Effect of dose rate of gamma irradiation on biochemical quality and browning of mushrooms Agaricus bisporus

In order to enhance the shelf-life of edible mature mushrooms Agaricus bisporus, 2 kGy ionising treatments were applied at two different dose rates: 4.5 kGy/h (I⁻) and 32 kGy/h (I⁺). Both I⁺ and I⁻ showed 2 and 4 days shelf-life enhancement compared to the control (C). Before day 9, no significant difference (p>0.05) in L^* value was detected in irradiated mushrooms. However, after day 9, the highest observed L^* value (whiteness) was obtained for the mushrooms irradiated in I⁻. Analyses of phenolic compounds revealed that mushrooms in I⁻ contained more phenols than I⁺ and C, the latter containing the lower level of phenols. The polyphenol oxidase (PPO) activities of irradiated mushrooms, analysed via catechol oxidase and dopa oxidase substrates, resulted in being significantly lowered (p0.05) compared to C, with a further decrease in I⁺. Analyses of the enzymes indicated that PPO activity was lower in I⁺, contrasting with its lower phenol concentration. Ionising treatments also increased significantly (p0.05) the phenylalanine ammonia-lyase (PAL) activity. The observation of mushrooms cellular membranes, by electronic microscopy, revealed a better preserved integrity in I⁻ than in I⁺. It is thus assumed that the browning effect observed in I⁺ was caused by both the decompartimentation of vacuolar phenol and by the entry of molecular oxygen into the cell cytoplasm. The synergetic effect of the residual active PPO and the molecular oxygen, in contact with the phenols, allowed an increased oxidation rate and, therefore, a more pronounced browning in I⁺ than in I⁻.     

Hydrolytically stable, diaminocarboxylic acid-based membranes buffering in the pH range from 6 to 8.5 for isoelectric trapping separations

Diaminocarboxylic acid carrier ampholytes, such as L-histidine, 2,3-diaminopropionic acid, L-ornithine, and L-lysine, were reacted with glycerol-1,3-diglycidyl ether (GDGE) and poly(vinyl alcohol) (PVA) in the presence of sodium hydroxide to produce hydrolytically and mechanically stable hydrogels, supported on a PVA substrate, for use as buffering membranes in isoelectric trapping (IET) separations. The pH values of the DACAPVA membranes were determined with the help of small-molecule pI markers and proteins and were found to be in the 6 < pH < 8.5 range. The membranes were successfully used to isoelectrically trap small ampholytes, desalt ampholyte solutions in IET mode, and effect the binary separation of chicken egg white proteins.     

Silicalite-filled poly(siloxane imide) membranes for removal of VOCs from water by pervaporation

Silicalite-filled poly(siloxane imide) (PSI) membranes were prepared for the separation of volatile organic compounds (VOCs) from water via pervaporation. PSI copolymer was synthesized by polycondensation of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with a siloxane-containing diamine, e.g., poly(dimethylsiloxane), bis(3-aminopropyl) terminated (PSX), added with 3,3-diaminodiphenyl sulfone (DDS). 2,4,6-Triamine pyrimidine (TAP) was added into the casting solution in order to enhance the compatibility between the polymeric matrix and the filler, silicalite. The PSI membranes were characterized by SEM. The surface morphology for the membrane with the addition of TAP differs from that without TAP. The latter seems to be consisting of particles in the membrane surface. The sorption selectivity of the PSI membranes for chloroform/water solutions was investigated, and there was a highest value for it around 50 wt.% of PSX content. The pervaporation performance of the membranes was studied with the separation of chloroform/water mixture. The silicalite-filled membrane with 120 μm thickness exhibit a high total permeation flux of 280 g m⁻² h⁻¹ with separation factor of 52.2 for 1.2 wt.% of the chloroform/water mixture.     

Complexation and Separation of Amines,Amino Acids,and Peptides by Functionalized Calix[<Emphasis Type="Italic">n</Emphasis>]arenes

The ability of calix[n]arenes to form complexes, to act as extractants in liquid–liquid extraction, and run as carriers in transport through liquid membranes of different biological amine compounds (e.g., ammonium ion, amines, amino acids, and peptides) has been the central topics of many reports. These features recommend the calix[n]arenes as competitive candidates for studying the interactions involved in host–guest recognition as well as useful receptors in separation processes. Some specific aspects of their applications in binding and separation of various amine compounds by extraction, and in transport through liquid membranes have therefore been considered. The effect of the factors that might influence the separation of above compounds by extraction, and the transport through liquid membranes using the calix [n]arenes has been presented.This revised version was published online in July 2005 with a corrected issue number.     

Cellulose acetate and polyethersulfone blend ultrafiltration membranes. Part I: Preparation and characterizations

The overall objective of this investigation is to achieve high‐performance membranes with respect to flux and rejection characteristics, with an interplay of blending polymers having desired qualities. Thus, cellulose diacetate and polyethersulfone as candidate materials, in the presence of polyethylene glycol 600 as a pore forming agent, were blended in 100/0, 95/5, 90/10, 85/15, 80,20 and 75/25% compositions using N,N′‐dimethylformamide as solvent and membranes were prepared by the phase inversion technique. Polymer blend composition, additive concentration, and casting and gelation conditions were standardized for the preparation of asymmetric membranes with various pore statistics and morphology. These blend membranes were characterized for compaction in ultrafiltration experiments at 414 kPa pressure in order to attain steady state flux and is reached within 4–5 hr. The pure water flux was measured at 345 kPa pressure and is determined largely by the composition of polyethersulfone and additive concentration. The flux was found to reach the highest values of 66.5 and 275 1/(cm² hr) at 0 and 10 wt% additive concentrations respectively, at 25% SPS content of the blend. Membrane hydraulic resistance derived by measuring water flux at various transmembrane pressure and by using an algorithm was found to be inversely proportional to pure water flux. Water content is estimated by simple drying and weighing procedures and found proportional to pure water flux for all the membranes. The molecular weight cut‐offs (MWCOs) of different membranes were determined with proteins of different molecular weights and found to vary from 20–69 kDa (globular proteins) depending on the PEG and SPS content in the casting dope. Skin surface porosity of the membranes were analyzed by scanning the frozen membrane samples using scanning electron microscopy (SEM) at different magnifications. The surface porosity is in direct correlation to the MWCO derived from solute retention experiments. Copyright © 2004 John Wiley & Sons, Ltd.     

Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes

Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Sn²⁺ and In³⁺ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn²⁺ and Cd²⁺ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.     

Transport properties of alkanes through ceramic thin zeolite MFI membranes

Polycrystalline randomly oriented defect free zeolite layers on porous α-Al₂O₃ supports are prepared with a thickness of less than 5 μm by in situ crystallisation of silicalite-1. The flux of alkanes is a function of the sorption and intracrystalline diffusion. In mixtures of strongly and weakly adsorbing gases and a high loadings of the strongly adsorbing molecule in the zeolite poze, the flux of the weakly adsorbing molecule is suppressed by the sorption and the mobility of the strongly adsorbing molecule resulting in pore-blocking effects. The separation of these mixtures is mainly based on the sorption and completely different from the permselectivity. At low loadings of the strongly adsorbing molecules the separation is based on the sorption and the diffusion and is the same as the permselectivity. Separation factors for the isomers of butane (n-butane/isobutane) and hexane (hexane/2,2-dimethylbutane) are respectively high (10) and very high (> 2000) at 200°C. These high separation factors are a strong evidence that the membrane shows selectivity by size-exclusion and that transport in pores larger than the zeolite MFI pores (possible defects, etc) can be neglected.     

Preparation and proton conductivity of poly(N‐methylbenzimidazole) doped with acid

To increase the solubility and film forming ability of polybenzimidazole (PBI), poly(N‐methylbenzimidazole) (PNMBI) with different degrees of methylation was synthesized. Chemical structure, degree of substitution, and solubility of PNMBI was studied. PNMBI is easier to be doped with acid than PBI. The basicity of PNMBI was improved with the introduction of methyl groups on the imidazole moiety. Effects of methylation degree, H₃PO₄ content and temperature on proton conductivity of PNMBI doped H₃PO₄ was studied. Proton conductivity of H₃PO₄ doped PNMBI‐1.2 membranes increases with increasing doping level. Temperature dependence of proton conductivity of H₃PO₄ doped PNMBI‐1.2 membranes follows the Arrhenius law. With an increase in the degree of substitution, proton conductivity of H₃PO₄ doped PNMBI decreases dramatically. The proton transport mechanism was also discussed. The proton conductivity of PNMBI/H₃PO₄ is mainly contributed by proton hopping or Grotthuss mechanism. Copyright © 2004 John Wiley & Sons, Ltd.     

A model for cation adsorption to clays and membranes

A cation adsorption model is presented and its recent applications are discussed. The model combines electrostatic equations with specific binding, and considers neutral and positively charged complexes between the negative surface sites and organic cations in a closed system. Extensions in the model account for dye aggregation in solution, and for the formation of solution complexes of inorganic cations, such as [M⁺⁺ Cl^–]⁺. The amounts of 45Ca²⁺ adsorbed to vesicles extracted from the plasma membranes of melon root cells could be adequately simulated and predicted. The binding coefficients determined for Ca²⁺, Na⁺, and Mg²⁺ are in the range of values previously deduced for binding to phospholipid components. Model calculations were applied to the test of hypotheses on the effect of salt stress on the growth of roots. The adsorption of monovalent organic cations to montmorillonite is characterized by binding coefficients that are at least six orders of magnitude larger than those of Na⁺, Mg²⁺, Ca²⁺, and Cd²⁺, or those of CdCl⁺ or CaCl⁺. Monovalent organic cations were found to adsorb 140–200% of the cation exchange capacity of the clay and to cause charge reversal. Deductions from adsorption results of acriflavin are consistent with those drawn from the application of other experimental methods. Preliminary results on the adsorption of divalent organic cations are presented. Agro-environmental applications of organo-clays are discussed.     

Synthesis and burst strength of water‐swollen immunoisolatory tubules

A series of amphiphilic hydrogel tubules have been prepared by copolymerizing/crosslinking hydrophilic poly(dimethylacrylamide) segments with hydrophobic di‐, tri‐, and octamethacrylate‐telechelic polyisobutylene crosslinkers, and their elastic modulus and burst strength in the water‐swollen state were investigated. Because the burst characteristics of hydrogels have not yet been quantitatively investigated, equipment was designed and built to generate fundamental insight into the burst properties of thin‐walled (200–250 μm) narrow lumen (2–3 mm i.d.) water‐swollen tubules. The theory developed to describe quantitatively the inflation behavior of thin‐walled rubber tubules was adapted to treat our experimental observations. Changes in the burst strength, elastic modulus, and expansion during the inflation of hydrogel tubules were interpreted in terms of the molecular weight of the hydrophilic segments between crosslinking sites (M_{c,hydrophilic}), which in turn was calculated according to the rubber elasticity theory. According to these investigations, the burst strength of our water‐swollen amphiphilic tubules is in the 0.2–0.5 MPa range, which is sufficient for implantation and immunoisolatory applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2075–2084, 2002