Ginger sizes are irregular and therefore necessitated sorting to enhance processing operations. Washed ginger rhizomes were graded according to three commonly occurring uniform sizes (big, medium and small) initially, using a Vernier Calipher. The three sizes were whole-dried separately at the same conditions and their drying rates were found to be inversely proportional to the size grades. The fresh ginger rhizome size grades as well as their milled powders were subjected to aroma discrimination by sensory evaluation and an Electronic nose in order to identify possible headspace aromatic differences, among the three ginger grades. Principal component analysis (PCA) maps of the data showed that the electronic nose successfully discriminated the aroma or volatile compounds of the three ginger grades in different clusters for each group, suggesting that they vary in chemical composition. Contrary to expectations, the flavour variations of the three ginger grades could not be detected by the human nose. The essential oil yields of the fresh and dried ginger samples were done. Characterization and quantification of the volatile components was conducted using a Shimadzu Gas chromotograph equipped with a flame ionisation detector and integrator, while identification of the compounds was conducted with a Mass Spectrometer selective detector.
Electronic nose successfully discriminated fresh ginger rhizomes graded according to sizes into small, medium and big, indicating different positioning of the headspace volatiles of the three ginger grades, in a pattern of signals from the 12 metallic oxide sensors. The signals were presented in coordinates and grouped together in a cluster of specific and separated coordinates for each grade (see fig. 1) in both the fresh and powdered ginger samples. This is an indication of the likely difference in chemical constituents and concentration of the volatiles of big, medium and small size grades.The essential oil yield reduced with increase in rhizome size, while the concentration of of chemical constituents of the essential oils increased with decrease in size grades. Backed with these findings, a manual hand grader was designed and fabricated by the author.