Combined effect of acetate and reduced water activity in survival of Salmonella typhimurium 7136.

Whereas Salmonella typhimurium 7136 will not grow at reduced water activity (aw), it was survival in such items as intermediate-moisture foods is of interest. Initial studies demonstrated that the addition of 0.3 M acetate (pH 4.7) to glycerol-Trypticase soy broth (BBL Microbiology Systems) solutions (aw 0.86) reduced the viability of S. typhimurium cells. The extent of death of cells exposed to reduced aw was increased by decreasing the pH or increasing the concentration of acetate. Acidification of glycerol-Trypticase soy broth reduced the D40 degrees C value exhibited by cells exposed to a range of aw solutions (0.65 to 0.92). Acetate appeared to affect survival more dramatically as aw values approached the minimum growth limit. Acidification with acetate also reduced cell survival in a variety of humectant solutions with an aw of 0.86 (glycerol, dextrose, and NaCl).     

Banking of non-viable skin allografts using high concentrations of glycerol or propylene glycol

The aims of this study were to investigate the kinetics of the current glycerol banking method for the preservation of non-viable skin allografts; to improve it with respect to efficiency and microbial safety; and to investigate the possibility of using propylene glycol in place of glycerol to provide a more rapid process. Skin grafts were preserved in 98% v/v glycerol (GLY) according to the method used in the Sheffield Skin Bank. During the addition and removal processes, the amounts of GLY and water in the skin were determined using the Karl Fischer method and HPLC respectively. Propylene glycol (PG) was investigated as an alternative to glycerol with the object of shortening the process. To avoid the need for prolonged storage in glycerol to disinfect the tissue, and to improve the effectiveness of disinfection, exposure to peracetic acid (PAA) was included and its influence on the kinetics of the preservation process was evaluated. The histological and ultrastructural appearances of skin that had been banked by these methods was also investigated. It was found that the permeation of GLY in skin probably involves two processes: diffusion and binding; the rate of transport was attenuated as the GLY concentration in the skin increased. The current incubation time could be shortened, but an inconveniently prolonged washout process was required. The substitution of PG for GLY accelerated the whole process, particularly the removal process, making the method more convenient for the emergency use of skin grafts in the clinic. The penetration of PG also involved diffusion and binding, but there was no attenuation of transport as the concentration increased. The addition of PAA sterilisation did not alter the transport of GLY or PG. Structural integrity was also maintained with the new banking treatments. An improved banking method can now be proposed; it can be completed in only one working day and the risk of disease transmission is reduced.     

Interaction of preservation methods and radiation sterilization in human skin processing,with particular insight on the impact of the final water content and collagen disruption. Part I: process validation,water activity and collagen changes in tissues cryopreserved or processed using 50, 85 or 98% glycerol solutions

Current regulatory requirements demand an in-depth understanding and validation of protocols used in tissue banking. The aim of this work was to characterize the quality of split thickness skin allografts cryopreserved or manufactured using highly concentrated solutions of glycerol (50, 85 or 98%), where tissue water activity (a_w), histology and birefringence changes were chosen as parameters. Consistent a_w outcomes validated the proposed processing protocols. While no significant changes in tissue quality were observed under bright-field microscopy or in collagen birefringence, in-process findings can be harnessed to fine-tune and optimize manufacturing outcomes in particular when further radiation sterilization is considered. Furthermore, exposing the tissues to 85% glycerol seems to derive the most efficient outcomes as far as a_w and control of microbiological growth.     

The biomechanical and histological sequelae of common skin banking methods

Human skin allografts are used worldwide as an adjunct for the healing of burns when autograft skin is not available or not indicated. Allograft skin comes from human cadaveric donors, and so must be preserved until use. This study forms the first investigation to compare the mechanical and histological integrity of human split-thickness skin grafts preserved by either glycerolisation or cryopreservation (with or without the cryoprotectant DMSO). Stress relaxation was used to assess mechanical properties, whilst histological analysis allowed for evaluation of structural integrity.     

Influence of water activity and temperature on survival of and colony formation by heat-stressed Chrysosporium farinicola aleuriospores.

The ability of sublethally heat-stressed aleuriospores of Chrysosporium farinicola to form colonies on yeast extract-glucose agar (YGA) supplemented with sufficient glucose, sorbitol, glycerol, and NaCl to achieve reduced water activity (aw) in the range of 0.88 to 0.95 was determined. The effects of the aw of diluent and incubation temperature during recovery and colony formation were also investigated. Aleuriospores harvested from 14-day-old cultures grown at 25 degrees C were less resistant to heat inactivation compared with aleuriospores from 20-day-cultures. Increased populations of heat-stressed aleuriospores were recovered as the aw of YGA was decreased from 0.95 (glucose and glycerol) and 0.94 (sorbitol) to 0.89 and 0.88, respectively. In NaCl-supplemented YGA, populations recovered at an aw of 0.94 were greatly reduced compared with populations detected at an aw of 0.92; no colonies were formed on NaCl-supplemented YGA at an aw of 0.88. Tolerance to aw values above 0.88 to 0.89 as influenced by solute type was in the order of glucose greater than sorbitol greater than glycerol greater than NaCl. Incubation at 20 degrees generally resulted in an increase in recoverable aleuriospores compared with incubation at 25 degrees C or at 30 degrees C for 14 days followed by 20 degrees C for 10 days. The lethal effect of NaCl on heat-stressed aleuriospores was enhanced at 30 degrees C. The retention of viability of aleuriospores held in sucrose-peptone water diluent (aw, 0.936) for 20 min was essentially the same as that observed when aleuriospores were held in peptone water (aw, 0.997).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of water activity and temperature on survival of and colony formation by heat-stressed Chrysosporium farinicola aleuriospores

The ability of sublethally heat-stressed aleuriospores of Chrysosporium farinicola to form colonies on yeast extract-glucose agar (YGA) supplemented with sufficient glucose, sorbitol, glycerol, and NaCl to achieve reduced water activity (aw) in the range of 0.88 to 0.95 was determined. The effects of the aw of diluent and incubation temperature during recovery and colony formation were also investigated. Aleuriospores harvested from 14-day-old cultures grown at 25 degrees C were less resistant to heat inactivation compared with aleuriospores from 20-day-cultures. Increased populations of heat-stressed aleuriospores were recovered as the aw of YGA was decreased from 0.95 (glucose and glycerol) and 0.94 (sorbitol) to 0.89 and 0.88, respectively. In NaCl-supplemented YGA, populations recovered at an aw of 0.94 were greatly reduced compared with populations detected at an aw of 0.92; no colonies were formed on NaCl-supplemented YGA at an aw of 0.88. Tolerance to aw values above 0.88 to 0.89 as influenced by solute type was in the order of glucose greater than sorbitol greater than glycerol greater than NaCl. Incubation at 20 degrees generally resulted in an increase in recoverable aleuriospores compared with incubation at 25 degrees C or at 30 degrees C for 14 days followed by 20 degrees C for 10 days. The lethal effect of NaCl on heat-stressed aleuriospores was enhanced at 30 degrees C. The retention of viability of aleuriospores held in sucrose-peptone water diluent (aw, 0.936) for 20 min was essentially the same as that observed when aleuriospores were held in peptone water (aw, 0.997).(ABSTRACT TRUNCATED AT 250 WORDS)     

Solute stresses affect growth patterns, endogenous water potentials and accumulation of sugars and sugar alcohols in cells of the biocontrol yeast Candida sake

AIM: To evaluate the effect of modifications of water activity (aw 0. 996-0.92) of a molasses medium with different solutes (glycerol, glucose, NaCl, proline or sorbitol) on growth, intracellular water potentials (psi(c)) and endogenous accumulation of polyols/sugars in the biocontrol yeast Candida sake. METHODS AND RESULTS: Modification of solute stress significantly influenced growth, psi(c) and accumulation of sugars (glucose/trehalose) and polyols (glycerol, erythritol, arabitol and mannitol) in the yeast cells. Regardless of the solute used to modify aw, growth was always decreased as water stress increased. Candida sake cells grew better in glycerol- and proline-amended media, but were sensitive to NaCl. The psi(c) measured using psychrometry showed a significant effect of solutes, aw and time. Cells from the 0.96 aw NaCl treatment presented the lowest psic value (- 5.20 MPa) while cells from unmodified media (aw = 0. 996) had the highest value (- 0.30 MPa). In unmodified medium, glycerol was the predominant reserve accumulated. Glycerol and arabitol were the major compounds accumulated in media modified with glucose or NaCl. In proline media, the concentration of arabitol increased. In glycerol- and sorbitol-amended media, the concentration of glycerol rose. Some correlations were obtained between compatible solutes and psi(c). CONCLUSIONS AND SIGNIFICANCE: This study demonstrates that subtle changes in physiological parameters significantly affect the endogenous contents of C. sake cells. It may be possible to utilize such physiological information to develop biocontrol inocula with improved quality.     

Improving low water activity and desiccation tolerance of the biocontrol agent Pantoea agglomerans CPA-2 by osmotic treatments

AIMS: To study the improvement of tolerance to low water activity (aw) and desiccation during spray drying in Pantoea agglomerans cells subjected to mild osmotic stress during growth. METHODS AND RESULTS: The micro-organism was cultured in an unmodified liquid (control) or in aw-modified media, and viability of these cells was evaluated on unstressed (0.995) and 0.96 aw stressed solid media, in order to check total viability and aw stress tolerance respectively. Significant improvements in viability on unmodified medium were observed with cells grown for 24 h in NaCl 0.98 aw, glycerol 0.98 aw and 0.97 aw and for 48 h in NaCl 0.98 aw and 0.97 aw modified media. Both yield improvements and water stress tolerance were achieved with low aw media. Cells grown for 24 h in NaCl 0.98 aw or for 48 h in NaCl 0.98 aw, 0.97 aw and 0.96 aw, glucose 0.97 aw and glycerol 0.97 aw showed improved aw stress tolerance in comparison with control cells. The best results were obtained with NaCl treatments (0.98 aw and 0.97 aw) which also exhibited better survival rates than control cells during spray-drying process and maintained their efficacy against postharvest fungal pathogens in apples and oranges. CONCLUSIONS: NaCl treatments are very appropriate for improving P. agglomerans low aw tolerance obtaining high production levels and maintaining biocontrol efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: Improving stress tolerance of biocontrol agents could be an efficient way to obtain consistency and maintain efficacy of biological control under practical conditions.     

Topical antioxidant vitamins C and E prevent UVB-radiation-induced peroxidation of eicosapentaenoic acid in pig skin

Eicosapentaenoic acid protects against UV-radiation-induced immunosuppression and photocarcinogenesis, but it is also prone to oxidative degradation, which may reduce or abolish its beneficial effects. The protective effect of topically applied vitamin E, vitamin C, or both against UVB-radiation-induced lipid peroxidation in the presence of eicosapentaenoic acid was investigated using an ex vivo pig skin model. Changes in the bioavailability of both antioxidants induced by UV radiation were studied in different skin compartments. The UVB-radiation dose used (25 kJ/m2) was similar to that required to induce immunosuppression in BALB/c mice. Exposure of pig skin with an epidermal eicosapentaenoic acid content of 1.0 +/- 0.3 mol% to UVB radiation resulted in an 85% increase of epidermal lipid peroxidation (P < 0.005). Topical application of vitamin E or vitamin C 60 min prior to UVB irradiation resulted in a major increase in both antioxidants in the stratum corneum and viable epidermis (P < 0.05). Vitamin E and vitamin C completely protected against UVB-radiation-induced lipid peroxidation (P < 0.005), but compared to vitamin E, a 500-fold higher vitamin C dose was needed. UVB irradiation induced a vitamin E consumption of up to 100% in the stratum corneum and viable epidermis, and a vitamin C consumption of only 21% in the stratum corneum. Simultaneously applied vitamin E and vitamin C also completely protected against UVB-radiation-induced lipid peroxidation (P < 0.05), and lower antioxidant doses were needed compared to vitamin E or vitamin C alone. In the presence of vitamin C, epidermal vitamin E was more stable upon UVB irradiation (P < 0.05), suggesting interaction between vitamin E and vitamin C. In conclusion, topically applied vitamin E and/or vitamin C efficiently protect against UVB-radiation-induced lipid peroxidation in the presence of eicosapentaenoic acid. The beneficial biological effects of eicosapentaenoic acid may therefore be improved if vitamin E and/or vitamin C are present in sufficient amounts. The ex vivo pig skin model provides a useful tool for assessing short-term biochemical effects related to UVB radiation, without the use of living experimental animals.     

Differences in the susceptibility of plant membrane lipids to peroxidation

Peroxidation of three membrane lipid preparations from plants was initiated using Fe-EDTA and ascorbate and quantified as the production of aldehydes and loss of esterified fatty acids. Using liposomes prepared from commercial soybean asolecithin, the degree of peroxidation was shown to be dependent on: the free radical dose, which was varied by the ascorbate concentration; the presence of tocopherol in the liposome; the configuration, of the liposome, multilamellar or unilamellar; and time after initiation. There were dramatic interactions among these factors which led to the conclusion that in comparing the susceptibility of different membrane preparations it is essential to examine the kinetics of the peroxidation reactions. The composition of the liposome was a major determinant of the degree of peroxidation and of the type of degradative reactions initiated by the oxygen free radicals. A fresh polar lipid extract from Typha pollen had very similar fatty acid composition to the soybean asolecithin, but was more resistant to peroxidation as shown by less aldehyde production and increased retention of unsaturated fatty acids after treatment. Similarly, microsomal membranes from the crowns of non-acclimated and cold acclimated winter wheat (Triticum aestivum L.) seedlings had a much higher linolenic acid content than soybean asolecithin but was much more resistant to peroxidation. In the winter wheat microsomes, the loss of esterified fatty acids was not selective for the unsaturated fatty acids; consequently, even with 40% degradation, the degree of unsaturation in the membrane did not decrease. These different reaction mechanisms which occur in plant membranes may explain why measurements of fatty acid unsaturation fail to detect peroxidative reactions during processes such as senescence, aging and environmental stress.     

Involvement of lipid peroxidation and organic peroxides in UVA-induced matrix metalloproteinase-1 expression

Ultraviolet A (UVA) irradiation causes human skin aging and skin cancer at least partially through the activation of matrix metalloproteinases (MMPs). MMP-1, the interstitial collagenase, is responsible for the degradation of collagen and is involved in tumor progression in human skin. The present study uses human skin fibroblast cells (FEK4) to investigate the involvement of lipid peroxidation and the role of peroxides as possible mediators in MMP-1 activation by UVA. Preincubation with the antioxidants butylated hydroxytoluene and Trolox reduced UVA-dependent MMP-1 upregulation, suggesting that peroxidation of membrane lipids is involved. Blocking the iron-driven generation of lipid peroxides and hydroxyl radicals by different iron chelators led to a decrease in UVA-induced MMP-1 mRNA accumulation. Moreover, modulation of glutathione peroxidase activity by use of the specific inhibitor mercaptosuccinate (MS) or by the depletion of glutathione (using buthionine-S, R-sulfoximine, BSO), enhanced the UVA-dependent MMP-1 response. Finally, UVA irradiation generated a significant increase in intracellular peroxide levels which is augmented by pretreatment of the cells with BSO or MS. Our results demonstrate that lipid peroxidation and the production of peroxides are important events in the signalling pathway of MMP-1 activation by UVA.     

Interrelationships between Water and cellular metabolism in Artemia cysts. VIII Sorption isotherms and derived thermodynamic quantities

An analysis of water vapor sorption by cysts of the brine shrimp, Artemia salina, has shown that at environmental water activities (aw) of 0.95 or less, the cysts equilibrate with the aw of their environment. Above this aw the metabolic activity of the cysts participates directly in their water content, and equilibration does not occur. In contrast, dried cysts killed by heat treatment or exposure to ammonia fumes equilibrated with all values of aw examined. Analysis of the temperature dependence of sorption isotherms revealed that below cyst hydrations of about 0.3 g H2O/g dried weight the temperature coefficient for water sorption was negative, but became positive at hydrations appreciably in excess of this value. Estimates for the differential and integral net enthalpy and entropy changes accompanying the sorption of water have been calculated from isotherms. These results have been interpreted and integrated with those from previous work on the hydration-dependence of metabolic activity. All of the examined hydration properties of the cysts have been shown to be due chiefly to the cellular component, and not the acellular shell. Analysis of the data by the Bradley equation has shown that the hydration behavior of the shell obeys this relationship, whereas that of the cellular component does not.     

Cryopreservation of fetal skin is improved by extracellular trehalose

In this study, we tested a non-permeating cryoprotectant, trehalose, in combination with dimethyl sulfoxide (Me(2)SO) in the cryopreservation of human fetal skin and compared it to Me(2)SO and glycerol, protocols that are routinely used by skin banks. The viability of fetal skin from four groups (fresh, and cryopreserved with glycerol, Me(2)SO, or trehalose/Me(2)SO) were evaluated using an in vitro membrane integrity assay and by transplantation to immunodeficient mice. The membrane integrity assay showed a 90% integrity in fresh, unfrozen fetal skin. The number of intact cells dropped to 23 and 44% in fetal skin cryopreserved with glycerol and Me(2)SO, respectively. When trehalose was added to the cryopreservation medium containing Me(2)SO, the membrane integrity rose to 65%. When transplanted to immunodeficient mice, fetal skin cryopreserved with trehalose/Me(2)SO showed a graft performance indistinguishable from fresh unfrozen fetal skin and strikingly better graft take than that of fetal skin cryopreserved with Me(2)SO or glycerol only. These results suggest that cryopreservation protocols routinely used the skin banks can be improved by combining sugars such as trehalose with a permeating cryoprotectant.     

Modulation of water activity on fungicide effect on Aspergillus niger growth in Sabouraud dextrose agar medium*

AIMS: To examine whether water activity (aw) in combination with low concentration of fungicides can be used to effectively control Aspergillus niger van Tieghem growth in cultural medium, the Sabouraud dextrose agar (SDA). The data would be used as baseline information for reducing A. niger contamination in insect artificial diets. METHODS AND RESULTS: Aspergillus niger was isolated from an insect artificial diet. Four concentration levels (i.e. 0, 1, 10 and 20 micromol) of two fungicides (i.e. amphotericin B and itraconazole) were tested against A. niger under four aw levels (i.e. 0.994, 0.961, 0.921 and 0.859) adjusted by including 0, 12.5, 25 and 38% of glycerol in the medium mixture. Aspergillus niger growth was significantly reduced at low fungicide concentration (1 micromol), and at reduced aw. The spore germination was prevented with either higher fungicide concentration (>10 micromol), or low aw in the medium (aw < 0.921). The two ecological determinants (fungicides and aw) showed a significant impact on A. niger survival in the medium (P < 0.0001). Itraconazole is more effective than amphotericin B in controlling A. niger contamination in the agar medium. CONCLUSION: Adjustment of aw (with 12.5% of glycerol) in combination with 1 mumol of itraconazole can effectively prevent A. niger growth in the SDA cultural medium. SIGNIFICANCE AND IMPACT OF THE STUDY: Aspergillus niger contaminations have frequently affected the quality of insects produced from mass rearing facilities. Low aw in combination with low fungicide concentration has the potential to become one of the most cost-effective management strategies to prevent A. niger contamination in insect artificial diets. The effect of fungicides and low aw in artificial diets on insect biology needs to be further examined.     

Process for the production of tilapia retorted skin gelatin hydrolysates with optimized antioxidative properties

Thermally hydrolyzed tilapia skin gelatin demonstrated noticeable free-radical scavenging and inhibition of lipid peroxidation. Five factors in production of retorted skin gelatin hydrolysate (RSGH) were screened using a fractional factorial design to identify critical factors. Phosphoric acid concentration, water/skin ratio, and retorting time had significant effects on α,α-diphenyl-β-picrylhydrazyl (DPPH) scavenging by RSGHs. A face-centered, central composite design in these three factors was used to collect data that resulted in strong response surface models of DPPH scavenging (R² = 0.977) and inhibition of lipid peroxidation (R² = 0.967). The most effective condition resulted in 80.3% DPPH scavenging and 75.0% inhibition of lipid peroxidation. The models were used to predict maxima for the two properties. These were 79.4% for DPPH scavenging activity and 77.3% for lipid peroxidation inhibition. Antioxidative tilapia RSGH has potential as a natural antioxidant because a large amount of low-priced skin by-products can be obtained from the tilapia filleting industry.     

Glass-fiber disks provide suitable medium to study polyol production and gene expression in Eurotium rubrum

Eurotium species often dominate the fungal population in stored grain and are responsible for spoilage. In this study we tested the usefulness of glass fiber disks to aid the analysis of growth, polyol content and gene expression in E. rubrum in response to various water activities. Growth measurements based on ergosterol content and conidial production indicated that E. rubrum grew as well at 0.86 aw as 0.98 aw. The rate of growth was considerably reduced at 0.83 aw and 0.78 aw. In contrast, under our conditions, Aspergillus flavus and A. nidulans were able to grow only in the highest water activity (0.98 aw). Mannitol was the predominant polyol in all three fungal species grown at 0.98 aw. When E. rubrum was grown at 0.86 aw or lower, glycerol comprised greater than 90% of the total polyols. After a shift from 0.86 aw to 0.98 aw, mannitol levels in E. rubrum increased to 89% of the total polyols within 24 h. Of six genes whose expression was measured by quantitative real-time PCR, three were affected by water activity. Expression of putative hydrophobin and mannitol dehydrogenase genes was higher at 0.98 aw than at 0.86 aw. A putative triacylglycerol lipase gene was expressed at higher levels in 0.86 aw.. The results of this study indicate that the disk method is suitable to study the effects of water activity on growth, polyol biosynthesis and gene expression in E. rubrum. The results also indicate the potential competitiveness of E. rubrum over A. flavus and A. nidulans in low water environments associated with stored grain.     

Enzymatic synthesis of tricaprylin in a solvent-free system: lipase regiospecificity as controlled by glycerol adsorption on silica gel

Enzymatic synthesis of tricaprylin from caprylic acid (octanoic acid) and glycerol was carried out under solvent-free conditions. Kinetics of mono-, di- and tricaprylin synthesis and caprylic acid esterification in standard conditions (free glycerol) were slightly different from those obtained in the case of silica gel adsorbed glycerol. The critical role of the silica gel which behaves as a "reservoir" is proposed and it was shown that the use of silica gel facilitates reactions and improves the conversion yields at high glycerol concentrations.     

The first characterization of free radicals formed from cellular COX-catalyzed peroxidation

Through free radical-mediated peroxidation, cyclooxygenase (COX) can metabolize dihomo-γ-linolenic acid (DGLA) and arachidonic acid (AA) to form well-known bioactive metabolites, namely, the 1-series of prostaglandins (PGs1) and the 2-series of prostaglandins (PGs2), respectively. Unlike PGs2, which are generally viewed as proinflammatory and procarcinogenic PGs, PGs1 may possess anti-inflammatory and anti-cancer activity. Previous studies using ovine COX along with spin trapping and the LC/ESR/MS technique have shown that certain exclusive free radicals are generated from different free radical reactions in DGLA and AA peroxidation. However, it has been unclear whether the differences were associated with the contrasting bioactivity of DGLA vs AA. The aim of this study was to refine the LC/MS and spin trapping technique to make it possible for the association between free radicals and cancer cell growth to be directly tested. Using a colon cancer cell line, HCA-7 colony 29, and LC/MS along with a solid-phase extraction, we were able to characterize the reduced forms of radical adducts (hydroxylamines) as the free radicals generated from cellular COX-catalyzed peroxidation. For the first time, free radicals formed in the COX-catalyzed peroxidation of AA vs DGLA and their association with cancer cell growth were assessed (cell proliferation via MTS and cell cycle distribution via propidium iodide staining) in the same experimental setting. The exclusive free radicals formed from the COX-catalyzed peroxidation of AA and DGLA were shown to be correlated with the cell growth response. Our results indicate that free radicals generated from the distinct radical reactions in COX-catalyzed peroxidation may represent the novel metabolites of AA and DGLA that correspond to their contrasting bioactivity.     

Effect of plasticizers (water and glycerol) on the diffusion of a small molecule in iota-carrageenan biopolymer films for edible coating application

Translational diffusion of a fluorescein probe has been measured in iota-carrageenan edible films containing different amounts of glycerol (0, 15, 30, and 45%), using fluorescence recovery after photobleaching (FRAP) experiments. The effects of this plasticizer as well as the plasticizing effect of water on the diffusion of fluorescein have been studied in this edible coating mainly composed of natural biopolymer. Diffusion coefficients of about 10(-13) m2 s(-1) have been measured in these films for water activity (aw) lower than 0.7. Above this water content threshold, fluorescein translational diffusion coefficient increases up to 10(-12) m2 s(-1). Another interesting information obtained from FRAP experiments on this system is the ratio of the diffusing molecules which are immobilized in the carrageenan matrix at aw lower than 0.98. Moreover, films containing more than 30% glycerol (w/w carrageenan) present a huge increase of the diffusion coefficient of fluorescein at high water activity (about 2 orders of magnitude), this effect being less pronounced at low water activity. The increase of diffusion seems to be only related to the water content, and glycerol only acts through the enhancement of water adsorption. Therefore, in biopolymer films containing polyol plasticizers, the gain in mobility could be devoted to the effect of the ubiquitous plasticizing molecule, water, whose adsorption is increased by the plasticizer.     

Effect of hypoxic breathing on cutaneous temperature recovery in man

Effect of hypoxia (12% O₂) on skin temperature recovery was studied on healthy young men. Forty male volunteers free of any respiratory disorder were randomly selected to participate in the study. Skin temperature, peripheral blood flow, heart rate and end expiratoryPO₂ andPCO₂ were measured. During hyoxic ventilation the peripheral blood flow was reduced and a corresponding drop in skin temperature occurred. This was partly due to hyperventilation associated with hypoxic ventilation. The recovery of skin temperature after cooling the hand for 2 min in cold water (10–12° C) took 5.5±0.1 min during normal air breathing; during hypoxic ventilation even after 9.1±0.3 min when the skin temperature recovery curve plateaued, the skin temperature remained about 2° C below control. The results of the present investigation indicate that hypoxia interferes with the normal functioning of the thermoregulatory mechanism in man. Hyperventilation associated with hypoxic ventilation is also partly responsible for incomplete recovery of skin temperature.