Decoupling Bifidogenic Growth from Antagonistic Activity: Species- and Time-Dependent Responses to Botanical Polyphenols

INTRODUCTION

Growth promotion of beneficial bacteria is an important criterion when screening candidates for microbiota-oriented functional foods, but enhanced proliferation does not necessarily indicate preservation of other microbial functions. This study investigated how polyphenol-rich botanical preparations influence both the growth of Bifidobacterium longum and B. animalis and the antagonistic activity of their post-culture supernatants against Escherichia coli.

METHODS

Polyphenol-rich preparations from Elaeagnus multiflora ‘Sweet Scarlet’, Vitis vinifera ‘Solaris’, and Amelanchier alnifolia ‘Smoky’ were evaluated individually and as binary or ternary blends. Polyphenolic profiles were characterized by UPLC-PDA-MS/MS. Bifidobacteria were cultured anaerobically for 72 h, and abundance was determined after 24, 48, and 72 h using optical-density measurements and strain-specific calibration curves. Post-culture supernatants were assessed for antagonistic activity against E. coli using inhibition-zone measurements.

RESULTS

The two species displayed clearly different growth kinetics. In B. longum, the strongest responses developed mainly during prolonged incubation. A multicomponent formulation reached 10.46 log units after 72 h compared with 9.08 in the control, corresponding to an approximately 24-fold increase. An individual botanical preparation acted earlier, reaching 10.27 versus 9.06 log units after 48 h. B. animalis responded more strongly at 48 h: individual preparations reached 9.00–9.04 log units versus 7.93 in the control, while one binary blend reached 9.25 log units, corresponding to an approximately 21-fold increase. At 72 h, another binary formulation produced the highest abundance, 9.58 versus 8.91 log units in the control.

Growth stimulation was not consistently accompanied by stronger antagonistic activity. For B. longum, the control supernatant produced a 14-mm inhibition zone against E. coli after 72 h, whereas one binary polyphenol combination increased this activity to 16 mm; several other formulations produced lower values. For B. animalis, the control reached 16 mm after 72 h, while the strongest polyphenol-containing culture reached 15 mm. Thus, formulations that promoted bifidobacterial growth did not necessarily maximize antagonistic activity.

CONCLUSIONS

These findings show that botanical polyphenols produce species-, formulation-, and time-dependent bifidogenic effects and that microbial growth and post-culture antagonistic function can be partially decoupled. Screening both endpoints may therefore improve selection of polyphenol–Bifidobacterium combinations for future synbiotic-oriented functional foods.

Funding: National Science Centre, Poland, grant No. 2020/39/D/NZ9/01810.