The volatile compounds formed by thermal degradation of the carotenoids present in Dunaliella bardawil were investigated by microwave irradiation (MW) and water bath heating (WB) in different conditions of temperature and time using central composite design. Volatiles extraction by solid phase microextraction (SPME) was optimized and performed at 40 °C for 15 minutes, and those in greater amount were quantified by a validated method of gas chromatography coupled to a quadrupole mass spectrometer (GC-qMS). Employing WB, 10, 12 and 120 ng mL -1 of β-cyclocitral, α-ionone e β-ionone, respectively, were obtained between 60 and 87 °C for 30-75 min, while by MW, 5, 5, 50 ng mL -1 were obtained between 75-107 °C for 1.5-2.8 min. Considering the shorter time of MW, it can be concluded that if the time necessary to obtain the best yield by WB is employed in multiple MW cycles, an amount 10 times greater of those compounds would be obtained by MW than by WB. The results suggest a new biotechnology application for the carotenoids of the microalgae of the Dunaliella genus.
Keywords: Dunaliella bardawil, β-cyclocitral, ionone, carotenoid, microwave, water bath
IntroductionMicroalgae are photosynthetic microorganisms widely distributed in marine, freshwater and terrestrial ecosystems.1,2 They produce a great diversity of compounds with high commercial value, such as polyunsaturated fatty acids, carotenoids, phycobilins, polysaccharides, vitamins and sterols. [3][4][5][6][7] The production of microalgae supplies the cosmetic and food supplement industries, and boosts the development of natural food products, an emerging and promising field for industrial application.8 Microalgae have properties typical of higher plants (efficient oxygenic photosynthesis and simplicity of nutritional requirements), but also biotechnological attributes of microbial cells (rapid growth in culture medium and capacity to accumulate or secrete metabolites of interest), 4 supporting large scale applications.Among the microalgae used to obtain carotenoids, two species of the genus Dunaliella, D. bardawil and D. salina stand out for the production of β-carotene in their chloroplasts. 9 The accumulation capacity of β-carotene in Dunaliella is influenced by stress factors in culture, such as high light intensity and salt concentration, low temperatures and/or nitrate deficiency. 10 Studies reported in the literature aimed at increasing the production of carotenoids in Dunaliella showed that its concentration varies in a range between 4 and 38 µg mL -1 .
11-14Herrero et al. 15 evaluated the chemical composition and antimicrobial activity of the pressurized extract of D. salina. Norisoprenoids such as α-ionone, β-ionone and β-cyclocitral, besides neophytadiene and phytol were observed, as well as antimicrobial activity associated to volatiles. Previously, Larrouche et al. 16 showed that β-ionone inhibits the respiratory chain, preventing microbial oxygen consumption.Norisoprenoids can be formed from carotenoids by external agents such as temperature, light...
