NON-DESTRUCTIVE EVALUATION OF FIRMNESS OF FRESH PINEAPPLE BY ACOUSTIC METHOD

Abstract

An acoustic impulse method was used for the non destructive firmness evaluation of pineapple fruit of a wide range of internal maturity. Batches of pineapple fruit (cv. Cayenne lisse), from Cote d'Ivoire, were harvested at 140, 143, 145 and 148 days after the floral induction treatment. Mechanical properties of pineapple fruit were also measured by using a texturometer. Deformation, tensile and puncture tests were carried out on each pineapple respectively on the whole fruit, a standard shaped specimen of skin and on the core part of three slices of each fruit. The chemical composition of the entire fruit pulp was then analyzed to determine refractometry index, total sugar content and titratable acidity. Pineapple fruit spectrum displayed three main revenant peaks for the spherical mode. The resonant frequency of greatest amplitude and the resulting elasticity coefficient decreased from 421 to 326 Hz and from 2 to 1.09 MPa respectively as the physiological development of the fruit increased. Pineapple stored at 10°C for a week exhibited lower resonant frequency and elasticity coefficient than references of the same maturity. Elasticity coefficient was found to be reasonably correlated to mechanical firmness (r=0.80) measured by deformation on individuel whole fruits. The relationship was improved (r=0.91) by using mean values for the different fruit batches. Elasticity had a significant correlation with titratable acidity (r=-0.69) and refractometry index (r=0.58), but was very poorly correlated to puncture core firmness (r=0.24). Elasticity coefficient, obtained from acoustic measurement, may be considered as a promising way for non-destructive evaluation of global pineapple firmness. (Resume d'auteur)