Effect Of Ultrasound On Qualities Of Squeezed Fresh Apple Juice

Ultrasound is a novel food processing technology which can trigger and/or strengthen the physical, chemical and biological processes with its thermal, mechanical and sonic cavitation effects to improve the textile and function of foods, what are difficult to be achieved by other technologies. This paper researched the effects of sonication, with different ultrasound temperature, time and power indensity, on qualities of squeezed fresh Fuji and Golden Delicious juice, such as physical and chemical properties, enzymatic browning, content of polyphenols and flavonoids, antioxidant activity, polyphenol oxidase and peroxidase activity, aroma compounds, metal elements et al. The research comprehensively investigated the application prospect of ultrasound in squeezed fresh fruit juice production.The results showed:1) ultrasound with different time, temperature and power intensity had no significant effects on total soluble solids, titratable acid and pH of the squeezed fresh Fuji and Golden Delicious apple juice;2) the dissolved oxygen of squeezed fresh apple juice was24%to36%, and could be reduced to zero rapidly and automatically. Ultrasound could reduce the dissolved oxygen of stirring water;3) ultrasound could decrease L*, b*values of squeezed fresh apple juice, but increase a*value rapidly, thus accelerated browning;4) ultrasound] promoted the reduction of the apple juice total polyphenols, total flavonoids and ORAC value, as well as the chlorogenic acid and epicatechin of squeezed fresh Fuji apple juice;5) the key factors for polyphenol oxidase activity were sonication temperature and power intensity, however, the effect of sonication time on polyphenol oxidase activity was insignificant. Ultrasound with low power intensity could greatly increase the activity of the polyphenol oxidase while weakened as the increase of power intensity;6) when sonication temperature was higher than40℃, ultrasound could accelerate the denaturation of peroxidase;7) determination on aroma compounds of squeezed fresh Fuji apple with Head Space Solid Phase Micro-Extraction (HS-SPME) and GC/MS showed that46aroma compounds were detected, esters, alkenes, aldehydes and alcohols are the most abundant aromas, the content being56.8%,11.66%,8.77%and6.04%, respectively;8) ultrasound reduced the content of the esters, as well as alcohols, aldehydes, olefins and phenols; power intensity and time were the key two factors on aromas of the juice, sonication with low intensity (105.50W/cm2) could seriously reduce the total content of the flavors. However, high temperature ultrasound was beneficial to the formation of esters;9) the content of Na, K, Ca, Mg, Mn, Pb of squeezed fresh Fuji apple juice was not significantly affected by sonication. But, Ti, Al, Zn, Fe, Cu content significantly increased. Sonicated for30min, the Ti content was increased by nearly100times; correspond, Al, Zn, Cu also had significant increase.10) heavy metals of Fuji apple juice before and after ultrasound were in accordance with the relevant provisions of the "GB19297-2003";11) after standing for the same time, sonicated squeezed-fresh apple juices had lower browning degree, better color stability and suspension stability than those without treated by ultrasound.