Abstract
Changes in environmental stress impact on secondary metabolite (SM) production profiles. Few studies have examined targeted SM production patterns in relation to interacting environmental conditions in stored cereals. The objectives were to examine the effect of water activity (aw; 0.95–0.90) x temperature (10–25 °C) on SM production on naturally contaminated stored wheat and that inoculated with Fusarium graminearum. Samples were analysed using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) on (a) total number of known SMs, (b) their concentrations and (c) changes under environmental stress. 24 Fusarium metabolites were quantified. Interestingly, statistical differences (ChisSq., p < 0.001) were observed in the number of SMs produced under different sets of interacting environmental conditions. The dominant metabolites in natural stored grain were deoxynivalenol (DON) and nivalenol (NIV) followed by a range of enniatins (A, A1, B, B1), apicidin and DON-3-glucoside at 10 °C. Increasing temperature promoted the biosynthesis of other SMs such as aurofusarin, moniliformin, zearalenone (ZEN) and their derivatives. Natural wheat + F. graminearum inoculation resulted in a significant increase in the number of metabolites produced (ChisSq., p < 0.001). For ZEN and its derivatives, more was produced under cooler storage conditions. Fusarin C was enhanced in contrast to that for the enniatin group. The relative ratios of certain groups of targeted SM changed with environmental stress. Both temperature and aw affected the amounts of metabolites present, especially of DON and ZEN. This study suggests that the dominant SMs produced in stored temperate cereals are the mycotoxins for which legislation exists. However, there are changes in the ratios of key metabolites which could influence the relative contamination with individual compounds. Thus, in the future, under more extreme environmental stresses, different dominant SMs may be formed which could make present legislation out of step with the future contamination which might occur.
Highlights
In cereal commodities, it is important to ensure that drying and storage is effective to ensure that spoilage moulds and mycotoxin contamination can be prevented or minimised [1]
The objectives of this study were to examine the effect of storage of natural wheat grain and that inoculated with F. graminearum stored at 0.90, 0.93, 0.95 aw and 10–25 ◦ C on (a) the range of mycotoxins and related secondary metabolite (SM) which may be produced, (b) their ranges and ratios of production
This study has focused on the effect of different steady state interacting storage environmental factors which may be conducive to Fusarium and other fungal colonization and the production of a range of targeted SMs produced either by the naturally contaminating mycobiota, or that inoculated with a F. graminearum strain
Summary
It is important to ensure that drying and storage is effective to ensure that spoilage moulds and mycotoxin contamination can be prevented or minimised [1]. Interacting environmental stresses of aw x temperature has been shown to change the relative amounts of related DON metabolites (DON, 3- and 15-acetyl DON and Nivalenol (NIV) [2]. The development of both molecular and analytical techniques has resulted in significant interest in the microbiomes of different food commodities and the production of different SMs which may impact on food quality/safety. Recently Zhang et al [3] examined both the fungal and bacterial microbiomes and the SM profile and changes in Pu-erh tea during fermentation. Some studies have examined SM profiles and compounds in single maize kernels and stored grain [4,5]
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