The tertiary phase of rennin action on α_s- and β-caseins

Abstract

Casein, whole a s -casein and y#-casein were incubated for 3 and 14 h with crystalline rennin, at pH 6-60 and 36 °C, both in phosphate buffer and in milk dialysate. Products obtained from both systems, comprising 30-83% calciumsensitive (Ca s ) components, gave similar patterns on starch gel electrophoresis. Whole casein and whole a s -casein were not so soluble in milk dialysate as in phosphate buffer. No significant differences in composition were observed between the Ca a and the calcium-insensitive (CaJ products from the same source.The a si -component of the Ca s product from rennin-treated whole a s -casein had faster gel mobility in comparison to the a si -component in the Ca s product from untreated whole a s -casein. Also, a si -casein yielded one faster-moving degradation product, while a S2 3 4 appeared unaltered after 14 h. The Ca s product of rennintreated yff-casein also had faster mobility than untreated /?-casein and yielded one faster degradation product and several minor ones of slower mobility. Arginine was the only ^-terminal amino acid found in the Ca 3 product of both rennin-treated and untreated a s -and yS-caseins. The arginine content increased from 3-48 and 4-98 moles/ 10 5 g to 5-12 and 6-38 moles/10 5 g in the Ca s products from rennin-treated /?-and a s -caseins, respectively.The primary and secondary phases of crystalline rennin action on casein and /c-casein were reported by El-Negoumy (1968): /e-casein was the only component attacked during 50 min of rennin action on whole casein. No other specific electrophoretic changes accompanied the appearance of coagulum characterizing the secondary phase. The tertiary phase of rennin action involves the degradation of a s -and

Etude du rôle des micro-organismes et des enzymes au cours de la maturation des fromages. II. - Influence de la présure commerciale

“…Or, bien que plusieurs études aient décrit l'action de la présure sur des solutions de caséine (Vanderpoorten et Weckx, 1972 ;Itoh et Thomasow, 1971 ;El-Negoumy, 1968et 1970Mickelsen et Fish, 1970 ;Pélissier et al, 1974) peu d'essais ont été réalisés afin de déterminer l'action de cette enzyme seule dans les caillés de fromagerie. Seuls Reiter et al (1969) puis Green et Foster (1974) ont étudié l'influence de la présure dans des caillés sans levains proche des fromages de Cheddar ou d'Edam.…”