Mathematical modeling of oxygen levels in a controlled atmosphere store for preservation of apple fruits

Abstract

Apple fruit preservation for long periods (up to eight months) needs low temperature, high humidity, low oxygen and high carbon di-oxide levels around the fruits. Controlled Atmosphere (CA) storage chambers can extend the shelf life of fruits by controlling the respiration rates of fruits. To achieve low respiration, low oxygen levels need to be created in the sealed chambers. A pressure swing adsorption nitrogen generator is used to generate 99% pure nitrogen, which is pumped into the sealed fruit chambers after achieving required temperature. Oxygen level of 20.8% is slowly lowered to 1 to 2% level. Storage chamber of 720 m3 is selected to conduct the kinetic study of lowering the oxygen level. Quantity of apples stores per batch is 150 metric tons. Time taken to lower the oxygen to required levels is 24 h. Rate of oxygen reduction is modeled mathematically and fitted to three mathematical equations, viz. exponential, second order polynomial and third order polynomial. Exponential model could explain the behavior with R2 value of 0.966. R2 value of 0.978 found for second order polynomial model. Best fit of predicted and experimental values found with polynomial model of third order with R2 value of 0.998. The modeled data will be useful for prediction of oxygen levels for both controlled atmosphere and modified atmosphere requirements for different fruits.