Predictive modelling of the radial growth of Aspergillus flavus and Fusarium proliferatum on paddy and white rice (Oryza sativa)

The growth of Aspergillus flavus 01 (AF01) and Fusarium proliferatum 01 (FP01) was studied on paddy and white rice, using a full factorial design with five temperature levels (20, 25, 30, 35 and 40 C) and five points of water activity (0.80, 0.85, 0.90, 0.95 and 0.99 aw). The maximum radial growth rates (mu max, mm.day? 1) and lag times (lambda, days) of both fungal strains were estimated by linear regression. When the obtained values were compared with the prediction of reported predictive models for growth of A. flavus 01 and F. proliferatum 01, none of the reported models was able to describe the growth as determined by water activity and temperature adequately. Therefore, new secondary models were developed to describe the obtained fungal radial growth rate of both strains on paddy and white rice as a function of temperature and water activity. The results showed that optimum radial growth rate of AF01 and FP01 were estimated at 0.99 aw/35 C and 0.99 aw/30 C, respectively. Both strains failed to grow at 0.80, 0.85 and 0.90 aw at all observed temperatures (except for AF01 at 0.90aw/35 C). Multi-factorial cardinal and General Polynomial models were the best models to describe combined influence of water activity and temperature on fungal growth rate on both matrices with the bias factors of 0.771-1.10 and accuracy factors of 1.102-1.297. These values should be concerned during storage to mitigate fungal growth on paddy and white rice.