Acoustic Envelope Detector for crispness assessment of biscuits

The crispness of food materials based on the force/displacement behavior and their acoustic nature was assessed using an Acoustic Envelope Detector (AED) attached to the Texture Analyzer, wherein six kinds of biscuits were used: Carr's Table Water, Crackerbread, Digestive, Dutch Crispbakes, Rich Tea fingers and Shortbread. The force/displacement and acoustic signals were simultaneously recorded during the breakup of biscuits. For each detected acoustic signal, there was a sudden drop in the compression force. The analysis of the force/displacement curve demonstrated the links between the second derivative of force curve and the acoustic event, indicating the energy released through the air of these crack events. The acoustic behavior of the biscuits was assessed in terms of maximum sound pressure level and the number of acoustic events, which were further interpreted as the acoustic events per unit area of newly created surface area and the acoustic event per unit time. The acoustic ranking of biscuits from instrumental assessment was in very good agreement with that from sensory panel tests. The normal integration time (1.25 ms) for the AED was generally effective in detecting acoustic signals for crisp biscuits, but a shorter integration time (0.25 ms) was found advantageous in detecting acoustic signals that occur within a very short time period and gave better differentiation of crisp biscuits.