Structural,morphological and magnetic characterization of metal-chitosan/poly (vinyl amine) complexes

Cu²⁺ and Ni²⁺ complexes of chitosan/poly(vinyl amine) (CS/PVAm) composites were prepared. The metal-CS/PVAm complexes were characterized by FT-IR spectroscopy, SEM-EDX, X-ray diffraction (XRD), and magnetic moment determination. FT-IR spectra of the metal-CS/PVAm complexes showed the characteristic bands of anhidroglucose unit were affected by the metal complexation, and new bands assigned to Me–N and Me-O bonds were observed. SEM images of the surface of metal-composite complexes show the influence of metal ion on the morphology of the complexes, the strong binding of Cu²⁺ and Ni²⁺, involving most of the amino groups, leading to a dense surface structure. The chemical composition on the surface of metal-CS/PVAm complexes was determined from EDX measurements. XRD provided information about the amorphous or crystalline nature of the composite and metal-composite complexes. Using magnetic susceptibility method, the oxidation degree of metal ions from the polymer phase, the homogeneous distribution of the ligand groups from the volume of the CS/PVAm beads, and the existence of the antiferromagnetic interactions between the metal ions were determined.     

Investigation of Electrochemical Properties of Carbon Nanofibers Prepared by CCVD Method

Carbon nanofibers, with diameters between 80 and 290 nm and specific area of 242 m²g^?1, have been prepared by the catalytic chemical vapor deposition method. After preparation, the powder was mixed with silicon oil in order to create a paste electrode. The electrochemical behavior of this type of electrode was investigated by cyclic voltammetry, using a solution of 10^?3 M ferrocenecarboxylic acid as mediator. The redox process is quasi-reversible, and it involves the transfer of electrons between Fe(II) and Fe(III).

The same mediator was used for the construction of a second-generation glucose biosensor. The mediator was co-immobilized with the enzyme in the carbon nanofibers paste. The sensor linearly responded to glucose, in the concentration range of 1.7 to 7 mM. A time of around 30 seconds was required to reach 95% of the maximum steady-state current.

Also, the oxidation of calf thymus DNA at the carbon nanofiber paste electrode was investigated by differential pulse voltammetry (DPV). A clear signal, due to guanine oxidation, was obtained in the case of single-stranded DNA.     

Impedimetric Measurements for Monitoring Avidin-Biotin Interaction on Self-Assembled Monolayer

Avidin-biotin has been controllable immobilized on the surface of gold electrodes using mercaptopropionic acid as self-assembled monolayer. Electrochemical impedance spectroscopy (EIS) was employed to investigate the changes that appear at the electrode surface in the presence of a redox mediator, K₃[Fe(CN)₆]. An electrical model more complex than that in other studies was used to interpret the EIS measurements (Randles circuit). This model is very useful because it takes into consideration both the transfer of electrons at the electrode/electrolyte interface and the diffusion of redox species through the double layer. The model allowed us to determine some important parameters like solution resistance R_sol, charge-transfer resistance R_ct, double-layer capacitance C_dl, Warburg resistance R_W, and the diffusion time constant τ. The EIS results proved that immobilization of avidin-biotin increased the charge-transfer resistance R_ct, due to the insulating character of these molecules.     

Polypropylene/Montmorillonite Nanocomposites Containing Nisin as Antimicrobial Food Packaging

Antimicrobial nanocomposites prepared with polypropylene, montmorillonite, and nisin were developed as food packaging material. Nisin was incorporated at 1, 2.5, and 5 % (w/w) and the characterization included antimicrobial, mechanical, thermal, barrier, and structural properties. Composite films inhibited the Gram-positive bacteria Listeria monocytogenes, Staphylococcus aureus, and Clostridium perfringens when tested on skimmed milk agar plates. Antimicrobial activity was released in food simulants after contact with the nanocomposites, increasing until 48 h in solutions containing the surfactant Tween 20 or acetic acid. The addition of nisin caused no significant modification in deformation at break values as compared with control films. However, results of tensile strength and Young modulus differed significantly among samples. The higher value for Young modulus was observed for films with 5 % nisin. Water vapor barrier properties were not significantly different among control and antimicrobial films, whereas oxygen permeability was higher for nanocomposites containing nisin. The nanocomposites tested had no significant differences in the melting temperature (165 to 167 °C), and the crystallization temperature ranged from 121 to 129 °C, with lower values for films containing 5 % nisin. Scanning electron microscopy showed that nanocomposites containing 1 and 2.5 % nisin present similar homogeneity to that of control films. Some film properties were affected after nisin incorporation in polypropylene/montmorillonite matrix but active antimicrobial films were obtained, showing suitable behavior as a food packaging material.     

Antioxidant, antihypertensive and antimicrobial properties of ovine milk caseinate hydrolyzed with a microbial protease

BACKGROUND: Bioactive peptides might be released from precursor proteins through enzymatic hydrolysis. These molecules could be potentially employed in health and food products. In this investigation, ovine milk caseinate hydrolysates obtained with a novel microbial protease derived from Bacillus sp. P7 were evaluated for antioxidant, antimicrobial, and angiotensin I‐converting enzyme (ACE)‐inhibitory activities. RESULTS: Antioxidant activity measured by the 2,2′‐azino‐bis‐(3‐ethylbenzothiazoline)‐6‐sulfonic acid method increased with hydrolysis time up to 2 h, remaining stable for up to 4 h. Hydrolysates showed low 2,2‐diphenyl‐1‐picrylhydrazyl radical‐scavenging abilities, with higher activity (31%) reached after 1 h of hydrolysis. Fe²⁺‐chelating ability was maximum for 0.5 h hydrolysates (83.3%), decreasing thereafter; and the higher reducing power was observed after 1 h of hydrolysis. ACE‐inhibitory activity was observed to increase up to 2 h of hydrolysis (94% of inhibition), declining afterwards. 3 h hydrolysates were shown to inhibit the growth of Bacillus cereus, Corynebacterium fimi, Aspergillus fumigatus, and Penicillium expansum. CONCLUSION: Ovine caseinate hydrolyzed with Bacillus sp. P7 protease presented antioxidant, antihypertensive, and antimicrobial activities. Hydrolysis time was observed to affect the evaluated bioactivities. Such hydrolysates might have potential applications in the food industry. Copyright © 2011 Society of Chemical Industry     

Optimization of frozen sour cherries vacuum drying process

The objective of this research was to optimize the vacuum-drying of frozen sour cherries in order to preserve health-beneficial phytochemicals, as well as textural characteristics. Investigated range of temperature was 46–74 °C and, of pressure, 17–583 mbar, in a new design of vacuum-dryer equipment. The total solids, a_w value, total phenolics, vitamin C, antioxidant activity, anthocyanin content, total colour change and firmness were used as quality indicators of dried sour cherry. Within the experimental range of studied variables, the optimum conditions of 54.03 °C and 148.16 mbar were established for vacuum drying of sour cherry. Separate validation experiments were conducted, under optimum conditions, to verify predictions and adequacy of the second-order polynomial models. Under these optimal conditions, the predicted amount of total phenolics was 744 mg CAE/100 dw, vitamin C 1.44 mg/100 g per dry weight (g dw), anthocyanin content 125 mg/100 g dw, IC₅₀ 3.23 mg/ml, total solids 70.72%, a_w value 0.646, total colour change 52.61 and firmness 3395.4 g. The investigated parameters had a significant effect on the quality of the dried sour cherries.     

Hybrid organic/inorganic composites based on silica and weak synthetic polyelectrolytes

The preparation and characterization of new organic/inorganic composites by the consecutive adsorption of weak polyelectrolytes on silica particles were studied in the article. Two polycations containing primary amine groups in the side chains, poly(vinylamine) or poly[N(β-aminoethylene) acrylamide], and poly(acrylic acid) as polyanion were used for the hybrid materials construction. The stability of the organic/inorganic composites has been increased by a heat-induced reaction at 150 °C. The organic/silica hybrids properties were monitored by potentiometric titration, laser light scattering, infrared spectroscopy, and thermogravimetric analysis. The adsorption of methylene blue by the composite materials has been tested. The dye adsorption capacity was strongly influenced by the dye concentration, the nature of the last adsorbed layer, the polyions concentration, and the composite thermal treatment.     

Optimisation of microwave‐assisted extraction of phenolic compounds from broccoli and its antioxidant activity

The effect of independent variables of microwave‐assisted extraction (MAE), extraction temperature (50–90 °C), microwave power (100–200 W), solvent concentration (methanol/water, 50–90%, v/v) and extraction time (1–27 min) on total phenolics and flavonoids contents as well as antioxidant activity of broccoli extracts was investigated. Response surface methodology was successfully applied for optimisation and the high correlation of the mathematical model indicated that a quadratic polynomial model could be used for optimisation of investigated responses. Considering the maximum amount of extracted total phenolics, total flavonoids and antioxidant activity expressed as ORAC value, the optimal conditions for all three investigated responses were obtained (temperature ?71.11 °C; microwave power ?167.03 W; solvent concentration ?75.95%; and extraction time 16.34 min), which is in agreement with optimal conditions obtained for each investigated responses. The development of simultaneously MAE methods for total phenolics, total flavonoids and antioxidant activity of broccoli extracts might simplify assessment of broccoli as valuables source of antioxidants.     

Original article: Supercritical CO2 extraction of soybean oil: process optimisation and triacylglycerol composition

Supercritical CO₂ extraction of soybean oil was performed. Response surface methodology was applied to evaluate the effects of pressure, temperature and extraction time on soybean oil yield. The analysis of variance showed that pressure and extraction time followed by the quadratic term of pressure and interaction between pressure and time had the significant effect on the oil yield. The maximum extraction yield (6.59/100 g soybeans) at constant CO₂ flow rate of 1.629 L per min was achieved at 50 °C, 300 bar and 4 h. The experimental values agreed well with those predicted by regression model. One‐stage diffusion model was successfully applied for modelling the kinetics of soybean oil. The main triacylglycerols of soybean oil were trilinolein, dilinoleoolein, dilinoleopalmitin and linoleooleopalmitin. Soybean oil extracted by supercritical CO₂ had higher levels of linoleic and linolenic acids and lower levels of palmitic and stearic acids compared to oil extracted by organic solvent.