C: Food Chemistry JFS C: Food Chemistry Characterization of Fish Sauce Aroma-Impact Compounds Using GC-MS, SPME-Osme-GCO, and Stevens’ Power Law Exponents A.J. PHAM, M.W. SCHILLING, Y. YOON, V.V. KAMADIA, AND D.L. MARSHALL ABSTRACT: The objectives of this study were to characterize volatile compounds and to determine the char- acteristic aromas associated with impact compounds in 4 fish sauces using solid-phase micro-extraction, gas chromatography-mass spectrometry, Osme, and gas chromatography olfactometry (SPME-Osme-GCO) coupled with Stevens’ Power Law. Compounds were separated using GCMS and GCO and were identified with the mass spec- tral database, aroma perceived at the sniffing port, retention indices, and verification of compounds by authentic standards in the GCMS and GCO. Aromas that were isolated and present in all 4 fish sauce samples at all concen- trations included fishy (trimethylamine), pungent and dirty socks (combination of butanoic, pentanoic, hexanoic, and heptanoic acids), cooked rice and buttery popcorn (2,6-dimethyl pyrazine), and sweet and cotton candy (ben- zaldehyde). All fish sauces contained the same aromas as determined by GCO and GCMS (verified using authentic standard compounds), but the odor intensity associated with each compound or group of compounds was variable for different fish sauce samples. Stevens’ Power Law exponents were also determined using this analytical technique, but exponents were not consistent for the same compounds that were found in all fish sauces. Stevens’ Power Law exponents ranged from 0.14 to 0.37, 0.24 to 0.34, 0.09 to 0.21, and 0.10 to 0.35 for dirty socks, fishy, buttery pop- corn, and sweet aromas, respectively. This demonstrates that there is variability in Stevens’ Power Law exponents for odorants within fish sauce samples. Keywords: aroma-impact compounds, fish sauce, gas chromatography olfactometry, Osme, Stevens’ Power Law exponents Introduction F ish sauce is a clear brown liquid condiment that is popular across Asia for its distinct flavor and taste. It is an important flavoring ingredient in most Asian households and provides a sub- stantial source of protein in the diet of certain classes in the re- gion. The manufacture of fish sauce varies from country to coun- try. However, the conventional method for its production involves the hydrolysis of a mixture of 3 parts fish to 1 to 2 parts salt that is fermented for 6 to 12 mo (Peralta and others 1996). The unique flavor (aroma and taste) of fish sauce is often used as a gauge to measure its quality; it is primarily due to protein and lipid degra- dation products formed by autolytic and bacterial enzymes during fermentation (Saisithi and others 1966; Beddows and others 1980). Factors that affect the quality and volatile compounds in fish sauce are species, origin, salt type, fish-to-salt ratio, fermentation condi- tions, and minor ingredients (Lopetcharat and others 2001). Various methods, such as steam distillation under reduced pres- sure, solvent extraction, and column concentration, have been used for the extraction and determination of volatile compounds in fish sauce (McIver and others 1982; Peralta and others 1996; Sanceda and others 2001). However, the majority of these meth- MS 20070851 Submitted 11/16/2007, Accepted 1/23/2008. Authors Pham, Schilling, Yoon, and Kamadia are with Dept. of Food Science, Nutri- tion, and Health Promotion, Mississippi Agricultural and Forestry Exper- iment Station, Mississippi State Univ., Box 9805, Mississippi State, MS 39762, U.S.A. Author Marshall is with College of Natural and Health Sciences, Univ. of Northern Colorado, Gunter 1000, Box 134, Greeley, CO 80639, U.S.A. Direct inquiries to author Schilling (E-mail: schilling@ foodscience.msstate.edu). ods are time-consuming and require the use of organic solvents. Methods that efficiently extract volatile compounds from the sam- ple matrix are continually being sought since this process is gen- erally the step at which analyte loss occurs (Steffen and Pawliszyn 1996). Solid-phase microextraction (SPME) is a solvent-free extrac- tion method where analytes are adsorbed by the fiber phase until equilibrium is reached in the system (Pawliszyn 2001). SPME is a simple, rapid, and sensitive technique that is gaining popularity as a method to extract the volatile components in foods, beverages, ingredients, and other botanicals (Yang and Peppard 1999). Even though SPME works well in food applications, it has limitations that include variable precision (Fernando and Gr¨ un 2001) and compe- tition between binding sites among volatile compounds (Yang and Peppard 1994). Gas chromatography olfactometry (GCO) is an instrumental tool that is utilized for the identification of aroma-impact compounds in foods. Osme is a time-intensity approach to GCO that directly estimates the magnitude of an odor by utilizing the human nose as the detector (McDaniel and others 1990). Osme makes use of a cross-modal matching technique that is based on Stevens’ Power Law, which matches the intensity of one attribute (such as aroma intensity) to that of another attribute (such as odorant concentra- tion) (Fu and others 2002). Trained panelists use a 15-point scale to rate the intensities of eluting aroma-active compounds. Stevens’ Power Law is a psychophysical law that explains the re- lationship between perceived intensity and the concentration of a sensory stimulus (Stevens 1971; Green and others 1996). This law demonstrates the effect of increasing the concentration of the stim- ulus on the magnitude of perceived intensity. Aromas of individual C268 JOURNAL OF FOOD SCIENCE—Vol. 73, Nr. 4, 2008 C  2008 Institute of Food Technologists doi: 10.1111/j.1750-3841.2008.00709.x Further reproduction without permission is prohibited