Thiswas used to determine whether antimicrobial effects of LAB
isolates were solely due to acid production. Cell free supernatants
(CFS) of the LAB test organisms were prepared by centrifuging 48 h
cultures (1078 cfu ml1) of LAB isolates at 10,000 rpm for 15 min.
The CFS were then filter sterilised using sterile syringe-driven
membrane filters (0.2 mm, ThermoFisher, UK). The CFS of test organisms
(ca. pH 4.2) were treated with filter sterilised 0.1 M NaOH
(S8045, Sigma) to raise the pH to 6.7 0.1. Neutralised and nonneutralised
CFS were tested against indicator organisms using the
well diffusion assay as described in Section 2.4.1.