Clarificação de suco de maracujá por microfiltração: análise experimental e modelagem matemática

Abstract

The yellow passion fruit (Passiflora edulis) is worldwide commercialized and Brazil is the world greatest producer, and approximately 95% of its production is focused in the beverage market. Conventional fruit juice clarification methods usually involve many batch processes, involving a high demand of time and energy. Membrane processes as microfiltration can be applied for microorganisms removal, providing a concentrated pulp and a clarified and sterilized fraction with higher sensorial properties. In this work, some pre-treatment procedures in the passion fruit pulp were studied before microfiltration, as centrifugation, enzymatic and chitosan treatments. The influence of the combination of these treatments in the physical-chemical characteristics of the passion fruit juice was evaluated, and also the effect of these treatments in the permeate flux during microfiltration. The effect of transmembrane pressure in the permeate flux was also evaluated, and so the physical-chemical characteristics of permeate after clarification. After obtaining the experimental data of permeate flux, the mathematical model proposed by FIELD et al. (1995) was applied in order to describe the mechanisms of fouling formation. A microfiltration module was used, based on the crossflow filtration method, with polyetherimide hollow-fiber membranes with 0,056 m2 of filtration area and 0,4μm average pore diameter. For the enzymatic treatment, the best condition for viscosity reduction was the combination of 1 mL/L of enzyme concentration and 44ºC for temperature. For chitosan treatment, pH values close to neutrality, chitosan concentration of 300 ppm and slow stirring time of 3 minutes were the conditions which induced the best pre-clarification. The enzymatic treatment was efficient in viscosity reduction, being able to reduce over 50% of the viscosity of passion fruit juice; centrifugation was effective in color, turbidity and viscosity reduction and chitosan treatment has shown to be an interest alternative for pretreatment, as presented the highest values of color and turbidity reductions among the observed pre-treatments. The combination of centrifugation at 4000 rpm and chitosan treatment presented the higher stabilized permeate flux during the filtrations, followed by centrifugation at 12000 rpm with enzymatic treatment. The increase of trasmembrane pressure did not influence the permeate flux. The microfiltration process was able to produce a clarified juice with no significant difference in the physical chemical characteristics in the permeate after each of the carried out pretreatments, except for the total soluble solids content, which presented a slight reduction in the clarified samples of juice without any pretreatment. The mathematic model used was able to explain the main mechanisms of fouling formation. It was concluded that in the filtrations with the raw juice, all fouling mechanisms could be satisfactorily fitted to the experimental data, with a slight predominance of the total pore blocking mechanism. In the other samples, the predominant mechanism observed was the formation of a gel layer, except for the chitosan pretreated sample, where the predominant mechanism was found to be the internal pore blocking. The microfiltration process was found to be effective, being capable of producing a clear juice without any pulp.