Modeling the Effect of Glucose Syrup on the Moisture Sorption Isotherm of Figs

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.     

Dilatometric Measurement of the Partial Molar Volume of Water Sorbed to Durum Wheat Flour

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.     

Influence of water activity and temperature on in vitro growth of surface cultures of a Phoma sp. and production of the pharmaceutical metabolites, squalestatins S1 and S2

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     

The Influence of Water Activity and Temperature on Germination,Growth and Sporulation of <Emphasis Type="Italic">Stachybotrys chartarum</Emphasis> Strains

The objectives were to determine the influence of water activity (a_w, 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 a_w and temperature and was fastest at 0.997–0.98 a_w between 15 and 30°C with complete germination within 24 h. Germ tube extension was found to be most rapid at similar a_w levels and 25–30°C. Mycelial growth rates of both strains were optimal at 0.997 a_w between 25 and 30°C, with very little growth at 37°C. Sporulation was optimum at 30°C at 0.997 a_w. However, under drier conditions, this was optimum at 25°C. This shows that there are differences in the ranges of a_w 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.     

Effect of the sugar-beet pulp water activity on the solid-state culture of Trichoderma viride TS

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.     

Impact of some environmental factors on growth and production of ochratoxin A of/by <Emphasis Type="Italic">Aspergillus tubingensis,A. niger</Emphasis>, and <Emphasis Type="Italic">A. carbonarius</Emphasis> isolated from moroccan grapes

The effects of temperature, water activity (a_w), 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 a_w. 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 a_w 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 a_w. However, for A. carbonarius, mean maximum amounts of OTA (0.22 μg/g) were observed at 25°C and 0.99 a_w. Analysis of variance showed that the effects of all single factors (a_w, isolate, temperature and incubation time) and their interactions on growth and OTA production were highly significant.     

Environment factors influence in vitro interspecific interactions between A. ochraceus and other maize spoilage fungi,growth and ochratoxin production

The effect of water availability (water activity,a_w; 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 a_w or temperature. However, with freely available water (0.995 a_w) 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 a_w) 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.     

Simultaneous Monitoring of Phosphine and of Phosphorus Species in Taihu Lake Sediments and Phosphine Emission from Lake Sediments

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 (TP_s) 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 TP_s 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 (TP_w) 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 TP_w content was high. Similarly, high Chl-a was consistent with higher water PH₃. Positive relationships between PH₃ and TP_w (average R² = 0.47±0.26) and Chl-a (average R² = 0.23±0.31) were observed in Taihu Lake water.     

Production of the fungal biocontrol agent Epicoccum nigrum by solid substrate fermentation: effect of water activity on accumulation of compatible solutes

Epicoccum nigrum conidia were produced by solid fermentation on wheat grains (cv. Rendeveaux and Brigadier) at different water activities (a_w). Conidial production was highest at high a_w(0.996) than at reduced a_w (0.98). However, conidial production at reduced a_w was improved when the a_w of the substrate was adjusted with a mixture of glycerol and water. Maximum levels ofconidiation were 7–11 × 10⁶ conidia g⁻¹ grain. The a_w 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 a_w. At reduced a_w 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 a_w, 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 a_w. 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.     

Stepped water activity control for efficient enzymatic interesterification

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     

Survival of alginate-entrapped cells of Azospirillum lipoferum during dehydration and storage in relation to water properties

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 (a_w). 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 a_w 0.18). A water content of 0.25 g/g DW (a_w=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 a_w (0.23), the number of living cells decreased during a short period (less than 15 days) corresponding to the product a_w stabilization, and then remained constant for more than 150 days. In addition, cell survival during storage was not affected by a_w values in the range 0–0.55. Above a_w=0.55, the higher the a_w 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     

Effect of the desiccation tolerance and cryopreservation methods on the viability of Citrus limon L. Burm cv. Eureka seeds

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<a_w<0.85) showing a high viability (>80%), however desiccation to 0.0526 g H₂O g⁻¹ d.b. (a_w = 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 a_w = 0.64). Two cooling/warming rates were tested on desiccated seeds (0.11<a_w<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 a_w = 0.64. Lethal ice formation was responsible for the loss of viability at a_w>0.64 corresponding to the unfrozen water fraction. The use of higher cooling/warming rates enables a wider range of desiccation conditions (0.33<a_w<0.76) in cryopreservation procedures. This work contributes to the optimization of cryopreservation methods of economically important germplasm.     

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria

The purpose of this study was to clarify the glass-transition behavior of bacteria (Cronobacter sakazakii) as a function of water activity (a_w). From the water sorption isotherm (298 K) for C. sakazakii, monolayer water content and monolayer a_w were determined to be 0.0724 g/g-dry matter and 0.252, respectively. Mechanical relaxation was investigated at 298 K. In a higher a_w range of over 0.529, the degree of mechanical relaxation increased with an increase in a_w. From the effect of a_w on the degree of mechanical relaxation, the mechanical a_wc (a_w 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 a_w of samples. From the linear fitting, two or three dynamical transition temperatures (low, middle, and high T_ds) were determined at each a_w. The low-T_d values (142–158 K) were almost independent from a_w. There was a minor effect of a_w on the middle T_d (214–234 K) except for the anhydrous sample (261 K). The high T_d (252–322 K) largely increased with the decrease in a_w. From the a_w dependence of the high T_d, the dynamical a_wc was determined to be 0.675, which was almost equivalent to the mechanical a_wc. The high T_d was assumed to be the glass-transition temperature (T_g), and anhydrous T_g was estimated to be 409 K. In addition, molecular relaxation time (τ) of the bacteria was calculated as a function of a_w. 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.     

Salmonella spp. are affected by different levels of water activity in closed microcosms

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     

Effect of Water Content on the Glass Transition Temperature of Calcium Maltobionate and its Application to the Characterization of Non-Arrhenius Viscosity Behavior

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.     

Comparison of the effects of temperature and water activity on growth rate of food spoilage moulds

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     

Factors determining the microflora of stored barley grain

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 a_w (20% water content) heated spontaneously when aeration was unrestricted, the maximum temperature attained increasing with a_w to 58 °C at 1·0 a_w (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 a_w; germination levels approaching 100% were retained only at about 0·7 a_w (13·5% water content). Colonisation by Aspergillus species was correlated with a_w and temperature and similar correlations with Penicillium species were also found, with P. verrucosum var. cyclopium abundant at 0·85-0·90 a_w (17·20% water content) and P. piceum, P. funiculosum and P. capsulatum at 0·90-0·95 a_w (20–25% water content). In sealed containers P. roquefortii occurred at 1·00 a_w (39% water content) and P. hordei at 0·90-0·92 a_w (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.     

Utilization of Unfermented Cassava Flour for the Production of an Indigenous African Fermented Food, Agbelima

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.     

Optimization of erythritol and glycerol accumulation in conidia of Beauveria bassiana by solid-state fermentation, using response surface methodology

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.     

Modelling the effect of water activity and temperature on growth rate and aflatoxin production by two isolates of Aspergillus flavus on paddy

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 (a_w) and temperature. Methods and Results: The growth of A. flavus on paddy and aflatoxin production were studied following a full factorial design with seven a_w 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 a_w. Both strains failed to grow at the marginal temperatures (10 and 43°C), regardless of the a_w studied, and at the a_w 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 a_w with optimal a_w of 0·98 and optimal temperature in the range of 25–30°C. Conclusions: The influences of a_w 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.