MODELING THERMAL SOFTENING KINETICS OF POTATOES USING FRACTIONAL CONVERSION OF RHEOLOGICAL PARAMETERS

Texture degradation in potatoes was investigated during heating of cylindrical test samples, 15 mm diameter and 30 mm long, in water at 60, 70, 80 and 90C by mechanical testing. The rheological parameters obtained from the axial and radial compression, creep and stress relaxation tests decreased exponentially with an increase in heating duration and temperature approaching steady levels corresponding to the remaining texture after prolonged heating. A single first-order kinetic model described the changes in various rheological parameters due to thermal softening of potatoes using fractional conversion technique indicating very high values of the coefficient of determination (R² > 0.97). In general, the visco-elastic test parameters were relatively more sensitive to texture degradation in potatoes in comparison with the quasi-static test parameters. Overall comparison showed that elasticity and viscosity parameters in Kelvin component of the 4-element model (E₂ and η₂) from creep tests and elasticity moduli from axial and radial compression tests (E_a and E_r) best presented the texture degradation kinetics in potatoes with R² ranging from 0.98 to 0.99.     

Modeling changes in rheological properties of potatoes during storage under constant and variable conditions

The changes in rheological properties of potatoes stored at 5, 15, 25 °C and variable (fluctuating) temperature for 16 or 26 weeks were evaluated in terms of elasticity and viscosity parameters using axial compression and creep tests. Cylindrical test specimens (15 mm diameter and 30 mm long) were used. A third-degree polynomial best fitted the force-deformation curves in axial compression test (R²=0.98-0.99) whereas a four-element (Burgers) mechanical model adequately described the creep response of potatoes (R²=0.95-0.99). The tangent modulus of elasticity in axial compression and elasticity and viscosity parameters in creep tests in general decreased significantly (P<0.05) with increase in storage time both under constant and variable storage conditions. The changes in rheological properties of potatoes stored under constant storage condition were sufficiently described by a modified exponential model (R²=0.89-0.96) except for the viscosity parameter of the Maxwell component of the four-element model. The logarithm of degradation rate constant, k, and the constant, n, were linearly related to storage temperature. For the variable storage condition, a bulk mean temperature (T_bm) was calculated to account for a series combination of storage time and temperature to which the potatoes were subjected. The changes in rheological properties due to variable storage temperature were then described as a function of T_bm and storage time, t_s, using stepwise multiple regression. The result indicated that except the viscosity parameter of the Maxwell component of the four-element model, it was possible to describe the changes in rheological properties as a function of T_bm and t_s (R²=0.84-0.99).     

COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENING

The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R²= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes.     

Relationship of Water Content to Textural Characteristics, Water Activity, and Thermal Conductivity of Some Commercial Sausages

Mechanical properties from cyclic low strain testing, texture profile parameters and thermal conductivity were evaluated for 7 types of commercial sausage products ranging in moisture content from 27.7% to 62.4% and a_w from 0.857 to 0.993. Hardness, fracturability, the apparent moduli, stress al 20% compression, mechanical hysteresis loss, and strain energy all increased with decreasing moisture level, while springiness and the degree of elasticity decreased. Moisture had no significant effect on cohesiveness. A linear relationship was observed between the a_w and the effective mole fraction of water in the brine, the exact nature of which depended on the thermal process which the product had received. Thermal conductivity decreased with decreasing moisture in a linear manner.     

Migration of antimony from PET trays into food simulant and food: determination of Arrhenius parameters and comparison of predicted and measured migration data

Migration experiments with small sheets cut out from ovenable PET trays were performed in two-sided contact with 3% acetic acid as food simulant at various temperatures. The fraction of diffusible antimony (Sb) was estimated to be 62% in the PET sample under study. Apparent diffusion coefficients of Sb in PET trays were determined experimentally. Measurement of migration between 20 and 150°C yielded a linear Arrhenius plot over a wide temperature range from which the activation energy (E _a) of 188?±?36?kJ?mol^?1 and the pre-exponential factor (D ₀) of 3.6?×?10¹⁴?cm²?s^?1 were determined for diffusing Sb species. E _a was similar to previously reported values for PET bottles obtained with a different experimental approach. E _a and D ₀ were applied as model parameters in migration modelling software for predicting the Sb transfer in real food. Ready meals intended for preparation in a baking oven were heated in the PET trays under study and the actual Sb migration into the food phase was measured by isotope dilution ICP-MS. It was shown that the predictive modelling reproduces correctly experimental data.     

Drying characteristics and thermal degradation kinetics of hardness,anthocyanin content and colour in purple‐ and red‐fleshed potato (Solanum tuberosum L.) during hot air drying

Purple‐fleshed potatoes (PFP) and red‐fleshed potatoes (RFP) were dried using hot air. The hardness, anthocyanin content and colour in PFP and RFP during drying were evaluated at 60, 70 and 80 °C. The hardness was characterised by a softening stage in the early drying period, followed by a hardening stage. The times to reach at the transition were 420, 300 and 240 min at 60, 70 and 80 °C, respectively, for PFP, and 480, 360 and 240 min for RFP. However, the moisture content of both PFP and RFP at the transition time was identical at 0.3 (d.b.). The two stages of hardness changes were well described by combining two modified first‐order kinetics models. The activation energy (E_a) for the degradation of anthocyanin in PFP and RFP was 25.12 and 28.43 kJ mol^?1, respectively. The E_a values demonstrated that the thermal sensitivity of PFP was higher than that of RFP.     

Thermal stability of processed PVC/bamboo blends: effect of compounding procedures

Polyvinyl chloride (PVC) was mixed with bamboo (Bambusa vulgaris) particle and additives by using PVC composite manufacturing system including initial dry blending with hot-cool mixing, followed by granulation via counter-rotating extrusion, and then consolidation by compression moulding to produce compression moulded board (CMB). The effects of different bamboo particle size (75 µm and 1 mm), bamboo particle loading (25 and 50% loading ratio), and differing processing lubricants content level (compositions 1 and 2) on the thermal stability of the composites were determined. Results show no significant trends in glass transition temperature (T_g) between dry blends, granules, and CMB, and between B. vulgaris particle loading at the respective processing steps. For samples with higher lubricant contents, the PVC T_g was observed to decrease up to 5?°C, possibly due to the reduced melt viscosity. The thermal decomposition temperature at 5% mass loss (T_?5%) appeared to decrease from dry blend to CMB due to sample degradation on further processing at higher temperatures. The use of 50% B. vulgaris particle loading also reduced the T_?5% values, assignable to bamboo particle degradation caused by the high processing temperatures. For oxidative induction time (OIT) testing, only granules and CMB from pure PVC composites system showed measurable oxidative times compared with OIT profiles of PVC/B. vulgaris composites system, suggestive of comparatively stabilized thermoplastic composites. This revealed that processing with bamboo particles does not contribute to degradation of PVC composites.     

Investigation of mechanical properties of sandwich panels made of paper honeycomb core and wood composite skins by experimental testing and finite element (FE) modelling methods

In this study, lightweight sandwich panels with different Kraft paper honeycomb core structures and wood composite skins were constructed. The influence of structural parameters, including core shape, cell size, core density, core and web thickness, and material properties of the core and skin layers on the mechanical behavior of these lightweight sandwich panels were studied by experimental testing and finite element modeling methods. The panels were subjected to compression and shear loadings. Test and simulation results indicated that core density and core shape mainly affected the panel stiffness under out-of-plane loading conditions (e.g. E _z , G _xz and G _yz ). Material properties of the skin layer affected the panel stiffness both under in-plane and out-of-plane loadings if the skin layer was orthotropic.     

白萝卜常规力学特性试验

为了获得白萝卜的力学性质并提供其在采收、运输、储藏及工业生产中必要的理论依据,以加载部位、方向、速度及含水率为影响因素进行试验,分析各因素对白萝卜常规力学特性(应力,弹性模量)的影响。结果表明:白萝卜的中部抗压能力较强、下部较弱(弹性模量分别为2.16,2.07 MPa);白萝卜是各向异性的,且轴向抗压能力比径向的强(弹性模量轴向2.19 MPa、径向1.98 MPa);含水率对弹性模量影响显著,且弹性模量随着含水率降低而增加。因此,白萝卜在运输和储藏过程中,应尽量避免径向受力。     

Osmotic dehydration of apple: Influence of sugar and water activity on tissue structure,rheological properties and water mobility

Osmotic dehydration of apple tissue (Malus pumila, Granny Smith cultivar) to water activity (a_w) 0.97 or 0.94 with maltose or maltose syrup solutions was studied and compared with previous results using glucose or trehalose as humectants. Structure (optical and transmission electronic microscopy observations), rheological properties (small scale dynamic oscillatory and creep/recovery measurements and large scale compression force-deformation testing), and water mobility (¹H NMR spectra) of parenchymatous apple tissue were significantly affected by osmotic treatments. Osmotically dehydrated apples became soft and extensible and lost crispness and hardness, while the behavior of the moduli G′ and G″ indicated weaker gels after osmosis. Compression properties of the tissues abruptly changed after osmotic dehydration to a_w 0.97, while reduction to a_w 0.94 led to a compression response more similar to that of untreated apples. Compression behavior and state and distribution of water in apple tissues were influenced by the osmotic agent employed and the a_w level, while in general mechanical spectra and creep analysis were not able for distinguishing physical differences between osmotic treatments assayed.     

Mitigation of enteric methane emissions through improving efficiency of energy utilization and productivity in lactating dairy cows

The data set used in the present study was obtained from 20 energy metabolism studies involving 579 lactating dairy cows (511 Holstein-Friesian, 36 Norwegian Red, and 32 Jersey-Holstein crossbreds) varying in genetic merit, lactation number, stage of lactation, and live weight. These cows were offered diets based on grass silage (n = 550) or fresh grass (n = 29), and their energy intake and outputs, including methane energy (CH₄-E), were measured in indirect open-circuit respiration calorimeter chambers. The objective was to use these data to evaluate relationships between CH₄-E output and a range of factors in animal production and energetic efficiency in lactating dairy cows under normal feeding regimens. The CH₄-E as a proportion of milk energy output (E_l), E_l adjusted to zero energy balance (E_l(0)), or intakes of gross energy (GE), digestible energy (DE), or metabolizable energy (ME) was significantly related to a wide range of variables associated with milk production (E_l and E_l(0)) and energy parameters (energy intake, metabolizability, partitioning, and utilization efficiencies). Three sets of linear relationships were developed with experimental effects removed. The CH₄-E/GE intake (r² = 0.50-0.62) and CH₄-E/E_l (r² = 0.41-0.68) were reduced with increasing feeding level, E_l/metabolic body weight (MBW; kg^0.75), E_l(0)/MBW, GE intake/MBW, DE intake/MBW, and ME intake/MBW. Increasing dietary ME/DE decreased CH₄-E/E_l (r² = 0.46) and CH₄-E/GE intake (r² = 0.72). Dietary ME concentration and ME/GE were also negatively related to CH₄-E/GE intake (r² = 0.47). However, increasing heat production/ME intake increased CH₄-E as a proportion of E_l (r² = 0.41), E_l(0) (r² = 0.67) and energy intake (GE, DE, and ME; r² = 0.62 and 0.70). These proportional CH₄-E variables were reduced with increasing ratios of E_l/ME intake and E_l(0)/ME intake and efficiency of ME use for lactation (r² = 0.49-0.70). Fitting CH₄-E/E_l or CH₄-E/E_l(0) against these energetic efficiencies in quadratic rather than linear relationships significantly increased r² values (0.49-0.67 vs. 0.59-0.87). In conclusion, CH₄-E as a proportion of energy intake (GE, DE, and ME) and milk production (E_l and E_l(0)) can be reduced by increasing milk yield and energetic efficiency of milk production or by reducing energy expenditure for maintenance. The selection of dairy cows with high energy utilization efficiencies and milk productivity offers an effective approach to reducing enteric CH₄ emission rates.     

纤维轴向压缩性能测试及其刺痒感属性判断

为探讨纤维材料的轴向压缩性能及其刺痒感属性,改进了测试装置与测试方法,对测试过程中纤维试样与测试头接触条件的转变及对应压缩曲线特征进行分析,提出了应用纤维轴向压缩性能判断其刺痒感属性的方法。结果表明:在进行纤维材料轴向压缩测试时,试样与测试头的接触条件会发生由"点接触"向"线接触"的转变,压缩性能测试应以"点接触"的结束为终结点;以纤维轴向压缩性能为依据判断其刺痒感属性时,纤维端与皮肤的接触条件应为"点接触",且应具有不少于0.2 mm的长度,并能承受不少于0.75 m N的轴向载荷。     

The Use of Fractional Conversion Technique to Investigate the Effects of Testing Parameters on Texture Degradation Kinetics

ABSTRACT: To study the effects of testing parameters on texture degradation, texture loss of potatoes heated at 80 °C was measured using an Instron universal testing machine as well as a texture analyzer under 2 instrument crosshead speeds, 2 sample sizes, and either compression or shear modes of mechanical deformation. Using the fractional conversion as a texture index, the kinetics of texture degradation of potatoes fitted a single 1^st order reaction model, and the rate constant (or D value) was shown to be independent of the test used to determine the texture index. The average D value was 30 ± 1.2 min at 80 °C.     

Flow Properties of Low-Pulp Concentrated Orange Juice: Serum Viscosity and Effect of Pulp Content

65° Brix serum samples from four concentrated orange juice (COJ) samples, between -19 and 30°C, were mildy shear-thinning fluids with negligible yield stress. The power law model described well the flow data. For one sample, the Powell-Eyring model also described the data. The activation energy of flow (E_a) for the samples was between 11.2–13.6 kcal/gmole. The power law parameters were determined for a 65°Brix sample as a function of pulp content (0–11%) between −19 and 30°C. At a fixed temperature, the apparent viscosity and the consistency index increased exponentially with pulp content. E_a decreased with increase in pulp content and reached a constant value of about 10.2 kcal/gmole. Data on a high-pulp (21.2%), 65° Brix, sample indicated the presence of yield stress, particularly at low temperatures. The Mizrahi-Berk model predicted reliable values of the yield stress.     

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.     

Impact of Thermal and Chemical Pretreatments on Physicochemical,Rheological, and Functional Properties of Sweet Potato (Ipomea batatas Lam) Flour

The impact of thermal and chemical pretreatments on the physicochemical, rheological, and functional properties of sweet potato flour was investigated. The chemical pretreatment consisted in dipping peeled sweet potatoes in 1 % (w/v) calcium chloride (CaCl₂), while the thermal pretreatment was achieved by blanching them in tap water at 90 °C for 1 min. Composition in flour moisture, protein, fat, non-reducing sugars, and starch was determined using standard methods. Particle size, color, gelatinization, and rheological properties were analyzed. The water absorption index (WAI) and water solubility index (WSI), as well as the swelling capacity (SC) and sorption isotherms, were determined. The reducing sugar content of sweet potato flour was slightly higher in CaCl₂-pretreated (SSPCaCl₂) samples than that in blanched (SSPB) and control (SSP) samples. However, the lightness of the SSPB sample was lower than that of the SSPCaCl₂ and SSP samples. SSPCaCl₂ sample had the higher value of enthalpy of gelatinization and elasticity modulus G′. The SC was higher in blanched samples. A slight increase in the constant of water binding energy (C _BET) was observed after the CaCl₂ treatment and a marked increase for the blanched sample. Owing to the differences induced by blanching and CaCl₂ pretreatments, CaCl₂-pretreated flour samples are more suitable for bread-making processes and can also be used in food formulations.     

Correlations of milk and serum element concentrations with production and management traits in dairy cows

The present study investigated the potential consequences, positive or negative, that selection for favorable production-related traits may have on concentrations of vitamin B₁₂ and key chemical elements in dairy cow milk and serum and the possible impact on milk healthiness, and associated benefits, for the dairy product consumer. Milk and serum samples (950 and 755, respectively) were collected from Holstein-Friesian dairy cows (n = 479) on 19 occasions over a 59-mo period, generating 34,258 individual records, and analyzed for concentrations of key trace and quantity elements, heavy metals, and milk vitamin B₁₂. These data were then matched to economically important production data (milk, fat, and protein yield) and management data (dry matter intake, liveweight, and body condition score). Multivariate animal models, including full pedigree information, were used to analyze data and investigate relationships between traits of interest. Results highlighted negative genetic correlations between many quantity and trace elements in both milk and serum with production and management traits. Milk yield was strongly negatively correlated with the milk quantity elements Mg and Ca (genetic correlation between traits, r_a = ?0.58 and ?0.63, respectively) as well as the trace elements Mn, Fe, Ni, Cu, Zn, and Mo (r_a = ?0.32, ?0.58, ?0.52, ?0.40, ?0.34, and ?0.96, respectively); and in serum, Mg, Ca, Co, Fe, and Zn (r_a = ?0.50, ?0.36, ?0.68, ?0.54, and ?0.90, respectively). Strong genetic correlations were noted between dry matter intake with V (r_a = 0.97), Fe (r_a = ?0.69), Ni (r_a = ?0.81), and Zn (r_a = ?0.75), and in serum, strong negative genetic correlations were observed between dry matter intake with Ca and Se (r_a = ?0.95 and ?0.88, respectively). Body condition score was negatively correlated with serum P, Cu, Se, and Pb (r_a = ?0.45, ?0.35, ?0.51, and ?0.64, respectively) and positively correlated with Mn, Fe, and Zn (r_a = 0.40, 0.71, and 0.55, respectively). Our results suggest that breeding strategies aimed at improving economically important production-related traits would most likely result in a negative impact on levels of beneficial nutrients within milk for human consumption (such as Mg, Ca, Fe, Zn, and Se).     

Water and Glycerol as Plasticizers Affect Mechanical and Water Vapor Barrier Properties of an Edible Wheat Gluten Film

Glycerol improved film extensibility but reduced film puncture strength, elasticity, and water vapor barrier properties. The plasticizing effect of water was highly temperature dependent. During hydration of gluten film, a sharp decrease in puncture strength, elasticity, and an increase of extensibility and water vapor transmission rate were observed at 5, 30 and 50°C for respective water contents of 30 (0,8 a_w,), 15 (0,7 a_w) and 5% (0,4 a_w). This was related to disruptive water-polymer hydrogen bonding and glass-to-rubber transition.     

Flexural properties of black locust (Robinia pseudoacacia L.) small clear wood specimens in relation to the direction of load application

LR , G_LT) were calculated in juvenile and mature black locust defect-free small wood specimens after loading in static bending alternately on true radial and tangential surfaces. For both juvenile and mature specimens, no significant differences (t-test, 95% probability level) were found between the radial and tangential moduli of elasticity and rigidity. Values of PMOE were found to be 27–32% higher than the corresponding values of MOE at the 15:1 span-to-depth ratio.

---

Biege-Eigenschaften von kleinen fehlerfreien Holzproben der Robinie (Robinia pseudoacacia L.) im Verh?ltnis zur Richtung des Kraftangriffs

LR , G_LT) wurden berechnet für juveniles und reifes Robinienholz. Die Berechnung erfolgte anhand von fehlerfreien Proben nach statischer Belastung, und zwar abwechselnd in genau radialer bzw. tangentialer Richtung. Für juvenile und Reifholzproben wurden keine statisch signifikanten Unterschiede gefunden zwischen den Werten des radialen MOE und der Schubmodule G_LR und G_LT (t-Test, 95% Niveau). Die Werte der reinen Biegemodule (PMOE) erwiesen sich als 27–32% h?her als die entsprechende MOE-Werte bei einem Verh?ltnis von Spannweiten zu Tiefe von 15:1.

     

Thermo-Kinetic Modeling of Peroxidase Inactivation during Blanching-Cooling of Corn on the Cob

A thermo-kinetic model of peroxidase inactivation in corn on the cob during blanching-cooling is developed. Heat transfer during the blanching-cooling step is modeled as a conduction process in well stirred media of constant temperature. Corn on the cob is considered as a finite cylinder with a single thermal diffusivity value. The kinetic parameters k_r and E_a are calculated by using an unsteady state trial and error procedure. The model allows the calculation of the peroxidase activity retention for the kernel, outer cob, and central cob. Theoretical results are compared against experimental data showing a very good agreement.