Interacting Environmental Stress Factors Affect Metabolomics Profiles in Stored Naturally Contaminated Maize

There is interest in understanding the relationship between naturally contaminated commodities and the potential for the production of different useful and toxic secondary metabolites (SMs). This study examined the impact of interacting abiotic stress parameters of water availability and temperature of stored naturally contaminated maize on the SM production profiles. Thus, the effect of steady-state storage water activity (a(w); 0.80–0.95) and temperature (20–35 °C) conditions on SM production patterns in naturally contaminated maize was examined. The samples were analysed using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) to evaluate (a) the total number of known SMs, (b) their concentrations, and (c) changes under two-way interacting environmental stress conditions. A total of 151 metabolites were quantified. These included those produced by species of the Aspergillus, Fusarium and Penicillium genera and other unspecified ones by other fungi or bacteria. There were significant differences in the numbers of SMs produced under different sets of interacting environmental conditions. The highest total number of SMs (80+) were present in maize stored at 20–25 °C and 0.95 a(w). In addition, there was a gradation of SM production with the least number of SMs (20–30) produced under the driest conditions of 0.80 a(w) at 20–30 °C. The only exception was at 35 °C, where different production patterns occurred. There were a total of 38 Aspergillus-related SMs, with most detected at >0.85 a(w), regardless of the temperature in the 50–500 ng/g range. For Fusarium-related SMs, the pattern was different, with approx. 10–12 SMs detected under all a(w) × temperature conditions with >50% produced at 500 ng/g. A total of 40–45 Penicillium-related SMs (50–500 ng/g) were detected in the stored maize but predominantly at 20–25 °C and 0.95 a(w). Fewer numbers of SMs were found under marginal interacting abiotic stress storage conditions in naturally contaminated maize. There were approx. eight other known fungal SM present, predominantly in low concentrations (<50 ng/g), regardless of interacting abiotic conditions. Other unspecified SMs present consisted of <20 in low concentrations. The effect of interacting abiotic stress factors for the production of different suites of SMs to take account of the different ecological niches of fungal genera may be beneficial for identifying biotechnologically useful SMs.