Rheological behaviour and colour changes of ginger paste during storage

Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high-density-polyethylene containers and stored at 5 +/- 1 and 25 +/- 1 degreesC for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20-80 degreesC. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s(-1) in 3 min, followed by a steady shear at 200 s(-1) for 3 min and finally decreasing linearly from 200 to 0 s(-1) in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel-Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol(-1). The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 +/- 1 degreesC in polyethyleneterephthalate or glass containers.