Characterizing Endogenous and Oxidative Low Molecular Weight Flavor/Aroma Compounds in Fresh Squeezed/Blended Pomegranate Juice

Little published information exists regarding flavor and aroma compounds in pomegranate (Punica granatum) juices.  Although arils have fruity and sweet characteristics, we found no publications describing volatile and semi-volatile compounds responsible for their typical flavor.  Only two reports were found delivering possible flavor compounds in processed juice, and seed plus rind.  Various extraction techniques are used with whole pomegranate fruit, arils or peels to produce juices.  Subsequently, we investigated flavor profiles in several ‘Wonderful’ juice preparations, and the oxidative changes in volatiles with an enzyme inhibitor and under low oxygen blending.  Hand-pressed (Miracloth) ‘Wonderful’ aril juice was analyzed, and compared with blended arils and arils blended with a lipoxygenase inhibitor, n-propyl gallate (n-PG), which restricts secondary volatile generation, arising from oxidation.  Comparisons were made with commercial pomegranate juice.  A DVB/Car/PDMS SPME was accomplished with 10-ml juice in the headspace of 20-ml vials for 12.5 minute exposure at 40°C, prior to injection into a HP6890/5973 GC-MS with a DB-5 column.  Compounds were identified in triplicate runs by HP ChemStation software searched against the NIST and Wiley libraries.  Miracloth expressed arils contained several low molecular weight esters, alcohols, aldehydes and terpenoids.  The predominant compounds were ethanol, hexanal, hexanol, a-pinene, b-pinene, limonene, 4-terpineol and bergamotene.  Also recovered were ethyl 2-methylbutanoate, (E)-2-hexenal, 2-methylbutyl acetate, ethyl hexanoate, and eucalyptol.  Several of these compounds are known to be flavor/aroma-important in fruits.  Most aromatic hydrocarbons are derived from the arils but recovery (~2 to 3%) did not approach levels found in commercial juice (22.8%).  Carboxylic acids (acetic and 2-methyl propanoic) were only recovered in peels (0.1 to 0.2%) and commercial juice (22.8%).  Terpenes comprised roughly 42 to 50% of the total volatiles recovered in arils which, was markedly higher than levels found in the peel (21%) and commercial juice (4.2%).  Esters were preserved well in arils and peels blended under low oxygen conditions and n-PG.  Certain compounds (1-butanol, 2,3-pentadione, 2-methyl propanic acid, 3-methyl-2-butenol, p-xylene and linolool) were only found in commercial ‘Wonderful’ juice whereas freshly sampled ‘Wonderful’ only delivered other compounds (1-propanol, 1-penten-3-one, 2-ethyl-furan, propyl acetate, 2-methyl-2-butenal, isobutyl acetate, (Z)-3-hexenal, hexanal, (Z)-2-hexenal, (E)-2-hexenal, (Z) 3-hexenol, hexanol, 2-methylbutyl acetate, (E,Z) and (E,E) 2,4-hexadienal, gamma-terpinene, and numerous terpenes) that were not found in the juice.  A long-term goal is to determine important compounds in juices that have flavor importance, while reducing oxidation of undesirable compounds during processing.