Characterization of Rennin-like Enzyme, Produced in Submerged Cultures of Aspergillus niger

Abstract

Aspergillus niger produced powerful milk-clotting activity when it was grown aerobically in submerged cultures. The enzyme could be produced in sweet rennet buffalo whey and in salted whey media without extraneous supplementation with other nutrients. Characterization studies on the activity produced in sweet whey media have revealed that the enzyme activity responded to dilution in a linear manner, thus permitting the prior adjustment of the milk-clotting time as desired. The addition of calcium chloride increased the milk-clotting activity in many cases up to 0.08 M as final concentration, whereas the incorporation of sodium chloride in the reaction mixture resulted in significant inhibition of the clotting reaction, particularly at high concentrat ions. The enzyme was heat-tolerant up to 60 °C. On the other hand, the milk-clotting reaction, catalyzed by this enzyme, had an optimum temperature range between 70 °C to 80 °C, thus suggesting possible activity protection by the presence of the substrate. The results obtained are discussed in the light of the feasible application of this enzyme as a substitute for animal rennet.

Produktionsbedingungen und Eigenschaften eines Milchgerinnungsenzyms, produziert von Aspergillus niger, wurden untersucht. Neben aeroben Bedingungen erwies sich Molke als geeignetes Substrat. Die Milchgerinnungsaktivität war der Enzymkonzentration proportional, so daß die gewünschte Gerinnungszeit vorher festgesetzt werden konnte. Zusatz von CaCl₂ bis 0.08 M steigerte die Gerinnungsaktivität. NaCl hemmte diese in höheren Konzentrationen. Das Enzym ist bis 60 °C thermostabil. Andererseits lagen die Optimaltemperaturen für die Gerinnungsreaktion zwischen 70 und 80 °C.