Extraction and activity determination of polyphenoloxidase in coffee

Abstract

Polyphenoloxidase (PFO) activity has been used to indicate the quality of coffee beverage. A traditional extraction method used for coffee polyphenoloxidase was compared to another in which phenol oxidation was avoided and phenols were eliminated by exclusion chromatography. An intermediate method was also tested. Activities were obtained by spectrophotometry, which is commonly used for coffee PFO determination, and O2 consumption. The traditional extraction method and spectrophotometry are inacurate to measure PFO activity since there is a significant interference of phenols present in the extracts. Consequentely, the data reported in the literature are not reproducible. PFO activity differentiated Soft coffee from Hard and Rio, but not between the lost two. Soft coffee presented higher PFO activity. For an accurate activity determination, antioxidants and phenol complexation is essential during extraction, as well as their elimination by exclusion chromatography. However, using this procedure and O2 consumption, PFO activity could still not differentiate the three coffee qualities, except Soft from the other two. Instead of 3,4 - dihydroxyphenylalanine, it is suggested that chlorogenic acid (5-caffeoylquinic acid) should be used as substrate.