Resumo

OSPINA MONSALVE, Diana Marcela; CIRO VELASQUEZ, Héctor José  e  ARISTIZABAL TORRES, Iván Darío. DETERMINATION OF SURFACE FRACTURE AND FIRMNESS FORCE IN LULO FRUIT (Solanum quitoense x Solanum hirtum). Rev.Fac.Nal.Agr.Medellín [online]. 2007, vol.60, n.2, pp. 4163-4178. ISSN 0304-2847.

A rheological characterization of lulo fruits (Solanum quitoense x Solanum hirtum) by using the test of unidirectional compression to firmness and fracture tests, according to two degrees of commercial maturity (inmature and mature) and four post harvesting times (0, 3, 6, 9 days) was done. Additionally physical and chemical properties were determined such as Brix degrees, pH and colour. The fruits were subjected to unidirectional compression by a texture analyzer and loading rate of 1 mm∙s. The tests of fracture were established in two loading senses (longitudinal and transversal) and the test of firmness was determined in two angles of incidence. Statistical analyses indicated that the rheological behavior of the fruit to fracture and firmness depended upon the post-harvesting time conditions and physiological condition (maturation), situation that shows the anisotropic and viscoelastic behavior of the product. The values of the indicated that the inmature fruit presents higher mechanical resistance to the compression with respect to the mature fruit. Nevertheless, the product present more resistance to mechanical fracture in longitudinal position showing mean values to the inmature fruits in longitudinal and transversal positions of 226 N and  84, 8 N, respectively. The mature fruits showed mean values of fracture force of 180 N and 68,5 N to longitudinal and transversal loading directions. The maximum firmness force to the pulp in mature fruits was of 1,4 N and 1,0 N to inmature fruit. The maximum force measured in the exocarpy showed a mean value of 14,4 N and 15,7 N to mature and inmature fruits respectively.

Palavras-chave : Fracture force; firmness force; physical and chemical properties; lulo fruit.