Effect of sodium chloride reduction or partial substitution with potassium chloride on the microbiological, biochemical and sensory characteristics of semi-hard and soft cheeses

Sodium reduction in the human diet is currently one of the main concerns for public health agencies and, consequently, has become a challenge for the food industries. In this study, the impact of reduced sodium chloride content (20%) or its partial substitution with potassium chloride in soft (“Camembert”-type) and semi-hard (“Reblochon”-type) cheeses was evaluated. Analyses included physicochemical and biochemical composition, microbial counts, 16S rRNA gene metabarcoding and metatranscriptomic analysis, volatile aroma compounds and sensory analysis. Regarding soft cheeses, the salt content of cheeses affected proteolysis at 21 days of ripening. RNA sequencing revealed that the relative activity of G. candidum increased, whereas that of P. camemberti decreased in reduced salt cheeses in comparison to the controls. Higher global intensity of odor and taste was observed in cheeses with reduced salt content, consistent with higher levels of alcohol and ester components. Regarding semi-hard cheeses, modifications of salt content did not significantly affect either their biochemical parameters and sensory characteristics or their technological microbial composition at day 21 of ripening. Finally, no impact of salt content was observed on the growth of the spoiler Yarrowia lipolytica in soft cheeses. In contrast, reducing salt content increased spoiler growth in semi-hard cheeses, as highlighted by a greater development of Pseudomonas that led to an increase in cheese proteolysis and lipolysis. In conclusion, the effect of reducing salt content is highly dependent on the cheese type. This factor should thus be taken into account by the dairy industry when the reduction of salt content is being considered. Moreover, the quality of raw products, in particular, the level of spoiler microorganisms, must be controlled before use during dairy processes

Overview of a surface-ripened cheese community functioning by meta-omics analyses

Cheese ripening is a complex biochemical process driven by microbial communities composed of both eukaryotes and prokaryotes. Surface-ripened cheeses are widely consumed all over the world and are appreciated for their characteristic flavor. Microbial community composition has been studied for a long time on surface-ripened cheeses, but only limited knowledge has been acquired about its in situ metabolic activities. We applied metagenomic, metatranscriptomic and biochemical analyses to an experimental surface-ripened cheese composed of nine microbial species during four weeks of ripening. By combining all of the data, we were able to obtain an overview of the cheese maturation process and to better understand the metabolic activities of the different community members and their possible interactions. Furthermore, differential expression analysis was used to select a set of biomarker genes, providing a valuable tool that can be used to monitor the cheese-making process

Number of differentially expressed genes according to ripening time.

<p>Number of differentially expressed genes according to ripening time.</p

Sequencing coverage (C) and percentage of genes (P) with at least an average of five uniquely mapped reads in the DNA-Seq dataset across the three replicates for each microbial genome during ripening.

<p>^aAA = <i>Arthrobacter arilaitensis</i>; BA = <i>Brevibacterium aurantiacum</i>; CC = <i>Corynebacterium casei</i>; DH = <i>Debaryomyces hansenii</i>; GC = <i>Geotrichum candidum</i>; HA = <i>Hafnia alvei</i>; KL = <i>Kluyveromyces lactis</i>; LL = <i>Lactococcus lactis</i>; SE = <i>Staphylococcus equorum</i></p><p>Sequencing coverage (C) and percentage of genes (P) with at least an average of five uniquely mapped reads in the DNA-Seq dataset across the three replicates for each microbial genome during ripening.</p

Protein degradation during surface-ripened cheese maturation.

<p>(A) Proteolysis and free amino acid concentration. Expression data observed for genes encoding proteases (B) and peptidases (C). Read numbers were normalized (according to the library size) to 50,000 reads per sampling day. SE: <i>Staphylococcus equorum</i>. BA: <i>Brevibacterium aurantiacum</i>. AA: <i>Arthrobacter arilaitensis</i>. HA: <i>Hafnia alvei</i>. CC: <i>Corynebacterium casei</i>. LL: <i>Lactococcus lactis</i>. KL: <i>Kluyveromyces lactis</i>. DH: <i>Debaryomyces hansenii</i>. GC: <i>Geotrichum candidum</i>.</p

Gene expression related to amino acid metabolism.

<p>For each pathway, the heatmap represents the expression dynamics over time (cumulative number of normalized reads per pathway) using a gray scale bar from 0 read in white to 500 reads in black. For seven pathways, histogram charts detail this dynamic per microbial species. CC: <i>Corynebacterium casei</i>, HA: <i>Hafnia alvei</i>, AA: <i>Arthrobacter arilaitensis</i>, BA: <i>Brevibacterium aurantiacum</i>, SE: <i>Staphylococcus equorum</i>, LL: <i>Lactococcus lactis</i>, KL: <i>Kluyveromyces lactis</i>, DH: <i>Debaryomyces hansenii</i>, GC: <i>Geotrichum candidum</i>.</p

Functional classification of the metatranscriptome during surface-ripened cheese maturation.

<p>Functional classes were determined according to KEGG annotations. Read counts corresponding to all species were cumulated. Read numbers were normalized (according to the library size) to 50,000 reads per sampling day.</p

Reference genomes used for mapping of the sequence reads.

<p>Reference genomes used for mapping of the sequence reads.</p