Investigation of the factors affecting the electrical conductivity of selected fruit juices during ohmic heating | |
| Author | Lamsal, Buddhi Prasad |
| Call Number | AIT Thesis no. AE-94-10 |
| Subject(s) | Electrochemistry Fruit juices--Pasteurization |
| Note | A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. AE-94-10 |
| Abstract | In the present study, electrical conductivity measurements were made directly during the ohmic heating process itself. Simple ohmic heating test cells were constructed of 38.5 mm ID acrylic pipe. Initial tests with the cells of different dimensions showed some variations in measuring the conductivity values of reference liquid (0.1 M NaCl solution). Based on the performance data, 10 cm long test cell was selected for conductivity measurements. The variations in electrical conductivity of orange, pineapple and tomato juices were investigated and modeled in terms of the easily measurable juice properties like total soluble solids and pH. Tests were conducted for juices obtained from the oranges at different maturity levels. In addition, the variations in the electrical conductivity were investigated due to the storage of juice and fruit, pre-heating effects and market conditions. In case of orange juices from fruits at different maturity levels, minimum conductivity value at 25 °C was 0.392 Sim for 9 months old fruits and maximum was 0.475 Sim for juice from 12 months old fruit. The differences in heating rates of the juice were explained by variations in total soluble solids and pH. Fresh fruit juices when stored at ambient conditions started to spoil after about 6 hours and could be monitored by variations in electrical conductivity. Considerable differences were observed in spoilage patterns of fruit juices for fresh unheated and pre-heated conditions. However, different methods of juice pre-heating like ohmic heating and conventional water bath heating didn't result in considerable differences in electrical conductivities. The electrical conductivity values of orange juice from fresh fruits showed least variations within 10 % of the mean value of 0.343 Sim at 25 °C and 0.971 Sim at 80 °C. Among the three fruit juices tested, tomato had highest conductivity followed by orange and pineapples in that order at a given temperature. At 25_ °C, mean conductivity values for pineapple and tomato were 0.295 Sim and 0.504 Sim with maximum variations in samples being about 20 % and 18.3 % respectively. Fresh orange juice conductivity showed least variation within samples of about 10 % at 25 °C. The variations in electrical conductivity of all juices were observed to be higher as temperature increased. The observed electrical conductivity values for the three juices in fresh, diluted or concentrated forms were modeled in terms of temperature and total soluble solids. Finally, the variations in electrical conductivity of mixed fruit juices were also investigated. |
| Year | 1994 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. AE-94-10 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Jindal, Vinod K. |
| Examination Committee(s) | Sarath G. Ilangantileke;Athapol Noomhorm; Vincent, Jean-Claude |
| Scholarship Donor(s) | The Royal British Government |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology |