Ultrafiltration of defatted whey: improving performance by limiting membrane fouling

Defatted whey was obtained by aggregating residual fat to calcium phosphate precipitates and separating the precipitate by membrane microfiltration (pore diameter 0·2 μm). When ultrafiltering this defatted whey the performance of an inorganic membrane (molecular mass cut-off, 10 kDa) was limited by the large concentration of Ca and phosphates. Consequently, the influence of the aggregation pH (either decreasing or constant) on membrane fouling has been studied for ultrafiltration (UF) of defatted sweet whey and defatted whey UF retentates (protein content up to 30g l–1). In all experiments protein rejection was 100%. When pH was kept constant during the pretreatment, membrane fouling was significantly lowered. Hydraulic resistances ascribed to irreversible fouling were in good agreement with fouled membrane analyses performed by i.r. and X-ray photoelectron spectroscopies. They showed that provided a low Ca and phosphate content was maintained in the microfiltrate, which was achieved at constant pH, no apatite was detected within the membrane, and proteins were less fouling. On the other hand, the amount of fouling material depended on the transmembrane pressure gradient along the hydraulic path. On the membrane surface, the higher the pressure, the higher the fouling. In the membrane bulk, the fouling heterogeneity depended on the ability of the defatted whey to precipitate apatite. If it did, the higher the pressure, the higher the calcium phosphate and the protein fouling. With other phosphate structures, the bulk fouling depended on the barrier formed by surface fouling layers and the protein concentration polarization layer, which were more resistant to solute and solvent transfer under higher pressure, where they were thicker.

Hydrolysis and large scale ultrafiltration study of alfalfa protein concentrate enzymatic hydrolysate

Batch enzymatic hydrolysis of insoluble Alfalfa Protein Concentrate by Delvolase was carried out at laboratory and at pilot-plant scale coupled to an ultrafiltration reactor with a mineral tubular membrane. Parametric studies were carried out on the batch system to determine the biochemical and hydrodynamical optimum conditions. The hydrolysis conditions selected were 40 degrees C, pH 9.5, initial substrate level 3 g protein/100 g and the enzyme substrate ratio 152 U/g protein. After 5 h of hydrolysis, 96% of the total amount of initial nitrogen was solubilized. The ultrafiltration conditions selected were a 10 000 Nominal Molecular Weight Cut-Off, a transmembrane pressure of 1.5 bar, a flux velocity of 0.8 m/s. Fifty percent of the initial nitrogen appeared in the permeate.

Ultrafiltration performance of heat-treated shamouti orange [Citrus sinensis (L.) Osbeck] juice

During ultrafiltration of orange juice with inorganic membranes, heating of the juice prior to the filtration experiment resulted in a significant increase of the fouling indices. The effect of the irreversible fouling (Rif) was always high, whereas the reversible fouling (Rrf) depended on the treatment. It was clearly seen that fouling was reduced after pectin degradation, but the heat treatment applied to the juice before filtration still resulted in reduced fluxes. It is suggested that pectins and proteins that undergo flocculation/coagulation during the heat treatment tend to interact with the membrane-filtering layer and to cause reduction of permeation flux. To clean the membrane to restore its pure water flux, close to the initial one, a proteolitic enzyme detergent wash was needed.