Review 2 , 5-Dimethyl-4-hydroxy-2 H-furan-3-one and its derivatives : analysis , synthesis and biosynthesisÐa review

2,5-Dimethyl-4-hydroxy-2H-furan-3-one is believed to be a key ̄avour constituent in many fruits and baked foods. The analytical and organic methods applied to the analysis of DMHF and its derivatives, synthesis and biosynthesis are reviewed. Possibilities for further elucidation of biosynthetic pathways and the biotechnological production of DMHF are considered. # 1999 Elsevier Science Ltd. All rights reserved. 1. The analysis of 2,5-dimethyl-4-hydroxy-2H-furan-3one and its derivatives 2,5-Dimethyl-4-hydroxy-2H-furan-3-one (DMHF) is widely distributed in nature and has a very low ̄avour threshold value in water (4 10ÿ5 mg/kg); hence, its eect on food aroma is considerable (Latrasse, 1991). 2,5-Dimethyl-4-hydroxy-2H-furan-3-one occurs in nature in four forms (Fig. 1): 2,5-dimethyl-4-hydroxy-2H-furan3-one glucoside (DMHF glucoside), 2,5-dimethyl-4hydroxy-2H-furan-3-one 60-O-malonyl-b-D-glucopyranoside (DMHF malonyl-glucoside), 2,5-dimethyl-4-methoxy-2H-furan-3-one (mesifuran) as well as the free aglycone (Latrasse, 1991; Mayerl, Naf, & Thomas, 1989; Roscher, Herderich, Steen, Schreier, & Schwab, 1996a). Recently, DMHF has attracted the interest of many researchers working in the ®eld of ̄avour analysis (Pickenhagen, Velluz, Passerat, & Ohlo, 1981), aroma generation through chemical (Schieberle, 1992) and enzymatic processes (Roscher, Schreier, & Schwab, 1997c), organic synthesis using enzymes as catalysts (Wong & Whitesides, 1985) and the sensory evaluation of complex ̄avour mixtures (Larsen, Poll, & Olsen, 1992). Analytical techniques such as HPLC with either UV (Lee & Nagy, 1987) or Photo Diode Array (PDA) detection (Zabetakis, Gramshaw, & Robinson, 1996), GLC-FID (Williams & Mottram, 1981) and GLC-MS (Withopf, Richling, Roscher, Schwab, & Schreier, 1997) have been used for the analysis of DMHF and derivatives. Recently, the ®rst studies on the biosynthesis of DMHF have taken place using either strawberry fruits (Hong, Huang, Reineccius, Harlander, & Labuza, 1990; Roscher et al., 1997c) or callus cultures (Zabetakis & Holden, 1996). Plant tissue culture techniques may provide useful tools for the elucidation of the biosynthetic pathway of strawberry ̄avour molecules, including manipulation of culture conditions to increase the net yield and further genetic manipulation (Zabetakis & Holden, 1997). In this review are considered ®rst the analysis of sources where the furanones occur naturally (e.g. fruits and other unprocessed material) and, second foodstus where occurrence results from exogenous processes, including the baking of bread, cooking of meat and manufacture of preserves. 1.1. Naturally occurring furanones Free DMHF was the ®rst furanone isolated and identi®ed, simultaneously in pineapple (Rodin, Himel, Silverstein, Leeper, & Gortner, 1965) and strawberry (Willhalm, Stoll, & Thomas, 1965). The aroma of DMHF has been described as having a rotten note (Rodin et al.), a caramel-like note (Shaw, Tatum, & Berry, 1969; Tonsbeek, Plancken, & Weerdhof, 1968), as being sweet, ̄oral and fruity (Miller, Libbey, & Yang, 1973) and becoming fruity and strawberry-like at low concentrations (Re, Mauren, & Ohlo, 1973). Food Chemistry 65 (1999) 139±151 0308-8146/99/$Ðsee front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(98)00203-9 * Corresponding author. E-mail: y.zabetakis@food.leeds. ac.uk Later, DMHF glucoside was identi®ed, ®rstly in strawberry (Mayerl et al., 1989); since then it has been regarded as the precursor of DMHF in all the fresh sources (eg fruits) where both compounds exist. It has also been detected in pineapple (Wu et al., 1990) and tomatoes (Krammer, Takeoka, & Buttery, 1994). The amounts of DMHF glucoside in pineapple (Wu, Kuo, Hartman, Rosen, & Ho, 1991) and strawberry (Wintoch, Krammer, & Schreier, 1991; Sanz, Perez, & Richardson, 1994) have been measured (Table 1). Recently, 2,5dimethyl-4-hydroxy-2H-furan-3-one 60O-malonyl-b-Dglucopyranoside (DMHF malonyl-glucoside) has been identi®ed in strawberry fruit (Fragaria ananassa, cv. Senga Sengana) (Roscher et al., 1996a) with a ratio of the malonylated glucoside to its non-acylated glucoconjugate of 1:1 in the ripe fruit. Its presence suggests that the glucosides may be important derivatives of free DMHF and that their biosynthesis is therefore worthy of further study. The synthesis of phenyl 60-O-malonyl-b-D-glucopyranoside has been reported (Roscher, Steen, Herderich, Schwab, & Schreier, 1996b). This compound together with the synthesized 60-O-malonylated-b-D-glucopyranosides of benzyl alcohol, 2-phenylethanol, geraniol, citronellol and DMHF have been used as references for the spectroscopic identi®cation of malonylated glucosides in plants (Withopf et al., 1997). This report indicated that malonylation of the glucoconjugates may be a common pathway in plant secondary metabolism. DMHF malonylglucoside was identi®ed in raspberry and strawberry. Mesifuran, described elsewhere as having a Xeres wine-like note (Hunter, Busek, & Radford, 1974), has been claimed to be the major ̄avour-active component of the arctic bramble (Pyysalo, Suihko, & Honkanen, 1977). The odour value of mesifuran was estimated to be extremely high (600,000), whereas the odour value Fig. 1. The structures of 2,5-dimethyl-4-hydroxy-2H-furan-3-one, 2,5-dimethyl-4-methoxy-2H-furan-3-one, 2,5-dimethyl-4-hydroxy-2H-furan-3-one glucoside and 2,5-dimethyl-4-hydroxy-2H-furan-3-one malonyl-glucoside. Table 1 The amounts of DMHF, DMHF glucoside and mesifuran in some fruits (mg of analyte kgÿ1 of fruit) Fruit DMHF DMHF glucoside Mesifuran Strawberry (cv. Elsanta) 20.9 4.3 79.5 Wild strawberry 16.7 10.9 12.1 Wild raspberries 0.1 nd tr Arctic bramble nd nd 18 Alphonso mango 2 nd nd Pineapple (from Ivory Coast) 7.4 nd 0.2 Pineapple (from Costa Rica) 0.7 0.4 nd Tomato (cv. Ace) 0.7 nd nd Tomato (var. 6203) nd tr nd Wine (various grape cultivars) 0.1±3.5 nd nd a Zabetakis and Holden, 1995. b Honkanen et al., 1980. c Kallio, 1976b. d Idstein and Schreier, 1985. e Pickenhagen et al., 1981. f Wu et al., 1991. g Krammer et al., 1994. h Buttery et al., 1995. i Guedes de Pinho and Bertrand, 1995. j tr: traces, nd: not detected. 140 I. Zabetakis et al. / Food Chemistry 65 (1999) 139±151