Relationship between Food Hardness and Frequency Response Using Swept-Sine Technique

Swept-Sine technique, which can measure impulse responses even in noisy conditions, was investigated for inexpensive, nondestructive, and instantaneous evaluation of food hardness. Jelly samples with hardness variations corresponding to gelatin content and avocados that softened with aging were used as samples. A logarithmic sweep sound was input to the samples through earphones. The sound wave passing through the sample was measured with a microphone. The impulse response of the sample was obtained by convolution integration of the input signal and the sound output from the sample. The Fourier transform was applied to the impulse response to investigate the relationship between the calculated frequency response and hardness. The amplitude and frequency of the peak of the frequency response tended to increase as the hardness of the sample increased. This suggests the possibility of nondestructively measuring the hardness of vegetables and fruits.