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.

The developed models can be used to estimate to what extent the change in grain ecosystem conditions affect the storage stability and safety of grains without the need for running long-standing storage study. By monitoring the intergranular relative humidity and temperature at different locations in the storage facility and inputting these data into the models, it is directly possible to assess either the conditions are conductive for the growth of A. flavus or aflatoxin production.

Understanding the water sorption characteristics of cereal is extremely essential for optimizing the drying process and ensuring storage stability. Water relation of rough rice was studied at 20, 30, 40 and 50°C over relative humidity (RH.) between 0.113 and 0.976 using the gravimetric technique. The isotherms displayed the general sigmoid, Type II pattern and exhibited the phenomenon of hysteresis where it was more pronounced at lower temperatures. The sorption characteristics were temperature dependence where the sorption capacity of the paddy increased as the temperature was decreased at fixed (RH). Among the models assessed for their ability to fit the sorption data, Oswin equation was the best followed by the third order polynomial, GAB, Smith, Chung-Pfost, and Henderson models. The monolayer moisture content was higher for desorption than adsorption and tend to decrease with the increase in temperature. Given the temperature dependence of the sorption isotherms the isosteric heats of sorption were calculated using Claussius-Clapeyron equation. The net isosteric heats decreased as the moisture content was increased and heats of desorption were greater than that of adsorption.

The main aim of this study was to evaluate the combined effects of temperature with water activity (aw) and CO2 with aw on the growth and aflatoxin production by Aspergillus flavus Link on paddy. The effects of temperature (20-30 °C) and aw (0.92-0.98) on the relationship between colony diameter and aflatoxin production, and the influence of aw (0.92-0.98) and CO2 (20-80%) on the growth and toxin production were studied using full factorial design. Colony diameters were regularly measured and aflatoxins were periodically analyzed using HPLC with fluorescence detector. The growth and aflatoxin formation increased with aw at the temperatures studied, and toxin production was positively correlated with the incubation time and colony diameter. Except at 0.92 aw, as much as 80% CO2 failed to inhibit the growth of fungi completely. However, at all aw levels studied the growth parameters as estimated by Baranyi function and aflatoxin were affected by the increment in CO2 where growth rates and aflatoxin were negatively correlated with CO2 while the lag phase durations were positively correlated with CO2. Under 0.98 aw, the atmosphere enriched with 20% and 80% CO2 lead to at least 59% and 88% reduction in growth and 47% and 97% in the toxin production, respectively. At 0.95 aw, the lag phases of both isolates in average increased by a factor of 1.7-12 when the CO2 levels in the headspace were between 20 and 80% compared to the control. The growth rate and lag phase durations under the modified atmospheres were successfully described using a polynomial equation (R2 > 0.97). The results of the study could form a basis of indicative guidelines on the possible control of A. flavus and aflatoxin in paddy during temporary storage prior to drying.

The effect of food additives reduction on quality attributes in steamed‐and‐fried instant noodles was investigated. Three additives, l‐ascorbic acid, l‐cysteine, and sodium bisulfite, were evaluated for their effect on deoxynivalenol (DON) reduction and sensory acceptability of instant noodles. After screening the different concentrations of three food additives, the maximum reduction of DON was optimized for the following concentration ranges: l‐ascorbic acid, 0–100 μg/g; l‐cysteine, 0–300 μg/g; and sodium bisulfite, 0–200 μg/g. The experimental results were fitted to a second‐order polynomial model, which gave a coefficient of determination (R2) of 0.987. The results indicated that the overall optimal condition resulting in the maximum DON reduction in instant noodles was obtained at the following combined level: sodium bisulfite, 167 μg/g; l‐cysteine, 254 μg/g; and l‐ascorbic acid, 23 μg/g. The sensory evaluation of noodles with the optimal condition of additives showed that the overall acceptability was in the range of “like slightly” and was not significantly (P > 0.05) different from the control sample. The optimized protocol produced a mixture that can reduce DON in instant noodles up to 67%. Modifying the processing of instant noodles by using additives may be useful to reduce the risk of DON exposure via instant noodles.