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Water Activity (water + activity)
Kinds of Water Activity Selected AbstractsEFFECT OF WATER ACTIVITY ON PHYSICAL PROPERTIES OF CONJUGATED LINOLEIC ACID (CLA) MICROCAPSULESJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2010MARIBEL JIMENEZ ABSTRACT The physical properties of spray drying powders must be considered for the design of equipment. Conjugated linoleic acid (CLA) microcapsules were spray dried by using the following as wall materials: whey protein concentrate (WPC), a blend of whey protein concentrate,maltodextrins (WPC-MD) and gum arabic (GA). These were prepared and their physical properties were studied. The bulk density, packed density, particle density, compressibility and color of the microcapsules were evaluated in a range of water activities from 0.108 to 0.898. No significant differences in the physical properties were found when WPC was used as a wall material in the microcapsules stored at the whole range of water activities tested. Maltodextrins conferred changes in some of the physical properties of the microcapsules (WPC-MD) upon storage at high water activities. GA microcapsules showed drastic changes in all physical properties studied at water activities above 0.628. PRACTICAL APPLICATIONS This work shows the best conditions for storing conjugated linoleic acid (CLA) microcapsules elaborated with different wall materials, which have been reported to have a high potential as a food additive because of the nutraceutical properties of CLA. This research should reveal the behavior of water activity during storage on physical properties, and make it possible to predict what characteristics need to be added to a food, besides being important for the design of equipment, packing and transport. [source] ATTRITION EVALUATION FOR SELECTED AGGLOMERATED FOOD POWDERS: THE EFFECT OF AGGLOMERATE SIZE AND WATER ACTIVITYJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2001HONG YAN ABSTRACT Investigation of the attrition of agglomerates is very important for assessing the agglomerate strength, compaction characteristics, and quality control. A one-term exponential attrition index model and the Hausner ratio were used to study the effects of agglomerate size and water activity on the attrition kinetics of some selected agglomerated food powders. It was found that the agglomerate size and water activity played significant roles in affecting the attrition: the larger the agglomerate size and the higher the water activity, the higher the attrition index under the same tap number. The Hausner ratio was well correlated with the attrition index at high tap numbers and might be used as a simple index to evaluate attrition severity for agglomerates. Knowing the effects of agglomerate size and water activity is very useful to minimize the attrition phenomenon during the handling and processing of agglomerated powders. [source] WATER ACTIVITY AND THE INACTIVATION OF ENTEROBACTER CLOACAE INOCULATED IN CHOCOLATE LIQUOR AND A MODEL SYSTEM BY PULSED ELECTRIC FIELD TREATMENTJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2002S. MI Effects of water activity (aw) on the inactivation of Enterobacter cloacae inoculated in chocolate liquor and in a model system of 0.1% (w/v) peptone water and glycerol by pulsed electric field (PEF) treatment were investigated. An electric field strength of 24.5 kV/cm, a total treatment time of 320 ,s, a pulse duration time of 4 ,s, a pulse delay time of 15 ,s, and a pulse cycle time of 15 s were selected for PEF treatment. The inactivation ofE. cloacae by PEF increased significantly as aw increased (P < 0. 05). As aw of chocolate liquor increased from 0.48 to 0.89, the log reduction of E. cloacae increased from 0.1 to 1.3. The measured temperature change inside the PEF treatment chamber was 0.4C when the log reduction was 1. 3. Similarly, as aw increased from 0. 51 to 0.91 in the model system, the log reduction increased from 0.4 to 1.3. E. cloacae surviving a low aw environment had high resistance to PEF. PEF inactivated E. cloacae in the chocolate liquor with aw of 0.85 by 1 log at O h incubation. However, the log reduction was only 0.1 when PEF treatment was applied to E. cloacae which was incubated for 2 h in the chocolate liquor with aw of 0.85 before PEF treatment. E. cloacae surviving the low aw environment might have resistance not only to the low aw but also to PEF. The resistance to low aw environment may need to be considered when the inactivation of microorganisms by PEF is evaluated. [source] INFLUENCE OF WATER ACTIVITY ON THE ACOUSTIC PROPERTIES OF BREAKFAST CEREALSJOURNAL OF TEXTURE STUDIES, Issue 5 2006EWA GONDEK ABSTRACT Corn and wheat bran flakes were compressed in a plastic cylinder and the generated vibrations were measured by a piezoelectric accelerometer. Amplitude,time records were thoroughly analyzed and the total acoustic energy in arbitrary units, number of acoustic events and energy of a single acoustic event were calculated. Relationships between the time of compression, frequency and sound intensity are presented as acoustograms. All parameters, except the energy of a single acoustic event, were strongly dependent on water activity (Aw). The flakes differed essentially in their ability to propagate vibrations. At low Aw's, both types of flakes were alike, but at higher Aw's, corn flakes damped high-frequency waves while wheat bran flakes did not show this property. [source] Effect of Calcium Propionate and Water Activity on Growth and Aflatoxins Production by,Aspergillus flavusJOURNAL OF FOOD SCIENCE, Issue 2 2010Sahib Alam ABSTRACT:, The efficacy of calcium propionate at 2 different doses (0.5% and 1%) against growth and aflatoxins production by,Aspergillus flavus,(A-2092) was investigated,in vitro,on Czapek yeast extract agar at different levels of water activity (aw) in the range of 0.94 to 0.996aw.,A. flavus,spores germinated on all calcium propionate and aw,treatments; however, 1% calcium propionate at 0.94 aw,delayed the germination process for up to 10 d. The growing rate of mycelia was slower (0.28 mm/d) at 1% calcium propionate and 0.94 aw. Aflatoxins (B1, B2, G1, and G2) were also produced minimally (36.1, 1, 1.86, and 1.01 ng/g of media, respectively) at the aforementioned dose rate of calcium propionate and water activity. It was concluded that addition of calcium propionate and aw,amelioration can prove effective tools for suppressing the germination, growth rate, and aflatoxins production by,A. flavus,in substrate. [source] Correlation between Moisture and Water Activity of Honeys Harvested in Different YearsJOURNAL OF FOOD SCIENCE, Issue 5 2004M.M. Cavia ABSTRACT: For the 1st time, a relationship has been investigated between moisture percentage (M) and water activity (aW) in honeys from 2 different harvesting years and 2 different climatic areas. Moisture was determined by measuring refractive index at 20°C, according to official methods. At the same time, aW of the same samples was assessed at exactly 20°C. Influence on the relationship of the crop's year, aging, and induced fine granulation was evaluated. The results show that, independent of all factors studied, an excellent and statistically significant linear correlation between both parameters [aW = 0.3114 + (0.0170 × M)] was found in all samples with a regression coefficient of 0.8809. The measurement of aW of honey is interesting but time-consuming. This study concludes that this parameter can be easily calculated from the moisture percentage, thus avoiding the use of expensive and slow equipment for aW measurement. [source] Compositional analysis and roasting behaviour of gevuina and macadamia nutsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2010John Birch Summary This study compares the composition of macadamia and gevuina nuts following natural abscission and air-drying of intact nuts and compares chemical and sensory properties on roasting gevuina nuts using a reported macadamia roasting process. The markedly higher fat content of macadamia (75% vs. 43%) reflected a higher percentage of protein, moisture, ash and carbohydrate in gevuina nuts. Gevuina nuts also had lower energy and pH values than macadamia. Water activities were similar. Both oils were around 80% monounsaturated, but differed widely in positional isomerism. On roasting, macadamia nuts developed sweet, nutty, buttery notes along with brown colour development (measured using L*, a*, b* values) after 20 min at 135 °C while gevuina nut colour and aroma took at least 30 min, where the aroma was more hazelnut-like. Extractable volatiles were significantly higher for macadamias following roasting. [source] Effect of water activity on the inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout filletsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2008Jennifer Leah Black Summary Water activity (aw) of ground beef, chicken breast meat, and trout fillets was modified to intermediate (aw 0.98,0.99) and lowest (aw 0.94,0.96) levels. The meat samples with modified and unaltered (native, aw 1.00) aw were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e-beam). Survivor curves were plotted and the D10 -values were calculated. The D10 -values ranged from 0.22 kGy for trout at native aw to 0.33 kGy for beef at intermediate, and chicken and trout at lowest aw. Regardless of the species, aw reduction increased E. coli resistance to e-beam, suggesting that even small depletion of unbound water from food increases survival. The difference of the D10 -values between the samples at intermediate and lowest aw was insignificant. E-beam could be used before aw -reducing techniques are applied to food products. However, this would require stringent microbial control following e-beam processing. The ,tailing' of survivors was observed for some samples with reduced aw. [source] EFFECT OF ANTICAKING AGENT ADDITION AND HEADSPACE REDUCTION IN THE POWDERED-DRINK MIX SENSORY STABILITYJOURNAL OF FOOD QUALITY, Issue 3 2006INAR A. CASTRO ABSTRACT The objective of the present study was to assess the effect of the addition of 0.2% anticaking agent "silicon dioxide" (S) and of 70.0% reduction of the headspace in the package (H) both individually and combined (SH), on the sensory and physicochemical characteristics of a powdered-drink mix over a shelf-life period of 120 days. The "difference from control" test was applied to 10 trained panelists in order to assess the four treatments at 30-day intervals throughout the experimental period, according to visual aspect of the powdered mix and drink flavor. The results demonstrated that a reduction of 70% of the headspace was the most effective treatment for product sensory stability. Water activity (Aw) was a more sensitive parameter than moisture content and ascorbic acid degradation. Although Aw has shown a significant difference over time, the sensory properties still seemed to be a better shelf-life indicator for powdered mixes. Based on the sensory alterations of the aspect of the powder, a reduction of headspace and the limiting of shelf life to between 60 and 90 days could be recommended for powdered-drink mixes packaged in polypropylene containers. [source] Limits of life in hostile environments: no barriers to biosphere function?ENVIRONMENTAL MICROBIOLOGY, Issue 12 2009Jim P. Williams Summary Environments that are hostile to life are characterized by reduced microbial activity which results in poor soil- and plant-health, low biomass and biodiversity, and feeble ecosystem development. Whereas the functional biosphere may primarily be constrained by water activity (aw) the mechanism(s) by which this occurs have not been fully elucidated. Remarkably we found that, for diverse species of xerophilic fungi at aw values of , 0.72, water activity per se did not limit cellular function. We provide evidence that chaotropic activity determined their biotic window, and obtained mycelial growth at water activities as low as 0.647 (below that recorded for any microbial species) by addition of compounds that reduced the net chaotropicity. Unexpectedly we found that some fungi grew optimally under chaotropic conditions, providing evidence for a previously uncharacterized class of extremophilic microbes. Further studies to elucidate the way in which solute activities interact to determine the limits of life may lead to enhanced biotechnological processes, and increased productivity of agricultural and natural ecosystems in arid and semiarid regions. [source] Control of Aspergillus section Flavi growth and aflatoxin accumulation by plant essential oilsJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2008R. Bluma Abstract Aims:, The antifungal effect of Pimpinella anisum (anise), Pëumus boldus (boldus), Mentha piperita (peppermint), Origanum vulgare (oregano) and Minthosthachys verticillata (peperina) essential oils against Aspergillus section Flavi (two isolates of Aspergillus parasiticus and two isolates of Aspergillus flavus) was evaluated in maize meal extract agar at 0·982 and 0·955 water activities, at 25°C. Methods and Results:, The percentage of germination, germ-tube elongation rate, growth rate and aflatoxin B1 (AFB1) accumulation at different essential oils concentrations were evaluated. Anise and boldus essential oils were the most inhibitory at 500 mg kg,1 to all growth parameters of the fungus. These essential oils inhibited the percentage of germination, germ-tube elongation rate and fungal growth. AFB1 accumulation was completely inhibited by anise, boldus and oregano essential oils. Peperina and peppermint essential oils inhibited AFB1 production by 85,90% in all concentrations assayed. Conclusions:, Anise and boldus essential oils could be considered as effective fungitoxicans for Aspergillus section flavi. Significance and Impact of the Study:, Our results suggest that these phytochemical compounds could be used alone or in conjunction with other substances to control the presence of aflatoxigenic fungi in stored maize. [source] EFFECT OF WATER ACTIVITY ON PHYSICAL PROPERTIES OF CONJUGATED LINOLEIC ACID (CLA) MICROCAPSULESJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2010MARIBEL JIMENEZ ABSTRACT The physical properties of spray drying powders must be considered for the design of equipment. Conjugated linoleic acid (CLA) microcapsules were spray dried by using the following as wall materials: whey protein concentrate (WPC), a blend of whey protein concentrate,maltodextrins (WPC-MD) and gum arabic (GA). These were prepared and their physical properties were studied. The bulk density, packed density, particle density, compressibility and color of the microcapsules were evaluated in a range of water activities from 0.108 to 0.898. No significant differences in the physical properties were found when WPC was used as a wall material in the microcapsules stored at the whole range of water activities tested. Maltodextrins conferred changes in some of the physical properties of the microcapsules (WPC-MD) upon storage at high water activities. GA microcapsules showed drastic changes in all physical properties studied at water activities above 0.628. PRACTICAL APPLICATIONS This work shows the best conditions for storing conjugated linoleic acid (CLA) microcapsules elaborated with different wall materials, which have been reported to have a high potential as a food additive because of the nutraceutical properties of CLA. This research should reveal the behavior of water activity during storage on physical properties, and make it possible to predict what characteristics need to be added to a food, besides being important for the design of equipment, packing and transport. [source] CONCENTRATION BOUNDARY CONDITIONS IN THE THEORETICAL ANALYSIS OF CONVECTIVE DRYING PROCESSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2007AHMET KAYA ABSTRACT In the theoretical analysis of convective drying process, two boundary conditions are common for concentration: constant concentration and convection. In this study, these two boundary conditions were comparatively examined by comparing theoretical results obtained with regard to experimental ones. Pumpkin (Cucurbita pepo) was considered as the product to be dried while air was the drying medium. The drying characteristics of pumpkin were determined for various values of drying air parameters, including temperature, velocity and relative humidity. Sorption isotherms of the dried pumpkin were also determined for different temperatures and water activities. The values of the effective moisture diffusivity, Deff, and the convective mass transfer coefficient, hm, were predicted, and these values were found to agree fairly well with those available in the existing literature. PRACTICAL APPLICATIONS Convective drying as well as other drying techniques are used in order to preserve and store agricultural products for longer periods by removing some of their moisture content. Drying is a complicated process involving simultaneous heat and mass transfer under transient conditions. Understanding the heat and mass transfer in the product will help to improve drying process parameters and hence the quality. [source] PHYSICAL AND SENSORY PROPERTIES OF MEATSTICK PRODUCTS AS AFFECTED BY FORMULATION AND DRYING: SENSORY-INSTRUMENTAL RELATIONSHIPSJOURNAL OF FOOD QUALITY, Issue 6 2002ANN BARRETT Shelf-stable meats are of interest to industry and are important in military ration development. Stability is commonly achieved through control of pH and water activity. However, reduction in moisture as a means to lower aw can significantly affect texture. Other ingredients, such as fat, can also potentially affect texture and possibly mitigate hardening due to lowered moisture. Meatsticks dried to three water activities, 0.88, 0.90, and 0.92, each from batters at three fat levels, 14, 17, and 21%, were produced, yielding products varying in both moisture and fat content. Products were subjected to mechanical and sensory testing and image and color analysis. Meatstick modulus, shear force, L* value, and percent of area of cut surfaces covered by separated fat were correlated with sensory assessments of interior hardness, hardness with skin, color, and visual fat, respectively. These parameters were significantly influenced by composition, particularly fat and protein contents and fat-protein interaction. [source] Characterization of Fish-Skin Gelatin Gels and Films Containing the Antimicrobial Enzyme LysozymeJOURNAL OF FOOD SCIENCE, Issue 5 2006C.K. Bower ABSTRACT:, Fish skins are rich in collagen and can be used to produce food-grade gelatin. Films cast from fish-skin gelatins are stable at room temperature and can act as a barrier when applied to foods. Lysozyme is a food-safe, antimicrobial enzyme that can also produce gels and films. When cold-water, fish-skin gelatin is enhanced with lysozyme, the resulting film has antimicrobial properties. The objective of this study was to characterize the effect on strength and barrier properties of lysozyme-enhanced fish-skin gelatin gels and films, and evaluate their activity against potential spoilage bacteria. Solutions containing 6.67% fish-skin gelatin were formulated to contain varying levels of hen-egg-white lysozyme. Gels were evaluated for strength, clarity, and viscoelastic properties. Films were evaluated for water activity, water vapor permeability, and antimicrobial barrier capabilities. Fish-skin gels containing 0.1% and 0.01% lysozyme had pH (4.8) and gelling-temperatures (2.1 °C) similar to lysozyme-free fish-skin gelatin controls. However, gel strength decreased (up to 20%). Turbidities of gels, with or without lysozyme, were comparable at all concentrations. Films cast with gelatin containing lysozyme demonstrated similar water vapor permeabilities and water activities. Lysozyme was still detectable in most fish gelatin films. More antimicrobial activity was retained in films cast with higher lysozyme concentrations and in films where lysozyme was added after the gelatin had been initially heated. These results suggest that fish-skin gelatin gels and films, when formulated with lysozyme, may provide a unique, functional barrier to increase the shelf life of food products. [source] Microencapsulation by Spray Drying of Multiple Emulsions Containing CarotenoidsJOURNAL OF FOOD SCIENCE, Issue 7 2004M.E. Rodríduez-Huezo ABSTRACT: Water-in-oil-in-water (W1/O/W2) multiple emulsions with 25% and 35% solids contents were spray-dried producing microcapsules with 3.9:1, 2.6:1, and 1.4:1 biopolymers blend to primary emulsion ratios and 0.25% (w/w) theoretical carotenoids concentration. Microcapsules with better morphology, encapsulation efficiency, and larger particle size were those obtained from higher biopolymers blend to primary emulsion ratios and solids content, but showed relatively higher carotenoids degradation kinetics than microcapsules made with lower biopolymers blend to primary emulsion ratios and solids content, which exhibited poorer morphology, encapsulation efficiency, and smaller particle size. Microcapsules stored at different water activities showed maximum carotenoids degradation at a water activity (aw) of 0.628, with lower carotenoids degradation occurring at lower or higher aw. [source] Storage Water Activity Effect on Oxidation and Sensory Properties of High-Oleic PeanutsJOURNAL OF FOOD SCIENCE, Issue 5 2002G.L. Baker Peanuts were stored under different water activities and maintained using saturated salt solutions, for 14 wks. Peroxide values, percent moisture, and sensory attributes were determined at 2 wk intervals. Peroxide values increased over time for all treatments. The highest oxidation values were observed in the peanuts held under 0.67 water activity, followed by 0.12, 0.52, 0.44 and 0.33, respectively. Moisture increased over time for all samples and correlated with the water activity of storage. Roast peanut flavor decreased with time and the decrease was greater at higher aw of storage. [source] VARIATIONS IN FLEXURAL AND COMPRESSIVE FRACTURE BEHAVIOR OF A BRITTLE CELLULAR FOOD (DRIED BREAD) IN RESPONSE TO MOISTURE SORPTIONJOURNAL OF TEXTURE STUDIES, Issue 5 2000Y. P. CHANG Mechanical properties of dried bread (a cellular baked product) equilibrated at different water activities (Aw) were measured using three-point bending and uniaxial compression to compare their responses to moisture sorption. The glass-to-rubber transition was clearly demarcated in all the mechanical property-Aw curves, although there were differences in critical Aw (0.32,0.56) at which the dramatic changes in mechanical properties occurred. The role of water appeared to be strictly that of a plasticizer where flexural mechanical parameters were concerned, leading to reduced modulus and fracture stress but increased fracture strain with increasing Aw. Uniaxial compression tests revealed moisture-induced mechanical antiplasticization effects on the material in the glassy state which resulted in maximum compressive fracture stress but minimum fracture strain over the Aw range from 0,0.56. Compressive modulus apparently was not affected much by moisture sorption up to an Aw of 0.43, above which it decreased sharply. [source] Use of a spouted bed to improve the storage stability of wheat germ followed in paper and polyethlyene packagesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 8 2005Füsun Yöndem-Makasc Abstract Stabilization of wheat germ by heating in a spouted bed for 180,540 s with air at 140,200 °C was studied. The lipase activity decreased by 6,65%. Wheat germ processed at 200 °C for 360 s was ranked highest in sensory evaluation, described as having ,a golden color' and ,nutty flavor', and its lipoxygenase activity had decreased by 91.2%. This product and raw wheat germ were stored in paper, polyethylene and vacuum-packed polyethylene pouches at 5 °C, room temperature (18,26 °C) and 40 °C, and the moisture contents, water activities, free fatty acid contents and peroxide values were followed for 20 weeks. The increases were faster in paper pouches than in the polyethylene ones; vacuum packaging in polyethylene did not bring about significant improvement. The peroxide values of raw samples exceeded 10 meq O2 kg,1 oil after 3,23 days while those of the processed samples stored at room temperature or 5 °C were still less than 10 after 20 weeks. The free fatty acid content and peroxide value changes were expressed by zero order kinetics, resulting in similar activation energies for the raw and processed samples. Copyright © 2005 Society of Chemical Industry [source] Effect of caking and stickiness on the retention of spray-dried encapsulated orange peel oilJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2003César I Beristain Abstract Flavour microcapsules containing amorphous carbohydrate as wall material can undergo changes such as crystallisation, clumping, sticking and caking during handling and storage. Such physical changes may lead to the release of entrapped flavours. The objective of this study was to investigate the effect of storage temperature and water activity on caking, stickiness and glass transition temperatures and to evaluate the relative degree of protection provided to orange peel oil entrapped in mesquite (Prosopis juliflora) gum by spray drying. The powders were stored at water activities (aw) ranging from 0.108 to 0.972 at 25 and 35 °C. The surface caking temperature (Tsc) and advance caking temperature (Tac) were determined by the modified ampoule and sealed glass tube methods respectively. The glass transition temperature was determined by differential scanning calorimetry. Changes in the amount of encapsulated oil were determined by Clevenger hydrodistillation. As expected, both Tsc and Tac decreased with increasing storage aw. Above aw 0.628 the powders caked and collapsed during storage at 35 °C. Below aw 0.628 the capsules were not damaged and high retention levels (above 90%) were obtained. Increasing aw in the range 0.743,0.972 caused progressive dissolution of the wall polymer, and the retention level dropped sharply. The volatiles are protected and retained by mesquite gum as long as the capsule structure remains intact. Copyright © 2003 Society of Chemical Industry [source] Physicochemical properties and application of pullulan edible films and coatings in fruit preservationJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2001Tony Diab Abstract The effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan-based edible films as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan films resulted in lower equilibrium moisture contents at low to intermediate water activities (aw), but much higher moisture contents at aw,>,0.75; estimates of monolayer values (within 4.1,5.9,gH2O,kg,1 solids) were given by application of the Brunauer,Emmett,Teller (BET) and Guggenheim,Anderson,DeBoer (GAB) models. A single glass,rubber transition (Tg), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15,30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the Tg vs moisture content data were successfully fitted to the Gordon,Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of , 300,488,kJ,mol,1. With large-deformation mechanical testing, large decreases in Young's moduli (tensile and three-point bend tests) were observed as a result of water- and/or polyol-mediated glass-to-rubber transition of the polymeric films. In the moisture content range of 2,8%, increases in flexural modulus (E) and maximum stress (,max) with small increases in moisture content were found for films made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the films, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were beneficial for extending the shelf-life of this fruit; the coated fruit showed much higher levels of CO2, a large reduction in internal O2, better firmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage. © 2001 Society of Chemical Industry [source] Halotaxis of cyanobacteria in an intertidal hypersaline microbial matENVIRONMENTAL MICROBIOLOGY, Issue 3 2010Katharina Kohls Summary An intertidal hypersaline cyanobacterial mat from Abu Dhabi (United Arab Emirates) exhibited a reversible change in its surface colour within several hours upon changes in salinity of the overlying water. The mat surface was orange-reddish at salinities above 15% and turned dark green at lower salinities. We investigated this phenomenon using a polyphasic approach that included denaturing gradient gel electrophoresis, microscopy, high-performance liquid chromatography, hyperspectral imaging, absorption spectroscopy, oxygen microsensor measurements and modelling of salinity dynamics. Filaments of Microcoleus chthonoplastes, identified based on 16S rRNA sequencing and morphology, were found to migrate up and down when salinity was decreased below or increased above 15%, respectively, causing the colour change of the mat uppermost layer. Migration occurred in light and in the dark, and could be induced by different salts, not only NaCl. The influence of salinity-dependent and independent physico-chemical parameters, such as water activity, oxygen solubility, H2S, gravity and light, was excluded, indicating that the observed migration was due to a direct response to salt stress. We propose to term this salinity-driven cyanobacterial migration as ,halotaxis', a process that might play a vital role in the survival of cyanobacteria in environments exposed to continuous salinity fluctuations such as intertidal flats. [source] Limits of life in hostile environments: no barriers to biosphere function?ENVIRONMENTAL MICROBIOLOGY, Issue 12 2009Jim P. Williams Summary Environments that are hostile to life are characterized by reduced microbial activity which results in poor soil- and plant-health, low biomass and biodiversity, and feeble ecosystem development. Whereas the functional biosphere may primarily be constrained by water activity (aw) the mechanism(s) by which this occurs have not been fully elucidated. Remarkably we found that, for diverse species of xerophilic fungi at aw values of , 0.72, water activity per se did not limit cellular function. We provide evidence that chaotropic activity determined their biotic window, and obtained mycelial growth at water activities as low as 0.647 (below that recorded for any microbial species) by addition of compounds that reduced the net chaotropicity. Unexpectedly we found that some fungi grew optimally under chaotropic conditions, providing evidence for a previously uncharacterized class of extremophilic microbes. Further studies to elucidate the way in which solute activities interact to determine the limits of life may lead to enhanced biotechnological processes, and increased productivity of agricultural and natural ecosystems in arid and semiarid regions. [source] Limits of life in MgCl2 -containing environments: chaotropicity defines the windowENVIRONMENTAL MICROBIOLOGY, Issue 3 2007John E. Hallsworth Summary The biosphere of planet Earth is delineated by physico-chemical conditions that are too harsh for, or inconsistent with, life processes and maintenance of the structure and function of biomolecules. To define the window of life on Earth (and perhaps gain insights into the limits that life could tolerate elsewhere), and hence understand some of the most unusual biological activities that operate at such extremes, it is necessary to understand the causes and cellular basis of systems failure beyond these windows. Because water plays such a central role in biomolecules and bioprocesses, its availability, properties and behaviour are among the key life-limiting parameters. Saline waters dominate the Earth, with the oceans holding 96.5% of the planet's water. Saline groundwater, inland seas or saltwater lakes hold another 1%, a quantity that exceeds the world's available freshwater. About one quarter of Earth's land mass is underlain by salt, often more than 100 m thick. Evaporite deposits contain hypersaline waters within and between their salt crystals, and even contain large subterranean salt lakes, and therefore represent significant microbial habitats. Salts have a major impact on the nature and extent of the biosphere, because solutes radically influence water's availability (water activity) and exert other activities that also affect biological systems (e.g. ionic, kosmotropic, chaotropic and those that affect cell turgor), and as a consequence can be major stressors of cellular systems. Despite the stressor effects of salts, hypersaline environments can be heavily populated with salt-tolerant or -dependent microbes, the halophiles. The most common salt in hypersaline environments is NaCl, but many evaporite deposits and brines are also rich in other salts, including MgCl2 (several hundred million tonnes of bischofite, MgCl2·6H2O, occur in one formation alone). Magnesium (Mg) is the third most abundant element dissolved in seawater and is ubiquitous in the Earth's crust, and throughout the Solar System, where it exists in association with a variety of anions. Magnesium chloride is exceptionally soluble in water, so can achieve high concentrations (> 5 M) in brines. However, while NaCl-dominated hypersaline environments are habitats for a rich variety of salt-adapted microbes, there are contradictory indications of life in MgCl2 -rich environments. In this work, we have sought to obtain new insights into how MgCl2 affects cellular systems, to assess whether MgCl2 can determine the window of life, and, if so, to derive a value for this window. We have dissected two relevant cellular stress-related activities of MgCl2 solutions, namely water activity reduction and chaotropicity, and analysed signatures of life at different concentrations of MgCl2 in a natural environment, namely the 0.05,5.05 M MgCl2 gradient of the seawater : hypersaline brine interface of Discovery Basin , a large, stable brine lake almost saturated with MgCl2, located on the Mediterranean Sea floor. We document here the exceptional chaotropicity of MgCl2, and show that this property, rather than water activity reduction, inhibits life by denaturing biological macromolecules. In vitro, a test enzyme was totally inhibited by MgCl2 at concentrations below 1 M; and culture medium with MgCl2 concentrations above 1.26 M inhibited the growth of microbes in samples taken from all parts of the Discovery interface. Although DNA and rRNA from key microbial groups (sulfate reducers and methanogens) were detected along the entire MgCl2 gradient of the seawater : Discovery brine interface, mRNA, a highly labile indicator of active microbes, was recovered only from the upper part of the chemocline at MgCl2 concentrations of less than 2.3 M. We also show that the extreme chaotropicity of MgCl2 at high concentrations not only denatures macromolecules, but also preserves the more stable ones: such indicator molecules, hitherto regarded as evidence of life, may thus be misleading signatures in chaotropic environments. Thus, the chaotropicity of MgCl2 would appear to be a window-of-life-determining parameter, and the results obtained here suggest that the upper MgCl2 concentration for life, in the absence of compensating (e.g. kosmotropic) solutes, is about 2.3 M. [source] Osmoadaptation in bacteria and archaea: common principles and differencesENVIRONMENTAL MICROBIOLOGY, Issue 12 2001Markus Roeßler The availability of water is the most important prerequisite for life of any living cell, and exposure of cells to hypersaline conditions always threatens the cells with a drastic loss of water. To re-establish the essential turgor pressure, cells increase the water activity of their cytoplasm by accumulation of compatible solutes, either by synthesis or by uptake. The ability to respond to increasing osmolality is well conserved in all three lines of descent and, here, we compare the osmoadaptive strategies of Bacteria and Archaea. The temporal sequence of events after an osmotic upshock will be discussed, with a focus on the most rapid response, notably the mechanisms of transport activation at the protein level, and different signals for osmolality will be compared. The spectrum of compatible solutes used by different organisms is rather diverse and a comparison of ,bacterial' and ,archaeal' compatible solutes will be given. [source] Enzymatic fatty acid exchange in glycero-phospholipids,EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 10 2003Patrick Adlercreutz Abstract Lipases can be used to exchange fatty acids in the sn -1 position of glycerophospholipids and phospholipase A2 is useful for the corresponding exchange reaction in the sn -2 position. In both cases, the exchange can be done in a one-step acidolysis process or in a two-step process. In the latter case, the original fatty acid in the desired position is removed by enzymatic hydrolysis or alcoholysis and after isolation of the resulting lysophospholipid, the new fatty acid is introduced, using the same enzyme, in an esterification reaction. Several synthesis examples from the literature are reviewed. Incorporation of a new fatty acid into the sn -1 position is more favourable than incorporation into the sn -2 position because of the magnitudes of the equilibrium constants of the reactions and because lipases can be used at much lower water activity than phospholipase A2. With the consecutive use of both enzymes highly pure products with defined fatty acids in both positions can be obtained. [source] Microbial life in glacial ice and implications for a cold origin of lifeFEMS MICROBIOLOGY ECOLOGY, Issue 2 2007P. Buford Price Abstract Application of physical and chemical concepts, complemented by studies of prokaryotes in ice cores and permafrost, has led to the present understanding of how microorganisms can metabolize at subfreezing temperatures on Earth and possibly on Mars and other cold planetary bodies. The habitats for life at subfreezing temperatures benefit from two unusual properties of ice. First, almost all ionic impurities are insoluble in the crystal structure of ice, which leads to a network of micron-diameter veins in which microorganisms may utilize ions for metabolism. Second, ice in contact with mineral surfaces develops a nanometre-thick film of unfrozen water that provides a second habitat that may allow microorganisms to extract energy from redox reactions with ions in the water film or ions in the mineral structure. On the early Earth and on icy planets, prebiotic molecules in veins in ice may have polymerized to RNA and polypeptides by virtue of the low water activity and high rate of encounter with each other in nearly one-dimensional trajectories in the veins. Prebiotic molecules may also have utilized grain surfaces to increase the rate of encounter and to exploit other physicochemical features of the surfaces. [source] The osmotic stress tolerance of basidiomycetous yeastsFEMS YEAST RESEARCH, Issue 4 2010Obakeng M. Tekolo Abstract The growth and accumulation of intracellular polyols at reduced water activity (aw) were studied in 40 basidiomycetous yeast strains. The growth of most strains showed greater tolerance to NaCl than sorbitol at the same aw. No strain was able to grow below 0.90aw. 13C nuclear magnetic resonance spectroscopy revealed that glycerol was the major solute accumulated intracellularly by all the yeasts when grown to 0.96aw (NaCl). Arabitol or mannitol was also accumulated in some yeasts, whereas a few only accumulated glycerol. Analysis of six yeasts in detail revealed that the intracellular glycerol concentrations of five yeasts increased significantly when grown at 0.96aw (NaCl or sorbitol) compared with growth at 0.998aw. Arabitol and mannitol concentrations also increased, but not to the same degree. Intracellular potassium concentrations decreased when grown at 0.96aw (NaCl or sorbitol) and sodium increased, but only when grown at 0.96aw (NaCl). The survival of nine strains was evaluated in soil cultures and it was found that all grew at 100% field capacity, whereas at lower field capacity, only some strains grew or survived. The growth of basidiomycetous yeasts appears to be more sensitive to reduced aw than ascomycetous yeasts. [source] Physiological characteristics of the biocontrol yeast Pichia anomala J121FEMS YEAST RESEARCH, Issue 3 2002Elisabeth Fredlund Abstract The yeast Pichia anomala J121 prevents mold spoilage and enhances preservation of moist grain in malfunctioning storage systems. Development of P. anomala J121 as a biocontrol agent requires in-depth knowledge about its physiology. P. anomala J121 grew under strictly anaerobic conditions, at temperatures between 3°C and 37°C, at pH values between 2.0 and 12.4, and at a water activity of 0.92 (NaCl) and 0.85 (glycerol). It could assimilate a wide range of C- and N-sources and produce killer toxin. A selective medium containing starch, nitrate, acetic acid, and chloramphenicol was developed for P. anomala. P. anomala was equally sensitive as Candida albicans to common antifungal compounds. Growth ability at a range of environmental conditions contributes to the competitive ability of the biocontrol yeast P. anomala J121. [source] Aspergillus oryzae in solid-state and submerged fermentationsFEMS YEAST RESEARCH, Issue 2 2002Progress report on a multi-disciplinary project Abstract We report the progress of a multi-disciplinary research project on solid-state fermentation (SSF) of the filamentous fungus Aspergillus oryzae. The molecular and physiological aspects of the fungus in submerged fermentation (SmF) and SSF are compared and we observe a number of differences correlated with the different growth conditions. First, the aerial hyphae which occur only in SSFs are mainly responsible for oxygen uptake. Second, SSF is characterised by gradients in temperature, water activity and nutrient concentration, and inside the hyphae different polyols are accumulating. Third, pelleted growth in SmF and mycelial growth in SSF show different gene expression and protein secretion patterns. With this approach we aim to expand our knowledge of mechanisms of fungal growth on solid substrates and to exploit the biotechnological applications. [source] | |||||||||||||||||||