Valérie Gagnaire

MicroRNAs (miRNAs) are small regulatory RNAs that regulate numerous biological processes and potentially impact human health. Despite their abundance in raw milk, little is known about their content in processed dairy products or how manufacturing affects their abundance and bioavailability. We characterized and compared the miRNA profiles of yogurt and cheese produced from the same raw milk from cows raised under agroecological or intensive systems, assessing compositional changes during processing, while accounting for farming system effects. High-throughput sequencing identified a total of 1,384 miRNAs, including 258 common to all matrices, forming a conserved milk-derived core. Processing into yogurt or cheese reduced milk-specific miRNAs while introducing microbial small RNAs from fermentation bacteria such as Lactococcus and Streptococcus thermophilus. Differential analysis revealed stable miRNomes across agroecological and intensive farming systems, but substantial processing-associated changes involving 29 and 353 miRNAs during cheese and yogurt production, respectively, and some miRNAs showed matrix-specific stability. These miRNAs were predicted to influence cell proliferation, metabolism, and protein-related pathways, suggesting shifts in the regulatory impact of milk-derived miRNAs in fermented dairy products. Overall, these findings underscore the dynamic nature of dairy miRNomes and the combined influence of processing and microbial activity in shaping miRNA composition.

Dairy products are major dietary sources of B vitamins. However, the impact of cow diet and dairy processing techniques on B vitamin concentrations remains unclear. This study investigated the effects of diet composition on B-vitamin content in raw milk and, in yogurt, and Cantal-type cheese produced therefrom. Forty Holstein and Montbéliarde-breed cows were assigned to either a grass-based agroecological system or a corn-based intensive system for 19 weeks. Vitamins B1, B2, B5, and B6 were quantified by liquid chromatography, and B9 and B12 by chemiluminescence. Milk from the agroecological system contained higher vitamin B2, and lower vitamin B5 concentrations than milk from the intensive system. This same pattern was also observed in cheese, but not in yogurt, showing impacts of technological processing. Adding probiotics into yogurts increased pyridoxal (B6) concentration. This study highlighted diet-related differences in B vitamin concentrations in raw milk, and these differences transferred to cheese but not to yogurt.

Reducing salt intake can mitigate the prevalence of metabolic disorders. In fermented foods such as cheeses, however, salt can impact the activity of desirable and undesirable microorganisms and thus affect their properties. This study aimed to investigate the effect of salt level on Swiss-type cheese ripening. Since proteolysis is a major event in cheese ripening, three strains of Lactobacillus helveticus were selected on the cell-envelope proteinase (CEP) they harbor. Their proteolytic activity on caseins was studied at six salt levels (0–4.5%) at pH 7.5 and 5.2. Swiss-type cheeses were manufactured at regular, increased, and decreased salt concentrations, and characterized for their composition and techno-functional properties. L. helveticus strains possessed and expressed the expected CEPs, as shown by PCR and shaving experiments. The two strains of L. helveticus that possessed at least the CEP PrtH3 showed the greatest proteolytic activity. Casein hydrolysis in vitro was similar or higher at pH 5.2, i.e., cheese pH, compared to pH 7.5, and slightly decreased at the highest salt concentrations (3.0 and 4.4%). Similarly, in ripened cheeses, these L. helveticus strains showed 1.5–2.4 more proteolysis, compared to the cheeses manufactured without L. helveticus. Regarding the salt effect, the 30% salt-reduced cheeses showed the same proteolysis as regular cheeses, while the upper-salted cheeses showed a slight decrease (−14%) of the non-protein fraction. The microbial and biochemical composition remained unchanged in the 30%-reduced cheeses. In contrast, Propionibacterium freudenreichii, used as ripening bacteria in Swiss cheese, grew more slowly in upper-salted (1.14%, w/w) cheeses, which induced concomitant changes in the metabolites they consumed (−40% lactic acid) or produced (fivefold decrease in propionic acid). Some cheese techno-functional properties were slightly decreased by salt reduction, as extrusion (−17%) and oiling off (−4%) compared to regular cheeses. Overall, this study showed that a 30% salt reduction has little impact in the properties of Swiss-type cheeses, and that starters and ripening cultures strains could be chosen to compensate changes induced by salt modifications in Swiss-type and other hard cheeses.