Impact of a well-defined indigenous starter on microbial communities and technological properties of raw milk during backslopping practice

Backslopping, which involves using the whey from a previous batch as a starter for a new production run, is one of the oldest traditional cheese-making methods and is still widely used today. However, this technique can sometimes lead to acidification failures, necessitating the use of industrial starters to quickly restart production and minimise economic loss. This study investigated the effect of using a well-defined indigenous starter culture on raw milk during backslopping. The microbial composition and technological characteristics of successive subcultures were analyzed during one month of backslopping with and without the starter added. The results showed that the indigenous starter remained highly stable in skim milk, predominantly drove homolactic fermentation. The raw milk alone displayed greater initial microbial diversity and metabolic variability but then stabilised and Lactococcus lactis became dominant from day four onwards of backslopping. The combination of the indigenous starter with the raw milk, rapidly established L. lactis dominance, directing the ecosystem towards homolactic fermentation from the start of backslopping. The addition of the indigenous starter impacted particularly subdominant populations and technological properties, resulting in an acidification that met the requirements of the Rocamadour PDO from the start of the backslopping. From day fifteen onwards, comparison of bacterial communities with and without the starter added became differentiated, demonstrating that adding the indigenous starter reduced variability in bacterial composition. Notably, coexistence between the indigenous starter and the raw milk flora was observed, suggesting that this could be a promising option for farmer producers to strengthen the link between the product and its microbial terroir.