An artificial casein micelle (ACM) solution was prepared, in which the concentrations of casein, calcium, phosphate, and citrate were close to those in skim milk. The viscosity of concentrated ACM solutions increased markedly at low temperature within several days. This phenomenon was similar to the one that takes place in highly concentrated skim milk, indicating that casein micelles play a determinant role in the viscosity increment of concentrated milk. The addition of lactose to concentrated ACM solution efficiently decreased its viscosity, suggesting a stabilizing effect of soluble lactose on casein micelles against their aggregation. The contents of micellar casein, calcium, and phosphate increased with the calcium content of the ACM solution, while the voluminosity of casein micelles decreased, and the viscosity increment of the concentrated ACM solution was accelerated. These results suggest that the increase in the interactions between casein micelles might accelerate the viscosity increment, and might overcome the suppressing effect of decreased voluminosity. The size distributions of ACM solutions were not influenced by their micellar calcium content, and almost no changes were observed after the significant increase in the viscosity, suggesting that interactions between casein micelles were weak and reversible.

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 Lactose intolerant people in Asia are about 80% population. People with lactose intolerant do not produce enough of the lactase enzyme to break down lactose contained in milk and milk products. One method for prevention, reduction or improvement is lactase supplementation, and fungal lactase (β-galactosidase) is used generally. Characteristics of fungal lactase is stability at acidic pH. Acidic stability of three lactases produced by Aspergillus oryzae, Penicillium multicolor and Aspergillus niger are different. Lactase from A. niger is most stable among them, but low-reactivity at neutral pH. Amino acid sequence homology among three fungal lactases is more than 70%, but relation between lactase character and structure is unknown. In Japan, lactase for lactose intolerance is regulated as drug and it is hard to purchase generally. A. oryzae is known as ‘Koji’ used for japanese traditional fermented foods such as miso, syoyu and sake. For this reason, lactase produced by A. oryzae is thought to be safe. If lactase can be obtained like U.S. dietary supplement, it is expected that lactase supplementation will be known widely.

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