A study of the pungency of ginger grown in Queensland

Ginger (Zingiber officinale) is a common ingredient in culinary dishes and has also been exploited for its medicinal properties for centuries. As one of the most significant spices in the Western world, with a history of usage from time immemorial in both China and India, the importance of evaluating ginger in terms of product quality cannot be underestimated. Ginger derivatives such as ginger powder, syruped ginger, volatile oil and oleoresin all show increasing levels of international trade, both industrially and retail-wise. Growing world demands for the development of a highly aromatic, flavoursome and pungent ginger means research will greatly benefit burgeoning domestics markets as well the exporting industry. An objective of this research project, in analyzing the pungent principles of ginger, was to develop a method of extracting oleoresin from fresh ginger using supercritical fluid-CO2. The application of heat is therefore avoided, reducing the degradation of the pungent principle. A further objective was to develop a technique to quantify the common pungent principles of ginger by high performance liquid chromatography and to use this to investigate the pungency of ginger based on the pungent principles (6-, 8- and 10-gingerols, 6-, 8- and 10-shogaols and zingerone) with respect to harvest time, growing location, ginger variety and storage conditions. In pursuing the objectives of this study, a methodology for the extraction of oleoresin from fresh ginger by supercritical fluid-CO2 was established. This may be of significance to the ginger industry as the oleoresin contained the maximum amount of the common pungent principles, although its actual composition was influenced by the temperature and pressure of the SF-CO2. Results indicated that the best harvest time, in terms of oleoresin yield and ginger with highest pungency score on a fresh and dry weight basis, was during April-May and March-April respectively. Soil types and the water regimes influenced the pungency, oleoresin and pungent principle levels of gmger. The different varieties of ginger produced differing oleoresin yields and pungency levels, the highest quality being the Queensland ginger. It was found that storage was detrimental to the pungent principles of ginger. There was a decrease in the amount of 6-, 8- and 10-gingerols on a dry weight basis, possibly due to the reaction with the acids in the ginger. Different storage conditions, such as temperature and duration, yielded different results on the basis of pungency. It is highly recommended that further investigation be undertaken in order to determine the best environment for storing fresh ginger. An additional study using IR spectroscopy produced promising results. Fresh ginger and ginger stored at 4°C, 12°C and 24°C were differentiated by FTIR in the region of 1800 - 1550 cm-1 and this simple and quick technique made IR spectroscopy a useful method of testing a large number of oleoresin samples