36E-78

T. THONGSOOK and D. M. Barrett. Dept. of Food Science and Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616-8598

Peroxidase (POD) is well known to recover its activity after heat treatment and cause significant deterioration in quality of various processed foods. This study attempts to investigate the detailed mechanisms involved in the heat inactivation and reactivation of this enzyme. Absorption spectroscopy, far-UV Circular Dichroism (CD)spectroscopy and enzymatic assays were carried out to study the reactivation following thermal denaturation of POD from broccoli and horseradish (HRP) at pH 7.0. The change in the far –UV CD corresponds to changes in the overall secondary structure of the enzyme, while the absorption spectrum in the 400 nm region (Soret region) corresponds to changes in the tertiary structure around the heme in the enzyme. Reactivation characteristics differed for Acidic (A), Neutral (N) and Basic (B) broccoli POD isoenzymes. The extent of reactivation varied from 0 to 50 % depending on the isoenzyme and heating conditions (temperature and time). The denaturation temperature allowing for maximum reactivation was 90^o C for A and HRP and 70^o C and 80^o C for B and N, respectively. Heat treatment disrupted polypeptide chain structure but the structure was reformed completely upon removal of heat for most treatments studied. Heat treatment resulted in a decrease in the Soret band absorption. Rapid restoration of the structure around the heme occurred upon removal of heat. Further structural alterations in the region around the heme occurred to a greater extent over long incubation at ambient temperature for the enzyme treated at high temperatures for short times compared to those treated with low temperatures for long times. Effect of BSA and pH were also investigated. A general mechanism for the reactivation of POD following heat treatment is discussed. This study provides basic understanding of this complex process, which could be useful for fruit and vegetable processing industries.

Session 36E, Fruit & Vegetable Products: General
8:30 AM - 12:00 PM, Monday AM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana