Georges Daufin

Recent and emerging applications of membrane processes in the food and dairy industry

Membrane processes have been major tools in food processing for more than 25 years. The food industry represents a significant part of the turnover of the membrane manufacturing industry world-wide. The main applications of membrane operations are in the dairy industry (whey protein concentration, milk protein standardization, etc.), followed by beverages (wine, beer, fruit juices, etc.) and egg products. Among the very numerous applications on an industrial scale, a few of the main separations which represent the latest advances in food processing, are reported. Clarification of fruit, vegetable and sugar juices by microfiltration or ultrafiltration allows the flow sheets to be simplified or the processes made cleaner and the final product quality improved. Enzymatic hydrolysis combined with selective ultrafiltration can produce beverages from vegetable proteins. In the beer industry, recovery of maturation and fermentation tank bottoms is already applied at industrial scale. During the last decade significant progress has been made with microfiltration membranes in rough beer clarification which is the most important challenge of this technology. In the wine industry the cascade cross-flow microfiltration (0.2 μ m pore diameter) – electrodialysis allows limpidity, microbiological and tartaric stability to be ensured. In the milk and dairy industry, bacteria removal and milk globular fat fractionation using cross-flow microfiltration for the production of drinking milk and cheese milk are reported. Cross-flow microfiltration (0.1 μ m) makes it possible to achieve the separation of skim milk micellar casein and soluble proteins. Both streams are given high added value in cheese making (retentate) through fractionation and isolation of soluble proteins ( β -lactoglobulin; α -lactalbumin) (permeate). At last, a large field of applications is emerging for the treatment of individual process streams at source for water and technical fluids re-use, and end-of-pipe treatment of wastewaters, while reducing sludge production and improving the final purified water quality.

Skimmilk crossflow microfiltration performance versus permeation flux to wall shear stress ratio

Crossflow microfiltration (MF) of skimmilk with a ceramic membrane (0.1 μm mean pore diameter) for the separation of casein micelles from whey proteins was performed at various constant flux, J (30–109 1 h−1 m−2) and efficient wall shear stress, τweff (23–97 Pa). The ratio (Jτweff) constitutes a basic parameter which characterizes competition between of convection and erosion at the membrane/solution interface. A critical value of (Jτweff) around 1.0 1 h−1 m−2 Pa−1 has been found: when (Jτweff) 1.0 1 h−1 m−2 Pa−1, short MF time with sharp increase of fouling resistance and sharp decrease of transmission. This critical value of (Jτweff) could be used as a predicative parameter for MF process permeability and selectivity for various operating conditions.

Treatment of dairy process waters by membrane operations for water reuse and milk constituents concentration

Abstract In the dairy industry non-accidental losses of milk or dairy products to sewer amount to 1–3% of the total milk processed. These significantly contribute to the 0.5–6.0 g COD/L of end-of-pipe wastewater. The major part of this polluting charge originates from starting, interrupting, and stopping dairy plant procedures, where milk-products are diluted with water and discharged to a purification station or collected to be spread on land. The very few works, that have been dedicated to the treatment of the so-called process waters (flushing waters, first rinse waters or “white waters”), show that nanofiltration (NF) or reverse osmosis (RO) is adequate for the concentration of milk components. The present work reports NF and RO performances (permeate flux, milk components rejection) of an effluent model solution (diluted skimmed milk). Performances of eight NF and RO membranes were compared by dead-end filtration. Crossflow experiments with NF and RO spiral-wound membranes confirm the results obtained by dead-end filtration. The results showed that one single membrane operation allowed the milk constituents to be concentrated in the retentate but reusable water of composition complying with the standard of purified water from process water was not reached. A finishing step (RO membrane, other) is needed for the production of reusable water.

Process steps for the preparation of purified fractions of α-lactalbumin and β-lactoglobulin from whey protein concentrates

Summary. Fractions enriched with a-lactalbumin (a-la) and b-lactoglobulin (b-lg) were produced by a process comprising the following successive steps: clarification‐defatting of whey protein concentrate, precipitation of a-lactalbumin, separation of soluble b-lactoglobulin, washing the precipitate, solubilization of the precipitate, concentration and purification of a-la. The present study evaluated the performance of the process, firstly on a laboratory scale with acid whey and then on a pilot scale with Gouda cheese whey. In both cases soluble b-lg was separated from the precipitate using diafiltration or microfiltration and the purities of a-la and b-lg were in the range 52‐83 and 85‐94% respectively. The purity of the b-lg fraction was higher using acid whey, which does not contain caseinomacropeptide, than using sweet whey. With the pilot scale plant, the recoveries (6% for a-la; 51% for b-lg) were disappointing, but ways of improving each step in the process are discussed. The fractionation of a-lactalbumin (a-la) and b-lactoglobulin (b-lg) from whey can be made easier by an increase in the apparent size of a-la at a pH close to its isoelectric point (Kronman et al. 1964; Bramaud et al. 1995). Pierre & Fauquant (1986) proposed a fractionation procedure based on this principle (adapted from Pearce, 1983, 1987) applicable to defatted rennet whey. Separation from the precipitate of the supernatant containing b-lg is carried out by centrifugation (CF) and the precipitate is solubilized at pH 7‐5. Bramaud (1995) showed that a-la could be obtained from rennet whey using citric acid at pH 3‐9 with an 81% precipitation eciency. The calcium present in the metalloprotein a-la is chelated by the citric acid and removed from the protein, causing its destabilization. De Wit & Bronts (1994) patented a process to obtain a fraction enriched in a-la in which calcium removal and pH adjustment are achieved by cation exchange at 26 ∞C, a procedure that limits the precipitation of bovine serum albumin (BSA) and immunoglobulins (Ig). The precipitate (a-la, BSA, Ig) can be separated from the soluble b-lg using CF

Ultrafiltration modes of operation for the separation of α-lactalbumin from acid casein whey

Abstract Whey is a complex protein mixture which contains two major proteins (β-lactoglobulin, α-lactalbumin), the size of which are close to each other. The separation of α-lactalbumin by membrane processes can be made more performing by the appropriate selection of the operation mode. The equations of the models for continuous, discontinuous concentration or diafiltration (single or combined) are developed. They show that performances (purity, yield) depend on initial purity (initial feed), on transmission (membrane and operating conditions) and on the operation mode. Simulations and experimental concentration and diafiltration operation modes are in good accordance. They show that continuous concentration up to a high volume reduction ratio (11–15) or a combined continuous concentration–diafiltration helps to obtain a fraction with both an enhanced purity and a satisfactory yield of α-lactalbumin in the permeate.

Whey protein fractionation: Isoelectric precipitation of α‐lactalbumin under gentle heat treatment

The selective precipitation of alpha-lactalbumin (alpha-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. In these conditions, beta-lactoglobulin remains soluble, whereas bovine serum albumin and immunoglobulins co-precipitate. Knowledge of the mechanism governing the alpha-LA precipitation influences the choice of operating conditions and enables optimization of the fractionation process. alpha-LA is a calcium metallo-protein and its isoelectric precipitation is governed by the protein-calcium complexation equilibrium. Citrate, a sequestrant of calcium, decreases the free calcium concentration and displaces the precipitation phenomenon to a lower temperature range. A study of the effect of citrate on the precipitation phenomena of whey proteins is presented. Whatever the citrate content, precipitation curves for bovine serum albumin (BSA) and alpha-LA intersect at a temperature around 45 degrees C. For a temperature of heat treatment lower than 40 degrees C, a selective enrichment in alpha-LA of the precipitated phase is observed. As addition of citrate leads to high alpha-LA precipitated fractions at a temperature around 35 degrees C, the precipitation step may be performed at this temperature. It results in a reduced heat denaturation of whey proteins and in a higher alpha-LA purity in the precipitated fraction. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 391-397, 1997.

Effects of proteins on electrokinetic properties of inorganic membranes during ultra- and micro-filtration

Abstract The streaming potential is measured across inorganic ultra-filtration and micro-filtration membranes to characterize them. Concurrently, electrophoretic mobility measurements are carried out to study the membrane material. The influence of whey proteins on the streaming potential and electrophoretic mobility is also studied. Results show that the membrane interface after adsorption has a surface property behavior similar to that of the proteins from a charge point of view. Moreover, the streaming potential considers two aspects of filtration which must take into account the steric and electric effects. In an electrolyte solution without proteins, the streaming potential depends only on charge repartition, determined by pH value. With whey proteins, the streaming potential depends on both charge repartition and permeate flux. If there is no inner fouling, the charge repartition is not affected and the streaming potential depends exclusively on flux; when there is an inner fouling by protein adsorption, the pore surface is modified and the streaming potential depends on both permeate flux and on electric charge of the oxide-solution interface.

Fouling during constant flux crossflow microfiltration of pretreated whey. Influence of transmembrane pressure gradient

Abstract Pretreatment of whey by microfiltration (MF) has emerged as a necessary step in producing high purity whey protein concentrates. In the MF of pretreated whey using a Carbosep M14 membrane (pore diameter 0.14 μm), proteins and calcium phosphate aggregates were responsible for fouling, which increased according to the “complete blocking” filtration law and accounted for a progressive decrease of the active filtering area. An operating mode with dynamic counter pressure (recirculation of the permeate co-current to the retentate), as opposed to static counter pressure, allowed lower overall fouling, a longer time of operation and better protein recovery because of more evenly distributed fouling along the membrane tube. At shorter times of operation, fouling was greater under higher transmembrane pressure (TP), so that the less fouled areas under lower TP were forced to filter larger volumes and consequently became fouled more rapidly. This involved a movement of the effective filtering area along the membrane tube, as evidenced by the systematic evolution of fouling heterogeneity as measured by infra-red spectroscopy.

Fouling of inorganic membranes during whey ultrafiltration : analytical methodology

Abstract Ultrafiltration of various types of whey was carried out through an inorganic membrane (M 4 Carbosep, 20000 Da cut-off). Fouling was evaluated as a hydraulic resistance ( R f ) and analysed with infrared (IR) and X -ray photoelectron ( XPS) spectroscopies, giving complementary results. Spectroscopic data are in a very good agreement with UF flux variations and R f values: the higher the transmembrane pressure or the whey protein content, the higher the fouling protein content. Proteins are found in the bulk of the membrane as well as on its surface, their concentration being higher in the latter case, whereas the phosphate/protein ratio lies often in the range 25–45% whatever the whey type or the operating conditions. Qualitatively, phosphate organization involves at least adsorbed hydrogen-phosphates and apatite structures resulting from several interactions between phosphate, protein, calcium and membrane. Only when the pH is increased up to 6.9 does PO 4 organization typically reach the apatite lattice. Its level is highest in the bulk of the membrane (4.1% relative to ZrO 2 ), representing nearly 85% of the protein content.

Retention of ions in nanofiltration at various ionic strength

Abstract Retention of a single salt solution was investigated versus the applied pressure, ion valencies and feed concentration using positively-charged membranes, obtained by chemical modification of ZrO 2 layer of UF membranes with a cross-linked polymer. Retention of coion was in agreement with the Donnan effect but coupling with either divalent counterion or the smallest coion (proton) was not accounted for. Mixtures of big positive organic solutes (antibiotics) and small cations were studied at increasing ionic strength (I). Retentions of membrane coions were plotted versus I −0.5 according to the semi-empirical model of ionic strength controlled retention the applicability of which was discussed and compared to the Donnan effect.