Ultrasonic Extraction of Tannin from Banana Peel and Its Antioxidant Activity

In order to develop plant polyphenols as natural antioxidants,the processing of tannins extracted from banana peels by ultrasonic was optimized by response surface test(ultrasound power,ultrasonic time,solid-liquid ratio,ethanol concentration)with tannin yield as an indicator. And its antioxidant properties and grease protection rate of tannins were investigated. The results showed that the optimal extraction parameters were ultrasonic power 430 W,ultrasonic time 40 min,solid-to-liquid ratio 1:42 g/mL,ethanol concentration 66%,and under the conditions the tannin yields reached 1.87%. As the concentration of tannins increased,the DPPH,superoxide anion and hydroxyl radical scavenging rates increased. And the semi-inhibitory concentrations of tannin extract on DPPH,superoxide anion hydroxyl radical scavenging was 0.300,1.185 and 0.730 mg/mL,among of which DPPH and hydroxyl radical were lower than those of V_C control group. With the increasing of the addition of tannin extracts,the peroxide value of soybean oil significantly decreased(P<0.05)and the oil protection rates were higher at 96 h during accelerated oxidation process. When the tannin addition was 0.04%,the soybean oil had the lowest peroxide value during accelerated oxidation and the soybean oil protection rates were significantly higher(P<0.05)than the other two groups(0.02% and 0.06%),indicating that the tannin extract could inhibit the oxidation of soybean oil.