Nanofiltration Enrichment of Milk Oligosaccharides (MOS) in Relation to Process Parameters

Abstract

Bioactive milk oligosaccharide concentrates are not yet available as functional food ingredients. The aim of the present study was to develop an optimized nanofiltration process for the enrichment of milk oligosaccharides by achieving a better permeation of milk salts and residual sugars during nanofiltration in an acidic (pH 5) or neutral (pH 7) environment. A bovine retentate produced by nanofiltration with a 100-fold increase in the milk oligosaccharide content in relation to total sugar content was applied. In addition, the process should be suitable for the enrichment of milk oligosaccharides in caprine milk. Milk oligosaccharides were identified by high performance anion exchange chromatography (HPAEC). Generally, a greater enrichment of milk oligosaccharides in the final nanofiltration retentate (14 % milk oligosaccharides by dry mass, 4-fold higher than in the first nanofiltration retentate, 140-fold higher than in the raw material) and a better separation of salts and residual sugars were achieved in bovine milk by nanofiltration at pH 5. The high milk oligosaccharide content in relation to the total sugar content in the final nanofiltration retentate (92 %, 10-fold higher than in the first nanofiltration retentate, 900-fold higher than in the starting sample) indicated a nearly complete permeation of monosaccharides and disaccharides. Nanofiltration of caprine milk resulted in a 31-fold higher milk oligosaccharide content in relation to total sugar content than in the starting sample. In the present work, the influence of the pH on the degree of enrichment of milk oligosaccharides by nanofiltration was evaluated for the first time.