Enhancement of thermal stability associated with the chemical treatment of bacterial (Gluconacetobacter xylinus) cellulose

Bacterial cellulose produced by Gluconacetobacter xylinus was treated with sodium carbonate (Na₂CO₃) and sodium hydroxide (NaOH) to remove entrapped noncellulosic materials. Fourier transform infrared (FTIR) spectroscopy has been used to investigate the effect of alkali on the chemical structure of bacterial cellulose. The changes in the crystalline nature of these membranes were analyzed using X‐ray diffraction (XRD) technique. The morphology and the removal of noncellulosic impurities followed by alkali treatment were studied using scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS). The enhanced thermal stability of bacterial cellulose was evident from thermogravimetric analysis (TGA). Further, the alkali treatments resulted in relatively pure form of cellulose, which finds application in various spheres. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Charge storage mechanism in vacuum deposited PVF films

Thermally stimulated discharge current (TSD) behavior of vacuum deposited polyvinyl fluoride (PVF) films has been studied as a function of various polarization parameters such as field (1.0 × 10³–14.0 × 10³ V/cm), temperature (313–453 K), time (3.6 × 10³–6.0 × 10³ sec), electrode work function (copper, silver, aluminum and indium) and thickness (2000–10000 Å). In a field dependent case the TSD spectra of PVF films show a single relaxation peak centered around 430 ± 1 K. The peak current, charge, peak position and activation energy associated with the peak depend strongly on the polarization parameters. The mechanism of origin of the relaxation peak has been attributed to the space charge polarization where the charge carriers injected at the electrode-polymer interface barrier are displaced at macroscopic distances and get subsequently trapped at trapping levels that are distributed in their activation energies and relaxation times.     

Mechanical and barrier properties of edible starch–protein‐based films

The present investigation dealt with the mechanical properties, water‐vapor transmission behavior at different relative humidity conditions, and DSC thermograms of edible films formulated using various proteins (casein, gelatin, albumin) in combination with starch and nonthermal as well as intense thermal blending. Nonthermal blended film showed in the DSC thermogram a double T_g, indicating poor miscibility of the components and, hence, a poor film‐forming property. However, the DSC thermogram of all the films based on intense thermal blending showed a single T_g, indicating the complete molecular miscibility of the components. Casein‐based film showed a lower water‐vapor transmission rate, water gain at different relative humidity conditions, and higher tensile strength compared to its counterparts containing gelatin and albumin. Since the casein–starch blend gave better film properties, a blend of hydrophobic carnauba wax and casein was prepared to compare the properties of hydrophilic–hydrophilic and hydrophobic–hydrophilic blends. Both these blends compared well with respect to the water‐vapor transmission rate. Wax‐based film showed multiphased behavior in the DSC thermograms and the percent elongation was lower as compared to the casein–starch blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 64–71, 2003     

Environmental water remediation using covalently functionalized zerovalent iron nanocomposites with 2-pyridinecarboxaldehyde via 3-aminopropyltrimethoxysilane and ethylenediamine

The adsorption technology involving nano zerovalent iron (NZVI) has been widely employed to remediate polluted water based on a number of economic aspects. However, this technology is facing a high challenge in the removal process of pollutants due to hydrolysis and stability characteristics of zerovalent iron. Therefore, this study is aimed to demonstrate a method for encapsulation and functionalization of NZVI nanoparticles with 3-aminopropyltrimethoxysilane (NH₂) and 2-pyridinecarboxaldehyde (PY), respectively to produce the target nanocomposite (NZVI-NH₂-PY). Zerovalent iron nanoparticles are also aimed to functionalize with ethylenediamine (ED) and 2-pyridine carboxaldehyde to produce NZVI-ED-PY nanocomposite. The TEM images showed that the sizes of NZVI-NH₂-PY and NZVI-ED-PY nanocomposites are in the range 3.33–4.35 and 5.42–10.36 nm, respectively. More characterization evidences were concluded by thermal gravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The two novel magnetic nanocomposites have been used for removal of Co(II), Zn(II), Pb(II), Cd(II), Hg(II), Cu(II) beside radioactive isotopes (⁶⁵Zn and ⁶⁰Co) from water. NZVI-NH₂-PY nanocomposite was more selective toward Hg(II), Pb(II) and Cd(II), while NZVI-ED-PY was more selective toward Z(II), Co(II) and Co(II). Different kinetic models were applied and the investigated metal ions were characterized to undergo the pseudo-second order using both NZVI-NH₂-PY and NZVI-ED-PY nanocomposites.     

Effect of preconditioning on physicochemical,microstructural, and sensory quality of vacuum-fried jackfruit chips

The effect of preconditioning steps in terms of either freezing or partial drying on the quality of vacuum-fried jackfruit (JF) chips was evaluated. Prepartial drying process of the JF bulb slices resulted in the lowest moisture content in the vacuum-fried chips. The rate of oil uptake by JF bulb slices was found to be almost same in control and prefrozen samples during frying process. However, prepartial drying of slices resulted in a slower rate of oil absorption. The total carotenoid content was found to be 1.81, 0.96, and 1.87?mg/100?g (db) in control, prepartially dried and prefrozen JF chips, respectively. The Hunter L-value of control, prepartially dried, and prefrozen chips was found to be 52.3, 39.4, and 48.5, respectively. The a-value was found to increase, whereas the b-value decreased during vacuum frying in all the JF chip samples, irrespective of preconditioning type adopted. Prefrozen JF chips were found to have highest crispy texture in terms of lowest instrumental breaking force compared to the control and prepartially dried JF chips. Prefrozen JF chips were found to have lowest bulk density and highest porosity. The micrograph of prepartially dried JF chips depicted dense and shriveled structure, whereas a porous structure in prefrozen chips. The preconditioning protocols of partial drying and freezing were found to affect the overall sensory acceptability scores significantly (P?相似文献   

Degradation Kinetics of Colour and Total Carotenoids in Jackfruit (Artocarpus heterophyllus) Bulb Slices During Hot Air Drying

The kinetics of colour and carotenoids degradation in jackfruit bulb slices was evaluated during hot air drying at 50, 60 and 70 °C. Visual colour as well as total carotenoids (TC) content was found to be influenced by the drying process. Tri-stimulus colour parameters such as Hunter L and b values decreased and a value increased during drying. The combination of Hunter L × b value was found to represent the colour change adequately. Degradation of TC and visual colour in terms of Hunter L × b value followed first-order reaction kinetics; however, zero-order reaction kinetics was found adequate to describe changes in total colour difference (TCD) and non-enzymatic browning (NEB). Dependence of the rate constant followed the Arrhenius relationship. The process activation energies (E _a) for Hunter L × b value, TCD, NEB and TC were 29.96, 27.21, 27.48 and 55.61 kJ/mol, respectively. Higher E _a for TC content indicated greater temperature sensitivity as compared with other colour parameters. Relationship of TC content and Hunter L × b value was found to be more consistent through regression analysis with R ² ≥ 0.979.     

Instrumental Textural Changes in Banana (Var. Pachbale) During Ripening Under Active and Passive Modified Atmosphere

Textural properties of modified atmosphere packaged banana (var. Pachbale), stored at 13 ± 1°C, followed by ethrel induced ripening at 30 ± 1°C were studied. Modified atmosphere included active as well as passive types involving flushing of polyethylene pouches (100 gauge) with specific gas mixture (3% O₂ + 5% CO₂ + 92% N₂) at partial vacuum (52.63 kPa), respectively. The MAP applications resulted in varied response of various textural parameters including penetration, shear, force-relaxation, and instrumental texture profile analysis. All the parameters showed a decline except adhesiveness with the progress in ripening. Both the gas flushed, as well as passive MAP stored samples, followed a trend similar to that for control ones, however, the partial vacuum packaged bananas showed persistence of overall texture followed by normal ripening under ethrel induction. The ripened fruits from all the three types of MAP applications did not show any impediment to the instrumental textural quality. In the case of partial vacuum packaged samples, a threshold low temperature duration of 30 days was found to be optimal to avoid abnormal ripening in terms of texture. The instrumental textural kinetic for TPA parameters was found to follow linear model for a longer duration of the storage at low temperature (13 ± 1°C) with high correlation coefficients ranging from 0.845 to 0.989.     

Effect of Hydrocolloid Pre-Treatment on Instrumental and Sensory Texture Attributes of Frozen Carrot (Daucus carota)

The effect of different hydrocolloids (pectin, carboxy methylcellulose, xanthan gum, and sodium alginate) pre-treatment used at different concentrations (0.2–0.4%) on instrumental texture parameters as well as on the sensory attributes of frozen-thawed pre-cut carrots was evaluated. Instrumental texture profile analysis of frozen-thawed carrot showed a significant (P < 0.05) increase in cohesiveness with an increase in the concentration of all the hydrocolloids. Nevertheless, the increase in springiness was not significant (P > 0.05) over the untreated control samples, whereas chewiness did not show consistent results with an increase of any of the hydrocolloids. As the concentration of hydrocolloids increased, the firmness values obtained by cutting the frozen-thawed carrot samples with a Warner Bratzler Blade were also found to increase. Higher texture retention after freezing and thawing was observed in xanthan gum (0.4%) pre-treated samples than other hydrocolloids used as well as than the control samples. It increased the firmness up to 196.2% than the control samples. However, 0.3% xanthan pre-treatment gave the best sensory results. Sensory acceptability increased on increasing the pectin and carboxy methylcellulose concentrations, while lower concentration levels of alginate pre-treatment showed higher sensory preference than the higher concentration levels. Based on the results, untreated frozen samples suffered from a detrimental texture and sensory deterioration during 15 months of frozen storage. The carrot tissue integrity was well retained during frozen storage in the hydrocolloid pre-treated samples.     

Studies on the antioxygenic activity of bitter gourd (Momordica charantia) and its fractions using various in vitro models

BACKGROUND: A study was undertaken to evaluate the antioxygenic activity of bitter gourd pulp and seed powders as well as their various solvent extracts using different methods and to minimise the oxidative deterioration of lipids by natural antioxidants. RESULTS: Bitter gourd pulp and seed powders at 20 g kg^?1 and their ethanol/water extracts exhibited stronger antioxygenic activity than other solvent extracts. Bitter gourd pulp and its extracts showed slightly higher antioxygenic activity than bitter gourd seed and its extracts. This may be attributed to the presence of higher amounts of phenolics and flavonoids, which have been reported as potential antioxidants. The seed portion of bitter gourd contained higher levels of total protein (188.3 g kg^?1), total fat (238.9 g kg^?1) and crude fibre (350.2 g kg^?1) than the pulp portion. Fatty acid analysis of bitter gourd seed oil indicated the presence of α‐eleostearic acid, an isomer of conjugated linolenic acid, as a major fatty acid, but this acid was absent in the pulp. CONCLUSION: The results of this study confirmed the presence of antioxygenic compounds in both bitter gourd pulp and seed. In particular, their ethanol/water extracts showed great potential as natural antioxidants to inhibit lipid peroxidation in foods. Copyright © 2010 Society of Chemical Industry