Rheological behaviour of aqueous systems of tragacanth and guar gums with storage time

Rheological properties of aqueous systems of tragacanth and guar gums at nominal concentration of 10 g/L were evaluated as a function of storage time (up to 47 days) under steady (at shear rates ranging from 0.01 to 1000 s⁻¹) and dynamic (at strain of 5% and angular frequency from 0.1 to 100 rad s⁻¹) shear testing conditions, using a controlled stress rheometer, at 25 °C.     

Surface tension and refractive index of guar and tragacanth gums aqueous dispersions at different polymer concentrations,polymer ratios and temperatures

Surface tension and refractive index of guar gum (GG) (up to 0.97% w/w) and tragacanth gum (TG) (up to 1.41% w/w) aqueous dispersions were determined for systems with only one and both gums (mixtures) (up to 1.25% w/w). Experimental determinations were carried out from 5 to 30 °C for surface tension and from 10 °C to 40 °C for refractive index. For mixtures, the effect of polymer ratio (1:3, 1:1 and 3:1) was analyzed at different total gum concentration and temperature. GG showed lower surface activity and refractive index than TG at the same experimental condition. Models for the estimation of surface tension and refractive index as function of gum concentration and temperature were proposed and satisfactorily tested. Both physical and optical properties, in the tested gum concentration range, allowed the determination of different behaviour for both gums because of a critical aggregation concentration for TG dispersions while this phenomenon was not observed for GG.     

Effects of methylcellulose,xanthan gum and carboxymethylcellulose on thermal properties of batter systems formulated with different flour combinations

The functionalities of hydrocolloid–flour mixtures in terms of the thermal properties of their resulting batter systems were investigated, and the effects of different thermal processes such as cooking–freezing–thawing (CFT) and freezing–cooking (FC) on thermal properties of the various batter systems were determined in this study. Differential scanning calorimetry (DSC) was used to determine thermal property parameters including gelatinization temperature (T_G), total enthalpies of gelatinization (ΔH_G), glass transition temperature (T_g), melting peak temperature (T_m), and total melting enthalpies (ΔH_m). The different thermal processes did not significantly affect either T_G or ΔH_G of batter systems, but they influenced the glass transition behavior and the ΔH_m of batter systems. The thermal processes also showed different effects on the batter systems containing different hydrocolloids such as methylcellulose (MC), carboxymethylcellulose (CMC), and xanthan gum (XG). The hydrocolloids shifted T_G upwards, depressed T_g, and increased T_m of batters. The effect of these hydrocolloids on glass transition temperature was more pronounced in raw samples (FC process) than in cooked samples and increased with increasing levels of CMC and MC used in the formulations. Batters with MC showed increased ΔH_m for all the thermal processes. CMC only showed significant effect on ΔH_m for cooked samples (CFT process). MC and CMC showed more pronounced effects on T_g for raw uncooked rice- and corn flour-based batters than on raw uncooked wheat flour-based batters. However, this special effect was not obvious in the batters containing 0.2% XG.     

Oleogel production based on binary and ternary mixtures of sodium caseinate,xanthan gum,and guar gum: Optimization of hydrocolloids concentration and drying method

We report the optimization of oleogel formulation based on sodium caseinate (CN, 0–4 g/100 g), xanthan gum (XG, 0–1 g/100 g), guar gum (GG, 0–1 g/100 g), and drying method (freeze and oven drier) using response surface methodology to achieve the desired oil binding capacity, textural, and rheological attributes. All the selected responses were successfully fitted by a quadratic model with determination coefficient values higher than .95 with the exception of firmness values which was fitted by linear model. There were considerable increases in all the responses for the samples containing ternary mixtures of protein-gum (CN:XG:GG) as well as binary mixtures (CN:GG and CN:XG) compared to samples containing protein or gums alone due to the synergistic effect of CN and gums on formation of highly ordered and strong gel network. Regression modeling demonstrated that freeze drying method led to significantly greater structure recovery values than those of oven drying method. The best formulation was the freeze dried oleogel containing 4 g/100 g CN, 0.43 g/100 g XG, and 0.98 g/100 g GG. Results showed that fabrication of oleogels with at least 94.5 g/100 g sunflower oil and characteristics similar to industrial shortening is feasible.     

Steady-shear flow of semidilute guar gum solutions with sucrose, glucose and sodium chloride at different temperatures

Steady-shear flow curves of aqueous solutions of guar gum at 0.22% at different temperatures (5-65 °C), guar gum (0.22%) with sugars (sucrose or glucose) at different sugar/water ratio (0.10, 0.20 and 0.40) at 5 °C, guar-sugar (at 0.40 sugar/water ratio) at different temperatures (5-65 °C) and guar gum and guar-sucrose (0.40 sucrose/water ratio) with NaCl (1%) at 5 °C, were determined using a controlled-stress rheometer over a wide range of shear rate (1-1000 s⁻¹). Apparent viscosity increased with decreasing temperature and increasing sugar content independent of sugar type. Synergic effect on apparent viscosity due to sugar addition was found and was correlated with sugar content. Salt addition decreased slightly the apparent viscosity and increased the shear-thinning behaviour of the guar gum solution. Steady-shear flow curves were satisfactorily described by the Cross model. Semi-empirical correlations of Cross model parameters with sugar content and temperature were obtained.     

Comparison of the viscosity of trehalose and sucrose solutions at various temperatures: Effect of guar gum addition

The viscosity of trehalose and sucrose solutions was measured and compared as well as the effect of adding guar gum. Viscosity measurements of trehalose and sucrose solutions were performed in the range 20-45 g/100 g; 0.1 g guar gum/100 g was added in mixed systems. Viscosity of trehalose or sucrose solutions was measured at 20, 27 and 34 °C. Trehalose solutions had always a higher viscosity than sucrose, with the biggest difference (p < 0.001) in the range 30-45 g/100 g. Addition of guar gum revealed a synergistic effect with both disaccharides, particularly for trehalose. Viscosity dependence on temperature was also analyzed by calculating activation energies for all systems studied.     

Rheological behaviour of fresh and frozen potato puree in steady and dynamic shear at different temperatures

Rheological behaviour of natural and commercial potato purees was studied in steady and dynamic shear conditions at sample temperatures ranging from 25–65 °C. Both types of puree were frozen-then-thawed to determine how changes occurring in their structure affected their rheological behaviour. All of the purees presented shear-thinning behaviour with yield stress. Dynamic shear data revealed weak gel-like behaviour in the purees: magnitudes of G were higher than those of G, and both increased with frequency. For fresh natural puree and fresh and frozen/thawed commercial puree, the frequency dependence of G increased, and the frequency dependence of G decreased with sample temperature. Processing weakened the structure of natural puree but resulted in a coarsely aggregated structure in commercial puree. The effect of sample temperature on dynamic parameters was more significant in processed than in fresh purees. The Cox-Merz rule was not applicable to the steady and dynamic shear data on all of the purees. For fresh natural puree, the two types of data conformed to the use of shift factor on frequency, and therefore for this product it would be possible to estimate steady shear data from dynamic shear data, and vice versa. For fresh commercial puree, the relationship between steady and dynamic shear data was non-linear. In both processed purees, the linearity or otherwise of the relationship between viscosities was dependent on sample temperature.     

Rheological behavior of binary and ternary mixtures of polysaccharides in aqueous medium

The rheological behavior of mixtures of xanthan with different galactomannans is examined to evaluate the influence of the structure of galactomannan and that of the mixture composition on the physical properties; the larger synergy is observed for locust bean gum in the presence of xanthan. It is also shown that pH has only a slight influence on the rheology down to pH = 3.59; at lower pH, the G′ modulus decreases significantly.Then, the behavior of xanthan–methylcellulose mixtures is studied, paying particular attention to the storage modulus (G′) of the system, often equated to “gel strength”. The modulus values for direct dissolution of the two polysaccharides in 0.1 M NaCl show that xanthan and methylcellulose are incompatible. The rheological behavior observed is in agreement with DSC results which indicate that no specific interaction between the two polymers exists. However, upon increasing temperature, the modulus of methylcellulose increases substantially between 65 and 70 °C because of physical gelation and dominates the rheology of the mixtures. When temperature is decreased to 37 °C, the clear methylcellulose gel formed remains stable, still giving the main contribution to the overall rheology of the system. Finally, ternary systems are studied when xanthan is mixed with galactomannan and methylcellulose. In this case H-bonds involved in galactomannan–xanthan interaction break when temperature increases causing a decrease in rheological moduli which is then compensated by the gelation of methylcellulose giving an original large increase in moduli for the ternary systems. This can be interpreted as the presence of two independent but interpenetrating networks. The role of pH for these ternary systems is interesting: it is still dominated by methylcellulose and nearly independent of acidic pH (down to pH = 1.8).     

Kinetics of water diffusion in corn grain during the alkaline cooking at different temperatures and calcium hydroxide concentration

The kinetics of corn grains hydration during the nixtamalization process is described for different temperatures, cooking times and Ca(OH)₂ concentrations. Samples were prepared using different cooking times from 0 to 120 min; cooking temperatures of 62, 72, 82, and 92 °C, and Ca(OH)₂ concentrations of 0.0%, 0.8%, 1.0%, and 2.0% related to the mass of corn grains. The fitting of the experimental data to the empirical Michaelis-Menten equation gives a good approach of the hydration process. From the first derivate of the Michaelis-Menten equation the rate of the corn grain hydration can be obtained. This mathematical model predicts the hydration and hydration rate of the corn grains during the cooking time of the nixtamalization process. Furthermore, with this proposed model, we can predict that for short times the rate reaches its maximum, and tends to zero for long times as the saturation of the grain is reached. It is concluded that hydration and hydration rate of white corn grains depends significantly on the temperature and cooking water lime concentration (P < 0.005).     

Concentrated O/W emulsions formulated by binary and ternary mixtures of sodium caseinate,xanthan and guar gums: rheological properties,microstructure, and stability

Food Science and Biotechnology - The effects of xanthan gum (XG) (0, 0.3, 0.6 wt%), guar gum (GG) (0, 0.3, 0.6 wt%) and XG:GG mixtures (0.3–0.3, 0.3–0.6, 0.6–0.3 and 0.6–0.6...     

Pyrraline formation prevented by sodium chloride encapsulated by binary blends of different starches and gum Arabic in aqueous model systems and cookies

Pyrraline is a common advanced glycation end product that is closely associated with various chronic diseases and frequently found in commonly consumed foods. In this study, pyrraline formation prevented by NaCl encapsulated by binary blends of different starches and gum arabic was investigated. The results show that in aqueous model systems with encapsulated NaCl addition, the reduction in pyrraline varied from 5.4% to 26.7%, with simultaneous decreases in the 3-deoxyglucosone (3-DG) concentration, which varied from 13.1% to 41.4%. In cookies with encapsulated NaCl addition, decreases in pyrraline varied from 10.2% to 31.6% accompanied by simultaneous decreases in 3-DG, which varied from 14.2% to 39.4%. However, NaCl encapsulation had no impact on the browning extent in aqueous model systems and on the basic sensory indicators of the manufactured cookies, including colour and salty taste.     

Combined effects of inulin,pectin and guar gum on the quality and stability of partially baked frozen bread

Many attempts have been made to increase the nutritional value of bread by adding dietary fibre. However, fibre enrichment is usually associated with various technological problems. The aim of this study was to optimise the composition of a blend of inulin, pectin and guar gum to enrich the fibre content of partially baked frozen bread without impairing its technological quality. We prepared 20 formulations following a central composite design, together with 4 control breads. Bread enriched with inulin had higher crumb hardness, lower specific volume, shape, moisture content, and crumb cohesiveness than control bread, but improved flavour. Pectin and guar improved moisture content and crumb cohesiveness. There was no interaction between inulin and pectin for any of the bread attributes investigated, while interactions between inulin and guar were small. In contrast, guar and pectin significantly interacted to decrease volume and increase crumb hardness and chewiness. A desirability function method identified the optimised blend as containing 3% inulin, 0.9–1% pectin and 0.3–0.4% guar. Bread enriched with such blend had the following characteristics: specific volume, 4.06 cm³/g; shape, 0.63; crumb hardness, 189 g; resilience, 0.36; cohesiveness, 0.84; chewiness, 169 g; and flavour score, 4.6. Experimental values were close to the predicted ones, with prediction errors below 10% for all attributes tested. The specific volume, crumb hardness and chewiness of the enriched bread were superior to those of unenriched bread. However, undesirable textural changes occurred in the enriched bread during 12 weeks of frozen storage, and these changes strongly depended on the fibre blend composition.     

Thermal and mechanical characteristics of polylactide filaments drawn at different temperatures

Polylactide (PLA) filaments produced by melt spin-drawing in different conditions (draw ratio, temperature of the draw roll) have been studied to demonstrate the influence of the process conditions on the tensile properties of the PLA filaments. Draw ratio varies from 2 to 3.5 and temperature of the draw roll from 80°C to 120°C. The thermal characteristics have been investigated using modulated differential scanning calorimetry (MDSC) and crystallinity using X-Ray Diffraction (XRD). Shrinkage of PLA multifilaments depending on the processing conditions is also investigated. It is demonstrated that the temperature of the draw roll is essential to obtain PLA filaments with optimum properties. At 80°C, the size of the lamellar crystals, measured using DRX, is not the highest. It is necessary to set the temperature of the draw roll at 110°C to obtain thick lamellar crystals. So, in those conditions, the PLA filaments have their optimum mechanical properties.     

不同贮藏温度下鲜切甘薯的生理生化变化

研究了鲜切甘薯在18、10、4℃下贮藏期间生理生化的变化。测定了呼吸强度、总酚含量、MDA、相对电导率、颜色饱和度及亮度,以及PPO、POD、PAL、CAT、SOD的活性。结果表明:切割伤害导致鲜切甘薯呼吸强度增大,引发膜脂过氧化程度加深,MDA含量和相对电导率增加。随着贮藏时间的延长,PAL活性呈现上升趋势,其催化底物总酚也随之增加,与果蔬组织褐变相关的PPO、POD等酶活性也相应增大。抗氧化体系的两种主要酶SOD、CAT变化趋势相近。低温贮藏能够有效地保持鲜切甘薯的感官品质,并能在一定程度上控制生理生化的变化。     

Measurement,prediction and correlation of density,viscosity, surface tension and ultrasonic velocity of different honey types at different temperatures

The aim of this study is to investigate the influence of temperature (20, 25, 30, 35, 40, 45 and 50 °C) and concentration on the evolution of different physical properties (density, viscosity, ultrasonic velocity and surface tension) of honeys. Temperature influences negatively all the physical properties of honey. A good correlation between density, viscosity, ultrasonic velocity and surface tension using linear and polynomial equations was observed. Also a good correlation between density, ultrasonic velocity and surface tension for all the honey samples (R² = 0.954) was obtained. The correlation between surface tension and viscosity was made using the Pelofsky model and an exponential model; the latter one describes better the correlation between surface tension and viscosity.     

Changes in physical and thermo-physical properties of sugarcane, palmyra-palm and date-palm juices at different concentration of sugar

The process of making jaggery from three natural juices by boiling could be divided into three zones: rise in temperature to boiling (Zone I), slow rise in both boiling temperature and total soluble solids (TSS) (Zone II) followed by rapid rise in boiling temperature with concomitant increase in viscosity and TSS (Zone III). The juice samples in Zone III exhibited changes in boiling temperature, viscosity and TSS from 105 to 121 °C, 4.5 to 988 mPa s and 54.6 to 81.9 (% w/w) for sugarcane (Saccharum officinarum); from 104 to120 °C, 41.6 to 559 mPa s and 46 to 81 (% w/w) for palmyra-palm (Borassus flabellifer L.); and from 103 to 121 °C, 22.9 to 417 mPa s and 51 to 81 (% w/w) for date-palm (Phoenix sylvestris L.). Colour change was rapid in Zone III. Difference in colour among these jaggery samples might be attributed to amount of reducing sugars present initially and respective changes in properties during juice concentration.     

Changes in mass transfer,thermal and physicochemical properties during nixtamalization of corn with and without agitation at different temperatures

White dent corn was nixtamalized in a Ca(OH)₂ [1.2% (w/v)] solution, at a 1:3 corn/water ratio, at 70, 80, 90 and 100 °C for 1 h, with and without mechanical agitation. After cooking the nixtamalized grains were steeped for 48 h. During cooking, kinetics of soluble and suspended solids and total sugar were determined, while that in the grain was determined the pericarp removed. During steeping, water and calcium absorption kinetics were determined in grains and apparent diffusion coefficients were calculated using Fick’s second law. Changes in thermal properties were determined. Cooking temperature and agitation had significant effects on the chemical and physical properties of grains and nejayote. Soluble and suspended solids and total sugar in nejayote showed a linear trend over time for different temperatures, while pericarp removal during both cooking and steeping reached over 90%. Cooking temperature had a significant effect on water and calcium absorption in grains. Calcium and water diffusion were described adequately using Fick’s model. Water and calcium diffusion coefficients values were 2.07–3.52 × 10⁻¹⁰ m² s⁻¹ and of 0.332–1.43 × 10⁻¹⁰ m² s⁻¹, respectively. Gelatinization temperature and enthalpy were significantly influenced by the temperature and time of the cooking.     

Multiplication of Salmonella enteritidis in egg yolks after inoculation outside, on, and inside vitelline membranes and storage at different temperatures

Prompt refrigeration to restrict bacterial growth is important for reducing eggborne transmission of Salmonella enterica serovar Enteritidis (SE). The nutrient-rich yolk interior is a relatively infrequent location for initial SE deposition in eggs, but migration across the vitelline membrane can result in rapid bacterial multiplication during storage at warm temperatures. The objective of the present study was to measure the multiplication of SE in yolks after introduction at three different locations and subsequent storage at a range of temperatures. Using an in vitro egg contamination model, approximately 100 CFU of SE was inoculated either inside yolks, onto the exterior surface of vitelline membranes, or into the adjacent albumen. After storage of samples from each inoculation group at 10, 15, 20, and 25°C for 24 h, SE was enumerated in yolks. For all three inoculation locations, the final SE levels in yolks increased significantly with increasing storage temperatures. At all storage temperatures, significant differences in SE multiplication were observed between inoculation sites (yolk inoculation>vitelline membrane inoculation>albumen inoculation). At 25°C, final log concentrations of 7.759 CFU of SE per ml (yolk inoculation), 2.014 CFU/ml (vitelline membrane inoculation), and 0.757 CFU/ml (albumen inoculation) were attained in yolks after storage. These results demonstrate that, even when the initial site of SE deposition is outside the egg yolk, substantial multiplication supported by yolk nutrients can occur during the first day of storage and the risk of bacterial growth increases at higher ambient storage temperatures.