Effects of some processing variables on system performance during clarification of blackberry juice by ultrafiltration

Ultrafiltration is increasingly used for clarification in fruit juice industry, since it has many advantages over the traditional methods. However, fouling of membranes is the main drawback of this process. In this study, depectinized blackberry juice samples were clarified by using membranes with MWCO values of 10, 30 and 50 kDa. In addition to process parameters such as temperature (20-40°C), transmembrane pressure difference (100-300 kPa) and membrane MWCO value, the effects of pre-flocculation with the use of gelatin-bentonite at different concentrations on the system performance were evaluated according to the response surface methodology. Membrane resistance, cake layer resistance and fouling resistance, which affect the total resistance during the process, were analyzed with the resistance-in-series model, and the contributions of each individual resistance to the total resistance were determined. The suitability of the experimental data to the pore blocking models was tested, and it was found that the data fitted well to the models evaluated with high correlation coefficients. The results obtained show that the MWCO value of the ultrafiltration membrane used is the most effective variable on both resistances and permeate flux. While the increase in temperature increased the permeate flux, it also caused an increase in the fouling resistance. Pre-flocculation with gelatin and bentonite also contributed to decreasing the fouling resistance and increasing the flux. The effects of the ultrafiltration process on various physicochemical properties of blackberry juice were also evaluated, and it was determined that the characteristics such as total phenolic contents, anthocyanins, total flavonoid and some color values and antioxidant capacity contents of the samples were affected at different levels from the process parameters. By taking into account the minimum total resistance and maximum flux value preference while preserving the phenolic components and antioxidant capacity of blackberry juice, it was determined that the gelatin-bentonite concentration used in the pre-flocculation was 120:600 mg/L, the membrane MWCO value was 50 kDa, the temperature was 20°C and the TMP value was 205 kPa, which would give optimum results.