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.     

DSC Study of the Thermophysical Properties of Aqueous Liquid and Semi-Liquid Foodstuffs at Freezing Temperatures

Differential scanning calorimetry (DSC) was used to study the thermophysical properties and phenomena occurring in aqueous liquid and semi-liquid foodstuffs at freezing temperatures. Investigations were carried out with fruit juice concentrates, sauces, soups and spinach purée. The phase transitions such as glass transition, irruptive recrys-talization (devitrification), ante-melting transition and melting are faithfully reflected by DSC curves. Besides depending on the temperature, these phenomena depend primarily on the mass fraction of water, and the fraction of other components in the dispersion system. The temperatures of phase transitions (solidification and melting), the latent heat of fusion (ΔH) and specific heat also depend on the same factors.     

Influence of Ultrasound on Freezing Rate of Immersion-frozen Apples

The use of power ultrasound within the food industry is an innovative subject. Application of sound to monitor a process or product is common, e.g. in quality assurance. However, the use of ultrasound to directly improve processes and products is less popular in food manufacturing. In the present work, ultrasound-assisted immersion freezing was investigated on apple samples. Because the apple parenchyma is mechanically anisotropic, the influence of applying ultrasound on radial or tangential orientated samples was also examined. Apple cylinders were immersed in an ultrasonic bath system, which operates at 40 kHz frequency. Experiments were carried out at a power level of 131.3 W (0.23 W/cm²), and ultrasound was applied intermittently for different times from temperatures below and close to the initial freezing point. Results showed that ultrasound application at 0°C or −1°C for 120 s in total, with 30 s intervals, significantly improved the freezing rate represented by the characteristic freezing time up to 8% (P < 0.05), compared to immersion freezing without ultrasound. Results of the effect of ultrasound waves applied on radial or tangential cut samples sonicated for 120 s from −1°C and/or 0°C indicated that at the power level considered there were no significant differences among the ultrasonic radial or tangential irradiated samples of these treatments, though the freezing rates were enhanced and different (P < 0.05) from the control treatment. Some evidence of the influence of ultrasound to induce primary nucleation was also observed.     

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.     

Thermophysical Properties of Okara During Drying

The simulation of heat transfer during thermal treatments of foods requires the knowledge of thermophysical properties of the material. In this study some thermophysical properties of okara, such as density, specific heat, thermal conductivity, thermal diffusivity, heat transfer coefficient, and mass transfer coefficient, were obtained during a drying process. Okara was extruded in the shape of spherical pellets and then dried in a fixed bed dryer from 78% of moisture content (w.b.) until 3%. During the drying process, the water content and the temperature of the samples were periodically measured. The thermal properties were obtained from empirical correlations found in the literature, which use the okara centesimal composition, analyzed in a laboratory, and the relative humidity and velocity of the drying air, measured during the process. The results in this study showed that it is possible to estimate the thermal properties cited using the experimental moisture content history and the centesimal composition of the food.     

不同品种金枪鱼肌肉组织的热物理特性

为研究不同品种金枪鱼肌肉组织的热物理学特性,对5个品种金枪鱼的背部与腹部肌肉进行主要营养成分测定与运用差示扫描量热的方法研究相变过程热特性,同时进行相关性与聚类分析。结果表明:金枪鱼肌肉的比热随温度升高而升高,在融化过程中出现峰值后回归稳定,不同品种金枪鱼的比热值相差不大;通过聚类分析可将样品分为3类,可以根据聚类分类特点指导解冻工艺,以进行差异性的解冻工艺与设备研发。     

Changes in Mitochondrial Properties During Low Temperature Storage of Apples

Mitochondria were isolated from ‘Cortland’ and ‘Winesap’ apples stored at 90% RH and either 1° or 5°C. Respiratory control ratios of mitochondria isolated from ‘Nured Winesap’ apples stored at 5°C were consistently lower than from those stored at 1°C. Succinoxidase and Ca ⁺² ATPase activity was higher in mitochondria of ‘Cortland’ apples stored at 1°C. Large increases were observed in mitochondrial Ca ⁺² uptake after 4 wk storage of ‘Nured Winesap’ apples at 5°C and after 1 wk storage of ‘Cortland’ apples at 1°C. Although no symptoms of chilling injury were observed in the tissue of either cultivar, the mitochondrial response suggested chilling resistance in ‘Nured Winesap’ apples and chilling sensitivity in ‘Cortland’ apples.     

Thermophysical Properties of Extruded Beef/Corn Flour Blends

Thermal properties, specific heat, and thermal conductivity of three beef/corn meal blends extruded to reach end product temperatures of = 91°C and 109°C were analyzed. Density was also measured and used to calculate thermal diffusivity. The extruded products had densities of 1,054 to 1,091 kg/m³; specific heat was 2.944 to 3.055 kJ/ kgK; and thermal conductivity, 0.26 to 0.39 W/mK. Calculated values of thermal diffusivity were 0.831 to 1.200 (xl0^-7m7sec). With the exception of specific heat, extrusion conditions and formulation affected some of the products physical characteristics and thermal properties.     

江苏富士苹果的理化及感官特性分析

江苏省苹果以丰县为集中产地,富士为主栽品种,隶属于黄河故道产区,为明确其鲜食特性的地域特点,对丰县富士糖酸含量、色泽和质构等理化指标和硬性、易碎性、多汁性、酸甜度等感官属性进行了测定,并与陕西富士进行了比较。结果显示丰县苹果蔗糖和苹果酸含量偏低,分别为陕西苹果的75.88%和58.90%。江苏苹果果皮L*为64.37,a*值为11.19,b*值为32.12,a*值低而L*、b*值高于陕西苹果,说明果皮红色弱而偏黄色;果肉L*值为81.19,b*值为29.00,L*值低而b*值高于陕西苹果,说明果肉色泽偏黄。质构仪测得江苏苹果的脆度显著高于陕西苹果。感官评价结果显示江苏苹果具有硬性低、易碎、易嚼、酸度低的特点,而多汁性和甜度差异不显著。在偏爱性比较中,73.7%的评价人员偏爱陕西苹果的色泽,而对滋味和质地的偏爱程度差异不显著。研究结果将为江苏富士品质评价提供借鉴。     

发育后期苹果的介电特性与理化特性的关系

为了解发育后期苹果的介电特性、生理特性和内部品质的变化规律以及三者之间的关系,采用同轴探头技术测量发育后期3 个月内‘富士’苹果在20～4 500 MHz间的相对介电常数ε’和介质损耗因子ε”,同时测量苹果果实的生理特性（乙烯释放量和呼吸强度）和内部品质（可溶性固形物含量（soluble solids content,SSC）、硬度、pH值和含水率）。结果表明：ε’随频率的增加而减小,ε”在2 000 MHz附近存在极小值;随着果实逐渐发育成熟,ε’和ε”逐渐减小。整个发育后期,果实的SSC和果汁的pH值呈上升趋势,硬度呈下降趋势;乙烯释放高峰出现在2 个呼吸高峰之间。ε’和ε”与SSC、硬度和pH值在特定的频率范围内存在较好的线性相关性。研究说明,苹果的介电特性是生理特性与内部品质的综合反映,根据介电参数值判断苹果的成熟情况以及用单一频率下的介电参数值评价苹果的内部品质均可行。     

热烫处理苹果片真空冻结特性

The vacuum freezing properties of blanched apple slices were investigated by comparing with traditional refrigerator freezing. Results showed that after 40 min vacuum freezing, a mass loss of 27.5% and the lowest frozen temperature of -27.6 ℃ were achieved in apple slices pretreated by blanching, while a mass loss of 22.9% and the lowest frozen temperature of -26.5 ℃ were obtained in non-blanched apple slices. The total process of vacuum freezing was divided into low pressure flash evaporation stage, ice crystal formation stage and deep freezing stage. Vacuum freezing caused less microstructural changes and less significant cell disruption and contributed to smaller thawing loss and weaker relative electrical conductivity in frozen-thawed apple slices in contrast to refrigerator freezing. Blanching pretreatment before freezing caused more severe damage to cell microstructure in apple slices than non-blanching pretreatment, resulting in a significant increase in thawing loss and relative electrical conductivity in frozen-thawed apple slices.     

Beet Pulp and Isolated Pectin Physicochemical Properties as Related to Freezing

Any potential effects of postharvest freezing storage of beets on physicochemical characteristics of isolated pectin and beet pulp were determined. Fresh beets were stored at -20°for up to 3 mo. At the end of storage, beets were thawed and shredded, and sucrose was extracted. Pectin was isolated using a combination of enzyme treatment and acid extraction. Yield, galacturonic acid content, methoxyl ester content, and molecular mass distributions of the isolated pectin were determined. Neutral and acidic sugar compositions in the nonstarchy polysaccharides (NSP) of the beet pulp were determined using enzyme hydrolysis and gas chromatography. Results showed that physicochemical characteristics of isolated pectin, and sugar composition of the NSP in the beet pulp were not notably influenced by the freeze/thaw cycle.     

Mechanical Properties of Gellan Gels in Relation to Divalent Cations

Mechanical behavior of gels formed with gellan polymer crosslinked by calcium and magnesium ions was studied to determine the influence of divalent ion type and polymer concentration. Failure strength and deformation were measured in compression and related to concentrations of gellan and bound cations in gel matrices. Insufficient cations formed weak, extensible gels. Maximum gel strength was achieved at 0.5 divalent cations/repeat tetrasaccharide unit, assumed to be the condition for maximal numbers of complete junction zones. At optimum cation levels gels with Ca⁺⁺ were about 1.2 times stronger than gels with Mg⁺⁺ at the same polymer concentration. Excessive cations weakened the gels. Twice as much reduction in gel strength resulted from additional Ca⁺⁺ as compared to the same additional amount of Mg⁺⁺. Differences between strengths of the gels may be attributable to polymer configurations at junction zones in relation to cation size.     

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.     

低温冷冻技术对纸张性能的影响

目前图书馆、档案馆多选用低温冷冻技术杀灭害虫。为研究该技术对纸张的影响,选择6种纸样(道林纸、字典纸、双胶纸、打字纸、新闻纸和试卷纸)进行180个周期的低温冷冻处理,测定其与室温下避光保存纸样的机械性能和水抽提液pH值等性能指标的相对变化。结果显示,各项性能指标相对变化率基本都不超过5%,只有打字纸冷冻后抗张指数相对变化率达到8. 6%。因此多次低温冷冻基本不会对纸张性能造成影响,还有利于缓解漂白程度较高的纸张保存过程中白度和抗张强度的下降程度,适宜用于图书档案的杀虫操作。     

Physical Properties of Canadian Grown Flaxseed in Relation to Its Processing

The average flaxseed length, width, thickness and 1000 seed mass were 4.64 mm, 2.37 mm, 1.0 mm and 5.77 g, respectively. The average surface area was 15.49 mm² while the sphericity and aspect ratio were 0.48 and 51.04%, respectively. The average bulk density was 652.16 kg/m³ while the true density was 784.36 kg/m³, and the corresponding porosity was 16.83%. The angle of repose for flaxseed was 24.40 while the terminal velocity was 2.9 m/s. The results showed that the mean value of static coefficient friction was least in case of plastic sheet while it is highest for rubber sheet.     

Properties of Potato Starch in Relation to Varieties and Environmental Factors

An extensive assortment of potato varieties in connection with different growing conditions was analyzed concerning several starch quality criteria. Significant variations were evident for starch content, phosphorus content of starch, and granule size distribution. On the contrary, amylose content varied only little. Environment had influence on starch content and viscosity behaviour. Fertilization effects could not be observed. This underlines the significant variety effect. The results clearly point out that an improved accentuation of potato starch quality is possible. In connection with a selected variety spectrum and altered separation strategies new markets for potato starch utilizers can be opened within short time.     

Physicochemical Properties of Mammalian Gelatin in Relation to Membrane Process Requirement

In any of the membrane process application, understanding of the characteristics of the feed solution is essential in order to achieve desired level of separation performance. In this study, in an effort to substitute evaporation with membrane processes partially, experiments were carried out to investigate the physicochemical properties of gelatins, namely, molecular weight distribution, pH, viscosity, isoelectric point, and gel strength, which are, of foremost, important parameters in the characterization of gelatin. Two different mammalian gelatins, i.e. from bovine (type B) and porcine (type A) sources, were used in this study. The pH was significantly varied for all gelatins in the vicinity of 4.75–5.51 (±0.01). Experimental result revealed that both sources of mammalian gelatin contained components of different molecular weights with wide distribution ranging from 10 to 400 kDa. Analysis of the molecular weight distribution result also showed strong correlation between average molecular weight and gel strength of gelatin. The isoelectric points of gelatins from bovine were 4.60 ± 0.08 to 5.25 ± 0.43 and porcine gelatins were in the range of 7–9.3, which agreed well with the results obtained from other researchers. The high bloom strength mammalian gelatins were also significantly more viscous and thus, had a higher melting point.     

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.