Acoustic impulse response technique

The firmness or stiffness of the apples can be measured using the acoustic impulse response technique (Chen and De Baerdemaeker, 1993). The fruit is gently impacted and the response signal is recorded. The frequency spectrum is calculated by means of a fast Fourier transformation. The firmness is then calculated from the mass and the first resonance frequency (Langenakens et al., 1997). The apple firmness measured through an acoustic impulse response technique showed a significant correlation with the sensory attributes of juiciness (De Smedt, 2000). The sensory descriptor 'floury' shows a correlation with the sensory attributes dealing with juiciness. This confirms the fact that the floury sensation in the mouth is due to the combination of a loss of texture and juiciness.

De Smedt (2000) established a statistical model between the sensory attributes of crispiness, floury and juiciness assessment at first bite and during chewing, in relation to the readings obtained from the confined compression test and from the acoustic impulse response technique. Reasonable correlation coefficients of 0.85 for juiciness and 0.71 for crispiness were observed. Although she concluded that the statistical models do not allow for continuous prediction of the sensory attributes that define mealiness, the instrumental parameters involved can be used to identify different commercial mealiness stages.

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