title: Effect of temperature and pH on the solubility of caseins: environmental influences on the dissociation of α(S)- and β-casein.
abstract: Selective precipitation is a common method for the isolation of β-casein, using the different calcium sensitivities of the individual caseins and the selective solubility of β-casein at a low temperature. In previous studies, it has been indicated that the β-casein yield depends on the physicochemical characteristics of the casein raw material used for fractionation. The objective of this study was to evaluate and compare the solubility of α(S)- and β-casein in solutions of micellar casein, sodium caseinate, and calcium caseinate as a function of pH and temperature. Additionally, the solubility of isolated α(S)- and β-casein fractions in demineralized water, ultrafiltration permeate, and a calcium-depleted milk salt solution was investigated depending on the pH and temperature. Furthermore, micellar casein, sodium caseinate, and calcium caseinate were subjected to a calcium chloride-precipitation process to determine the solubility of α(S)- and β-casein in calcium chloride precipitate, which is produced during selective precipitation, as a function of temperature and pH. Generally, the temperature had only a marginal influence on the α(S)-casein solubility compared with the β-casein solubility, whereas the solubility was shown to be strongly influenced by the pH. Our results suggest that the yield of β-casein obtained during isolation by means of selective precipitation may be a result of the solubility characteristics of α(S)- and β-casein in calcium chloride precipitate. Manufacturers may consider a simple solubility experiment before the β-casein isolation process by means of selective precipitation to predict β-casein yield.
authors.affiliation: Department of Dairy Science and Technology, Institute of Food Science and Biotechnology, University of Hohenheim, Garbenstr. 21, 70599 Stuttgart, Germany. antonie.post@uni-hohenheim.de
authors.forename: A E
authors.initials: AE
authors.lastname: Post
authors.forename: B
authors.initials: B
authors.lastname: Arnold
authors.forename: J
authors.initials: J
authors.lastname: Weiss
authors.forename: J
authors.initials: J
authors.lastname: Hinrichs
mesh_terms: D000818:Animals; D002118:Calcium; D002364:Caseins / Q000737:chemistry* / Q000302:isolation & purification*; D011232:Chemical Precipitation; D006863:Hydrogen-Ion Concentration; D008027:Light; D008823:Micelles; D008892:Milk / Q000737:chemistry; D012542:Scattering, Radiation; D012995:Solubility; D012996:Solutions; D013696:Temperature; D014867:Water
chemical_list: D002364:Caseins; D008823:Micelles; D012996:Solutions; C484216:calcium caseinate; D014867:Water; D002118:Calcium