Abstract
Introduction. Fruit firmness and pulp starch content are two physicochemical traits of great interest for a climacteric fruit such as mango. These two indicators have long been recognised as relevant to the study of fruit maturity at harvest and during ripening and storage. However, very few works have been conducted on the relationship between starch content, one of the major components of mango pulp at harvest, and whole-fruit firmness.Materials and methods. Firmness evaluation of the whole fruit was carried out using both a destructive mechanical method and a non-destructive acoustic impulse response method. Penetration force F5 (N) was measured at 5.5 mm depth when a cylindrical plunger (diameter: 6.35 mm) with a conical tip penetrated unpeeled fruit at a speed of 3 mm·s-1. A global elasticity coefficient, E (Pa), was estimated from the greatest resonance frequency of the whole fruit, obtained by the acoustic impulse response technique. Starch content was determined on a representative sample of whole pulp of each fruit. Analysis of glucose released by starch hydrolysis was carried out by ionic chromatography. Experiments were performed on 133 fruits (cvs. Keitt and Amelie) covering a wide range of maturity stages.Results and discussion. Starch content was highly correlated with the two firmness parameters E and F5. The best correlation coefficients were obtained for Keitt mangoes (r = 0.89 for E; r = 0.88 for F5) and for all the fruit of the two varieties (r = 0.83 for E; r = 0.76 for F5). On the contrary, starch content was poorly correlated with penetration force F5 (r = 0.60) for Amelie mangoes, the elasticity coefficient, E, remaining, however , highly correlated with starch content (r = 0.75).Conclusion. The acoustic impulse response technique appears to be a useful tool for predicting mango fruit shelf life by simultaneously allowing whole-fruit firmness estimation and pulp starch content evaluation. The correlation level obtained between the elasticity coefficient, E, and pulp starch content depends on the mango variety. In the case of a high correlation level such as for Keitt mangoes, the acoustic impulse technique could give information on the starch degradation level in mango as reliable as those obtained by using a destructive iodine test.