Central Composite Rotatable Experimental Design Research Articles

Effects of maturity stage and mild heat treatments on quality of minimally processed kiwifruit

A central composite rotatable experimental design was used on kiwifruits of two distinct maturity stages (firm ripe and soft ripe), subjected to mild heat pre-treatments by immersion during 10–90 min in water at temperatures of 25–50 °C. Minimal processing of the fruits was performed 24 h after the heat treatment and soluble solid content, colour and texture properties were analysed in the samples during the whole storage period (0–10 days). For both maturity stages, the effect of heat treatment on colour was negligible. For fruits of the early maturity stage (firm ripe), total content of soluble solids increased with the mild heat pre-treatments. Pre-treatments avoided texture breakdown in firm ripe kiwi slices. Firmness, the most sensitive parameter, is increased or preserved using treatment periods of up to 40 min. Favourable responses were evidenced immediately after them and during the whole storage period. Therefore, mild heat pre-treatments, when applied to firm ripe kiwi at temperatures below 45 °C during less than 25 min improve the quality, mainly the firmness, colour being only marginally affected.

Optimisation of the acidulation process of soapstock from the neutralisation of rice bran oil

Soapstock from the neutralisation of rice bran oil was characterised through the most important parameters with direct influence on the acidulation process. A central composite rotational experimental design of two levels was used. The responses of the trials were γ -oryzanol concentration in the acid oil and process time necessary for total hydrolysis of the soaps present. The optimal process conditions were determined using the response surface methodology. Adjustments were made to second order mathematical models and validity was verified by analysis of variance using the STATISTICA program. The process variables studied were: molar ratio - sulphuric acid/soaps (0.55-0.95) and process temperature (70- 100 °C ). The results indicated that the process temperature does not significantly interfere in the concentration of γ -oryzanol of the acid oil, but it does affect process time. In the different concentrations of sulphuric acid added, represented by the molar ratio of sulphuric acid/soaps, the concentration of γ -oryzanol varied between 3.13 and 3.74 %. Through the superposition of the areas of the response surface contour curves the optimal process parameters were determined: process temperature of 95 °C and molar ratio of sulphuric acid/soaps of 0.74, resulting in a γ -oryzanol concentration of 3.64 % and a process time of 90 minutes.

Isolation of brandy aroma by countercurrent supercritical fluid extraction

Optimization of the countercurrent supercritical fluid extraction (CC-SFE) conditions to obtain high quality brandy aroma extracts is presented. The main variables that influence CC extraction selectivity and efficiency have been studied, such as extraction pressure and temperature and sample flow rate (related to the solvent-to-feed ratio). A rotatable central composite experimental design is used to optimize the combination of these experimental. Experiments have been performed with brandy using a CC-SFE system at pilot plant scale. The beverage is put directly in contact with the carbon dioxide in a packed column and the extracts are recovered in two different fractionation cells, where depressurization occurs. For each experiment, two extracted fractions and a raffinate are obtained and its aroma characterized by gas chromatography. A statistical study of the data obtained is performed including analysis of variance (ANOVA), fitting of a regression model and response surface study. The obtained results allow to know the variables that clearly influence the process and also show the interest of CC-SFE as an useful technique to obtain high-value concentrated brandy aroma extracts.

Mineralization of a sorbed polycyclic aromatic hydrocarbon in two soils using catalyzed hydrogen peroxide

Hydrogen peroxide (H 2O 2) catalyzed by soluble iron or naturally occurring soil minerals, (i.e., modified Fenton's reagent) was investigated as a basis for mineralizing sorbed and NAPL-phase benzo[ a]pyrene (BaP), a hydrophobic and toxic polycyclic aromatic hydrocarbon, in two soils of different complexity. 14C-Benzo[ a]pyrene was added to silica sand and a silt loam soil, and mineralization was investigated using three-level central composite rotatable experimental designs. The effects of H 2O 2 concentration, slurry volume, and iron(II) amendment were investigated in the silica sand systems. In a Palouse loess silt loam soil, the variables included H 2O 2 concentration, slurry volume, and pH, with H 2O 2 catalyzed by naturally occurring iron oxyhydroxides. Regression equations generated from the data were used to develop three-dimensional response surfaces describing BaP mineralization. Based on the recovery of 14C-CO 2, 70% BaP mineralization was achieved in the sand within 24 h using 15 M H 2O 2 and an iron(II) concentration of 6.6 mM with a slurry volume of 0.3×the field capacity of the sand. For the silt loam soil, 85% mineralization of BaP was observed using 15 M H 2O 2, no iron amendment, and a slurry volume of 20×the soil field capacity. The balance of the radiolabeled carbon remained as unreacted BaP in the soil fraction. Gas-purge measurements over 5 d confirmed negligible desorption under nontreatment conditions. However, oxidation reactions were complete within 24 h and promoted up to 85% BaP mineralization, documenting that the natural rate of desorption/dissolution did not control the rate of oxidation and mineralization of the BaP. The results show that catalyzed H 2O 2 has the ability to rapidly mineralize sorbed/NAPL-phase BaP and that partitioning, which is often the rate-limiting factor in soil remediation, does not appear to limit the rate of vigorous Fenton-like treatment.

Study of the total replacement of egg by white lupine protein, emulsifiers and xanthan gum in yellow cakes

The possibility of a total substitution of egg proteins in yellow cakes by vegetable proteins isolated from white lupine seeds was studied. The effects of several components on hardness, moisture content, volume, and shape characteristics of lupine-cakes were evaluated, using response surface methodology. Baking powder, soy lecithin, and mono- and diglycerides (MDG), were studied through a central composite rotatable experimental design and an optimization of the leavening agent proportion was achieved; however, an undesirable collapse of the cakes was observed. This problem was solved by the combined use of emulsifiers (MDG) and hydrocolloids (xanthan gum) in a second experimental design. Xanthan gum improved the internal structure of crumb, reducing shrinkage and increasing the cake height. Optimum contents for the lupine-gum-emulsifier system were: 2.2% baking powder, 4.5% MDG, and 0.55% xanthan gum, all relative to the total weight of flour and sugar.

Evidence for Simultaneous Abiotic−Biotic Oxidations in a Microbial-Fenton's System

The conditions that support the simultaneous activity of hydroxyl radicals (OH.) and heterotrophic aerobic bacterial metabolism were investigated using two probe compounds: (1) tetrachloroethene (PCE) for the detection of OH. generated by an iron-nitrilotriacetic acid (Fe-NTA) catalyzed Fenton-like reaction and (2) oxalate (OA) for the detection of heterotrophic metabolism of Xanthobacter flavus. In the absence of the bacterium in the quasi-steady-state Fenton's system, only PCE oxidation was observed; conversely, only OA assimilation was found in non-Fenton's systems containing X. flavus. In combined Fenton's-microbial systems, loss of both probes was observed. PCE oxidation increased and heterotrophic assimilation of OA declined as a function of an increase in the quasi-steady-state H2O2 concentration. Central composite rotatable experimental designs were used to determine the conditions that provide maximum simultaneous abiotic-biotic oxidations, which were achieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NTA. These results demonstrate that heterotrophic bacterial metabolism can occur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbial oxygen source or as a source of chemical oxidants. In addition, hybrid abiotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.

A foundation for the risk-based treatment of gasoline-contaminated soils using modified Fenton's reactions

The relative oxidation of representative aromatic and aliphatic hydrocarbons found in gasoline was evaluated to provide the foundation for risk-based treatment of petroleum-contaminated soils and groundwater using modified Fenton's reagent (catalyzed hydrogen peroxide). Aromatic components of gasoline are considered more hazardous than the aliphatic fractions due to their higher mobility in the subsurface and their higher acute and chronic toxicities. Benzene, toluene, and mixed xylenes (BTX) were selected as aromatic compounds representative of unleaded gasoline, while nonane, decane, and dodecane (NDD) were used as model aliphatic compounds. The effects of hydrogen peroxide (H 2O 2) concentration, iron catalyst concentration, and pH on the degree of treatment of the model compounds were investigated using central composite rotatable experimental designs. Oxidation of the aromatic compounds required less iron and less H 2O 2 than did oxidation of the aliphatic compounds, while proceeding more effectively at near-neutral pH. Greater than 95% of the BTX was treated at near-neutral pH using 2.5% H 2O 2 and 12.5 mM iron (III), while only 37% nonane, 7% decane, and 1% dodecane oxidation was achieved under the same conditions. The results show that the more toxic and mobile aromatic fraction was more effectively oxidized using less H 2O 2 and more economical conditions, including near-neutral pH, compared to the aliphatic fraction. A process design based on treating only the aromatic fraction of petroleum may provide significantly lower costs when using modified Fenton's reagent for the treatment of contaminated soils and groundwater.

Optimization of simultaneous chemical and biological mineralization of perchloroethylene.

Optimization of the simultaneous chemical and biological mineralization of perchloroethylene (PCE) by modified Fenton's reagent and Xanthobacter flavus was investigated by using a central composite rotatable experimental design. Concentrations of PCE, hydrogen peroxide, and ferrous iron and the microbial cell number were set as variables. Percent mineralization of PCE to CO2 was investigated as a response. A second-order, quadratic response surface model was generated and fit the data adequately, with a correlation coefficient of 0.72. Analysis of the results showed that the PCE concentration had no significant effect within the tested boundaries of the model, while the other variables, hydrogen peroxide and iron concentrations and cell number, were significant at alpha = 0.05 for the mineralization of PCE. The 14C radiotracer studies showed that the simultaneous chemical and biological reactions increased the extent of mineralization of PCE by more than 10% over stand-alone Fenton reactions.

Mineralization of sorbed and NAPL-phase hexadecane by catalyzed hydrogen peroxide

The oxidation and mineralization of hexadecane in silica sand slurries was investigated using aggressive Fenton-like reactions [high concentrations of hydrogen peroxide and an iron (II) catalyst]. When spiked with 0.1 mmol kg −1 hexadecane, 56% of the hydrocarbon was sorbed to the silica sand and most of the remaining hexadecane was found as nonaqueous phase liquid (NAPL). Gas-purge methodology documented that hexadecane desorption from the silica sand slurries was negligible over 72 h. Three process variables [hydrogen peroxide concentration, slurry volume and soluble iron (II) amendment] were studied to determine their effects on hexadecane oxidation. A central composite rotatable experimental design was used to determine the most effective oxidation conditions as well as possible interactions between variables. In addition to investigating the oxidation of the parent compound, parallel experiments were conducted using 14C-hexadecane to evaluate its mineralization. The recovery of 14C-CO 2 confirmed that under the most effective conditions (high concentrations of hydrogen peroxide and low slurry volumes), 83% of the sorbed and NAPL-phase hexadecane was mineralized to CO 2 and H 2O. The iron (II) concentration had a negligible effect on parent compound degradation within the range investigated (5 to 25 mM) but was a significant variable in promoting the mineralization of hexadecane. The results show that under aggressive Fenton-like conditions, even a highly hydrophobic compound that is sorbed and in a NAPL-phase can be oxidized to its thermodynamic endpoints.

Study on modeling of wire EDM process

Wire electrical discharge machining (WEDM) technology has been used widely in production, aerospace/aircraft, medical and virtually all areas of conductive material machining. Its complexity and stochastic nature have stimulated numerous attempts to model it accurately. This paper presents an attempt at modeling the process through Response Surface Methodology and Artificial Neural Networks. A response surface model based on a central composite rotatable experimental design, and a 4-16-3 size back-propagation neural network have been developed. The pulse-width, the time between two pulses, the wire mechanical tension and the injection set-point are selected as the factors (input parameters), whilst the cutting speed, the surface roughness and the surface waviness are the responses (output parameters). The two models are compared for goodness of fit. Verification experiments have been carried out to check the validity of the developed models. It is concluded that both models provide accurate results for the process.

Changes in CIELab colour parameters due to extrusion of rice-greengram blend: a response surface approach

Rice-greengram blend was extruded using a co-rotating twin-screw extruder. A central composite rotatable experimental design was employed to determine the effect of barrel temperature and screw speed on the colour of the extrudates using the CIE Lab system of measurement. The colour parameters (L ∗, a ∗ and b ∗ values) were related (r≥ 0.876, P ≤ 0.01) to the extrusion variables by a second degree polynomial. The lightness (L ∗) and yellowness (b ∗) of the extrudates showed marked changes due to extrusion cooking, and were mostly dependent on the barrel temperature.

Parametric optimization and surface characterization of wire electrical discharge machining process

Wire electrical discharge machining (WEDM) technology has been widely used in conductive material machining. The WEDM process, which is a combination of electrodynamic, electromagnetic, thermaldynamic, and hydrodynamic actions, exhibits a complex and stochastic nature. Its performance, in terms of surface finish and machining productivity, is affected by many factors. This paper presents an attempt at optimization of the process parametric combinations by modeling the process using artificial neural networks (ANN) and characterizes the WEDMed surface through time series techniques. A feed-forward back-propagation neural network based on a central composite rotatable experimental design is developed to model the machining process. Optimal parametric combinations are selected for the process. The periodic component of the surface texture is identified, and an autoregressive AR(3) model is used to describe its stochastic component.

Evaluation of iron catalysts for the Fenton-like remediation of diesel-contaminated soils

The treatment of a diesel-contaminated soil with hydrogen peroxide catalyzed by six iron compounds and by naturally-occurring minerals in which the hydrogen peroxide is stabilized by phosphate was investigated using central composite rotatable experimental designs. Iron (III) perchlorate and iron (III) nitrate with 1.5 M hydrogen peroxide promoted > 99% oxidation of 1000 mg kg −1 diesel in a Palouse loess soil. Other iron catalysts (iron (III) sulfate, iron (II) sulfate, iron (II) perchlorate) provided 70–80% diesel oxidation under similar reaction conditions. The oxidation reactions were complete within one hour and minimal desorption occurred over 90 h, suggesting that the diesel was oxidized, at least in part, in the sorbed phase. Iron (II) compounds were less effective catalysts than iron (III) species owing to the initial loss of hydrogen peroxide in oxidizing iron (II) to iron (III). The effectiveness of the iron catalysts also correlated with the lowest rates at which their anionic component quenches hydroxyl radicals. Monobasic potassium phosphate was also investigated as a mechanism to enhance the mineral-catalyzed Fenton-like remediation of diesel in the Palouse loess, but resulted in only 40% diesel loss. A central composite design used to investigate the effect of hydrogen peroxide volume on the Fenton-like remediation of the diesel-contaminated Palouse loess showed that a solution sufficient to saturate the soil (3.5 ml (5 g soil) −1) provided the optimum volume. Based on these optimization results, the estimated chemical cost for the remediation of 1000 mg kg −1 diesel in the Palouse loess was $52 (907 kg) −1 (ton).

Optimization of Separation of Fat-Soluble Vitamins by Supercritical Fluid Chromatography Using Serial Micropacked Columns

The advantages of using two on-line coupled micropacked columns in supercritical fluid chromatography for analyzing fat-soluble vitamins are evaluated. A rotatable central composite experimental design is used to optimize the combination of some experimental variables (temperature gradient and pressure gradient) involved in the chromatographic separation. Relative standard deviations obtained under the conditions of the experimental design giving the highest response are also included. The analysis of fat-soluble vitamins occurring in real-life samples (a pharmaceutical preparation for newborns and an infant formula) is presented.

Optimization of fat-soluble vitamin separation by supercritical fluid chromatography

Fat-soluble vitamin separation, achievable using a micropacked SFC column loaded with Cw 20M, is optimized using a rotatable central composite experimental design. Two chromatographic response functions, based on relative retention and the number of peaks resolved are proposed. Temperature and pressure gradients giving the best response in the experimental region are obtained and the effect of their variation on separation is evaluated. Relative standard deviations resulting from both absolute and normalized peak areas are also given.

Growth Models for Helianthus annuus L. and Zinnia elegans Jacq.1

Abstract A second degree central composite rotatable experimental design with 5 environmental variables (root temperature, day and night temperature daylength, and light intensity) was used to estimate growth response surfaces for Helianthus annuus cv. Mammoth and Zinnia elegans cv. Eldorado grown in controlled environment chambers. Fresh and dry weight of shoots, dry weight of roots, and total dry weight for sunflowers produced estimated equations suitable for first approximation response surfaces. The model predicted maximum growth (weight) of sunflowers occurred outside of the design space. More experimentation is needed at root temperature >26.7°C, day/night temperature >37.8°, light intensity >37800 lux and daylength >23 hours to find those conditions that maximize growth with the 5 environmental variables in the present study. Additional experiments at the boundary of design space are suggested for substantial improvements in the present model for sunflowers. In zinnia lack of significance of the estimated equation was observed for all measured growth parameters (fresh and dry weight of shoots, dry weight of roots, total dry weight, number of leaves, stem length, and leaf area). A leaf disorder resembling calcium deficiency was noted on zinnia plants grown at a root temperature of 26.7°C.

Ethylation of Benzene. A Statistical Study

A central composite rotatable experimental design was constructed for a statistical study of the ethylation of benzene in the liquid phase, with aluminum chloride catalyst, in an agitated tank system. The conversion of benzene and ethylene and the yield of monoethyl- and diethylbenzene are characterized by the response surface technique. In the experimental range studied, agitation rate has no significant effect. Catalyst concentration, rate of ethylene Flow, and temperature are the influential factors. The response surfaces may be adequately approximated by planes.