Towards solutions of challenges of present-day Gouda cheese production

Gouda cheese is a nutritious and popular fermented dairy product that has been made for centuries in the Low Countries. However, industrial Gouda cheese production still faces several challenges. Hence, because of different sources of variation, the quality of the cheeses produced within one cheese company might vary largely, from better to worse. Whereas this reflects the natural, artisan character of Gouda cheese production, it is of course preferable that the cheese quality is as high and as stable as possible. This is only possible when all sources of variability are well understood, and the critical process parameters are under control.

Hereto, the whole fermentation and ripening process of one type of Gouda cheese was studied in detail. The dynamics of the microbial species and metabolites were quantified using various state-of-the-art techniques. It turned out that the culturable fraction of bacteria varied largely around the selling time point of the cheeses, which hence was a first source of variability. Additionally, three different primary starter culture mixtures were applied in rotation, a common approach in Gouda cheese production to protect the cultures toward bacteriophages. These cultures should be very similar, but they resulted in significantly different concentrations of key metabolites, such as acetoin, responsible for the buttery aroma of Gouda cheese. Moreover, the cultures differed in their abundance of leuconostocs, which also resulted in different levels of competitiveness of the cultures against non-starter lactic acid bacteria (NSLAB), such as Loigolactobacillus rennini and Tetragenococcus halophilus. These NSLAB species belong to the house microbiota present in a company, and they can eighter improve or worsen the cheese flavor.

A typical defect that NSLAB species can cause, is the formation of cracks in the cheese body. Several cheeses with cracks were investigated during the present study, and Loil. rennini was identified as the sole species responsible for this cheese defect. The underlying pathways were unraveled using shotgun metagenomics combined with meta-metabolomics. This species was abundant in the cheese brine, which proved that the brine effectively acted as an inoculation source for the cheeses. The brine also acted as a dynamic reservoir of microorganisms and consequently requires regular monitoring. The evolution of the metabolites and the microbial composition of a completely new brine was also investigated. Within three months, the brine was colonized, although it took up to nine months before a stable microbial consortium was reached with T. halophilus as the main species.

To ensure a reproducible Gouda cheese quality, adjunct starter cultures can be applied in addition to the primary starter culture mixtures. Several NSLAB isolates from the cheeses and brines were collected during this study, and two selected adjunct strains were applied in Gouda cheese productions carried out at pilot scale, namely a Lacticaseibacillus paracasei strain and a T. halophilus strain. Whereas the former species is a common cheese adjunct, the latter has never been reported as a cheese adjunct. Both adjuncts had some effects, but they did not lead to a significantly different cheese flavor. Nevertheless, the potential of T. halophilus as cheese adjunct was demonstrated.