Characterisation of the microflora during ripening of a Norwegian semi-hard cheese with adjunct culture of propionic acid bacteria

The microflora of a semi-hard, washed curd, Norwegian cheese with an added adjunct culture of propionic acid bacteria (PAB) was investigated throughout ripening by phenotypic and physiological tests, API test and 16S rRNA sequencing. Cheeses were made at two commercial Norwegian dairies using different milk treatments (pasteurisation versus microfiltration plus pasteurisation) and the same type of starter cultures. Microflora in the cheese varied according to different plant site, milk treatment, and ripening time. PAB dominated the microflora throughout the ripening process. Leuconostoc spp., most probably from the starter, dominated among the isolates from the cheese using microfiltered and pasteurised milk; however, after 40 weeks of ripening non-starter lactic acid bacteria specie Lactobacillus casei/paracasei and Leuconostoc spp. dominated at the dairy using pasteurised milk. Cheese made at the two plants on two subsequent days showed almost identical microflora throughout ripening.