Enzymatic browning of muscadine grape products
1995
Lamikanra, O.
Muscadine grape polyphenoloxidase (PPO) was purified by filtration through a 0.2 micro membrane filter and by HPLC. Reactivity of the active fraction from the "Welder" muscadine grape per unit protein increased 33-fold over the values recorded for the crude extract. Electrophoretic analysis and activity stain showed that the enzyme in this cultivar displayed a single band with a molecular size lower than the non-PPO proteins. Optimum pH for activity was 4.5, and the enzyme was stable at temperatures up to 30 degrees C. Browning of muscadine wine does not appear to be significantly enzyme catalyzed. Total phenol content of the wine was unaffected by the browning process which was effectively inhibited by potassium metabisulfite. Tiron and EDTA had no significant effect, and diethyldithiocarbamate slightly retarded the rate of browning. The reaction appears to proceed by way of a heterolytic reaction pathway that does not involve phenolic compounds, possibly a Maillard-type reaction. Enzymatic catalyzed browning of muscadine grape products thus appear to be limited to juices and non-wine products of the grape.
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