Vitamin C (ascorbic acid) is one of the most important and popular vitamins and is contained in most fruits and vegetables; the problem with vitamin C is its easy degradation during pre-treatment and storage. In this study, kinetics modeling of degradation of ascorbic acid (Vitamin C) in commonly consumed vegetables; lettuce, cabbage and carrot under room and fridge temperatures ranges of (17.5 21)0C and (6.5 9.5)0C respectively were investigated and samples after storing at various room and fridge temperatures and timings were prepared for analysis. High Pressure liquid chromatographic (HPLC) was used for determination of the AA of the vegetable samples which consisted of an isocratic elution procedure with UV-Visible detection at 245nm.The rate constants and half-lives were calculated using the integrated law method. Activation energy and forecast were determined using Arrhenius equation and time series analysis. Degradation of ascorbic acid in the commonly consumed vegetables under the same pretreatment procedures followed the first-order kinetic model, as the average coefficient of determination (R2-value) was greater than 0.91. The rate constant of ascorbic acid degradation for Lettuce, Cabbage and carrot under the same room and fridge temperature conditions of 17.50C and 6.50C were 0.7806,0.1141 and 0.2634day-1 and 0.5165, 0.3214, 0.2273 day-1respectively. Their half-lives were 0.8879, 6.0749,2.6315day1 and 1.3420, 2.1566 and 3.0494 day-1, activation energies; 0.48575, 4.8353, 1.4519 Kcal/mol and 19.4052, 23.3180, 25.7018 Kcal/mol in room and fridge temperatures respectively. The forecast in 66 days at room temperature of 17.5 0C, cabbage exhibited 0.0051 mg/100g while carrot in 28days at fridge temperature of 6.5 0C exhibited 0.0066mg/100g. The proposed models were ln(C) = ln( C0) - 0.7806, ln(C) = ln( C0) - 0.1141, ln(C) = ln( C0) - 0.2634 at room temperature((17.50C) and ln(C) = ln( C0) - 0.5165, ln(C) = ln( C0) - 0.3214, ln(C) = ln( C0) - 0.2273 at fridge temperature (6.50C). The most appropriate vegetable under the room temperature drying and storage is the cabbage and carrot at fridge temperature storage. This is because their rate constant depicted from the model equations was lower, half life longer, activation energy higher and forecast longer.
Key words: HPLC, Lettuce, Cabbage, carrot, Room and Fridge Temperature, Ascorbic Acid, Rate Constant, Activation Energy, models, Forecast
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