Annika Mäyrä-Mäkinen

Antimicrobial activity of 2-pyrrolidone-5-carboxylic acid produced by lactic acid bacteria

Thirteen Lactobacillus and five Pediococcus strains were shown to produce an antimicrobial agent, 2-pyrrolidone-5-carboxylic acid (PCA). PCA inhibited many spoilage bacteria, particularly Enterobacter cloacae 1575, Pseudomonas fluorescens KJLG, and P. putida 1560-2. The antimicrobial activity of PCA did not change at higher temperatures. However, the activity was destroyed rapidly by neutralization with ammonium hydroxide. PCA showed slightly lower antimicrobial activity than lactic acid.

Production of β-galactosidase by Streptococcus salivarius subsp thermophilus 11F

The production of β-galactosidase by an autolytic strain of Streptococcus salivarius subsp thermophilus 11F was investigated in batch and fed-batch 2-L working volume stirred tank bioreactors. β-Galactosidase was released into the medium upon cell lysis within 1–2 h after the maximum biomass quantity was reached. In batch fermentations the highest β-galactosidase activity of 69 U ml−1 was obtained when the temperature was increased to 42°C after a 4-h growth period at 30°C. In fed-batch experiments the highest β-galactosidase activity of 74 U ml−1 was obtained at a constant 37°C.