Effect of the use of chlorine usage in milking equipment cleaning procedures on raw milk microbiota

Background: Sodium hypochlorite (NaClO) is generally used for disinfection of milking equipment ensuring milk hygienic quality. Different studies showed that the chlorine can affect milk microbial population, encouraging the comprehension of the relationship between the use of chlorine products and milk microbiota, which represents a key point for raw milk cheese production. Objectives: The aim of the study was to evaluate the influence of NaClO on raw milk microbiota and the deriving whey-starter bacterial composition in Trentingrana PDO cheese production. Methods: Three farms were involved in the study. Milk was collected thrice weekly during the NaClO usage (six-weeks period, C) and in a subsequent, analogous, nonchlorine detergent period (NC). Fourweeks interval was established between the two experimental periods. The deriving whey-starter was sampled too. Samples were submitted to microbiological analyses (Standard Plate Count, coliforms, staphylococci, Lactic Acid Bacteria) and to metagenomic analysis. To this aim, 16S rRNA gene (V3-V4 region) was sequenced by Illumina MiSeq platform. Data analyses were performed with QIIME pipeline. Results: No significant differences were observed but higher SPC and LAB counts were recorded in milk going from period C to period NC. The metagenomic analysis of milk showed a distinctive microbiota composition for the three farms during the whole experimental period, moreover we evidenced a significant difference in microbial population related to chlorine use. The use of chlorine was found to affect the whey-starter population; Lactobacillus helveticus was predominant during period C and significantly reduced during period NC, whereas Lb. delbrueckii had the exact opposite trend.