Lactic acid bacteria bioprotection applied to the malting process. Part II: Substrate impact and mycotoxin reduction

Lactic acid bacteria (LAB) with antifungal activity can be applied to the malting process in order to improve the microbial stability and safety of malt. The main objectives of this project was to evaluate the influence of the antifungal activity of LAB cell-free-supernatant (cfs) in the malting process and to investigate antifungal effects of selected LAB towards the mould growth and mycotoxin production of Fusarium culmorum. The impact of substrate concentration on the production of LAB antifungal compounds and the changes in the malt quality attributes was also investigated. Barley grains infected with F. culmorum were used in the malting trials. Lactobacillus amylovorus and Lactobacillus reuteri cfs were generated in a wort based substrate and applied in the early stages of malting. F.culmorum growth was quantified and the mycotoxin deoxynivalenol (DON) was detected in the malted grains. The various supernatants were characterized based on their sugar and organic acid composition. Antifungal metabolites were quantified using a QuEChERS and HPLC-UV/PDA method. Standard EBC methods were used to evaluate the malt quality attributes. Results show that L.reuteri R29 cfs produced in 3°P substrate successfully inhibited Fusarium growth by 23% and mycotoxin DON by 83%. Using a 3°P wort substrate concentration, 68% of the phenyllactic acid (PLA) was produced, when compared to the 12°P substrate. PLA plays an essential role in the supernatant antifungal activity. Malt quality attributes resulted in highly modified grains, lower pH, higher colouration, and higher extract yield.