The unsupervised PCA was used to identify potential outliers (according to Hotelling’s ellipse and Leverage plot) and natural clusters ( Tres, Ruiz-Samblas, van der Veer, & van Ruth, 2013). PCA revealed the presence of natural clusters for both geographical origin and cultivar type. BMN 673 Eight samples (3 Jazz, 2 Golden Delicious, and 3 Braeburn) were removed from further analyses after classification as outliers. Partial least squares discriminant analysis (PLS-DA) was conducted using the APCI-MS fingerprint (matrix comprised of 202 samples and 120 variables) to
construct the classification models for the verification of the cultivar and geographical provenance of the clarified apple juices. Log transformation, mean centring and auto-scaling of the spectral dataset was applied prior to conducting the PLS-DA analysis. Pretreatment of spectral dataset allowed the removal of the offset from the data, reduced the heteroscedasticity (skewness) of the data and enable comparison of the spectral data based on an equal basis. The entire dataset was divided randomly into subsets that were used for the development of the classification models (143 samples,
70.8% of the total samples, namely internal validation set) and their validation (59 samples, 29.2%, namely external validation set). A leave-one-out (LOO) selleck kinase inhibitor full cross validation was also used to evaluate the performance of the models constructed using the training Nabilone dataset and the optimal number of principle components (PCs) required to achieve the best classification from the constructed models was also calculated. All statistical treatments of the APCI-MS fingerprint were conducted using Unscrambler version 9.7 (Camo A/S, Norway). Sixteen volatile flavour compounds were detected and identified
in the headspace of the fresh monocultivar apple juices (Table 1), the identified compounds were mainly aldehydes, alkyl-esters, alcohols and carboxylic acids. The compositional flavour profile of the apple juices was found to be in accordance with previously published data in apple juices and fresh cut apple samples (Aprea et al., 2011, Aprea et al., 2012, Dimick et al., 1983, Komthong et al., 2007 and López et al., 2007). Granny Smith apple juices were characterised as having the lowest alkyl-esters concentration (with the exception of ethyl hexanoate) and the highest concentration of cis-3-hexen-1-ol and trans-2-hexenal and intermediate concentrations of hexanal, and 2-methylbutanol. Cis-3-hexen-1-ol and trans-2-hexenal are both related with strong green-grassy flavour notes which together with hexanal are considered the main contributor of green flavour in apples and their derivatives (Komthong, Hayakawa, Katoh, Igura, & Shimoda, 2006). Aprea et al.