Plasma-chemical reactions at polyphenolic surfaces- Influence of non-thermal plasma with respect to fresh produce processing F. Grzegorzewski 1,3 , O. Schlüter 1 , J. Ehlbeck 2 , L. W. Kroh 3 , S. Rohn 3 1 Leibniz-Institute for Agricultural Engineering Potsdam-Bornim (reg. Assoc.), Max Eyth-Allee 100, D- 14469 Potsdam, Germany 2 Leibniz-Institute for Plasma Science and Technology, Felix-Hausdorff-Str. 2, D-17489 Greifswald, Germany 3 Chair of Food Analysis, Department of Food Technology and Food Chemistry, Technische Universität Berlin, Gustav Meyer-Allee 25, D-13355 Berlin, Germany Food is subject to physical, chemical, and biological deterioration. To retain the characteristics of fresh or freshly-prepared foods, mild preservation technologies are gaining more and more importance. Non-thermal atmospheric pressure plasma is an innovative and emerging technology that seems to be a promising alternative to thermal conservation treatments, since an efficient inactivation of microorganisms comes along with a moderate heating of the treated surface [1]. Despite the inherent advantages of cold plasmas for preservation purposes there are to our knowledge no studies known that investigate the interactions of energetically highly reactive plasma species (electrons, UV photons, reactive oxygen species (ROS), radicals) with dietary bioactive compounds. The aim of this study was to explore the stability of selected flavonoids after exposure to a cold atmospheric pressure plasma jet [2]. From the many compounds that exist in plants flavonoids are most commonly known for their high antioxidant activity, protecting cells against the damaging effects of reactive oxygen species, such as singlet oxygen, superoxide, peroxyl radicals, hydroxyl radicals and peroxynitrite [3]. They are thus ideal target compounds to study the influence of plasma- immanent species on the stability and chemical behaviour of phytochemicals. Reactions were carried out at various radio- frequency voltages, using different feeding gas mixtures, and gas flow rates. Degradation was followed by high performance liquid chromatography/diode-array detection (HPLC/DAD). The modified samples are further characterised using contact angle measurements, X-ray photoelectron (XPS) spectroscopy and attenuated total reflectance- Fourier transform infrared (ATR-FTIR) spectroscopy. Results show that polyphenolics degrade upon plasmo-chemical reactions, probably due the presence of ROS and radicals in the plasma effluent (Fig.1). The degradation rate depends on the polyphenolics substition pattern. Furthermore plasma treatment leads to a significant decrease in contact angle owing to the incorporation of oxygen-containing functional groups. Using XPS these oxygen- containing groups can be identified as C-O, C=O and O-C=O. This is in agreement to results showing that during roasting and cooking processes oxidative species lead to the formation of characteristic low molecular weight degradation products [4, 5]. 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 120 140 Plasma exposure / s Degradation / % kämpferol quercetin myricetin taxifolin quercetin-4'-O-monoglycoside rutin quercetin-3,4'-diglycoside Fig.1 Degradation of polyhenolics 1 References [1] M. Moisan et al., Int. J. of Pharmaceutics 226, 1, (2001). [2] R. Brandenburg et al., Contrib. Plasma Phys. 47, 72, (2007). [3] S. V. Jovanovic et al., J. Am. Chem. Soc. 116, 4846, (1994). [4] S. Rohn et al., J.Agric. Food Chem. 55, 1568, (2007). [5] S. Bergelt et al., (2008) submitted.