Effect of anti-oxidants on growth and lactic acid production by Streptococcus mutans

The effects of three anti-oxidants--tertiary butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT)--on both growth and lactic acid production by eight cariogenic strains of Streptococcus mutans were investigated. Synergistic inhibitory effects of potassium sorbate on lactic acid production were also determined. All three anti-oxidants are phenolic derivatives and are commonly used in food systems due to their excellent "carry-through" properties during processing. Growth inhibition was determined by turbidity measurements at 600 nm. Lactic acid was assayed by gas chromatography, and bacterial DNA was assayed by the diphenylamine reaction. There were reduced growth levels of S. mutans due to the anti-oxidants and potassium sorbate for at least 12 hr, with TBHQ and BHA still inhibiting growth at 24 hr. Nearly all concentrations of anti-oxidants and potassium sorbate reduced lactic acid production by S. mutans, but only TBHQ significantly inhibited lactic acid production when the amount of acid per microgram DNA was calculated. A synergistic reduction of lactic acid production by S. mutans does occur in most combinations of potassium sorbate with anti-oxidants.