br Declarations Funding None for the paper

Declarations Funding: None for the paper in question. Competing interests: Florent Morio has received speaker's fees from Gilead, Basilea, and MSD and travel grants from Gilead, MSD, Pfizer, Basilea, and Astellas. Ethical approval: Not relevant for the paper in question.
Introduction Lactic Furosemide bacteria (LAB) are key microorganisms used for the production of various bakery products. They substantially improve nutritional and technological properties, as well as the flavour. However, current research is predominantly focused on their antimicrobial properties and potential applications as food bio-preservatives (Dalié, Deschamps, & Richard-Forget, 2010). The use of such LAB has the potential to replace chemical preservatives, such as calcium propionate, which would allow a “clean label” and hence lead to higher consumer acceptance (Pawlowska, Zannini, Coffey, & Arendt, 2012). In recent years, several strains of different genera have been found to express antimicrobial activity in vitro and in situ against food spoilage fungi (Axel et al., 2016, Crowley et al., 2013). The antifungal activity of LAB is predominantly based on complex synergistic effects between several compounds. The production of these compounds is highly dependent on the strain and growth substrate. The exact interactions between the bacterial metabolites which create this synergistic effect are not yet fully understood. However, several metabolites that contribute to the antifungal activity have been identified and characterised. These metabolites, amongst others, include carboxylic acids (Ryan, Dal Bello, & Arendt, 2008) and 3-hydroxypropionaldehyde (3-HPA) also known as reuterin (Lüthi-Peng, Dileme, & Puhan, 2002). Recently, the production and activity of 3-phenyllactic acid (PLA) has received great attention (Mu, Yu, Zhu, Zhang, & Jiang, 2012). This broad-spectrum antimicrobial compound originates in LAB fermented products from the catabolism of phenylalanine (Phe). Thereby, the Phe first undergoes a transamination by transferring the amino group onto a keto-acid acceptor. The synthesised phenylpyruvic acid is then reduced to PLA by a dehydrogenase (Vermeulen, Gánzle, & Vogel, 2006). The antifungal activity of PLA is also dependent on a synergistic mechanism with other bacterial metabolites. Nevertheless, if the metabolic pathway yielding PLA is promoted, the antifungal activity is likely to increase. This could expand the field of application for LAB as bio-preservatives. A very promising antimicrobial agent is the multicomponent system called reuterin, which results from the conversion of glycerol to 3-HPA (Engels et al., 2016, pp. 1–13). The antimicrobial activity of reuterin is, according to Schaefer et al. (2010), mainly based on its reactivity with free thiol groups of proteins, inducing oxidative stress in the target cells. It is understood that 3-HPA is released upon enzymatic dehydration of glycerol. Recent research conducted by Engels et al. (2016, pp. 1–13) suggests a rapid in situ conversion to acrolein, which is mainly responsible for the antimicrobial activity of the reuterin system. However, if sufficient amounts of carbohydrates, in particular glucose, are available, 3-HPA is further reduced to 1,3-propanediol which has no antimicrobial activity (Gänzle, 2015). Unfortunately, the research on reuterin so far has mainly focused on its industrial use as precursor for the synthesis of acrolein, not on food applications. To date, there are only two studies conducted by Gomez-Torres, Vila, Gaya, and Garde (2014) and Ortiz-Rivera et al. (2017) available, investigating a possible application of reuterin as an antibacterial agent in a food system. As Gänzle (2015) observed, the applicability of reuterin, particularly in heat treated food systems, remains unclear. Further research is required, in particular to elucidate the effect of glycerol on bacterial growth and reuterin production.