共查询到20条相似文献,搜索用时 15 毫秒
1.
Moisture sorption isotherms of figs with and without glucose syrup (at 20% and 40%, w/w) were determined at 5 °C, 25 °C, and 40 °C. A static gravimetric method was used under 0.11–0.84 water activity ranges for
the determination of sorption isotherms that were found to be typical type ΙΙΙ for control sample. The inclusion of glucose
syrup had significant effects on the sorption isotherms, and the moisture content of samples at each a
w decreased with increasing temperature. The experimental data were fitted well with two-parameter Brunauer–Emmet–Teller, three-parameter
Guggenheim–Anderson–de Boer, and four-parameter Peleg models that all had R
2 of greater than 0.99. The net isosteric heats of sorption were estimated using the Clausius–Clapeyron equation from the equilibrium
data at different temperatures. It was found that the addition of glucose syrup significantly increased the amount of monolayer
water and the isosteric heat of sorption. Both water activity and isosteric heat of sorption increased with glucose syrup
level and the shape and status of sorption isotherms tend to change toward the typical sigmoid shape of most food systems. 相似文献
2.
《Bioscience, biotechnology, and biochemistry》2013,77(7):1565-1568
Moisture sorption isotherms were measured at 25 °C for untreated, dry-heated and pre-gelatinized durum wheat flour samples. The isotherms could be expressed by the Guggenheim-Anderson-de Boer equation. The amount of water sorbed to the untreated flour was highest for low water activity, with water sorbed to the pre-gelatinized and dry-heated flour samples following. The dry-heated and pregelatinized flour samples exhibited the same dependence of the moisture content on the partial molar volume of water at 25 °C as the untreated flour. The partial molar volume of water was ca. 9 cm3/mol at a moisture content of 0.03 kg-H2O/kg-d.m. The volume increased with increasing moisture content, and reached a constant value of ca. 17.5 cm3/mol at a moisture content of 0.2 kg-H2O/kg-d.m. or higher. 相似文献
3.
C. J. Baxter N. Magan B. Lane H. G. Wildman 《Applied microbiology and biotechnology》1998,49(3):328-332
A Phoma sp., known to produce the pharmaceutically active metabolites squalestatin 1 (S1) and squalestatin 2 (S2), was cultured on
malt-extract/agar (MEA) over a range of water activities (a
w, 0.995–0.90) and temperatures (10–35 °C) to investigate the influence on growth and metabolite production. Use of the ionic
solute NaCl to adjust a
w resulted in significantly lower (P < 0.01) squalestatin yields than when the Phoma sp. was grown on MEA amended with the non-ionic solute glycerol. Water activity and temperature and their interactions were
highly significant factors (P < 0.001) affecting growth of the Phoma sp., with optimum conditions of 0.998–0.980 a
w and 25 °C. Squalestatin production was similarly influenced by a
w, temperature, time and their interactions (P < 0.001). S1 and S2 production occurred over a narrower a
w and temperature range than growth, with a slightly lower optimum a
w range of 0.995–0.980 a
w. The optimum temperature for squalestatin production varied from 20 °C (S1) to 25 °C (S2) and yields of S2 were up to 1000
times lower than those of S1. The ratio of S1 and S2 produced by the Phoma sp. was influenced by a
w and temperature, with highest values at 0.99–0.98 a
w, and at 15 °C. Incubation times of 28 days gave highest yields of both S1 and S2. Up to 2000-fold increases in squalestatin
yields were measured at optimum environmental conditions, compared to the unmodified MEA. This indicates the need to consider
such factors in screening systems used to detect biologically active lead compounds produced by fungi.
Received: 2 June 1997 / Received last revision: 6 November 1997 / Accepted: 7 November 1997 相似文献
4.
The objectives were to determine the influence of water activity (aw, 0.997–0.92) and temperature (10–37°C) and their interactions on conidial germination, mycelial growth and sporulation of
two strains of Stachybotrys chartarum in vitro on a potato dextrose medium. Studies were carried out by modifying the medium with glycerol and either spread plating
with conidia to evaluate germination and germ tube extension or centrally inoculating treatment media for measuring mycelial
growth rates and harvesting whole colonies for determining sporulation. Overall, germination of conidia was significantly
influenced by aw and temperature and was fastest at 0.997–0.98 aw between 15 and 30°C with complete germination within 24 h. Germ tube extension was found to be most rapid at similar aw levels and 25–30°C. Mycelial growth rates of both strains were optimal at 0.997 aw between 25 and 30°C, with very little growth at 37°C. Sporulation was optimum at 30°C at 0.997 aw. However, under drier conditions, this was optimum at 25°C. This shows that there are differences in the ranges of aw x temperature for germination and growth and for sporulation. This may help in understanding the role of this fungal species
in damp buildings and conditions under which immune-compromised patients may be at risk when exposed to such contaminants
in the indoor air environment. 相似文献
5.
Summary The growth and the sporulation of Trichoderma viride TS in relation to water activity (a
w) of sugar-beet pulp medium was studied. It was found that the maximum growth, monitored by protein production, substrate
utilization and pH alteration, appeared at a
w=0.990–0.992. Optimal water activity of the medium for sporogenesis was 0.980. It was observed that both physiological phenomena
appeared in narrow ranges of water activity which caused the rigorous a
w control in solid-state fermentation to be postulated. 相似文献
6.
Atar Selouane Driss Bouya Ahmed Lebrihi C. Decock Amina Bouseta 《Journal of microbiology (Seoul, Korea)》2009,47(4):411-419
The effects of temperature, water activity (aw), incubation time, and their combinations on radial growth and ochratoxin A (OTA) production of/by eight Aspergillus niger aggregate strains (six A. tubingensis and two A. niger) and four A. carbonarius isolated from Moroccan grapes were studied. Optimal conditions for the growth of most studied strains were shown to be at
25°C and 0.95 aw. No growth was observed at 10°C regardless of the water activity and isolates. The optimal temperature for OTA production
was in the range of 25°C∼30°C for A. carbonarius and 30°C∼37°C for A. niger aggregate. The optimal aw for toxin production was 0.95∼0.99 for A. carbonarius and 0.90∼0.95 for A. niger aggregate. Mean OTA concentration produced by all the isolates of A. niger aggregate tested at all sampling times shows that maximum amount of OTA (0.24 μg/g) was produced at 37°C and 0.90 aw. However, for A. carbonarius, mean maximum amounts of OTA (0.22 μg/g) were observed at 25°C and 0.99 aw. Analysis of variance showed that the effects of all single factors (aw, isolate, temperature and incubation time) and their interactions on growth and OTA production were highly significant. 相似文献
7.
The effect of water availability (water activity,aw; 0.995–0.90) and temperature (18–30 °) on in vitro interactions between an ochratoxin producing strain of Aspergillus ochraceus and six other spoilage fungi was assessed in dual culture experiments on a maize meal-based agar medium. Inprimary resource
capture of nutrient substrate, A. ochraceus was dominant against many of the interacting species, being able to overgrow and replace A. candidus, and sometimes A. flavus and the Eurotium spp. regardless of aw or temperature. However, with freely available water (0.995 aw) A. alternata and A. niger were dominant, with mutual antagonism between A. ochraceus and A. flavus at 25–30 °C. In the driest conditions tested (0.90 aw) there was also mutual antagonism between A. ochraceus and the two Eurotium spp. Overall, under allconditions tested the Index of Dominance for A. ochraceus was much higher than for other competing species combined suggesting that A. ochraceus wasa good competitive colonist able to replace a numberof other species. However, the growth rate ofA. ochraceus was modified and decreased by the interaction with competitors. Interaction between A. ochraceus and species such as A. alternata (18°C/0.995) and Eurotium spp. (0.995–0.95 and 25–30 °C) resulted in a significant stimulation of ochratoxin production. Theresults are discussed in
relation to the effect that environmental factors have on the possible competitiveness of A. ochraceus in the maizegrain ecosystem and the role of ochratoxin in nicheexclusion of competitors.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Simultaneous Monitoring of Phosphine and of Phosphorus Species in Taihu Lake Sediments and Phosphine Emission from Lake Sediments 总被引:4,自引:0,他引:4
Phosphine (PH3) was monitored in the Taihu Lake in China by a GC/NPD method, coupled with cryo-trapping enrichment technology. Results showed
that PH3 was universally detected in sediments, lake water and atmosphere of the Taihu Lake area. Total phosphorus (TPs) and fractions of different phosphorus species in lake sediments were separately measured as dissolved phosphate (DP), phosphorus
bound to aluminum (Al-P), iron (Fe-P) and calcium (Ca-P), occluded phosphorus (OP), and organic phosphorus (Org-P) by sequential
chemical extraction. High PH3 levels were correlated with high TPs values in sediments and with eutrophication at different sites. In addition, a positive linear correlation equation was obtained
between the concentrations of PH3 in lake sediments and of the phosphorus fractions. The resulting multiple linear regression equation is PH3 = −165 + 63.3 DP + 0.736 Al-P + 2.33 Ca-P + 2.29 Org-P. The flux of PH3 across the sediment–water interface was estimated from sediment core incubation in May and October 2002. The annual average
sediment–water flux of PH3 was estimated at ca. 0.0138±0.005 pg dm−2 h−1, the average yearly emission value of PH3 from Taihu Lake sediments to water was calculated to be 28.3±10.2 g year−1, which causes a water PH3 concentration of up to 0.178±0.064 pmol dm−3. The real importance of PH3 could be higher, because PH3 could be consumed in the oxic sediment–water boundary layer and in the water column. Spatial and temporal distributions of
total phosphorus (TPw) and chlorophyll a (Chl-a) in the water column of Taihu Lake were measured over the study period. Higher water PH3 has also been found where the TPw content was high. Similarly, high Chl-a was consistent with higher water PH3. Positive relationships between PH3 and TPw (average R2 = 0.47±0.26) and Chl-a (average R2 = 0.23±0.31) were observed in Taihu Lake water. 相似文献
9.
Epicoccum nigrum conidia were produced by solid fermentation on wheat grains (cv. Rendeveaux and Brigadier) at different water activities
(aw). Conidial production was highest at high aw(0.996) than at reduced aw (0.98). However, conidial production at reduced aw was improved when the aw of the substrate was adjusted with a mixture of glycerol and water. Maximum levels ofconidiation were 7–11 × 106 conidia g−1 grain. The aw of the solid substrate affected the pattern of accumulation of compatible solutes in the conidia. Mannitol was the main polyol
in all conidialtypes. However, the amounts of mannitol were higher in conidia produced at high aw. At reduced aw the conidia of E. nigrum accumulated moreglycerol, which is more efficient in the osmorregulation proccess than mannitol. Arabitol accumulated in
low amounts, specifically in conidia produced at the lower aw, on cv. Rendeveaux but not on cv. Brigadier. Trehalose was detected in higher amounts in cv. Rendeveaux than in cv. Brigadier,
andthe amounts were higher in conidia produced at high aw. A significant amount of endogenous solutes was detected in the washing liquid used for the separation of the conidia.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
The benefits of controlling water activity, a
w, during enzymatically catalysed synthesis reactions, such as reverse-hydrolytic reactions promoted by lipases, are now well
recognized. Numerous techniques for controlling a
w in the laboratory and their implementation in continuous reactors have been discussed in the published literature. However,
in enzymatic interesterification reactions, such as acidolysis and transesterification, it is not appropriate merely to maintain
the a
w of the reaction system at one value since the two stages of the reaction, namely the cleavage of the original acyl bond and
the formation of a new one, are best carried out at different levels of water activity – the former at a high a
w and the latter at a lower one. The use of a continuous packed-bed hollow-fibre reactor has been described in this article
for carrying out solvent-free acidolysis of ethyl laurate with octanoic acid with in situ a
w control, using air that has been pre-equilibrated with saturated salt solutions to the desired a
w. At a single optimum (a
w = 0.54), the highest steady-state conversion to ethyl octanoate was 32%. However, it is possible to obtain a steady-state
conversion of 46% by operating the reactor with a step change in the water activity, from an initial value of unity to 0.23.
Received: 10 February 1998 / Received revision: 2 June 1998 / Accepted: 7 June 1998 相似文献
11.
Etienne Paul Jacques Fages Philippe Blanc Gerard Goma Alain Pareilleux 《Applied microbiology and biotechnology》1993,40(1):34-39
Survival of alginate-entrapped cells of Azospirillum lipoferum was studied during dehydration using a dry air stream and during prolonged storage at various constant water activity values (aw). During the drying operation, the viability loss remained almost constant from the initial water content to 0.35 g water/g dry weight (DW) corresponding to a 98.5% water removal, strongly increased until a water content of 0.25 g/g DW and then stopped until the end of the drying operational (final aw 0.18). A water content of 0.25 g/g DW (aw=0.55) corresponded to the critical point of the moisture sorption isotherm curve from which water became restricted to the dry material. A high drying rate (5 g/g DW per hour) was shown to be more detrimental for cell viability than a low drying rate (1.18 g/g DW per hour). When the product was stored in a closed chamber with a regulated aw (0.23), the number of living cells decreased during a short period (less than 15 days) corresponding to the product aw stabilization, and then remained constant for more than 150 days. In addition, cell survival during storage was not affected by aw values in the range 0–0.55. Above aw=0.55, the higher the aw and the storage duration, the lower the residual survival percentage. The influence of the drying and storage conditions on the cell death rate are discussed with regard to both the mechanisms generally involved in viability loss and the hydration properties of water.
Correspondence to: A. Pareilleux 相似文献
12.
《Cryobiology》2019
Cryopreservation of the germplasm for long-term periods is of great importance to maintain the genetic resource. Argentina is one of the world's highest lemon producing country. The performance of different cooling/warming rates in the cryopreservation method of Citrus limon L. Burm cv. Eureka seeds and their influence on the interval of optimal moisture content in the desiccation stage were analyzed. Water sorption isotherm was determined and modeled using D'Arcy & Watt equation; it provided important information concerning the amounts of water associated to strong, weak and multimolecular binding sites along the sorption isotherm. Seeds tolerated a wide range of desiccation conditions (0.1<aw<0.85) showing a high viability (>80%), however desiccation to 0.0526 g H2O g−1 d.b. (aw = 0.0901) produced a significant loss of viability. Differential Scanning Calorimetry was used to identify the thermal transitions of lipids and water in the seed; enthalpies were used to calculate the unfrozen water fraction (0.19 g H2O g−1 d.b. corresponding to aw = 0.64). Two cooling/warming rates were tested on desiccated seeds (0.11<aw<0.85): i) 200 °C min−1 (reached with seeds placed inside a closed cryogenic vial); ii) 1000 °C min−1 (reached with aluminum-foiled seeds placed in a perforated cryogenic vial). For both methods, viability was maximum (83.3%) at aw = 0.64. Lethal ice formation was responsible for the loss of viability at aw>0.64 corresponding to the unfrozen water fraction. The use of higher cooling/warming rates enables a wider range of desiccation conditions (0.33<aw<0.76) in cryopreservation procedures. This work contributes to the optimization of cryopreservation methods of economically important germplasm. 相似文献
13.
《Biophysical journal》2022,121(20):3874-3882
The purpose of this study was to clarify the glass-transition behavior of bacteria (Cronobacter sakazakii) as a function of water activity (aw). From the water sorption isotherm (298 K) for C. sakazakii, monolayer water content and monolayer aw were determined to be 0.0724 g/g-dry matter and 0.252, respectively. Mechanical relaxation was investigated at 298 K. In a higher aw range of over 0.529, the degree of mechanical relaxation increased with an increase in aw. From the effect of aw on the degree of mechanical relaxation, the mechanical awc (aw at which mechanical glass transition occurs at 298 K) was determined to be 0.667. Mean-square displacement of atoms in the bacteria was investigated by incoherent elastic neutron scattering. The mean-square displacement increased gradually with an increase in temperature depending on the aw of samples. From the linear fitting, two or three dynamical transition temperatures (low, middle, and high Tds) were determined at each aw. The low-Td values (142–158 K) were almost independent from aw. There was a minor effect of aw on the middle Td (214–234 K) except for the anhydrous sample (261 K). The high Td (252–322 K) largely increased with the decrease in aw. From the aw dependence of the high Td, the dynamical awc was determined to be 0.675, which was almost equivalent to the mechanical awc. The high Td was assumed to be the glass-transition temperature (Tg), and anhydrous Tg was estimated to be 409 K. In addition, molecular relaxation time (τ) of the bacteria was calculated as a function of aw. From the result, it is suggested that the progress of metabolism in the bacterial system requires a lower τ than approximately 6 × 10?5 s. 相似文献
14.
C L Eriksson de Rezende E T Mallinson A Gupte S W Joseph 《Journal of industrial microbiology & biotechnology》2001,26(4):222-225
Controlling water activity (a
w) can significantly impact the growth of Salmonella in poultry litter and manure — a phenomenon that was studied quantitatively using two common serotypes of Salmonella. The quantitative effect of changes in levels of a
w on Salmonella populations was determined using inoculated, frosted glass rectangles placed in closed chambers (microcosms). Glass rectangles
with known concentrations of Salmonella enteritidis and S. brandenburg were placed in microcosms maintained at an a
w level of 0.893 for 24 h at room temperature (RT) and then transferred to other microcosms maintained at the same temperature
but with higher a
w levels (0.932 and 0.987). Salmonella populations on the slides were quantified at 4, 18, 24, and 48 h. Slightly elevated levels of a
w (<0.1, i.e., 10% equilibrium relative humidity) for 24 h resulted in a 100-fold increase in counts of Salmonella. The data also suggested that in vitro adaptation to dry environments may occur when the organisms are exposed to alternating levels of relatively high and low
(0.987 and 0.893) levels of a
w. Any increased tolerance of Salmonella to reduced levels of a
w could be the result of physico-chemical changes in the organism due to selective environmental pressure, formation of a protective
biofilm, and/or entry into a dormant state. Results from this study are compatible with those from previously reported on-farm
surveys, reinforcing the contention that maintaining a
w below 0.85 in and around litter/manure surfaces in poultry or livestock bedding areas may be a critical factor in safe production
of food. Journal of Industrial Microbiology & Biotechnology (2001) 26, 222–225.
Received 18 May 2000/ Accepted in revised form 24 January 2001 相似文献
15.
Ken Fukami Kiyoshi Kawai Sayaka Takeuchi Yoshito Harada Yoshio Hagura 《Food biophysics》2016,11(4):410-416
To understand the fundamental physical properties of calcium maltobionate (MBCa), its water sorption isotherm, glass transition temperature (T g), and viscosity (η) were investigated and compared with those of maltobionic acid (MBH) and maltose. Although amorphous maltose crystalized at water activity (a w) higher than 0.43, MBCa and MBH maintained an amorphous state over the whole a w range. In addition, MBCa had a higher T g and greater resistance to water plasticizing than MBH and maltose. These properties of MBCa likely originate from the strong interaction between MBCa and water induced by electrostatic interactions. Moreover, the effects of temperature and water content on η of an aqueous MBCa solution were evaluated, and its behavior was described using a semi-empirical approach based on a combination of T g extrapolated by the Gordon-Taylor equation and a non-Arrhenius formula known as the Vogel–Fulcher–Tammann equation. This result will be useful for understating the effect of MBCa addition on the solution’s properties. 相似文献
16.
Comparison of the effects of temperature and water activity on growth rate of food spoilage moulds 总被引:1,自引:0,他引:1
Sautour M Soares Mansur C Divies C Bensoussan M Dantigny P 《Journal of industrial microbiology & biotechnology》2002,28(6):311-315
The influence of temperature (T) and water activity (a
w) on the growth rate (μ) of seven moulds (Alternaria alternata, Aspergillus flavus, Cladosporium cladosporioides, Mucor racemosus, Penicillium chrysogenum, Rhizopus oryzae and Trichoderma harzianum) was assessed in suboptimal conditions. Firstly, the dependence of fungal growth on temperature, at a
w 0.99, was modelled through an approach described previously for bacteria. A dimensionless growth rate variable: μ
dimα=μ/μ
optα depended on the following normalised temperature: T
dim=(T−T
min)/(T
opt− T
min) according to a power function: μ
dimα=[T
dim]
α
, where α was an exponent to be estimated. Secondly, the same approach was used to describe the influence of a
w on fungal growth, at the respective optimum temperatures for each mould. Similarly, μ
dimβ=μ/μ
optβ depended on the following normalised water activity: a
wdim=(a
w−a
wmin)/(a
wopt−a
wmin) according to a power function: μ
dimβ=[a
wdim]β. Results show: (i) for each mould, the α-value is significantly less than the β-value, confirming that water activity has a greater influence than temperature on fungal development; (ii) the α-values and the β-values depend on the mould; (iii) the α-value is less than 1 for the mesophilic mould A. flavus, whereas the other moulds are characterised by higher α-values ranging from 1.10 to 1.54; (iv) the mesophilic A. flavus exhibits a low β-value, 1.50, compared to the hydrophilic T. harzianum, β=2.44, while β-values are within the range (1.71–2.37) for the other moulds. Journal of Industrial Microbiology & Biotechnology (2002) 28, 311–315 DOI: 10.1038/sj/jim/7000248
Received 27 June 2001/ Accepted in revised form 04 February 2002 相似文献
17.
Factors determining the microflora of stored barley grain 总被引:3,自引:0,他引:3
Colonisation of barley grain has been studied during storage at different water contents and with and without restriction of the air supply to simulate conditions in unsealed silos. Grain stored with a water activity >0·9 aw (20% water content) heated spontaneously when aeration was unrestricted, the maximum temperature attained increasing with aw to 58 °C at 1·0 aw (39% water content). The presence of many unripe grains increased the tendency to heat at a given mean water content. Although heating was prevented by sheeting to restrict the air supply, it could occur subsequently when the sheeting was removed. Both heating and restriction of the air supply were associated with increased carbon dioxide (to >25%) and decreased oxygen concentrations (to <5%). Germination of grain after 6·9 months storage was correlated with aw; germination levels approaching 100% were retained only at about 0·7 aw (13·5% water content). Colonisation by Aspergillus species was correlated with aw and temperature and similar correlations with Penicillium species were also found, with P. verrucosum var. cyclopium abundant at 0·85-0·90 aw (17·20% water content) and P. piceum, P. funiculosum and P. capsulatum at 0·90-0·95 aw (20–25% water content). In sealed containers P. roquefortii occurred at 1·00 aw (39% water content) and P. hordei at 0·90-0·92 aw (20–22% water content). Spores of fungi and actinomycetes formed during spontaneous heating of grain survived 6 months sealed storage although Absidia corymbifera and Micropolyspora faeni may have declined in numbers. Fungicides applied to the ripening grain had only limited effect on the colonisation of the grain during storage. 相似文献
18.
Wisdom Kofi Amoa-Awua Margaret Owusu Patrick Feglo 《World journal of microbiology & biotechnology》2005,21(6-7):1201-1207
Summary Unfermented cassava flour, also called high quality cassava flour (HQCF) is used as a partial substitute for wheat flour in
the baking industry. This work was carried out to produce an indigenous fermented cassava dough, agbelima, from high quality
cassava flour in order to diversify uses for the flour. An isolate of each of the dominant species of lactic acid bacteria
isolated from agbelima, was used to ferment reconstituted HQCF dough into agbelima, whilst pH changes, population on MRS,
and the organoleptic quality were assessed. The antimicrobial properties of the fermenting samples against three enteric pathogens
were also investigated. Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus fermentum and Leuconostoc mesenteroides were isolated at levels of 1010, 109, 109 and 108 c.f.u. g−1 respectively in agbelima. All isolates and a control sample, produced agbelima with pH of between 4.11 and 3.82 in 48 h,
and ANOVA showed no significant difference between the pH of the samples at P ≤ 0.05. Spontaneous fermentation of the reconstituted dough was possible, because the flour was found to contain Lactobacillus plantarum at a level of 106 c.f.u. g−1 as well as the other species isolated from agbelima. Counts of Gram-positive catalase-negative rods and cocci on MRS in all
the fermented samples were at levels of 108 to 109 c.f.u. g−1, with ANOVA showing no significant difference between the populations at P ≤ 0.05. Three enteric pathogens, Salmonella typhimurium 9, Echerichia coli D2188 and Vibrio cholerae C-230, inoculated into the samples at 106 to 107 c.f.u. g−1 at the start of fermentation, could not be detected in 10 g of any of the samples at the end of 48 h fermentation. A taste
panel preferred banku - a stiff porridge made from a combination of fermented maize dough and fermented cassava dough – prepared
with fermented HQCF dough to banku prepared with a market sample of agbelima or reconstituted agbelima flour. Processing the
highly perishable cassava roots into high quality cassava flour, therefore, offers a means for preserving cassava, which can
subsequently be used for both industrial and traditional purposes. 相似文献
19.
Entomopathogenic fungi are widely produced for use as mycoinsecticides. Therefore, improvement of the shelf life of fungal
propagules under good and adverse conditions should be a pre-requisite of their production. In order to improve conidial physiology
as well as mycoinsecticide efficiency, culture conditions may be varied. The Doehlert design was used to generate response
surfaces with an estimation of the parameters of the quadratic model allowing the study of three different factors at a different
number of levels. This experimental design was applied to optimize water activity (a
w), pH, and fermentation time for Beauveria bassiana conidial production and accumulation of polyols in solid-state fermentation. Thus, it was possible to identify the region
in the experimental range in which the optimum values of these parameters were simultaneously achieved. Maximal conidia production
was achieved at pH 5–6 and a
w=0.999. Under these conditions, polyol accumulation was 3 mg erythritol/g conidia and 29.6 mg glycerol/g conidia. However,
maximal polyol accumulation was achieved at pH 4.5 and a
w 0.950; erythritol production increased 33-fold and glycerol production 4.5-fold. Under these conditions conidia production
was 1,000 times lower. The possibilities of increasing the quality of the biocontrol agent without neglecting yield are discussed. 相似文献
20.
Aims: This study was conducted to characterize the growth of and aflatoxin production by Aspergillus flavus on paddy and to develop kinetic models describing the growth rate as a function of water activity (aw) and temperature. Methods and Results: The growth of A. flavus on paddy and aflatoxin production were studied following a full factorial design with seven aw levels within the range of 0·82–0·99 and seven temperatures between 10 and 43°C. The growth of the fungi, expressed as colony diameter (mm), was measured daily, and the aflatoxins were analysed using HPLC with a fluorescence detector. The maximum colony growth rates of both isolates were estimated by fitting the primary model of Baranyi to growth data. Three potentially suitable secondary models, Rosso, polynomial and Davey, were assessed for their ability to describe the radial growth rate as a function of temperature and aw. Both strains failed to grow at the marginal temperatures (10 and 43°C), regardless of the aw studied, and at the aw level of 0·82, regardless of temperature. Despite that the predictions of all studied models showed good agreement with the observed growth rates, Davey model proved to be the best predictor of the experimental data. The cardinal parameters as estimated by Rosso model were comparable to those reported in previous studies. Toxins were detected in the range of 0·86–0·99 aw with optimal aw of 0·98 and optimal temperature in the range of 25–30°C. Conclusions: The influences of aw and temperature on the growth of A. flavus and aflatoxin production were successfully characterized, and the models developed were found to be capable of providing good, related estimates of the growth rates. Significance and Impact of the Study: The results of this study could be effectively implemented in minimizing the risk of aflatoxin contamination of the paddy at postharvest. 相似文献