Firstly,　whey　protein　isolate　(WPI)　was　hydrolyzed　by　trypsin　at　constant　conditions　(i.e.,　pH　8.5,　37　＇C,　enzyme/substrate　ratio:　0.5%,　5　h)　to　prepare　whey　protein　hydrolysates　(WPH).　Secondly,　this　study　evaluated　the　influence　of　milieu　conditions　on　emulsifying　properties　of　WPH.　Namely,　pH　values　(3-7)　and　ionic　strength　(0.1　mol/L　and　1　mol/L)　by　means　of　the　addition　with　different　salts　(NaCl,　KCl,　CaCl2,　MgCl2)　were　combined　with　heat　treatment　of　WPH　prior　emulsification.　For　emulsion　characterization,　particle　size　distributions　were　measured　by　laser　diffraction,　emulsion　stability　was　evaluated　by　STEP　technique,　and　mass　spectrometry　was　used　to　identify　individual　precipitated　peptides　due　to　heat　treatment　or　the　changes　of　milieu　conditions.　It　was　found　that　the　charge-shielding　effect　caused　by　the　increase　in　ionic　strength　at　pH3　led　to　significant　emulsion　flocculation,　while　the　effect　of　ionic　strength　on　the　emulsification　characteristics　of　WPH　at　pH7　was　insignificant.　In　addition,　at　the　isoelectric　point　of　WPH　(pH4),　heat　treatment　significantly　improved　the　emulsification　characteristics　of　WPH,　especially　for　the　sample　group　with　the　addition　of　CaCl2.　Combining　the　composition　of　the　precipitated　peptides　at　different　environmental　conditions　and　the　corresponding　emulsification　characteristics,　f(41-60),　f(71-91),　and　f(78-101)　released　from　!-Lg　are　believed　to　make　an　important　contribution　to　the　emulsification　characteristics　of　WPH.　©　2023　Chinese　Institute　of　Food　Science　and　Technology.　All　rights　reserved.