Ryan-Stoneham and Tong [117] studied the degradation kinetics of chlorophyll in peas as a function of pH. The objective of their investigation was to determine the kinetic parameters of chlorophyll degradation as a function of pH in the constant pH kinetic reactor at pH of 5.5, 6.2, 6.8 and 7.5 and develop a mathematical model that related the rate
constant of chlorophyll as a function of temperature and pH. They concluded that the pH of vegetables during thermal processing is not constant. The magnitude of pH changes is dependent upon the type of vegetable, the initial pH and the time–temperature history of the vegetable of interest (whether high-temperature short-time or low-tem- perature long-time). The prediction of chlorophyll con- centration would be more accurate by treating pH as a variable and by knowing the chlorophyll degradation kinetics as a function of pH. A simpler approach can be applied to improve the accuracy of the prediction assuming the pH of the vegetable remained constant at an average pH value (between the initial and final pH values) and the rate constant at that average pH is known for a specified pro- cessing condition and product.