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. Corn-starch 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 sub-stantially between products. High correlations (r = 0.841–0.998) were observed between sensory attributes and instrumentally determined mechani-cal 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 crush-ing, time-domain signal processing and a novel voice recognition technique utilizing frequency spectrograms were successfully employed for understand-ing the differences in the sensory properties of various products. Microstruc-ture 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. PRACTICAL APPLICATIONS The sensory perception of crispy and crunchy food products is primarily a function of their mechanical response and emission of sounds durin