Concentration of thickening & gelling food additives by ultrafiltration: comparison of flat sheet and tubular membranes

Concentration of thickening & gelling food additives by ultrafiltration: comparison of flat sheet and tubular membranes

rt i c [ e Carrageenans and pectins are widely used for their rheological properties in many foods, as well as industrial applications. In their proce...

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rt i c [ e Carrageenans and pectins are widely used for their rheological properties in many foods, as well as industrial applications. In their processing, Degussa Texturant Systems uses ultrafiltration as a concentration step. The aim of this study was to compare organic flat sheet and mineral tubular modules for carrageenan and pectin concentrations. Mineral tubular membranes led to higher flux performances than organic flat sheet membranes. The comparison of energy and membrane renewal costs did not make it possible to draw definitive conclusions on the choice between both modules. Nevertheless, subject to a life expectancy of more than ten years and to high operating times, mineral membranes should be more economic to operate. ......

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Anne Osmond 1, Fabienne Bartv, & H~l~ne Carr~ree'3 iDegussa Texturant Systems France SAS, D~partement Recherche, 50500 Baupte, France; eLaboratoire de G~nie et Microbiologie des Proc~d& Alimentaires, INRA, 78850 Thiverval-Grignon, France; 3Present address: Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, 11 100 Narbonne, France. "~Corresponding author: [email protected] ~:.~................ : arrageenans and pectins are widely used for their i thickening and gelling properties in many foods, as well ~'~,J: as in industrial applications (e.g. ice cream, sauce, dairy desserts, flans, jams and jellies, meat preserves, confectionery, etc) These applications are linked to the complex rheological properties of the products. The pseudo-plastic fluids are widely characterized by an empirical functional relationship known as the 'power law'. This relationship, which was originally proposed by Oswald & de Waele is written as: "~ = K ~ n o r

laa= K'~ n-1

where ~: is the shear stress (Pa), 9, the shear rate (sq), ~aa, the apparent viscosity of the fluid (Pa.s) and K & n are constants (n <1 for pseudoplastic fluids). K (Pa.s n) is a measure of the consistency of the fluid (the higher the value of K the more viscous the fluid) and n, the structure index, is a measure of the degree of non-Newtonian behaviour (the lower the structure index, the more non-Newtonian properties the fluid possesses). Production of carrageenans and pectins is based on two phenomena: high-temperature solubility and coagulation with organic solvents (Figure 1). Carrageenans are extracted from red alga Rhodophyceae, whereas pectin is extracted from apples or lemons. After solubilization in hot water in presence of an alkaline agent for carrageenan and an acid for pectin, insoluble substances are eliminated by press-filtration using an adjuvant such as Kieselguhr. Concentration of this clarified syrup is achieved by ultrafiltration (UF). Carrageenans and pectins are then recovered by precipitation in isopropanol, where they coagulate. Finally, they are dried and ground. The concentration step means less alcohol is consumed in the precipitation step, which in turn reduces the energy

Filtration+Separation

consumpnon required for the recovery of the alcohol through distillation. For this concentration step, UF is a good choice compared to evaporation or freezing because it has a lower energy cost [1]. Moreover, UF allows a partial purification through the elimination of tannins and calcium ions [2]. However the UF process has to be operated at a temperature higher than the gelling point of the products (70 °C for kappa carrageenans & 60 °C for pectins). Operating at high temperatures (80 °C for carrageenans & 70 °C for pectins) has the advantage of decreasing the apparent viscosity of the products. Nevertheless, such high temperatures can shorten the life of the membranes, especially in the case of organic membranes. Membrane modules most appropriate for viscous fluids are the tubular and the flat sheet modules [3]. Moreover, it is well known that mineral membranes are more resistant to high temperature, but they have a greater purchase COSt.

The aim of this paper is to compare organic flat sheet membranes and mineral tubular membranes for the concentration of carrageenans and pectins, in terms of permeate flux performances and operating costs. The theological characteristics of carrageenans and pectins are also presented.

Two different batch pilot units were used in the experiments (Table 1). The flat sheet filtration pilot unit had a higher filtration surface than the tubular filtration unit. In each, the feed solution was contained in a tank and connected to the membrane module with the assistance of a Moineau feed

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High pressure liquid chromatograph (HPLC), equipped with two size exclusion columns was used to determine the molecular weights of the products. Two detectors were placed at the column outlet: a light diffusion detector and a refractometer.

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Two different carrageenans were used, a thickening agent (lambda carrageenan) and a gelling agent (kappa carrageenan). Carrageenan solutions were obtained by dissolution of carrageenan powder under strong agitation at 80 °C until completely dissolved. Prior to dissolution the carrageenan powder was wetted with isopropanol. The initial concentration of carrageenan was 1.4%. Pectin powder was wetted with alcohol and the pectin solutions were obtained under strong agitation at room temperature. The initial concentration of pectin was 0.6%.

A HAAKE Rheowin Pro-RS1 rheometer, fitted with a cone-and-plate device (60 mm diameter, 2 °) was used.

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eccentric rotor pump. A positive displacement gear pump equipped with a speed regulator made it possible to set different crossflow velocities. Transmembrane pressure was controlled by a valve set on the retentate loop. Temperature regulation w a s ensured by a heat exchanger set on the retentate loop. Operating conditions such as transmembrane pressure and crossflow velocity were fixed according to background. Indeed, crossflow velocity determination is fundamental because it must be high enough to ensure high permeate fluxes, but velocities that are too high lead to products degradation through shearing.

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5;i'becAo(~fical Pro(,~erti, es For gelling additives such as kappa carrageenan and pectin, apparent viscosity can be determined only under high temperature conditions. The apparent viscosity of carrageenans and pectins were measured at the same temperatures as the operating filtration temperatures, i.e. 80 °C for carrageenans & 70 °C for pectins. The apparent viscosities of these products at different concentrations are shown in Figure 2. It can be observed that the apparent viscosities increased with concentration. Between the carrageenans, lambda carrageenan (thickening) was more Tubular system viscous than the kappa carrageenan (gelling). This can be explained by the Mineral (zirconium oxide) 0.16 m 2 higher molecular weight of the former 6 0 litres (1500 kD) compared to the latter 4 5 litres (500 kD). 1 min intervals The consistency of the fluid, K, and the structure index, n, are plotted as a

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function of the concentration in Figure 3. For every product, n was close to 1. Indeed, we broke free from the pseudoplastic character of the fluids because of the high temperatures.

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Figure 2: Apparent viscosity measured for 7 = 1 0 s "I vs concentration. Carrageenans [& lambda & • kappa) T = 8 0 °C & pectins [e) T = 7 0 °C.

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~£1o~ec ~i~:~ '; ~/~/e ! ~~>,t It is important to ensure that the texturing properties were not altered during the UF process, notably through shearing by the pumps, in the valves [4] or at the membrane wall. For each product thickening or gelling properties can be correlated to molecular weight. Table 2 shows the molecular weights of the products before and after UE The precision of the molecular weight analyser was approximately +10%, we can conclude that the lambda carrageenan was partially altered by the UF treatment, whereas kappa carrageenan and the pectins were not. ~-

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-0.8 In the carrageenan production process, UF is used to concentrate solutions twice at 80 °C. The permeate fluxes obtained with organic flat sheet and mineral tubular membranes were compared under these conditions. Results are shown in Figure 4. In the case of mineral tubular membranes, permeate fluxes were almost equal for lambda and kappa carrageenans, whereas organic flat sheet membranes led to higher permeate

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Concentration (kg/kg) Figure 3: Lambda ( - - - - ) and kappa ( - - - - ) carrageenans consistancy and structure behaviour indexes vs concentration (T = 8 0 °C).

M o l e c u l a r w e i g h t before UF [ M W o) (kD) Lambda carrageenan

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1470 1500 1560 1620 460 670 560 140 130 145 160

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rticl e This could be explained by a higher degree of adsorption of kappa carrageenan on the mineral membranes. For both carrageenans, mineral tubular membranes led to higher permeate fluxes (Jrnineral) than the organic flat sheet membranes (Jorganic). The difference between the membranes was higher for lambda carrageenan

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(the mean value of the ratio Jmineral/Jorganicwas approximately 3) than for kappa carrageenan, which was adsorbed more to the mineral membranes (the mean value of the ratio

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For the pectins, the permeate fluxes were compared at 70 °C and in the concentration range of 0.5-1.7%. The permeate flux with the mineral tubular membranes was higher than with the organic flat sheet membranes

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Figure 4: Comparison of permeate fluxes obtained with organic flat sheet membranes (e) and mineral tubular (A) membranes during carrageenans (lambda & kappa) concentration (T = 80 °C).

(Figure 5), with a ratio Jmineral/Jorganicof approximately 1.3.

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For this comparison, only the energy and membrane renewal costs were taken into account. Other costs such as cleaning or labour costs were assumed not to differ greatly between membrane systems. Tubular membrane modules require more energy than flat sheet modules. The energy consumption per permeate volume 1O0 unit was estimated to be 5.3 kWh/m 3 for the flat sheet module and 24 kWh/m 3 for the tubular module. The energy cost was assumed to be ~0.06/kWh. For the flat sheet module, the • membrane replacement costs, including the membrane supports, were estimated to be ~ 60 ~618/m 2. For the tubular mineral membranes, the costs were assumed to be ~g1830/m 2, but due to their better flux 4o performances, the tubular mineral membrane surface should be lower than the organic membrane surface. The 2O lifetime of the organic flat sheet membranes was considered to be three years, and more than ten years for mineral I I membranes. However, as we had no 00.5 1.0 1.5 experimental data, we made several Concentration (% kg/kg) arbitrary assumptions, e.g. ten, 13 & 20 years for the lifetime of mineral Figure 5: Comparison of permeate fluxes obtained with organic flat membranes. sheet (e) and mineral tubular (A) membranes during lemon pectin The influence of these assumptions can concentration (T 70 °C). be seen in Figure 6, where the UF operating costs of both systems are shown fluxes for kappa carrageenan. As the apparent viscosity of against operation time. If the lifetime of the tubular membranes kappa carrageenan is lower than that of lambda carrageenan, is below ten years, this system is always more expensive than the we might have expected higher permeate fluxes for kappa flat sheet system over an operating period of 20 years. Hmvever, carrageenan. This was confirmed in the case of organic flat when the lifetime is 13 years, the system is as expensive as the sheet membranes, but not with the mineral tubular membranes. flat sheet system. Therefore, tubular membranes can be more

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"'.,,, economical than flat sheet membranes if their lifetime is longer than 13 years. If a lifetime of 20 years is considered, the tubular system becomes more economical as soon as eight years of operation have passed. Indeed, the higher the operating life of the tubular membranes, the lower their percentage in total costs (Table 3), so the tubular membranes become more economic after shorter operating periods. The repartition of costs was different according to the two systems (Table 3). Whereas the energy cost predominated in the case of the tubular UF, it was significantly lower than the membranes cost (87%) for the flat sheet modules.

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Mineral tubular membranes were shown to have a higher flux performance than organic flat sheet membranes for the concentration of carrageenan and pectin solutions. However, the increase in the permeate flux depended on the filtered products, the gain being the highest for lambda carrageenans. The economic assessment did not provide definitive conclusions on the choice between organic flat sheet and mineral tubular membranes because of the unknown life span of mineral tubular membranes. It has been shown that life span was a key parameter when choosing whether to use organic flat sheet membranes or mineral tubular membranes for the concentration of carrageenan and pectin. Nevertheless, assuming a lifetime greater than 13 years (i.e. much greater than the assumed organic membrane life span) and prolonged operating times, mineral membranes become more economical. To complete the study, mineral flat sheet membranes which have recently appeared on the market should also be tested. They combine the advantages of a mineral membrane's long lifetime with the low energy consumption of a flat sheet membrane. •

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Alvarez R, S Alvarez, F J A Rius, F-A Riera & J Coca. 1998. o Polyssacharides (alginates, agar, carraghdnanes, pectines, txanthane), Les s~parations par membrane dans les proc~d& de l'industrie alimentaire, G Daufin, F Rend & E Aimar, Lavoisier Tech & Doc Eds, Paris, France, p.509-530. 0 Carr6re H & F Bart. 1999. Influence of fluid rheology on I 1 I filtration, Membrane process in the food industry, 15 20 0 5 0 ACUMTEA Course, Toulouse, France, 17-18 November. Operation time (years) Aimar P, M Meireles-Masbernat, G Gdsan-Guiziou, B Chaufer & J K Liou. 1998. Op6rations fi membranes Figure G: Operating costs vs operation time poreuses, Les s~parations par membrane dans les proc~d~s for organic flat sheet and mineral tubular de l'industrie alimentaire, G Daufin, F Rend & P Aimar, membranes, according to assumptions based Lavoisier Tech & Doc Eds, Paris, France, p.7-66. on the mineral membrane life time Vandanjon L, N Rossignol, P Jaouen, J M Robert & F (Graph A = ten years, Graph B = 1 3 years & Quemeneur. 1999. Effect of shear on two microalgae Graph C = 2 0 years). species. Contribution of pumps and valves in Membrane lifetime (years) Energy Cost (%) Membrane cost (%) tangential Flat sheet module 3 13 87 flow systems, ,

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abstract translations As a service to readers who understand German, French or Spanish better than English, the abstracts for the Refereed Paper in this issue follow in these languages.

C o n c e n t r a t i o n of T h i c k e n i n g a n d G e l l i n g F o o d A d d i t i v e s b y U l t r a f i l t r a t i o n : C o m p a r i s o n of Flat Sheet and Tubular Membranes by Anne

Osrnond,

Fabienne

Bart

& H61~ne Carr~re

Konzentration von Andickungs- und Gelierzus~tzen fur Nahrungsmittel mittels Ultrafiltration: Vergleich yon Planschicht- und rohrfbrmigen Membranen von Anne Osmond, Fabienne Bart & H~l~ne Carr~re

Karrageene und Pektine werden aufgrund ihrer rheologischen Eigenschaften weithin in zahlreichen Nahrungsmitteln wie auch in Industrieanwendungen verwendet. In ihren Verarbeitungsprozessen setzt die Firma Degussa Texturant Systems Ultrafiltration als Konzentrationsstufe ein. Das Ziel dieser Untersuchung bestand darin, organische Planschicht- und rohrf6rmige Mineralstoffmodule in Bezug auf Karrageen~ und Pektinkonzentrationen zu vergleichen. Bie rohrf6rmigen Mineralstoffmembranen waren h6here Wasserdurchtrittsleistungen als bei Planschichtmembranen zu beobachten. Der Vergleich yon Energiekosten und Membranerneuerungskosten lief~ keine definitiven Schliisse hinsichtlich der Wahl zwischen den beiden Modulen zu. Nichtsdestoweniger m~issten Mineralstoffmembrane vorbehaltlich einer Standzeit von mehr als zehn Jahren und hoher Betriebszeiten wirtschaftlicheren Betrieb erm6glichen. (5 sn, 6 figs, 3 tabs, 4 refs)

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Concentration d'~paississement et de g~lification en ultrafiltration d'additifs alimentaires : comparaison entre membranes planes et tubulaires par Anne Osmond, Fabienne Bart et H~l~ne Carr~re

Le carragh~nane et les pectines sont largement utilis~s pour leurs propri~t~s rh~ologiques dans beaucoup d'aliments ainsi que dans des applications industrielles. Dans leur fabrication, Degussa Texturant Systems emploie l'ultrafiltration comme ~tape de concentration. Le but de cette ~tude ~tait de comparer des modules de membranes organiques planes ~ des tubulaires fi base min~rale pour le processus de concentration du carragh~nane et de la pectine. Les membranes tubulaires min~rales ont conduit fi des meilleurs flux que les membranes planes organiques. La comparaison des cofits d'~nergie et de renouvellement des membranes front pas permis de tirer des conclusions d~finitives sur le choix entre ces deux types de modules. N~anmoins, ~tant donn~ leur esp~rance de vie de plus de dix ann~es et leur taux op~ratoire ~lev~, les membranes min~rales devraient ~tre plus ~conomiques ~ utiliser. (5 pags, 6 figs,3 tabs, 4 refs)

La concentraci6n de aditivos alimentarios para el espesamiento y la gelificaci6n por medio de ultrafiltraje: comparaci~n entre membranas de chapa enderezada y tubulares por Anne Osmond, Fabienne Bart y H~l~ne Carr~re

Se usan ampliamente las carrageninas y las pectinas por sus propiedades reol6gicas en un gran nfimero de alimentos, como tambi~n en aplicaciones industriales. En su elabora¢i6n, Degussa Texturant Systems usa el ultrafiltraje como etapa de concentraci6n. E1 objetivo de este estudio rue comparar m6dulos de membranas orgfinicas de chapa enderezada y minerales tubulares para ¢oncentraciones de carrageninas y pectinas. Las membranas minerales tubulares resultaron en rendimientos del flujo superiores a los de las membranas org~nicas de chapa enderezada. La comparaci6n de los costes de renovaci6n de energia y membranas no permiti6 el establecimiento de conclusiones definitivas sobre la selecci6n entre los dos m6dulos. Sin embargo, sujeto a una expectativa de vida fltil superior a diez afios y grandes periodos de funcionamiento, las membranas minerales deberfin ser m~s econ6micas en su funcionamiento. (5 prigs, 6 figs, 3 tabs, 4 refs)

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