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Low Aw (low + aw)

Distribution by Scientific Domains

Life Sciences	50%
Chemistry	50%

Selected Abstracts

Response surface methodology study of the combined effects of temperature, pH, and aw on the growth rate of Trichoderma asperellum

JOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2007
B.A.D. Begoude
Abstract Aims:, To evaluate the influence of environmental parameters (water activity aw, temperature, and pH) on the radial growth rate of Trichoderma asperellum (strains PR10, PR11, PR12, and 659-7), an antagonist of Phytophthora megakarya, the causal agent of cocoa black pod disease. Methods and Results:, The radial growth of four strains of T. asperellum was monitored for 30 days on modified PDA medium. Six levels of aw (0·995, 0·980, 0·960, 0·930, 0·910, and 0·880) were combined with three values of pH (4·5, 6·5, and 8·5) and three incubation temperatures (20, 25, and 30°C). Whatever the strain, mycelial growth rate was optimal at aw between 0·995 and 0·980, independently of the temperature and pH. Each strain appeared to be very sensitive to aw reduction. In addition, all four strains were able to grow at all temperatures and pH values (4·5,8·5) tested, highest growth rate being observed at 30°C and at pH 4·5,6·5. The use of response surface methodology to model the combined effects of aw, temperature, and pH on the radial growth rate of the T. asperellum strains confirmed the observed results. In our model, growth of the T. asperellum strains showed a greater dependence on aw than on temperature or pH under in vitro conditions. Conclusion:,aw is a crucial environmental factor. Low aw can prevent growth of T. asperellum strains under some conditions. The observed and predicted radial growth rate of strain PR11 showed its greater capacity to support low aw (0·93) as compared with other tested strains at 20°C. This is in agreement with its better protective level when applied in medium-scale trials on cocoa plantations. Significance and Impact of the Study:, This study should contribute towards improving the biocontrol efficacy of T. asperellum strains used against P. megakarya. Integrated into a broader study of the impact of environmental factors on the biocontrol agent,pathogen system, this work should help to build a more rational control strategy, possibly involving the use of a compatible adjuvant protecting T. asperellum against desiccation. [source]

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

LETTERS IN APPLIED MICROBIOLOGY, Issue 5 2005
X. Ni
Abstract 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 ,mol) 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 ,mol), and at reduced aw. The spore germination was prevented with either higher fungicide concentration (>10 ,mol), 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 ,mol 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. [source]

INFLUENCE OF WATER ACTIVITY ON THE ACOUSTIC PROPERTIES OF BREAKFAST CEREALS

JOURNAL OF TEXTURE STUDIES, Issue 5 2006
EWA 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]

Response surface methodology study of the combined effects of temperature, pH, and aw on the growth rate of Trichoderma asperellum

WATER ACTIVITY AND THE INACTIVATION OF ENTEROBACTER CLOACAE INOCULATED IN CHOCOLATE LIQUOR AND A MODEL SYSTEM BY PULSED ELECTRIC FIELD TREATMENT

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2002
S. 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]

Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan Films

JOURNAL OF FOOD SCIENCE, Issue 2 2006
Lai Hoong Cheng
ABSTRACT Konjac glucomannan (KGM)-edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM-based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (aw), namely at low aw (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher aw (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (-OH groups) for water adsorption. The presence of polyols at low aw appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%. [source]

Chemical composition and physical properties of extruded snacks containing crab-processing by-product

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 11 2003
Michael G Murphy
Abstract The crab-processing industries generate millions of pounds of by-product annually, which results in a loss of edible product and presents a considerable waste disposal problem. The purpose of this research was to investigate the use of crab-processing by-product (CB) in the development of a calcium-rich expanded snack. The specific objectives were to examine the effects of type of CB (wet or dry), feed composition and screw speed (150 or 250 rpm) on selected properties of extruded snacks. Product formulations consisting of 0,400 g kg,1 CB combined with corn meal and potato flakes were processed in a twin-screw extruder. The resulting extrudates were analysed for proximate and mineral (calcium, sodium) composition, pH, water activity (aw), total plate count, bulk density, expansion ratio and colour. Both CB type and level of incorporation had significant effects (P < 0.05) on the calcium content, expansion ratio, bulk density and pH of the extrudates. Increasing the CB level resulted in increased calcium content (from 5.1 to 52.4 mg g,1) and pH (from 6.1 to 8.8). Screw speed had no significant effects (P > 0.05) on expansion ratio and bulk density. A high processing temperature (157 °C) and low aw resulted in undetectable microbial growth on the extrudates. This research demonstrates that ground crab-processing by-product can be successfully incorporated into an expanded snack product. Further research will evaluate consumer response to this novel value-added product. Copyright © 2003 Society of Chemical Industry [source]