A spectrophotometric bioassay was used to screen selected food ingredients intended for the development of functional foods to influence the growth of good gut bacteria. Dose-response profiles displaying growth, and the magnitude of deviation from the growth of controls, were generated for probiotic lactobacillus reuteri, Lactobacillus rhamnosus, Bifidobacterium lactis and pathogens Escherichia coli, SalmonellaTyphimurium and staphylococcus aureus. Ingredients were manuka honey UMF™ 20+ (dose-dependently increased probiotics and decreased pathogens); bee pollen (biphasic growth effects against all); Rosehips and BroccoSprout (increased all dose-dependently); blackcurrant oil (little effect) and propolis (inhibited all strains). Ingredients were also bioassayed in pairs to assess desirable or undesirable synergistic interactions. Observed synergies included mānuka honey (predominantly desirable); rosehips or BroccoSprouts (desirable and undesirable); blackcurrant oil (desirable) and propolis (tended towards synergies reinforcing its antimicrobial effects), collectively revealing a complex web of interactions which varied by ingredient and bacterial strain. Manuka honey was particularly effective at influencing gut bacteria. The surprising frequency of undesirable synergistic interactions illustrates the importance of pre-testing potential ingredient combinations intended for use in functional food.

Rosendale, D. et al. (2008)