Hiromi Murakami
Osaka Municipal Technical Research Institute, Japan
Title: Microbial Conversion of Lactose to Calcium Lactobionate
Biography
Biography: Hiromi Murakami
Abstract
Objective: Concerned about utilization of lactose and development of high-soluble calcium supplement, with an interest on biological oxidation of oligosaccharide, we examined microbial and enzymatic oxidation of lactose and aimed to establish effective production systems of calcium lactobionate. Lactobionate, b-1,4-D-galactosyl-D-gluconate, is an oxidized product of lactose. It has been reported to have mineral-absorption-promoting effects, Biffidobacterium-growing activity, moisturizing effect, and high solubility in water. Despite its useful properties, lactobionate has been supplied only in a small scale by chemical oxidation because there is no easy and efficient way to produce it.
Results: As for fermentation, we isolated a mutant strain of Burkholderia cepacia which has no b-galactosidase activity to avoid hydrolysis of lactose and has sugar-tolerance to react with concentrated lactose. After 4-day cultivation, lactose was completely disappeared and the equivalent molarity of calcium lactobionate was accumulated. In the case of 10-day-fed-batch culture, the final concentration of the product reached 400 g/L in 100% yield. The product was purified from culture supernatant by ethanol precipitation.
As for microbial conversion, cells were incubated with 100 to 200 g/L of lactose and half mole equivalent calcium carbonate to lactose. The oxidation activity of the cells was defined as the amount of cells which produced 1 mmol of D-gluconate per minute from 0.1M D-glucose under the assay conditions. When 2 U/mL of cells were incubated with 100 , 150 and 200 g/Lof lactose, it took 18, 27 and 48 h for 100% conversion. Reuse of resting cells was available for repeated conversions. Cells of Gluconobacter sp.were also used for microbial conversion. As for enzymatic conversion, we isolated a strain of Paraconiothyrium sp. which secreted a stable oxidase in culture. These biological conversion systems of lactose were effective to produce calcium lactobionate with high yield, no by-product, easy purification, and easy operation in one-pot synthesis.