Effects of microwave heating on quality attributes of pineapple juice

The effects of microwave heating on the quality attributes of pineapple juice were investigated in this study. The experiments were conducted based on the central composite design of response surface methodology to analyze the relationship of mass evaporation rate at different initial masses of pineapple juice (100-250 g) on the physiochemical properties of pineapple juice. The results showed to have significant parabolic increment, except the sugar content of pineapple juice behaved linearly with the mass evaporation rate. The diffusion of moisture was well explained by the Fick's second law. The modified Arrhenius model was used to estimate the activation energy (1.02-3.20 kW/kg). The drying model of Henderson and Pabis could fit well into the kinetic behavior of concentrating pineapple juice. The change of quality attributes, particularly browning effect and proteolytic activity could be minimized using low initial mass of juice and heated at short duration for high evaporation rate. Practical applications Microwave oven has been widely used for food heating and juice concentrating because of its convenience in fast heating. Juice is concentrated to minimize storage and transportation cost. However, overheating could change quality attributes of pineapple juice, especially the browning effect and proteolytic activity, as well as the ratio of sugar-to-acid affecting pineapple taste. The findings revealed that small volume and short heating duration could reduce the change of quality attributes, even at high evaporate rate. The parameters vary according to the water and sugar content which affect the heat capacity of juice. Large volume limits moisture diffusion as explained by Fick's second law. The monolayer drying model of Henderson and Pabis could fit to the concentrating process satisfactory. Microwave heating could be used to concentrate pineapple juice with minimal effects on quality attributes, if small volume at shorter time was used in the process.