In ready-to-eat salads, a low pH is often applied in the salad dressing. The effect of pH on the colour change of blanched-frozen-and-thawed broccoli was studied. Different acids were used to achieve the pH values in buffer solutions. A model on chlorophyll degradation in fruits and vegetables was developed based on a simplification of existing knowledge. From integral non-linear regression analysis, it was concluded that the pH gradient at the boundary between product and buffer solution had a marked effect at low pH values. Furthermore, based on the analyses and the obtained residuals, another colour degrading process was revealed that gradually increases in relative importance at higher pH values. The effect of the five acids applied could be attributed to a single proportionality factor, probably related to the hydrophilic nature of the acid applied. The statistical analysis showed a percentage variance accounted for (R2adj) of more than 99.6ÐThe apparent rate of colour degradation was found to be linearly related to the concentration of hydrogen ions. ? 2001 Elsevier Science Ltd. All rights reserved.