Evaluation of anthocyanin content on blackberry juice (Rubus spp.) processed by microfiltration

摘要

Small red fruits have been attracting the attention of producers and consumers, especially after news reports about the benefits they provide to the human health due to the presence of high content of phenolic compounds with antioxidant capacity. Besides being a good source of natural antioxidants, vitamins and minerals, blackberries are rich in phenolic acids, flavonoids, including anthocyanins, conferring to the juice a highly attractive colour, but also a instability to some severe heat treatments, which can result in darkened and cooked taste products. The target is to process the initial raw materials by less aggressive techniques. This study aimed to evaluate the effect of microfiltration process on the anthocyanins content from blackberry juice. The juice was obtained from pressing blackberry fruits in a depulper machine with a 0.8 mm sieve. Before microfiltration, the juice was centrifuged and submitted to an enzymatic hydrolysis for 30 min with 400 ppm of pectic enzyme at 35 °C in order to reduce the insoluble solids content, the viscosity and hence increase the permeate flux during microfiltration. Microfiltration was carried out in a plate and frame module with fluorinated membranes of 0.15 micron pore size and total permeation area of 0.36 m~2 at 35°C and transmembrane pressure of 5 bar. The retentate stream was recirculated back to the feed tank and the permeate was continuously collected. The average permeate flux was 22 L/hm2 and the volumetric concentration factor reached 7. The anthocyanin content of the single strength blackberry juice was 46 mg/100g and of the permeate juice 43 mg/100g, proving the effectiveness of the microfiltration process for the maintenance of the anthocyanin concentration of the blackberry juice. These results motivate the continuity of new researches on the application of membrane technology to fruit juice processing.