1. on normal physiological function in humans.
Dietary Antioxidant
A substance in foods that significantly decreases the adverse effects of reactive species, such as reactive oxygen (ROS) and nitrogen species,
on normal physiological function in humans.
Dietary Reference Intakes, Foods and Nutrition Board 2000 NatlAcadPress

2. Some antioxidants in foods
vitamin C
vitamin E
carotenoids
glucosinolates
polyphenols flavonoids catechins isoflavones phenolic acids… …
The main antioxidants present in food

3. 1-Biosensors for the detection of polyphenols
Tyr O2
H2O2
: tyrosinase
Tyrosinase from mushroom (SIGMA)
Tyrosinase
(EC ) or monophenol monooxygenase
2 e-
Electrode
x mV/AgAgCl
tyrosinase (EC ) or catechol oxidase
There is 2 kinds of tyrosinase.
The first one is a monophenol monooxygenase which can catalyse two types of successive transformations :
In presence of oxygen, the oxidation of a monophenol in catechol (ACTIVITE CRESOLASE)
then, the oxidation of this catechol in O-quinone (benzoquinone) (ACTIVITE CATECHOLASE)
The second tyrosinase can only catalyse the oxidation of catechol in benzoquinone.
The third tyrosinase is derivated from a plant source Amorphophallus companulatus
The most sensitive to phenols biosensors are based on tyrosinase. Mushroom tyrosinase (EC ) as monooxygenase catalyses oxidation of phenols with catechol production. Further oxidation of catechols produces quinones.
tyrosinase from a plant source Amorphophallus companulatus
Calibration :
Substrat : 1,2-benzenediol = catechol
Catechol Equivalent (CE)

4. Determination of the reduction potential of benzoquinone
Scan rate : 50 mV/s

5. Calibration curve Linear range : 0,1  60 µM Sensitivity : 166 mA.M-1
300 mU /electrode
Limit of Detection : µM

6. Real samples : Grapes 100% 0.097 74% 0.0334 0.657 4.5% 21.5% 0.193
weight
74%
21.5%
4.5%
100%
0.097
0.657
0.193
µmol CE
/g product
0.0334
Pulp
Seeds
Skin
0.096

7. : Laccase (EC 1.10.3.2 ) or Urishiol oxidaseOH O
1,4-benzenediol… O2
Electrode
Lac
2 e-
H2O2
x mV/AgAgCl
Lac
: Laccase (EC ) or Urishiol oxidase
Calibration :
substrats : 1,2-benzenediol

8. 2-Biosensor for the determination of an antioxidant capacity
Electrode
2 e-
Oxidation
O2• -
SOD
H2O2
2H+
: superoxide dismutase (EC )
response
Xanthine
XOD O2
Uric Acid
SOD : This enzyme brings about the dismutation of superoxide radicals…. Spontaneous dismutation can also lead to the superoxide decomposition : (2 O2• - + 2H+ donne O2 + H2O2 )
Cette enzyme provoque la dismutation des radicaux superoxide… La présence d’antioxydants induira une diminution de la réponse du biocapteur
XOD
: xanthine oxidase (EC )

9. Lab-on-a-chip ROS Sample line generation (antioxidant) Water chamber
Mixing section
Water
Detection chamber
TiO2 nanoparticule
UV light
SOD-based biosensor