Membrane separation limits for the isolation of mono- and di-saccharides from compounds with similar molecular weights including a theoretical selectivity analysis and a new calculation approach

Nano-and ultrafiltration selectivities (Sij) for fructose, glucose, sucrose, polyphenols, malic acid, and min-erals were investigated based on sugar separation from apple juices. The selectivity between total sugar and total phenolic content (TPC) was 3, and for monosaccharides versus TPC, it was 4 (cut-off 350- 500 Da). The sugar reduction is hardly possible due to considerable losses of TPC. The selectivities of min-erals and malic acid versus monosaccharides ranged from 8 to 12 (cut-off 300 Da). Here, the losses of valuable compounds are acceptable (<15 %). In the cases of minerals, malic acid, and glucose versus sucrose, the values were 199, 250.5, and 26.5, respectively. Sij is highest when the rejection for the larger compound (Rj) is close to unity (pore radius equals solute radius). Selectivity values are often not very meaningful in practice. A new simplified selectivity Sij(99) with fixed Rj = 0.99 (for Rj >= 0.99) could be helpful.(c) 2022 Published by Elsevier Ltd.