Discoloration of coleslaw is caused by chlorophyll degradation

Coleslaw tissue was extracted and analyzed spectrophotometrically for chlorophyll and its derivatives to determine their relationship to tissue discoloration and/or browning at 5 degrees C under reduced oxygen conditions. A general rapid decrease in chlorophyll a and b was noted after 2-3 days, with a concomitant increase in the amount of pheophytin a and b. The pheophytin was then converted to pheophorbide a and b, which resulted in gray/brown coleslaw after 12-15 days of storage. Polyphenol oxidase activity in cabbage was determined to be very low (81.6 units/g fresh tissue), whereas chlorophyllase activity was very high (23 nmol/min/g fresh tissue). This result suggested that the gray/brown pigments formed were mainly the result of chlorophyll degradation. No change in pH (similar to 4.6) was observed during storage. A substantial change in the color of the product was, however, observed as analyzed by blue light reflection with an Agtron colorimeter. The pathway for chlorophyll degradation in coleslaw at 5 degrees C was determined to be chlorophyll --> pheophytin --> pheophorbide. The rapid conversion of chlorophyll to pheophytin suggests rapid acidic removal of Mg2+ upon addition of dressing, whereas the rather slow conversion of pheophytin to pheophorbide suggests an enzymatic reaction that is possibly mediated by the enzyme chlorophyllase.