MATHEMATICAL MODELS FOR VACUUM-MICROWAVE CONCENTRATION BEHAVIOR OF PINEAPPLE JUICE

Laboratory scale microwave vacuum was designed and developed to concentrate pineapple juice. Pineapple juice was concentrated from initial concentration of 12.26 +/- 0.11 to 61.21 +/- 1.47 degrees Brix at three different microwave power densities (0.451, 0.925 and 1.536 W/g) under four levels of vacuum pressure (200, 300, 400 and 500 mbar). The effect of operating conditions (vacuum pressure and microwave power density) on evaporation rate of pineapple concentrate was investigated to select the most appropriate empirical relationships for the prediction of change in pineapple juice concentration during microwave-vacuum evaporation (MVE) under different conditions. The experimental data were fitted to various empirical models (Lewis, Page, modified Page, Henderson and Pabis, Two terms, Two term exponential, Logarithmic and Wang and Singh) to determine the most appropriate representation of the concentration behavior of pineapple juice under vacuum-microwave environment. The empirical models were compared according to three statistical parameters, the correlation coefficient (R-2), reduce chi-square (chi(2)) and root mean square error (RMSE). The modified Page model gave the highest R-2 and lowest chi(2) and RMSE values and thus, predicted evaporation characteristics of the pineapple concentrate more accurately. Based on the multiple regression analysis, the relationship of model constants and coefficient was expressed in terms of microwave power density and vacuum pressure. Validation of the selected model was determined with the experimental data. The result showed the suitability of the modified Page model in describing evaporation rate of pineapple concentrate.