Build aroma models to optimize production of Thai fish sauce.

Thai fish sauce, or nam-pla, a clear amber-colored liquid with a distinctive flavor and aroma, is a popular condiment in Southeast Asia. However, elsewhere the consumption of fish sauce is limited due to its strong and sometimes unpleasant odor. This is probably because southeast Asian fish sauce is often made from anchovies, salt and water, and is intensely flavored.

Researchers in Thailand and colleagues elsewhere set out to characterize the aroma compounds in Thai fish sauce. Their intent was to develop data that could be used to construct aroma models for sensory testing, which, in turn, could be used to indicate the compounds responsible for either pleasant or unpleasant odors in fish sauce. This information could be harnessed to improve production and storage practices, and possibly develop a more appealing product.

The scientists isolated and identified the key aroma compounds found in two premium commercial Thai fish sauces. Qualitative and quantitative analyses of the volatile compounds in the sauces were performed using headspace solid-phase microextraction and direct solvent extraction-solvent-assisted flavor evaporation (DSE-SAFE) techniques. These were followed by analysis using gas chromatography-mass spectrometry. The investigators used gas chromatography-olfactometry and aroma extract dilution analysis (AEDA) to screen the potent odorants in the DSE-SAFE aroma extracts of the sauces.

AEDA revealed that there were 28 odor-active compounds in the flavor dilution factor range of 3 to 19,683. Among them, acetic acid, 3-(methylthio)propanal (methional), 2-methylpropanoic acid, butanoic acid, 3-methyl-butanoic acid, 4-hydroxy-2,5-dimethyl-3( 2H )-furanone (HDMF), 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone (HEMF), and 2-phenylacetic acid had the highest flavor dilution factors.

Twenty odorants were quantified by stable isotope dilution assays. Their odor activity values were calculated by the researchers. Trimethylamine (a fishy odor), 2-methylpropanal (a malty, dark chocolate odor), 3-methylbutanal (a malty, dark chocolate odor), acetic acid (a sour odor), propanoic acid (a cheesy odor), 2-methylpropanoic acid (a cheesy odor), butanoic acid (a cheesy odor), 3-methylbutanoic acid (cheesy, sweaty odors), and methional (a cooked potato odor) had the highest odor activity values: greater than 100.

Further information. Jirawat Yongsawatdigul, Food Protein Research Unit, School of Food Technology, Institute of Agricultural Technology, Suranaree University of Technology, Nakon Ratchasima, Thailand; phone: [phone]; fax: [phone]; email: [e-mail].