Thermophysical Properties of Papaya Puree

The effects of soluble solids content and temperature on thermal properties of papaya puree were studied. Density and specific heat were measured using a pycnometer and differential scanning calorimeter, respectively, while thermal conductivity was measured using a line heat source probe. Thermal diffusivity was then calculated from the experimental results of the specific heat, thermal conductivity, and density. Thermal properties of papaya puree were experimentally determined within a soluble solids content range of 10 to 25 °Brix and temperature between 40 and 80°C. The density, specific heat, thermal conductivity, and thermal diffusivity of papaya puree were found to be in the ranges of 1014.6 to 1098.9 kg/m³, 3.652 to 4.092 kJ/kg °C, 0.452 to 0.685 W/m °C, and 1.127?×?10^?7 to 1.650?×?10^?7 m²/s, respectively. Moreover, the empirical models for each property as a function of soluble solids content and temperature were obtained.     

Viscosity Reduction by Homogenization of Orange Juice Concentrate in a Pilot Plant Taste Evaporator

Controlling viscosity is critical to efficient evaporation and pumping of citrus concentrates. Viscosity was reduced by a commercial homogenizer installed between the third and fourth stage of a pilot plant TASTE evaporator. Juice was concentrated to 65°Brix with and without homogenization. The results showed a 13% decrease in viscosity due to homogenization. Mean non-homogenized values were 279 mPa.s (s.d. = 7.5) on the 65°Brix control and 242 mPa.s (s.d. = 10) on the homogenized concentrate, both measured at 3.50 set¹, which was calculated to be the shear rate for these samples within the third stage of this evaporator. This decrease in viscosity also reduced the energy consumption about 3 to 4% or produced a higher (2 to 3) °Brix concentrate. Homogenization did not significantly affect the juice color, acid, pulp or vitamin C.     

Prediction of 5–MF Formation in an Industrial Apple-Juice Evaporator

The rate of formation of 5-hydroxymethylfurfural (5-HMF) in apple juice with soluble solids ranging from 15 to 69°Brix at 100, 104, 108 or 112°C was experimentally determined. Different mechanisms of reaction were proposed and corresponding kinetic models were derived. The model that provided the best fit to experimental data corresponded to a first-order initiation step, followed by an autocatalytic period limited by consumption of reactants. The resulting kinetic equations were incorporated into the mathematical model of a triple-effect apple-juice evaporator. The simulation values obtained for the content of 5-HMF in the concentrated apple juice were in good agreement with observed industrial levels. From simulation runs 5-HMF generation was strongly related to the temperature level at the first evaporation effect.     

Thermal conductivity of tomato paste

Experimental measurements of the thermal conductivity and thermal diffusivity of tomato paste at concentrations of 27–44° Brix are reported. The thermal conductivity was measured in a guarded hot-plate apparatus while the diffusivity was estimated by a simplified transient method. The thermal conductivity (λ) values fell in the region of 0·460–0·660 W m^?1 K^?1, decreasing with increasing solids concentration and increasing as the temperature was raised from 30 to 50°C. The temperature effect was less pronounced at higher solids concentration. The thermal diffusivity of tomato paste at 35° Brix and 20°C was estimated as 1·42 × 10^?7 m² s^?1, which is in good agreement with data from the steady-state method.     

THERMOPHYSICAL PROPERTIES OF PINK GUAVA JUICE AT 9 AND 11°BRIX

The effect of temperature on the conservation of pseudoplastic characteristics and on the physical properties of pink guava juice (Psidium guajava L.) variety Beaumont: B‐30 with two different total soluble solids (9°Brix and 11°Brix) was investigated. It was found that the juice exhibits pseudoplastic behavior in the range of shear rate between 40 to 160 s^?1 and within pasteurization temperature of 60–90C. While the flow behavior index (n) and density (p) increased, consistency coefficient (K), thermal conductivity (k) and specific heat capacity (C_p) decreased with increasing temperature. The linear regression equations or models for flow behavior index, consistency coefficient, density, thermal conductivity and specific heat capacity were determined with correlation coefficients ranging from 0.75 to 1.00.     

Preparation and Storage of 72° Brix Orange Juice Concentrate

Each year, thousands of tons of citrus concentrate are stored and transported throughout the world at 62° Brix. Increasing this concentration to 72° Brix can result in substantial savings. Fresh orange juice, treated mechanically or with pectic enzymes to reduce its viscosity, was concentrated to 72° Brix in a commercial processing plant, then samples were stored in barrels in a tank farm at ?7 or at 4°C. At monthly intervals, samples were blended to make 41.8° Brix Frozen Concentrated Orange Juice. The enzyme-treated samples had lower viscosity than those mechanically treated. Vitamin C retention levels were > 94% after 6 months storage at 4°C. Taste evaluations rated the product ‘very good’ and furfural levels were well below that which indicates off flavors. Browning tended to increase with storage time and temperature.     

Relationship between the thermal conductivity and rheological behavior of acerola pulp: Effect of concentration and temperature

This study aimed to evaluate the thermal conductivity and rheological behavior of acerola pulp at concentrations of 5.5, 7.5, 9.5, 11.5 and 13.5 °Brix and temperatures of 20, 30, 40, 50 and 60 °C. Among the models used to determine conductivity, Maxwell-Eucken was used for data acquisition. Linear equations were fitted to evaluate the influences of concentration and temperature on the thermal conductivity of the pulp. The pulp structure, particle sizes and relation between insoluble and soluble solids were also discussed. The rheological behavior, specifically apparent viscosity versus shear rate, was influenced by both the soluble solids content and the temperature. Among the mathematical models used to test the fit of the experimental data, the Herschel–Bulkley model provided the best statistical adjustments and was then used to determine the rheological parameters. Apparent viscosity was correlated with temperature by the Arrhenius equation. Acerola pulps were shear thinning and thermal conductivity increases with viscosity decreasing with increasing temperature. The structures and concentrations had an impact upon the effective thermal conductivity. The temperature and concentration values have been fixed and equation expressing conductivity as a function of apparent viscosity was proposed, which enable the evaluation of an existing relationship between the two properties.     

Influence of Temperature and Solid Concentration on the Physical Properties of Noni (Morinda citrifolia L.) Juice

The effect of temperature on the physical properties of fresh noni (Morinda citrifolia L.) juice with three different solid concentrations (5, 10, and 15°Brix) was investigated. The flow behaviour index (n) and thermal conductivity (k) were found to increase with the increase in temperature. On the other hand, the juice density (??) and consistency coefficient (K) were found to decrease with increasing temperature. The increase in solid concentration leads to increase juice density and consistency coefficient, but reduce flow behaviour index and thermal conductivity. The experimental data were then correlated with temperature and solid concentration using nonlinear regression equations or empirical models. It was found that the physical properties calculated using proposed equations agree well with the experimental data with coefficient of determinations (R ² ) ranged from 0.9897 to 0.9998.     

Rheological Aspects of Spanish Honeys

The purpose of this work was to investigate the rheological behavior of Spanish honeys under different conditions (at different temperatures and concentrations). All the samples were characterized to determine their physicochemical (moisture, ⁰Brix, pH, ash, conductivity, color, total acidity, diastase activity, 5-hydroxymethylfurfural content, sugar content) and thermal (glass transition temperature) profiles. The honeys samples (80.4–82 ⁰Brix) behaved as Newtonian fluid; as expected, their viscosity increased with the solid content and decreased with the temperature. Two experimental viscosity models (Arrhenius and Vogel–Taumman–Fulcher) were checked using the experimental data to correlate the influence of temperature on honey viscosity. A simplified model was proposed to describe the combined effect of the temperatures and concentrations (⁰Brix) on the viscosity of Spanish honeys. The dynamic viscosity and complex viscosity had the same magnitude at 40 °C, 45 °C, and 50 °C for of all the samples and the Cox Merz rule could be applied at these temperatures.     

Influence of Moisture Content and Temperature on Thermal Conductivity and Thermal Diffusivity of Rice Flours

The thermal conductivity and thermal diffusivity for four types of rice flours and one type of rice protein were determined at temperatures ranging from 4.8 to 36.8?°C, bulk densities 535 to 875.8 kg m^?3, and moisture contents 2.6 to 16.7% (w.b.), using a KD2 Thermal Properties Analyzer. The thermal conductivity of rice flours and rice protein increased with the increase in temperature, moisture content as well as with increase in bulk density. Thermal diffusivity decreased with increase in moisture content, increase in temperature and bulk density. The thermal conductivities values obtained were within the range of 0.045 to 0.124 W m^?1 K^?1 whereas the thermal diffusivity values were in the range of 0.094 to 0.138 mm² s^?1.     

紫甘薯浓缩汁的流变特性研究

采用CV-Ⅲ+型数字流变仪对不同温度(25℃,50℃,75℃)和不同浓度(10°Brix,20°Brix,30°Brix,40°Brix,50°Brix,60°Brix)下的紫甘薯浓缩汁的流变特性进行了研究,结果表明:在所研究的温度和浓度范围内,紫甘薯浓缩汁为牛顿流体;回归分析表明,温度对粘度的影响符合Arrhenius方程,浓度对粘度的影响可以用指数方程更准确的表示,并依此推导并验证了温度和浓度对紫甘薯浓缩汁粘度综合影响的方程模型。     

温度和糖度对金丝小枣浓缩汁贮藏稳定性的影响

以产于山东省乐陵市金丝小枣的浓缩汁为试材,研究了不同糖度浓缩枣汁在不同条件贮藏过程中的浊度、活性蛋白(HAP)、Vc、Chroma值和L*值的变化,探讨了温度和糖度与浓缩枣汁贮藏稳定性的关系。结果表明:4℃是保持金丝小枣浓缩汁贮藏稳定性、色泽和营养成分等贮藏品质及浑浊和沉淀出现时间的理想温度;70°Brix金丝小枣浓缩汁在不同温度下贮藏的效果均优于50°Brix和60°Brix枣汁,色泽变化相对较小,出现浑浊和沉淀的时间较晚。     

Flow Properties of Low-Pulp Concentrated Orange Juice: Effect of Temperature and Concentration

Three 65° Brix low-pulp concentrated orange juice (COJ) samples, between −19 and 30°C were shear-thinning (pseudoplastic) fluids with negligible magnitudes of yield stress. The simple power law model fit welt the shear rate-shear stress data. For one sample, the Powell-Eyring model also described the data well. The Arrhenius model described the effect of temperature on the apparent viscosity and the consistency index of the power law model. The activation energy of flow (E_a) was 10.7 ± 0.2 kcal/g mole. The models of Harper and El Sahrigi and Christiansen and Craig were suitable for describing the combined effect of temperature and shear rate. The magnitude of E_a decreased with decrease in concentration. Apparent viscosity and K increased exponeitially with concentration.     

Nonenzymatic Browning in Apple Juice Concentrate during Storage

Rate of browning in Red Delicious and Granny Smith apple juice concentrates during storage was investigated. Color development at 65°, 70° and 75°Brix and storage temperatures of 5°, 20° and 37°C were compared over 120 days. Color deterioration occured at a faster rate in Red Delicious. Reaction at different concentration and storage conditions was exponential, following an Arrhenius-type dependence with temperature. Activation energy for a solids content of 65 - 75°Brix ranged from 16.4 - 19.3 Kcal/mole. Influence of juice variety on activation energy was negligible. Water activity results are in general agreement with those reported by other investigators. A satisfactory correlation to predict commercial concentrate browning has been obtained. All other things being equal, thermal history is a critical factor to obtain a lighter color concentrate.     

Physical-Chemical Characteristics of Partially Clarified Guava Juice and Concentrate

Partially clarified guava juice concentrate was prepared from single strength guava puree (5.5°Brix) by treatment with pectinase (2 hr at 50°C), extraction of juice with a rack-and-cloth press, and vacuum concentration to 23°Brix. The concentrate had the following characteristics: density, 1.10; pH, 3.16; total acids, 4.67%; ash, 1.51%; moisture, 72.4%; ascorbic acid, 867 mg%; viscosity, 4.4 cp; and CIE L* 39.2, CIE a* 10.33, CIE b* 27.11.     

Quality of Freeze Concentrated Orange Juice

Pasteurized Valencia and Temple orange juices concentrated to 45°Brix by freeze concentration retained their fresh juice flavor. Direct steam infusion heating to inactivate enzymes allowed more rapid heating than indirect heating and successfully lowered juice peel oil during vacuum cooling. Except for considerable pulp reduction of feedstream juices, there were few differences from normal citrus juice recovery procedures for freeze concentration. Since the product retained most of the aroma constituents of fresh juice, careful handling and high quality feed juice prior to freeze concentration was much more important than for evaporation. Fresh juice freeze concentrated to 45°B, then pasteurized at temperatures of 80°, 97° and 111°C had reduced sucrose (up to 25%) as the temperature increased to 111°C.     

Passion Fruit Juice Concentration by Ultrafiltration and Evaporation

Passion fruit juice was pretreated with pectinase, centrifugation, and pasteurization. The resulting juice was processed by Ultrafiltration (UF) to 20°Brix. The UF permeate was concentrated by evaporation to 70°Brix and combined with the UF retentate to form the final concentrated product at 40°Brix. The pretreatments caused approximately 20% flavor losses, but accomplished more than 50% flux increases. The UF recovered many important flavor constituents, and improved the rate of evaporation. The final concentrated product contained more than 30% of juice flavor. Results of sensory evaluation indicated that flavor of the reconstituted juice was inferior to fresh juice, but the two juices were not significantly different in overall acceptance.     

Thermophysical Properties of Sugarcane,Palmyra Palm,and Date-palm Granular Jaggery

Effect of moisture content on thermo-physical properties of sugarcane, palmyra palm, and date-palm granular jaggery were investigated. Thermal conductivity and diffusivity were determined by line-heat-source transient heat-transfer methodology, while specific heat was calculated from additional data on bulk density of the samples. Thermal conductivity, diffusivity, specific heat, and bulk density was found to vary from 0.08 to 0.39 W m^?1 K^?1, 0.10 to 0.13 × 10^?6 m² s^?1, 1.19 to 2.97 kJ kg^?1 K^?1, and 510 to 1310 kg m^?3, respectively, for a moisture range of 2.0–14.3 (%d.b.); all at an average temperature of 30°C. All these properties except—thermal diffusivity—followed an increasing trend; with the increase in moisture content, each showed a high correlation coefficients. The variation of thermal diffusivity was found to be insignificant.     

Some Physical,Chemical, and Rheological Properties of Sweet Sorghum (Sorghum Bicolor (L) Moench) Pekmez (Molasses)

Some physical, chemical properties and the rheological behaviour of the sweet sorghum (Sorghum bicolor L Moench) pekmez (molasses) were determined. The rheological behaviour of the sweet sorghum pekmez (concentrated sorghum juice) with different soluble solid contents (75.1, 72.4, 66.5, and 59.4 °Brix) was determined in the temperature range of 10, 20, 30, 40, and 50°C using a rotational viscometer equipped with spindle 5 at the speed (share rate) of 5, 10, 20, 50, and 100 rpm. An empirical power law model was used to describe the rheological behavior of the sweet sorghum pekmez with correlation coefficients (R²) between 0.922 and 0.986. The sweet sorghum pekmez exhibited a pseudoplastic behavior. An Arrhenius equation was used to describe the effect of temperature on viscosity and E_a value of the sweet sorghum pekmez was calculated as 31 350 J/mol. Depending on the soluble solids contents, the activation energies for flow of diluted samples vary from 52.27 to 24.50 kJmol^?1. The effect of °Brix on viscosity can be described by the power-law equation. Experimental data were fitted to power law and exponential model in order to describe the effect of temperature and soluble dry matter content. Density and Electrical conductivity were measured 1.3915 g/cm³ and 13.53 mS/cm, respectively. The color as L, a and b value were measured 19.07, + 4.0, and + 2.18, respectively.     

Influence of Water Activity on the Nonenzymatic Browning of Apple Juice Concentrate during Storage

Highly concentrated clarified apple juice was kept in storage at 37°C over a period of 100 days. The soluble solids content ranged from 65–90.5°Brix. Color development was monitored as O.D. at 420 nm. A maximum nonenzymatic browning rate (NEB_r) was found to occur between water activities 0.53 and 0.55. It was assumed that (1) dilution of reactants was responsible for the browning rate reduction at high water contents white (2) viscosity inhibited the color formation at low water activities. Viscosity ranged from 48 to 1.3 × 10⁶ cp and increased sharply when the commercial levels of concentration (70–72°Brix) were exceeded.