Elsevier

Journal of Food Engineering

Volume 42, Issue 4, December 1999, Pages 215-224
Journal of Food Engineering

Crossflow microfiltration of passion fruit juice after partial enzymatic liquefaction

https://doi.org/10.1016/S0260-8774(99)00124-7Get rights and content

Abstract

To obtain clarified passion fruit juice, crossflow microfiltration after enzymatic liquefaction was studied using ceramic membranes with 0.2 μm pore size. The effect of a high-rate enzymatic treatment for the degradation of suspended solids was assessed, resulting in the selection of a commercial enzymatic preparation. Partial enzymatic liquefaction of cell-wall polysaccharides prior to microfiltration provided an unusual pattern of flux increase after a short decline when crossflow velocity was high (7 m s−1). It was found that a synergistic effect between pectinase and cellulase activities enhanced permeate flux increase. With total recycling at 36°C, the combination of low transmembrane pressure (150 kPa) and high enzyme concentration (1 ml l−1) provided the highest flux (113 l h−1 m−2). These conditions were then assessed with concentration in order to verify industrial feasibility and evaluate physico-chemical characteristics of final products. A volumetric reduction ratio of 3 was maintained during 18 h without any decrease in permeate flux, which fluctuated around 40 l h−1 m−2. The quality of permeate was satisfying even its aromatic strength was weakened. Retentate had similar characteristics of raw juice and could be recycled in order to use its residual enzyme activity.

Introduction

Yellow passion fruit (Passiflora eduils var. flavicarpa) juice is marketed world-wide, principally because of its pleasant unique aroma and flavour. Nevertheless, the flavour of passion fruit is extremely sensitive to change as a result of heat processing (Whitfield & Last, 1986). Conventional stabilisation methods, such as thermal pasteurisation, induce general losses in flavour volatile concentration, and specific changes in aromatic compounds, even when short-duration procedures are applied (Casimir, Kefford & Whitfield, 1981). Membrane-based techniques, on the other hand, do not involve the application of heat. Microfiltration can be used to separate juices into a fibrous concentrated pulp, and a clarified fraction free of spoilage micro-organisms. The `commercially sterile' clarified fraction can then undergo non-thermal membrane concentration, and eventually whole juice reconstitution by combination with the pasteurised pulp, in order to obtain a product with improved sensorial properties (Ganlmann, 1993). Also, a superior quality clarified passion fruit juice could make a strong impact in new market areas, such as clear juice blends, liqueurs and related products, carbonated soft drinks, and in all applications where suspended solids have a negative effect on final product quality.

A major constraint in relation to the microfiltration of juices rich in pulp, is the formation of a highly swollen fouling layer on the membrane surface, which greatly reduces performance. For fruit juice, the fouling materials are mainly composed of cell-wall polysaccharides such as pectin, cellulose, lignin and hemicellulose (Yu, Chiang & Hwang, 1986). To enhance filtration performance, fruit juices are usually treated before filtration with enzyme preparations aimed at hydrolysing mainly soluble polysaccharides responsible for high viscosity Chiang and Yu, 1987, Cheryan and Alvarez, 1995. This treatment is effective on juices with relatively low pulp content. Nevertheless, when it comes to pulpy juices, microfiltration processes undergo difficulties and poor flux generally result. Apparently, a more aggressive enzymatic degradation is required, not only to reduce viscosity but also to liquefy insoluble cell-wall polysaccharides which are retained by the membrane.

The research described in this paper was undertaken to investigate the effects of enzymatic liquefaction of cell-wall polysaccharides prior to microfiltration, in order to introduce inside a juice plant a processing line for the production of clarified passion fruit juice without any new waste disposal.

Section snippets

Passion fruit juice

All juice was processed at the juice plant of Passicol S.A. (Chinchiná, Colombia) using fully ripe fruit from plantations located in the department of Caldas, between 1500 and 1800 m altitude. Juice was taken from the industrial processing line after peel removal, enzymatic treatment of pulp (15 min) at ambient temperature for the separation of the seeds from juice sacs (20 μl l−1 of Ultrazym 100 G®, NOVO, Denmark), seed removal, juice finishing and centrifugation at 1000 g (1.8–2 min) in order

Selection of enzyme preparation

In order to investigate the influence of varying enzyme activity composition upon overall filtration performance, four different commercial enzyme preparations with a wide variety of different activities were used to pretreat juice prior to microfiltration in permeate recycling mode (Table 1). A strong positive effect on permeate flux was observed in all cases where the juice was enzymatically treated, but the magnitude of this effect depended on the preparation (Fig. 1). Preparations

Conclusion

Passion fruit juice has a high content of suspended solids which causes rapid fouling of the membrane during microfiltration. With total recycling (VRR=1), the effect of partial enzymatic liquefaction of insoluble cell-wall polysaccharides of the juice prior to microfiltration produced an unusual flux pattern, characterised by an increase of flux after an abrupt decrease. This increase is not only due to a viscosity decrease but to an important decrease of suspended solids concentration in the

Acknowledgements

The authors wish to thank Passicol S.A. (Chinchiná, Colombia), Colciencias (project n° 1106-07-283-95), the French Foreign Affairs Ministry (PRI project), for the financial support and especially Gorge A. Martinez, Victor M. Amu, Anne Leblanc for the valuable help provided to this work.

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