Investigations into the pre-cooling rates of apples in controlled atmosphere storage chambers

Abstract: The objective of the present investigation was to model the rate of cooling of apples in a fruit storage unit using forced air pre-cooling. Apples of Royal, Red, Rich-a-red and Golden Delicious varieties were procured from Shimla and Royal Delicious from the Kinnaur region of Himachal Pradesh, India. Apples were transported in refrigerated and non-refrigerated vehicles. After grading and sorting on a fully automatic machine, the apples were subjected to a cooling process. Apples were placed in perforated plastic crates and stacked in a controlled atmosphere chamber of 720 m³ capacity. Temperature profiles of apples were recorded with a programmable logic controller connected to sensors. The effect of variety, initial apple temperature, and fruit quantity per chamber on the cooling rate were investigated. Initial fruit temperature significantly affected the cooling time. The apple variety did not significantly affect the cooling time, except that slow cooling was observed for golden delicious in the last cooling stage. Varied masses of apples resulted in a proportionate increase in cooling time. Cooling times were 132, 113, 78, and 65 hours for a mass of 165, 150, 140, and 130 Metric Tons (MT), respectively. Correlation coefficients ranged from 0.970 to 0.979 for different varieties. The rate of cooling with apple mass was modeled with linear, exponential, and polynomial and found to best fit with the exponential model with R² values of 0.99, 0.96, 0.95, 0.966 for 165, 150, 140, and 130 MT, respectively. The time taken to cool 150 MT of apples was 97, 114, and 147 hours from an initial temperature of 35.2, 28.4, and 15.6^oC, respectively. The drop rate was exponential, with R² values in the range of 0.936 to 0.973.