Enzyme biosensors food analysis

Stability, duration, sensitivity, interference, and availability of substrates to contact enzymes are the criteria for the success of an enzyme sensor. These criteria depend on sources of enzymes, immobilization techniques, and transducers used. Food matrices are much more complicated than the clinical samples, hence, these criteria become extremely important for the application of the enzyme sensor in food analysis. An extensive list of the response time, detection limits, and stability of biosensors was summarized by Wagner (59). 

Fundamental approaches for enzyme electrochemical biosensors applied to food analysis... 

Table 13.2 summarises the different approaches used to construct enzyme electrochemical biosensors for application to food analysis based on the different types of enzymes available. Generally, the main problems of many of the proposed amperometric devices have been poor selectivity due to high potential values required to monitor the enzyme reaction, and poor sensitivity. Typical interferences in food samples are reducing compounds, such as ascorbic acid, uric acid, bilirubin and acetaminophen. Electrocatalysts, redox mediators or a second enzyme coupled reaction have been used to overcome these problems (see Table 13.2), in order to achieve the required specifications in terms of selectivity and sensitivity. 

Another advantage offered by ICPs is that the eleetroehemieal synthesis allows the direet deposition of the polymer on the electrode surfaee, while simultaneously trapping the protein molecules. It is thus possible to control the spatial distribution of the immobilized enzymes, the film thickness and modulate the enzyme activity by changing the state of the polymer. Because of these ICPs have been used in the fabrication of biosensors in various fields such as Health eare, immuno sensors, DNA sensors, environmental monitoring, and food analysis. 

Prodromidis, M.I., Karayannis, M.I. (2002). Enzyme based amperometric biosensors for food analysis. Electroanalysis 14 241-61. 

The quality assessment of food and fodder products requires analysis of protein, carbohydrates and fat. The enzyme electrode-based analyzers originally developed for clinical chemistry have found only limited application in food analysis because they are only suitable for the determination of one parameter, mostly glucose or a disaccharide. The increasing concern for food quality require new types of biosensors allowing residual and hygiene control and on-line measurement of age and freshness (Tschannen, 1988). 

Since hydrogen peroxide is the product of reactions catalysed by a huge number of oxidase enzymes and is essential in food, pharmaceutical, and envitonmental analysis, its detection was and remains a necessity. Many attempts have been made in order to develop a biosensor that would be sensitive, stable, inexpensive and easy to handle. The most popular and efficient of them are amperometric enzyme biosensors, which utihsed different types of mediators and enzymes, mosdy peroxidase and catalase. Unfortunately many of the sensors developed do not mea the requirements for a practical device, which has a balance of technological charaaeristics (sensitivity, reliability, stability) and commercial adaptability (easy of mass production and low price). Thus a window of opportunity still remains open for future development. We hope that the present work will inspire other researches for further advances in the area of biosensors, in particular sensors for detection of such an important analyte as hydrogen peroxide. 

Sensors used for determination of pesticide (pro-poxur, paraoxon) residues in vegetables are enzymatic multimembrane devices whose functioning is based on the principle of inhibition of the activity of an enzyme such as acetylcholine esterase. This reaction is monitored by a pH sensor. The response of such biosensors to herbicides and pesticides opens a new area of testing possibilities in food analysis. 

The detection of biologically active molecules with high selectivity is a very important task for researchers working in the field of analytical electrochemistry. Biosensors fabricated from conducting polymers and enzymes can be utilized in various fields, such as in medical diagnosis and food analysis in order to detect glucose,... 

In principle, enzyme-based biosensors have potential application in the agro-food analysis, within three main areas that are food safety, food quality, and process control. The term food safety involves the concept of the production and marketing of harmless food, monitoring the presence of contaminants, such as residues of pesticides, fertilizers, heavy metals, and other toxic organic compounds also used as additives. Food quality is related not only to safety but mainly to nutritional value and acceptability. Thus, in this context freshness, appearance, flavor, texture, and composition are food characteristics that have to be controlled. Moreover, enzyme biosensors allow the determination and quantification, on-line, of compounds of interest in process control, such as fermentation, sugar, alcohols contents, and so on. 

In the following section an example of the use of disposable graphite sensor based for food analysis will be described. In particular, the use of these sensors to develop enzymatic biosensors for pesticide detection based on AChE (acetylcholinesterase) enzyme inhibition will be described. 

In a third example case, p-carbolines are inhibitors of monoamine oxidases (MAO-A and MAO-B) and can be found in foods, hallucinogenic plants or certain plant dmgs. The referred article described a fast analysis method for p-carbolines based on the inhibition of MAO [79]. The MAO-A is inhibited by all three tested P-carbolines (harmane, norharmane and harmaline), while MAO-B is inhibited only by norharmane. The presence of norharmane in mixtures of p-carbolines can be identified based on the difference between the cumulative inhibition of MAO-A by all p-carbolines and MAO-B inhibition. The enzymes were immobilized on screen-printed electrodes modified with a stabilized film of Pmssian blue that contain also copper. Benzylamine was used as substrate for the enzymatic reaction and the hydrogen peroxide formed was measured amperometrically at —50 mV. The developed biosensors were used for food analysis. The detection limits obtained were 5.0 pM for harmane and 2.5 pM for both harmaline and norharmane. 

Engineered variants of enzymes could be another approach in biosensor design for the discrimination and detection of various enzyme-inhibiting compounds when used in combination with chemometric data analysis using ANN. The crucial issues that should be addressed in the development of new analytical methods are the possibility of simultaneous and discriminative monitoring of several contaminants in a multi-component sample and the conversion of the biosensing systems to marketable devices suitable for large-scale environmental and food applications. 

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