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Q. LEI and W. L. Boatright. Department of Animal Sciences, University of Kentucky, Lexington, KY 40546-0215

JUSTIFICATION The typical beany off-flavor associated with soybean and soy products is a major problem retarding their extend utilization in human foods. Very recently, dimethyl trisulfide (DMTS) was reported in hydrolyzed vegetable proteins and our previous research revealed that DMTS was one of the most potent odorants for both soy protein isolates (SPI) and soy protein concentrates (SPC) based on static and concentrated headspace analysis and aroma extract dilution assay.

OBJECTIVES The objective of our current research is to investigate which factors influence the occurrence of DMTS in SPC.

METHODS Deuterium-labeled DMTS was synthesized and used as an internal standard to quantify DMTS from SPC samples and from SPC receiving various treatments in order to investigate how these treatments influence the occurrence of DMTS in SPC.

RESULTS DMTS concentration in SPC samples ranged from 4.33 to 56.59 ppb. With an odor threshold of 10 ppt in water, DMTS has the highest reported odor value of any compounds found in SPC. The occurrence of DMTS was increased when dry SPC samples were heated at 120°C. Addition of ascorbic acid into SPC slurry also resulted in higher DMTS concentration, which was related to the final concentration of ascorbic acid added. Further results indicated that DMTS in SPC was reduced by treatments with sodium benzoate, EDTA or acidic condition (pH 4.6).

SIGNIFICACE Results from current research provide information about the factors influencing the occurrence of DMTS in SPC and such information can be employed to control the level of DMTS and to improve SPC flavor. Furthermore, these results also supply clues about the formation mechanism of DMTS in SPC.