Quality of dry ginger (Zingiber officinale) by different drying methods.

Ginger rhizomes sliced to various lengths of 5, 10, 15, 20, 30, 40, 50 mm and whole rhizomes were dried from an initial moisture content of 81.3 % to final moisture content of less than 10 % by various drying methods like sun drying, solar tunnel drying and cabinet tray drying at temperatures of 50, 55, 60 and 65 °C. Slicing of ginger rhizomes significantly reduced the drying time of ginger in all the drying methods. It was observed that drying of whole ginger rhizomes under sun took the maximum time (9 days) followed by solar tunnel drying (8 days). Significant reduction in essential oil and oleoresin content of dry ginger was found as the slice length decreased. The important constituents of ginger essential oil like zingiberene, limonene, linalool, geraniol and nerolidol as determined using a gas chromatography was also found to decrease during slicing and as the drying temperature increased. The pungency constituents in the oleoresin of ginger like total gingerols and total shogoals as determined using a reverse phase high performance liquid chromatography also showed a decreasing trend on slicing and with the increase in drying temperature. It was observed from the drying studies that whole ginger rhizomes dried under sun drying or in a solar tunnel drier retained the maximum essential oil (13.9 mg/g) and oleoresin content (45.2 mg/g) of dry ginger. In mechanical drying, the drying temperature of 60 °C was considered optimum however there was about 12.2 % loss in essential oil at this temperature.