Rheological Studies on Starch — Flow Behaviour of Wheat Starch Pastes

Influence of dispersion of fibrillated cellulose on the reinforcement of coated papers

The use of cellulose micro/nanofibrils (CMNFs) as reinforcement paper additive at industrial scale is delayed due to inconsistent results, suggesting a lack of proper consideration of some key parameters. The high influence of fibrillated nanocellulose dispersion has been recently identified as a key parameter for paper bulk reinforcement but it has not been studied for surface coating applications yet. This paper studies the effect of CMNF dispersion degree prior to their addition and during mixing with starch on the reinforcement of paper by coating. Results show that this effect depends on the type of CMNFs since it is related to the surface interactions. For a given formulation, a correlation is observed between the CMNF dispersion and the CMNF/starch mixing agitation with the rheology of the coating formulation which highly affects the paper properties. The optimal dispersion degree is different for each nanocellulose, but the best mechanical properties were always achieved at the lowest viscosity of the coating formulation. In general, the initial state of the nanocellulose 3D network, influences the mixing and smooth application of the coating and affects the reinforcement effect. Therefore, the CMNF industrial implementation in coating formulations will be facilitated by the on-line control of formulations prior to their surface application.

Blends of Cactus Cladode Powder with Corn Starch, Milk Proteins and Gelatin: Rheological Evaluation and Application to a Soup Model

Cactus cladodes (Opuntia ficus-indica) is a valuable source of dietary fibers. In this study, peeled cladode powder was produced by air drying at 40 °C and was characterized for its color, dietary fiber content, and rheological behavior. Cladode powder aqueous suspensions of 3% w/w were prepared and the effect of protein (gelatin, sodium caseinate, and whey protein) or salts (NaCl/CaCl2) on the blend’s viscosity was investigated. Additionally, cladode powder was incorporated in a soup model, aiming at substituting corn starch. Our powder had an appealing green color, but its deterioration was fast when it was exposed to light. A shear-thinning behavior was observed in all cladode-protein mixtures, but viscosity values depended considerably on the protein type and the pH values. Notably, gelatin addition led to higher apparent viscosity of cladode powder at pH 6, suggesting interactions with cladode mucilage, but this effect was reversed at pH 4, below gelatin isoelectric point. The Ostwald-de Waele model successfully correlated viscosity-shear rates data, whereas the Casson model presented a good fit mainly in starch containing systems. Corn starch substitution by cladode powder, in the soup model, led to lower consistency coefficient values. In soups, the logarithmic mixing law was applied at different corn starch: cladode powder ratios to highlight their possible interactions. The values obtained diverged slightly downwards from the logarithmic mixing law. When purified mucilage was added—instead of cladode powder—the samples diverged slightly upwards from the logarithmic mixing law.

Pregelatinized Drum-Dried Wheat Starch of Different Swelling Behavior as Clean-Labeled Oil Replacers in Oil-in-Water Emulsions

Drum-drying results in pregelatinized starch with relatively low starch fragmentation and a great ability to absorb water and swell at room temperature. However, the effect of the degree of cold particle swelling and the thickening potential of drum-dried starch on its suitability as oil replacer in low-fat oil-in-water emulsions has received little attention. In this work, the potential of three pregelatinized drum-dried starches with almost identical molecular structure (as measured by size exclusion chromatography) and Water Binding Capacity (WBC), but different swelling behavior, was investigated to replace up to 60% oil in a mayonnaise-like emulsion system. The microstructure, stability, and rheology of the oil-in-water emulsions were noticeably affected by the substitution of oil with a pregelatinized drum-dried starch paste. Specifically, reduced-fat emulsions presented smaller droplet-size, a higher consistency index and increased emulsion stability, especially against freeze-thaw cycles, compared to the control full-fat mayonnaise. Importantly, the differences in cold swelling behavior (rather than simply assessing WBC) greatly influenced the consistency index and stability of low-fat emulsions, and results showed that drum-dried starch particles with high swelling potential perform better as oil replacers.

Functionality of Native Starches in Food Systems: Cluster Analysis Grouping of Rheological Properties in Different Product Matrices

Industrial application of starch as a texture-forming agent is primarily limited to preparations obtained from waxy corn and potatoes. The main reason behind this is its functionality, which depends mostly on rheological properties. However, in food product matrices, these properties change. Despite the vast amount of information on the rheological properties of various starches, the rational choice of thickener appears to be an extremely difficult task. The aim of the work is to systemize the information on the rheological properties of most popular starches in matrices of various food products, applying principal component and cluster analyses. The investigated material is potato and corn starch of the normal and waxy varieties. Binary mixtures containing salts or sweetening agents, as well as four different food products (ketchup, mayonnaise, pudding, and jelly), are investigated. It was found that compared to normal varieties, waxy starches reveal many similar rheological properties in all investigated models and food systems. Furthermore, in most applications, one waxy starch variety may be substituted by another, with no significant impact on the rheological properties and texture of the food product. Moreover, waxy starch preparations are less altered by the presence of cosolutes, i.e., salts and sugar alcohols. Starch model systems were proven to be useful only for rapid thickener screening tests and cannot be recommended as a final reference for the quality design of food products.

Starch Characteristics Linked to Gluten-Free Products

The increasing prevalence of coeliac disease (CD) and gluten-related disorders has led to increasing consumer demand for gluten-free products with quality characteristics similar to wheat bread. The replacement of gluten in cereal-based products remains a challenge for scientists, due to its unique role in network formation, which entraps air bubbles. When gluten is removed from a flour, starch is the main component left. Starch is used as gelling, thickening, adhesion, moisture-retention, stabilizing, film forming, texturizing and anti-staling ingredient. The extent of these properties varies depending on the starch source. The starches can additionally be modified increasing or decreasing certain properties of the starch, depending on the application. Starch plays an important role in the formulation of bakery products and has an even more important role in gluten-free products. In gluten-free products, starch is incorporated into the food formulation to improve baking characteristics such as the specific volume, colour and crumb structure and texture. This review covers a number of topics relating to starch; including; an overview of common and lesser researched starches; chemical composition; morphology; digestibility; functionality and methods of modification. The emphasis of this review is on starch and its properties with respect to the quality of gluten-free products.

Morphological, Thermal, and Rheological Properties of Starches from Maize Mutants Deficient in Starch Synthase III

Morphological, thermal, and rheological properties of starches from maize mutants deficient in starch synthase III (SSIII) with a common genetic background (W64A) were studied and compared with the wild type. SSIII deficiency reduced granule size of the starches from 16.7 to ∼11 μm (volume-weighted mean). Thermal analysis showed that SSIII deficiency decreased the enthalpy change of starch during gelatinization. Steady shear analysis showed that SSIII deficiency decreased the consistency coefficient and yield stress during steady shearing, whereas additional deficiency in granule-bound starch synthase (GBSS) increased these values. Dynamic oscillatory analysis showed that SSIII deficiency decreased G' at 90 °C during heating and increased it when the paste was cooled to 25 °C at 40 Hz during a frequency sweep. Additional GBSS deficiency further decreased the G'. Structural and compositional bases responsible for these changes in physical properties of the starches are discussed. This study highlighted the relationship between SSIII and some physicochemical properties of maize starch.

Thixotropic properties of waxy potato starch depending on the degree of the granules pasting

This paper presents the rheological instability (thixotropy/antithixotropy) of waxy potato starch (WPS) pastes depending on their concentration (1-5% w/w) and pasting temperature (80, 95 and autoclaved: 121°C, at 0.1MPa). The hysteresis loop, apparent viscosity at constant shear rate as well as the in-shear structural recovery tests with and without pre-shearing were applied. The pastes were also characterized by the granularity profile, molecular weight, polydispersity and optical transmittance. Differences in rheological properties of the pastes prepared at 80 and 95°C as well as autoclaved resulted from degree of granules pasting. At 121 °C dissolution of the granules occurred, while at the lower temperatures only the partial pasting of the granules took place. Pasting temperature of WPS significantly influenced rheological parameters of the resulted pastes which had thixotropic, antithixotropic or mixed thixotropic/antithixotropic behavior. Autoclaved pastes, regardless their concentration were antithixotropic as demonstrated by the areas of hysteresis loops derived from the flow curves signalized by the degree of structure recovery (DSR) which exceeded unity. The apparent viscosity of WPS pasted at 121°C strongly decreased as compared to the samples pasted at lower temperatures. Samples pasted at 80 and 95°C showed both thixotropic and antithixotropic behavior, with a predominance of the latter. The starch concentration played an important role in the formation of the rheological properties of the resulted pastes. Its influence was strongly connected with the degree of the granules pasting, therefore with the temperature of pastes preparation. For the pastes prepared at 80 and 95°C the values of thixotropy and apparent viscosity increased, while the values of DSR decreased with an increase of concentration. In the autoclaved pastes the antithixotropy, DSR and apparent viscosity increased with increasing starch concentration. It was also found that apart from the concentration and temperature also the shear rate influence the thixotropic behavior.

Materials for suspension (semi-solid) electrodes for energy and water technologies

Conducting suspension electrodes for novel flow-assisted electrochemical systems such as grid energy storage, water deionization, and water treatment.

Chemical composition and functional properties of native chestnut starch (Castanea sativa Mill)

Starch isolation methods can change their physico-chemical and functional characteristics hindering the establishment of a starch-food functionality relation. A simple high yield and soft isolation method was applied for chestnut (Castanea sativa Mill) starch consisting in steeping and fruit disintegration in a 25 mM sodium bisulfite solution and purification by sedimentation. Starch integrity, physico-chemical composition, morphology and functional properties were determined, being observed significant differences from previous described methods for chestnut starch isolation. The X-ray pattern was of B-type, with a degree of crystallinity ranging from 51% to 9%, dependent on the starch moisture content. The onset, peak, and conclusion gelatinization temperatures were 57.1°C, 61.9°C and 67.9°C, respectively. Total amylose content was 26.6%, and there was not found any evidence for lipid complexed amylose. Swelling power at 90°C was 19 g/g starch, and the amount of leached amylose was 78% of the total amylose content. Native chestnut starch presents a type B pasting profile similar to corn starch but with a lower gelatinization (56.1°C) and peak viscosity (79.5°C) temperatures, making native chestnut starch a potential technological alternative to corn starch, especially in application where lower processing temperatures are needed.

Role of vacuum steps added before and after steaming treatment of maize starch. Impact on pasting, morphological and rheological properties

Standard maize starch (SMS) was hydrothermally treated by three processes; DV-HMT (Direct Vapor-Heat Moisture Treatment), RP-HMT (Reduced-Pressurized Heat Moisture Treatment) and DIC (in French: Détente Instantanée Contrôlée, instantaneous controlled pressure drop). Impact of processes were studied in order to determine the role of added steps of vacuum before and after treatment of starch by live steam at different pressures (1, 1.5, 2, 2.5 and 3 bar) on morphological, pasting (Brabender) and rheological properties of SMS suspension. The three treatments tend to modify the physical properties of starch on the same way, but the extent of these modifications depends on the process and on the level presure applied. The intensity of modifications follows this order: DIC>RP-HMT>DV-HMT. This was attributed to the presence of the initial vacuum step (DIC and RP-HMT) which intensified the transfer phenomena and to the mechanical effect induced by the abrupt decompression towards vacuum (DIC) leading to weakness of starch granules. The treatments changed the shape and distribution size of granules. The sizes were shifted towards higher values after the treatment due both to the improvement of swelling capacity of granules and to the presence of agglomerates particles of different sizes as confirmed by scanning electron microscopy. The agglomerates glued together by gelatinized granules were favored by the direct contact of starch with steam during the treatments. The results showed for all treatments, a reduction of the consistency coefficient (k) and of the yield stress (τ0) of starch suspensions with increasing of process intensity. For severe conditions (3 bar), no difference between the treatments was observed; a complete fluidization of starch suspensions (the consistencies were too weak to be detected), τ0 vanished and the rheological behavior tended to a Newtonian type. Elastic modulus (G'), measured during gelation at 25°C, decreased dramatically (G'<1 Pa), that revealed the loss of rigidity and disappearance of granular integrity of starch.

The Fractional derivative rheological model and the linear viscoelastic behavior of hydrocolloids

This study was aimed at evaluating the possibility to use the Friedrich-Braun fractional derivative rheological model to assess the viscoelastic properties of xanthan gum with rice starch and sweet potato starch. The Friedrich-Braun fractional derivative rheological model allows to describe viscoelastic properties comprehensively, starting from the behaviour characteristic of purely viscous fluids to the behaviour corresponding to elastic solids. The Friedrich-Braun fractional derivative rheological model has one more virtue which distinguishes it from other models, it allows to determine the relationship between stress and strain and the impact of each of them on viscoelastic properties on the tested material. An analysis of the data described using the Friedrich-Braun fractional derivative rheological model allows to state that all the tested mixtures of starch with xanthan gum form macromolecular gels exhibiting behaviour typical of viscoelastic quasi-solid bodies. The Friedrich-Braun fractional derivative rheological model and 8 rheological parameters of this model allow to determine changes in the structure of the examined starch - xanthan gum mixtures. Similarly important is the possibility to find out the trend and changes going on in this structure as well as their causes.

Effect of storage time on the retrogradation of banana starch extrudate

Starch was isolated from banana starch and the retrogradation phenomenon was studied using diverse techniques, including an enzymatic measurement. Wide-angle X-ray scattering (WAXS) showed that the sample stored for 7 h presented small peaks and when the storage time increased the peaks increased in intensity. The type of diffraction pattern found in banana extrudates is typical of the A-type crystal polymorph. The crystallinity index from the diffractograms, showed a plateau after approximately 20 h of storage. The short-range order measurement with Fourier transform infrared (FTIR) spectroscopy showed that banana starch retrogradation reached a maximum value at approximately 11 h of storage, a value that agrees with the results obtained with differential scanning calorimetry (DSC), because the maximum enthalpy value (approximately 5 J/g) was calculated in the stored sample for 8 h, without changes in the stored samples for more time. Retrograded resistant starch values did not change after 12 h of storage, obtaining the maximum starch retrogradation level. FTIR, DSC, and the enzymatic technique showed the changes at the molecular level in starch during storage; in the case of WAXS, they determine the long-range order that explains the differences found in the starch retrogradation pattern measurement in banana starch.

Hydrolysis of wheat starch and its effect on the falling number procedure: mathematical model

A population balance model was developed for wheat starch hydrolysis to simulate the performance parameters of a viscosity-based device, known as the Falling Number instrument. The instrument is widely used as an indirect means to gauge the level of preharvest sprout activity in cereal grains such as wheat and barley. The model consists of three competing kinetics: starch gelatinization, enzymatic hydrolysis, and enzyme thermal deactivation. Using established principles of starch rheology and fluid mechanics, the model simulates the velocity profiles of the falling stirrer, starch gel viscosity, and the Falling Number readings at various levels of alpha-amylase. Model predictions for the velocity of the stirrer at any time during the downward fall, as well as the prediction of the total time needed for the fall, defined as the Falling Number, were in fair agreement with experimental measurements. There was better agreement between the modeled viscosity and the final viscosity of the starch gel as measured by a precision rheometer than there was with the measured Falling Number.