Drying and Properties of Solid Residue from Guava (Psidium guajava) Pulp Processing

Abstract

The solid residue from pulp production of guava (Psidium guajava) represents around 30% of the raw material. The drying of this residue on drier’ trays at 45, 50, 55, 60, 65 and 70 °C was investigated. After drying, the material was ground in one of two types of mills: a knife or a hammer mill. Guava flour samples were characterized according to their water absorption capacity (WAC), oil holding capacity (OHC), emulsifying and foaming properties, lycopene, total carotenoids and phenolic compounds. The drying curves show typical behaviour and five mathematical models (two-term exponential, Henderson and Pabis, diffusion approximation, Page and logarithmic) were constructed. Of the models tested for the temperatures applied in the experiment, only the Henderson and Pabis model, when adjusted to the experimental data obtained at temperatures of 45 to 50 °C did not represent the drying kinetics of the guava processing solid residue, with coefficients of determination of 0.9376 and 0.6905, respectively. The type of mill and the drying temperature influenced the phenolic compounds, lycopene and total carotenoids. The WAC was higher than the OHC for all drying temperatures, due to the high content of dietary fiber in this residue.