Les hautes pressions hydrostatiques et leurs applications en sciences des aliments, une étude : des phénomènes thermiques liés à la compression , des cinétiques d'inactivation microbienne, des traitements en pression pulsée et en pression de dioxyde de carbone

L’objectif de cette thèse étant d’apporter une contribution scientifique à l’application des Hautes Pressions Hydrostatiques aux procédés de traitement des aliments, le manuscrit a été présenté sous la forme de cinq Chapitres. Cette thèse a permis de mettre en évidence un certain nombre de résultats originaux. 1- Les effets thermiques liés à la compression doivent être pris en compte dans tout traitement de pasteurisation. La température initiale du produit et la cinétique de compression doivent être optimisées afin de pouvoir compenser l’accroissement de température. 2- La sensibilité des micro-organismes vis-à-vis de la pression est modifiée par les propriétés intrinsèques de l’aliment (pH, activité de l’eau, composition de la matrice alimentaire...). L’inactivation sous HPH des deux micro-organismes (Escherichia coli et Listeria innocua) dans le jus de kiwi était plus importante que celle observée au sein du jus d’ananas � milieu encore plus favorable à l’inactivation que le lait entier. 3- Les cinétiques d’inactivation sous HPH ne semblent pas suivre les cinétiques traditionnelles du 1er ordre. Ainsi des modèles alternatifs ont du être étudiés pour ces cinétiques. Le modèle de Weibull peut être utilisé pour les cinétiques d’inactivation sous hautes pressions des micro-organismes. 4- Les traitements par pression pulsée constituent une alternative intéressante aux traitements conventionnels en continu. Cependant il est nécessaire d’optimiser divers paramètres : la durée de chaque pulse, le nombre de pulses et la valeur de la pression afin d’atteindre le niveau optimal de réduction des micro-organismes (E-coli et L. innocua), compatible avec une application industrielle. 5- La durée et la température du stockage des aliments après un traitement HPH doivent être optimisées afin d’accroître la sécurité des jus de fruits traités et d’éviter la reprise de croissance des micro-organismes endommagés. 6- Le traitement utilisant le dioxyde de carbone d’une part et la pression pulsée d’autre part peut être une voie efficace pour l’inactivation des micro-organismes dans le lait écrémé tout en réduisant le niveau de pression requis. La principale conclusion de cette thèse est que les traitements sous Hautes Pressions Hydrostatiques (HPH) présentent un grand intérêt pour l’inactivation de micro-organismes dans des milieux divers (lait, jus de fruits) si les paramètres gouvernant le procédé (pression, température, durée, élévation de température liée à la compression, température initiale du milieu fluide transmetteur et de l’aliment, la nature de l’aliment et des micro-organismes contaminants) sont clairement identifiés et si le traitement (pression pulsée ou pression continue, utilisation de CO2...) est adapté.The objective of this thesis is to bring a scientific contribution concerning the application of high pressures in Food Science. This thesis is divided in five main Chapters. This thesis allowed pointing out some important results. 1. The thermal effects of compression should be taken into account when HHP pasteurization processes are developed. Initial temperature of the food product and compression rate should carefully be selected in order to compensate the compression heating. 2. The pressure sensitivity of microorganisms is affected by the general intrinsic food properties such as pH and water activity as well as the composition of the food matrix (inactivation of both microorganisms by HHP in kiwifruit juice was higher than the inactivation in pineapple juice which is higher than the inactivation in whole milk). 3. The HHP inactivation kinetics need not follow traditional first-order kinetics, hence alternative inactivation models are ought to be found. Weibull model can be used for HHP inactivation kinetics of microorganisms. 4. The pulsed pressure treatment could be an alternative to continuous HHP, but optimization should be done between the pulse holding time, the number of pulses and the pressure level to reach the desirable number of log-reduction of microorganisms (E. coli and L. innocua) compatible with an industrial application. 5. The storage duration and storage temperature after HHP treatment should carefully be optimized to increase the safety of HHP treated fruit juices since the growth of injured microorganisms can be avoided during storage. 6. The high pressure carbon dioxide (HPCD) treatment in combination with pulsed pressure can be an efficient way to inactivate the microorganisms in skim milk and to reduce the maximum pressure level for the desired log-reduction. The main conclusion of this thesis indicated that HHP treatment has the potential to inactivate microorganisms in several foods (milk, pineapple and kiwifruit juices) if the process parameters (pressure, temperature, holding time, compression heating, initial temperature of the pressure transmitting fluid and food product, nature of the food and target microorganisms) are identified clearly and if the treatment (pulsed or continuous pressure treatment, HPCD) is selected accordingly

Modeling and predicting the biofilm formation of Salmonella Virchow with respect to temperature and pH

Biofilm formation of Salmonella Virchow was monitored with respect to time at three different temperature (20, 25 and 27.5 °C) and pH (5.2, 5.9 and 6.6) values. As the temperature increased at a constant pH level, biofilm formation decreased while as the pH level increased at a constant temperature, biofilm formation increased. Modified Gompertz equation with high adjusted determination coefficient (Radj2) and low mean square error (MSE) values produced reasonable fits for the biofilm formation under all conditions. Parameters of the modified Gompertz equation could be described in terms of temperature and pH by use of a second order polynomial function. In general, as temperature increased maximum biofilm quantity, maximum biofilm formation rate and time of acceleration of biofilm formation decreased; whereas, as pH increased; maximum biofilm quantity, maximum biofilm formation rate and time of acceleration of biofilm formation increased. Two temperature (23 and 26 °C) and pH (5.3 and 6.3) values were used up to 24 h to predict the biofilm formation of S. Virchow. Although the predictions did not perfectly match with the data, reasonable estimates were obtained. In principle, modeling and predicting the biofilm formation of different microorganisms on different surfaces under various conditions could be possible

Geleneksel Yöntem ve Mikrodalga ile Kuşkonmazın (Aparagus Offıcınalıs l.) Kurutulmasının Model Tabanlı Karşılaştırılması

In this study, asparagus slices were dried with traditional oven and microwave oven methods. Model based approach was used to investigate the differences and similarities between two drying methods. Weibullian and linear equations were used as the primary and secondary models, respectively. Secondary model integrated into the primary model could successfully be used to describe the moisture ratio of asparagus in one-step procedure. Appropriate fits were obtained for both drying techniques, but microwave drying had slightly better fit than the conventional drying. Tailing was observed for the curves of traditional drying whereas sigmoidal curves were observed for microwave drying. The time parameter (δ) value of the lowest power of the microwave drying (100 W) was just one third of the δ value of the highest temperature of the traditional drying (90 °C) indicating that microwave drying was effective method in terms of time comparing to traditional drying.Bu çalışmada kuşkonmaz dilimleri farklı sıcaklıklarda geleneksel fırın veya farklı güç seviyelerindeki mikrodalga fırın ile kurutulmuştur. İki kurutma yöntemi arasındaki fark ve benzerliklerin araştırılmasında model tabanlı yaklaşım kullanılmıştır. Birincil ve ikincil modeller olarak sırasıyla Weibullian model ve doğrusal denklem kullanılmıştır. Birincil modele bütünleştirilen ikincil model, tek aşamalı yöntemle kuşkonmazın nem oranını tanımlamak için başarıyla kullanılabilmiştir. Her iki kurutma tekniği için uygun modeller elde edilmiştir, ancak mikrodalgada geleneksel kurutmadan daha yüksek uygunluk görülmüştür. Geleneksel kurutma eğrileri için kuyruklu, mikrodalga kurutma için s-biçimli eğriler gözlenmiştir. Mikrodalga kurutmanın en düşük gücünün (100 W) zaman parametresi (δ) değeri, geleneksel kurutmanın en yüksek sıcaklığının (90 °C) δ değerinin sadece üçte biridir, bu da mikrodalga kurutmanın geleneksel kurutmaya kıyasla zaman açısından etkili bir yöntem olduğunu göstermiştir

The impact of UV-C irradiation on spoilage microorganisms and colour of orange juice

The effect of UV-C irradiation on inactivation of spoilage microorganisms and colour of freshly squeezed orange juice were investigated. Orange juice samples were intentionally fermented in order to increase the natural microflora which were mostly composed of yeasts and then exposed to UV-C irradiation at an intensity level of 1.32 mW/cm2 and sample depth of 0.153 cm for several exposure times by using a collimated beam apparatus. Applied UV dose was in the range of 0 and 108.42 mJ/cm2. Resistance of yeast to UV light and existence of suspended particles limited the effectiveness of the process. Survival data obtained for yeasts was either described by the Weibull or traditional first-order model and goodness-of-fit of these models was investigated. Weibull model produced a better fit to the data with higher adjusted determination coefficient (R2 adj) and lower mean square error (MSE) values which were 0.99 and 0.003, respectively. Time and UV dose of first decimal reduction were obtained as 5.7 min and 31 mJ/cm2, respectively. The data suggests that biodosimetric studies performed by using inoculated microorganisms for assesment of the efficiency of UV irradiation treatment in the shelf life extension of juices must be carefully evaluated. UV-C irradiation had no influence on the colour of orange juice.Izmir Institute of Technology (2008IYTE19

Effect of Pink Rock Rose Extract with or Without Ascorbic Acid and Sodium Ascorbate for the Preservation of Ready-to-Eat Frankfurter Type Sausages

This study aimed to determine the effect of pink rock rose extract (PRR) with or without ascorbic acid and sodium ascorbate for improving the shelf life of sausages. Analyzed parameters were DPPH radical scavenging capacity of PRR extract; total aerobic count, thiobarbituric acid reactive substance, heme iron, pH, water activity, proximate composition, and color values of MAP packaged sausages for 12 weeks at 4 °C. Treatments: (1) Control (0.02% ascorbic acid and 0.05% sodium ascorbate – AA-SA), (2) electrostatic spray application of PRR extract (2%) – ES-PRR, (3) 0.02% AA and, 0.05% PRR extract, (4) 0.05% SA and 0.02% PRR, (5) 0.07% PRR extract. PRR extract had the half maximal inhibitory concentration (IC50) value of 13.04 ± 0.133 µg/mL. Sausages formulated with 0.07% PRR had the lowest microbial growth rate, followed by AA-PRR formulation. The AA-PRR treatment had the lowest TBARS values for most of the storage. This study reveals that PRR extract can be added as a natural antioxidant in sausages, and it could be used as a replacement or for the reduction of ascorbic acid and sodium ascorbate in sausage formulations

Yüksek hidrostatik basıncın (YHB) lager biranın kalite parametreleri ve raf ömrü üzerindeki etkisi

Filtered bright and unfiltered hazy lager beer samples were either treated with high hydrostatic pressure (200, 250, 300, 350 MPa for 3, 5 and 10 min at 10°C and 20°C) or conventional heat pasteurization (60°C for 15 min). Treatments did not affect ethanol, extract, fermentation degree, density and pH in comparison with untreated beers. Both treatments produced microbiologically stable products. Bitterness, color, protein sensitivity and chill haze parameters were affected by both the HHP and heat treatment. A storage period of 56 days showed that HHP and heat pasteurization had similar results in terms of pH and color. However, HHP treated samples had lower bitterness and protein sensitivity and higher chill haze values than the heat pasteurized samples which indicates HHP treatment had a positive effect on bitterness and protein sensitivity at the end of the storage period. The microbiological stability of HHP treated beers was comparable with heat-treated beers, and the development of both lactic and acetic acid bacteria was inhibited for 56 days of storage. Unfiltered beer samples had 7. 48, 7.15 and 2.64 log10cfu/ml of total yeasts, total aerobic and lactic acid bacteria counts, respectively. No colony formation of lactic acid bacteria was observed when the samples were pressurized at pressures equal to or higher than 300 MPa at 10°C and 20°C for 5 and 10 min. Total aerobic and total yeasts counts demonstrated more than 6 and 7 log-cycle reduction when pressurized at 350 MPa at 10°C and 20°C for 10 min, respectively. Heat treatment gave similar results in terms of log reductions as HHP.M.S. - Master of Scienc

Reassessment of Thin-Layer Drying Models for Foods: A Critical Short Communication

Modeling the thin-layer drying of foods is based on describing the moisture ratio versus time data by using a suitable mathematical model or models. Several models were proposed for this purpose and almost all studies were related to the application of these models to the data, a comparison and selecting the best-fitted model. A careful inspection of the existing drying data in literature revealed that there are only a limited number of curves and, therefore, the use of some models, especially the complex ones and the ones that require a transformation of the data, should be avoided. These were listed based on evidence with the use of both synthetic and published drying data. Moreover, the use of some models were encouraged, again based on evidence. Eventually, some suggestions were given to the researchers who plan to use mathematical models for their drying studies. These will help to reduce the time of the analyses and will also avoid the arbitrary usage of the models

Control of Listeria monocytogenes in milk by using phage cocktail

Biocontrol applications such as using phages against the contamination of Listeria monocytogenes are promising trends in terms of reducing the use of chemical additives in food industry. The aim of this study was to determine the effectiveness of Listex P100 phage (phage P100) on different Listeria monocytogenes strains (PL2, PL3, PL9 and PL10) in pasteurized milk and broth. Survival data of L. monocytogenes were successfully described by Weibull model. Time parameter of the Weibull model was used to evaluate the phage-resistances of L. monocytogenes strains. The reduction of L. monocytogenes was greater in broth than in milk regardless of the temperature level and it was significantly higher at 30 °C than at 4 °C in both media. The reductions of L. monocytogenes strains by the phage treatment were between 2.7 to 3.4 log10 units at 30 °C and 1.4 to 2.1 log10 units at 4 °C after 4 days of incubation in broth whereas 1.9 to 2.9 log10 units and 1.0 to1.6 log10 units were observed after 4 days of incubation in milk at 30 °C and 4 °C, respectively. It was found that L. monocytogenes PL2 is the most phage-resistant strain in broth at 30 °C and at 4 °C, and in milk at 30 °C, while L. monocytogenes PL9 is the most phage-resistant L. monocytogenes strain in milk at 4 °C. This study demonstrated P100 phage could be used to control L. monocytogenes counts in milk

Gıda biliminde yüksek durgun-sıvı basınç (ydb) uygulamaları: sıkıştırma ısısı, mikrobiyal etkisizleştirme devinimi, vurgulu basınç ve yüksek basınç karbon dioksit işlemleri üzerine bir çalışma

In this study the action of high hydrostatic pressure (HHP) on compression heating of liquid foods and pressure transmitting fluids, inactivation of Escherichia coli and Listeria innocua in different food media (milk and fruit juices), pulsed pressure and high pressure carbon dioxide treatments was investigated. The experimental results in this study allowed pointing out some important results: (i) The thermal effects of compression should be taken into account when HHP pasteurization processes are developed. Initial temperature of the food product and compression rate should carefully be selected in order to compensate the compression heating; (ii) The HHP inactivation kinetics need not follow traditional first-order kinetics, hence alternative inactivation models are ought to be found. Weibull model can be used for HHP inactivation kinetics of microorganisms; (iii) The pulsed pressure treatment could be an alternative to continuous HHP, but optimization should be done between the pulse holding time, the number of pulses and the pressure level to reach the desirable number of log-reduction of microorganisms (E. coli and L. innocua) compatible with an industrial application; (iv) The storage duration and storage temperature after HHP treatment should carefully be optimized to increase the safety of HHP treated fruit juices since the growth of injured microorganisms can be avoided during storage; (v) The high pressure carbon dioxide (HPCD) treatment in combination with pulsed pressure can be an efficient way to inactivate the microorganisms in skim milk and to reduce the maximum pressure level for the desired log-reduction.Ph.D. - Doctoral Progra