SELF-INDUCED INHIBITION OF GROWTH OF STREPTOCOCCUS-SALIVARIUS SUBSP THERMOPHILUS BY ACTIVATION OF THE LACTOPEROXIDASE SYSTEM

Seasonal inhibition (Spring inhibition) of thermophilic cheese starter culture growth has been investigated. Hydrogen peroxide accumulated t o a concentration of over 20 mu M during growth of Streptococcus saliv arius subsp. thermophilus in UHT milk. When lactoperoxidase at normal raw milk concentration was added to the growth medium, inhibition of g rowth of the organism occurred. Inhibition was related to the concentr ation of lactoperoxidase present in the growth medium. Studies on the seasonal variation in lactoperoxidase concentration in milk from the R iverina region of New South Wales, revealed peaks following the late W inter-Spring calving period of sufficient magnitude to account for inh ibition of the growth of S. salivarius subsp. thermophilus. A highly s ensitive method based on fluorescence spectroscopy is described for th e analysis of hydrogen peroxide in milk. No hydrogen peroxide could be detected (sensitivity limit 0.05 mu M) in fresh raw milk during the S pring period.