Stress relaxation behaviour of high acyl gellan gels

Stress relaxation behaviour of high acyl gellan gels has been investigated, and data were fitted successfully by a seven elements empirical model and a four term modified Maxwell model with three fixed relaxation times (20, 200 and 2000 s). In addition, the effect of testing parameters on stress relaxation characteristics and the relationship between those characteristics and intrinsic gel properties were studied. High acyl gellan gels were tested in stress relaxation with different cross‐head speeds (0.1–10 mm s^?1) to applied strains (3–30%). The results showed that the cross‐head speed had little effect on stress relaxation behaviour of gels. With increasing the applied strain, the initial stress and the equilibrium stress increased. The equilibrium stresses from relaxation measurement were positively related to the hardness from TPA tests (R² = 0.991). Relaxation appeared to be associated with the shifting of cross‐links in the gel matrix.     

Assignation of Sweet Cherry Selections to 3 Taste Groupings Based on Perceived Sweetness and Sourness

ABSTRACT: Providing consumers with basic taste properties of sweet cherries at point of purchase would allow consumers to make purchase decisions based on fruit's intrinsic sensory attributes. The objective of this study was to develop a model to predict taste-grouping assignation of cherries into the following categories: (1) low sweetness/high sourness, (2) balance between sweetness and sourness, and (3) high sweetness/low sourness. A sensory panel (n = 10) was trained to recognize sweetness and sourness in 5 cultivars of sweet cherries and assign a taste grouping based on the perceived balance of sweetness and sourness. Four of these same cultivars were then evaluated for sweetness and sourness by a consumer panel (n = 117) and instrumentally for titratable acidity (TA) and soluble solids concentration (SSC). Results showed that for 3 of the 4 cherry cultivars, the sweetness/sourness balance of the cherries was not significantly different as evaluated instrumentally or by the trained panel. However, the balance determined by the consumer and the trained panel was different for 3 of the 4 cherry cultivars (P < 0.05). Based on trained panel perceived sweetness and sourness, a multinomial logit model was developed to predict the assignation of cherry taste grouping. The likelihood of group assignment depended on both the perceived sweetness and sourness of the cherry, with taste groupings agreed upon for 3 of 5 sweet cherry cultivars. As previous studies have indicated a positive relationship between cherry sweetness and sourness to consumer acceptance, these groupings show promise for assisting consumers in cherry selection at the point of purchase. Practical Applications: The prediction models proposed in this study suggest that both sweetness and sourness are important in the cherry characterization and the ratio between the 2 attributes may be appropriate for making taste-grouping assignments. These groupings may then be used to provide additional sensory information to consumers to assist them in cherry selection at the point of purchase.     

Modelling of rheological characteristics of various spaghetti types

Spaghetti enriched with resistant starch was produced to increase the dietary fibre intake of consumers. In the product base it was compared to bran and control spaghetti regarding to viscoelastic properties. Viscoelastic properties were tested by relaxation and creep tests by using TA-XT2i texture analyser. The viscoelastic properties gave structural information. Relaxation and creep data were analysed by generalized Maxwell (two- and three-termed), Peleg & Normand, Burgers and Peleg models, respectively. For relaxation three-termed Maxwell and for creep behaviour Burgers model represented viscoelastic behaviour satisfactorily. In general, bran spaghetti was found to have the lowest elasticity. All the samples started to loose their elasticity as cooking time proceeded and it became easy to deform them. Instrumentally, spaghetti with resistant starch was found to be better than bran enriched spaghetti.     

Prediction of viscoelastic properties of peanut-based 3D printable food ink

Viscoelastic properties of 3D printable peanut-based food ink were investigated using frequency sweep and relaxation test. The incorporation of xanthan gum (XG) improved the shear thinning behavior (n value ranging from 0.139 to 0.261) and lowered the η*, G′, and G′′ values, thus making food ink 3D printable. The addition of XG also caused a downward shift in the relaxation curve. This study evaluates the possibility of an artificial neural network (ANN) approach as a substitute for the Maxwell three-element and Peleg model for predicting the viscoelastic behavior of food ink. The results revealed that all three models accurately predicted the decay forces. The inclusion of XG decreased the hardness and enhanced the cohesiveness, so enabling the 3D printing of food ink. The hardness was highly positively correlated with Maxwell model parameters F_e, F₁, F₂, F_3, and Peleg constant k₂ (0.57) and negatively correlated with k₁ (−0.76).     

Mass transfer evaluation of ultrasonic osmotic dehydration of cherry tomatoes in sucrose and salt solutions

In order to elaborate dehydration and osmotic equilibrium characteristics of cherry tomatoes and to analyse the applicability of Peleg model in prediction of equilibrium moisture content and the methodology of Crank’s solution to Fick’s diffusion law in calculation of effective diffusivity, cherry tomatoes were osmotically treated in ternary solution (water, sucrose and NaCl) with or without ultrasound at 30 °C. Results indicated that, a time cumulative effect of ultrasound occurred about 30 min for water loss (WL), while for sugar gain it happened after 45 min, which made the dehydration efficiency index best at the ultrasonic power of 150 W for 40 min. As a function of salt content, the equilibrium WL followed well the first order exponential decay model, and the equilibrium salt content followed well the second order polynomial. A great relative error (29.13%) between the practical determination and the predicted value indicated that Peleg model was not suitable for prediction of equilibrium moisture content. A great truncation error (865%) occurred when moisture effective diffusivity (6.66 × 10^?9 m² s^?1) was calculated with Crank’s solution to Fick’s diffusion law by letting n = 1 as compared to that (0.77 × 10^?9 m² s^?1) by letting n = 100.     

Stress relaxation/creep compliance behaviour of kashar cheese: Scanning electron microscopy observations

In this study, uniaxial and creep analyses were used to characterise stress relaxation and creep compliance behaviour of kashar cheese as a function of different compression (1.5, 3.0, 4.5, 6.0 and 7.5 mm) and stress (12.25, 24.50, 36.75, 49.00 and 61.25 kPa) levels. For this purpose, mechanical simulation models, namely generalised Maxwell, Nussinovitch, Peleg and Burger models were used to simulate the viscoelastic behaviour of kashar cheese as a function of different compression and stress levels. The results revealed that the compression levels could remarkably change internal structure and deformation properties of kashar cheese. Stress relaxation test demonstrated that kashar cheese showed more elastic behaviour, namely higher resistance to deformation at higher compression levels. Creep tests showed that rigidity of kashar cheese decreased as the stress level applied increased. Scanning electron microscopy (SEM) images showed that compression resulted in a less homogeneous protein matrix, an interrupted casein/fat network, and destroyed fat globules by forcing them to exude from the cheese surface. These results should be useful for dairy industry.     

Stress relaxation of reconstituted cassava dough

The viscoelastic characteristics of reconstituted cassava dough were evaluated using a stress-relaxation test. Cassava parenchyma (peeled root) processed under different cooking conditions and left at either −5 or −20 °C for 24 h was used to obtain flour, which was reconstituted into dough. Two stress-relaxation models (Maxwell two-termed and Peleg) were fitted to experimental data. Both models were valid for quantifying the relaxation behaviour; but the Maxwell model was better to predict experimental data. Most dough rheological attributes depend on the cooking method and the storage temperature. Dough samples made with flour from parenchyma boiled and left at −20 °C for 24 h had higher values of elasticity moduli, higher viscosity values and lower values of Peleg constants.     

Stress relaxation characteristics of low-fat chicken sausages made in Argentina

Low-fat sausages were prepared with fresh chicken breast meat and formulated with different levels of added fat, whey protein concentrate, and hydrocolloids (xanthan and guar gums) to study the effect of composition on the stress relaxation behavior of the products. Stress relaxation experiments were conducted on precooked sausages at 25°C. Generalized Maxwell and empirical Peleg models were used to predict the stress relaxation behavior of the material. A model with seven maxwellian elements in parallel with a pure elastic element showed a very good agreement with experimental data. Results show that the proposed model satisfactorily fits the experimental data better than Peleg's model or Maxwell models with less elements. The relaxation time distribution functions were obtained. The characteristic relaxation time was shorter (2500s) for the formulations with no added fat which produced a less elastic product while the sausages with added fat showed longer characteristic relaxation time (5000s). The stress relaxation experiment differentiated the viscoelastic nature of different formulations due to reduction of fat content.     

Physicochemical Characteristics,Antioxidant Activity,Organic Acid and Sugar Contents of 12 Sweet Cherry (Prunus Avium L.) Cultivars Grown in Turkey

Physical characteristics, antioxidant activity and chemical constituents of 12 cultivars (Prunus avium L.) of sweet cherry (Belge, Bing, Dalbasti, Durona di Cesena, Lambert, Merton Late, Starks Gold, Summit, Sweetheart, Van, Vista, and 0–900 Ziraat) were investigated. Significant differences (P < 0.05) were observed among tested cultivars for pH, total soluble solid, hardness, color parameters, antioxidant activities and pomological measurements (P < 0.05). The color parameters were important tools for the determination of fruit maturity and anthocyanin contents. Belge cultivar showed the highest levels of total phenolic and anthocyanin, while Starks Gold contained the lowest level of anthocyanins. The darker cultivars, measured by ABTS^+?, DPPH^? and FRAP, exhibited higher antioxidant activities than the lighter ones. Bing (42.78 g/kg) and Sweetheart (40.53 g/kg) cultivars contained higher levels of malic acid, which was the most intense organic acid in sweet cherries. Four different sugars were observed in the samples and their concentrations ordered as glucose > fructose >> sucrose > xylose. Sugar alcohol in the cherries was represented by sorbitol (more than 90%) and its concentration varied between 13.93 and 27.12 g/kg. As a result significant differences were observed among the physical properties and chemical constituents of the cherry cultivars.     

Mechanical strength and rheological behaviour of barley kernels

Basic mechanical and rheological properties (stress relaxation behaviour) of single barley kernels under uni-axial compression were studied. The mechanical properties studied were the modulus of elasticity, yield and ultimate compressive strength, and the modulus of toughness as influenced by the moisture content. The stress relaxation experiments also included the effect of deformation rates and strain levels.
Results indicated that with an increase in moisture content, the strength of the barley kernels decreased while the energy required to cause rupture in the kernel increased initially and then decreased. The stress relaxation behaviour of barley kernels was described by a threeterm Maxwell model with a Maximum Relative Difference (MRD) ≤5%, when compared with one- and two-term Maxwell models. The elastic component (E¹) and relaxation time constant (τ¹) of the first term of the three-term Maxwell model decreased linearly with increase in moisture content. Of the different variables studied, moisture content had a significant influence on both of these parameters.     

Viscoelastic behavior of persimmons dried at constant air temperature

The viscoelastic behavior of dried persimmons at different air-drying temperatures and velocities was evaluated. Air temperatures and velocities were varied according to a second-order central composite design, with temperature ranging from 40°C to 70°C and air velocity from 0.8 to 2.0 m/s. After drying, persimmons were equilibrated at four different water activities: 0.432, 0.576, 0.625 and 0.751. The rheological behavior of dried and conditioned persimmons was studied under uniaxial compression–relaxation tests. Three different rheological models were fitted to the experimental relaxation curves: Maxwell, Generalized Maxwell and Peleg and Normand. Based on the root mean square of residuals, the Generalized Maxwell model showed the best fit and a regression analysis was applied to obtain response surfaces for the model parameters. The dependence of the rheological properties on water activity was also analysed. Results showed that only the linear effect of air temperature was significant at a 5% level on the equilibrium stress and relaxation times. In a general way, these parameters increased with increasing air temperature and decreasing water activity.     

Rheological properties of cereal starch gels and Mesona Blumes gum mixtures

The effect of Mesona Blumes gum (MBG) was examined on steady and dynamic shear of MBG/rice starch and MBG/wheat starch gels. In addition, stress relaxation and creep tests were performed for two types of cereal starch gels. The flow curves of both MBG/starch gels exhibited pseudoplastic behavior at shear rates between 0.01 and 10 s⁻¹, and the data were fitted into the power law model (R² = 0.91–0.98). Dynamic mechanical spectrum showed that all gels were strong gels in frequency between 0.1 and 10 Hz. Stress relaxation data at different strains indicated a strain‐softening phenomenon for both gels. Data were fitted into Maxwell model (R² = 0.91–0.98). Creep curves were conducted at the shear stress 6.4 Pa within linear viscoelastic region of both MBG/starch gels. Data were fitted into Burgers model (R² = 0.91–0.98). Apparent viscosity η, storage moduli G′, equilibrium stress relaxation modulus G_e and zero apparent viscosity η₀ of MBG/rice starch gels decreased in the following order: 6/0>6/0.5>6/0.35>6/0.1 (starch/gum w/w). Whereas η, G′, G_e, and η₀ of MBG/wheat starch gels increased gradually along side the increase of MBG contents. The stress relaxation time λ of MBG/rice starch gels increased in the following order: 6/0<6/0.5<6/0.35<6/0.1 (starch/gum w/w) while λ of MBG/wheat starch gels decreased gradually with the increase of MBG level. The influence of MBG on two examined cereal starch is totally opposite.     

Physical and viscoelastic properties of carrots during drying

It is essential to understand the physical and mechanical properties of a product since these properties affect the structure, texture, and ultimately consumer acceptance. The effect of drying conditions on dynamic viscoelastic properties, stress relaxation function and creep compliance, and physical properties, such as moisture distribution, color parameters, and shrinkage, was studied. An increase in drying temperature and duration resulted in a decrease in moisture content and volume, which were highly correlated (R = .988). Water evaporation followed the falling rate period, demonstrating that the water transport was limited by internal resistances. The decomposition of carotenoids led to a decrease in magnitude of color parameters (L, a, and b), between 30.1% and 51.6% with 4 hr drying. It was observed that the material shrinkage and moisture content highly affected the mechanical properties; increased stress relaxation modulus and decreased creep compliance values of the sample. The creep behavior, expressed with Burger's model (R² ≥ .986), was highly dependent on moisture content. The linear viscoelastic region of carrots was found to be at strains lower than 3%. The three-element Maxwell model well fitted to describe the viscoelastic behavior of carrots (R² ≥ .999, RMSE ≤ 2.08 × 10⁻⁴). The storage moduli (G′) were higher than loss moduli (G″), indicating that samples presented solid-like behavior. The findings can be used to improve the textural attributes of carrots and carrot-based products.     

Evaluation of chemical constituents and antioxidant activity of sweet cherry (Prunus avium L.) cultivars

This research was undertaken to evaluate the sugars, organic acids, phenolic compositions and antioxidant capacities of sweet cherry cultivars (Van, Noir de Guben, Larian and 0‐900 Ziraat) grown in Turkey. High‐performance liquid chromatographic methods were used to identify and quantify four sugars (sucrose, glucose, fructose and sorbitol) and four organic acids (malic, citric, shikimic, and fumaric acid). The major organic acid was found as malic acid (8.54–10.02 g kg^?1 of FW). With regard to sugars, glucose was present in the largest amounts (44.71–48.31 g kg^?1 of FW) for sweet cherry cultivars. The sum of sugars ranged from 103.87 (Larian) to 113.13 g kg^?1 of FW (0‐900 Ziraat) and that of organic acids from 12.01 (0‐900 Ziraat) to 14.17 g kg^?1 of FW (Noir de Guben). A total of eleven phenolic compounds were identified and quantified in sweet cherry cultivars, including hydroxycinnamic acids (3), anthocyanins (5), flavan‐3‐ols (2) and flavonol (1) compounds. Total phenolic contents ranged from 88.72 (Van) to 239.54 (Noir de Guben) mg/100 g of FW, while antioxidant activities ranged from 2.02 to 7.75 μm Trolox equivalents g^?1 of FW.     

Dynamics of Changes in Viscoelastic Properties of a Tofu During Frying

The viscoelastic properties of a tofu were characterized using the stress relaxation test after deep-fat frying at 147–172°C for 0 to 5 minutes. The results were expressed with a model with two Maxwell elements and a residual spring in parallel. Each elastic modulus and relaxation time followed zero order reaction kinetics. The Arrhenius temperature dependency was applied for the modeling of reaction rate constant, k. The activation energies for the viscoelastic properties were 1.00 × 10⁵ ? 1.49 × 10⁵ J/mol. There was a good agreement between the measured and computed data (R² = 0.976 ? 0.988).     

Temperature dependent hydration kinetics of Cicer arietinum splits

This study on hydration kinetics of chickpea (Cicer arietinum) in water at different temperature was conducted to assess the adequacy of models to describe absorption phenomena during soaking. The diffusion coefficient values calculated using two different forms of Fick’s second law were all of the order of 10^?9 m²/s. Peleg, Weibull and Exponential models were fitted to the soaked sample data. Adequacy of models was determined using coefficient of determination (R²), root mean square error (RMSE) and chi-square (χ²). The variation in moisture content of chickpea splits at different temperatures during hydration depicts an initial high rate of moisture absorption in the primary phase followed by slower absorption during the relaxation or secondary phase of hydration. The linearity in the curve during the initial stages of moisture absorption showed the uptake process was diffusion controlled. The results of non-linear regression analysis of fitting the models revealed that the Peleg model described the process of hydration better than did the other two models with R² ? 99.06%, RMSE ? 2.95 and χ² ? 0.001 for all the fitted models. Temperature had a positive and significant effect on the water absorption capacities and absorption was an endothermic process.     

Non-Destructive Estimation of Mechanical and Chemical Properties of Persimmons by Ultrasonic Spectroscopy

Fruit properties, including ripeness, are still being measured destructively in most countries. Recently, an increased attention has been given to non-destructive methods, such as ultrasonic techniques, for quality assessment of food commodities. The aim of this study was to evaluate the feasibility of ultrasonic spectroscopy to monitor the changes of mechanical properties (rupture force and modulus of elasticity) and chemical properties (soluble solids content) in two cultivars of persimmons (Karaj and Shomali) during 3 weeks of storage. Samples’ ultrasonic properties such as ultrasonic velocity and attenuation coefficient were analyzed with transducers, and their textural properties were obtained using destructive compression test and their refractometric properties were measured from its fresh-squeezed juice in laboratory. Mechanical and chemical properties were statistically modeled from ultrasonic parameters. The results showed that our proposed model could predict persimmons’ mechanical and chemical properties well, i.e., rupture force (R² = 0.893/0.837; RMSE = 3.683/3.849 for Shomali and Karaj cultivars, respectively), modulus of elasticity (R² = 0.826/0.861; RMSE = 0.231/0.217 for Shomali and Karaj cultivars, respectively) and soluble solids content (R² = 0.931/0.987; RMSE = 0.519/0.851 for Shomali and Karaj cultivars, respectively).     

Comparison of Peleg and Azuara et al. models in the modeling mass transfer during pile salting of goat sheets

Application of the Peleg and Azuara et al. models for describing mass transfer during pile salting of goat sheets using different mixtures of NaCl, KCl, CaCl₂ and MgCl₂ was investigated The high coefficient of determination (R² > 0.97 and R² > 0.95 for Peleg and Azuara et al. models, respectively) and the modulus of mean relative errors (MRE < 10% for both models) indicated the acceptability of both Peleg and Azuara et al. models for predicting both moisture loss and salt uptake. The equilibrium moisture and salt contents were estimated using Peleg rate constants and Azuara et al. model parameters. Equilibrium moisture (x_w) and salt contents (x_s) varied from 0.522 to 0.860 g water/g db and from 0.311 to 0.352 g NaCl/g db respectively. Multiple comparison of means showed that x_w and x_s predicted by the Peleg model were lower than those estimated by the Azuara et al. model. The values differed by 1.86–13.6% for x_w and by 1.13–10.57% for x_s.     

Variety–compound–quality relationship of 12 sweet cherry varieties by HPLC-chemometric analysis

In this study, 12 sweet cherry varieties grown in Shandong (China) were compared based on their quality indices and high performance liquid chromatography (HPLC) fingerprints, along with chemometric discrimination by similarity analysis, hierarchical clustering analysis and principal component analysis. The established sample preparation and analysis methods represented a non-targeted and practical approach with reasonably high sensitivity, precision, stability and reproducibility, providing comprehensive evaluation of the quality of sweet cherries while allowing the tentative classification of cherry varieties. The results revealed the variety-dependent nature of the HPLC fingerprints of sweet cherries, and the fruit groupings according to their chemical composition (three groups based on phenolics, or four groups if organic acids were of main interest). All cherries were rich in organic acids, hydroxycinnamic acids, hydroxybenzoic acids, anthocyanins, flavan-3-ols, flavonols and other flavonoids, with malic acid, cyanidin-3-O-rutinoside, p-coumaroylquinic acid, neochlorogenic acid and rutin as the characteristic compounds (in the range of 0.57–1.80, 0.002–1.390, 0.370–3.083, 0.38–1.87 and 0.020–0.167 mg g⁻¹ fruit fresh weight, respectively). While anthocyanin and flavonol patterns were useful for a varietal assignment of cherries, cyanidin-3-O-rutinoside could represent a preliminary index for grouping similar cultivars and colours.     

Influence of Drying Temperature and Rehydration on Selected Textural Properties of Carrots

Cubes of carrots dried at 60, 70, 80, and 90°C were rehydrated up to 180 min at 20°C and up to 10 min at 95°C. Kinetics of cutting strength were determined for the samples soaked at 95°C. Compression stress relaxation behavior of the samples was studied on carrots rehydrated at 20 and 95°C. Kinetics of cutting strength were satisfactorily described by means of a first-order kinetic model. The compression stress relaxation of carrots was analyzed using five element Maxwell and empirical Peleg models. Both of the models were found to be appropriate for characterizing viscoelastic properties of dried and rehydrated carrot cubes. The results indicated that the use of low drying temperatures was suitable for preserving the quality attributes of carrots after rehydration, and drying air temperature of 60°C was chosen as the most appropriate for hot air processing of carrots.