Strategies for the extension of the shelf life of ready to eat prickly pear fruits

The prickly pear fruit (Opuntia ficus indica L. Miller) belongs to the Cactaceae family. The fruit is a berry, composed by an epicarp and the pulp, which represents the edible portion. At maturation, the epicarp turns yellow, red or white, depending on the cultivar. In Italy, the prickly pear is mainly cultivated in Sicily (90% of the national production). The fruit is very sensitive to low storage temperatures (< 5 degrees C) which cause chilling injuries. The fruits can be successfully commercialized as a ready-to-eat product, peeled and suitably packaged. The main limit to its production is the formation of off-flavours due to different factors, such as the growth of microorganism and the action of endogenous enzymes (lipid oxidation). In fact, the oxidoreductases are directly responsible for the lipid oxidation, which has influence on the production of off-flavours, on the structure and on the shelf-life of the fruit. The lipoxygenase (LOX) is a dioxygenase which catalyzes the oxidation of polyunsaturated fatty acids to hydroperoxides. The aim of this work was to compare different packaging technologies to extend the shelf life of ready-to-eat prickly pear fruits. The LOX activity, microbial counts and gas composition were evaluated for non-treated samples packed in ordinary atmosphere and in two modified atmospheres having different O-2 and CO2 composition (MA1 5% O-2, 2% CO2, 93% N-2; MA2 2% O-2, 5% CO2, 93% N-2) and for samples treated either with a blanching or with a blanching followed by a dipping in a citric acid solution. The pretreatment conditions are essential for the LOX activity, in particular the blanching reduced its activity by at least 30% especially in combination with fruit acidification and limited the microbial proliferation. As a result of suitable pretreatment and packaging operations the shelf life of ready-to-eat prickly pears can be successfully extended.