No abstract

The anions of milk have been successfully analysed by ion chromatography coupled with suppressed conductivity detection. With an appropriate sample preparation (ultrafiltration alone, or combined with dry mineralization), this method enabled simultaneous identification and quantification of chloride, phosphate and citrate ions with good repeatability (relative standard deviations of about 1%). Moreover, good sensibility (Iess th an 20 Ilglkg) and no interference between ions and other matrix components were determined. It was also shown that this method olters a very promising alternative for studying changes in the salt balance of milk du ring some technological treatments (acidification and increase of ionic strength of milk). ion chromatography / milk / anion Résumé-Analyse des anions du lait par chromatographie ionique-Les anions du lait ont été analysés par chromatographie ionique couplée à une détection par conductimétrie avec autosuppression. Avec une préparation d'échantillon appropriée (ultrafiltration seule ou combinée avec une minéralisation par voie sèche), cette méthode a permis l'identification et la quantification simultanée des ions chlorure, phosphate et citrate avec de bonnes répétabilités (déviations standard relatives d'environ 1 %). De plus, de bonnes sensibilités (inférieures à 20 1l9/kg) et aucune interférence entre les ions à doser et les autres composés du milieu ont été déterminées. Par ailleurs, cette méthode constitue un excellent moyen pour étudier des changements d'équilibres salins durant certains traitements technologiques comme l'acidification ou l'augmentation de force ionique de laits. chromatographie ionique / lait / anion

-Cleaning-in-place NaOH solutions from a milk standardisation dairy plant are reused for several days before being discharged to the purification station. During reuse the surface tension of the industrial cleaning solutions was reduced from~70 mJ . m -2 for newly prepared NaOH down tõ 30 mJ . m -2 during the week. The decrease was rapid during the first few reuse cycles and stabilised thereafter, while the polluting load and suspended solids increased inversely. The cleaning efficiency test consisted of an ultrafiltration membrane fouled with whey proteins, which was cleaned using these cleaning solutions, either without any treatment, or following crossflow micro-and nanofiltration. It was found that microfiltrates and nanofiltrates with both low surface tension and suspended solids resulted in higher efficiency and cleanliness, and a much faster cleaning rate. The effects of suspended solids and low surface tension will have to be further studied to determine the role of each parameter and confirmed on stainless steel surfaces and in a milk processing plant. . La diminution est rapide pendant les premières dizaines de cycles puis se stabilise ensuite, tandis que la charge polluante et les matières en suspension augmentent. L'efficacité et la vitesse de nettoyage par ces solutions industrielles, sans traitement ou après épuration par microfiltration ou nanofiltration tangentielle, ont été quantifiées à l'aide d'une méthode utilisant une membrane d'ultrafiltration colmatée par des protéines de lactosé-rum. Les microfiltrats et les nanofiltrats sont plus efficaces que la solution industrielle réutilisée dont ils proviennent et même que la solution de soude caustique fraîche. 357

diameter. During skimmed milk MF the fouling, mainly due to a deposit of casein micelles at the membrane surface, is dependent on a critical permeation flux, Jcrit, to wall shear stress, τ w ratio [2, 5]. Under this critical ratio the performance (permeability 1. INTRODUCTION Separation and concentration of casein micelles from soluble proteins of skimmed milk can be achieved by crossflow microfiltration, MF, using a 0.1 µm mean pore

Sorne experimental evidence is accumulating in the literature which shows that the mean cross-flow velocity is not an effective parame ter for the characterisation of the cross-flow transport in membrane separation processes. The aim of this work was to determine the most appropriate parameters (among the wall shear stress, t w ' the wall shear rate, y, the Reynolds number, Re, and the mean cross-flow velocity, v) that should be used to assess the limiting and critical fluxes in turbulent regime. The experiments were applied to skimmed milk microfiitration (MF) using a tubu-Jar ceramic membrane (0.1 IJ.m mean pore diameter) for the separation of casein micelles from the solluble proteins. These experiments were conducted with several membrane geometries (seven or 19 channel s, 40 or 85.6 cm long) and seve rai rigs. Unlike Re and v, t w made it possible to assess the Iimiting and critical permeation fluxes in milk MF (0.1 IJ.m),whatever the membrane geometry. It was consequently concluded to be an effective parameter to account for cake filtration and to study the crossflow filtration scale-up. The wall shear rate, calculated by assuming the turbulence damped at the membrane surface and the flow laminar, was not suitable for the assessment of the Iimiting and critical fluxes in turbulent regime.