Method for determining a casein content and a serum protein content in a liquid food such as raw or weakly pasteurized milk, characterized in that it comprises the successive stages consisting in: a) forming a solution of said liquid food by adding a buffer of predetermined pH, said solution comprising said serum proteins and said caseins, the caseins being in coagulated form in suspension in the solution and the serum proteins are dissolved in the solution； b) shake the solution to form a homogeneous mixture of serum proteins and caseins； c) acquiring a plurality of front fluorescence spectra of said mixture, said front fluorescence spectra resulting from an excitation of said homogeneous mixture by at least one electromagnetic radiation of determined wavelength； d) dilute the mixture by adding a predetermined amount of water to separate by filtration the soluble serum proteins from the coagulated caseins suspended in the solution； e) acquiring a plurality of right angle fluorescence spectra of said diluted mixture, said right angle fluorescence spectra resulting from an excitation of the diluted mixture by at least one electromagnetic radiation of determined wavelength； and f) determining the casein content and the serum protein content of the liquid food by applying a multi-path analysis to the front fluorescence spectra and to the right angle fluorescence spectra.Procédé de détermination d'une teneur en caséines et d'une teneur en protéines sériques dans un aliment liquide tel qu'un lait cru ou faiblement pasteurisé, caractérisé par le fait qu'il comprend les étapes successives consistant à : a) former une solution dudit aliment liquide en ajoutant un tampon de pH prédéterminé, ladite solution comprenant lesdites protéines sériques et lesdites caséines, les caséines étant sous forme coagulée en suspension dans la solution et les protéines sériques sont solubilisées dans la solution ； b) agiter la solution pour former un mélange homogène des protéines sériques et
