Changes in Not-from-concentrate 'Wonderful' Pomegranate Juice through Pilot Plant Pressing, Ultrafiltration, and HTST Pasteurization and Storage

Consumer awareness of health benefits in phytonutrient-rich foods and aggressive marketing have resulted in expanding markets for superfruits.  Superfruits have become mainstream within the juice and functional beverage category.  Yet, health promoting polyphenolic compounds are susceptible to polymerization and degradation during processing, and can produce undesirable bitterness and astringency.  The long-term success of pomegranate use and expanding markets may not be sustained if possible off-flavors associated with processing, bitterness and astringency are not studied, understood, and ultimately resolved.  A pilot plant hydraulic press was used to press 80 Kg whole ‘Wonderful’ pomegranates, resulting in not-from-concentrate (NFC) juice that was ultrafiltered (0.2 µm, polyvinylidene fluoride, BRO/BUF pilot membrane unit) prior to cold-fill HTST pasteurization (MicroThermics).  The experiment consisted of 2 repeated presses and ultrafiltrations, and excess juice resulted in a 3^rd repeated batch, used for pasteurization and storage in 250-ml glass bottles at 4 °C.  Qualitative parameters (color, °Brix, pH, TA), anthocyanidins, organic acids and volatiles (SPME GC-MS) were analyzed.

Color generally increased after crude pressing upon pasteurization, then a*, b* and C* decreased through 2 months storage at 4 °C.  However, L*, b* and hue often increased through storage at 25 °C.  Titratable acidity (% citric acid) increased from pasteurization (24.2) through 2 months storage at both 4 and 25 °C to 28.2 and 29.2, respectively.  Oxalic acid decreased while malic and citric acids increased through storage at 4 °C.  Delphinidin, cyanidin and pelargonidin all increased slightly from crude press through ultrafiltration then all decreased upon pasteurization, and markedly through 2 months storage at both 4 and 25 °C.  Total anthocyanidins decreased 55.8% and 95.8% through 2 months storage at 4 and 25 °C, respectively.  The following compounds decreased from pasteurization through storage, at both temperatures: 2-methyl-3-buten-2-ol, ethyl acetate, (Z) & (E)-3-hexenol, 1-hexanol, 1,4-cineole, linalool, 4-terpineol and α-terpineol.  Yet, β-damascenone and 2,4-dibutylphenol increased, across the board.  Ethanol and 1-octanol increased only at 25 °C.  Compounds such as β-myrcene, ethyl hexanoate, α-cedrene, β-cedrene and italicene were observed in crude pressed and ultrafiltered juices, and sometimes immediately after pasteurization (day 0) but, were lost through storage.  On the other hand, benzaldehyde, hexyl acetate and 2-ethyl-1-hexanol were only observed after 1 month storage.  Statistical interpretation and attempts to correlate anthocyanins with quality and volatile compounds is underway.