Microbiological characterization of Gioddu, an Italian fermented milk

Abstract Gioddu, also known as “Miciuratu”, “Mezzoraddu”, or “Latte ischidu” (literally meaning acidulous milk), is the sole variety of traditional Italian fermented milk. The aim of the present study was to elucidate the microbiota as well as the mycobiota occurring in artisan Gioddu samples collected from three Sardinian producers by combining the results of viable counting on selective culture media and, high-throughput sequencing. Physico-chemical parameters were also measured. The overall low pH values (3.80–4.22) detected in the analyzed Gioddu samples attested the strong acidifying activity carried out by lactic acid bacteria during fermentation. Viable counts revealed the presence of presumptive lactococci, presumptive lactobacilli, and non-Saccharomyces yeasts. A complex (kefir-like) microbiota of bacteria and yeasts was unveiled through sequencing. In more detail, the dominance of Lactobacillus delbrueckii was highlighted in all the samples, thus representing the key species in Gioddu fermentation together with Streptococcus thermophilus, whose presence suggested the establishment of a yogurt-like protocooperation. Unexpectedly, samples from two out of the three producers revealed the presence of Lactobacillus kefiri in all the three analyzed batches, thus representing an absolute novelty and suggesting the presence of bioactive compounds (e.g. exopolysaccharides) similar with those present in milk kefir beverage. Mycobiota population, studied for the very first time, revealed a more complex population where Kluyveromyces marxianus, Galactomyces candidum and Geotrichum galactomyces constituted the core mycobiota. Further research is needed to disclose the presence in Gioddu of probiotic cultures and bioactive compounds (e.g. exopolysacchariGalactomyces candidumdes, angiotensin-converting enzyme inhibitory peptides, antimicrobial compounds) with potential health-benefits for the consumers.