Effect of fibers and whole grain content on quality attributes of extruded cereals

Incorporation of fiber in cereals may lead to quality issues, thus decreasing consumer acceptance. This is partially due to deterioration of the microstructure, one of the primary quality attributes of cereals. The objective of this study was to better understand the mechanisms by which dietary fibers affect the quality of cereal products during extrusion-cooking. The study quantified the effect of amount and type of fiber and whole grain on (i) texture, (ii) structure, and (iii) rehydration properties of extruded cereals. New innovative methods were applied and combined with traditional techniques to characterize both the structure and the rehydration properties. Extruded cereals were produced using a starch-based recipe (whole and wheat flours) and two sources of fibers (oat bran concentrate and wheat bran). The oat and wheat bran levels used in this study were 0, 10, and 20%. The different mixtures were extruded in a pilot twin-screw extruder BC21 (Clextral) and then sugar coated after drying. Mechanical properties of extruded cereals were investigated by compression test. The cellular structure was observed by X-ray tomography. The quality of coating (thickness, homogeneity) was analyzed by optical coherence tomography. The rehydration properties of such cereals in milk were evaluated by magnetic resonance imaging and optical coherence tomography. This work revealed that structure assessment of extruded cereals may lead to a better understanding of the effect of fiber addition on texture and rehydration properties. The application of innovative methods, such as optical coherence tomography and magnetic resonance imaging, was found to be useful to quantify the structural properties

MRI texture analysis as means for addressing rehydration and milk diffusion in cereals

Cereals microstructure is one of the primary quality attributes of cereals. Cereals rehydration and milk diffusion depends on such microstructure and thus, the crispiness and the texture, which will make it more palatable for the final consumer. Magnetic Resonance Imaging (MRI) is a very powerful tomographic tool since acquisition parameter leads to a wide possibility for identifying textures, structures and liquids mobility. It is suited for noninvasive imaging of water and fats. Rehydration and diffusion cereals processes were measured by MRI at different times and using two different kinds of milk, varying their fat level. Several images were obtained. A combination of textural analysis (based on the analysis of histograms) and segmentation methods (in order to understand the rehydration level of each variety of cereals) were performed. According to the rehydration level, no advisable clustering behaviour was found. Nevertheless, some differences were noticeable between the coating, the type of milk and the variety of cereals

Influence of citric acid and water on thermoplastic wheat flour/poly(lactic acid) blends. I: Thermal, mechanical and morphological properties

Wheat flour was plasticized with glycerol and compounded with poly(lactic acid) in a one-step twin-screw extrusion process in the presence of citric acid with or without extra water. The influence of these additives on process parameters and thermal, mechanical and morphological properties of injected samples from the prepared blends, was then studied. Citric acid acted as a compatibilizer by promoting depolymerization of both starch and PLA. For an extrusion without extra water, the amount of citric acid (2 parts for 75 parts of flour, 25 parts of PLA and 15 parts of glycerol) has to be limited to avoid mechanical properties degradation. Water, added during the extrusion, improved the whole process, minimizing PLA depolymerization, favoring starch plasticization by citric acid and thus improving phases repartition

Matériaux à base de maïs : de la qualité finale à la sélection variétale via le procédé de mise en forme

Que les matériaux à base de maïs soient considérés comme des substituts des matériaux plastiques, ou qu'ils se présentent comme des produits alimentaires expansés (céréales petit-déjeuner, biscuits...), il est important de pouvoir évaluer leurs propriétés mécaniques, pour adapter les conditions de transformation, favoriser la sélection de la matière première et optimiser leur qualité. Par analogie avec le modèle des solides composites, l'analyse thermomécanique dynamique (DMA) montre que le comportement dépend fortement de l'adhésion entre amidon et particules protéiques. Les variations de viscosité élongationnelle avec la teneur en protéines et son lien avec le module élastique E', pour T>Tg+30°C, suggèrent que cette morphologie est fonction des mécanismes d'écoulement et d'expansion lors du procédé. En établissant les relations structure-procédé-propriétés, ces travaux ont favorisé la sélection variétale et la conception de produits céréaliers à la texture optimisée

Sirènement de boîte de vitesses automobile : confrontation calcul/essais en contexte réel

Le sirènement de boîte de vitesses est un bruit associé aux vibrations carter. La source excitatrice de nature paramétrique (raideur périodique) résulte du contact étroit entre dentures et de leurs micro-géométries. Pour des cas réels, la prédiction reste un problème difficile. Des méthodes numériques permettent de le traiter des échelles micro (denture) aux échelles macro (carter). Un modèle complet de 1,2 millions de ddl est mis en uvre. Les résultats numériques sont confrontés à ceux d essais expérimentaux (100 voies de mesures). De nombreux régimes de fonctionnement ont été réalisés

Influence of citric acid on thermoplastic wheat flour/poly (lactic acid) blends. II. Barrier properties and water vapor sorption isotherms

The effects of citric acid on wheat flour/glycerol/poly(lactic) acid (PLA) blends prepared by one-step twin-screw extrusion have been studied to improve barrier properties of starch based materials. A series of injected samples were produced from prepared compounds with varying ratio (0-20 part) of citric acid. The effects of citric acid on the water vapor permeability, oxygen permeability and water solubility in the film were then investigated. The barrier properties results proved that citric acid behaves as compatibilizing agent between starch and PLA phases for ratios between 0 and 10 parts. When the added amount exceeds 10 parts, CA acted as a plasticizer and/or promoted the hydrolysis of the starch glycosidic bonds

Cyclocholates as Chiral Selectors for Capillary Gas Chromatography - Effect of Temperature Conditioning on the Chromatographic Behavior of the Stationary Phase

International audienc

High-performance liquid chromatographic investigation of the enantioselectivity and mechanism of chiral recognition of new cholic acid-based stationary phases

International audienc

Cereals bran enhancement in food products: A physical properties approach to address technical challenges and opportunities

Amongst consumer’s key trends, bringing nutritional balance and specific health benefits in combination with naturality, freshness and authenticity in food products is a strong opportunity for food developers. In many diets worldwide, dietary fibers are missing and using cereals bran as a source of dietary fibers is a potential approach, which suits consumer’s needs. However, being able to deliver the right amount of fibers through wholegrain or cereals bran while still proposing appealing products to the consumers is a technical challenge. More bran usually means more raw cereal taste as well as less palatable products, and thus less liking by consumers. The study presented here aims at tackling the texturization issue using a food physics and structure approach following three different angles: (i) anticipating the processability of wholegrain flours from different cultivars, (ii) assessing the role of added cereals bran in cereals products and (iii) assessing the physical and structural changes that brans undergo when submitted to a thermomechanical process. As a first step, the physical properties of whole wheat flours from different cultivars were assessed by several analytical methods such as RVA (Rapid Visco Analyser) and dynamic rheology, and also by extrusion at lab scale in order to anticipate their ability to expand under extrusion-cooking. Product porous structure was rather related to the proteins quality than to the fibers content, in the range tested here. In the second stream, wholewheat recipes were added with two types of bran at different levels (20, 40 and 60%, db): wheat bran, rich in arabinoxylans (non-soluble), and oat bran, rich in β-glucans (soluble). Brans were found to act as particles (with supramolecular structure) leading to a lower product porosity due to limitation in cells growth (as assessed by X-ray tomography). Product hardness (measured by compression test) depended on the type of the added brans (insoluble vs. soluble). Unlike bran, the addition of fiber ingredients (e.g. resistant dextrin added from 5 to 20%, db) without any supramolecular structure led to a decrease in porosity due to the thickening of the walls for a constant cells size. The different mechanism of texturization between bran and fiber ingredients may be due to a better mixing of the components of the recipe with the isolated fiber. The final part aimed at characterizing the physical properties of brans after being treated by a thermomechanical process, e.g. extrusion-cooking. In this purpose, bran supramolecular structure was observed by X-ray tomography and their rheological properties were assessed in comparison to unprocessed bran. The decrease in the rheological properties of processed bran may be favorable for their use in products where texture can be more pleasurable for the consumers. In conclusion, using physical and structural characterization of bran and wholegrain products is key to complement the chemical characterization. Chemical structure is needed to link it to fiber functionality (role in physiology such as immune system, stress, gut microbiota, prebiotic effect and satiety, as described by van der Kamp et al., 2010). In complement, physical approach and structure assessment at higher lengthscale is key for the selection of adequate process technology and processing conditions, as well as for the optimization of final product performance (such as texture).status: accepte

Matériaux à base de biopolymères du maïs (élaboration et comportement mécanique)

Les relations entre la structure et les propriétés de produits à base de farine de maïs, texturés par un traitement thermomécanique, ont été abordées en utilisant des matériaux modèles denses fabriqués par (300 J.g-1,T=120ʿC) et thermomoulage (140ʿC), constitués d'amidon et de zéine. La transition vitreuse de ces matériaux est identique à celle de l'amidon pur (MC 12 %). Les matériaux mélanges ont un comportement fragile, ce qui est interprété par la faible adhésion entre les constituants. Pour de faibles teneurs en zéine ( 32 %), elle occupe une phase continue. Les propriétés mécaniques les plus faibles sont observées quand les phases sont co-continues (entre 15 et 32 %). Après expansion par micro-ondes (1000W, 10s), les matériaux denses biphasiques ont des masses volumiques plus élevées que celle du matériau amylacé. La variation des structures et des masses volumiques en fonction du taux de protéines est expliquée par la modification de la viscosité élongationnelle et du module caoutchoutique. L'étude de la structure alvéolaire par tomographie RX suggère que la présence de particules dans la matrice d'amidon modifie le processus de nucléation et de croissance des bulles, pour des températures d'expansion identiques.The structure-properties relationships of corn flour based materials submitted to a thermomechanical treatment were studied by using starch-zein blends dense materials, made by extrusion (300 J.g-1, T = 120ʿC) and thermomoulding (140ʿC). Glass transition temperature of corn flour and starch-zein materials is similar to the one of pure starch (MC 12 %). Blend materials present a fragile behaviour, distinct from the ductile one of starch, which is explained by the weak adhesion between the components. For low zein contents ( 32 %), zein is continuous. The mechanical properties were the lowest in the co-continuous domain (between 15 and 32 % zein). After expansion by microwaves (1000W, 10s), the biphasic dense materials present higher densities than the one of the starchy materials. Structure and densities variations with zein content were explained by the variations of the elongational viscosity and rubbery elastic modulus E'. The observations of the cellular structure by X-ray tomography suggest that particles in the starchy matrix change the nucleation and the mechanism of bubble growth.NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF