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Clarification and concentration of melon juice using membrane processes
Innovative Food Science and Emerging Technologies 6 (2005) 213 – 220 www.elsevier.com/locate/ifset
Clarification and concentration of melon juice using membrane processes Fabrice Vaillanta,b, Mady Cissea,c, Marco Chaverrib, Ana Perezb, Manuel Dorniera,c,*, Floribeth Viquezb, Claudie Dhuique-Mayera a
Centre de Coope´ration Internationale en Recherche Agronomique pour le De´veloppement (CIRAD), Tropical Fruits Department (FLHOR), Avenue Agropolis, TA 50/PS4, 34398 Montpellier Cedex 5, France b Centro Nacional de Ciencia y Tecnologia de Alimentos (CITA), Universidad de Costa Rica, Codigo Postal 2060, San Jose, Costa Rica c Ecole Nationale Supe´rieure des Industries Alimentaires (ENSIA), Tropical Food Department (SIARC), 1101 av. Agropolis, CS 24501, 34093 Montpellier Cedex 5, France Received 15 June 2004; accepted 22 November 2004
Abstract Melon juice obtained from fruits discarded by exporters was first clarified by crossflow microfiltration and then concentrated by osmotic evaporation (OE). The resulting clarified melon juice was highly similar to the initial juice, except for insoluble solids and carotenoids, which were concentrated in the retentate. Average permeation flux was relatively high (about 80 L h1 m2), with continuous extraction of retentate at a volumetric reduction ratio of 3. After concentration of the clarified melon juice to as much as 550 g kg1 of total soluble solids using a continuous feed-and-bleed procedure of OE, we found that almost the entire composition of the product was preserved. This integrated membrane process permitted two valuable products to be obtained: a clarified concentrate of melon juice that had not undergone any thermal treatment, and a glowing-orange retentate that was enriched in provitamin A. D 2004 Elsevier Ltd. All rights reserved. Keywords: Melon; Fruit juice; Crossflow microfiltration; Osmotic evaporation; Clarification; Concentration Industrial relevance: The increasing quality demand for fresh fruits results in an increase in rejected melons. Juice processing could overcome the product losses occurring but thermal sensitivity of melon juice flavour prohibits conventional thermal processing. Interestingly this paper attempts to use membrane processes for microbial stabilisation and concentration. The authors present a novel way of using permeate (clear juice) as well as retentate (pulpy juice). Enzyme activities in the products during and after processing may need some attention prior to industrial application of the process.
1. Introduction During the last decade, melon (Cucumis melo L.) has become a major exchange commodity for tropical countries able to supply northern markets and meet a strengthening offseason domestic demand. In 2002, off-season melon imports accounted for about one third of year-round consumption in the USA and EU (CNUCED/OMC, 2003). The high quality required by these markets means that almost 20% of production is rejected as export quality, often just because * Corresponding author. Centre de Coope´ ration Internationale en Recherche Agronomique pour le De´veloppement (CIRAD), Tropical Fruits Department (FLHOR), Avenue Agropolis, TA 50/PS4, 34398 Montpellier Cedex 5, France. Fax: +33 4 67 61 44 33. E-mail address: [email protected] (M. Dornier). 1466-8564/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2004.11.004
fruits are misshapen, too big, or too small. In Costa Rica alone—one of the world’s largest melon exporters—rejected fruits represent more than 10,000 t. While some fruits can be sold at low prices on the domestic market, most are considered as waste and as presenting significant environmental problems. Nonetheless, such rejected fruits present good internal characteristics and should be used by the juice industry for their pleasant aroma and relatively high sugar content. But previous experiments have shown that the mild distinctive flavour of melon juice is very sensitive to thermal treatment, resulting in poor-quality final products (Galeb, Wrolstad, & McDaniel, 2002; Nath & Ranganna, 1977). Hence, despite the potential demand, traditional fruit juice industries do not consider melon sort-outs as valuable raw material.
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bCold processQ membrane technologies represent an alternative to high-temperature treatments. Crossflow microfiltration (CMF) has been applied successfully to some highly thermosensitive juices, resulting in microbiologically stabilized clarified juice that preserves the major part of the fruit’s original aroma (Cassano, Jiao, & Drioli, 2004; Matta, Moretti, & Cabral, 2004; Vaillant, Millan, O’Brien, Dornier, Decloux, & Reynes, 1999). The application of CMF to melon juice has not yet been reported. As well, an innovative concentration technology such as osmotic evaporation (OE) may allow concentrating melon juice and thus add value to the product. Both these technologies appear appropriate for concentrating the thermosensitive juice (Cassano et al., 2004; Hogan, Canning, Peterson, Johnson, & Michaels, 1998; Vaillant, Jeanton, Dornier, O’brien, Reynes, & Decloux, 2001). The research described in this paper was undertaken to study the effects of CMF and OE on the physico-chemical, nutritional, and microbiological qualities of melon juice.
2. Materials and methods 2.1. Fruit and juice processing Ripe cantaloupe melons (cultivar Veracruz) of good appearance but discarded by exporters because of their
misshapen form or inappropriate size were provided by Exporpack SA (Guanacaste Province, Costa Rica). The fruits were then processed according to the procedure shown in Fig. 1. Trials were carried out with fresh melon fruit collected no more than 2 days before processing. When an experimental design was implemented, experiments were conducted with the same homogenized juice batch, divided into lots of 25 kg each, and kept frozen at 20 8C. 2.2. Microfiltration The microfiltration unit featured a ceramic multichannel membrane (MembraloxR 1P19-40; Pall-Exekia, Bazet, France) that had a total effective filtration area of 0.24 m2 and an average pore diameter of 0.2 Am. Before microfiltration, melon juice was macerated at 35 8C for 1 h with enzymatic solution RapidaseR Tropical Cloud (DSM, France). According to the supplier, this enzymatic preparation is obtained from a selected GRAS strain of Aspergillus niger. It mainly consists of hemicellulase and cellulase activities. For incubation, the CMF temperature was fixed at 35 8C, the highest temperature at which melon juice can be held for 2 h without being recognized as different (at 5% confidence level) by panellists during a triangular test, using fresh melon juice as standard. In spite of the high pH of the juice, no significant sensorial change by fermentation or oxidation was detected during this step. Crossflow velocity was about 7 m s1. According to Vaillant et al. (1999), all trials were carried out with continuous juice feed and permeate collection at flow F p. The feed-and-bleed procedure was also followed in the long-term trials by implementing continuous extraction of retentate at flow F r, calculated according to Eq. (1), when the volumetric reduction ratio (VRR; defined as the ratio between the cumulated volumes of the feed and of the retentate) set-up was reached. Extraction flow for retentate ( F r) was adjusted every 5 min through a microvalve: Fr ¼ Fp =ðVRR 1Þ
ð1Þ
2.3. Concentration procedure
Fig. 1. General processing diagram.
The OE pilot plant used was already described by Cisse, Vaillant, Perez, Dornier, & Reynes (in press) and the procedure that followed was slightly modified from Vaillant, Jeanton et al. (2001). The unit featured a module containing polypropylene hollow fibres (10 m2). The concentration procedure involved feeding through a closed loop (hold-up volume, 7.5 L). The juice circulated with an average tangential velocity of 0.20 m s1 inside the fibres. The loop was continuously fed with cold clarified juice (6 8C). When the total soluble solid content set-up (TSSFinal) was reached, concentrate was extracted at rate F c, which was calculated from water evaporation flow ( F w) according to
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Eq. (2) to keep the degree of concentration constant inside the loop: Fw Fc ¼ ð2Þ TSSFinal 1 TSSInitial Calcium chloride brine was circulated continuously along the other side of the membrane. It was constantly maintained at near saturation (between 5.3 and 5.6 mol L1) by adding calcium chloride crystals to the feed tank. The brine’s circulation velocity was evaluated at 0.02 m s1 in the cartridge. Temperature was maintained almost constant in both compartments at 26F1 8C (juice) and 31F2 8C (brine). Evaporation flow was registered, using an electromagnetic flow meter (Krohne Messtechnik, GmbH, Duisburg, Germany) connected to a computer. All trials involving OE concentration were carried out over 12 h, including 3 h of continuous extraction of concentrate. 2.4. Chemical and physical analyses Fresh melon juice (F), permeate (P), retentate (R) at VRR=3, and concentrated juice (C) were collected at different stages of the integrated membrane process (Fig. 1). Samples were analysed for pH, titratable acidity, and density using standard methods (AOAC, 1990). Total soluble solids content (TSS) was measured with an Abbe refractometer (Atago, Japan). Carotenoids were extracted with ethanol/hexane at 4/3 (vol/vol) according to Taungbodhitham, Jones, Wahlqvist, & Briggs (1998) and dissolved in 1 mL of dichloromethane and 1 mL of a mixture of methyl tert-butyl ether and methanol at 80:20. They were then analysed by HPLC according to the methodology described by Caris-Veyrat, Schmid, Carail, & Bo¨hm (2003) using the h-apo-8Vcarotenal as internal standard. This method is based on the works of Roussef & Raley (1996) and Lessin, Catigani, & Schwarz (1997). It allows to quantify the different carotenoids in the fruits and their cis–trans isomers, which could
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appear during processing. The HPLC system (Agilent 1100 Series, Massy, France) featured a C30 column (2504.6 mm, i.d.=5 Am; YMC Europe, GmbH, Germany) and a photodiode array detector (Agilent Technologies). Carotenoids were quantified, using calibration curves with pure reagents. Mean recovery was 84% for h-carotene. Polyphenols were evaluated, using the method described by Slinkard & Singleton (1977). Vitamin C was assessed by HPLC, using the method as modified by Kacem, Marshall, Mathews, & Gregory (1986) and Brause, Woollard, & Indyk (2003). Sucrose, fructose, and glucose were also determined by HPLC, following Englyst & Cummings (1984). Colour measurement was done on 30 mL samples in Petri dishes backed with white tiles, using a colorimeter HunterLab DP 9000 (28 standard observer and illuminant C). Data were expressed in terms of L*, a*, and b* parameters; hue angle (H8=tan1(b*/a*)); and colour purity (C8=(a*2+b*2)1/2). Viscosity was measured with a glass Oswald capillary viscosimeter. Water activity was determined with an a w meter (Aqua lab model CS-2). Total flora, yeasts, and moulds were assessed using standard methods (Vanderzant & Splittstoesser, 1992).
3. Results and discussion 3.1. Microfiltration of melon juice 3.1.1. Optimising operating conditions Fig. 2 shows the variation of permeate flux during a typical microfiltration trial. For all trials with enzyme-treated melon juice, three phases were observed: (1) between VRR=1 and 1.5, formation of a fouling layer with a significant decrease of permeate flux to a minimum (almost 50% of the initial flux); (2) VRR=1.5–2.5, a significant increase (about 30%) in flux density; and (3) a decrease in the last phase. The increase in flux density (phase 2) after the formation of a fouling layer has already been described for
Fig. 2. Permeate flux and volumetric reduction ratio (VRR) during the clarification by crossflow microfiltration ( P tM=150 kPa, enzymatic treatment: 0.25 mL L1).
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Table 1 Main physico-chemical, microbiological, and nutritional characteristics of processed melon juices (in parenthesis, standard deviation from six experiments) Characteristic
Feed
Permeate
Retentatea
Concentrateb
Total soluble solids TSS (g kg1) pH (20 8C)
88 (1)
70 (1)
91 (1)
550 (2)
7.10 (0.05) 23 (1) 0.99 (0.02) 2.8 (0.1) 1030 (4) 2.1 (0.2) 0.45
6.81 (0.05) 43 (2) 0.99 (0.02) 1.3 (0.1) 1026 (4) 1.7 (0.2) nd
7.01 (0.05) 25 (1) 0.99 (0.02) 3.5 (0.1) 1028 (4) 0.90 (0.1) 1.45
3.59 (0.05) 42 (2) 0.88 (0.02) 19 (1) 1204 (4) 1.2 (0.2) nd
0.89 (0.09) 125 (10) 148 (10) 329 (30) 3.5104
0.83 (0.07) 157 (10) 186 (20) 400 (40) b30
0.62 (0.05) 148 (10) 160 (10) 358 (40) 3.0104
0.85 (0.09) 162 (10) 220 (20) 410 (40) 0.3104
b30
b30
b30
b30
3000 (700)
0.61 (0.08)
9000 (900)
–
57.1 20.4 56.6 70.2 60.2
53.8 2.3 21.5 83 21.6
53.9 33.2 63.4 62.3 71.5
62.9/52.3c 4.0/2.2c 30.5/19.9c 82.5/83.7c 30.8/20.0c
Titratable acidity (g kg1 TSS) Water activity (25 8C) Viscosity (25 8C, mPa s) Density (kg m3) Polyphenols (g kg1 TSS) h-Carotene (g kg1 TSS) Vitamin C (g kg1 TSS) Glucose (g kg1 TSS) Fructose (g kg1 TSS) Sucrose (g kg1 TSS) Total flora (CFU mL1) Yeast and moulds (CFU mL1) Turbidity (NTU) Colour L* a* b* Hue Chroma
To define the optimal transmembrane pressure (P tM) and enzyme concentration, an experimental design was implemented. The surface response, corresponding to the permeate flux reached at VRR=3, is presented as a contour plot in Fig. 3 (data analysed, using stepwise multiple regression). Fig. 3 shows that a lower P tM gives rise to improved permeate flux density at VRR=3, whereas an optimal enzyme concentration exists at about 0.2 mL L1 for lower P tM. As P tM increases, the optimal enzyme concentration also increases. The negative effect of high P tM indicates that the fouling layer is highly sensitive to compression as it becomes less permeable when pressure increases. Thus, to obtain high-permeate flux density at VRR=3 (around 88 L h1 m2), P tM should be maintained at the lowest value possible (120 kPa). Also, for economic reasons, enzyme concentration should be fixed at 0.15 mL L1, corresponding to the lowest concentration that can give rise to a high flux permeate density (N80 L h1 m2). These processing conditions were implemented during trials, following a feed-and-bleed procedure when VRR=3 was reached. The turbidity mainly depends on the pulp content of the product. Even if the reproducibility of the turbidity measurements was poor (between 10% and 20% mainly due to sampling), this parameter could be correlated reasonably well to VRR (Fig. 4). As shown in Fig. 5, the retentate’s turbidity increased from an initial value of about 2800 NTU until VRR=3 was reached, when it was about 8500 NTU. This value was almost constantly maintained, corresponding to a likewise almost constant VRR. The turbidity could then be used as an in-line indicator for VRR. During the last phase, the flux permeate density was kept high between 70 and 80 L
nd=not detected. a At VRR=3. b Sample collected at the end of the OE trial (after 12 h). c After dilution of samples to 70 g kg1 of TSS.
other pulpy fruit juices (Vaillant, Dornier et al., 2001). Nevertheless, in the case of melon juice, this increase is surprisingly high. As processing variables were all kept constant, this phenomenon can only be attributed to an intrinsic change of the rheological properties of the retentate after VRR=1.5. One hypothesis suggests that a higher concentration of cell wall fragments has a better bremovingQ Q effect over the fouling layer, while viscosity increases only by 20% between the feed (F) at VRR=1 and the retentate (R) at VRR=3 (Table 1). But, at values higher than VRR=3, in addition to increased viscosity, a higher concentration of particles increases the risks of blocking some of the membrane’s pores. For this reason, VRR=3 was chosen as the optimal VRR, corresponding to a higher permeate yield while permitting the maintenance of a high flux density.
Fig. 3. Permeate flux (expressed in L h1 m2) reached at VRR 3 during the clarification by crossflow microfiltration vs. transmembrane pressure (P tM) and enzyme concentration used for maceration.
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Fig. 4. Correlation between the volumetric reduction ratio (VRR) and the turbidity of the retentate obtained during the clarification by crossflow microfiltration.
h1 m2, with flux variation being attributed to temperature. We could maintain an almost steady permeate flux for 40 min, following the continuous feed-and-bleed procedure. These results show that melon juice can be microfiltered continuously with an acceptably high average permeation flux (about 75 L h1 m2), while retentate can be extracted at half this rate, giving rise to a global yield of clarified juice of about 67%. These results demonstrate good potential for the industrial application of CMF to melon juice, as processing results are comparable with those reported by the wine and apple industries (Daufin, Escudier, Carrere, Fillaudeau, & Decloux, 2001). Furthermore, the filtrability of the melon juice should still be improved by optimizing the activity spectrum of the enzymatic solution used for the partial liquefaction before filtration.
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3.1.2. Main characteristics of clarified melon juice and retentate The most relevant physico-chemical, nutritional, and microbiological properties of the initial juice (F), permeate (P), and retentate at VRR=3 (R) are reported in Table 1. Total soluble solids content as measured by a refractometer appeared to be higher in the retentate than in the recovered permeate. As already mentioned, this observation is probably related to the presence of a high suspended solids content in the pulpy products that can interfere with the measurement of the refractive index (Cisse et al., in press; Vaillant et al., 1999). Even so, concentrations of the three main sugars (glucose, fructose, and sucrose) measured by HPLC were not significantly different for the two juices. Titratable acidity and pH of the feed and the retentate were very similar. The organic acids content of the permeate increased (titratable acidity2 and 0.3 pH). This result could be explained by a lactic fermentation in the permeate during processing. However, this hypothesis is contradicted by the sugar contents that did not decrease and by the total flora that was strongly removed in the permeate. Surprisingly, the total flora did not increase in the retentate. Microorganisms that are retained by the membrane could be partially destroyed by the high shear stress in the circuit. For some nutritional compounds—specifically, polyphenol compounds and vitamin C—a loss was noted during processing, at about 19% and 7%, respectively, in permeate and 57% and 30% in retentate. Loss of phenol compounds probably resulted from the continuous action of polyphenol oxidases, which were partly retained in the retentate where they remained active. Loss of vitamin C may have been due to oxygen exposure. This loss could have been drastically
Fig. 5. Permeate flux behavior during a feed and bleed microfiltration trial (P tM=150 kPa, enzymatic treatment: 0.15 mL L1).
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reduced by implementing a degassing treatment before microfiltration. The main carotenoid compound found in the fresh melon juice (F) was h-carotene, at 40.7 mg L1 (equivalent to 0.45 g kg1 TSS). Its content varied in the different products obtained during the process. Neither cis isomers nor oxidized compounds appeared, which is in accordance with the low processing temperature. Table 1 shows a total retention of h-carotene in the retentate (135.3 mg L1, equivalent to 1.45 g kg1 TSS). This compound was concentrated about 3.3 times, which accords with the value of the VRR reached. This result also accorded with higher positive a* and b* values, as the colour of the retentate was deep orange, in contrast to the clarified juice, which was translucent, showing very pale yellow hues. The h-carotene was retained in the retentate probably because it is strongly associated with membrane and wall structures of the cell fragments (i.e., the pulp). These results are correlated to those of Galeb et al. (2002), who showed that carotenoids remained in the press cake and the filter pads during the clarification of melon juice using dead-end filtration. Hence, in parallel with the production of clear melon juice, microfiltration appears to be a genuine alternative for concentrating h-carotene. There is worldwide interest for natural and cheap h-carotene sources (Spanos, Chen, & Schwarz, 1993), not only for its high provitamin A activity and its colouring properties in food, but also for being an effective antioxidant as reported by clinical studies (Krinsky, 1989). Consequently, the retentate may be highly valuable for commercialising as part of tailor-made drinks that combine nutritional and functional properties with colour. Microbiological analyses showed that CMF can ensure microbiological stability of the juice in a single operation. Preliminary organoleptic tests performed on clarified juice and retentate show that the permeate gave off a very good melon aroma that could be easily
recognised, whereas the retentate presented very little melon aroma and had an oily texture that was certainly a result of the high concentration of h-carotene. 3.2. Osmotic evaporation 3.2.1. Concentration trials Clarified juice, obtained after microfiltration, was concentrated by OE from 70 to 550 g kg1 of TSS. Experimental results showed that water evaporation flux decreased from 0.70 to 0.57 kg h1 m2 when juice TSS reached 550 g kg1 (Fig. 6). When extracting concentrate, evaporation flux remained constant, agreeing with results obtained for other fruit juices (Cisse et al., in press; Vaillant, Jeanton et al., 2001). The low water evaporation fluxes were similar to those obtained with other clarified juices, where the same membrane was used. Thus, such fluxes appear to be a characteristic of the membrane rather than of the juice. When the TSS set-up was reached and the evaporation flow remained constant, clarified melon juice concentrated at 550 g kg1 of TSS could be continuously extracted at 83 mL h1 m2 and the OE unit fed at a rate of 653 mL h1 m2 with clarified juice at 70 g kg1 of TSS. These flows were somewhat low, but taking into account that other bcoldQ concentration processes such as reverse osmosis do not allow to reach a TSS as high as 300 of TSS kg1 (Jariel, Reynes, Courel, Durand, Dornier, & Deblay, 1996), OE appears to be an effective alternative. Also, it must be noted that the membrane used in these trials was not specific for OE. Trials carried out on a laboratory scale on sucrose solutions and with thinner membranes gave rise to much higher water evaporation fluxes of about 10 L h1 m2 (Courel, Dornier, Herry, Rios, & Reynes, 2000). Also, it should be pointed out that porous organic hydrophobic membranes such as the one used here are cheap compared with the membranes used for reverse osmosis.
Fig. 6. Evolution of evaporation flux ( F w) and total soluble solids (TSS) during the osmotic concentration of the clarified melon juice from 70 to 550 g kg1 of TSS.
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3.2.2. Characteristics of the concentrate Table 1 lists the main characteristics of the initial clarified melon juice (P) and the concentrate (C). Expressing the results by kilograms of TSS, we can see that the OE concentrate had very similar values to the clarified juice for acidity, glucose, fructose, and sucrose contents. Total flora enumeration in the concentrate showed recontamination of the product during handling because the initial clarified juice (CMF permeate) was almost free of microorganisms. This problem should be easily resolved using an aseptic connection between the filter and the concentrator. No significant loss of vitamin C was noted, compared with the initial clarified juice, but a loss of phenol compounds (about 30%) is again observed. This loss may be also explained by the presence of polyphenol oxidases in the clarified juice, which continues acting during processing. The juice’s colour, when compared after redilution to the feed TSS, was completely preserved, indicating the absence of Maillard reactions. This result is really interesting in comparison with the classical thermal processes of concentration. According to Galeb et al. (2002), melon juice is especially sensitive to nonenzymatic browning even using HTST treatment (browning rates from 2 to 12 times higher than for pear or grape juices). The chemical composition of the product was then not significantly modified by the process and the concentrate was very close to the initial clarified juice. These results are in accordance with other studies carried out with other different fruit juices (Cisse et al., in press; Rodrigues, Menezes, Cabral, Dornier, & Rios, 2004; Vaillant, Jeanton et al., 2001). They confirmed that the osmotic evaporation allows to preserve better the quality of the raw material than the classical thermal evaporation. We can also noticed that the melon juice concentrate presented a pH below 4 that is more suitable for conservation during storage.
4. Conclusions Crossflow microfiltration of melon juice allows attainment of a relatively high average permeation flux density (about 75 L h1 m2), with constant extraction of retentate at VRR=3 and giving rise to a global yield of microbiological stabilized clarified juice of about 67%. The clarified juice presents physico-chemical and nutritional properties that are comparable with fresh melon juice, except for the absence of suspended solids and carotenoids, which remained totally concentrated in the retentate. The retentate presents a glowing orange colour because of the high concentration of h-carotene. The clarified juice can also be concentrated at low temperatures by OE to as high as 550 g TSS kg1 to obtain a concentrated melon juice that also preserves the main physico-chemical and nutritional properties. This integrated membrane process is a genuinely innovative way of treating melon juice, as it allows high-value products to be obtained from fruits discarded
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by the fresh market. On one hand, the clarified melon juice and its concentrate can be marketed as part of fruit beverages to which they can contribute fruit sugars and specific aroma; on the other hand, a pulpy juice (retentate), which is enriched in provitamin A and can be used as raw material to extract h-carotene or directly in functional drinks, is obtained.
Acknowledgements The authors wish to thank the French agency AIRE De´veloppement for its valuable financial help and EXPORPACK SA for providing us with melons.
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Spanos, G. A., Chen, H., & Schwarz, S. J. (1993). Supercritical CO2 extraction of h-carotene from sweet potatoes. Journal of Food Science, 58, 817 – 820. Taungbodhitham, A. K., Jones, G. P., Wahlqvist, M. L., & Briggs, D. R. (1998). Evaluation of extraction method for the analysis of carotenoids in fruits and vegetables. Food Chemistry, 63, 577 – 584. Vaillant, F., Jeanton, E., Dornier, M., O’brien, G. M., Reynes, M., & Decloux, M. (2001). Concentration of passion fruit juice on an industrial pilot scale using osmotic evaporation. Journal of Food Engineering, 47(3), 195 – 202. Vaillant, F., Millan, P., O’Brien, G., Dornier, M., Decloux, M., & Reynes, M. (1999). Crossflow microfiltration of passion fruit juice after partial enzymatic liquefaction. Journal of Food Engineering, 42, 215 – 224. Vaillant, F., Dornier, M., Decloux, M., & Reynes, M. (2001). Strategy for economical optimisation of the clarification of pulpy fruit juices using crossflow microfiltration. Journal of Food Engineering, 48, 83 – 90. Vanderzant, C., & Splittstoesser, D. F. (1992). Compendium of methods for the microbiological examination of foods. Washington, DC7 Public Health Association.
Clarification and concentration of melon juice using membrane processes Fabrice Vaillanta,b, Mady Cissea,c, Marco Chaverrib, Ana Perezb, Manuel Dorniera,c,*, Floribeth Viquezb, Claudie Dhuique-Mayera a
Centre de Coope´ration Internationale en Recherche Agronomique pour le De´veloppement (CIRAD), Tropical Fruits Department (FLHOR), Avenue Agropolis, TA 50/PS4, 34398 Montpellier Cedex 5, France b Centro Nacional de Ciencia y Tecnologia de Alimentos (CITA), Universidad de Costa Rica, Codigo Postal 2060, San Jose, Costa Rica c Ecole Nationale Supe´rieure des Industries Alimentaires (ENSIA), Tropical Food Department (SIARC), 1101 av. Agropolis, CS 24501, 34093 Montpellier Cedex 5, France Received 15 June 2004; accepted 22 November 2004
Abstract Melon juice obtained from fruits discarded by exporters was first clarified by crossflow microfiltration and then concentrated by osmotic evaporation (OE). The resulting clarified melon juice was highly similar to the initial juice, except for insoluble solids and carotenoids, which were concentrated in the retentate. Average permeation flux was relatively high (about 80 L h1 m2), with continuous extraction of retentate at a volumetric reduction ratio of 3. After concentration of the clarified melon juice to as much as 550 g kg1 of total soluble solids using a continuous feed-and-bleed procedure of OE, we found that almost the entire composition of the product was preserved. This integrated membrane process permitted two valuable products to be obtained: a clarified concentrate of melon juice that had not undergone any thermal treatment, and a glowing-orange retentate that was enriched in provitamin A. D 2004 Elsevier Ltd. All rights reserved. Keywords: Melon; Fruit juice; Crossflow microfiltration; Osmotic evaporation; Clarification; Concentration Industrial relevance: The increasing quality demand for fresh fruits results in an increase in rejected melons. Juice processing could overcome the product losses occurring but thermal sensitivity of melon juice flavour prohibits conventional thermal processing. Interestingly this paper attempts to use membrane processes for microbial stabilisation and concentration. The authors present a novel way of using permeate (clear juice) as well as retentate (pulpy juice). Enzyme activities in the products during and after processing may need some attention prior to industrial application of the process.
1. Introduction During the last decade, melon (Cucumis melo L.) has become a major exchange commodity for tropical countries able to supply northern markets and meet a strengthening offseason domestic demand. In 2002, off-season melon imports accounted for about one third of year-round consumption in the USA and EU (CNUCED/OMC, 2003). The high quality required by these markets means that almost 20% of production is rejected as export quality, often just because * Corresponding author. Centre de Coope´ ration Internationale en Recherche Agronomique pour le De´veloppement (CIRAD), Tropical Fruits Department (FLHOR), Avenue Agropolis, TA 50/PS4, 34398 Montpellier Cedex 5, France. Fax: +33 4 67 61 44 33. E-mail address: [email protected] (M. Dornier). 1466-8564/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2004.11.004
fruits are misshapen, too big, or too small. In Costa Rica alone—one of the world’s largest melon exporters—rejected fruits represent more than 10,000 t. While some fruits can be sold at low prices on the domestic market, most are considered as waste and as presenting significant environmental problems. Nonetheless, such rejected fruits present good internal characteristics and should be used by the juice industry for their pleasant aroma and relatively high sugar content. But previous experiments have shown that the mild distinctive flavour of melon juice is very sensitive to thermal treatment, resulting in poor-quality final products (Galeb, Wrolstad, & McDaniel, 2002; Nath & Ranganna, 1977). Hence, despite the potential demand, traditional fruit juice industries do not consider melon sort-outs as valuable raw material.
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bCold processQ membrane technologies represent an alternative to high-temperature treatments. Crossflow microfiltration (CMF) has been applied successfully to some highly thermosensitive juices, resulting in microbiologically stabilized clarified juice that preserves the major part of the fruit’s original aroma (Cassano, Jiao, & Drioli, 2004; Matta, Moretti, & Cabral, 2004; Vaillant, Millan, O’Brien, Dornier, Decloux, & Reynes, 1999). The application of CMF to melon juice has not yet been reported. As well, an innovative concentration technology such as osmotic evaporation (OE) may allow concentrating melon juice and thus add value to the product. Both these technologies appear appropriate for concentrating the thermosensitive juice (Cassano et al., 2004; Hogan, Canning, Peterson, Johnson, & Michaels, 1998; Vaillant, Jeanton, Dornier, O’brien, Reynes, & Decloux, 2001). The research described in this paper was undertaken to study the effects of CMF and OE on the physico-chemical, nutritional, and microbiological qualities of melon juice.
2. Materials and methods 2.1. Fruit and juice processing Ripe cantaloupe melons (cultivar Veracruz) of good appearance but discarded by exporters because of their
misshapen form or inappropriate size were provided by Exporpack SA (Guanacaste Province, Costa Rica). The fruits were then processed according to the procedure shown in Fig. 1. Trials were carried out with fresh melon fruit collected no more than 2 days before processing. When an experimental design was implemented, experiments were conducted with the same homogenized juice batch, divided into lots of 25 kg each, and kept frozen at 20 8C. 2.2. Microfiltration The microfiltration unit featured a ceramic multichannel membrane (MembraloxR 1P19-40; Pall-Exekia, Bazet, France) that had a total effective filtration area of 0.24 m2 and an average pore diameter of 0.2 Am. Before microfiltration, melon juice was macerated at 35 8C for 1 h with enzymatic solution RapidaseR Tropical Cloud (DSM, France). According to the supplier, this enzymatic preparation is obtained from a selected GRAS strain of Aspergillus niger. It mainly consists of hemicellulase and cellulase activities. For incubation, the CMF temperature was fixed at 35 8C, the highest temperature at which melon juice can be held for 2 h without being recognized as different (at 5% confidence level) by panellists during a triangular test, using fresh melon juice as standard. In spite of the high pH of the juice, no significant sensorial change by fermentation or oxidation was detected during this step. Crossflow velocity was about 7 m s1. According to Vaillant et al. (1999), all trials were carried out with continuous juice feed and permeate collection at flow F p. The feed-and-bleed procedure was also followed in the long-term trials by implementing continuous extraction of retentate at flow F r, calculated according to Eq. (1), when the volumetric reduction ratio (VRR; defined as the ratio between the cumulated volumes of the feed and of the retentate) set-up was reached. Extraction flow for retentate ( F r) was adjusted every 5 min through a microvalve: Fr ¼ Fp =ðVRR 1Þ
ð1Þ
2.3. Concentration procedure
Fig. 1. General processing diagram.
The OE pilot plant used was already described by Cisse, Vaillant, Perez, Dornier, & Reynes (in press) and the procedure that followed was slightly modified from Vaillant, Jeanton et al. (2001). The unit featured a module containing polypropylene hollow fibres (10 m2). The concentration procedure involved feeding through a closed loop (hold-up volume, 7.5 L). The juice circulated with an average tangential velocity of 0.20 m s1 inside the fibres. The loop was continuously fed with cold clarified juice (6 8C). When the total soluble solid content set-up (TSSFinal) was reached, concentrate was extracted at rate F c, which was calculated from water evaporation flow ( F w) according to
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Eq. (2) to keep the degree of concentration constant inside the loop: Fw Fc ¼ ð2Þ TSSFinal 1 TSSInitial Calcium chloride brine was circulated continuously along the other side of the membrane. It was constantly maintained at near saturation (between 5.3 and 5.6 mol L1) by adding calcium chloride crystals to the feed tank. The brine’s circulation velocity was evaluated at 0.02 m s1 in the cartridge. Temperature was maintained almost constant in both compartments at 26F1 8C (juice) and 31F2 8C (brine). Evaporation flow was registered, using an electromagnetic flow meter (Krohne Messtechnik, GmbH, Duisburg, Germany) connected to a computer. All trials involving OE concentration were carried out over 12 h, including 3 h of continuous extraction of concentrate. 2.4. Chemical and physical analyses Fresh melon juice (F), permeate (P), retentate (R) at VRR=3, and concentrated juice (C) were collected at different stages of the integrated membrane process (Fig. 1). Samples were analysed for pH, titratable acidity, and density using standard methods (AOAC, 1990). Total soluble solids content (TSS) was measured with an Abbe refractometer (Atago, Japan). Carotenoids were extracted with ethanol/hexane at 4/3 (vol/vol) according to Taungbodhitham, Jones, Wahlqvist, & Briggs (1998) and dissolved in 1 mL of dichloromethane and 1 mL of a mixture of methyl tert-butyl ether and methanol at 80:20. They were then analysed by HPLC according to the methodology described by Caris-Veyrat, Schmid, Carail, & Bo¨hm (2003) using the h-apo-8Vcarotenal as internal standard. This method is based on the works of Roussef & Raley (1996) and Lessin, Catigani, & Schwarz (1997). It allows to quantify the different carotenoids in the fruits and their cis–trans isomers, which could
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appear during processing. The HPLC system (Agilent 1100 Series, Massy, France) featured a C30 column (2504.6 mm, i.d.=5 Am; YMC Europe, GmbH, Germany) and a photodiode array detector (Agilent Technologies). Carotenoids were quantified, using calibration curves with pure reagents. Mean recovery was 84% for h-carotene. Polyphenols were evaluated, using the method described by Slinkard & Singleton (1977). Vitamin C was assessed by HPLC, using the method as modified by Kacem, Marshall, Mathews, & Gregory (1986) and Brause, Woollard, & Indyk (2003). Sucrose, fructose, and glucose were also determined by HPLC, following Englyst & Cummings (1984). Colour measurement was done on 30 mL samples in Petri dishes backed with white tiles, using a colorimeter HunterLab DP 9000 (28 standard observer and illuminant C). Data were expressed in terms of L*, a*, and b* parameters; hue angle (H8=tan1(b*/a*)); and colour purity (C8=(a*2+b*2)1/2). Viscosity was measured with a glass Oswald capillary viscosimeter. Water activity was determined with an a w meter (Aqua lab model CS-2). Total flora, yeasts, and moulds were assessed using standard methods (Vanderzant & Splittstoesser, 1992).
3. Results and discussion 3.1. Microfiltration of melon juice 3.1.1. Optimising operating conditions Fig. 2 shows the variation of permeate flux during a typical microfiltration trial. For all trials with enzyme-treated melon juice, three phases were observed: (1) between VRR=1 and 1.5, formation of a fouling layer with a significant decrease of permeate flux to a minimum (almost 50% of the initial flux); (2) VRR=1.5–2.5, a significant increase (about 30%) in flux density; and (3) a decrease in the last phase. The increase in flux density (phase 2) after the formation of a fouling layer has already been described for
Fig. 2. Permeate flux and volumetric reduction ratio (VRR) during the clarification by crossflow microfiltration ( P tM=150 kPa, enzymatic treatment: 0.25 mL L1).
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Table 1 Main physico-chemical, microbiological, and nutritional characteristics of processed melon juices (in parenthesis, standard deviation from six experiments) Characteristic
Feed
Permeate
Retentatea
Concentrateb
Total soluble solids TSS (g kg1) pH (20 8C)
88 (1)
70 (1)
91 (1)
550 (2)
7.10 (0.05) 23 (1) 0.99 (0.02) 2.8 (0.1) 1030 (4) 2.1 (0.2) 0.45
6.81 (0.05) 43 (2) 0.99 (0.02) 1.3 (0.1) 1026 (4) 1.7 (0.2) nd
7.01 (0.05) 25 (1) 0.99 (0.02) 3.5 (0.1) 1028 (4) 0.90 (0.1) 1.45
3.59 (0.05) 42 (2) 0.88 (0.02) 19 (1) 1204 (4) 1.2 (0.2) nd
0.89 (0.09) 125 (10) 148 (10) 329 (30) 3.5104
0.83 (0.07) 157 (10) 186 (20) 400 (40) b30
0.62 (0.05) 148 (10) 160 (10) 358 (40) 3.0104
0.85 (0.09) 162 (10) 220 (20) 410 (40) 0.3104
b30
b30
b30
b30
3000 (700)
0.61 (0.08)
9000 (900)
–
57.1 20.4 56.6 70.2 60.2
53.8 2.3 21.5 83 21.6
53.9 33.2 63.4 62.3 71.5
62.9/52.3c 4.0/2.2c 30.5/19.9c 82.5/83.7c 30.8/20.0c
Titratable acidity (g kg1 TSS) Water activity (25 8C) Viscosity (25 8C, mPa s) Density (kg m3) Polyphenols (g kg1 TSS) h-Carotene (g kg1 TSS) Vitamin C (g kg1 TSS) Glucose (g kg1 TSS) Fructose (g kg1 TSS) Sucrose (g kg1 TSS) Total flora (CFU mL1) Yeast and moulds (CFU mL1) Turbidity (NTU) Colour L* a* b* Hue Chroma
To define the optimal transmembrane pressure (P tM) and enzyme concentration, an experimental design was implemented. The surface response, corresponding to the permeate flux reached at VRR=3, is presented as a contour plot in Fig. 3 (data analysed, using stepwise multiple regression). Fig. 3 shows that a lower P tM gives rise to improved permeate flux density at VRR=3, whereas an optimal enzyme concentration exists at about 0.2 mL L1 for lower P tM. As P tM increases, the optimal enzyme concentration also increases. The negative effect of high P tM indicates that the fouling layer is highly sensitive to compression as it becomes less permeable when pressure increases. Thus, to obtain high-permeate flux density at VRR=3 (around 88 L h1 m2), P tM should be maintained at the lowest value possible (120 kPa). Also, for economic reasons, enzyme concentration should be fixed at 0.15 mL L1, corresponding to the lowest concentration that can give rise to a high flux permeate density (N80 L h1 m2). These processing conditions were implemented during trials, following a feed-and-bleed procedure when VRR=3 was reached. The turbidity mainly depends on the pulp content of the product. Even if the reproducibility of the turbidity measurements was poor (between 10% and 20% mainly due to sampling), this parameter could be correlated reasonably well to VRR (Fig. 4). As shown in Fig. 5, the retentate’s turbidity increased from an initial value of about 2800 NTU until VRR=3 was reached, when it was about 8500 NTU. This value was almost constantly maintained, corresponding to a likewise almost constant VRR. The turbidity could then be used as an in-line indicator for VRR. During the last phase, the flux permeate density was kept high between 70 and 80 L
nd=not detected. a At VRR=3. b Sample collected at the end of the OE trial (after 12 h). c After dilution of samples to 70 g kg1 of TSS.
other pulpy fruit juices (Vaillant, Dornier et al., 2001). Nevertheless, in the case of melon juice, this increase is surprisingly high. As processing variables were all kept constant, this phenomenon can only be attributed to an intrinsic change of the rheological properties of the retentate after VRR=1.5. One hypothesis suggests that a higher concentration of cell wall fragments has a better bremovingQ Q effect over the fouling layer, while viscosity increases only by 20% between the feed (F) at VRR=1 and the retentate (R) at VRR=3 (Table 1). But, at values higher than VRR=3, in addition to increased viscosity, a higher concentration of particles increases the risks of blocking some of the membrane’s pores. For this reason, VRR=3 was chosen as the optimal VRR, corresponding to a higher permeate yield while permitting the maintenance of a high flux density.
Fig. 3. Permeate flux (expressed in L h1 m2) reached at VRR 3 during the clarification by crossflow microfiltration vs. transmembrane pressure (P tM) and enzyme concentration used for maceration.
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Fig. 4. Correlation between the volumetric reduction ratio (VRR) and the turbidity of the retentate obtained during the clarification by crossflow microfiltration.
h1 m2, with flux variation being attributed to temperature. We could maintain an almost steady permeate flux for 40 min, following the continuous feed-and-bleed procedure. These results show that melon juice can be microfiltered continuously with an acceptably high average permeation flux (about 75 L h1 m2), while retentate can be extracted at half this rate, giving rise to a global yield of clarified juice of about 67%. These results demonstrate good potential for the industrial application of CMF to melon juice, as processing results are comparable with those reported by the wine and apple industries (Daufin, Escudier, Carrere, Fillaudeau, & Decloux, 2001). Furthermore, the filtrability of the melon juice should still be improved by optimizing the activity spectrum of the enzymatic solution used for the partial liquefaction before filtration.
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3.1.2. Main characteristics of clarified melon juice and retentate The most relevant physico-chemical, nutritional, and microbiological properties of the initial juice (F), permeate (P), and retentate at VRR=3 (R) are reported in Table 1. Total soluble solids content as measured by a refractometer appeared to be higher in the retentate than in the recovered permeate. As already mentioned, this observation is probably related to the presence of a high suspended solids content in the pulpy products that can interfere with the measurement of the refractive index (Cisse et al., in press; Vaillant et al., 1999). Even so, concentrations of the three main sugars (glucose, fructose, and sucrose) measured by HPLC were not significantly different for the two juices. Titratable acidity and pH of the feed and the retentate were very similar. The organic acids content of the permeate increased (titratable acidity2 and 0.3 pH). This result could be explained by a lactic fermentation in the permeate during processing. However, this hypothesis is contradicted by the sugar contents that did not decrease and by the total flora that was strongly removed in the permeate. Surprisingly, the total flora did not increase in the retentate. Microorganisms that are retained by the membrane could be partially destroyed by the high shear stress in the circuit. For some nutritional compounds—specifically, polyphenol compounds and vitamin C—a loss was noted during processing, at about 19% and 7%, respectively, in permeate and 57% and 30% in retentate. Loss of phenol compounds probably resulted from the continuous action of polyphenol oxidases, which were partly retained in the retentate where they remained active. Loss of vitamin C may have been due to oxygen exposure. This loss could have been drastically
Fig. 5. Permeate flux behavior during a feed and bleed microfiltration trial (P tM=150 kPa, enzymatic treatment: 0.15 mL L1).
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reduced by implementing a degassing treatment before microfiltration. The main carotenoid compound found in the fresh melon juice (F) was h-carotene, at 40.7 mg L1 (equivalent to 0.45 g kg1 TSS). Its content varied in the different products obtained during the process. Neither cis isomers nor oxidized compounds appeared, which is in accordance with the low processing temperature. Table 1 shows a total retention of h-carotene in the retentate (135.3 mg L1, equivalent to 1.45 g kg1 TSS). This compound was concentrated about 3.3 times, which accords with the value of the VRR reached. This result also accorded with higher positive a* and b* values, as the colour of the retentate was deep orange, in contrast to the clarified juice, which was translucent, showing very pale yellow hues. The h-carotene was retained in the retentate probably because it is strongly associated with membrane and wall structures of the cell fragments (i.e., the pulp). These results are correlated to those of Galeb et al. (2002), who showed that carotenoids remained in the press cake and the filter pads during the clarification of melon juice using dead-end filtration. Hence, in parallel with the production of clear melon juice, microfiltration appears to be a genuine alternative for concentrating h-carotene. There is worldwide interest for natural and cheap h-carotene sources (Spanos, Chen, & Schwarz, 1993), not only for its high provitamin A activity and its colouring properties in food, but also for being an effective antioxidant as reported by clinical studies (Krinsky, 1989). Consequently, the retentate may be highly valuable for commercialising as part of tailor-made drinks that combine nutritional and functional properties with colour. Microbiological analyses showed that CMF can ensure microbiological stability of the juice in a single operation. Preliminary organoleptic tests performed on clarified juice and retentate show that the permeate gave off a very good melon aroma that could be easily
recognised, whereas the retentate presented very little melon aroma and had an oily texture that was certainly a result of the high concentration of h-carotene. 3.2. Osmotic evaporation 3.2.1. Concentration trials Clarified juice, obtained after microfiltration, was concentrated by OE from 70 to 550 g kg1 of TSS. Experimental results showed that water evaporation flux decreased from 0.70 to 0.57 kg h1 m2 when juice TSS reached 550 g kg1 (Fig. 6). When extracting concentrate, evaporation flux remained constant, agreeing with results obtained for other fruit juices (Cisse et al., in press; Vaillant, Jeanton et al., 2001). The low water evaporation fluxes were similar to those obtained with other clarified juices, where the same membrane was used. Thus, such fluxes appear to be a characteristic of the membrane rather than of the juice. When the TSS set-up was reached and the evaporation flow remained constant, clarified melon juice concentrated at 550 g kg1 of TSS could be continuously extracted at 83 mL h1 m2 and the OE unit fed at a rate of 653 mL h1 m2 with clarified juice at 70 g kg1 of TSS. These flows were somewhat low, but taking into account that other bcoldQ concentration processes such as reverse osmosis do not allow to reach a TSS as high as 300 of TSS kg1 (Jariel, Reynes, Courel, Durand, Dornier, & Deblay, 1996), OE appears to be an effective alternative. Also, it must be noted that the membrane used in these trials was not specific for OE. Trials carried out on a laboratory scale on sucrose solutions and with thinner membranes gave rise to much higher water evaporation fluxes of about 10 L h1 m2 (Courel, Dornier, Herry, Rios, & Reynes, 2000). Also, it should be pointed out that porous organic hydrophobic membranes such as the one used here are cheap compared with the membranes used for reverse osmosis.
Fig. 6. Evolution of evaporation flux ( F w) and total soluble solids (TSS) during the osmotic concentration of the clarified melon juice from 70 to 550 g kg1 of TSS.
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3.2.2. Characteristics of the concentrate Table 1 lists the main characteristics of the initial clarified melon juice (P) and the concentrate (C). Expressing the results by kilograms of TSS, we can see that the OE concentrate had very similar values to the clarified juice for acidity, glucose, fructose, and sucrose contents. Total flora enumeration in the concentrate showed recontamination of the product during handling because the initial clarified juice (CMF permeate) was almost free of microorganisms. This problem should be easily resolved using an aseptic connection between the filter and the concentrator. No significant loss of vitamin C was noted, compared with the initial clarified juice, but a loss of phenol compounds (about 30%) is again observed. This loss may be also explained by the presence of polyphenol oxidases in the clarified juice, which continues acting during processing. The juice’s colour, when compared after redilution to the feed TSS, was completely preserved, indicating the absence of Maillard reactions. This result is really interesting in comparison with the classical thermal processes of concentration. According to Galeb et al. (2002), melon juice is especially sensitive to nonenzymatic browning even using HTST treatment (browning rates from 2 to 12 times higher than for pear or grape juices). The chemical composition of the product was then not significantly modified by the process and the concentrate was very close to the initial clarified juice. These results are in accordance with other studies carried out with other different fruit juices (Cisse et al., in press; Rodrigues, Menezes, Cabral, Dornier, & Rios, 2004; Vaillant, Jeanton et al., 2001). They confirmed that the osmotic evaporation allows to preserve better the quality of the raw material than the classical thermal evaporation. We can also noticed that the melon juice concentrate presented a pH below 4 that is more suitable for conservation during storage.
4. Conclusions Crossflow microfiltration of melon juice allows attainment of a relatively high average permeation flux density (about 75 L h1 m2), with constant extraction of retentate at VRR=3 and giving rise to a global yield of microbiological stabilized clarified juice of about 67%. The clarified juice presents physico-chemical and nutritional properties that are comparable with fresh melon juice, except for the absence of suspended solids and carotenoids, which remained totally concentrated in the retentate. The retentate presents a glowing orange colour because of the high concentration of h-carotene. The clarified juice can also be concentrated at low temperatures by OE to as high as 550 g TSS kg1 to obtain a concentrated melon juice that also preserves the main physico-chemical and nutritional properties. This integrated membrane process is a genuinely innovative way of treating melon juice, as it allows high-value products to be obtained from fruits discarded
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by the fresh market. On one hand, the clarified melon juice and its concentrate can be marketed as part of fruit beverages to which they can contribute fruit sugars and specific aroma; on the other hand, a pulpy juice (retentate), which is enriched in provitamin A and can be used as raw material to extract h-carotene or directly in functional drinks, is obtained.
Acknowledgements The authors wish to thank the French agency AIRE De´veloppement for its valuable financial help and EXPORPACK SA for providing us with melons.
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