Feasibility of Spray Drying Concentrated Acid Whey After Nanofiltration

Concentration of acid whey and crystallisation of lactose followed by spray drying in the production of acid whey powder are severely restricted by the presence of lactic acid (LA) and calcium (Ca). These compounds cause stickiness during spray drying. The present study examined the effects of removing LA and Ca by membrane processing to varying extents in order to improve the feasibility of the spray drying of an acid whey stream. Spray drying of unaltered acid whey achieved a powder recovery of ~ 18% in the collection vessel and ~ 31% in the cyclone. Removal of LA and Ca by 30 and 40%, respectively, by nanofiltration significantly increased the powder recovery to ~ 58% in the collection vessel. Powder particles decreased in size giving a D[4,3] of ~ 18 μm, with SEM images confirming the presence of well separated spherical powder particles. A solubility of > 75% was also achieved. However, removing Ca > 60% compromised the spray drying process. FTIR analysis suggested that water molecules in the hydration layer of lactose and the structural changes of both lactose and protein molecules at the molecular level appeared to play an important role in governing the extent of the drying feasibility. In addition, the formation of calcium lactate may restrict the diffusion of lactose molecules, once the appropriate stoichiometry was reached. Thus, manipulating LA and Ca concentrations in a particular acid whey stream can improve the spray drying process and production of a non-sticky acid whey powder