Chemical characterization of sicilian prickly pear (Opuntia ficus indica) and perspectives for the storage of its juice.
In this work, Sicilian cultivars of prickly pear (Opuntia ficus indica) were partially characterized from a chemical point of view, and the possibility of long-term storage of their juice was investigated. The acidity of the prickly pear juice turned out to be very low (0.02%) and the pH very high (6.4-6.5) if compared with values found in other common fruit juices. In the perspective of processing and storage conditions according to Italian law, the acidity has been corrected by adding the proper amount of tartaric and/or phosphoric acid. The sugar content (mainly glucose and fructose) is very high (11-12%), and also L-ascorbic acid is present in considerable amount (31-38 mg/100 g). Among the transition metals, a high content of manganese(II) (1.7-2.9 ppm) and good amounts of iron(III) (0.6-1.2 ppm) and zinc(II) (0.3-0.4 ppm) were found. In particular, such ions appear to be present mainly in the thick skin of the fruit or "trapped" inside the pulp. Pectin methylesterase (PME) seems to be present in very small amount and/or is not highly active. Furthermore, PME activity decreases considerably after the necessary adjustment of the pH and the thermal treatment requested for long-term storage. After approximately 2 months, none of the juices prepared was affected by noticeable sedimentation of the pulp. Finally, different samples of prickly pear juice were sensorially analyzed, employing descriptors such as color, aroma, viscosity, acidity, sweetness, and off-flavors. The results obtained can be considered very satisfactory, and the juice has been widely appreciated when compared with other products commonly available on the market such as pear and peach juices.