Prepurification of ?-lactalbumin with ultrafiltration ceramic membranes from acid casein whey: study of operating conditions

Abstract

-A promising way to produce purified a-lactalbumin (a-LA) is to perform a two-step cascade. The first step of pre-purifying presented herein, consists of ultrafiltration (UF) fractionation of acid casein whey, aiming at increasing the purity of a-LA in the filtrate by total retention of bovine serum albumin and immunoglobulins with only a limited transmission of b-lactoglobulin. The outcome of the present work is a guideline which includes the proper selection of ceramic UF membrane molecular mass cut-off (MMCO) (from 150 to 300 kg·mol -1 ), operating conditions (physico-chemistry, hydrodynamics) and operation mode for achieving satisfactory performance. Irreversible membrane fouling, mainly due to b-lactoblobulin (b-LG), the major protein of the feed solution, and physico-chemical characteristics of the whey protein sources (initial a-LA purity and concentration; heat denaturation of proteins) were shown as selection parameters of prime importance with regard to the target of the prepurification step. Whey protein concentrate in liquid form (PS 90) was to be preferred versus the same grade in powder form and the less concentrated liquid (PS 75). By processing that liquid PS 90, a-LA purity in the permeate was increased from around 0.25 in the initial feed to around 0.44 with a yield of around 0.53 with Céram membranes of MMCO of 300 kg·mol -1 . Stationary ultrafiltration flux was around 64 L·h -1 ·m -2 at a volume reduction ratio of 9.a-lactalbumin / whey / purity / ultrafiltration Résumé -Pré-purification de l'a-lactalbumine par ultrafiltration de lactosérum acide sur membrane céramique : étude des conditions opératoires. La production d'a-lactalbumine (a-LA) de pureté élevée peut se faire par une cascade de 2 opérations, dont la première, présentée ici, est une étape de pré-purification. Il s'agit d'un fractionnement par ultrafiltration d'un lactosérum de caséine acide afin d'obtenir une pureté en a-LA améliorée dans le filtrat en retenant totalement la sérum-albumine bovine et les immunoglobulines. Le présent travail débouche sur un recueil de recommandations qui inclut le choix du seuil de coupure de la membrane, des conditions physicochimiques et hydrodynamiques et du mode de conduite pour obtenir des performances satisfaisantes. Le colmatage irréversible de la membrane et les caractéristiques physico-chimiques de la source de protéines de lactosérum (pureté et concentration initiale en a-LA ; dénaturation des * Correspondence and reprints

Purification of ?-lactalbumin from a prepurified acid whey: Ultrafiltration or precipitation

“…The feeds used in the present work were prepared according to the principles of α-LA prepurification reported by Muller et al [15]. Nonetheless, the actual operating conditions were adapted to the whey protein fractions specially selected for the present work.…”

“…Detailed flow-sheets for the industrial manufacture of liquids PS 75 and PS 90 have been reported by Muller [13] and Gésan et al [9]. PS 90 ultrafiltrate and PS 90 microfiltrate were prepared as described by Muller et al [15] and were used as feeds for the ultrafiltration route (Fig. 1).…”

“…The first step consists of an UF separation performed with proper operating conditions: a 300 kg·mol -1 molecular mass cut-off (MMCO) inorganic membrane, clarified acid casein whey, pH 7.0, ionic strength: 0.2 mol·L -1 , protein concentration: 7 g·L -1 , continuous concentration up to VRR 11, tangential flow velocity: 6 m·s -1 , temperature 50°C and transmembrane pressure: ∆P 1.0 bar [15]. This first step yields a permeate with increased α-LA purity (0.44 vs. 0.25 première étape (microfiltration, ultrafiltration).…”

Fractionation of pasteurized skim milk proteins by dynamic filtration

“…At the test pH of 6, a-La proteins and the membrane are negatively charged and repulsion forces may explain the lower transmission. We can compare our data with those of Muller et al (2003) who used mineral membranes of 150 kDa. They reported a higher a-La transmission of 0.4, but at a lower permeate flux of about 50 L h À1 m À2 .…”

“…The next fractionation step is the separation and purification of major whey proteins such as a-La and b-Lg which present various applications for the food and pharmaceutical industries. a-La is used as food additive in infant formula (Muller, Chaufer, Merin, & Daufin, 2003) due to its high tryptophan content and nutritional value and has also medical applications due to its high cytotoxicity (Svensson, Hakansson, Mossberg, Linse, & Svanborg, 2000). b-Lg proteins have important emulsification and gelling properties (Cayot & Lorient, 1997;Dunlap & Coté, 2005).…”