Direct‎ ‎Mathematical‎ ‎Models‎ ‎for‎ ‎Estimating‎ ‎the‎ ‎Shelf‎ Life of Second‎- ‎and Zero-Order Degradation Relationships of Food and Drugs

‎Recently‎, ‎a direct model for evaluating the shelf life of lemon juice‎, ‎depending on the loss of ascorbic acid concentration with time was derived by Al-Zubaidy and Khalil (Food Chem‎. ‎101 (2017) 254–259)‎. ‎By using this model‎, ‎one could directly estimate the expiration date at any residual ratio and any specific temperature of the first-order degradation rate‎. ‎But‎, ‎in general‎, ‎the kinetic model for degradation process is not limited to first-order reactions‎, ‎as it could be second-‎, ‎or zero-order according to the experimental data‎. ‎Therefore‎, ‎two direct models have been developed to evaluate shelf life based on these orders‎. ‎These models have been verified using previously published results for vitamins C (zero-order) and D3 (2nd-order) in coconut powder‎. ‎The results indicate that the prediction of shelf life for food‎, ‎drugs and so on can also be evaluated directly for second-‎, ‎and zero-order degradation processes using the developed models in the same way to that of pre-published for first order‎. ‎A characteristic feature of the presented degradation orders is that the input data for determining the rate constant must be in percentage (\%) rather than the real concentration in contrast to that of first order‎. ‎It was concluded that the use of the derived equations avoids the complications resulting from changing the unit of the rate constant with the change in the reaction order‎. ‎In addition to the gained simplicity when dealing with the developed models‎.