Abstract
Falling in between reverse osmosis (RO) and ultrafiltration (UF), nanofiltration (NF) or loose RO, newly developed, is finding growing applications in the food industry which are reviewed.
It is one of the most important properties of NF membrane that makes some solutes pass through or not rejected. NF membrane rejects uncharged molecules due to size exclusion and charged components due to electrostatic interaction between charged membrane and them. A negative rejection coefficient of a more permeable ion than the same charged ions in a solution by NF can be observed due to the Donnan effect, maintaining electroneutrality. These characteristics of NF have been exploited in the food industry.
Applications of NF are summarized into five groups, as follows : 1) Desalination. 2) Concentration. Higher concentration of fruit juices by NF is established due to less different osmotic pressure across the membrane than RO. In the combination of 1) and 2), NF has been successfully applied into partial desalination and pre-concentration in the whey processing system of the dairy industry. 3) Fractionation due to size exclusion and/or electrostatic interaction has attracted researchers in separation of some oligosaccharides, amino acids and peptides from bio-products. 4) Decolorization. Color materials are easily rejected by NF. The lighter products from permeate of soy sauce or the imitated one have widened the soy sauce application area. 5) Taste modification. It was found that some unfavorable organoleptic materials in reconstituted skim milk are less rejected. The modified taste concentrate of it has been used for a non-fat milk product. A high grade ice cream, developed from NF concentrate of whole milk, gives us better taste due to less ash content of it and non-heat concentration.
