SummaryA general model of the kinetics of microbial growth has been developed involving the kinet.ics of incorporat,ion of srtbstrat,e into biomass and t.he maintenance energy requiremetit,s.Results obt.ained from bat.ch cultures of the yeast Saccharo7tiyces cerevisiae growing in synthetic media at. pH 5.1 and 30°C permitted all biological parameters in the model to be calciilated.Values obtained for these pat ameters were: maximiim specific glricose ript8ake rate (ps,,,), 2.08 g/g biomassihr; apparent llichaelis constant, for glucose ( K s ) , . hlass balances for aerobic and anaerobic cnlt*iires confirmed the results obtained from the generalized model. Iles\ilts presented suggested Lhe operation of a mechanism for regulating energy-yielding met abolisni which illvolved an eqriilibrinm between the systems of oxidative phosphorylation and dephosphorylat,ion and was dependent iipon the level of cat abolite repression.
With the aim of studying pre‐rinsing and cleaning of a milk storage tank, different representative samples are collected during the process and their components (protein, sugar and lipid) analysed. The main conclusions of this study may be summarized as follows: (1) The mean thickness of milk remaining in the tank ranges around 20 μm. It depends on the dropping time and on the possible presence of milk foam. (2) The different main milk components do not exhibit the same removal rate and sugar seems to be completely removable by rinsing only. (3) Prerinsing may be characterized by four periods of which one depends on a diffusion mechanism. (4) Pre‐rinse is a very rapid process which mainly depends on the pre‐rinse solution volume used per unit of soiled surface. (5) Hard water, osmosed water alone or admixed with a surface active agent or caustic soda (1%) lead to the same results.
Un dispositif expérimental simulant la paroi d'un tank de stockage est constitué d'une plaque verticale qui est souillée sur une hauteur de 2,25 m par 10 dm' de solution. La plaque est rincée .par un film tombant homogène.Les résultats suivants sont obtenus: -La quantité de souillure restant sur la plaque après égouttage dépend de la viscosité de la solution de souillure.-La cinétique du rinçage qui dépend de l'aptitude au rinçage des composants de la souillure est simulée par un modèle qui comprend trois phases. La première phase, d'ordre zéro, assure l'élimination des fortes épaisseurs de souillure. La deuxième phase, d'ordre un, assure l'élimination de souillures piégées dans les rugosités de la surface. La dernière phase, d'ordre supérieur à un, paraît contrôlée par des phénomènes de surface.-Les petites molécules sont éliminées plus rapidement que les protéines et la matière grasse du lait. La vitesse d'élimination par rinçage croît selon le composé dans l'ordre suivant : matière grasse de lait homogénéisé et micelles de caséine, matière grasse du lait non homogénéisé, protéines du lactosérum et caséine soluble, NaOH et HN03, f1uorescéinate de sodium, saccharose et lactose, NaCI.Un parallèle est établi entre le rinçage des tanks de stockage et celui des canalisations.Mots clés: Rinçage -Film tombant -Mécanismes -Cinétique -Produits laitiers -Solution de nettoyage.
SummaryStudy of rinsing mechanisms using a falling film on a vertical surface soiled by model solutions and dairy products -Process modeling.An experimental deviee which comprised a 3 m high vertical plate was built to simulate the wall of a storage tank. The plate was soiled with a falling film of model soiling solution and rinsed by means of a homogenous falling film of osmosed water. A sampling deviee comprising a high speed sampler was used to quantify total soil removed by rinsing and rinsing kinetics. The main results obtained were : -Soil amount remaining on the plate after dripping off depended on soiling solution viscosity in agreement with VAN ROSSUM's theory (1958). The composition of the soil removed by rinsing was similar to the composition of the soiling solution.-Rinsing kinetics could be simulated by a model involving three phases. This model took into account plate rugosity, residuaI soiling and rinsing ability of deposit components. The first phase whose order was equal to zero controlled removal of soiling film overlaying plate rugosity. The second phase whose order was equal to one controlled removal of soiling film contained into plate rugosity. The third phase whose order was superior to one seemed to be controlled by surface phenomena.-Small molecules were removed more rapidly than milk pratein and fat. Rinsing removal rate increased according to compounds in the following order : homogenized milk fat and casein micelles, non homogenized milk fat, whey proteins and soluble casein, NaOH and HN03, Na-fluorescein, sucrase and lactose, NaCI.-A parallel was established between rinsing of storage tanks and rinsing of pipes.
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