Electrochemical enzyme biosensors based on calcium phosphate materials for tyramine detection in food samples

Electrochemical tyrosinase biosensors for tyramine determination were developed by the immobilization of the enzyme in calcium phosphate materials (CaPs) followed by cross-linking with glutaraldehyde. Tyramine was detected by the electrochemical reduction at -0.1 V of the o- enzymatically-formed dopaquinone. Three different CaPs were explored as immobilization systems, monetite, brushite and brushite cement. Biosensors based on brushite matrices provide better analytical properties than the monetite one. Compared to brushite, a 10-fold increase of sensitivity was obtained with the brushite cement-based biosensor, which highlights the effect of brushite crystal formation in the presence of the enzyme in the biosensor performance. Several variables involved in the enzyme immobilization method such as glutaraldehyde cross-linking time, PPO/brushite ratio and thickness of the brushite-enzyme film were investigated. Furthermore, the effects of pH and temperature on biosensor performance were also optimized. Brushite cement-PPO-GA biosensor resulted in a reliable, highly sensitive, fast, inexpensive and easy analytical method for tyramine detection. Under optimal conditions (time of 15 min, a ratio of 1.0 and 50 mu g of the brushite-enzyme mixture, 20 degrees C and pH 6,0), a linear range of 5.8 x 10(-7) to 1.6 x 10(-5), sensitivity 1.50 x 10(3) mA M-1 cm(-2), detection limit, 4.85 x 10(-8) M and a response time, 6 s were obtained. The suitability of the proposed biosensor to determine the tyramine content in cheese samples has been explored. The mean analytical recovery of added tyramine in gouda and brie cheeses were found to be 95.5 +/- 5.8 and 96.9 +/- 7.5 respectively. A study of the tyramine content evolution over the course of a week under inadequate storage showed the importance of monitoring the degradation of certain foods.