Multivariate modelling of odour profiles and volatile compounds in apples

It is known that perceived odours are mainly the result of mixture of odorants [1] and the components of a mixture may lose their individual identity and a new mixture with a specific odour quality could emerge. Aim of this study was to investigate the interaction between the perceived odours in apple and the complex mixture of volatiles compounds released from fruit by a multivariate approach which is necessary because perceived odour is, in general, evoked by the combination of several compounds. Chemometric techniques, like as Principal Component Analysis (PCA) and Partial Least Square (PLS) were applied to two data sets related to 18 different apple varieties: one based on odour profiling (through both ortho-nasal or retro-nasal evaluation) performed by a trained panel (15 judges) and the other based on SPME-GC-MS analysis of volatile compounds. The sensory panel characterised the apples through 31 descriptors for odour (by smelling the sample) and flavour (by tasting it), while 72 compounds were quantified by GC analysis. In PCA scores plots apple varieties were grouped similarly using either sensory profiling or volatile compounds suggesting a relationship between the two determinations. Regression models based on PLS allowed the identification of those compounds highly contributing to most of the odours arising from the complex mixture of volatile compound as released by apples. For example the most influent compounds contributing to fruity attributes resulted to belong to the class of acetate esters: in the case of “pear” and “banana” descriptors, the models are built using the same compounds but with different weights. Thus, the different perceived odours are due to their relative proportions abundance rather than their presence/absence. In conclusion, appropriate chemometric analyses may help into the elucidation of the interaction between the perceived odours from real food and the complex mixture of volatiles compounds released. [1] Le Berre et al. (2008). Just noticeable differences in component concentrations modify the odor quality of a blending mixture. Chemical Senses, 33, 389 -395