Volatile terpene analyses in milk and cheeses by solid-phase microextraction technique

Terpenes are lipophilic aliphatic compounds involved, as secondary metabolites, in plant pollination, in plant resistance to predation and infection. These compounds abound in certain species, particularly dicotyledons and, if ingested by herbivores, could be subsequently found in associated milk, cheese and meat. Terpenes have then recently attracted interest both for their possible impact on cheese sensory properties and potential terroir-biomarkers in milk and cheese. Various techniques were used for their determination including dynamic headspace gas chromatography-mass spectrometry or purge-and-trap but also headspace solid-phase microextraction (HS-SPME) was suggested for its low costs and easy use. The aim of this work was the development of a HS-SPME method with a three-phasic fiber to analyse these compounds in milk and cheese that could allow to detect a higher number of compounds with respect to the other fibers generally used in literature. The better extraction method defined, both from the qualitative as well as the quantitative point of view, included a treatment of sample (milk or cheese) with a NaH2PO4 solution and an absorption in the headspace for 1 h at 53 °C. During a research supported by Pro-Alpe Project of Italy Government, this method was applied to analyse milks and cheeses produced by cows fed in diversified grassland. This method allowed to isolate and identify many monoterpenes, as limonene, β-pinene and p-cymene, and also sesquitertenes as β-caryophyllene and t,t-farnesol. Therefore, the proposed method could satisfactorily perform qualitative and quantitative analyses of terpene compounds and be suitable to define terpene profile in dairy products and their link to grazing management.