Effect Of Ultrasound On Aroma Compounds Of Freshly-squeezed Orange Juice And Its Mechanism

Aroma affects the quality of orange juice greatly, however, aroma compounds reduce a lot in storage and processing. Ultrasonic treatment, a non-thermal processing technology, which is used in sterilization, can reduce the loss of aroma compounds. In the research of ultrasonic treatment of orange juice, it mainly involves in the physicochemical properties and bioactivators, rather than aroma compounds in orange juice. In addition to free aroma compounds, potential bound aroma compounds can be released in many fruits according to former studies.This paper mainly studied the effect of ultrasonic treatment on the bound aroma compounds of freshly-squeezed orange juice, the effect of ultrasonic treatment on the overall aroma compounds, and the transformation pathway of the main aroma active compounds in the processing of ultrasound.The main conclusions are as follows:1、Ultrasonic treatment could release some bound aroma compounds to a certain extent. The order of three factors was A (ultrasonic intensity)>B (ultrasonic temperature)>C (ultrasonic time), and the optimal ultrasonic conditions was5.05W/cm2,10min,15℃.2、Compared ultrasound with enzyme hydrolysis, the varieties and contents of released bound aroma compounds were very different. The products of enzymatic hydrolysis were mainly C6alcohols and some terpenes, hydroxyl esters and aldehydes, while the products of ultrasonic treatment were alcohols and esters. Sensory analysis showed that, the orange juice of enzyme hydrolysis was rich with sweet fragrance in flavor, but had slight putrid odor. The ultrasonic sample had a little grass flavor and sweetness, with no bad smell.3、Compared the overall aroma compounds before and after ultrasonic treatment, two new compounds were produced (Selinene, Gurjunene), while some original flavors disappeared (Nonanal, Citronellal). Most of the varieties didn’t change, but the contents changed. Overall, the ultrasonic treatment made the alcohols and aldehydes in orange juice convert into esters better, which enabled the fragrance more outstanding. But the content of carvone increased, which was an adverse compound in the orange juice.4、Identified by GC-O, aroma active compounds did not change after ultrasonic treatment. According to the fuzzy score of sensory evaluation method, ultrasonic treatment could improve the overall sensory quality of orange juice, but the quality would be lower if the ultrasonic intensity was too large or the temperature was too high.5、Ultrasound could accelerate reactions within the juice system These reactions would occur slowly in a long-time storage, but ultrasound could accelerate it significantly.6、Ultrasound could accelerate the oxidation of limonene in orange juice, which makes the content of limonene decrease, and the content of a-terpineol and D-carvone increase. The content of dissolved oxygen in the medium was high when treated by ultrasound, which promoted the oxidation of limonene; ultrasound also produced instant high temperature and high pressure, which provided energy for linalool to generate a-terpineol; besides, a-pinene and β-myrcene remained stable under ultrasonic treatment.