title: Production and characterization of a milk-clotting enzyme from Aspergillus oryzae MTCC 5341.
abstract: Microbial milk-clotting enzymes are valued as calf rennet substitutes in the cheese industry. Aspergillus oryzae MTCC 5341 was identified to produce the highest milk-clotting activity during screening of 16 fungal strains. Solid state fermentation using wheat bran along with 4% defatted soy flour and 2% skim milk powder as substrate was optimal for growth of A. oryzae and production of the enzyme. Nearly 40,000 U/g bran of milk-clotting activity was present at the end of 120 h. The enzyme could be recovered by percolating the bran with 0.1 M sodium chloride for 60 min at 4 degrees Celsius. The decolorized enzyme preparation had high ratio of milk clotting to proteolytic activity. Affinity precipitation with alginate and subsequent elution with 0.5 M sodium chloride containing 0.2 M CaCl(2) resulted in an enzyme preparation with specific activity of 3,500 U/mg and 72% yield. Optimum pH and temperature for activity of the enzyme were characterized as 6.3 and 55 degrees Celsius, respectively. Milk-clotting enzyme showed differential degree of hydrolysis on casein components. High ratio of milk clotting to proteolytic activity coupled with low thermal stability strengthens the potential usefulness of milk-clotting enzyme of A. oryzae MTCC 5341 as a substitute for calf rennet in cheese manufacturing.
authors.affiliation: Department of Protein Chemistry & Technology, Central Food Technological Research Institute, Mysore 570020, India.
authors.forename: Kurutahalli S
authors.initials: KS
authors.lastname: Vishwanatha
authors.forename: A G
authors.initials: AG
authors.lastname: Appu Rao
authors.forename: Sridevi Annapurna
authors.initials: SA
authors.lastname: Singh
mesh_terms: D016282:Aspartic Acid Endopeptidases / Q000737:chemistry* / Q000302:isolation & purification*; D001236:Aspergillus oryzae / Q000201:enzymology* / Q000254:growth & development; D002611:Cheese; D012085:Chymosin; D004795:Enzyme Stability; D005285:Fermentation; D005524:Food Technology; D005656:Fungal Proteins / Q000737:chemistry* / Q000302:isolation & purification*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007218:Industrial Microbiology
chemical_list: D005656:Fungal Proteins; C025350:rennet; D016282:Aspartic Acid Endopeptidases; C022517:rennin-like enzyme (Aspergillus ochraceus); D012085:Chymosin