Donatella Peressini

Starch–methylcellulose based edible films: rheological properties of film-forming dispersions

Abstract The rheological properties of edible film-forming dispersions containing corn starch, methylcellulose (MC) and glycerol were studied using oscillatory and steady shear flow tests. The combined effects of glycerol content and blending levels of MC with starch on the rheological properties of dispersion were evaluated. The flow curves showed shear-thinning behaviour. Mechanical spectra and Cox–Merz superposition of steady-shear viscosity and dynamic viscosity were consistent with polymer solutions containing topological entanglement interactions of chains. Dispersion stability results showed total recovery of the viscoelastic properties of dispersions subject to high strains, as expected for entangled polymers. MC was the main factor influencing apparent viscosity and viscoelastic properties.

Rheological characterization of traditional and light mayonnaises

Abstract Mayonnaises are oil in water emulsions with a texture that is particularly appreciated by consumers. The actual nutritional trend towards low-calorie foods has increased the interest in fat substitutes without altering the consistency of the product. From this point of view rheological properties may give a quantitative contribution to texture characterization and control when using different formulations. The rheological approach has been applied to typical commercial normal and light mayonnaises with a fat content ranging from 76 to 48%. These materials have shown a viscoelastic behaviour that was measured by means of both oscillatory and creep-recovery tests. The storage modulus, the compliance and the yield stress were found to increase when increasing the fat content. A modified Bolhin theory was used to relate structural parameters to rheological dynamical measurements. Thus the emulsion stability was quantified by means of a pseudoplastic-coordination number (z) and the value of G′ at 1 Hz . From the creep test the value of the yield stress was determined and in the case of the light mayonnaise was very close to a normal emulsion whereas the corresponding viscoelastic properties were very different. This implies that to reproduce an assumed texture, it is necessary to perform all the tests outlined.

Synergistic effect of different dietary fibres in pasta on in vitro starch digestion

Pasta is traditionally manufactured using only durum wheat semolina, but it is possible to incorporate other flours or ingredients into pasta in order to increase its nutritional value to the consumer, compared to conventional pasta. For this reason, pasta was prepared substituting durum wheat semolina with 15% of enriched dietary fibre flours (Glucagel, inulin Raftiline® HPX, inulin Raftiline® GR, psyllium and oat). Moreover, all dietary fibres (excluded Glucagel) were added in combination in order to evaluate their possible antagonistic or synergic effect on predicted glycaemic response. In general, all enriched dietary fibre pasta sample showed a significant decrease (except for pasta containing a combination of 7.5% inulin Raftiline® GR and 7.5% oat bran flour) in reducing sugars released and standardised AUC values compared to control pasta. However, this study showed that the combination of dietary fibres in pasta formulation led to an antagonistic effect on the predicted glycaemic response.

Effect of TiO2 photocatalytic activity in a HDPE-based food packaging on the structural and microbiological stability of a short-ripened cheese.

A high density polyethylene (HDPE)/calcium carbonate (CaCO(3)) film containing TiO(2) was prepared via blown film extrusion process. The photocatalytic properties of this film were evaluated by voltammetric, UV-Vis spectrophotometric and gas chromatographic measurements following the decomposition rate of suitably selected molecular probes, such as 4-hydroxybenzoic acid and methylene blue. The film containing 1% w/w of TiO(2) displayed a profitable and reproducible photoinduced degradation activity towards target organic compounds. The effect of packaging photocatalytic activity on the structural and microbiological stability of a short-ripened cheese was studied. Cheese structure was assessed by dynamic, small deformation rheological tests. A container consisting of a multilayer material, where the layer brought in contact with the food, made from the HDPE+CaCO(3)+TiO(2) composite matrix, was able to provide a greater maintenance of the original cheese structure than a rigid container currently used, mainly due to the inhibition of lactic acid bacteria and coliforms.

Study of the Maillard reaction in model systems under conditions related to the industrial process of pasta thermal VHT treatment

Non-enzymatic browning (NEB) due to the Maillard reaction (MR) was studied in a closed starch/glucose/lysine model system (20 g kg−1 glucose, 10 g kg−1 lysine) in order to analyse conditions favouring reactivity during an industrial process of pasta VHT (very high temperature) thermal treatment. The closed model pastes gave data on the NEB progress during the pasta drying cycle as a function of temperature, time and water activity (aw). Indicators such as headspace CO 2 , optical density and colour showed an increase of MR as the initial aw increased from 0.50 to 0.91. During the initial stages of drying, a combination of high temperatures and high aw led to the most likely conditions for NEB. © 1999 Society of Chemical Industry

Filled-snacks production by co-extrusion-cooking. Part 3. A rheological-based method to compare filler processing properties

Abstract Filled snacks are new industrial co-extruded products made by a dough shell and an internal filler constituted by salty or sweet cream. Due to different rheological characteristics of fillers and dough, it is difficult to choose operational variables capable of guaranteeing a complete filling. This work aims to determine the optimal rheological properties of both filler and dough to make an optimal product without undesired voids. A typical dough and several fillers have been considered and rheologically characterised by means of dynamic oscillation, steady shear flow and creep tests. A dynamic temperature ramp test at 1 Hz was performed to determine temperature dependency of the tested material. A time–temperature shifting technique based on a modification of the Cox–Merz rule and on weak gel model was applied to extend the flow curve range and to overcome temperature experimental difficulties. The obtained data, expressed by a power law correlation, were inserted in a numerical algorithm previously developed, and the internal swelling of the dough followed by a recovery was computed during mixed flow inside the extrusion head. It was suggested that a greater recovery implies a better filling capability because the filler may follow the dough during swelling. Simulations indicated that a complete filling was obtained only for the materials exhibiting a quite stable network during the flow. The experimental results obtained by preparing different industrial filled snacks confirmed the simulative predictions. Quantification of the network shear stability was determined by comparing the loss modulus (G″) and shear viscosity (η) values. In particular G″ versus frequency and η versus shear rate were fitted by a power law model and the best fillers must present a ratio between their exponents close to 1.

Filled snack production by coextrusion-cooking: 1. Rheological modelling of the process

Filled snack production has been considered and modelled by considering the rheological properties of the different components. The possibility of inserting the filler directly inside the extruder head allows post-extrusion swelling to decrease thus increasing the product quality. To find the optimum position of the filler nozzle with respect to the head extruder orifice, a rheological model was developed by assuming power law behaviour for both dough and filler tangential stresses and a single relaxation time mechanism for the normal stresses shown by dough. The internal swelling was computed numerically for typical industrial conditions and a validation of the model was done by varying around the mass flow rate of dough, the flow indexes of the two components, the consistency index of dough, and finally some geometrical conditions. It was found that the system did not depend too much on the geometry, but is very sensitive to dough and filler rheological properties. The simulation predictions appeared to be in agreement with industrial expectations, predicting a short distance between nozzle and extruder head.

Release Behavior and Stability of Encapsulated d-Limonene from Emulsion-Based Edible Films

Edible films may act as carriers of active molecules, such as flavors. This possibility confers to them the status of active packaging. Two different film-forming biopolymers, gluten and ι-carrageenans, have been compared. D-Limonene was added to the two film formulations, and its release kinetics from emulsion-based edible films was assessed with HS-SPME. Results obtained for edible films were compared with D-limonene released from the fatty matrix called Grindsted Barrier System 2000 (GBS). Comparing ι-carrageenans with gluten-emulsified film, the latter showed more interesting encapsulating properties: in fact, D-limonene was retained by gluten film during the process needed for film preparation, and it was released gradually during analysis time. D-Limonene did not show great affinity to ι-carrageenans film, maybe due to high aroma compound hydrophobicity. Carvone release from the three different matrices was also measured to verify the effect of oxygen barrier performances of edible films to prevent D-limonene oxidation. Further investigations were carried out by FT-IR and liquid permeability measurements. Gluten film seemed to better protect D-limonene from oxidation. Gluten-based edible films represent an interesting opportunity as active packaging: they could retain and release aroma compounds gradually, showing different mechanical and nutritional properties from those of lipid-based ingredients.

Filled snack production by co-extrusion-cooking: 2. Effect of processing on cereal mixtures

Filled snack production has been considered from several point of views. In this work, the effect of the operational variables on the cereal mixture constituting the external part of this product has been studied. A typical flour blend was characterised and used in a previous developed model to simulate the extrusion conditions and to show process damage. Chemical and rheological methods are proposed as experimental techniques capable of measuring the damage induced by the process. The link between chemical contents and mechanical damage was proposed on the basis of the thermal history and of the mechanical power input. The simulation results obtained by a new proposed extrusion model applied to a real twin co-extruder, made it possible to predict damage such as the lysine decrease, and to show the effect of different screw speeds. It appeared that the computed results are in an acceptable agreement with industrial evidence.

Relation between ultrasonic properties, rheology and baking quality for bread doughs of widely differing formulation

BACKGROUND The objective was to evaluate whether an ultrasonic reflectance technique has predictive capacity for breadmaking performance of doughs made under a wide range of formulation conditions. Two flours of contrasting dough strength augmented with different levels of ingredients (inulin, oil, emulsifier or salt) were used to produce different bread doughs with a wide range of properties. Breadmaking performance was evaluated by conventional large-strain rheological tests on the dough and by assessment of loaf quality. The ultrasound tests were performed with a broadband reflectance technique in the frequency range of 0.3-6 MHz. RESULTS Principal component analysis showed that ultrasonic attenuation and phase velocity at frequencies between 0.3 and 3 MHz are good predictors for rheological and bread scoring characteristics. CONCLUSIONS Ultrasonic parameters had predictive capacity for breadmaking performance for a wide range of dough formulations. Lower frequency attenuation coefficients correlated well with conventional quality indices of both the dough and the bread.