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Modelling The Effect Of Temperature And Water Activity In The Growth Boundaries Of Aspergillus Flavus Isolates From Corn Andrea L. ASTORECA*1, Graciela VAAMONDE1, Ana M. DALCERO2, Antonio J. RAMOS3, Sonia S. MARIN3. 1 Food Microbiology Laboratory, Department of Organic Chemistry, Faculty of Natural Sciences, Buenos Aires University, Campus, Buenos Aires, Argentine. 2 Micology Laboratory, Department of Microbiology and Inmunology, Faculty of Sciences, Physical Chemical and Natural, Río Cuarto National University, Argentine. 3 Food Technology Department, Lleida University, UTPV-CeRTA, Rovira Roure 191, Lleida, Spain. The aim of this study was to develop a modelling approach to quantify the effect of temperature (10-40ºC), water activity (0.80-0.98), isolate (BAF4273, 4274, 4275) and media (Czapek yeast agar: CYA, corn extract medium: CEM) on the growth rates and growth boundaries (growth-no growth interface) of three A. flavus isolated from corn in Argentina. For each treatment, Petri plates were centrally needle-inoculated, sealed in polyethylene bags separately by aW and incubated for a 28 days. Two perpendicular diameters of the growing colonies were daily measured and plotted against time. Non linear regression was applied to estimate the maximum growth rate (μmax, mm/day), lag phase prior to growth (λ, days) and maximum colony diameter according to the primary model of Barany & Roberts (1994). The average estimates were further fitted to the secondary model proposed by Rosso & Robinson (2001) to describe the effect of temperature and aW on fungal growth rate. No growth was observed at 10ºC at any of the assayed temperature and media over the 28-day-incubation period. At the maximum studied temperature (40ºC) any of the isolates grew on CEM regardless the aW while at 15ºC only the BAF4273 isolate were not able to growth in this media. In the temperatures and aW range studied, the optimal conditions of growth for the assayed A. flavus isolates on both tested medium were 0.98 aW and 35ºC with mean growth rates of 18.6 and 16.9 mm/day on CYA and CEM, respectively. However, a statically differences between the growth rates reached for the isolates in both medium was observed, being that higher in CYA than in CEM medium. Regarding the performance of the developed models, predictions for fungal growth rate on CYA were more accurate compared to those on CEM media. The observations of fungal growth rate at optimal conditions showed rather good agreement compared to marginal ones, for which the slight deviations of model prediction from data were evident. While estimation of optimum aW for growth was consistent around 0.97 for all the isolates at all the assayed conditions, the optimum estimated temperature varied from 31 to 33 depending on the isolate and media used for the modelling and estimation. Maximum growth rate and lag phase for the growth of three A. flavus isolates were estimated through Baranyi?s primary model. No growth was observed under extreme temperature conditions and at 15ºC <0.90 aW on CYA media. It is graphically depicted that the probability plot shifted to lower water activities for the same temperature level as time advances, for all the assayed fungal isolates. The probability of growth was lower at the lowest water activities assayed. Finally, the probability of growth is always under 50% when water availability is under 0.81 aW on CYA, and almost null for all assayed isolates on CEM after 14 days of incubation. Probabilities of growth for the assayed isolates over 90% were predicted in the range 0.87-0.93 aW at 14-37ºC in a week-period. Thus for safe storage of crops such as corn, and aW <0.85 should be maintained and temperatures in the range 15-38ºC should be avoided; alternatively, cool storage (<10ºC) could be applied.