The formation of 2,5-dimethyl-4-hydroxy-2H-furan-3-one by cell-free extracts of Methylobacterium extorquens and strawberry (Fragaria  ananassa cv. Elsanta) Panagiotis Koutsompogeras a , Adamantini Kyriacou b , Ioannis Zabetakis a, * a Laboratory of Food Chemistry, Department of Chemistry, University of Athens, GR-157 71, Athens, Greece b Department of Dietetics and Nutritional Science, Harokopio University of Athens, GR-176 76, Athens, Greece Received 16 October 2006; received in revised form 23 January 2007; accepted 8 March 2007 Abstract The formation of 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF), using the bacterial cells of Methylobacterium extorquens (strain with CABI registration number: IMI 369321) and strawberry cells (Fragaria  ananassacv. Elsanta), was studied. A combined mixture of the bacterial cell-free extract plus the strawberry extract was used as the enzymatic source. The pH of all the experimental aliquots was pH 6.0. The studied substrates were short-chain alcohols, carbohydrates and one amino acid. DMHF was analyzed by HPLC with UV detection at 280 nm. When 1,2-propanediol, 1-propanol, sucrose and fructose were used as substrates, the best production rates of DMHF were achieved, having a combined mixture of the bacterium and strawberry (minus the achenes) as the enzymic source. On the other hand, glucose, 1,2-propanediol, 2-propanol and fructose were the best substrates for the production of DMHF when a com- bined mixture of the bacterium and achenes served as the enzymic source. All results were obtained by comparing the production of DMHF from the strawberry extract alone and the bacterium plus the strawberry, without the achenes (in the first case) and the produc- tion of DMHF from the achene extract alone and the bacterium plus the achenes (in the second case). Moreover, the dehydrogenation activities of these three enzyme sources were determined by measuring the absorption of NADH at 340 nm. The substrate which was used for this series of the experiments was 1,2-propanediol. These results indicate the undoubted cooperation between the plant and the bacterial cells. This paper reports, for the first time, the formation of DMHF by bacterial and plant cell-free extracts. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Flavour; 2,5-Dimethyl-4-hydroxy-2H-furan-3-one (DMHF); Achenes; Strawberry; Methylobacterium extorquens 1. Introduction Methylotrophic bacteria and their relationships with the host plants have been subjects of interest, from both theo- retical and practical points of view, for a significant num- ber of years (Holland & Polacco, 1994). The interest in methylotrophy, regarding the food industry, began to rise since new applications of methylotrophs have been demon- strated (Anthony, 1982). Moreover, microorganisms that live together with plants represent a huge majority of the total microbe population. Methylotrophic bacteria are involved in many interesting in vivo interactions between plants and bacteria. The species of pink pigmented faculta- tive methylotrophs (PPFMs) is biologically very significant because of its intimate relationship with the plant (Holland & Polacco, 1994). One of the most important components of strawberry fla- vour is 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF) (Bood & Zabetakis, 2002). The synthesis of DMHF in straw- berry, as well as its synthesis performed by microorganisms, has been studied by various research groups over the past decade (Perez, Olias, Sanz, & Olias, 1996; Zabetakis & Hol- den, 1996; Hequet, Sancelme, Bolte, & Demuynck, 1996). Fructose 1,6-biphosphate was found to be a precursor mol- ecule of DMHF (Roscher, Bringmann, Schreier, & Schwab, 0308-8146/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2007.03.025 * Corresponding author. E-mail address: izabet@chem.uoa.gr (I. Zabetakis). www.elsevier.com/locate/foodchem Food Chemistry 104 (2007) 1654–1661 Food Chemistry