Discrimination amongst Alliums using an electronic nose

Pyruvic acid content determination and, to lesser extents, thiosulphinates determination and organoleptic tests are used for assessing the eating characteristics of onions and other Allium spp. Each of these methods has inherent limitations, especially when large numbers of samples are to be evaluated. With a view to developing a more convenient quality evaluation method, an electronic nose was used to discriminate flavour and aroma characteristics amongst garlic, leek, shallot, bulb onion and spring onion. Differences in relative sensor response to headspace volatiles over macerated samples of these five different Allium types were recorded. Principal Component Analysis (PCA) showed some separation among the five types. PCA and Mahalanobis' D-2 statistic suggested similarities in headspace volatiles for shallot, spring and bulb onions and differences for leek and, especially, garlic. Multiple linear regression analyses (Y = alpha + beta(1)X(1) + (beta(1)X(2); N-(X,N- Y) = 5) of the first two principal component values (PCA 1 [X-1] and PCA 2 [X-2]) accounted for not less tan 90% of the total variation in pyruvic acid concentration (Y1), total soluble solids content (Y2) and percentage dry matter content (Y3) of the Allium types. These relationships suggest that electronic nose discrimination was on the basis of quality characteristics that relate to Allium flavour. This work has shown that the electronic nose has potential for flavour characteristic-based discrimination amongst Allium types. Future work will explore this potential within a single Allium spp.