The effects of operating conditions on pomegranate juice quality during the Ohmic heating process | |
| Author | Theradech Lerdvilaianunt |
| Call Number | AIT Thesis no.FB-09-03 |
| Subject(s) | Pomegranate Cookery (Pomegranates) |
| Note | A thesis submitted in partial fulfi llment 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. FB-09-03 |
| Abstract | In the past few years, the dietary sources of antioxidant phenolic have been increasingly studied. Pomegranate is one of the foods reported to have considerably high antioxidant activity (Gil, 2000). However, when foods undergo a heating process, the quality may be reduced due to various reasons including uneven heat distribution. Such drawbacks usually take place when more conventional heating methods are used as they tend to require longer processing time. Ohmic heating, which is a thermal processing technique for food material, which exhibits the characteristic of an electrical resistor, that generates heat by passing alternating current through a food particle resulting in rapid and uniform heating, may be effectively used in order to solve such problems. This study aims at investigating effects of operating conditions of the ohmic heating process on three qualities of pomegranate juice, namely the electrical conductivity (EC), color, and antioxidant activity. Three static ohmic heating units were constructed from a cylindrical acrylic 38.5 mm in outside diameter along with the three inter-electrode gaps of the test cells of 100 mm 120 mm, and 150 mm in length. Based on the performance data, 10 cm long test cell was selected for the electrical conductivity determination of pomegranate juice. The findings show that EC is affected by voltage gradients, temperature and total soluble solid contents. The voltage gradients have influence on the electrical conductivity of pomegranate juice. The ranges of the electrical conductivity values at three voltage gradients, namely 10V/cm, 12V/cm, and 15 V/cm were 0.56 to 1.64 S/m, 0.65 to 1.74 S/m and 0.68 to 1.75 at the temperature range of 30°C-80°C. Moreover, the electrical conductivity values of pomegranate juice linearly increased with the increase of total soluble solid and the correlated temperature at all voltage gradients, but fluctuation could be observed with 10 V Icm. At 10.5°Brix, 12.5°Brix, 14.5°Brix, the electrical conductivity increased from 0.63 to 1.53 S/m, from 0.65 to 1.74 S/m, and from 0.81 to 1.91 S/m respectively. Using the newly constructed mathematical model, the results show that the electrical conductivity values are more influenced by the total soluble solid than they are by the temperature at all three voltage gradients. All three mathematical model the model's prediction of 12 V/cm was the most accurate when compared with those of 10 V/cm and 15 V/cm. The Hunter Lab D25-PC2 colorimeter (Hunter Laboratory) was used to measure the color of pomegranate juice. The CIELAB parameters of a*, b* and L * values tended to decrease when the treatment temperature increased at 40°C, 50 DC, 60°C, 70 DC, 80 DC. Consequently, the total color different values (TCD) tended to increase when the treatment temperature and voltage gradients increased. The decrease in L * and a * values usually result in the darker colors of pomegranate juice. Finally, the 2, 2-diphenyl-l-picylhydrazyl radical (DPPH) was generally used to the free radical scavenging activity of natural antioxidants. the findings indicate that voltage gradients and temperature have direct effects on antioxidant activity as the former seem to raise the amount of the latter. |
| Year | 2009 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. FB-09-03 |
| Type | Thesis |
| 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;Salokhe, Vilas M.; |
| Scholarship Donor(s) | Royal Thai Government (RTG); |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2009 |