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Khaldi M.,French National Institute for Agricultural Research | Khaldi M.,Lille University of Science and Technology | Khaldi M.,Institute National Agronomique Of Tunisie | Ronse G.,French National Institute for Agricultural Research | And 15 more authors.
International Journal of Chemical Engineering | Year: 2015

Few investigations have attempted to connect the mechanism of dairy fouling to the chemical reaction of denaturation (unfolding and aggregation) occurring in the bulk. The objective of this study is to contribute to this aspect in order to propose innovative controls to limit fouling deposit formation. Experimental investigations have been carried out to observe the relationship between the deposit mass distribution generated in plate heat exchangers (PHE) by a whey protein isolate (WPI) mainly composed of β-lactoglobulin (β-Lg) and the ratio between the unfolding and aggregation rate constants. Experiments using a PHE were carried out at a pilot scale to identify the deposit distribution of a model fouling solution with different calcium contents. In parallel, laboratory experiments were performed to determine the unfolding/aggregation rate constants. Data analysis showed that (i) β-Lg denaturation is highly dependent on the calcium content, (ii) for each fouling solution, irrespective of the imposed temperature profile, the deposit mass in each channel and the ratio between the unfolding and aggregation rate constants seem to be well correlated. This study demonstrates that both the knowledge of the thermal profile and the β-Lg denaturation rate constants are required in order to predict accurately the deposit distribution along the PHE. © 2015 Marwa Khaldi et al. Source

Bornaz S.,Ecole Superieure des Industries Alimentaires de Tunis | Sahli A.,Institute National Agronomique Of Tunisie | Maaoui M.,Institute National Agronomique Of Tunisie | Sifi S.,Office National de lhuile | Aiachi M.,Institute Of Lolivier
Acta Horticulturae | Year: 2012

An experimental investigation was carried out to evaluate the effect of stoning on yield and composition of virgin olive oil derived from three olive cultivars ('Chemlali', 'Chetoui' and 'Zalmati') representing the main domesticated material used in Tunisia. The action of stone mill and the de-stoner in olive paste preparation was compared and their effects on quality of yielded oils were evaluated. Also, composition of pulp oil and stone oil were compared. The oil yield of stoned olive decreased slightly but the effect of stoning depends on cultivar. In fact, 'Chetoui' appears as the most suitable cultivar to such treatment. On the other hand, stoning can improve the oxidative stability and the alcohols content of the extracted oils. In addition, stoning had no effect on the phenols content and on the acidic, triglyceridic and sterolic fractions. The comparison between pulp and stone oils characteristics showed a richness of the stone oil in certain fatty acids (C18:2, C20:0 and C20:1) and in LLL triglyceride in addition to total sterols, total alcohols, carotenoids and chlorophylls oil contents. However, the composition of the stone in aliphatic alcohols, terpenic alcohols and erythrodiol+uvaol depends on cultivar. This rich composition in minor compounds makes the stone oil an important product which can be valorized in the chemical and pharmaceutical industries. Source

Guizani N.,Muscat College | Al-Saidi G.S.,Muscat College | Rahman M.S.,Muscat College | Bornaz S.,Ecole Superieure des Industries Alimentaires de Tunis | Al-Alawi A.A.,Muscat College
Journal of Food Engineering | Year: 2010

The state diagram of Deglet Nour dates was developed using freezing curve, glass transition line, and maximal-freeze-concentration condition. Freezing points and glass transition temperature were measured by differential scanning calorimetry (DSC) as a function of water content. Freezing points were fitted to the Clausius-Clapeyron equation adjusted with un-freezable water, and glass transition was fitted to the Gordon-Taylor model. Glass transition decreased with a decrease in solids content, confirming the plasticizing effect of water on date solids. Freezing point data indicated the temperature when ice formed and dates would be most stable in terms of its deterioration if it can be stored below its glass transition. Maximum-freeze-concentration conditions was found as Xs ′ (characteristic solids content) = 0.78 g/g sample, with the characteristic temperature as Tg ′ (characteristics glass transition) = -48 °C and Tm ′ (characteristic end point of freezing) = -38.2 °C. These characteristics indicated that 0.22 g/g sample water in date was un-freezable (i.e. bound with solids or unable to form ice). The developed state diagram can be used in determining the stability of dates during storage as a function of temperature and moisture content. Moreover, it can be used to determine optimum drying and freezing conditions. © 2010 Elsevier Ltd. All rights reserved. Source

Khemakhem M.,Ecole Superieure des Industries Alimentaires de Tunis | Khemakhem M.,Tunis el Manar University | Papadimitriou V.,National Hellenic Research Foundation | Sotiroudis G.,National Hellenic Research Foundation | And 5 more authors.
Food Chemistry | Year: 2016

A water soluble humic acid and melanin-like polymer complex (OMWW-ASP) was isolated from olive mill waste waters (OMWW) by ammonium sulfate fractionation to be used as natural additive in food preparations. The dark polymer complex was further characterized by a variety of biochemical, physicochemical and spectroscopic techniques. OMWW-ASP is composed mainly of proteins associated with polyphenols and carbohydrates and the distribution of its relative molecular size was determined between about 5 and 190kDa. SDS-PAGE shows the presence of a well separated protein band of 21.3kDa and a low molecular weight peptide. The OMWW-ASP complex exhibits a monotonically increasing UV-Vis absorption spectrum and it contains stable radicals. Antioxidant activity measurements reveal the ability of the OMWW protein fraction to scavenge both the cationic 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) radical, as well as the stable nitroxide free radical 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL). © 2016 Elsevier Ltd. Source

Lakoud A.,Ecole Superieure des Industries Alimentaires de Tunis | Curet S.,French National Center for Scientific Research | Hassouna M.,Ecole Superieure des Industries Alimentaires de Tunis
International Food Operations and Processing Simulation Workshop, FoodOPS 2015 | Year: 2015

This study focuses on the hydration process of dates from experimental and numerical investigations. Dry Tunisian Deglet Nour dates were hydrated at a laboratory scale by using saturated air. A theoretical model based on a finite element scheme was developed to describe mass transfer phenomena that occur during the hydration process. This model considers the real shape of dates with a 2D axisymmetric analysis. Both moisture diffusivity and convective mass transfer coefficient of dates were estimated by using an optimization algorithm based on a least square approach from experimental and numerical average moisture contents. Overall, the experimental moisture contents as a function of hydration time were found in good agreement with the simulated values for various operating conditions. Such a methodology can now be used as a predictive tool to simulate the hydration of dates in order to improve the quality of final product and reducing processing time. © 2015 DIME UNIVERSITÀ DI GENOVA. Source

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