Лако-красочные материалы — производство

Principal component analysis (PCA) is another technique used; it works differently, but the resulting map can often look very similar. The analysis works using a process of identifying correlations between the different variables used in describing the data (i. e. the sensory descriptors used in the profiles). It then searches for the combination of variables that best describes the maximum amount of variation in the data, and draws an axis through the centre of the group of observa­tions, so that the sum of the residual distances is minimized; this is called the first principal component. The second principal component is then drawn at right angles to the first and explains the maximum amount of the remaining variation.

In addition to depicting the associations among the original vari­ables, PCA can be used to describe the relative ‘locations’ of the measured samples. A plot of principal component scores for a set of products reveals groupings of the samples that may not have been readily apparent from the original data.

Figure 8.4 is a multidimensional scaling map derived from the profiling data shown in Figure 8.3. With only seven samples to compare, this is a very simple map; however, it serves to illustrate the kind of information that can be derived from this type of analysis.

The samples are grouped so that those that are most similar in odour character are closest together on the map (e. g. Lilial® and Bourgeo — nal®), and those that are most different are furthest apart (e. g. cycla­men aldehyde and Lyral®). The arrows indicate the direction of increasing perception of the odour characteristics shown. Only the odour characteristics that significantly correlate with the distribution of the samples across the map are shown; these are the characteristics that are responsible for the systematic differences between the samples.

All the materials were perceived to be floral and muguet in character, so these characteristics are not shown on the map. Cyclamen aldehyde, Lilial® and Bourgeonal® are the most fruity of the samples and are grouped together on the right-hand side of the map, while Lyral® and

hydroxycitronellal are the sweetest materials and Mayol® is the most herbal.