Rheology of solid Gazıantep Pekmez

Production of grape pekmez by Ohmic heating-assisted vacuum evaporation

Pekmez is a concentrated syrup-like food conventionally produced by vacuum evaporation process from sugar-rich fruits. In this study, the applicability of grape pekmez production by ohmic heating assisted vacuum evaporation (ΩVE) method was investigated. Conventional vacuum evaporation (CVE) and ΩVE methods were compared in terms of physicochemical properties, HMF (5-hydroxymethylfurfural) contents, rheological properties, and energy consumptions. ΩVE was run at four different voltage gradients (17.5, 20, 22.5, and 25 V/cm). Total process times for grape pekmez production were determined as 57, 28.5, 32, 39, and 50 minutes for CVE, ΩVE (25 V/cm), ΩVE (22.5 V/cm), ΩVE (20 V/cm) and ΩVE (17.5 V/cm), respectively. Energy consumption of CVE method was higher than ΩVE method for all voltage gradients. Energy efficiency increased as the voltage gradient increased. There was no significant difference between CVE and ΩVE methods for HMF contents. The results show that the ΩVE method could be an alternative to the CVE process for grape pekmez production.

Optimization of grape juice deacidification using mixture of adsorbents: A case study of Pekmez

Grape syrup (Pekmez or Dooshab) is one of the nutritious products developed through grape processing. One of the main challenges in the industrial manufacture of this product is the utilization of traditional pekmez earth for tartaric acid adsorption. The objectives of this study were to investigate the effect of calcium carbonate, nano-silica, alumina, and activated carbon as adsorbents and also contact time in grape juice deacidification, and to determine the effects of these adsorbents on the physicochemical properties of grape juice by using the Box-Behnken statistical design. By applying different amounts of these adsorbents in grape juice, the magnitude of acidity decrement and the physicochemical properties such as acidity, pH, transmittance, the amount of reducing sugars, formalin index, and adsorption efficiency were investigated. Data analysis showed that different mixtures of adsorbents at different concentrations had significant effects on acidity and pH of the samples but no effects on the level of reducing sugars and formalin index were observed (p > .05). According to the results, the adsorption capacity with the highest calcium carbonate content (0.7 g/100 ml) was about 88%; the maximum acidity decrements of up to 92% were achieved using the treatments containing calcium carbonate, nano-silica, and activated carbon, while alumina failed to affect the acidity of the samples. Optimum conditions were obtained in 1.27, 0.21, 0.7, and 0.07 g/100 ml alumina, nano-silica, calcium carbonate, and activated carbon, respectively, resulting pH 4.3 and acidity 0.37% in grape syrup.

Experimental study of physical and rheological properties of grape juice using different temperatures and concentrations. Part I: Cabernet Sauvignon

The effect of the temperature and concentration on rheological behavior of Cabernet Sauvignon juice concentrates was assessed using a rheometer over a wide range of temperature (1-66°C) and concentrations (13.6-45.0Brix) at shear rates of 0.84-212.1 1/s. The Ostwald-De Waele was the best rheological model fitted the data (R²=0.99957 and relative error=7.77%). The Cabernet Sauvignon juice concentrates presented a non-Newtonian pseudoplastic behavior (n<1). The consistency levels were significantly reduced with the increase of temperature and increased with the increase of the concentrations. The flow activation energy ranged from 28.87 (45.0Brix) to 38.05KJ/mol (37.0Brix) with a R²=0.9798 for both cases. Density and specific heat were influenced by both temperature and concentration; however, thermal conductivity was only influenced by concentration. The Cabernet Sauvignon juice concentrates will be useful as wine chaptalization agent in future studies.

Rheological Behaviour and Time Dependent Characterisation of Gilaboru Juice (Viburnum opulus L.)

The flow curves and time-dependent rheological behaviour of gilaboru ( Viburnum opulus L.), a traditional drink in the middle Anatolia region of Turkey, with different solid concentrations (59.7, 56.3, 53.1, 43 and 35°Brix) were studied at different temperatures (5-60°C) using a controlled stress rheometer. Gilaboru samples exhibited thixotropic behaviour for all concentrations, both in the forward and backward measurements were characterised by the power law. A single equation was proposed for the apparent viscosity 1. Temperature played a major role in determining the magnitudes of the apparent viscosity 1. The completely destructed gilaboru samples flow curves were also measured after subjecting the samples to a high shear rate for 2h. After eliminating thixotropy by shearing, samples showed shearthinning properties that fitted well to the power law model. Three models were used to describe the time-dependent behaviour, namely, the second-order structural kinetic, Weltman and first-order stress decay models. Among the models, the first-order stress decay model fitted well compared to the second- order structural kinetic and Weltman models.

The effects of production methods and storage on the chemical constituents of apple pekmez

The purposes of this study were to investigate the effects of two different pekmez production methods namely open pan evaporation (OPE) and vacuum evaporation (VE) on the final products, and to observe the changes in constituents as well as aromatic components after 4 months of storage. The initial and poststorage (4 months) 5-hydroxymethyl furfural (HMF) content in OPE apple pekmez were respectively 5.48, and 7.04 mg/kg. No HMF was detected in VE apple pekmez. Both initial and poststorage content of phenolic compounds was higher in VE pekmez compared to OPE pekmez. The effects of production methods and storage time were statistically significant on phenolic compounds in apple pekmez. The content of all analyzed minerals except calcium has significantly decreased in pekmez compared to raw material on dry weight basis. OPE resulted in a 55.97 % loss in the amount of ascorbic acid, whereas the loss in VE has been 23.45 %. Poststorage loss in ascorbic acid has respectively been 69.54, and 89.28 %, for VE and OPE samples. None of the aromatic components of fresh apple was detected in pekmez.

Influence of temperature, concentration and shear rate on the rheological behavior of malay apple (Syzygium malaccense) juice

Summary The aim of this study was to evaluate the rheological behavior of malay apple, a traditional Amazonian fruit with high bioactive properties, at different temperatures and soluble solids concentrations. The experiments were carried out in a Brookfield R/S Plus rheometer with concentric cylinders geometry. Power Law, Herschel-Bulkley, Mizrahi-Berk, and Sisko rheological models were fitted to the experimental data. The malay apple juice (pulp and skin) showed a pseudoplastic behavior for all temperatures and concentrations with flow behavior indexes lower than 1. The temperature effect on the samples’ apparent viscosity was analyzed by the Arrhenius equation. The activation energy increased with a decrease in the soluble solids concentration, showing that the lower the concentration, the greater the temperature influence on the apparent viscosity. The soluble solids effect was described by the exponential equation. The exponential factor increased with the temperature increasing, showing that the higher the temperature, the greater the effect of the soluble solids concentration on samples’ apparent viscosity. Finally, a triparametric mathematical model combining temperature, concentration, and shear rate was proposed aiming to evaluate its effects on the samples’ apparent viscosity and has accurately adjusted to the data with high correlation index R2.

Rheological behaviour of enzyme clarified sapota (Achras sapota L) juice at different concentration and temperatures

Rheological behaviour of enzyme clarified sapota (Achras sapota L.) juice at different temperatures (10 to 85 °C) and total soluble solid content (10.2 to 55.6 °brix) corresponding to a water activity (aw) (0.986 to 0.865) was studied using controlled stress rheometer by coaxial cylinders attachment. The rheological parameter shear stress (Pa) was measured upto a shear rate of 1,000 s(-1). The investigation showed that the enzyme clarified sapota juice and its concentrates behaved like a Newtonian liquid and the viscosity (η) values were in the range 4.340 to 56.418 mPa s depending upon temperature and concentration studied. The temperature dependency of viscosity of enzyme clarified sapota juice was described by Arrhenius equation (r > 0.94) and activation energy (Ea) for viscous flow was in the range 5.218 to 25.439 KJ/mol depending upon concentration. The effect of total soluble solid content on flow activation energy was described by exponential relationship (r > 0.95, rmse% <13.5, p < 0.01) and that of water activity was described by power law relation (r > 0.99, rmse% <5.80, p < 0.01). The effect of total soluble solid content on viscosity of enzyme clarified sapota juice followed second order exponential type relationship (r > 0.99, rmse% < 3.53) at the temperature used. The effect of water activity on viscosity of enzyme clarified sapota juice followed power law equation (r > 0.98, rmse% < 4.38). A single equation representing combined effect of temperature and total soluble solid content/water activity on viscosity of enzyme clarified sapota was established.

Steady, dynamic, creep/recovery, and textural properties of yoghurt/molasses blends: Temperature sweep tests and applicability of Cox–Merz rule

In this study, physicochemical, rheological (steady, dynamic, and creep/recovery), and textural properties of yoghurt/molasses blends (0, 5, 10, and 15% molasses) were investigated. The blends showed shear thinning behavior, as described by Ostwald de Waele model ( R2 ≥ 0.955). Consistency coefficient value ( K) of the blends decreased with increasing molasses concentration in the sample. Storage modulus ( G′) of blends was higher than loss modulus ( G″), exhibiting weak gel-like behavior. Molasses addition decreased G′ and G″ values. Temperature sweep tests indicated that blends followed Arrhenius relationship. A modified Cox–Merz rule was applicable using shift factors. Compliance values ( J(t)) increased as molasses concentration increased, revealing that deformation stability and internal viscosity ( η1) decreased with concentration. Creep behavior was characterized using Burger model. Obtained J data as a function of time could be satisfactorily fitted to Burger model ( R2 ≥ 0.994). The final percentage recovery of blends remarkably decreased with the increase of molasses concentration. Firmness, consistency, cohesiveness, and viscosity index values decreased with molasses addition. According to the results of the current study, molasses amount to be added to the yoghurt should be determined regarding rheological properties since resistance of the sample to deformation decreased with increase in molasses concentration.

Rheological characteristics of inulin solution at low concentrations: Effect of temperature and solid content

The rheological properties of inulin solution was investigated at different solid content (Xs) ranging from 1 to 12 % at wide range of temperatures ranging from 10 to 85 °C. The rheological parameter shear stress was measured upto a shear rate of 300 s(-1) using concentric cylinders attachment by controlled stress rheometer. The investigation showed that the inulin solution behaved like Newtonian liquid and viscosity (η) was in the range 2.0998 to 3.2439 mPa s depending upon the concentration and temperature studied. The temperature dependency of Newtonian viscosity of inulin solution was described by Arrhenius equation (r > 0.88, p < 0.05) and activation energy (Ea) for viscous flow was in the range 2.111 to 3.013 kJ/mol depending upon the solid content studied. The flow activation energy (Ea) of inulin solution was significantly (p < 0.05) affected by solid content and described by exponential type equation (r = 0.9646, rmse% = 1.07, p < 0.001). Effect of solid content on Newtonian viscosity was described by linear as well as power law models depending upon the temperature studied. The combined effect of temperature and solid content on Newtonian viscosity of inulin solution was described by power law type equation and represented as η = 0.8835* (Xs)(0.0731) *Exp(296.410/T), (r = 0.9538, p < 0.001, rmse% = 0.15) Where η is Newtonian viscosity in mPa s, Xs is solid content in % and T is temperature in Kelvin (K).

Rheological Characteristics of Juniperus drupacea Fruit Juice (pekmez) Concentrated by Boiling

Rheological parameters of Juniperus drupacea fruit pekmez were evaluated using a rotational viscometer at 10, 20, 30, 40, and 50 °C and at concentrations of 62.8, 68.9, 72.0, and 75.2% total soluble solids. The flow characteristics of Juniperus drupacea fruit pekmez were described by the power law and Herschel—Bulkley models. The Herschel—Bulkley model was found to be the best to describe the rheological property with the coefficient of determination higher than 0.993. Juniperus drupacea pekmez exhibited a time-independent shear thickening behavior. The effect of temperature on viscosity can be described by means of an Arrhenius equation. Depending on the soluble solid contents, the activation energies for flow of diluted samples vary from 78.23 to 60.38 kJ/mol. The effect of soluble solids on viscosity can be described by an exponential equation. Experimental data were fitted to several models in order to describe the effect of temperature and soluble solid content. The combined effect of temperature and soluble solid content on viscosity was also formulated.