Lait 45 (1965) 3-26
DOI: 10.1051/lait:1965441-4421

La protéolyse de la caséine par les enzymes intracellulaires de certaines bactéries

S. POZNANSKI^{a, b}, J. LENOIR^a and G. MOCQUOT<sup>a

a</sup>  Laboratoire de Recherches de la Chaire de Technologie (I.N.R.A.), Ecole Nationale Supérieure Agronomique de Grignon (S:-et-O.) et Station Centrale de Recherches Laitières et de Technologie des Produits Animaux, Centre National de Recherches Zootechniques, I.N.R.A., Jouy-en-Josas (Seine-et-Oise)
^b  Adresse actuelle : Chaire de Technologie Laitière, Université Agricole, Olsztyn (Pologne)

Abstract - The proteolysis of casein under the action of certain bacterial endoenzymes
The proteolytic activity of the endoenzymes from four bacterial strains, belonging to species Streptococcus thermophilus, Lacto-bacillus bulgaricus and Micrococcus caseolyticus (strain 77 and 79) on casein substrates, at pH 5.6, has been determined.
The enzymes which were used for the experiments were pre-pared from each bacterial strain ; they were used either separately or in combination, with or without the addition of rennin, with or without the addition of 4,5 p. 100 salt.
The extent of proteolysis has been estimated by determining the nitrogen which does not precipate by calcium and also the non protein nitrogen, after 2, 6, 12 and 24 days at a temperature of 30° C.
Among the various endoenzymes, only those from L. bulgaricus give an appreciable proteolytic action on whole casein. The enzymes from S. thermophilus and M. caseolyticus are more able to decompose the intermediary products formed during casein hydrolysis, as shown by their action on casein to which rennin has been added. The enzymes from M. caseolyticus 79 are not very active.
Compared to the "general proteolytic action" of rennin, the activity of the bacterial enzymes appears rather weak. But, when the nature of the products formed during hydrolysis is considered, the situation looks different: while most of the products resulting from rennin activity are insoluble in trichloroacetic acid, most of those from the endoenzymes are soluble in the same reagent.
When the endoenzymes are combined together, they seem more active than when they act separately; their activity decreases markedly in the presence of 4,5 p. 100 salt.
The activity of the bacterial enzymes also varies with the kind of substrate used. Proteolysis is more marked on native casein than on isoelectric casein; particulary this is the case with L. bulgaricus enzymes and with the combined enzymes and rennin.
The α_s and χ casein are more susceptible to the effect of the combined enzymes than native casein