Quantification of selective transport of fructose and glucose during membrane filtration of pomegranate juice

Pomegranate (Punica granatum L.) is a nutrient-dense fruit with proven health-promoting effects due to the presence of polyphenols. Fructose and glucose are known as the main contributors to the juice sweetness. Pressure-driven membrane operations offer new opportunities and perspectives for efficiently recovering phenolic compounds without losing their activity. We investigated the fractionation of clarified juice with three commercial polyamide-thin film composite membranes having a molecular weight cut-off (MWCO) of 1-3.5 kDa. All selected membranes allowed to concentrate more than 80% of phenolic compounds, while glucose and fructose recovery are more than 60% and 70%, respectively. Among the studied membranes, the General Electric (GE Osmonics, USA) Desal GK membrane (MWCO 3.5 kDa) exhibit highest permeate concentration and selectivity of fructose at 18 bar, in total recycle mode. In the batch concentration mode, the permeate concentration decreases with time. The filtration process is mathematically described as a coupled phenomenon of the mass transport in the polarization layer over the membrane surface and selective transport in the membrane itself, for all three species. The model result is in good agreement with experimental observations under the total recycle and batch operation mode, for both the permeate flux and permeate concentration of three species. The recovery of glucose and fructose is in the range of 60% and 70%, respectively. The permeate is enriched with fructose, which is selectively transported over glucose using the GK membrane, whereas glucose is preferentially transported using GH membrane for the same feed solution. The selectivity of fructose increases with cross-flow rate. Maximum selectivity is obtained at the transmembrane pressure of 18 bar.