Influência da secagem convectiva em leito fixo sobre as propriedades da folha de oliveira (Olea europaea L.)

Abstract

The main of this work was to carry out a study of the convective drying of the olive leaf in fixed bed and its influence on leaf characteristics. The performance of the study included the following steps: characterization of the olive fresh leaf as to the composition centesimal, content of phenolic compounds, antioxidant activity, color parameters and obtaining equilibrium isotherms; Analysis of the drying process through the analysis of the characteristic curves and the mathematical description of the process; Checking the influence of the drying conditions (temperature and air velocity) on the process time and on the percentage of loss of the phenolic compounds content and the antioxidant activity, besides the color parameters; Optimization of the drying conditions for a shorter process time and less loss of the original leaf characteristic; And morphological analysis of the surface. The evaluation of the influence of the drying conditions on the responses was made from a central rotational composite planning with air temperature varying between 45,9 and 74,1 ºC and air velocity varying between 0,77 and 1,62 m/s. Regarding the values corresponding to the constituents of the fresh leaf composition, the mean values for moisture, lipids, ashes, proteins and carbohydrates were 51,65 %, 2,71 %, 3,06 %, 5,79 % and 36,76%, respectively. Regarding the content of total phenolic compounds and antioxidant activity, the average values found for fresh leaf were 22,77 mg EAG/gss and 92,73 %, respectively. The color parameters L*, a* and b* for the fresh leaf presented the mean values of 18,95, -7,67 and 32,02, respectively. The desorption isotherms showed a sigmoidal behavior and the GAB model was chosen to represent the experimental behavior. In the evaluation of drying kinetics, only the period corresponding to the decreasing drying rate was verified, and the Henderson and Pabis and Page models fit satisfactorily to the experimental data. By analyzing the influence of the drying conditions on the responses, a significant influence of both temperature and air velocity on the drying time could be verified. Regarding the percentage of loss of total phenolic compounds content, only the temperature had an influence on this response, while in relation to the loss percentage of the antioxidant activity, none of the variables had a significant influence. Considering the color parameters, the only significant influence verified was that of the drying temperature on the green coloration of the leaf. From the optimization of the process, it was verified that drying at temperature of 54,4 ºC and air velocity of 1.62 m/s provided a shorter process time associated with less loss of the original characteristics of the leaf. In the proposed study, it was possible to satisfactorily describe the drying process of olive leaves, as well as to verify how this process impacts on the properties of the leaf.