The investigation of the effect of freeze concentration assisted by centrifugation on the yield and phenolic content of quince, pomegranate and black carrot juices

The aim of this study was to apply "centrifugation assisted by block freeze concentration technique", as a novel technique of concentration process, on quince, pomegranate and black carrot juices and to investigate the effects of this novel technique on the quality properties of concentrated juices. Moreover, with the use of this technique it was aimed to produce concentrated juices which have higher nutritional and sensory properties, reduced physical and chemical changes, longer storage and easy packaging properties. For this purpose, fresh sequezed quince (12.9ºBx), pomegranate (15.1ºBx) and black carrot (10.6ºBx) juices were filled in centrifuge tubes and frozen in a static freezer. Frozen samples were centrifuged at 4500 rpm for 35 min at 25ºC. The concentrated solution which was obtained after the removal of formed ice by filtration was frozen again at the same conditions and the same processes were repeated (cycle). The total solid soluble content, pH, color values, total phenolic content, vitamin C, antioxidant capacity (DPPH), the thawing fraction, percentage of concentrate, efficiency of concentration and recovered solute values were calculated for each cycle. According to the results of the successive two cycles for quince juice and three cycles for pomegranate and black carrot juices, the amount of remaining solutions after the removal of ice content decreased and in contrary to increase in total soluble solid content, the concentration efficiency decreased. For this reason the concentration cycles were not repeated anymore. The percentage of concentrate was calculated 54.40±8.66%, 85.61±4.16%, 67.34±4.54% and the recovered solute values reached to 0.70, 0.63 and 0.73 kg/kg for quince, pomegranate and black carrot juices. By increasing the number of the cycles, the total phenolic and vitamin C content and antioxidant capacity decreased. After the cycles, total phenolic content and vitamin C content calculated for quince juice 776.11 mg GAE/L and 1021.45 mg/L, for pomegranate juice 2834.06 mg GAE/L and 724.59 mg/L, for black carrot juice 2171.64 mg GAE/L and 1174.37. Keywords: quince juice, pomegranate juice, black carrot juice, freeze concentration, centrifugation, quality properties