Satisfactory R2 Values Research Articles

Batch and continuous fixed-bed column adsorption of Cs+ and Sr2+ onto montmorillonite–iron oxide composite: Comparative and competitive study

A montmorillonite–iron oxide composite (MIOC) was prepared to assess its effectiveness in the removal of Cs+ and Sr2+ from aqueous solution. A comparative and competitive adsorption study was conducted in single and binary systems. Used materials have been characterized by X-ray diffraction (XRD) and Infrared spectroscopy. Adsorption of Cs+ and Sr2+ as a function of contact time and pH was investigated, adsorption data of single metal solutions were well fitted to the Freundlich–Langmuir isotherm models. Equilibrium isotherms for the binary removal of Cs+ and Sr2+ by MIOC have been analyzed by using non modified and extended Langmuir models with a satisfactory R 2 values. Neutral solution pH was found to be favorable for both single and binary systems. The adsorption model analysis revealed that MIOC was more selective for Sr than Cs. The maximum adsorption capacities for individual Cs+ and Sr2+ solutions were 52.6 and 55.5 mg g−1, respectively. While the maximum uptakes in the binary system were 41.6 and 47.6 mg g−1 for Cs+ and Sr2+, respectively. Column adsorption experiments were carried out at room temperature under the effect of various operating parameters such as bed depth, initial cation concentration and flow rate, Breakthrough curves were well fitted to the Thomas model. Desorption experiments were also conducted to assess the possibility for the reuse of adsorbent and the recovery of cations.

Thermal Diffusivity and Specific Heat of Bovine Milk Affected by Temperature and Composition

Abstract The sizing of equipment used in food processing, particularly heat exchangers and other equipment that require pumping of products, requires accurate data of thermophysical properties. Milk is one of the most processed liquid food fluids in the world and currently data on its thermophysical properties are limited. In a previous paper (Alcântara et al., 2010) density and dynamic viscosity data of bovine milk were presented and how these properties are affected by temperature and composition, in ranges commonly encountered in food processing. Here the thermal diffusivity and specific heat data for milk are presented, evaluating the effect of composition (moisture, fat, lactose, protein and minerals contents) and temperature (only for thermal diffusivity). Linear regression was used and the best models were selected based on the determination coefficient (R²), lack of fit, significance parameters and root mean square error (RMSE) values. Predictive ability of fitted models was compared with Choi and Okos (1986) correlations. Thermal diffusivity ranged from (1.00 to 9.03) × 10-7 m2•s-1 and specific heat from (3.078 to 4.121) kJ•kg-1•K-1. Thermal diffusivity presented a polynomial quadratic behavior affected by temperature and composition, except for lactose concentration which showed no significant effect (p›0.05). For specific heat, increase in the moisture content led to an increase in the specific heat while elevations in fat, protein, lactose and mineral contents promoted a decrease of this property. In both cases the fitted models showed satisfactory R² values, nonsignificant lack of fit (p›0.05) and significant parameters (p‹0.05), with RMSE values lower than Choi and Okos (1986) correlations. From the properties presented here and in the earlier paper, accurate calculations can be made for correct sizing and adaptation of equipment, as well as provide information of other thermophysical properties such as thermal conductivity and thermal expansion coefficient.

Effects of High Pressure and Mild Heat on Endogenous Microflora and on the Inactivation and Sublethal Injury of Escherichia coli Inoculated into Fruit Juices and Vegetable Soup

The objective of this study was to determine the effects of high-pressure treatments and mild temperatures on endogenous microflora and Escherichia coli CECT 515 artificially inoculated into orange and apple juices and vegetable soup. In general, the viability of aerobic bacteria was significantly reduced as pressure and temperature increased. Although the greatest reduction in the concentration of aerobic mesophilic vegetative cells was reached at 350 MPa and 60°C, the same reduction occurred in fruit juices at 350 MPa and 20°C. Yeasts and molds were below the level of detection (l log CFU/ml) for the fruit juices and did not exceed 2 log CFU/ml for vegetable soup. Foods inoculated with E. coli were subjected to several treatments as indicated by the mathematical model applied in response surface methodology to obtain the maximum information with the minimum number of experiments. The number of tests for a range of pressures (150 to 350 MPa) and temperatures (20 to 60°C) was limited to 11. The models were considered adequate because of satisfactory R2 values. The optimum process parameters (pressure and temperature) for a 6-log reduction of E. coli were obtained at 248.25 MPa and 59.91°C in orange juice, 203.50 MPa and 57.18°C in apple juice, and 269.8 MPa and 59.9°C in vegetable soup. Sublethal injury of E. coli occurred as pressure and temperature increased. Nearly all of the E. coli cells were injured at 350 MPa and 20°C in fruit juices and after all treatments in vegetable soup.