Volatile terpene detection in milk and cheeses by solid-phase microextraction method

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 as potential terroir-biomarkers in milk and cheese. In fact the individuation of suitable chemical markers able to distinguish samples on the basis of different parameters as geographical origin, transformation process or agronomic treatment is important to define traceability and then food authenticity. Various techniques were used by other authors for determination of terpenoidic compounds including dynamic headspace or purge-and-trap technique or liquid-liquid extraction but these methods are expensive and long time consuming. Static headspace solid-phase microextraction (HS-SPME) is used in our laboratories for its low costs, easy use, sensibility and solvent-less approach. The objective of this work was the development of a HS-SPME method to analyse these compounds in milk and cheeses of different origins that could allow to detect a higher number of compounds with respect to the other techniques generally used in literature. We used three different methods of extraction to find the best one to detect terpenoids compounds. The first sample preparation estimated the presence of terpenes in dairy products with the addition of NaCl to improve the ionic strength of the matrix, followed by SPME extraction. The second preparation included a treatment of the sample (fat milk or cheese) with a NaH2PO4 solution and an absorption in the headspace. Moreover, dairy matrices were distilled under vacuum in presence of liquid nitrogen and the distilled acqueous solutions were analyzed by HS-SPME hyphenated in all cases with gas chromatography-mass spectrometry technique. For all types of sample preparation a three-phasic fiber was used. Results showed that from the qualitative as well as the quantitative point of view, the vacuum distillation followed by static headspace technique was the most efficient method to extract and detect the major number of terpenoidic and norisoprenoid components. This method could be useful in the valorisation and identification of typical dairy products.