Free and bound volatile compounds in juice and peel of Jincheng oranges

Free and glycosidically bound volatile compounds in juice and peel of Jincheng oranges were investigated. Solid phase microextraction (SPME) was used for extraction of free volatile compounds. Bound volatile compounds in juice were isolated by using Amberlite XAD-2 column adsorption and methanol elution. Subsequently, they were hydrolyzed by almond β-glucosidase. Acid hydrolysis was also applied on the release of the bound fraction in juice. Both free and bound volatile compounds were then determined by GC-MS. A total of 26 and 40 free volatile compounds were identified in juice and peel, respectively. Terpenes followed by aldehydes were the major free volatile compounds both in juice and peel. Eleven and ten aglycons hydrolyzed by enzyme were identified in juice and peel, respectively. Benzenic compounds and hydroxyl esters were the main bound volatile compounds in juice, while C₁₃-norisoprenoid and monoterpenes were the most abundant bound volatile compounds in peel. 3-Oxo-α-ionol (41%) predominated in bound fraction of peel. Five aglycons hydrolyzed by acid were found in juice. p-Vinylguaiacol and eugenol were the two compounds found both after enzymatic and acid hydrolysis. Rhamnose, xylose, and glucose were determined as sugar moieties in juice.