Hybrid biosensors to estimate lactose in milk

Hybrid biosensors for the determination of lactose were developed. Saccharomyces cerevisiae was entrapped in agar. Lactases (Lactozym and β-galactosidase of Enterobacter agglomerans) were adsorbed onto diethylaminoethyl cellulose (DE-52). Catalytic components were confined between the surface of a gas-permeable membrane of a CO2 electrode and a dialysis membrane. Lactases hydrolysed lactose and Saccharomyces cerevisiae fermented glucose and galactose producing CO2. This gas was measured by a CO2 electrode. These biosensors showed Nernstian characteristics. The semilogarithmic concentration range was between 0.5% and 10%. The lifetime of these biosensors was two weeks and two months, respectively. The results were applied to lactose analysis in milk samples. Validation of the assays was made on milk of several dairy brands by comparison with a spectrophotometric method.