Characterization of the mechanical properties of the sweet passion fruit (Passiflora ligularis Juss.)

The sweet passion fruit figures prominently among the fruits exported by Colombia. The fruit is an ovoid berry with a thick and brittle peel that changes from green to bright yellow, depending on the degree of maturity. The weight of the fruit is 113 grams on average and about 60% of the fruit is edible. The sweet passion fruit is harvested manually. During the harvest and the subsequent handling and transport to the places of packaging and marketing, the fruit is subjected to multiple loads which may cause deterioration in different ways, resulting in significant product losses. Rheological tests were performed (unidirectional compression, puncture and shear) in order to determine the mechanical response of the fruit to the forces exerted on it during harvest and post-harvest handling. The tests were performed using a texture analyzer (TA.XT Plus of Stable Micro Systems®). For each type of rheological test, the specific conditions of the shape and size of the probe, and the speed and depth of penetration were defined. The tests were carry out with 35 fruits, with and without the polyethylene mallalon, at fruit maturity stages 4 and 5. It was found that the firmness of the fruits in the unidirectional compression, longitudinal direction and with a degree of maturity 4, was 117.4 N, similar to that found for the transversal direction but using “mallalón”. Under these conditions, the contact stresses should not exceed 600 kPa, while the force required for a transversal shearing of the skin of the fruit was 43.8 N. The mechanical behavior of the sweet passion corresponds to a viscoelastic, anisotropic and variable material.