Role of ultrafiltration process in pomegranate juice clarification: effect on bioactive compounds and formation of bio-colorants

The purpose of clarification pomegranate juice by ultrafiltration process was its effect on bioactive compounds and degradation of bio-colorants during processing. For this aim, the effect of temperatures (20 and 30°C) and pressures (1.5, 2 and 2.5 bar) on anthocyanin, phenol, tannin and color indices were investigated. The results showed that the applied treatments significantly reduced anthocyanin in pomegranate juice. Treatments of 20°C-2 bar and 30°C-2 bar with 2.8 and 14.34% had the lowest and highest decrease in anthocyanin content, respectively. All treatments applied significantly reduced the total phenol content of pomegranate juice by 15-28-27%. Treatments of 20°C-2 bar and 30°C-2 bar with 6563.6 and 5696.9 mg/L had the highest and lowest phenols, respectively. The total tannin content for 20ºC and 30°C was 700.6 and 746.7 mg/L, respectively. The rate of reduction was between 39.34% for 1.5 bar-30°C treatment and 49.7% for 2.5 bar-20°C treatment. The total color density at 20°C and 30ºC was 1.09 and 1.17, respectively. Due to the rapid degradation of anthocyanins and tannins at high temperatures and generation of dark brown pigments, the total color density increased. The rate of tannin color reduction was between 39.34% for 1.5 bar-30°C treatment and 49.7% for 2.5-bar-20°C treatment. It was concluded that the effect of membrane process on tannin color reduction (45%) was more than anthocyanin color (23%). Regarding the browning index of permeation, the highest and lowest decreases equal to 34.45 and 19.88% were related to 2.5 bar-20°C and 2 bar-30°C, respectively.