Lipidomic and Metabolomic Signatures of the Traditional Fermented Milk Product Gioddu

Fermented dairy products such as yogurt, kefir, and traditional cheeses are increasingly consumed worldwide for their nutritional and probiotic properties. Lipidomic profiling provides valuable insights into microbial-driven biochemical changes during fermentation. In this study, we performed a comprehensive untargeted lipidomic analysis of sheep milk and Gioddu, a traditional Sardinian fermented dairy product. Using UHPLC-QTOF-MS platform, we observed that fermentation significantly reshaped the lipidome. Gioddu samples showed higher levels of phosphatidylethanolamines (PE) and lysophosphatidylethanolamines (LPE), together with a pronounced reduction in sphingolipids (glucosylceramides, ceramides, sphingomyelins) and glycerophospholipids (phosphatidylinositols, phosphatidylserines, phosphatidylcholines) compared to sheep milk. These findings align with known enzymatic activities of lactic acid bacteria (LAB), including phospholipases A1 and A2, phosphatidylinositol-specific phospholipase C (PI-PLC), and sphingomyelinase. Fermentation also affected triglycerides, with reduced levels of FA 18:1-containing species, suggesting the selective lipolysis of monounsaturated fatty acids by microbial lipases. Complementary metabolomic profiling revealed reduced levels of simple sugars such as galactose and inositol in Gioddu samples, consistent with their use as primary carbon sources during early fermentation. Conversely, a marked accumulation of carboxylic acids (succinic, malic, hydroxyisovaleric, hydroxyglutaric, glyceric) was revealed, reflecting enhanced microbial fermentative activity. Increased levels of amino acids, including alanine, serine, proline, and ethanolamine, further highlighted active proteolysis and membrane remodeling driven by LAB metabolism. These findings show that LAB enzymes play a key role in modifying the lipidome of fermented dairy products, highlighting their metabolic flexibility and potential impact on nutritional and health properties. This integrated approach sheds new light on the metabolic plasticity of fermentative processes and underscores the value of omics-based tools in understanding traditional food systems.