CHANGES IN CHEMICAL-COMPOSITION OF CATALYTICALLY HYDROGENATED ORANGE OIL (CITRUS-SINENSIS)

Orange oil obtained from fresh fruit peels by cold pressing was subjec ted to hydrogenation at 60, 70 and 80 degrees C and 0.46 MPa (H-2 pres sure) over Adam's catalyst (PtO2 at 0.5 and 0.75%, w/w). The chemical composition of neat and hydrogenated oils was established by high-reso lution gas chromatography (HRGC) with flame ionization (FID) and mass spectrometric (MS) detection. The principal components of orange oil w ere monoterpenes (limonene 94.00%, alpha-pinene 0.54%, sabinene 0.74%, beta-myrcene 1.18%), followed by oxygenated compounds such as alcohol s (linalool 0.89% and alpha-terpineol 0.06%) and aldehydes (citral-Z 0 .09%, citral-E 0.14%, citronellal 0.07%). HRGC-FID-MS analysis of the hydrogenated mixtures revealed the presence of over twenty components, mainly the products of hydrogenation of limonene, citral, linalool, b eta-myrcene, sabinene and beta-ocimene. alpha-Pinene and aliphatic ald ehydes did not react under these conditions. The appearance of alpha-t erpinolene and the increase of gamma-terpinene concentration from 0.05 % to 0.15% in the modified oils indicated isomerization associated wit h hydrogenation. Citral (E- and Z-) was converted into citronellal (0. 06-0.12%) and dihydrocitronellal (0.06-0.16%). Linalool was transforme d into 3,7-dimethyl-1-octen-3-ol (0.42-0.63%) and 3,7-dimethyloctan-3- ol (0.11-0.32%). Various isomers formed by H-2 addition to the endo an d exo double bonds in limonene constituted the main products (up to 95 %) in the hydrogenated orange oils. The concentration of hydrogenated products increased from 62.78 to 89.76% when the temperature dropped f rom 80 to 60 degrees C at a catalyst concentration of 0.5% (w/w). A sm aller change was observed with 0.75% (w/w) catalyst.