Effects of skim milk pre-acidification and retentate pH-restoration on spray-drying performance, physico-chemical and functional properties of milk protein concentrates

This study investigates the effects of pre-acidification (pH 6.7-5.4) of skim milk, followed by pH-restoration of the retentates, on spray-drying performance, physico-chemical properties and functionality of the resulting milk protein concentrate (MPC). Powder recovery decreased with decreasing pH of pre-acidification but improved with pH-restoration. Colloidal calcium was gradually solubilized with decreasing pH of pre-acidification but was slightly recovered by pH-restoration. Dissociation of micellar caseins increased with decreasing pH of pre-acidification of skim milk and was further increased by pH-restoration. Casein micelles maintained their overall structures at pre-acidification pH of 6.7-6.0, and partially disintegrated into loosely entangled aggregates at pH 5.7-5.4; while after pH-restoration, micelles generally maintained their overall structures at pre-acidification pH of 6.0, and completely disintegrated at pH 5.7-5.4. Solubility and emulsifying properties of MPC improved with decreasing pH of pre-acidification and with pH-restoration. Heat stability of MPC declined with decreasing pH of pre-acidification but improved with pH-restoration.