Using a rice-based model weaning food, the effect of Lactococcus lactis on the growth and survival of a range of enteric pathogens has been investigated. The starter organism used produces the bacteriocin nisin and the physiological L-lactate isomer, thus avoiding the risk of D-lactate acidosis when consumed by infants. L. lactis was a less effective antagonist than stronger acid producers such as the DL lactate producer, Lactobacillus plantarum, and only produced a potentially useful inhibition of pathogens when present in a large numerical superiority (>105:1). Prefermentation of the weaning food with L. lactis for 24 h produced a product with a pH of 3.7–3.8 containing ≈ 0.25% lactate (>96% L-lactate). The prefermented product was bactericidal for pathogens introduced subsequently. Despite the production of 100–150 international units nisin per g during fermentation, the inhibition of pathogens could be ascribed to acid production alone.

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