The bitter orange varieties used for the distillation of their leaves, are the same used for the flower extraction; to these must be added the Paraguay bitter orange (bitter sweet orange). For the petitgrain extraction in Italy, France and Tunisia, is used the foliage obtained from the annual pruning of the trees (leaves and canes without raw fruits). The pruning is usually practised from the end of June—October in Provence (France), and in April in Sicily and Calabria (Italy). Generally are obtained 3—5 kg of vegetable material by pruning each tree. The foliage obtained from sunny and aerated field is preferred, for the quality of the oil obtained, than that obtained from thick cultivated fields. The foliage collected must be clean, prior to the distillation, of all woody material. The yields of oil are higher from the young leaves that from the aged ones, and from the fresh one than those faded. The trees cultivated on the plain give lower yields than those cultivated uphill and the yields between January and June are higher than for the pruning performed in the period August and October. The distillation of raw material must be carried out immediately after the harvest, in order to avoid possible enzymatic phenomena that would modify the chemical composition of the oil. Storing of the foliage for different days, however, can determine a linear increase of the yields, from about 0.4 per cent to 0.6 per cent, but with a subsequent rapid decrease to less than 0.2 per cent (Igolen, 1946; Guenther, 1949; Gildmeister and Hoffmann, 1959; Rolet etal., 1998).
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