Development of biosensor based on immobilized L-glutamate oxidase for determination of monosodium glutamate in food.

A monosodium glutamate (MSG) biosensor with immobilized L-glutamate oxidase (L-GLOD) has been developed and studied for analysis of MSG in sauces, soup etc. The immobilized enzymatic membrane was attached with oxygen electrode with a push cap system. The detection limit of the sensor was 1 mg/dl and the standard curve was found to be linear upto 20 mg/dl. Response time of the sensor was 2 min. Cross-linking with glutaraldehyde in presence of Bovine Serum Albumin (BSA) as a spacer molecule has been used for immobilization. Optimization of the sensor was done with an increase in L-GLOD concentration (6.3-31.5 IU) and also with increase in loading volume of enzyme solution (5-20 microl). Optimization of pH and temperature was also studied. The permeability of O2 through different membrane was studied with and without immobilized L-GLOD. The enzymatic membrane was used for over 20 measurements and stability of the membrane was observed.

Isolation, purification, and characterization of L-glutamate oxidase from Streptomyces sp. 18G

An extracellular L-glutamate oxidase (GLOD) was purified from soil-isolated Streptomyces sp 18G. The enzyme had a molecular weight of approximately 120,000 and consisted of two identical subunits, each with a molecular weight of 61,000. The isoelectric point was pH 8.5 and the enzyme had an optimal pH between 7.0-7.4. GLOD showed the maximum activity at 37ºC. The GLOD activity was stable at pH ranging from 6.5 to 7.0 for 1 hr. Among 21 amino acids tested for substrate specificity, L-glutamate was almost exclusively oxidized. D-glutamate and L-aspartate were oxidized but only to extents of 0.79 percent and 0.53 percent, respectively.