As is detailed in the Fulvestrant nmr PCA bi-plot (Fig. 1) the apple juice extracted
from Golden Delicious exhibited a similar flavour profile to that of Granny Smith with high concentrations of volatile compounds related with green-grassy notes (trans-2-hexenal and 1-hexanal and cis-3-hexenol) and low concentrations of acetates. The latter has been also confirmed by Ting et al. (2012) who reported lower concentrations of acetates in the headspace of fresh cut Golden Delicious samples compared to other apple cultivars i.e. Red Delicious, Jonagold or Fuji. Moreover, the aldehyde to alcohol ratio is indicative of ripeness, as aldehydes can be metabolised to alcohols and subsequently esterified with the present carboxylic acids (Defilippi, Dandekar, & Kader, 2005). Based on GC–MS data, the aldehydes and their corresponding
alcohols ratios were higher for Golden Delicious and Granny Smith juices implying a lower level of ripeness for the specific fruit samples. Pink Lady and Braeburn were characterised as having moderate concentrations of most of the identified flavour compounds, apart from a marked elevation in concentration for trans-2-hexenal in Braeburn. Jazz had the greatest fruity-ethereal-flowery flavour type compounds as indicated by the higher concentration of acetates (2-methylpropyl, butyl, 2-methylbutyl, and hexyl acetates) and the low green-grassy odour related compounds (cis-3-hexen-1-ol and trans-2-hexanal). Regardless the cultivar type, acetates find more and more specifically butyl and hexyl acetate were
the dominant esters in the headspace of the apple juices, this has previously been reported in other studies (Aprea et al., 2012, Kato et al., 2003, Komthong et al., 2007 and Ting et al., 2012). 1-Butanol was the most abundant alcohol in the headspace of the juices followed by 1-hexanol. In contrast to esters and aldehydes, alcohols are generally characterised as having higher odour threshold and thus they are considered as secondary contributors to apple flavour perception (Echeverrı́a, Graell, López, & Lara, 2004). It is also interesting that 1-butanol was highly correlated (according to BCKDHA Pearson’s test) with butyl acetate (r = 0.926, p < 0.001), hexyl acetate (r = 0.898, p < 0.001), trans-2-hexenal (r = −0.777, p < 0.001) and hexanal (r = −0.748, p < 0.01) and it could be surmised that these compounds are generated by a similar metabolic pathway during apple ripening. Finally, it should be noted that in the present work the major sesquiterpene found in the headspace of apples e.g. alpha-farnesene was not detected. This could be attributed either to the adopted protocol for the identification and quantification of the volatiles by GC or to the post juice extraction treatments e.g. enzymatic clarification and pectinase inactivation by heating.