A reaction kinetic approach for the description of reversible (unfolding) and irreversible (aggregation) denaturation of β-lactoglobulin (β-Lg) was developed in this study. This novel ap- proach allows the calculation of the content of native, partially unfolded and irreversibly denatured β-Lg as a function of the heat treatment time. Moreover, it is able to give a mathematical inter- pretation of the sharp bend on the Arrhenius plot of the formal denaturation rate constant which is characteristic of the denaturation behaviour of both major whey proteins, α-lactalbumin and β- lactoglobulin. The developed theoretical backgrounds were applied for the denaturation kinetics of β-Lg in a protein solution containing 50 g·L −1 of the isolated whey protein fraction and verified by means of differential scanning calorimetry. β-lactoglobulin / thermal denaturation / unfolding / aggregation / reaction kinetic

Influence de la pasteurisation du lait et de la temperature de cuisson sur les composes volatils du Malatya, fromage fermier de type Halloumi. Du Malatya, un fromage fermier de type Halloumi, a ete fabrique a partir de lait cru et de lait pasteurise, et les cailles obtenus ont ete cuits dans du lactoserum chauffe a 60, 70, 80 ou 90 °C. Apres 30 ou 90 jours d'affinage, la composition en volatils des fromages a ete caracterisee. Cent deux composes volatils incluant 11 acides, 13 esters, 6 aldehydes, 26 alcools, 2 lactones, 5 composes soufres, 5 terpenes et 19 composes divers ont ete identifies par micro-extraction en phase solide et chromatographie gazeuse couplee a la spectrometrie de masse (CG-MS). L'utilisation du lait cru pour la fabrication a abouti a un profil en volatils plus riche et la majorite des volatils etaient presents en quantite plus importante dans les fromages au lait cru par rapport aux fromages au lait pasteurise. Les fromages au lait cru contenaient des teneurs plus elevees en acides, esters et cetones, et des teneurs moins elevees en aldehydes et composes soufres. Une analyse en composante principale (ACP) a permis de simplifier l'interpretation des donnees de CG-MS et de differencier les fromages au lait cru des fromages au lait pasteurise. Les echantillons ont egalement ete classifies sur la base de la temperature de cuisson par ACP, mais aucune distribution reguliere n'a pu etre observee. Ces resultats suggerent que la pasteurisation du lait de fabrication a un effet sur la composition en volatils plus marque que celui de la temperature de cuisson du caille.

The objective of this research was to evaluate the effect of the combination of PEF with conventional heat treatment on the microbial inactivation of Salmonella enteritidis in skim milk. The purpose was to identify possible synergies that would make it possible to design minimal treatment regimes. Heat-resistance parameters (D$theta$ and z) were firstly determined using a temperature-controlled water bath. Then, the effect of the PEF treatment followed by a heat treatment on the inactivation of Salmonella enteritidis in skim milk was evaluated using a PEF of 47 kV·cm-1/ 500 ns / 60 Hz, and a temperature of 62 °C for 19 s, at a volumetric flow rate of 5 L·h-1. The effect of PEF or heating only was also studied with the same equipment. From the heat-resistance parameters previously determined, continuous heat processing at 62 °C for 19 s should give an inactivation ratio of 1.7 log. PEF processing of the milk resulted in a decimal reduction of 1.2 ± 0.3 log and the combination of the two operations gave a reduction of Salmonella enteritidis equal to 2.3 ± 0.4 log. The results suggested that the combination of PEF and heating was more effective than each on its own. However, the lethality of the two treatments was additive rather than synergistic.

To assess the relationship between conditions of milk production and cheese contents of components of nutritional interest, it is necessary to know to what extent the compositional variability of cheese depends on that of milk.The respective effects of milk composition and the cheese-making process on cheese compositional variability in components of nutritional interest were therefore studied under real conditions of cheese production considering four different cheese-making technologies.The nutritional characteristics of the original milk were subject to high variations partly due to animal species (cow vs. goat).Apart from the aspects related to the dry matter content of cheese, the cheese compositional variability in fatty acids, -carotene, xanthophylls and vitamin E depended mainly on the composition of the original milk.For vitamin A, it was partially influenced by both the original milk composition and the cheese-making process.Regarding folates and minerals, as well as total antioxidant capacity, the cheese composition varied mainly with the cheese-making process.In addition, the cheese-making technology had a significant effect on the cheese composition in minerals and folates, but did not influence the other components affected by the cheesemaking process.Consequently, the cheese contents of fat-soluble compounds depend directly on the conditions of milk production.On the contrary, the composition of cheese in water-soluble compounds varies independently of the conditions of milk production.The total antioxidant capacity of pressed cheeses, unlike the original milk, was positively correlated with some fat-soluble antioxidants.It could therefore be influenced by the conditions of milk production. cheese-making process / milk composition / fatty acid / vitamin / mineral

International audience

In spite of its high production (18000 T yearly), very few studies have been devoted to Cantal, a French AOC ("Appellation d'Origine Contrôlée") cheese variety whose making process is close to that of Cheddar.To improve the knowledge of this type of cheese, two ripened Cantal cheeses issued from raw milk and two different industrial processes were biochemically, physicochemically, structurally and microbiologically characterised through the analysis of both cheese sectors and juices extracted by pressure.The results obtained were compared with Cheddar and Emmental cheeses.The main differences between Cheddar and Cantal cheeses of the same age were a higher rate of proteolysis for Cantal cheese shown by both the total nitrogen content and the TCA soluble nitrogen in the respective cheese juices, and higher Ca T content as well as an increased molar Ca T /P T ratio in the Cantal cheese.Free amino contents in the cheese aqueous phase were similar but individual variations suggested an effect of the secondary ripening microflora provided by the raw milk used.Microbial counts done on different media showed a dominant mesophilic and thermophilic lactic acid bacteria flora, a subdominant flora composed of various ripening bacteria and yeasts and a very low level of some coliforms and of Pseudomonas.An amount of 44 neutral volatile compounds were identified but 3 of them determined by GC-MS (ethanol, 2-butanone and 2-butanol) represented more than 95% of the total peak area.Some variations in these main compounds as well as in minor ones confirmed a difference in the native microflora in the two studied Cantal cheeses.Nevertheless, these data appeared in the range of those reported for Cheddar.The microstructure of fat determined by confocal laser scanning micrography showed that little is present in Cantal cheese as intact fat globules.Most of this component appeared as free fat included in the casein matrix with a high ability to oil off, especially the part which is near the crust.As well as offering a precise characterisation of many compositional aspects of ripened Cantal cheese, this study opens the way for further works on the process kinetics carried out in the making processes and for a better knowledge of the ecosystem metabolism.Cantal cheese / composition / ripening / proteolysis / mineral composition / microbial flora / neutral volatile compound / fat microstructure

In India both dairy and fruit sectors face problems of lack of basic infrastructure for handling peaks in production.Mango is considered as king of the fruits, but its production is highly seasonal.Lack of adequate infrastructure in many places results in huge losses due to low keeping quality.In the dairy industry, buttermilk, a by-product of butter production, is mostly left unutilized.Buttermilk is a good source of valuable milk proteins and lactose; its high phospholipids content makes dried buttermilk a good functional ingredient in food formulations.In this study, blends with different levels of mango juice and buttermilk were spray dried viz., 5:95, 10:90, 15:85 and 20:80 at feed temperature of 40-55 °C and compressed air pressure of 68-170 kPa.It was observed that the various processing parameters such as outlet air temperature, total solids and blend proportions had a profound effect on the characteristics of the resultant powder.The viscosity of blends increased with an increase in the mango juice proportion in the blend.High acid content of the blends had no negative effect on thermal stability of the blends before and after spray drying.This is probably due to the fact that a relatively low feed temperature (45 °C) was used and the exposure of the blends to high temperatures was only momentary during drying process.It was found that increments in the inclusion of mango solids had a positive effect on the resultant yield of powder.An increase in solid content of the blends up to 35% resulted in a steep increase in yield, which was adjudged as the optimal total solids for drying.Further increase in total solids of the blends resulted in reduced yields.The outlet air temperatures of the spray drier were optimized at a range of 85-90 °C for all the blends.Sensory evaluation studies by an in-house panel affirmed that the blend with 20:80 ratio of mango juice: buttermilk, respectively, possessed the desired sensory characteristics.spray drying / buttermilk / mango juice / juice-milk blends / Kulfi

Spray drying is used for the manufacture of many consumer and industrial products such as instant dairy and food products, laundry detergents, pharmaceuticals, ceramics and agrochemicals.During spray drying, agglomerates of powder particles are formed, which determine the instant properties of the powder.Agglomeration during spray drying is considered to be a difficult process to control.The main cause of this is the complex interaction of the process variables: the atomization process, the mixing of spray and hot air, the drying of suspension droplets and the collision of particles which might lead to coalescence or agglomeration.As a consequence, agglomeration during spray drying is operated by trial-and-error.In an EC-sponsored project, named the EDECAD project and co-ordinated by NIZO food research, an industrially validated computer model, using Computational Fluid Dynamics (CFD) technology, to predict agglomeration processes in spray drying machines is developed.An Euler-Lagrange approach with appropriate elementary models for drying, collision, coalescence and agglomeration of the dispersed phase is used.The main result of the EDECAD project is a so-called "Design Tool", which establishes relations between the configuration of the drying installation (geometry, nozzle selection), process conditions, product composition and final powder properties.The Design Tool is being validated on pilot-plant scale and industrial scale.It will provide a tool for improved design and optimisation of spray drying and agglomeration equipment, to improve the quality of products and to increase the productivity of such equipment.This paper introduces the approach of the project and some preliminary results.spray drying / agglomeration / computational fluid dynamics / modeling

The atomization stage in spray drying of a liquid requires a spray of droplets with a high surface-to-mass ratio. Dried products that result from moisture evaporation of atomized spray can be prepared to reach the desired particle size distribution through control of atomization variables. To meet these requirements, many atomization techniques such as pressure nozzles, two-fluid noz- zles and rotary atomizers have been used in spray dryers. Many authors have proposed various rela- tionships between droplet size, physical properties (e.g. viscosity of concentrate) and technological parameters (e.g. nozzle pressure). To optimize the moisture content in milk powder, it is necessary to control the thermodynamic parameters of the drying air, the conditions of the atomization and the properties of the concentrate. Droplet size varies in direct relationship with viscosity to the power of 0.17-0.25. There are, in fact, two possible solutions for measuring online viscosity: either an on- line viscometer (direct measurement) or measurement of the amperage of the concentrate extraction pump (indirect measurement). The aim of this study was therefore to develop an indirect method to estimate the viscosity of a concentrate after concentration by filtration or vacuum evaporation and before spray drying. For example, while varying the viscosity of different dairy products (concen- trated whey, and whole and skim milk) by changing the parameters of concentration by vacuum evaporation, we obtained a very good correlation between concentrate viscosity and the extraction pump amperage, whatever the product. Concentration parameters can be modified during evapora- tion to obtain a concentrate of the same viscosity, whatever its temperature or total solid content, just by following the extraction pump amperage.

Proprietes thermiques et structurales de la matiere grasse de lait de dromadaire. 1. Formes cristallines obtenues lors d'un refroidissement lent. Les proprietes thermiques et structurales de la matiere grasse anhydre extraite du lait de dromadaire (ADMF) ont ete etudiees par une nouvelle technique qui permet des mesures simultanees, sur un meme echantillon, des signaux de microcalorimetrie differentielle a balayage (DSC) et de diffraction des rayons X en fonction du temps et de la temperature. L'etude des proprietes thermiques de la matiere grasse du lait de chamelle, en relation avec sa composition, revet un interet particulier si l'on considere les conditions extremes de temperature auxquelles ce mammifere est adapte. Cet article, qui est le premier d'une serie, est consacre a l'etude des organisations cristallines formees par les triacylglycerols (TG) de l'ADMF lors d'un refroidissement a 0,1 °C.min -1 . Les formes cristallines obtenues a partir de 29,5 °C correspondent a une structure lamellaire a deux longueurs de chaines (2L = 42,3 A) et a un empilement lateral des chaines d'acides gras de type β'. La plage de cristallisation couvre un domaine d'environ 75-80 °C, similaire a celui observe pour la matiere grasse laitiere bovine, bien que la temperature finale de fusion soit plus elevee pour le dromadaire d'environ 5 a 8 °C. Les enregistrements de DSC observes a la cristallisation comme a la fusion revelent l'existence d'environ 6 evenements thermiques qui contrastent avec l'apparente simplicite du comportement structural. Une analyse fine des pics de diffraction des rayons X et de leurs evolutions a aussi montre l'existence d'autres empilements longitudinaux mais sans pouvoir differencier ces structures de maniere univoque. Une croissance cristalline de type epitaxie est proposee pour expliquer ce comportement structural.