Abstract:

S. thermophilus grx02, a strain sensitive to ofloxacin, was used as starter culture to produce fermented milk, and
the effect of residual ofloxacin on the growth curve of the strain and the texture and rheological behavior of fermented milk
was studied. The results showed that the growth rate of S. thermophilus grx02 was markedly decreased when the amount
of residual loxacin was 1.0 μg/mL. At the same time, the adhesiveness, gumminess and chewiness of fermented milk were
also reduced remarkably. When the residual amount of ofloxacin rose to 0.5 μg/mL, the storage stability and rheological
properties of fermented milk changed significantly, and the gel stability and resistance to mechanical movement and
temperature variations also declined (P < 0.05). These findings suggest that the residual amount of ofloxacin in raw milk
used for the processing of fermented dairy product should be lower than 0.5 μg/mL.

Key words: ofloxacin, S. thermophilus, fermented milk, texture, rheological behavior