Title: Stability of headspace volatiles in a ‘Fallglo’ tangerine juice-NaCl matrix system at room temperature Authors
Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: March 9, 2012
Publication Date: April 1, 2012
Citation: Bai, J., Baldwin, E.A., Plotto, A. 2011. Stability of headspace volatiles in a ‘Fallglo’ tangerine juice-NaCl matrix system at room temperature. Proceedings of Florida State Horticultural Society. 124:207-212. Interpretive Summary: There is a risk when analyzing headspace volatile concentrations by gas chromatography if the sample sits in an autosampler at room temperature for a period of time. Depending on the chemical type of volatile, time at room temperature may result in more or less concentration in the space above the liquid sample or headspace which skews reslults.
Technical Abstract: 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 a internal standard, 3-hexanone in a sample vial 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 changes caused 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 the IS: 3-hexanone, hexanal, E-2-hexenal, ß-pinene, octanal, d-limonene, linalool, nonanal, butyl-2-methylpropionate, copaene, caryophyllene, and valencene. However, there were no differences for four terpenes: a-thujene, a-pinene, a-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 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 favorable compounds in competition for binding sites on SPME. 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.