Study On Free And Bound Volatile Compounds In Oranges And Its Processing Products

Aroma is one of the most important attribute to orange products quality. Nevertheless, the characteristic aroma active compounds lost seriously during the process and storage of orange juice and that result in the quality deterioration. Consequently, it is significant to keep the characteristic aroma of the orange products in order to enhance the sensory quality of the orange products and competitiveness of the orange processing enterprises. The present study focused on the aroma enhancement of 9 varieties of oranges and its products produced in Songzi and Yichang of China. SPME-GC-MS was used for the analysis of free volatiles of these oranges, and Amberlite XAD-2 resin was used to isolate and extract the bound volatiles. In addition, the free and bound volatile compound in oranges at different maturities, the effect of acid and enzymatic hydrolysis, the sugar moiety of the bound volatile compounds in oranges, the free and bound volatile compounds in pulp and peel of oranges, the free volatile compounds in orange wines produced by different methods, the effect of fermentation on the free and bound volatile compounds in orange juice, the effect of pasteurization on bound volatile compounds in orange juice, the immobilization of P-glucosidase and its enzymatic properties, the effect of immobilizedβ-glucosidase on the released of bound volatile compounds in orange juice were also studied.The main research subjects and results are listed as follows:1, Study on the extraction and hydrolysis of the free and bound volatile compounds in oranges.Amberlite XAD-2 resin was used to extract and separate the free and bound volatile compounds in orange juice. The effect of different organic solvents on the extraction of free volatile compounds was studied. The results showed that diethyl ether/pentane was more suitable to extract the free volatile compounds than diethyl ether/dichloromethane. Nevertheless, with respect to Solid Phase Microextraction (SPME), SPME was more rapid and suitable for extraction and concentration of the free volatile compounds.There was a great difference on the detection of free and bound volatile compounds in orange juice between HP-5 and DB-WAX columns. More volatile compounds were detected by HP-5 than DB-WAX which could be more completely to show the actual aroma of the orange juice. While there were several volatile compounds detected only by DB-WAX, and this indicates that the effect of detection on free and bound volatile compounds was complementary.The primary and secondary factor analysis showed that time was the most important factor influencing enzymatic effects, followed were temperature and amount of enzyme. The optimum conditions were as follows:temperature (40℃), time (24 h), amount of enzyme (300 U). The effect of acid hydrolysis on bound volatile compounds was related on pH value and temperature. The bound volatile compounds hydrolyzed by acid at different conditions showed a great difference. Totally 5,11,6, and 2 bound volatile compounds were detected at ph 1.0 (100℃) for 30min, pH 1.0 (40℃) for 4 days, pH 2.0 (40℃) for 4 days, and pH 3.0 (40℃) for 4 days respectively.A great difference existed on the bound volatile compounds between acid and enzymatic hydrolysis. Sensory analysis indicates that the bound volatile compounds hydrolyzed by acid had a pungent smell with a weak citrus odour, on the contrary, the compounds hydrolyzed by enzyme have a sweat, citrus-like smell.2, Study on free and bound volatile compounds in peel and pulp of oranges.The free volatile compounds identified in pulp and peel of oranges had a great difference, 26 and 40 compounds were detected respectively, mainly were terpenes. Similarly, a great difference on bound volatile compounds between pulp and peel was also observed,11 and 10 compounds were found in pulp and peel respectively.3, Study on sugar moiety of glycosidically bound volatile compounds.GC analysis showed that rhamnose, xylose and glucose were the sugars linked with the volatile compounds in oranges.4, Study on free and bound volatile compounds in different varieties of citrus fruits.The free and bound volatile compounds in 9 different varieties of citrus fruits were analyzed. The results showed that 26 and 11 (Jincheng),36 and 5 (Hamlin),31 and 11 (Qixuecheng),24 and 9 (lime),10 and 13(Guoqing 1),18 and 11 (Miyagawa Wase),23 and 5 (Owari satsuma),28 and 6 (white grapefruit),29 and 4 (pink grapefruit). The free volatile compounds in sweet oranges were the most abundant, followed were grapefruits, lime and Satsuma Mandarins.5, Study on free and bound volatile compounds in oranges during different maturation.There was a great difference on the content and species of free and bound volatile compounds between different maturities.12 and 5,13 and 12,26 and 11 free and bound compounds in pulp in the three different stages. The content of free volatile compounds in pulp at mature green stage was the highest, while it was the lowest at ripe stage. Adverse results were obtained with regard to the number of the free volatile compounds. The content and number of the bound volatile compounds in pulp was the highest. The content of free volatile compounds in peel increased during maturing, while the content and number of the bound volatile compounds decreased during maturing. 6, Study on free and bound volatile compounds in oranges during processing.Both sensory and GC-MS analysis showed no large differences on volatile components of orange wines produced by spontaneous and inoculated fermentations,17 and 19 compounds were detected respectively. It's in agreement with the results of the GC-MS that marked differences were found between wines with and without skin contact. GC-MS analysis showed that fermentation had a great effect on the free and bound volatile components in orange juice. Most of the compounds identified both in orange juice and wine showed a significant difference on amounts after fermentation. Many free volatile compounds missed after fermentation, especially the terpenes. Adversely, most of the esters found in orange wine were new formed compounds during fermentation. Almost all of the bound volatile compounds in orange juice were released during fermentation.7, Study on immobilization ofβ-glucosidase and the effect on the hydrolysis of bound volatiles.Sodium alginate was more suitable for the immobilization ofβ-glucosidase than chitosan. The optimum conditions for the immobilization of P-glucosidase were:concentration of sodium alginate 3.5%, concentration of cross-linking agent 1%, cross-linking time 3 h, immobilization time 2 h, Concentration of CaCl23%. The optimum reaction conditions of free and immobilized glucosidase were as follows:temperature 70℃of free glucosidase and 55℃of immobilized glucosidase, pH value 5.0 both of free and immobilized glucosidase, Km 14.89 mol/L of free glucosidase and 0.59 mol/L of immobilized enzyme. In addition, the immobilized glucosidase had good storage stability and could hydrolyze the bound volatile compounds effectively.