## 3 Results  
### Co-culture of Lactobacillus Rhammosus Strains and Saccharomyces Cerevisiae  
(i)Effect of co-cultivation on bacterial growth  
The growth curves of three _L. rhamnus_ strains showed the same pattern in monoculture as in co-culture with _S. cerevisiae_ (Figure 1A,D,G). Viable cell counts (CFU/mL) revealed a stationary growth phase after 9 h for _L. rhamnus_ strains ATCC 9595 (Figure 1D) and RW-9595M (Figure 1G), and 12 h for _L. rhamnus_ R0011 (Figure 1A). The quantification in genome copy numbers of _L. rhamnus_ ATCC 9595 obtained by PMA-qPCR were lower than those obtained by qPCR, indicating the presence of dead cells, especially in co-culture, with 95 % viability. Nevertheless, as for the other strains, plate counts did not decrease during fermentation (Figure 1E,F). These results indicate that viability of targeted strains persisted in mono- and co-culture, despite the media culture acidity until 48 h (pH \(<\) 3.5). 2. Effect of co-culture on sugar consumption and metabolite production Differences in sugar consumption and metabolite production were found between the monoculture and co-culture fermentations (Figure 2A-F). In monoculture fermentation, lactose consumption by _L. rhamnosus_ ATCC 9595 was significantly higher (p \(<\) 0.05) in relation to co-culture. However, the amount of lactic acid detected was the same in both types of culture (Figure 2A-C). Comparison of the conversion rates of lactose to lactic acid by _L. rhamnosus_ RW-959 SM and R0011 in mono and co-culture showed no significant differences (p \(<\) 0.05). _L. rhamnosus_ R0011 produced 1.8 g/L less lactic acid than the other strains at the end of the process due to a lower lactose consumption. Throughout fermentation, pH values for co-culture with _L. rhamnosus_ R0011 were 5% and 2.7% higher than the pH values of RW-959 SM and ATCC 9595, respectively (Supplemental Figure S1). After 24 h of fermentation, the presence of acetic acid was observed in media. Acetic acid concentrations in culture broth were significantly (p \(<\) 0.05) superior in monoculture (Supplemental Figure S2) compared to co-culture for _L. rhamnosus_ ATCC 9595 (54%) and RW-959 SM (38%). _L. rhamnosus_ R0011 did not show any difference between culture types for acetic acid concentration. Additionally, the content of phenolic acids from corn steep liquor such as ferulic acid, 4-hydroxybenzoic acid, caffe acid, and p-coumaric acid, were determined [38]. After 48 h of fermentation, the profile of phenolic acids was modified by the _L. rhamnosus_ strains. Ferulic acid decreased while caffe acid increased and protocatechuic acid appeared in culture broth (Supplemental Table S4). The phenolic acid profile for yeast monoculture did not show any difference compared to non-fermented medium; therefore, this activity was linked to LAB (data not shown). Figure 1: Growth of _L. rhamnosus_ strains in mono (��❝  
3. Effect of co-culture on exopolysaccharideaccharide (EPS) production  
Exopolysaccharideaccharide production was modified between monoculture and co-culture for all tested strains (Figure 2D-F). The _L. rhamnus_ R0011 strain had a 12-hour delay to maximal EPS concentration in co-culture compared to monoculture. After 48 hours, EPS concentration was higher in co-culture (99 mg/L; 39%) for strain R0011, but along the entire process, total EPS production was similar to that obtained in monoculture. In contrast, for _L. rhamnus_ ATCC 9595 and RW-9595M, EPS production in co-culture was significantly different (p \(<\) 0.05) from monoculture after the 48-hour fermentation period, with an increase of 49% (224 mg/L) and 42% (568 mg/L), respectively. Strain RW-9595M showed a production of EPS 81% (1095 mg/L) and 66% (888 mg/L) higher than strains R0011 and ATCC 9595, respectively. Co-culture appears to have a positive effect on EPS production, even under acid stress. Principal Component Analysis (PCA) was carried out on the combined data for all three _L. rhamnus_ strains in mono and co-culture.