Physical and rheological characterization of seeds of three legume trees Caracterización física y reológica de semillas de tres leguminosas arbóreas

Summary The Chilean algarrobo (Prosopis chilensis (Mol) Stuntz), the tara (Caesalpinea spinosa (Mol) Kuntze) and the honey locust (Gleditsia triacanthos L) have an interesting potential for the development of arid zones. The endosperm of the seeds of these species has a galactomannan-type gum which has the property of thickening and stabilizing emulsions. This study evaluates the physical characteristics of the pods and seeds, and the rheological properties of the gums of these species. We studied fruits of five ecotypes of algarrobo (Coquimbo and Metropolitan Regions), of tara from the Coquimbo Region and of honey locust (three-spined acacia) from the Metropolitan Region. We measured the dimensions of the pods, number of seeds per pod, seed weight, gum yield and color parameters of the cotyledon and gum, and the rheological properties of the gums extracted. Gums were extracted manually and dried at 50o C. The seeds of algarrobo weighed 0.04 g; their gum yield varied between 25.5% and 31.5%. The seeds of tara weighed 0.14 g and those of the acacia 0.16 g, with a gum yield of 31.0% and 40.1%, respectively. The gums had high luminosity and high contribution of yellow, along with low contribution of red. The dispersions of all the studied gums showed a non-Newtonian Herschel-Bulkley behavior corresponding to an inelastic fluid, independent of time. The apparent viscosity of the gum of algarrobo fluctuated between 0.020 and 0.12; that of tara between 0.06 and 1.3, and that of honey locust between 0.034 and 0.08 Pa*s. The gums of these species have rheological characteristics which would allow their addition to foods.