Abstract
ABSTRACTIn the first part of this study, pineapple juice concentrated by microwave vacuum evaporation (MVE) and rotary vacuum evaporation (RVE) process were compared in terms of evaporation rate, electrical energy, color and apparent viscosity (µa). MVE provided 2.21 times higher evaporation rate and used 5.32 times less energy than RVE. Pineapple juice concentrates from MVE gave better color quality than from RVE at the same evaporation condition. However, there was a significant difference inµa of pineapple juice concentrates between the two evaporation methods. The second part was to investigate the effect of temperature and total solid soluble (TSS) on rheological behavior of concentrate pineapple juice from MVE. The values of consistency coefficient (k) were in the range of 23.855–257.771 Pa·sn, which decreased with the increasing temperature and concentration. The effect of temperature on k was described by Arrhenius model. The activation energy of k was in the range of 9.74–10.13 kJ/mol K. The power equation showed that the consistency coefficient non‐linearly increased with an increase in concentration. The effect of temperature and concentration on k of pineapple juice concentrate could be determined in terms of single logarithmic. Predicted models were developed to calculate k as a function of temperature and concentration. The result of validation showed the suitability of the mathematical model prediction in describing k of pineapple juice concentrate.PRACTICAL APPLICATIONSVacuum evaporation process has the advantage being of highly efficient technology and provides high product quality. The vacuum evaporation is a unit operation in fruit juice processing by which fruit juice is evaporated at sub‐atmospheric pressure. Under subatmospheric pressure, the operation can be completed at lower temperature, and hence produce higher quality of concentrate juice than a conventional process, which is conducted at atmospheric pressure. In this study, the effect of heating system of vacuum evaporation between external heating by rotary vacuum and internal heating by microwave vacuum on juice quality and evaporation performances was investigated. For the food industry, characterization of flow behavior is essential for determining the processing operation and transport phenomena of liquid food, and flow behavior parameters are defined as a set of parameters indicating the food quality indexes. The relationship of temperature and concentration of pineapple juice on rheological behavior of pineapple concentrate was determined to develop mathematical model for predicting the change of flow behavior during the process.
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