Increasing Gelatin Content Research Articles

Polycaprolactone diacrylate crosslinked biodegradable semi-interpenetrating networks of polyacrylamide and gelatin for controlled drug delivery

A biodegradable semi-interpenetrating hydrogel network (semi-IPN) of polyacrylamide and gelatin was prepared using polycaprolactone diacrylate (mol. wt ∼ 640) as a crosslinker. The drug–polymer interaction and IPN formation were investigated by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and thermal gravimetric analysis (TGA). Scanning electron micrographs of lyophilized matrices revealed porous internal structure with varying pore sizes under equilibrium hydrated conditions, depending upon formulation composition. pH-dependent swelling and degradation was enhanced with increasing gelatin content and decreasing crosslinker concentration (Cs). Compression modulus (CM) (at 20% strain) increased significantly from 23 ± 1.4 to 75 ± 2.7 kPa (p < 0.02) with increasing Cs (from 0.5 to 2.0 mol%), while it decreased from 162 ± 6.4 to 23 ± 1.4 kPa (p < 0.05) with decreasing PAm/G ratio. Cell viability studies by MTT assay showed excellent cytocompatibility of matrices with fibroblast L929 cells. Curcumin, a hydrophobic phytochemical, was loaded by a diffusion method and its release profile was investigated in 4% w/v aqueous BSA solution at 75 rpm (at 37 ± 0.2 °C). Fitting of drug release data in the Korsmeyer–Peppas model suggested sustained release behavior up to 10 days with a combination of diffusion and erosion mechanism (0.5 < n < 1.0; Mt/M∞ ≤ 0.6). The newly developed porous, biodegradable and elastic semi-IPNs may serve as an ideal matrix for controlled drug release and wound healing applications. The possibilities can be explored for pharmaceutical and tissue engineering applications.

Preparation of gelatin microparticles using water-in-water (w/w) emulsification technique

Gelatin microparticles were prepared using water-in-water (w/w) emulsification technique, in which aqueous solutions of gelatin and polypropylene glycol (PEG) were employed as dispersed phase and continuous phase, respectively. The effect of gelatin and PEG concentrations on the size of gelatin microparticles were evaluated. The size of the gelatin microparticles decreased with the increase in PEG concentration and increased with the increase in gelatin concentration. The gelatin microparticles obtained through this process were nearly perfect spheres with smooth surface. The gelatin microparticles, both un-crosslinked and crosslinked, were found to be fully amorphous in nature. The un-crosslinked gelatin microparticles were found to swell instantaneously (within 10 s) whereas the crosslinked ones were quite resistant to water uptake.

Complexation behavior of gelatin with amphiphilic drug imipramine hydrochloride as studied by conductimetry, surface tensiometry and circular dichroism studies

Herein we report our studies carried out on the interaction between IMP and gelatin in aqueous medium at 25 °C using conductimetry, surface tensiometry and circular dichroism (CD) techniques. Both surface tensiometry and conductimetry results indicate that the drug interacts with the gelatin in a surfactant-like manner, i.e., both critical aggregation (cac) and polymer saturation points (psp) were observed. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule. The decrease in cac on increasing gelatin concentration is an indication of the strong interaction between gelatin and IMP. However, at low concentration of gelatin the interaction was not much strong as exposed by surface tension study, i.e., the cac was not very clear (as with higher gelatin concentrations). As usual, the psp increased on increasing the gelatin concentration and was always higher than the critical micelle concentration of the drug in pure aqueous medium. Using CD measurements the influence of IMP on the secondary structure of gelatin in aqueous solutions was also investigated. CD studies (performed at very low drug concentrations) illustrated that the random coil content of gelatin increases with increasing drug concentration. Free energies of aggregation (Δ G agg) and micellization (Δ G mic) were computed with the help of degrees of micelle ionization obtained from the specific conductivity – [IMP] plots.

Preparation and evaluation of ciprofloxacin loaded chitosan-gelatin composite films for wound healing activity.

Natural polymers are used as lead compounds for design of drugs in treatment of different ailments. Chitosan and gelatin have proven wound healing properties individually. As both have wound healing property, the combination of these two polymers and incorporation of drugs into the composite films may show improvement in wound healing activity. Thus, the composite films and drug loaded films were evaluated for various in vitro evaluation tests to ascertain the applicability of prepared combination for wound healing activity. The composite films were prepared with increase in gelatin concentration and the drug loaded films were prepared with increased concentrations of drug in optimized composite film. These films were evaluated for thickness, folding endurance, water absorption capacity, antibacterial activity, tensile strength, drug load, content uniformity, in vitro drug release by diffusion studies and in vivo wound healing studies by excision wound model using albino rats. The drug loaded films shown significant difference in folding endurance, water absorption capacity, antibacterial activity when compared to optimized blank composite film. There was no significant difference in thickness and tensile strength of drug loaded films when compared to blank composite films. Percentage of wound contraction was more for wounds treated with ciprofloxacin loaded composite film than blank composite film. With the above results, it was concluded that ciprofloxacin loaded chitosan-gelatin composite films had shown more wound healing property than chitosan-gelatin blank composite film and blank chitosan film without interfering in strength of film. Keywords: Ciprofloxacin; Chitosan; Gelatin; Drug loaded films; Wound healing; Tensile strength.

Functionalization of biomimetic calcium phosphate bone cements with alendronate

Bisphosphonates (BPs) are widely employed for the treatment of a variety of bone disorders. We have previously successfully added small amounts of BPs into calcium phosphate bone cements in order to enhance their bio-functionality. In this work we were able to increase greatly the amount of BP introduced in the cement, thanks to suitable modifications of composition. In particular, we utilized biomimetic α-tricalcium phosphate (α-TCP) cements at different gelatin contents (10, 15 and 20 wt.%) to introduce Disodium Alendronate up to a concentration of 25 mM. Due to the small liquid/powder ratio (0.22 ml/g) the lengthening of the setting times due to alendronate is quite modest. The rate of transformation of α-TCP into calcium deficient hydroxyapatite slightly decreases as a function of alendronate content, whereas it increases with increasing gelatin concentration. Moreover, relatively high alendronate concentrations provoke significant reduction of the compressive strength of the cements. The results of in vitro tests indicate that alendronate-containing cements significantly affect osteoclast proliferation and differentiation, whereas they promote osteoblast differentiation, to an extent which depends on cement composition.

Development of a model describing the effect of temperature, water activity and (gel) structure on growth and ochratoxin A production by Aspergillus carbonarius in vitro and evaluation in food matrices of different viscosity

The present study aimed: (i) to develop models for the combined effect of water activity (0.99, 0.94 and 0.90), microstructure expressed as 0, 5, 10 and 20% w/v gelatin, and temperature (15, 20 and 25 °C), on growth and OTA production rates by Aspergillus carbonarius; and (ii) to evaluate the performance of the developed models on food matrices (jelly, custard and marmalade) of different viscosity at pH 5.5. The square root of biomass increase rate (fungal growth rate) and OTA production rate were determined by the Baranyi model and were further modeled as a function of temperature, gelatin concentration and a w by applying polynomial models. Time for visible growth and the upper asymptote of the OTA production curve were also determined by the Baranyi model. Increase in gelatin concentration resulted in a significant delay in all parameters describing fungal growth and OTA production rates, at all temperatures and a w. The effect of microstructure on fungal growth and OTA production rates was less evident at stress conditions of a w and temperature. Detection time for visible fungal growth was markedly influenced by a w and temperature. Coefficients of determination were 0.899 and 0.887 for the models predicting the square root ( μ max ) of growth and OTA production rate, respectively. Predictions of growth rate agreed well with the recorded data of custard and marmalade, while observations of OTA production rate indicated low agreement with model predictions, in all food matrices except for marmalade. The present findings may provide a basis for reliable assessment of the risk of fungal growth and OTA production in foods of different structural and rheological properties.

Surface Functionalization of Titanium with Chitosan/Gelatin via Electrophoretic Deposition: Characterization and Cell Behavior

The electrophoretic deposition (EPD) is a versatile and cost-effective technique for fabricating advanced coatings. In this study, chitosan/gelatin (CS/G) coatings were prepared on titanium substrates via EPD. The prepared coatings were characterized using fluorescence microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and shear bond strength testing. It was found that CS/G coatings had a similar macroporous structure. The gelatin content in the CS/G coatings gradually increased with the increase of the gelatin in the blend solutions. The shear bond strength of the CS/G coatings also increased with the increasing gelatin content. In vitro biological tests demonstrated that human MG63 osteoblast-like cells achieved better affinity on the coatings with higher gelatin content. Therefore, it was concluded that EPD was an effective and efficient technique to prepare CS/G coatings on the titanium surface and that CS/G coatings with higher gelatin content were promising candidates for further loading of functional agents.

Morphology, release characteristics, and antimicrobial effect of nisin-loaded electrospun gelatin fiber mat.

Gelatin electrospun (e-spun) fiber mats containing nisin were produced by electrostatic spinning of gelatin-nisin in 70% (vol/vol) acetic acid aqueous solutions. Varying nisin loading concentration (0 to 3% [wt/wt]) did not affect the fiber average diameter, whereas increasing gelatin concentration from 20 to 24% (wt/vol) caused an increase in the average diameter. All nisin-loaded gelatin e-spun fiber mats demonstrated inhibition against Lactobacillus plantarum TISTR 850. However, all fiber mats were fragile and easily dissolved in water. Cross-linking by saturated glutaraldehyde vapor at 37 degrees C for 5 min was done to strengthen the mat. Tensile strength, Young's modulus, and elongation of the cross-linked gelatin-nisin e-spun fiber mats varied in the range of 2.6 to 20.3 MPa, 163 to 966 MPa, and 1.7 to 5.9% , respectively. Cross-linking did not affect the mat's inhibition activity against L. plantarum TISTR 850. Nisin retention in cross-linked antimicrobial gelatin e-spun fiber mats was in the range of 1.0 to 1.22% . Increasing temperature caused an increase in nisin release, but increasing water activity did not cause a significant difference in nisin release over 50 h. After storage at 25 degrees C for 5 months, the antimicrobial gelatin e-spun fiber mat still showed inhibition against L. plantarum TISTR 850. The mats also inhibited the growth of Staphylococcus aureus and Listeria monocytogenes but not Salmonella Typhimurium.

Effect of strontium and gelatin on the reactivity of α-tricalcium phosphate

The hydrolysis reaction of alpha-tricalcium phosphate (alpha-TCP) is of great interest because of its widespread use in the preparation of biomaterials for hard tissue repair. The aim of this study was to investigate how this reaction is influenced by the presence of a bioactive ion, Sr(2+), and of a biopolymer, gelatin, which were previously reported to affect the setting reaction of alpha-TCP-based cements. Hydrolysis experiments were carried out at different Sr(2+) concentrations (0, 5, 10, 20 at.%) in solutions at different gelatin concentrations (0, 0.1, 0.5, 1.0 wt.%). The results indicate that Sr(2+) delays the conversion of alpha-TCP into calcium-deficient hydroxyapatite (CDHA). The structural and morphological modifications of CDHA obtained from solutions at increasing Sr(2+) concentrations indicate that during hydrolysis strontium enters the structure of CDHA, where it partially substitutes for calcium. On the contrary, alpha-TCP hydrolysis rate increases on increasing gelatin concentration. Gelatin promotes conversion of alpha-TCP into octacalcium phosphate, and strongly interacts with the nucleating and growing crystals.

Drug release kinetics and transport mechanisms from semi-interpenetrating networks of gelatin and poly(ethylene glycol) diacrylate.

To elucidate the key parameters affecting solute transport from semi-interpenetrating networks (sIPNs) comprised of poly(ethylene glycol) diacrylate (PEGdA) and gelatin that are partially crosslinked, water-swellable and biodegradable. Effects of material compositions, solute size, solubility, and loading density have been investigated. sIPNs of following gelatin/PEGdA weight-to-weight ratios were prepared: 10:15, 10:20, 10:30, 15:15, 20:15. Five model solutes of different physicochemical properties were selected, i.e. silver sulfadiazine (AgSD), bupivacaine hydrochloride (Bup), sulfadiazine sodium (NaSD), keratinocyte growth factor (KGF), and bovine serum albumin conjugated with fluorescein isothiocyanate (BSA-FITC). Release studies were performed and the results were analyzed using three hydrogel based common theories (free volume, hydrodynamic and obstruction). The release kinetics of model solutes was influenced by each factor under investigation. Specifically, the initial release rates and intra-gel diffusivity decreased with increasing PEGdA content or increasing solute molecular weight. However, the initial release rate and intra-gel diffusivity increased with increasing gelatin content or increasing solute water solubility, which contradicted with the classical hydrogel based solute transport theories, i.e. increasing polymer volume leads to decreased solute diffusivity within the gel. This analysis provides structure-functional information of the sIPN as a potential therapeutic delivery matrix.

The role of formulation excipients in the development of lyophilised fast-disintegrating tablets

Despite recent success, many fast-disintegrating tablets (FDTs) still face problems of low mechanical strength, poor mouth-feel and higher disintegration times. This study aimed to optimise FDTs using a progressive three-stage approach. A series of hardness, fracturability and disintegration time tests were performed on the formulations at each stage. During Stage I, tablets were prepared in concentrations between 2% and 5% w/w, and were formulated at each concentration as single and combination bloom strength gelatin (BSG) using 75 and 225 BSGs. Analysis revealed that both hardness and disintegration time increased with an increase in gelatin concentration. A combination (5% gelatin) FDT comprising a 50:50 ratio of 75:225 BSGs (hardness: 13.7 ± 0.9 N and disintegration time: 24.1 ± 0.6 s) was judged the most ideal, and was carried forward to Stage II: the addition of the saccharides sorbitol, mannitol and sucrose in concentrations between 10% and 80% w/w. The best properties were exhibited by mannitol-containing formulations (50%-hardness: 30.9 ± 2.8 N and disintegration time: 13.3 ± 2.1 s), which were carried forward to the next stage: the addition of viscosity-modifying polymers to improve mouth-feel and aid pre-gastric retention. Addition of carbopol 974P-NF resulted in the enhancement of viscosity with a compromise of the hardness of the tablet, whereas Pluronic F127 (6%) showed an increase in disintegration time and viscosity with retention of mechanical properties.

Preparation, morphology and pH sensitivity of hybrid hydrolyzed polyacrylonitirile‐blend‐gelatin hydrogel fibers

AbstractBACKGROUND: Polyacrylonitrile (PAN) artificial muscles have attracted considerable attention for their fast responses. This research work is based on the preparation of novel pH‐sensitive hydrogel fibers derived from hydrolyzed PAN and gelatin by wet spinning and chemical modification.RESULTS: Through characterization of the fiber dynamic and static pH‐sensitive behavior, pH response times were found to improve greatly with increasing gelatin content. At a weight ratio of 3 to 7 (PAN:gelatin), the best response times were obtained at 0.59 s for elongation and 1.14 s for contraction. Study of the chemical structures of hydrolyzed PAN and gelatin, as well as the surface morphology of the hydrogel fibers, indicated that the mechanism of formation of hydrogel fibers is closely interconnected with their pH‐sensitive behavior. From the standpoint of the mechanism we also found that the addition of urea gave rise to hydrogel fibers with a controllable morphology, influenced by the pH‐sensitive behavior.CONCLUSION: The hydrogel system reported here is simple in preparation, but quite complex in chemical structure. The strong response of the fibers to pH provides some idea on the development of new artificial muscle systems. Copyright © 2008 Society of Chemical Industry

Effect of pH, water activity and gel micro-structure, including oxygen profiles and rheological characterization, on the growth kinetics of Salmonella Typhimurium

In this study, the growth of Salmonella Typhimurium in Tryptic Soy Broth was examined at different pH (4.50–5.50), water activity a w (0.970–0.992) and gelatin concentration (0%, 1% and 5% ) at 20 °C. Experiments in TSB with 0% gelatin were carried out in shaken erlenmeyers, in the weak 1% gelatin media in petri plates and in the firm 5% gelatin media in gel cassettes. A quantification of gel strength was performed by rheological measurements and the influence of oxygen supply on the growth of S. Typhimurium was investigated. pH, as well as a w as well as gelatin concentration had an influence on the growth rate. Both in broth and in gelatinized media, lowering pH or water activity caused a decrease of growth rate. In media with 1% gelatin a reduction of growth rate and maximal cell density was observed compared to broth at all conditions. However, the effects of decreasing pH and a w were less pronounced. A further increase in gelatin concentration to 5% gelatin caused a small or no additional drop of growth rate. The final oxygen concentration dropped from 5.5 ppm in stirred broth to anoxic values in petri plates, also when 0% and 5% gelatin media were tested in this recipient. Probably, not stirring the medium, which leads to anoxic conditions, has a more pronounced effect on the growth rate of S. Typhimurium then medium solidness. Finally, growth data were fitted with the primary model of Baranyi and Roberts [Baranyi, J. and Roberts, T. A., 1994. A dynamic approach to predicting bacterial growth in food. International Journal of Food Microbiology 23, 277–294]. An additional factor was introduced into the secondary model of Ross et al. [Ross, T. and Ratkowsky, D. A. and Mellefont, L. A. and McMeekin, T. A., 2003. Modelling the effects of temperature, water activity, pH and lactic acid concentration on the growth rate of Escherichia coli. International Journal of Food Microbiology 82, 33–43.] to incorporate the effect of gelatin concentration, next to the effect of pH and a w. A two step and a global regression procedure were applied. Both procedures were able to fit the data well, but the global regression procedure led to smaller standard errors on the parameters.

The investigation of swollen process in gelatin gel by using positron annihilation spectroscopy

AbstractThe change of free volume hole radius and bound state of water in the biopolymer gel swollen with water were investigated by positron annihilation lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC). In this study, gelatin with multiple helix structure of polypeptide (MW ∼100,000) was used as biopolymer. To examine into bound state of water in gelatin gel, the weight percentage of freezing and non‐freezing water against total water in gelatin gels were calculated from fusion enthalpy of DSC curves. Accompanied with the increase of gelatin concentration, the percentage of non‐freezing water increased while that of freezing water decreased, and above 60%(w/w) of gelatin concentration, percentage of non‐freezing water reached approximately 100%(w/w). Since the change in bound state of water results from network structure of gelatin gel, free volume hole radius of gelatin gels with different concentrations were characterized from positron annihilation lifetime spectra using PATFIT‐88 program. The lifetime of o‐Ps became longer or the size of free volume hole increased accompanied with the increase of water content. It is considered that the hydrophilic sites, carboxyl groups in gelatin molecules, locate inside of the helix and hydrophobic groups locate outside of the helix. This means that once the water molecules penetrate into the gelatin network, they are attracted by carboxyl groups inside the helix structure and the hydrogen bonds are formed between water and carboxyl groups. The water molecules localized inside the helix expand the helix surface outward by the thermal motion, leading to the increase of free volume hole radius. This idea assumes localization of positrons in the vicinity of the hydrophilic group and the influence of local potential on lifetimes of positron and positronium. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Porous Gelatin Hydrogels: 1. Cryogenic Formation and Structure Analysis

In the present work, porous gelatin scaffolds were prepared by cryogenic treatment of a chemically cross-linked gelatin hydrogel, followed by removal of the ice crystals formed through lyophilization. This technique often leads to porous gels with a less porous skin. A simple method has been developed to solve this problem. The present study demonstrates that the hydrogel pore size decreased with an increasing gelatin concentration and with an increasing cooling rate of the gelatin hydrogel. Variation of the cryogenic parameters applied also enabled us to develop scaffolds with different pore morphologies (spherical versus transversal channel-like pores). In our opinion, this is the first paper in which temperature gradients during controlled cryogenic treatment were applied to induce a pore size gradient in gelatin hydrogels. With a newly designed cryo-unit, temperature gradients of 10 and 30 degrees C were implemented during the freezing step, resulting in scaffolds with average pore diameters of, respectively, +/-116 and +/-330 microm. In both cases, the porosity and pore size decreased gradually through the scaffolds. Pore size and structure analysis of the matrices was accomplished through a combination of microcomputed tomography using different software packages (microCTanalySIS and Octopus), scanning electron microscopy analysis, and helium pycnometry.

Effect of process variables on particle size and viability of Bifidobacterium lactis Bb-12 in genipin-gelatin microspheres

Gelatin microspheres cross-linked with genipin were developed to encapsulate the probiotic Bifidobacterium lactis Bb-12 The effects of different gelatin concentrations (10–19% w/v), bloom strengths (175 and 300), surfactants, stirring rates during emulsion formation and genipin concentrations (0–10 mM) on the microsphere sizes and viability of bacterial cells were investigated. Principal Component Analysis revealed microsphere size distribution differed depending on the presence or absence of surfactants as well as a trend of increasing micropshere size with increasing gelatin concentration and bloom strength. Lower stirring rates resulted in larger microspheres with higher encapsulation yields of bifidobacteria Microsphere size and cell viability were not significantly (p < 0.05) influenced by increasing genipin concentrations up to 10 mM whereas microsphere stability in simulated gastric juice increased with increasing genipin concentration. The encapsulation yields were higher in 175 bloom strength gelatin microspheres than in 300. Cold-stage scanning electron microscopy showed encapsulated bacteria distributed throughout the genipin cross-linked gelatin matrix.

Properties of Alaska Pollock Skin Gelatin: A Comparison with Tilapia and Pork Skin Gelatins

ABSTRACT: The objective of this work was to compare the physiochemical and rheological properties of Alaska pollock skin gelatin (AG) to those obtained for tilapia and pork skin gelatins. Results were also obtained for some mixed gels containing AG and pork skin gelatin, or AG and tilapia gelatin. AG contained about 7% hydroxyproline (Hyp), which was lower than that of tilapia (∼11%) or pork skin gelatin (∼13%). Most of the protein fractions in AG were α chain, β chain, and other oligomers. The gel strength of AG was 98 gram‐force at 10 °C, and increased at a greater rate than other gelatins with decreasing temperature. The gel melting point of AG was the lowest with the oil‐drop method, while the viscosity of AG was the highest of the samples studied. The rheological properties of gelatins were determined using small amplitude oscillatory shear testing. G′ was nearly independent of frequency for most of the gelatin gels, but AG gels showed a slight dependence on G′ and a minimum in G″. G′ was found to be a power law function of concentration for all gelatins used: G′= k × Cn. In rheological measurements, AG also showed the lowest gel melting temperature and sharpest melting region. Increasing gelatin concentration resulted in a higher melting temperature and a broader melting region for all gelatin gels. For both the AG‐pork and AG‐tilapia mixed gels, the gel melting temperatures decreased and melting regions narrowed as the AG fraction was increased.

Simultaneous analysis of the structural and mechanical changes during large deformation of whey protein isolate/gelatin gels at the macro and micro levels

The effect of microstructure on the fracture properties of whey protein isolate (WPI) gels with varying amounts of gelatin was analysed on the macro (mm scale) and micro (μm scale) levels. Eight percent WPI particulate gels with 0–6% gelatin were prepared at a pH near the isoelectric point of whey protein. The tensile stage was placed directly under the confocal laser-scanning microscope (CLSM). The structural changes of the gel during the deformation are visualized in series of micrographs with simultaneous recording of stress and strain data with the tensile stage. The pure whey protein gel exhibited uneven failure at the macro level, where the crack propagated between the whey protein clusters, whereas the crack propagated smoothly through the gelatin phase in the whey/gelatin gel system. At higher magnification the pure WPI protein gel showed porous failure behaviour and gradually ruptured. The WPI gel with high gelatin concentration followed the rheological response of the gelatin phase, resulting in stretched failure behaviour with rapid rupture. The micro strain was calculated directly from micrographs, with the pure WPI gel reaching a seven times higher micro strain than the macro strain. The difference between micro and macro strain decreases with increasing gelatin concentration. Threshold crack propagation values were identified at both the macro and micro levels, and the start of structural failure was observed long before any mechanical response. The fracture dynamics of mixed biopolymer gels can be analysed with this approach both structurally and rheologically at different length scales, contributing to a more comprehensive understanding of the failure behaviour.

Size-controlled synthesis of ZnO nanoparticles and their photoluminescence properties

Nanocrystalline ZnO powders have been synthesized by means of a novel gel-network precipitation method using gelatin as a template at lower temperature condition. The products were characterized by using TG-DTA, XRD and TEM techniques. The products appeared to be regularly spherical or elliptical and their sizes range from 20 to 40 nm. The average particle size increased with increasing calcining temperature, and decreased with increasing gelatin concentration. Furthermore, the photoluminescence (PL) spectra of the ZnO nanopowders were also investigated. The relative luminescent intensities for the ultraviolet band and green emission band showed a dependence on preparation conditions. The probable mechanism was discussed.

Influence of a gel microstructure as modified by gelatin concentration on Listeria innocua growth

The effects of a gelatin gel microstructure as modified by increasing concentration of the gel agent on Listeria innocua growth is studied in a modified BHI medium, mimicking a (semi-)solid food product, at 12 °C and an initial pH of 6.2. Viable counts of the cells were followed as a function of incubation time. The cell growth data were fitted with a classical growth model to estimate the maximum specific growth rate and maximum cell concentration. The micro-colony morphology was also examined with light microscopy and image analysis techniques. The gel microstructure had a slight effect on the growth rate, which generally reduced as the gelatin concentration increased. However, within the range of 50 and 200 g L − 1 and beyond 300 g L − 1 gelatin, the growth rate remained approximately constant and was not affected by the increase in gelatin concentration. A distinct morphological change from large and diffuse through compact and round, up to a more compact, elliptic micro-colony was observed with increasing gelatin concentration. On the contrary, no change in maximum cell concentration was observed within the gel concentration range studied.