Simultaneous Estimation and Modeling of Thermophysical Properties of Big-Eyed Tuna and Pacific Cod

The thermophysical properties (thermal conductivity, thermal diffusivity, and specific heat) of big-eyed tuna and pacific cod were measured at various temperatures (5–50°C) by the modified version of current probe method. The optimal prediction models for these thermophysical properties were determined. The random model was applied to predict the thermal conductivity of seafood in a wide range of temperature and it provided the accurate predictions for the samples. The thermal diffusivities of the samples could be predicted by Martens’s equation. An additive relationship exists between the specific heat of the sample, the composition, and the specific heat of each component.     

Thermophysical Properties of Pulp and Rind of Papaya Cv. Maradol

Thermophysical properties of pulp and rind of papaya (Carica papaya L., cv. Maradol) were measured at 20, 30, 40, 50, and 60°C and modeled as a function of temperature. Thermal conductivity, specific heat capacity, and apparent density were measured using the line heat-source probe, differential scanning calorimetry, and the liquid displacement method. For pulp, the values of thermal conductivity, specific heat and apparent density ranged from 0.668 to 0.755 W/m K, from 3019 to 3732 J/kg K, and from 991 to 1036 kg/m³, respectively. The corresponding values for rind of papaya ranged from 0.651 to 0.714 W/m K from 2756 to 3282 J/kg K and from 1019 to 1043 kg/m³. Although thermal conductivity and apparent density of pulp and rind of papaya were significantly (p < 0.05) dependent on temperature, specific heat capacity and thermal diffusivity of pulp and rind of papaya were not affected by temperature in the measurement range.     

Simultaneous Estimation of the Thermophysical Properties of Selected Liquid Dairy Products by a Transient Heat Flow Probe Method

The thermophysical properties of reconstituted whole milk, skim milk, and whey were measured at various temperatures and concentrations. A new method for the simultaneous determination of thermophysical properties using a modified version of current probe theory method was proposed. Two new correction coefficients were introduced, and using the values of these coefficients and an approximate solution of the heat conduction equation, the thermal conductivity and thermal diffusivity of each sample were determined. The specific heat of each sample was estimated from the definition of thermal diffusivity. These properties were expressed as a function of concentration and temperature.     

Physical properties of acerola and blueberry pulps

In this work, some physical properties of acerola and blueberry pulps were determined. The density was determined by the pycnometer method; the electrical conductivity using a conductivimeter; the thermal diffusivity by a method based on the analytical solution of heat diffusion equation; the specific heat capacity by a modified method of mixtures; and the thermal conductivity from the knowledge of other properties. Results showed that the density of acerola pulp, in the temperature range between 303 and 353 K, varies between 0.97 and 1.03 kg m⁻³; for blueberry it ranged between 0.98 and 1.05 kg m⁻³. Electrical conductivity was between 1.69 and 8.48 mS cm⁻¹ for acerola pulp and between 0.79 and 3.86 mS cm⁻¹ for blueberry. Specific heat, thermal diffusivity and thermal conductivity of acerola pulp at approximately 313 K showed values of 4172.49 J kg⁻¹ K⁻¹, 1.53 × 10⁻⁷ m² s and 0.65 W m⁻¹ K⁻¹, respectively. For blueberry, these values were 4050.39 J kg⁻¹ K⁻¹, 1.51 × 10⁻⁷ m² s and 0.64 W m⁻¹ K⁻¹.     

Mechanical Properties of Pumpkin

Mechanical properties of three common varieties of pumpkin were evaluated and statistically compared. Toughness, rupture force, shear strength, and cutting force were determined for Jarrahdale, Jap, and Butternut varieties. The investigation was carried out in three cases of flesh, skin and unpeeled product, ignoring the toughness and rupture force of flesh. Relative contribution of skin to unpeeled case of each property was estimated. Varieties were found statistically alike in rupture force, toughness, and maximum shear strength force of unpeeled cases. Also the skin of three varieties showed similar strength in shear (p>0.05). Jap and Butternut varieties for some other properties showed close values. Maximum shear strength force of flesh, shear strength of unpeeled case, and relative contribution of skin to shear strength of unpeeled case were close (p>0.05) for these varieties. Jarrahdale had no difference in shear strength of flesh with two other varieties. It was also similar (p>0.05) to Jap in relative contribution of skin to shear strength, rupture force, and toughness of unpeeled case.     

Effect of Soluble Solids Concentration and Temperature on Thermo-Physical and Rheological Properties of Mango Puree

Thermo-physical and rheological properties of mango pulp were evaluated at different temperatures (20, 40, 60, and 80°C) and total soluble solids concentrations (15, 20, 32, and 40°Brix). Thermal properties were primarily dependent on the moisture content of the sample, and increased with temperature and decreased with soluble solids concentrations. Density showed a reverse trend. Glass transition temperatures increased with an increase in soluble solids concentrations indicating better stability. Empirical models developed for each thermal property as a function of temperature and soluble solids concentrations (R² > 0.90) generally showed better predictions than published models. Mango puree exhibited pseudo-plastic behavior during steady shear measurements, and the power law model well described their flow behavior. Consistency coefficient increased with soluble solids concentrations and decreased with temperature. The flow behavior index ranged between 0.27 and 0.38 but did not show a clear trend either with soluble solids concentrations or temperature. Small amplitude oscillatory shear measurements revealed that mango puree behaved like a weak gel and demonstrated visco-elastic properties.     

Thermal Properties of Sweet Potato with its Moisture Content and Temperature

Thermal properties of sweet potato were experimentally determined and modeled as a function of temperature and moisture content. The purpose is to develop empirical correlations that could predict thermal properties during sweet potato processing. Thermal conductivity from the study was 0.49 ± 0.038 Wm^?1K^?1 (mean ± s.d.), thermal diffusivity was 1.2?×?10^?7 ± 9.05?×?10^?9 m²s^?1, specific heat was 3660 ± 477.4 Jkg^?1K^?1, and density was 1212 ± 73.5 kgm^?3. All properties were determined within temperature range of 20 to 60°C and moisture content range of 0.45 to 0.75 w.b. Prediction models for the thermal properties of sweet potato were developed as a function of product temperature and moisture content with experimental data from this study. Mechanistic models were also developed for thermophysical properties of sweet potato using major food components of the product. Developed models were all presented and compared.     

Thermophysical properties and thermal behavior of leafy vegetables packaged in clamshells

Little is known about the thermophysical properties of fresh-cut lettuce other than heat of respiration. Empirical correlations based on food composition remain the only way to estimate the thermophysical properties of fresh-cut lettuce. The objectives of this study were (i) to determine the thermophysical properties of several baby-leaf lettuce and brassica greens and (ii) to verify the measured thermophysical properties by using them in a heat transfer model and comparing the predicted product temperatures with measured product temperatures in a simulated interruption of a cold chain. Density, leaf thickness, thermal conductivity, specific heat and water activity from nine varieties of baby-leaf lettuce and brassica greens were measured. A broken cold chain was simulated in a low temperature incubator set at 10 °C for a length of time before readjustment at 2 °C. Results showed that density (1078–1112 kg m⁻³), leaf thickness (0.18–0.54 mm), thermal conductivity (0.55–0.70 W (m °C)⁻¹) and specific heat (3.1–4.3 kJ (kg °C)⁻¹) varied significantly (P < 0.05) between varieties. However, no significant differences were observed for water activity (0.959 ± 0.006). Using thermophysical properties as input in the heat transfer model, experimental and calculated temperatures were well correlated (R² = 0.98) with a root mean square error of 0.57 °C over the 10–40 mg CO₂ (kg h)⁻¹ range of respiration rate. The measured thermophysical properties adequately predicted the temperature of the baby-leaf greens during simulated broken cold chains. A sensitivity analysis performed with the heat transfer model showed that the thermal conductivity, the specific heat and the density were relatively more important on the thermal behaviour of the baby-leaf greens than the heat of respiration.     

Simultaneous estimation of the thermophysical properties of three kinds of fruit juices based on the measured result by a transient heat flow probe method

The thermophysical properties of three kinds of fruit juices (grape juice, orange juice, and pineapple juice) were measured at various temperatures (10–50 °C) and concentrations (10–50%). A new method for the simultaneous determination of thermophysical properties using a modified version of current probe theory method was proposed. The temperature changes of the probe upon insertion in the sample were fitted to an approximate solution of the heat conduction equation, and the values of two parameters in that solution were determined. Using the values of these parameters, the thermal conductivity and thermal diffusivity of each sample were determined. The specific heat of each sample was estimated from the definition of thermal diffusivity. These thermophysical properties were expressed as a function of concentration and temperature.     

番茄浆料的流变特性

对不同浓度的番茄浆料在30～60℃时的流变学性质进行了研究.结果显示,番茄浆料为假塑体系,屈服应力值的范围比较宽(40～140Pa).通过回归分析得到数学模型K=K0exp(Ea/RT)和K=Aexp(BC).可以分别用来描述温度和浓度对番茄浆料稠度系数的影响.利用这些方程,可以预测实际加工过程中不同温度和不同浓度条件下番茄浆料的粘度.     

Permeability Properties of Fruit Puree Edible Films

The potential of fruit purees as edible mass transfer barriers was studied. Water vapor and oxygen permeabilities (WVP and O₂P) of peach puree films were evaluated at different relative humidities (RH) and temperatures (T). Peach puree was not a good water barrier. Peach and apricot films exhibited lower WVPs than pear and apple films. Calcium addition, RH increases and T decreases resulted in increased WVP values for peach puree edible films. WVPs of peach films were compared with other edible and synthetic films. Peach puree films were good oxygen barriers. RH increases resulted in exponential increases in O₂P. Most edible and many synthetic polymers showed higher O₂Ps at equivalent conditions.     

Thermophysical properties of medium grain rough rice (<Emphasis Type="Italic">LIDO cultivar</Emphasis>) at medium and low temperatures

Bulk density, specific heat capacity, bulk thermal conductivity and bulk thermal diffusivity of medium-grain rough rice (LIDO cultivar) have been studied. Specific heat was determined by DSC, thermal conductivity by the probe method and bulk thermal conductivity indirectly from bulk density, specific heat capacity and bulk thermal conductivity. All the thermal properties have been determined at different moisture contents and temperatures used during cooling and storage operations and the effect of these variables has been investigated. It has been shown that moisture content has the greatest effect on specific heat and bulk thermal conductivity. Temperature also affected these thermal properties, but to a smaller extent. Mathematical expressions have been developed to determine each of these thermophysical properties as a function of moisture content and temperature.List of Abbreviations and Symbols C_p Specific heat capacity (kJ/kg °C) - k Bulk thermal conductivity (W/m °C) - T Temperature (ºC) - W Moisture content (%, d.b.) - Bulk thermal diffusivity (m²/s) - Bulk density (kg/m³)     

Composition‐Based Prediction of Temperature‐Dependent Thermophysical Food Properties: Reevaluating Component Groups and Prediction Models

Prediction of temperature‐dependent thermophysical properties (thermal conductivity, density, specific heat, and thermal diffusivity) is an important component of process design for food manufacturing. Current models for prediction of thermophysical properties of foods are based on the composition, specifically, fat, carbohydrate, protein, fiber, water, and ash contents, all of which change with temperature. The objectives of this investigation were to reevaluate and improve the prediction expressions for thermophysical properties. Previously published data were analyzed over the temperature range from 10 to 150 °C. These data were analyzed to create a series of relationships between the thermophysical properties and temperature for each food component, as well as to identify the dependence of the thermophysical properties on more specific structural properties of the fats, carbohydrates, and proteins. Results from this investigation revealed that the relationships between the thermophysical properties of the major constituents of foods and temperature can be statistically described by linear expressions, in contrast to the current polynomial models. Links between variability in thermophysical properties and structural properties were observed. Relationships for several thermophysical properties based on more specific constituents have been identified. Distinctions between simple sugars (fructose, glucose, and lactose) and complex carbohydrates (starch, pectin, and cellulose) have been proposed. The relationships between the thermophysical properties and proteins revealed a potential correlation with the molecular weight of the protein. The significance of relating variability in constituent thermophysical properties with structural properties––such as molecular mass––could significantly improve composition‐based prediction models and, consequently, the effectiveness of process design.     

Thermophysical properties of mango pulp (Mangifera indica L. cv. Tommy Atkins)

The density, heat capacity and thermal conductivity of mango pulp (Mangifera indica L. cv. Tommy Atkins) were determined at moisture contents of between 0.9 and 0.52 kg kg⁻¹ (w.b.) and temperatures of between 20 and 80 °C. The experimental data were satisfactorily fitted (explained variation values >99.1%) as functions of the moisture content and temperature by using multivariate linear models. In the range of conditions considered, the moisture content exhibits a greater influence on the studied properties than temperature.     

Thermophysical Properties of SweetPotato Puree at Freezing and Refrigeration Temperatures

The thermophysical properties (initial freezing point, unfreezable water, enthalpy of freezing, and specific heat) of alginate-restructured sweet potato (SP) puree at freezing and refrigeration temperatures were determined using differential scanning calorimetry. Restructuring of SP puree increased the amount of unfreezable (bound) water in the puree from 0.44 g H₂O/g solids to about 0.56 g H₂O/g solids and reduced the freezing point from ?2.5 to ?3.2°C. During freezing (or melting), the specific heat increased from about 1.9 to 90 kJ/kg. After freezing, the specific heats of restructured and nonrestructured SP puree were respectively 3.695 and 3.404 kJ/kg. Between 358 and 403 kJ/kg of heat have to be removed when SP puree (at 20°C) is to be frozen to ?40°C.     

热处理对菠萝果浆感官品质的影响研究

运用高压蒸汽、沸水及微波三种热处理方法对菠萝果浆进行灭菌处理,考察灭菌后果浆的感官品质,并测定了常温贮藏两周后菠萝果浆的感官指标,比较三种方式对果浆造成的影响。结果表明:高压蒸汽处理对菠萝果浆的感官品质影响较大,菠萝的特征风味、滋味损失较严重;沸水处理能较好的保留菠萝果浆特有的风味物质,但也不能杜绝蒸煮味的产生,对菠萝果浆品质有一定的影响;微波处理能很好地保持菠萝果浆原有的风味,几乎没有蒸煮味产生。结果说明,在实验的三种热处理方式中,微波处理对菠萝果浆的感官品质保持最有利。     

Dielectric Properties of Pea Puree at 915 MHz and 2450 MHz as a Function of Temperature

Dielectric properties [dielectric constant (e′) and loss factor (e″)] of 20% (w/w) pea puree with and without fortification of 3.5 mg thiamin/ 100g pea puree at 915 MHz and 2450 MHz were measured from 25 to 125°C by the cavity perturbation techniaue. Thiamin did not affect dielectric properties at ihe concentration studied. The dielectric constant decreased as frequency and temperature increased. The loss factor increased as temperature increased at 915 MHz. However, the relationship between loss factor and temperature was not direct at 2450 MHz due to the contributions of dipolar and ionic losses.     

滚筒干燥过程中叶丝状态变化对其热物性的影响

为了分析烟草热湿加工处理中的传热过程,通过自行搭建的滚筒干燥过程中烟丝热物性在线测试平台,利用瞬态平面热源法测定了滚筒干燥过程中烟丝的热物性,考察分析了该过程中烟丝温度、含水率对烟丝导热系数、热扩散系数、体积热容的影响。结果表明:①当含水率相同时,烟丝导热系数、体积热容随着烟丝温度的升高而增大,热扩散系数随温度的升高而降低;②当烟丝温度相同时,烟丝导热系数、体积热容随含水率的降低而减小,热扩散系数随着含水率的降低而增大;③干燥过程中,烟丝含水率逐渐减小,烟丝温度逐渐升高,烟丝导热系数在温度与含水率的共同作用下整体有减小的趋势,表明烟丝含水率对导热系数的影响较温度显著。     

红枣芋泥的配方优化及产品特性研究

红枣芋泥是一种以新鲜芋泥为主要成分,加入适当比例红枣泥、白砂糖、柠檬酸及食盐混合调配而成的一种健康的食品。以红枣芋泥的感官评价特性为指标,在单因素试验的基础上,通过正交试验优化红枣芋泥的配方工艺;采用顶空固相微萃取制备样品,联合气质联用测定红枣芋泥主要的挥发性物质;并初步建立了芋泥的营养评价标准。通过优化得到红枣芋泥最佳配方为红枣泥10％、白砂糖3％、柠檬酸0．07％、食盐0．2％。分析表明,红枣芋泥的风味物质中相对含量较高的依次为酮类、醛类、酯类、酸类和芳香族化合物,并且较国内市场上的泥类产品具有更好的口感和风味。     

Development of a Versatile Database for Transport Properties of Foods

The requirement of reliable data on transport properties of foods has emerged in the last decade due to their importance in the design and simulation of food processing operations. An international effort to obtain and analyze the published data has been made recently, due to the lack of reliable theoretical predictive models. In this framework, a user-friendly database system for the storage and maintenance of the transport properties of foodstuffs is proposed and developed in a Microsoft Access environment. The system allows the end-user to input and retrieve data, as well as to view diagrams with single or comparative data and predict values via a fully featured user-friendly interface. Currently the database has registered over 250 articles, which correspond to approximately 1200 records for the thermal conductivity and 1780 records for moisture diffusivity. Due to its flexibility, the system can be used as an universal template for developing similar database systems.