Inhibitory effect of caramelisation products on enzymic browning

Caramelisation products (CP) were prepared by heating a sucrose solution (1.47 M) at 200 °C under various conditions to study the inhibitory activity of CP on enzymic browning. Inhibition by fractionated CP was measured by enzymic kinetic analysis of polyphenol oxidase (PPO) and o-dihydroxyphenols, such as 4-methylcatechol (4-MC), catechol, caffeic acid and DL-3,4-dihydroxyphenylalanine (DL-DOPA). Colour intensity of CP produced at pH 4 was higher than that produced at pH 6 and pH 8, and increased with heating time. The reducing power of CP and their inhibitory effect on enzymic browning increased with prolonged heating and with increased amounts of CP. CP heated at pH 4 and pH 6 for 90 min gave a relative inhibitory activity on enzymic browning of 85.8% and 72.2%, respectively. One of two CP fractions obtained by Biogel P6 column chromatography had an inhibitory effect on enzymic browning, with the fraction having a molecular weight of 1000–3000 showing the highest activity. Based on the double reciprocal plot of the PPO and 4-MC system, the active fraction of CP appeared to be a competitive inhibitor and was most effective on inhibition of catechol browning, followed by caffeic acid and DL-DOPA.