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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Crop Bioprotection Research » Research » Publications at this Location » Publication #78185
Title: SOYBEAN LIPOXYGENASE IS ACTIVE ON NONAQUEOUS MEDIA AT LOW MOISTURES

Author
item Gardner, Harold
item Grove, Marilyn
item KELLER, NANCY - TEXAS A&M, COLLEGE STN

Submitted to: Annual Meeting and Expo of the American Oil Chemists' Society
Publication Type: Abstract Only
Publication Acceptance Date: 5/11/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Soybean extracts (pH 7.5) and linoleate (pH 7.5) were mixed separately with cellulose and then dried overnight by vacuum desiccation. The dried cellulose/linoleate and cellulose/soybean composites were mixed just prior to incubation at four relative humidities ranging between 52% and 95%. Controls were treated the same, except the soybean extracts were inactivated by heating prior to mixing with cellulose. Oxidation of linoleate occurred at all relative humidities compared to much lower values of the controls. The oxidation rate at 95% relative humidity was greater than obtained at lower humidities. Little difference could be seen between the oxidation rates obtained at humidities lower than 95%. Because it was determined that the cellulose composite required about 24 hours to achieve moisture equilibrium, experiments were also completed after an additional overnight equilibration at the designated relative humidity before mixing the cellulose/linoleate with cellulose/soybean extract. Under these conditions, the initial rate of oxidation was markedly increased compared with the samples incubated immediately after drying, and there was a notable positive correlation in oxidation rate with increasing relative humidity. That the oxidation was principally enzymatic was shown by chiral analysis of the linoleate hydroperoxides formed. The main product was 13S- hydroperoxy-9Z,11E-octadecadienoic acid followed by significant percentage of 9S-hydroperoxy-10E,12Z-octadecadienoic acid. Because the "dry" reaction products were somewhat more racemic than a short-time aqueous incubation of soybean extract with linoleate at pH 7.5, autoxidation appeared to be initiated by the lipoxygenase reaction in dry media. The results to defense of seeds from attack by storage fungi will be discussed.