The effect of rice fibre fractions on the growth of co-cultures of probiotics.

The fermentation of rice dietary fibre was measured by the cell yield, pH, optical density specific growth rate and biomass using nine co-cultures of four probiotics at 0, 6, 24 and 48 h incubation. The results from the fermentation of the soluble, insoluble and total dietary fibre (SDF, IDF, and TDF) of two rice varieties were compared. Overall there was no significant difference (p < 0.05) in the fermentation of the six different rice fibre fractions. However, co-cultures showed a preference for glucose as a fermentation substrate rather than the fibre fractions. Bifidobacteria species produced a higher cell count than the Lactobacillus species after 24 and 48 h of fermentation (p < 0.05). There was evidence of synergistic activity with increased growth observed when lactobacilli and Bifidobacterium were grown together. Growth was limited by the pH reaching 4.2-4.45. Specific growth rates of the co-cultures varied for different culture combinations. Combinations of the same species produced less biomass than combinations of mixed species. Bifidobacterium breve + Bifidobacterium longum + Lactobacillus rhamnosus was the most efficient. These findings showed that synergism between microorganisms in co-cultures affected the degree of fermentation of dietary fibre.