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RESEARCH PRODUCT

Screening of Lactococcus lactis starters with Absorbance Reduction Activity Method (ARAm)

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Lactococcus lactis is one of the most used species in the dairy industry. This species has the ability to reduce to very negative values the redox potential (Eh) of food matrices, making it one of the most reducing Lactic Acid Bacteria (LAB) [1]. This reducing activity influences oxidation-reduction reactions involved in the organoleptic quality of the product and prevents the undesired microorganisms development [2–4]. The main mechanism involved are exofacial thiol groups, NoxE NADH Oxidase and the Electron Transport Chain mechanism [5-7]. For Eh measurement, the commonly used method consists of a redox probe placed in a liquid medium or food matrix [8]. With this probe, Cachon et al. (2002) proposed an innovative procedure allowing to compare reducing activity of LAB, according to their maximum reduction rate, based on their reduction kinetic vs. time. Despite its accuracy, this method can be complex, time-consuming and expensive for the screening of many strains. Michelon et al. (2013), proposed an agar milk screening using colored oxidation-reduction indicators to quickly categorize, with a reducing power score, a large number of LAB strains. This method was used successfully for screening a large bank of LAB and mutants’ strains. However, while this screening method showed significant inter-species differences, it was difficult to identify intra-species ones [9].In order to differentiate several strains belonging to the same species, we developed a new method combining Cachon et al. (2002) and Michelon et al. (2013) procedures with high throughput screening. This routinely method allows to compare until 30 L. lactis strains simultaneously and can be applied on frozen and freeze-dried mixed starters.1. Brasca et al. 2007. J Appl Microbiol 103,1516–24 2. Caldeo et al. 2016. J Dairy Res 83,479–86 3. Nouaille et al.2014. Appl Environ Microbiol 80,7028–35 4. Abraham et al. 2007. Int Dairy J 17,954–60 5. Michelon et al. 2010. FEBS J 277,2282–906. Tachon et al. 2010. Appl Environ Microbiol 76,1311–9 7. Roussel et al. 2022. Food Res Int 156,1111-548. Cachon et al., 2002. Lait 82,281–8 9. Michelon et al. 2013. J Biosci Bioeng 115,229–32