Production of pineapple juice concentrate by microwave vacuum evaporation | |
| Author | Rittichai Assawarachan |
| Call Number | AIT Diss. no.FB-10-02 |
| Subject(s) | Fruit juices, Concentrated Pineapple juice |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Food Engineerin g and Bioprocess Technology, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. FB-10-02 |
| Abstract | In the present study, the potential of microwave vacuum technology was investigated to improve the quality of pineapple concentrate evaporation. A laboratory - scale microwave vacuum evaporation (MVE) system was created. The pineapple juice was concentrated by MVE from the initial concentration of 12.26 0.11 to 61.21 1.47 o Brix at three different microwave power densities (0.451, 0.925, and 1.536 W/g) and under four levels of vacuum pressure (200, 300, 400, and 500 mbar), which provided evapor ation temperature at 55, 65, 75, and 85 o C respectively . Microwave power density significantly influenced the concentration in the exponential form, while it was slightly affected by vacuum. The experimental data was fitted to various empirical models to fi nd the most appropriate representation of the concentration behavior of pineapple juice under vacuum - microwave environment. The empirical models were evaluated by three statistical parameters, the correlation coefficient ( R 2 ), reduce d chi - square ( 2 ), and root mean square error ( RMSE ). The modified Page model gave the highest R 2 , lowest 2 , and minimum RMSE values, which are 0.9955 - 0.9989, 0.0788 - 0.8555, and 0.2475 - 0.8765 respectively, thus this model predicted evapo ration characteristics of the pineapple concentrate more accurately. Based on the multiple regression analysis, the relationship of model constants and coefficient were expressed in terms of the microwave power density and vacuum pressure.Additional imp rovement of the kinetics of color degradation pineapple juice was also investigated during MVE at various microwave power (90, 185, 300 W). Color changes of pineapple juice concentrate were measured by lightness values ( L * ), redness values ( a* ), yellowness ( b * ) values, total color difference ( TCD ), and brown pigment formation index (A 420 ). These were used to determine the color quality loss of pineapple juice. Three kinetic models namely zero order, first order, and combined kinetic model were used to deter mine the appropriate model for describing the change in color parameters. The result indicated that L * and b * can be fitted with both first order and combined kinetic model, while a * can be fitted with only zero order kinetic and TCD followed only the comb ined kinetic model. The results suggested that microwave power has a significant effect on the color change of pineapple juice. It was focused that MVE at 185 W gives the highest quality. The computed values of activation energy were 11.23 ±0.85, 43.55±1.1 5, 30.59±2.75, 24.64±1.11, 41.32±1.24, and 78.18±2.12 kJ/mol for evaporation rate, L * , a * , b * , TCD and A 420 of pineapple juice concentrate, respectively. Various concentration methods namely microwave vacuum evaporation (MVE), microwave heating evaporati on (MHE) and rotary vacuum evaporation (RVE) were investigated for their effects on the evaporation rate, kinetic of color degradation and the rheological behavior of pineapple juice. The evaporation rates of the juice at 60.5 o Brix concentration were obser ved to be 89.07 ± 0.27, 83.67 ± 0.15, and 40.39 ± 0.89 min - 1 for MVE, MHE and RVE, respectively. In relation to temperature and shear rate, the observed appearance viscosities ( a ) decreased as these two parameters increased, for all co ncentration methods. Among the three methods, pineapple concentrate from MHE has higher appearance viscosities values than those from MVE and RVE. However, the Duncan test indicates no significant difference of appearance viscosity between MVE and RVE. The relationship between temperature and total soluble solid (TSS) on rheological behaviors of pineapple concentrate was evaluated at different temperatures of 55, 65, and 75 o C and at various concentrations of 25, 40, and 60.5 o Brix. The experimental data fitt edwell with the power law equation. All conditions provide the value of flow behavior index ( n ) less than 1, which indicates the non - Newtonian or shear - thinning nature ( pseudoplastic ) of pineapple juice. The temperature statistically gives no appreciable effect on the flow behavior index. The flow activation energy of pineapple concentrate varies from 9.14 to 10.13 kJ/mol o K. The result shows that greater the flow activation energy, greater the concentration effect on rheological properties. The effect of c oncentration on the consistency coefficient could be represented by power law model. The single logarithmic function represents the relationship between temperature, concentration and consistency coefficient of pineapple juice concentrate. The accuracy of the established prediction model was evaluated by comparing the experimental data and predicted mathematical model of consistency coefficient . The prediction model gives a high R 2 of more than 0.9991, indicating that this model has very high performance fo r describing consistency coefficient of pineapple concentrate. |
| Year | 2010 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. FB-10-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Athapol Noomhorm |
| Examination Committee(s) | Rakshit, Sudip Kumar;Anal, Anil Kumar;Soni, Peeyush |
| Scholarship Donor(s) | Royal Thai Government Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2010 |