Secagem de caqui em condições controladas : efeito sobre a qualidade do produto e consumo energetico. / Drying of caqui in controlled conditions: effect on the product quality and energy consumption.

AUTOR(ES)

Joel Fernando Nicoleti

DATA DE PUBLICAÇÃO

2005

RESUMO

Aiming to understand the effect of drying conditions on the quality of dried persimmon as well as on the energetic consumption, this work investigated the viability of a process control strategy based on fixed temperature inside the product, which was compared with the conventional process that uses fixed air temperature. In order to evaluate the effect of air velocity and drying temperatures, a second order central composite rotable design combined with response surface methodology was applied. Product shrinkage presented a linear relation with moisture content and was essentially independent of drying conditions, including the control strategy adopted. Drying curves could be adequately described by the analytic solution of the second Fick s Law considering shrinkage and effective diffusivity as function of the moisture content. The rehydration indexes of the dried product were similar for control with fixed air temperature and with fixed temperature inside fruit. The viscoelastic properties of dried persimmon rehydrated at different water activities were satisfactorily determined by adjusting the generalized Maxwell model to the relaxation curves and, as a general rule, the relaxation time and equilibrium stress parameters increased with increasing drying temperatures and air velocity, as well as with decreasing water activities. Only the linear effect of the temperature, in both control strategies, was significant (p<0.05) on the viscoelastic parameters. In spite of the high dispersion of experimental data of vitamin C content due to heterogeneity of samples, a model based on the WLF (Williams-Landel-Ferry) kinetics, which uses the glass transition temperature as an indicator of the molecular mobility, could be successfully fitted to experimental curves of the nutrient degradation in function of drying time. The effect of air velocity was significant only to the energetic consumption, leading to the conclusion that the drying processes of persimmon carried out with low air velocity require less energy, without affecting quality of the dried fruit, since quality parameters were not significantly influenced by this variable.

ASSUNTO(S)

controle automatico caqui energy consumption quality of products secagem kaki energia - consumo drying qualidade dos produtos automatic control

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