Stability of Headspace Volatiles in a ‘Fallglo’ Tangerine Juice Matrix System at Room Temperature

摘要

Gas chromatography systems are usually equipped with autosamplers. Samples held in the autosampler tray can stay up to one day or longer at room temperature, if the tray is not equipped with a cooling mechanism. The objective of this research was to determine if holding samples at room temperature influences measurement of volatiles by using ‘Fallglo’ tangerine juice as a model. Tangerine juice mixed with saturated NaCl containing an internal standard (IS), 3-hexanone, was held in the autosampler for different periods of time at 25 °C, incubated at 40 °C, and then exposed to a solid phase microextraction (SPME) fiber to absorb volatiles at 75-min intervals prior to be analyzed by a GC-MS system. Results showed that there were significant changescaused by a 24 h or longer holding time at 25 °C in absolute peak area (APA) for 12 volatiles out of a total of 16 compounds detected, including hexanal, E-2-hexenal, B-pinene, octanal, d-limonene, linalool, nonanal, butyl-2-methylpropionate, copaene,caryophyllene, and valencene and the IS, 3-hexanone. However, there were no differences for four terpenes: alpha-thujene, alpha-pinene, alpha-terpinene and p-cymene. Three aldehydes (hexanal, E-2-hexenal and octanal) increased linearly at a rate of 144%,238%, and 127% per day, respectively. The proportion agrees with a Henry’s law based model. Butyl 2-methylpropionate, the only ester detected, decreased in both absolute and relative amounts (relative to IS), indicating that esters may not be favorablecompounds in competition for binding sites on the SPME fiber chosen. Terpenes and terpene alcohols increased in absolute amount but decreased in relative amount as holding time was extended. The research confirmed that extended holding time at room temperature markedly influenced the profile of volatile measurements, and the change in IS during holding period did not represent other volatile components.