New Glucose Biosensor Analytical Tool for Approximate Assessment

EDITURA ACADEMIEI ROMNE http://www.ear.ro

Romanian Journal of Food Science

Official Journal of the Romanian Association of Food Professionals

http://www.asiar.ro

Romanian Journal of Food Science 2011, 1(1): 1625 16

New glucose biosensor: analytical tool for approximate assessment of acrylamide formation in processed potatoes Carmen CREANGA * and Nabil EL MURR * University of Nantes CEISAM (UMR-CNRS 6230), B.P. 92208 44322 Nantes Cedex 03, France Received 2 October 2010; received in revised form 5 November 2010; accepted 8 November 2010

Abstract

The disposable glucose biosensor that was developed is based on the concept of redox-flexible biosensor. It associates two enzymes, the glucose oxidase (GOx) and horse radish peroxidase (HRP), with the same redox mediator, namely, a derivative of ferrocene/ferricinium couple (FcR/FcR+). The detection step combines the basic principles of the first and second generations of glucose biosensors with the addition of an important alternative for the detection of hydrogen peroxide (H2O2) based on redox mediated peroxidase reaction. Such a configuration offers the option to work either in oxidation or in reduction mode. For measuring low concentrations of glucose, the anodic mode is affected by the competition between the ferricinium cation and the oxygen for the oxidation of glucose in the presence of GOx. Only the cathodic detection mode prevails in these cases. The use of carboxy-ferrocene as a mediator permits to develop a sensitive biosensor capable of measuring concentrations as low as 0.01 mM, which makes it suitable to quantify glucose in potato varieties appropriate for frying and roasting, i.e. which contain small amounts of reducing sugars. By using this biosensor, the existence of good correlations between the amount of glucose in the raw potatoes and the colour index assigned to corresponding chips and to their acrylamide contents were showed. Additionally, these results show promising outlook for the assessment of the formation of suspected carcinogen acrylamide in cooked potatoes.

Keywords: glucose biosensor, acrylamide, potato.

1. Introduction

In 2002 the University of Stockholm and the Swedish National Food Authority (SNFA) published the results of a research survey, which showed that unexpectedly high levels of acrylamide were generated in a wide range of starch-rich foods when cooked at high temperatures (Tareke et al., 2002; Website 1). Further research has quickly confirmed these results and established that the main pathway for acrylamide formation in food is linked to the * Corresponding authors: E-mail addresses: [email protected] (C. Creanga), [email protected] (N. El Murr).

Maillard reaction, which involves the thermal degradation of aminoacids (asparagine) in the presence of reducing sugars (glucose, fructose) (Mottram et al., 2002; Stadler et al., 2002). This finding was of great importance, since acrylamide is classified by the International Agency for Research on Cancer (IARC) as probably carcinogenic to humans (Website 2).

Due to concerns on the possible risks of dietary exposure to acrylamide for public health, a consultation was held by the FAO/WHO in June 2002 (Health Implications of Acrylamide in Food, Report of the FAO/WHO Consultation, 2002) (Website 3). The highest acrylamide levels were found in potato chips (French fries), potato crisps.

New glucose biosensor: analytical tool for approximate assessment of acrylamide formation in processed potatoes


and other fried, deep-fried or oven-baked potato products. Several reports have mentioned the good correlation between formation of acrylamide and the reducing sugars concentration (glucose/fructose) in raw potatoes (Amrein et al., 2003; Biedermann-Brem et al., 2003; Thomas et al., 2004; Fiselier and Grob, 2005; Sheperd et al., 2010; Website 4). Controlling reducing sugars content can therefore help to restrain acrylamide levels in cooked potato products. It can also help to predict quickly the amount of acrylamide which may be formed. The analytical methods commonly used for measurements of sugars (Gas Chromatography, Spectrophotometry) often require expert staff and especially a long and tedious sample preparation. Biosensors have the advantage of being sensitive analytical tools, easy to use even by unskilled people and allow to achieve rapid and inexpensive measures. In this context, the glucose biosensor seemed to be useful for rapid assessment of acrylamide formation in French fries by simply measuring glucose in raw potatoes. The measurement of glucose alone (without fructose) could, in many cases, provide a useful approximate prediction for acrylamide formation. For this purpose, a new disposable mediated enzyme based biosensor was developed. It is capable of measuring low concentrations of glucose (0.011 mM), in accordance with the needs of potato industries, which process potatoes with very little reducing sugars content. 2. Materials and methods 2.1. Chemicals

Glucose oxidase (GOx, code GO3AC), horse radish peroxidase (HRP, code HRP4C) and Mutarotase (MUR1F) were purchased from Biozyme UK. Phosphate buffered solutions were prepared using KH2PO4, K2HPO4, and KCl, all commercially available from Fluka. Ferrocene derivatives were purchased from Aldrich. Aqueous solutions were prepared in distilled water. All chemicals were of the highest analytical grade and used as received. 2.2. Apparatus

Cyclic voltammetry and chronoamperometry experiments were carried out with a PG580 Potentiostat from UniScan, UK. Electrochemical characterization and analytical measurements were performed using screen-printed electrochemical cells (Gwent Group Ltd., UK) in a two-electrode configuration consisting of a circular carbon

working electrode (6 mm diameter) surrounded by an Ag/AgCl ring, which served as the reference and counter electrode. 2.3. Disposable biosensor and sample preparation

The general procedure for preparing the biosensors has been previously described (Creanga and El Murr, 2010a). Samples were prepared by crushing potato strips with water in a blender, and a few millilitres of the juice were filtered through cotton placed at the bottom of a plastic syringe. 2.4. Assay procedure

A volume of 40 L of the filtered potatoes solution was placed on the surface of the biosensor to measure glucose. The sample solution was left to react for 3 minutes before applying a potential of 0.1 V vs Ag/AgCl on the surface of the working electrode in chronoamperometry mode for 20 seconds. The program that controls the PG580 UniScan potentiostat allows for the operation to be automatically managed by creating a cascade profile that sets the delay time for reactions to the end, the applied potential, and the chronoampero-metry duration. To approximate the industrial use of the biosensor, a single measurement was normally performed. Only in the case of a flagrant error a second measurement was carried out. 3. Results and discussion 3.1. Potatoes and acrylamide

In spite of considerable cultural and national differences in food consumption patterns and cooking traditions, potatoes are considered to be one of the most important nutritional sources all around the world. To focus world attention on the importance of the potato in providing food security and alleviating poverty, 2008 was declared by United Nations the International Year of the Potato. Tables 1, 2 and 3 (Website 5) show that the world potato sector is undergoing major changes. Until the early 1990s, most potatoes were grown and consumed in Europe, North America and countries of the former Soviet Union. Since then, there has been a dramatic increase in potato production and demand in Asia, Africa and Latin America, where output rose from less than 30 million tonnes in the early 1960s to more than 165 million tonnes in 2007. FAO data show that in 2005, for the first time, the developing worlds potato production exceeded that of the developed world. China is now the biggest potato producer and almost a third of all potatoes is harvested in China and India (Website 5).

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Carmen CREANGA and Nabil EL MURR


Table 1. World potato production, 19912007

1991 1993 1995 1997 1999 2001 2003 2005 2007 Year Countries Potato production, Million tons Developed 183.13 199.31 177.47 174.63 165.93 166.93 160.97 159.97 159.89 Developing 84.86 101.95 108.50 128.72 135.15 145.92 152.11 160.01 165.41 WORLD 267.99 301.26 285.97 303.35 301.08 312.85 313.08 319.98 325.30

Much of the potato production is destined for

processing industries which, nowadays, promote in particular the production of frozen foods to be fried or baked at high temperature. The growth of the fast food industry in the last 20 years spurred the shift toward frozen potato products, mainly French fries, which became the most preferred product by children and adolescents. The discovery of the formation of acrylamide, a substance classified as a human neurotoxin, showing genotoxic and carcinogenic properties (Website 6), in starch-rich foods, such as potatoes, when cooked at elevated temperatures (Website 7), associated with the huge potatoes market (Tables 13), have attracted consi-derable attention from researchers and government agencies. Two main areas have been targeted: the first relates to the understanding and prediction of acrylamide production and the second to the approaches for reducing its formation.

Table 2. Top ten potato producers, 2007

No. Country Quantity, tons 1. China 72,040,000 2. Russian Fed. 36,784,200 3. India 26,280,000 4. United States 20,373,267 5. Ukraine 19,102,300 6. Poland 11,791,072 7. Germany 11,643,769 8. Belarus 8,743,976 9. Netherlands 7,200,000 10. France 6,271,000

Table 3. Potato consumption, by region, 2005

Consumption Region Population Total food,

tons kg per capita

Africa 904,388,000 12,571,000 13.9 Asia/Oceania 3,934,644,000 94,038,000 23.9 Europe 739,203,000 64,902,000 87.8 Latin America 562,270,000 11,639,000 20.7 North America 330,400,000 19,824,000 60.0 World 6,484,792,000 202,974,000 31.3

Several research groups (Mottram et al., 2002;

Stadler et al., 2002) have proposed that the main pathway to acrylamide formation in food is via the

reaction between asparagine and a carbonyl source (e.g. reducing sugars) catalysed by basic ammonium salts. Glucose and fructose are the important reactants so far identified. Both asparagine and reducing sugars can be found in potatoes in higher amounts than in any other starch-rich food products, and when they react at cooking temperatures, acrylamide is formed as a result of the Maillard reaction, which gives the fried potatoes their characteristic browning. Therefore, factors which affect the concentration of precursors (in particular reducing sugars) such as crop variety, maturity at harvesting, temperature and time of storage (Hebeisen et al., 2005) and level of nitrogen and phosphorous in the soil (Heuser et al., 2005) affect acrylamide formation in the cooked product. A number of recent studies have followed the amino acid and sugar content of potatoes during storage. Generally, storage at 220C for several months had little effect on the free asparagine content, and where different cultivars were compared, all responded in a similar way. The relative stability of amino acid content during storage at low temperatures contrasts markedly with large increases seen in glucose, fructose, and sucrose concentrations (Lea et al., 2007 and references therein). Storage of potatoes at temperatures below 810C has shown to increase the concentration of reducing sugars drastically and thus increase the acrylamide formation when frying the potatoes. Therefore, controlling storage conditions of potatoes is a simple method for reducing sugar contents and, consequently, acrylamide levels in cooked potato products.

Glucose and fructose are the major constituents of reducing sugar in potato tuber. Invertase hydrolyzed sucrose into equimolar glucose and fructose ratio. However, different turnover rates of glucose and fructose may cause the ratio to deviate from exact equimolarity. Many studies have shown that there was a strong correlation between the reducing sugar content in raw potatoes (the total reducing sugar or glucose or fructose alone) and acrylamide level in corresponding chips after frying. Thus, the measurement of glucose, failing to measure the three major precursor compounds of acrylamide (asparagine, fructose, and glucose), can

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be used as a marker for the assessment of possible formation of acrylamide (Ohara-Takada et al. 2005; Brunton et al., 2007; Website 8). This measure can indicate if potatoes are suitable for roasting or frying regarding acrylamide formation and the colour of the end product. From the perspective of industrial use, or even at home, the determination of this quality should be simple, in order to enable routine control by unskilled people. Furthermore, the device to measure glucose should not be very sophisticated, but, at the same time, it should allow sensitive measurements. They include the acceptable quantities of reducing sugars in raw potatoes (less than 1 g/kg) (Biedermann-Brem et al., 2003; Fiselier and Grob, 2005) that enable after frying or roasting to obtain end products of very good quality and containing the smallest amount of acrylamide. 3.2. Glucose biosensor Biosensors are analytical tools, which combine a biochemical recognition component with a physical transducer. The biological sensing element can be an enzyme, antibody, DNA sequence, or even a micro-organism. The biochemical component serves to catalyse selectively a reaction or facilitate a binding event. The transducer converts the biochemical event into a measurable signal, thus providing the means for detecting it. Signal measurement is based on concurrent change in a physiochemical parameter (e.g. heat, electron transfer, light, ion or proton flow, etc.).

Biosensors using redox enzymes, more particularly the glucose oxidase (GOx), are by far the most studied. Their popularity is largely the result of scientific advances in the fields of analytical chemistry and also because of their large economic and commercial success. Different generations of oxidase-based biosensors have been developed in particular to improve their analytical properties, mainly their detection limit and selectivity, under the influence of the interference of many substances present in complex matrices of real samples (e.g., blood, food).

Since Clark and Lyons (1962) proposed the original concept of glucose enzyme electrodes, the number of publications dedicated to the preparation of new

modified electrodes for the amperometric analysis of glucose has continued to grow. The main driving force for this expansion has undoubtedly been the need to manufacture reliable devices for monitoring diabetes. The great demand for home-care devices and the huge market for blood glucose analysis formed the basis of the rapid growth in development of amperometric glucose biosensors. Many groups worldwide have conducted research, generating an enormous number of publications and leading to considerable improvements in the original concept (Wang, 2008 and references therein).

The research accomplished during almost 50 years has mainly led to two generations of glucose biosensor. The first generation is based on the oxidation reaction (reactions 14) that associates glucose with its natural oxygen substrate.

The measurement of glucose is based on the electrochemical quantification of either the decrease of oxygen concentration (reaction 3) or the increase of hydrogen peroxide concentration (reaction 4). Practically, the measurement of H2O2 formation is simpler. It is commonly achieved at a potential of approximately +0.6 V vs. Ag/AgCl on a platinum electrode.

The first-generation biosensor, which depends on oxygen, had the advantage of measuring low glucose concentrations, but it also had the disadvantage of low oxygen availability and fluctuation of its concentration. This behaviour reduced the upper limit of detection and impaired the accuracy of measurements. Both disadvantages were major drawbacks for blood glucose analysis, which led many teams to develop new approaches to avoid the restriction of oxygen for glucose measurement (Gough et al., 1985; Reach and Wilson, 1992; Wang and Lu, 1998; Wang et al., 2001).

One successful approach was the use of redox mediators to substitute the oxygen in the oxidation reaction of glucose in the presence of GOx and to shuttle electrons between flavine adenine dinucleo-tide (FAD), the redox active centre of GOx, and the electrode surface (Wang, 2008 and references therein). This approach formed the foundation of the second generation of glucose biosensors.

Glucose + GOx(FAD)

GOx(FADH2) + O2O2 + 4H+ + 4e-

H2O2

Gluconolactone + GOx(FADH2) (1)

GOx(FAD) + H2O2 (2)

2H2O (3)

O2 + 2H+ + 2e- (4)

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The second-generation glucose biosensor is based on reactions 5, 6, and 7 where Mox and Mred are the oxidized and, respectively, the reduced forms of the artificial mediator that exchanges electrons between the FAD of GOx and the electrode surface. The reduced form Mred is oxidized at the electrode surface to generate Mox, which, like oxygen in reaction 2, regenerates the oxidized form of GOx and the reduced form of the mediator. Thus, the redox mediator is involved at the electrode surface in a catalytic regeneration mechanism (EC), studied by Savant and Vianello (1967), which amplifies the anodic current produced at the electrode. The catalytic current generated in the (EC) mechanism is directly related to the concentration of the chemical species, which does not exchange electrons with the electrode surface (GOx here), but with the electro-generated species (reaction 6). The derivatives of ferrocene ((C5H5)2Fe or FcH) were the first artificial redox mediators and probably the most commonly used in the oxidation reaction of glucose in the presence of GOx (Cass et al., 1984; Frew and Hill, 1987). This has enabled the successful production and marketing of reliable and easy-to-use biosensors for glucose measurement in blood. Many other artificial redox mediators such as ferricyanide, transition metal complexes and polymers, and phenothiazine have been used to relay electrons between the working electrode surface of the biosensor and GOx, permitting the preparation of a wide variety of reagentless glucose biosensors (Shichiri et al., 1982; Degani and Heller, 1987; Pishko et al., 1990; Maidan and Heller, 1992; Vijayakumar et al., 1996; Popescu et al., 1996; Wang, 2001).

As far as glucose measurement in blood is concerned, the second-generation of glucose biosensor has solved the problems observed with those of the first generation. In particular, (1) it is not dependent on the oxygen and is not disturbed by its fluctuation; (2) the potential applied at the working electrode is less anodic than the one for H2O2 detection, which avoids interference from side electro-active products; and (3) it offers a significantly higher upper limit for the linear range that matches physiological concentrations of glucose in blood.

The tremendous success of the amperometric biosensor for glucose measurement in blood and the ease of its use showed that other activities, such as bioprocess monitoring, as well as food and environmental analysis, could take advantage of these advances. The application of biosensors to these other activities remains rare in contrast to the huge success in biological analysis. On the one hand, unlike glucose measurement in blood, biosensors for environmental or food analyses are dependent on niche-type markets, where the demand is varied and the sale volume quite low. On the other hand, the technical specifications of biosensors needed for these fragmented markets are not identical to those developed for glucose analysis in blood, particularly regarding interferences, detection limits, and concentration scale levels. To bring biosensors into such a fragmented market, new and flexible designs should be considered. In this context, the possibilities to combine the basic principles of the two generations of glucose biosensor with the addition of an important alternative for the detection of H2O2 based on redox mediated peroxidase reaction (reactions 8 and 9) were examined.

This combination leads to redox flexible biosensors or bioassays that offer the option to work either in oxidation or in reduction mode (Figure 1) (Charpentier and El Murr, 1995; Rondeau et al., 1999; Serban et al., 2004; Serban and El Murr, 2006; Creanga and El Murr, 2010a, 2011). In such a configuration, the same ferrocene/ferricinium couple (FcR/FcR+) acts as the redox mediator for the oxidation of the reduced form of glucose oxidase and for the reduction of the oxidized form of peroxidase. The advantage of this system is the usage of the reduction mode for measuring low amounts of glucose substrate. The disadvantage is mainly caused by the participation of the oxidized form of the mediator (FcR+), used for the quantify-cation of H2O2, in the reaction of oxidation of glucose catalyzed by GOx. This interfering reaction affects the signal amplitude and thus the reliability of the measurement.

Glucose + GOx(FAD)

GOx(FADH2) + 2Mox2Mred

Gluconolactone + GOx(FADH2) (5)

GOx(FAD) + 2Mred + 2H+ (6)

2Mox + 2e- (7)

2Mox + 2e 2Mred (9)

H2O2 + 2Mred + 2H+ 2H2O + 2Mox (8)HRP

2Mox + 2e 2Mred (9)2Mox + 2e 2Mred (9)



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Gluconic acid Glucose

Anodic mode2FcR

-2e2FcR+

O2

H2OH2O2

Cathodic mode

2FcR

2FcR+

+2e

K2

GOx

HRP

K1

K3

Interference

Gluconic acid Glucose

Anodic mode2FcR

-2e2FcR+

O2

H2OH2O2

Cathodic mode

2FcR

2FcR+

+2e

K2K2

GOxGOx

HRPHRP

K1K1

K3K3

InterferenceInterference

Figure 1. General scheme of reactions that can occur at the surface of the biosensor before

and after the heterogeneous electron transfer reactions.

The amplitude of the interference depends on the redox mediators, which influence the rate constants K2 and K3 of the two mediated enzymatic reactions, which take place in the solution deposited on the surface of the biosensor (Creanga and El Murr, 2010b). Such interference is particularly detrimental when measuring samples with low concentrations of glucose. A large number of ferrocene derivatives were tested and some of them, in particular the carboxy- ferrocene (FcCO2H), were found to strongly disadvantage the reaction rate K2 compared to K3. In this case, reactions 1, 2, 8 and 9 occur preferentially so that the current resulting from the reduction of the ferricinium derivative will be proportional to the amount of glucose. The advantage of this biosensor, although limited by the oxygen availability, is the ability to measure accurately concentrations as low as about 0.01 mM of glucose. This makes it a very suitable biosensor for measuring glucose in potato varieties appropriate for frying and roasting, i.e. which contain small amounts of reducing sugars. 3.3. Glucose biosensors for potatoes analysis

The great demand for measuring blood glucose for diabetics has boosted the development of various analytical tools for self-monitoring. This has brought into the market several devices easy to use and which virtually do not require tedious calibration. It seemed interesting to test such devices for analysis of glucose in aqueous media other than blood to find out if they could be used for measuring glucose in the juice of potatoes. The most popular devices

available on the home care market are the second generation type amperometric biosensors. A typical calibration curve obtained with such devices is shown in Figure 1: this graph indicates that the values displayed by the device do not reflect the real concentrations of standard glucose solutions because the biosensor is tailored for measurements in blood. This does not represent a handicap for its use in other media since it offers a linear range accessible by simple calibration. Calibration curve in Figure 2 shows that the glucometer presents a linear range between 1 and 5.5 g/L for aqueous standard solutions of glucose. Between 0.6 and 1 g/L the signal decreases significantly and below 0.6 g/L the glucometer indicates no value (see insert in Figure 2). Given these analytical behaviours, such a glucometer is not satisfactory for potato industries. Indeed, the objective regarding acrylamide is to use potatoes containing less than 1 g/kg of reducing sugars (Biedermann-Brem et al., 2003; Fiselier and Grob, 2005), value which corresponds to approximately 0.5 g/kg of glucose.

The redox-flexible glucose biosensor, developed using various ferrocene derivatives as mediators, was also tested and its ability to measure low concentrations of glucose was examined. Figure 3 shows the calibration curves in the anodic and cathodic mode obtained with a redox-flexible biosensor using the couple Fc(CO2H)/[Fc(CO2H)]+ as mediator. In the anodic mode, this biosensor acts as a second generation biosensor and does not allow accurate measurements for low substrate concentra-tions, due to the competition between oxygen and

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Figure 2. Calibration curve obtained with blood glucometer device.

y = - 66.861x - 0.329R2 = 0.999-10

-8

-6

-4

-2

0

2

4

0,0 0,1 0,2 0,3 0,4

Glucose, g/L

Cur

rent

, A

Anodic modeCathodic mode

Figure 3. Anodic and cathodic calibration curves

obtained with a redox-flexible biosensor. ferricinium cation for the oxidation of glucose (Martens et al., 1995; Creanga and El Murr, 2010b). On the contrary, in cathodic mode, the biosensor shows good sensitivity (66.8 A.L/g) and linear range (0.004 - 0.01 g/L), which makes it appropriate for the analysis of potato juices even with very low glucose levels.

Measuring glucose in raw potatoes provides a good estimate of the colour of French fries (Roe et al., 1990; Khanabari and Thomson, 1993; Pritchard and Adam, 1994). In the potato processing industry, fry colour is often assessed using the chips colour chart recommended by the US Department of Agriculture (USDA), which has seven grades starting from light coloured chips to dark coloured chips. Figure 4 shows the comparative results

obtained from different varieties of potatoes for which the amount of glucose was measured using the biosensor and the colour of fried strips evaluated using the USDA colour chart. The obtained correlation shows that the glucose biosensor can be used to predict the colour of fried potatoes in a quick and easy way.

y = 0,51x - 0,94R2 = 0,82

0,000,200,400,600,801,00

1,201,401,601,802,00

1,5 2 2,5 3 3,5 4 4,5 5

Colour index

Glu

cose

, g/k

g

Figure 4. Correlation between glucose content in raw potatoes measured with the redox-flexible biosensor

and index colours of corresponding French fries.

Several studies have shown that there is a correlation between the chips colour, resulting from the Maillard reaction between reducing sugars and asparagine, and the amount of acrylamide in French fries (Ohara-Takada et al., 2005; Brunton et al.,

y = 1.870x - 0.205R2 = 0.999

0

1

2

3

4

5

0 1 2 3 4 5 Standard glucose solutions, g/L

Glucose measured with glucometer, g/L

0

0.25

0.5

0.75

1

0 0.25 0.5 0.75 1

y = 1.870x - 0.205R2 = 0.999

0

1

2

3

4

5

0 1 2 3 4 5 Standard glucose solutions, g/L

Glu

cose

mea

sure

d w

ith g

luco

met

er, g

/L

0

0.25

0.5

0.75

1

0 0.25 0.5 0.75 1

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2007; Website 8). The correlation shown in Figure 3 suggests that the most promising application for the use of biosensor would be the rapid, cheap, and simple assessment of acrylamide formation in cooked potatoes by measuring the amount of glucose in the raw material. The first results in this area are given in Figure 5, which shows the relationship between the amount of glucose in different varieties of raw potatoes, measured by the biosensor, and the amount of acrylamide in the corresponding French fries, determined by HPLC-MS/MS analysis carried out by a private laboratory. In this experiment, the potato strips were fried for 6 minutes in oil bath maintained at 180C.

Karlena

ProxyDesiree

Celina

Solara

Melody

Linday = 34.49x + 91.71

R2 = 0.795

0

100

200

300

400

500

600

0 2 4 6 8 10 12Glucose, g/kg

Acr

ylam

ide,

g/

kg

Figure 5. Correlation between glucose content in

different raw potatoes varieties measured with the redox-flexible biosensor and acrylamide content

in corresponding French fries.

4. Conclusions

Disposable redox-flexible amperometric biosen-sors using appropriate mediator and operating in cathodic mode are suitable for the analysis of the juices of potato varieties that contain very low glucose levels. This type of biosensor is inexpensive and easy to use even by unskilled people. It is sensitive, presents a wide linear range and is able to measure glucose concentrations as small as 20 mg/L. Validation has been performed on real samples and showed the existence of a good correlation between the amount of glucose measured in raw potatoes with the new disposable biosensor and the colour of the corresponding French fries. First experiments performed on a limited number of potato samples gave promising results and showed the prospect to assess the formation of the suspected carcinogen acrylamide using the glucose biosensor.

The present study is currently extending to a large number of samples of different potato varieties. Acknowledgments

The authors of this paper would like to thank Gwent Group Ltd., UK, who provided them with the disposable electrochemical transducers, Aviko, which allowed them to validate the biosensor in their potatoes processing plant in Holland and the European Commission for financial support (Grant: COOP-CT-31588).

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Website 4. http://www.teagasc.ie/ashtown/research/ preparedfoods/ACRYLAMIDE%20EoPR.pdf.

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Abbreviations FAD flavine adenine dinucleotide FAO Food and Agriculture Organization of the United

Nations FcR/FcR+ ferrocene/ferricinium couple GOx glucose oxidase H2O2 hydrogen peroxide HRP horse radish peroxidase K reaction rate Mox/Mred oxidized/reduced mediator

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2011-no1-03-Creanga-El-Murr-p162011-no1-03-Creanga-El-Murr-p17-25

New Glucose Biosensor Analytical Tool for Approximate Assessment

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