Behaviour of Aspergillus parasiticus in aflatoxin production as influenced by storage parameters using response surface methodology approach

Abstract

Aspergillus parasiticus is a pre-harvest and postharvest pathogen that is known to produce aflatoxin; however, it is less studied compared to A. flavus. Inappropriate storage conditions are a cause of food spoilage and growth of mycotoxigenic fungi especially in low moisture foods thus constituting hazards to health. Hence, this study investigated the behaviour of A. parasiticus on aflatoxin production in inoculated wheat flour as influenced by storage conditions using the response surface methodology. Twenty experimental runs consisting of independent variables (incubation temperature (A), time (B) and (C) moisture content) and responses (aflatoxin concentrations, i.e., AFB1, AFB2, AFG1, AFG2 and AFTOT) were developed. A central composite face-centered design was used with lower and upper limits: A (25–35 °C), B (7–15 days) and C (15–25%), while the non-inoculated wheat flour served as the negative control. Aflatoxin production was determined using High Performance Liquid Chromatography (HPLC) according to standard procedures. Numerical and graphical process variables were optimized, adequate models were predicted and optimal point prediction for aflatoxin concentration was determined. AFG1 concentrations ranged from 1.10 to 360.06 μg/g, AFG2 (0.91–446.94 μg/g), AFB2 (7.95–488.77 μg/g), AFB1 (17.21–20,666.6 μg/g) and AFTOT (15.91–21,851.09 μg/g). Aflatoxin concentration increased with increase in ‘B’ and ‘A’ but decreased with prolonged increase in ‘B’. AFB1 concentrations in A. parasiticus inoculated wheat flour increased at prolonged ‘B’ and ‘A’ at constant moisture (12.09%). A reduced cubic model was significantly adequate to describe the relationship between process variables and responses (AFG1 and AFG2), cubic model (AFB1 and AFTOT) and a transformed square root cubic model for AFG2 concentrations (p ≤ 0.05). ‘A’ influenced AFG1 production more than ‘C’ while ‘C’ and ‘A’ had no significant effect on AFG2 production. Process variables ‘AB’ influenced AFB2 concentrations more than ‘C’ while ‘A’ had a more significant effect on the AFTOT production than ‘B’ (p ≤ 0.05). The predicted (R2) and adjusted coefficient of regression (adj R2) were in reasonable agreement. After optimal point prediction and validation, minimum aflatoxin concentration ≤ 0 μg/g could be achieved at the predicted conditions (A = 30.42 °C, B = 10.58 days and C = 14.49%) except in AFG2 (3.33 μg/g).