Ability of lactic acid bacteria isolated from cheese to biotransform terpenes

Terpenes are secondary metabolites with a broad structural diversity synthesized by higher plants, algae and fungi. They exhibit a wide range of biological action such as animals and insects attraction, plant protection from disease, infestation and predation and antimicrobial, antiparasitic, insecticidal, antioxidant/prooxidant activities. Many authors showed that these molecules could be used as tracers of cheese produced over mountain pastures as they can be transferred from the plant ingested by herbivores to the associated milk and cheese. While the antimicrobial effect of terpenes is already known the capability of lactic acid bacteria isolated from cheese to degrade these compounds has never been investigated. In this work five lactic acid bacteria strains, Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, Streptococcus thermophilus, Streptococcus macedonicus e Lactobacillus paracasei, isolated from cheese and belonging to the DIVAPRA collection, were grown on a synthetic medium (M17 broth) in presence of alpha-pinene, one of the most spread terpenes both in vegetation and derived dairy products. The standard of alpha-pinene used in this work contained myrtenal, alpha-campholenal and alpha-terpineol as impurities. Cultures were incubated at 37°C for 48 hours, collected at 6, 24 and 48 hours and analyzed by headspace-solid phase microextraction coupled with gas chromatography-mass spectrometry. Results showed that alpha-pinene did not occur degradation, but one of its impurities, the alpha-campholenic aldehyde, was biotransformed into a new terpene, in particular an isomer of borneol. All strains were able to perform the biodegradation pathway of the alpha-campholenal. The highlighted activity was dependent both on the strain and the incubation time. In fact L. paracasei strain showed the highest degradation activity and parallely the highest yield of the borneol isomer; L. lactis as well as L. cremoris showed also a biotransformation activity with very similar kinetic trends. S. macedonicus and S. thermophylus instead showed less yield of the degradation product. All strains showed an increase in the production of the borneol isomer with a maximum at 24 h of growth except for L. paracasei which continued to increase the compound production until 48 h. The preliminary results obtained in this study must be confirmed with further experiments using other terpenoids as substrate and other growth media, in order to check deeply the ability of dairy cultures to metabolize this type of compounds.