understanding the differences in the sensory properties of various products. Microstructure features, including average cell diameter (1.00-2.94 mm), average wall thickness (0.04-0.27 mm) and cell number density (7-193 cell/cm³), were characterized noninvasively using X-ray microtomography, and proved to be critical in relating sensory perception of the cellular extrudates to their mechanical-acoustic signatures. The sensory perception of crispy and crunchy food products is primarily a function of their mechanical response and emission of sounds during fracture. The current study was focused on understanding these relationships in the context of brittle extruded foods. The mechanical-acoustic techniques outlined in this study have the potential of reducing the time, costs and subjectivity involved in evaluation of new foods by human panels, and can be a useful tool in the overall product development cycle. These techniques need not be limited only to food systems, as properties of any rigid, fracturable material can be characterized based on its mechanical-acoustic signature.