A review on the toxicology and dietetic role of bacterial cellulose

Bacterial cellulose (BC) is a biopolymer synthesized by certain acetic acid bacteria strains. The safety of BC regarding its potential use in food applications is here reviewed. The acute, sub-acute and subchronic oral toxicity assays showed that consumption of BC had no adverse effects in rats. Several studies demonstrated that BC is not genotoxic, did not induce chromosomal aberrations in CHO cells under both non-activating and metabolic activating conditions, is inactive in the in vitro Rat Primary Hepatocyte Unscheduled DNA Synthesis Assay, had no reproductive toxicity in mice and exerted no embryotoxicity and teratogenicity effects in rats. Several studies on the BC in biomedical applications further reinforces its safety: a primary eye and dermal irritation studies in the rabbit showed that BC was non-irritating. The inflammatory reaction to subcutaneously implanted BC has been evaluated in animal models and for different periods of time, demonstrating that BC is biocompatible and does not trigger a harsh inflammatory reaction. Altogether, and considering its longstanding history of human consumption in Asian countries, as well as its utilization in biomedical devices, it may be concluded that BC is safe for applications in food technology.FCT -Fuel Cell Technologies Program(NORTE-01-0145-FEDER-000004)info:eu-repo/semantics/publishedVersio

Clarification of sugar palm sap using a pilot scale microfiltration

It is known that microfiltration can be used for clarification and cold sterilization of beverage and drink products. In this study the sugar palm sap was clarified using a pilot scale of crossflow microfiltration system. The membrane used was tubular ceramic membrane (ZrO2-TiO2) with pore size 0.1 and 0.2 µm. The experiments were carried out with batch mode at constant crossflow velocity 3.5 m.s-1 and 50 °C. It was found that the turbidity and number of microorganism in the permeate for both membrane pore size were reduced greatly while total soluble solid did not significantly decreased. The permeate flux behavior and fouling were also investigated. The permeate flux decreased greatly with processing time due to membrane fouling. The irreversible fouling of both membrane pore size also increased greatly indicating that the irreversible fouling was a major cause of fouling

Preparation and characterization of sulfonated polysulfone and N-phthloyl chitosan blend composite cation-exchange membrane for desalination

Sulfonated polysulfone (sPSf) was prepared and used as a polymer matrix for cation-exchange membranes (CEM). The sulfonation reaction was carried out at room temperature and the degree of sulfonation was calculated by titration method. Blend composite membranes were prepared using different ratios of sPSf and modified chitosan (CS). Membrane properties were studied in terms of water flux, water swelling ratio, molecular weight cut off (MWCO), ion-exchange capacity (IEC) and contact angle measurement. Charge on the membrane was confirmed by ionic diffusion potential (DP). It was observed that, DP increased with the increase in the concentration of sPSf. The membrane sPSf:CS 60:40 showed 1000Da MWCO, 14.6mV diffusion potential (DP) and 0.083mM/g of IEC. Similarly sPSf:CS 90:10 showed 10,000Da MWCO, 71.7mV diffusion potential (DP) and 0.176mM/g of IEC. Moreover, membrane sPSf:CS 60:40 showed 93%, 89% and 69% for MgSO 4, Na 2SO 4 and NaCl rejection respectively

An investigation of dielectric properties of biological cells using RC-model

This paper proposes a method for estimating cell dielectric properties of a spherical triple shell and ellipsoidal shell models from the Laplace and RC approaches. With a combination of various theoretical parameters such as cell dielectrophoretic velocity, angular velocity of electro-rotation (ER) and two critical frequencies of dielectrophoresis (DEP), these approaches will improve the predictability of the dielectric properties. The calibration of the model parameters to these experimental data results in estimations of the cellís electrical properties depending on the geometric structure of the assumed model

Elastic constant of Dendrobium protoplasts in AC electric fields

This work reports elongation of Dendrobium protoplasts in an ac electric field between two cylindrical electrodes. A protoplast firstly was translated towards an electrode by dielectrophoretic force in 17 kV.m-1 field strength at 1 MHz, and secondly it was elongated due to an interaction between an induced electric dipole (μ) and the electric field (E). Protoplast elongation was observed by varying both the field strength at 30, 45, 60, and 85 kV.m-1 and field frequency at 0.5, 1, 5, and 10 MHz. For a given field frequency and field strength, a parameter a/b (major/minor axis) was measured as the protoplast elongation.Two-step elongation and restoration phases were observed. The former was completed within 2 minutes of field exposure, and the latter was completed within 15 seconds regardless of the field exposure time between 3 and 20 minutes. The evidence of a complete restoration indicated that the elasticity of the protoplast membrane obeyed Hooke’s law. This study also found that elastic constant k of the membrane varied non-linearly with the field strength. It was found to be from 0.04 to 0.08 mN.m-1, dependent on the field frequency

Effect of polyethylene glycol on characteristics of chitosan membranes

This work reports the influence of polyethylene glycol (PEG) on characteristics of chitosan membranes. Parameters used for membrane characterization were hydraulic permeability (Lp), molecular weight cut off (MWCO), and membrane impedance (Z). The results obtained from LP and Z imply that larger a amount of PEG addition enhances membrane porosity and enlarges the pore size. The prepared membranes were ultrafiltration type, with MWCO slightly greater than 35 kDa. Membranes without PEG additioncould be nanofiltration type with Lp value of 0.4x10-11 m3 N-1 s-1, 10-20 times smaller than the other

Flux, rejection and fouling during microfiltration and ultrafiltration of sugar palm sap using a pilot plant scale

The possibility of using a pilot plant scale microfiltration (MF) and ultrafiltration (UF) to clarify and reduce number of bacteria, yeast and mould of sugar palm sap was studied. The membrane used was multi channel tubular ceramic membrane (ZrO2-TiO2) with membrane pore size 0.2 and 0.1 μm and molecular weight cut off (MWCO) 300 and 50 kDa for microfiltration and ultrafiltration respectively. The experiment was carried out to investigate the rejection of the components in sugar palm sap, permeate flux and fouling characteristics. The results showed that the turbidity, the total solid, the viscosity and the numbers of bacteria, yeast and mould in the permeate obtained by MF and UF were reduced significantly compared to those of fresh sugar palm sap. The total soluble solid, total sugar, reducing sugar and pH were not affected by MF and UF. The permeate fluxes for all membranes were reduced greatly as the volume concentration ratio (VCR) increased due to severe fouling. The irreversible fouling on membrane surface and/or inside the membrane tended to increase with increasing membrane pore size or MWCO. The result also suggested that protein and small particle in the sugar palm sap were probably responsible for the internal fouling of large pore size membrane. According to the physical, chemical and microorganism quality results, both MF and UF showed the potential use for improving the quality of sugar palm sap but flux reduction due to fouling was a major problem affecting the process performance

Characterization of cellulose membranes produced by Acetobacter xyllinum

Cellulose membranes formed by Acetobacter xylinum under known cell density in a culture medium were characterized. A dead end testing unit was used for water flux and filtration of Chlorella sp. and bovine serum albumin (BSA). This study found that the cells formed membranes faster in sucrose supplemented coconut juice than in the standard Schramm & Hestrin's medium. For two-day formed membranes in the former medium, an increase in cell density from 1 × 108 to 2 × 108 cfu.ml-1 reduced water flux and, hence, reduced the hydraulic permeability coefficient (Lp) from 3.6 × 10-10 to 0.5 × 10-10 m3N-1s-1. These membranes were asymmetric-hydrophilic type with thickness less than 6.0 μm. Membrane porosity was found to vary from 1.4% to 2.4%, with the averaged pore size 0.08 μm. Under 100 kPa filtration, two-day formed membranes in sucrose supplemented coconut juice with higher cell density rejected Chlorella cells and BSA by 99.8% and 98.4%, respectively

Dielectrophoresis of Tetraselmis sp., a unicellular green alga, in travelling electric fields analyzed using the RC model for a spheroid

Dielectrophoresis of a unicellular green alga, Tetraselmis sp., in a travelling electric field was analyzed using an RC(resistor-capacitor)-model, instead of the Laplace approach reported in our previous work. The model consists of resistorcapacitorpairs in series to represent the conductive and the capacitive properties of the shell and the inner part of the spheroid.The model is mathematically simpler than the Laplace model and the RC approach is experimentally superior because only thelower critical frequency [LCF] and cell translational speed are required to be measured experimentally. The effective compleximpedance of the spheroid was mathematically modeled to obtain the Clausius-Mossotti factor ([CMF]) as a function of celldielectric properties. Spectra of dielectrophoretic velocity and the lower critical frequency of the marine green alga, Tetraselmissp. were investigated to determine cell dielectric properties using a manual curve-fitting method. Effects of arsenic at differentconcentrations on the cell were examined to verify the model. Arsenic severely decreases cytoplasmic conductance (c)whereas it increases membrane conductance (m). Effects were easily observable even at the lowest concentration of arsenicused experimentally (1 ppm). The method offers a practical means of manipulating small plant cells and for rapid screeningfor effects on the dielectric properties of cells of various applied experimental treatments