Factors Affecting the Growth and Production of Milk-Clotting Enzyme by Amylomyces rouxii in Rice Liquid Medium

Pei-Jing Yu and Cheng-Chun Chou*

Graduate Institute of Food Science and Technology, National Taiwan University, 59, Lane 144, Keelung Rd., Sec. 4, Taipei, Taiwan

Article history:
Received August 28, 2004
Accepted June 28, 2005

Key words:
Amylomyces rouxii, milk-clotting enzyme, rice liquid culture

Summary:
Amylomyces rouxii is one of the main fungi usually coexisting with yeasts in Chinese yeast ball, the starter of chiu-niang, a traditional Chinese fermented product from rice. In the present study, growth and production of milk-clotting enzyme (MCE) in gelatinous rice liquid culture of A. rouxii as influenced by waxy (gelatinous) rice content in the medium (5–20 %), temperature (25–40 °C), cultivation time (1–6 days), shaking speeds (0–150 rpm) and metal ions (Na⁺, K⁺, Zn²⁺, Mg²⁺, Mn²⁺, Cu²⁺, Ca²⁺, Fe³⁺ and Al³⁺) were investigated. Results revealed that rice content in the medium, shaking speed, temperature and cultivation time all affected the mycelial propagation and the production of milk-clotting enzyme by A. rouxii in the rice liquid culture. The maximum milk-clotting enzyme activity of ca. 1.22 unit/mL of medium was observed in the 3-day static culture of test organism grown at 30 °C in the medium containing 20 % of gelatinous rice, while mycelial propagation increased with the increase of cultivation time and shaking speed. Furthermore, a significant increase (p<0.05) in the milk-clotting enzyme activity of ca. 1.90 unit/mL of medium, which was about 1.55-fold of the control, was observed when Al³⁺ was added to the rice liquid medium.

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