2.2.2. Determination of ascorbic acid The spectrophotometric method (Pepkowitz, 1943; Robinson & Stotz, 1945) for determination of ascorbic acid was performed by using Unicam UV–VIS (UV-2) spectrophotometer at a wavelength of 500 nm against xylene. The loss of ascorbic acid in citrus juice concen- trates was calculated by using the standard equation for a first-order reaction given below:
lnC ¼ lnC0 kt
where C, the concentration at time t; C0, the concentra- tion at time zero; k, the first-order rate constant; t, the storage time (week).