Effect of moisture on wheat grains lipid patterns and infection with Fusarium graminearum.

Suitable conditions of temperature and humidity are required to maintain wheat grains quality, but during processing and storage, the grains can be exposed to adverse environmental conditions and presence of infectious fungi. Fusarium graminearum, the main causal agent of Fusarium head blight on wheat, affects crop yields and grain quality by alteration of their biochemical components and mycotoxin contamination, which reduces the possibilities of wheat end use and compromises food safety. Lipid degradation by hydrolytic, oxidative and microbial deterioration is the predominant cause of the loss of sensory acceptability, nutritional value and baking quality. The aim of this research was to determine the influence of adverse environmental conditions -as the increasing moisture - on lipid patterns of whole wheat flours contaminated with F. graminearum in relation to the infection degree. In vitro cultures of F. graminearum were carried out on wheat grains under different degrees of relative humidity (11, 50, 75 and 100%) throughout 45 days of incubation at 28 °C. The fungal biomass measured by q-PCR increased proportionally with the humidity. A decrease in the signals of saturated (palmitic and estearic) and unsaturated (oleic, linoleic and linolenic) fatty acids, analyzed as fatty acid methyl esters (FAMEs) by GC-MS, was observed in relation with the humidity and infection degree. The degradation rate of the lipids was high during the first 15 days of incubation, reaching the fatty acids content, values around 20-40% of those found in the control. From that moment on, the rate of degradation was slower or even null. It was observed that in all treatments, the linolenic acid reached the highest degradation ratio in comparison with the other fatty acids, which may be caused by the action of lipoxygenases. The lipase activity and the content of deoxynivalenol were also determinate on the flours. The lipase activity increased until day 25 of incubation reaching twice the initial value. The deoxynivalenol content also increased along incubation while fatty acids decreased. Our results demonstrated that the magnitude in the signal of fatty acids in whole wheat flours varied in relation to the degree of humidity and fungal infection of the grains from which they were obtained. Otherwise, lipids and their oxidation products are related with the pathogenesis and production of mycotoxins. These observations highlight the importance of an adequate manipulation of wheat grains on the processing chain to prevent quality changes and mycotoxins contamination.