Análise da resistência à desidratação dos tecidos do pericarpo e do endosperma do fruto de café arábica

Abstract

This work was carried out in the Laboratory of Agricultural Products of the Department of Engineering from the Federal University of Lavras. Coffee (Coffea arabica L.) fruits of cultivar Catuaí vermelho were harvested at a commercial property located in the city of Ingaí – MG, Brazil. Only the ripest fruits were chosen for analysis. This work aimed at analyzing the coffee fruit drying kinetics, as well as their parts separately (exocarp + a portion of mesocarp; mesocarp; endocarp and endosperm). We also aimed at determining the sorption isotherms and elaborating a drying model for the coffee fruit parts. The harvested and selected coffee fruits had an average initial water content of 68%. The other fruit parts (exocarp + a portion of mesocarp; endocarp and endosperm) were manually separated and the mesocarp was extracted by a centrifuge machine. To obtain the portion of peeled coffee fruits, we used a set of devices that peel the grains, separate their pulp and the green fruit. The coffee fruits were submitted to drying in a system composed of air conditioning coupled to a fixed layer drier (SCAL) with air flow of 20m3.min1.m -2, air temperature of 40ºC and relative humidity values of 10%, 17.5%; 25% and 32.5%. For the adjustment of mathematical models, non-linear regression analyses, by Gauss-Newton methodology, were carried out using software STATISTICA 7.0® (Statsoft, Tulsa, USA). The best model was chosen as a function of the statistic parameters: estimation standard deviation (SE), relative average error (P) and determination coefficient (R2). For content of balance water, the best adjustments to the experimental data were obtained by models Sigma, Copace, Sabbab, modified Gab and modified Henderson for natural coffee; endosperm and peeled fruit; exocarp + part of mesocarp, mesocarp and endosperm; and endocarp, respectively. Midilli’s model was the best one for natural coffee; peeled; exocarp + part of mesocarp; mesocarp; endocarp at RH of 17.5%; 25%; 32.5%; and endosperm at RH of 10; 17.5 and 32.5%. For endocarp at RH of 10%, the best model was the diffusion approximation, and for endosperm at RH of 25%, the best adjustment was presented by Page’s model. Resistance as to water outflow, regardless of the process or the coffee fruit part, is greater when the coffee fruits are dried at the lowest relative humidity; being that the natural coffee was the most resistant treatment, whereas the exocarp + a portion of mesocarp was the least resistant one.