Austrian Raw-Milk Hard-Cheese Ripening Involves Successional Dynamics of Non-Inoculated Bacteria and Fungi

Narciso M Quijada,Martin Wagner,Christian Guse,Stefanie U Wetzels,Benjamin Zwirzitz,Evelyne Selberherr,Stephan Schmitz-Esser,Monika Dzieciol,Cameron R Strachan

doi:10.3390/foods9121851

Narciso M Quijada, Martin Wagner + Show 7 more

Open Access

https://doi.org/10.3390/foods9121851

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Abstract

Cheese ripening involves successional changes of the rind microbial composition that harbors a key role on the quality and safety of the final products. In this study, we analyzed the evolution of the rind microbiota (bacteria and fungi) throughout the ripening of Austrian Vorarlberger Bergkäse (VB), an artisanal surface-ripened cheese, by using quantitative and qualitative approaches. The real-time quantitative PCR results revealed that bacteria were more abundant than fungi in VB rinds throughout ripening, although both kingdoms were abundant along the process. The qualitative investigation was performed by high-throughput gene-targeted (amplicon) sequencing. The results showed dynamic changes of the rind microbiota throughout ripening. In the fresh products, VB rinds were dominated by Staphylococcus equorum and Candida. At early ripening times (14–30 days) Psychrobacter and Debaryomyces flourished, although their high abundance was limited to these time points. At the latest ripening times (90–160 days), VB rinds were dominated by S. equorum, Brevibacterium, Corynebacterium, and Scopulariopsis. Strong correlations were shown for specific bacteria and fungi linked to specific ripening periods. This study deepens our understanding of VB ripening and highlights different bacteria and fungi associated to specific ripening periods which may influence the organoleptic properties of the final products.

Highlights

Since the first known appearance of cheese production at ~5000 Bacterial cell equivalents (BCE), it has spread worldwide and experienced extensive changes in manufacturing between different regions, affected by distinct technical, social and economic conditions [1,2]
The results confirmed that fungi, in terms of fungal cell equivalents (FCEs), are abundant on Vorarlberger Bergkäse (VB) rinds throughout ripening, even though their values were lower than bacterial cell equivalents (BCEs) (Figure 1)
We aimed to quantify fungi on VB rinds, and, by doing so, we evaluated two methodologies, quantitative PCR (qPCR) and digital PCR (dPCR), both targeting the 18S rRNA gene, which has been previously recommended for fungal quantification [24,51,52,53]. qPCR has been widely used for fungal quantification in dairy products, as it overcomes biases related to cultivation-dependent methods [18,19,20]

Summary

Introduction

Since the first known appearance of cheese production at ~5000 BCE, it has spread worldwide and experienced extensive changes in manufacturing between different regions, affected by distinct technical, social and economic conditions [1,2]. In surface-ripened cheeses, the activity of the rind microbiota, which differ from the cheese core microbiota, is pivotal for the ripening and the development of the organoleptic properties of the products [3]. Cheese ripening is a complex metabolic process and the cheese rind microbiota undergoes dynamic changes to adapt to nutrient availability, pH, environmental factors (temperature, salt content, etc.) and competition against other microorganisms [7]. The microbial composition of surface-ripened cheeses varies throughout ripening and between the different manufacture conditions and products

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