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

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

1-Biosensors for the detection of polyphenols Tyr O2 H2O2 : tyrosinase Tyrosinase from mushroom (SIGMA) Tyrosinase (EC 1.14.18.1) or monophenol monooxygenase 2 e- Electrode x mV/AgAgCl tyrosinase (EC 1.10.3.1) 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 1.14.18.1) 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)

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

Calibration curve Linear range : 0,1  60 µM Sensitivity : 166 mA.M-1 300 mU /electrode Limit of Detection : 6.10-2 µM

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

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

2-Biosensor for the determination of an antioxidant capacity Electrode 2 e- Oxidation O2• - SOD H2O2 2H+ : superoxide dismutase (EC 1.15.1.1) 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 1.1.3.22)

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