A Historical Review on the Identification of Mesifurane 2,5-dimethyl-4

Oct 2, 2017 - 84 compound presented had evidently a very short half-life and, after later re-evaluation of the IR-analyses and. 85 the NMR data it bec...
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A Historical Review on the Identification of Mesifurane 2,5-dimethyl-4methoxy-3(2H)-furanone and its Occurrence in Berries and Fruits Heikki Kallio J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b00519 • Publication Date (Web): 28 Feb 2018 Downloaded from http://pubs.acs.org on March 2, 2018

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Journal of Agricultural and Food Chemistry

A Historical Review on the Identification of Mesifurane 2,5-dimethyl-4-methoxy-3(2H)furanone and its Occurrence in Berries and Fruits Heikki P. Kallio1,2 1

Food Chemistry and Food Development, Department of Biochemistry, University of Turku, FI-20014 Turku, Finland; 2The Kevo Subarctic Research Institute, University of Turku, FI-20014 Turku, Finland

Tel.: +358 40 5033024; fax: +358 29 450 5040; e-mail address: [email protected]

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ABSTRACT

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Mesifurane, 2,5-dimethyl-4-methoxy-3(2H)-furanone is a natural compound, and a world-wide used flavoring

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for foods, beverages and cosmetics. Global sales of mesifurane is around USD 100 million. Its significance as a

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flavor-impact compound in some Nordic berries was discovered in early 1970’s in Finland. The synthesized

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mesifurane was used as a key-compound in aroma mixes exploited in a Finnish patent. Mesifurane is a

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significant flavorant in arctic brambles, mango, strawberries and many other fruits and berries, and is an

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enzymatic methylation product of 2,5-dimethyl-4-hydroxy-3(2H)-furanone. Due to the dimed information of

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the history of the commonly used trivial name, mesifurane, it is time to lift the vail and reveal the background

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towards the present situation. The key-player was a northern berry arctic bramble (Rubus arcticus), the Finnish

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name of which is mesimarja. Forty years ago the limiting factors in aroma research were technical, but

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nowadays they are in surplus of information.

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Keywords: arctic bramble, DMMF, mesifurane, 2,5-dimethyl-4-mehtoxy-3(2H)-furanone

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Arctic bramble, Rubus arcticus L. and related berries

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Arctic bramble (Rubus arcticus L.) is a boreal Eurasiatic berry and one of the Finnish wild natural treasures. It

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has become more and more rare due to changed practices in agriculture and forestry1,2 but the berry is still

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commonly used for traditional liqueur production and for special delicacies. In addition to Middle and South-

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East Finland, arctic bramble is a natural resource even in Finnish Lapland. The species exists especially in the

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deep valleys of Teno, Kevojoki, and Pulmankijoki rivers up to as north as 70°N, thoroughly investigated by

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Mäkinen et al. (Figure 1). The rich existence in these northern subarctic areas is due to the local climatic

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conditions in the river valleys.3

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According to Tammisola, natural populations of arctic bramble which are richly fruiting, contain several

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incompatibility classes of the self-incompatible natural plant.4 This fact together with the reduced natural

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growth areas may be one reason of the dramatically decreased fruit crops of wild arctic bramble berries in

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Finland. In order to secure the maintenance and management of the cultivations, molecular and morphological

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methods have been developed to monitor the relative densities of different R. arcticus cultivars on field.5

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The aroma of arctic bramble is fruity fragrant and highly unique among all the Rubus berries. Biology, breeding

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and cultivation of arctic bramble have widely been investigated in Finland and Sweden.1,4,6-8 Also hybrids of R.

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arcticus and R. stellatus6 as well as of R. arcticus and R. idaeus9-11 have been developed for commercial

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cultivation. Material for the aroma studies were mainly donations of doctors Annikki Ryynänen and Erkki

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Huokuna (Agricultural Research Centre of Finland, South-Savo Experiment Station) and of doctor Gunny

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Larsson (the Swedish University of Agricultural Sciences, Sweden).

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Discovery, isolation and identification of the major aroma-impact compound of arctic bramble

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The research on arctic bramble started with isolation of carbonyl compounds and by fractionating them as 2,4-

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dinitrophenylhydrazones in various classes by TLC. Analysis of the derivatives was carried out with packed

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column GC by using reference compounds.12 Acetone, diacetyl, methyl butanal, 2-butenal and pentenal were

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shown to decrease during ripening of the berry. However, it was immediately recognized that the ultimate goal

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could not be reached without GC-MS analysis of the volatiles with proper open tubular glass capillary columns,

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which were not commercially available by that time. Thus, the columns had to be prepared by the research

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group. Briefly, after drawing in a tunnel furnace, the inside surface of the capillary tubing was etched with

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CH2Cl2 pyrolysis at high temperature followed by a static coating procedure with an FFAP liquid phase.13 The

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columns were used for GC-FID and GC-MS analyses of arctic bramble aroma compounds and later for many

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other purposes.

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In addition to maximize the number of compounds to be identified, the interest was also focused on searching

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the most relevant fractions/compounds with typical arctic bramble aroma. Limitations of the packed GC

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columns were understood, but the only option was to carry out the sniffing procedure from the column outlet

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with the instrumentation available. Also the sniffing sessions as such were highly preliminary and robust and

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the results were not sufficient to be published in a quality Journal. However, the interesting area framed on the

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chromatogram in Figure 2,14 “sweet, pungent, arctic bramble”, gave a clear guideline how to proceed. The

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volatile fraction obtained from juice by vacuum distillation retained the typical natural aroma, and description

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of the compounds representing the marked peak area in Figure 2 was not far away from that of the juice.

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Chromatogram obtained with a wall-coated, open tubular galss capillary column of the same arctic bramble

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volatile fraction is presented in Figure 3 with three mass spectra inserted.15 Peak 137 is the most abundant

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compound in the distillate covering one third of all the volatiles, and, represents the framed major peak in

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Figure 2. Sniffing at GC exit revealed the arctic bramble aroma characteristics of the compound. Isolation of

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this unknown from the extract of the distillate was carried out with preparative gas chromatography (Figure

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4a), and purity of > 98 % was reached (Figure 4b),16 sufficient for further analyses. Returning the compound

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back to the de-aromatized juice restored surprisingly well the natural aroma. Among any berry aroma profiles

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it is unusual that one character impact compound is this dominant.

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The major compound of the concentrated arctic bramble distillate (Figure 3) was found to be the unknown

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with MW 142.14 Also two hybrids between raspberry and arctic bramble were found to contain this

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compound.17 In order to reveal the secret of the character impact unknown, it was isolated and analyzed with

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capillary-GC-EI-MS, HR-MS, 1H NMR, UV, IR and sensory methods, and proper reference compounds were

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synthesized.16

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This seemingly simple protocol to identify a small molecule with MW 142, was in the end not trivial 45 years

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ago, at the time when glass capillary columns were not yet even commonly used. A research group including

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several PhD students in the area of berry and mushroom aromas was guided by Dr. Erkki Honkanen, the actual

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“founder” of the scientific aroma chemistry of foods in Finland.

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HR-MS analysis of the isolated compound gave a more accurate estimate of the molar mass, 142.0629

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(C7H10O3). No elements other than 12C, 13C, O and H were found. The unknown was DNPH-reactive (contained a

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carbonyl moiety) and showed keto-enol tautomerism with KOH treatment. NMR revealed with no doubt the

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existence of an –O-CH3 substituent. A possible –C(=O)-CH3 group based on NMR analysis was, however, the

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highly misleading misinformation. Thus, the first conclusions of the structure ended up to 4-methoxy-4-

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hexene-2,3-dione. Because the research group had no protocol to synthesize this methoxylated vicinal dione,

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they proceeded with synthesis of a non-methoxylated reference compound 4-hexene-2,3-dione.18,19 Later it

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was shown, that the compound synthesized was the correct reference compound to the unknown but not with

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the structure expected.

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Information of the discovery of 4-methoxy-4-hexene-2,3-dione as “a key aroma compound in arctic bramble”

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was sent in spring 1974 to the organizers of The Fourth International Congress of Food Science and Technology

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to be held in Madrid, Spain on September 23rd-27th 1974.

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The summary of the analysis was accepted in the Abstract Book as Abstract 1a. 13 and denoted as an oral

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presentation.20 The congress was a forum where, in addition to the aroma analysis, the progress in preparation

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and use of capillary GC-columns were presented. At the congress, according to Mr. Mans Boelens, the dione

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compound presented had evidently a very short half-life and, after later re-evaluation of the IR-analyses and

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the NMR data it became clear that the unknown compound was 2,5-dimethyl-4-methoxy-3(2H)-furanone (MW

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142.154, monoisotopic mass 142.063, CAS 4077-47-8). The new submission ended up to the final publication.16

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The compound earlier synthesized as a reference to the dione-structured unknown was later proved not to

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have an open structure as expected. Instead, it was 2,5-dimethyl-3(2H)-furanone and, in the end, the “correct”

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reference compound to our unknown. 2,5-dimethyl-4-methoxy-3(2H)-furanone (DMMF) became public as

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mesifurane for the first time in the Congress Proceedings according to the Finnish name “mesimarja” (nectar

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berry) of arctic bramble.16

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The NMR and UV analyses (Figure 6a, b) matched with the confirmed structure,16 and the UV spectra in Figure

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6b are a clear sign of the keto-enol tautomerism of the compound. Also 2,5-dimethyl-4-hydroxy-3(2H)-

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furanone (DMHF, furaneol®) was identified in the arctic bramble distillate (compound 219, Figure 3).15, 21

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As a late consolation, an open-chain dione compound, 3,4-dihydroxy-3-hexene-2,5-dione, has been shown by

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Engel, Hofmann and Schieberle (2001) to have caramel flavor22 similar to that of 4-hydroxy-2,5-dimethyl-3(2H)-

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furanone. NMR analyses proved that the odor-active open chain tautomer was present only in lipophilic

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solvents. The cyclic form (diacetylformoin) was odorless and existed in aqueous solutions.

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Mesifurane in other berries and fruits

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In addition to Rubus arcticus, the berries of a Pacific type of arctic bramble native at the Aleutian Islands (Rubus

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arcticus ssp. stellatus Sm.) have a weak aroma of artic bramble R.a..6 The berries contain significant amounts of

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mesifurane but less than the Finnish arctic bramble.23 Hybrids of arctic bramble and raspberry (R. idaeus L.)

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developed at the Agricultural Research Centre of Finland,10 were also quite rich in the compound,24 and also

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raspberries were later found to contain low amounts of mesifurane.25 The research group of Dr. Honkanen

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further verified existence of the compound both in wild strawberries (Fragaria vesca L.) and in the strawberry

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(Fragaria x ananassa) cultivar ‘Senga Sengana’.26 They defined mesifurane to be a key aroma compound in

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strawberries, as later verified also by Larssen and Poll27 and numerous other research groups. In a thorough

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comparison between ten strawberry varieties the content of mesifurane was found to vary between 0.3 and

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1.7 mg/kg of fresh berries.28,29 Pérez et al.30, and Siegmund, Bagdonaite and Leitner31 have determined even

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five times higher contents of mesifurane in different strawberry varieties. A NIL (Near Isogenic Line) collection

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has been recently shown to be a good tool for the genetic dissection of accumulation of volatiles, including

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mesifurane, in wild strawberries.32

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Frozen storage of strawberries cause loss of DMMF.29 Stability of DMMF and DMHF were further studied by the

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research group of Honkanen, and half-lives of the compounds at room temperature at pH 4 were 320 and 100

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days, respectively.33 Roscher, Schwab and Schreier34 have also verified that mesifurane is more stable than

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DMHF at a wide pH range.

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Already in 1974, Hunter, Bucek and Radford found 2,5-dimethyl-4-methoxy-3(2H)-furanone in Alphonso mango

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by GC-MS using a stainless steel capillary column coated with Carbowax 20M liquid phase.35 They also

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displayed IR spectrum of the synthesized reference compound. Since the early studies of arctic bramble,

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mango and strawberry, also many other fruits such as bacuri,36 cape gooseberry,37 capuacu,38 champa,39

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guava,40 kiwifruit,41 lychee,42passion fruit,43 pepino ,44 and pineapple,45 are known to contain 2,5-dimethyl-4-

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methoxy-3(2H)-furanone at various extent as a natural aroma compound. In most cases, also its hydroxyl

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counterpart, DMHF, has been co-identified which is an indication of their close relation in the metabolome.

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The research group of Cruz-Rus et al.46 has recently introduced methods for screening of mesifurane in

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strawberries based on optimized PCR analysis of the key gene FaOMT. This may be a starting point for fast

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screening tools in breeding of strawberries and maybe also other fruits and berries with superior flavor

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properties.

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Biosynthesis and properties of mesifurane

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Biosynthesis of mesifurane in arctic bramble berries has not been investigated but it was hypothesized in the

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PhD Thesis of Kallio21 to be a ripening-related enzymatic methylation of the corresponding 2,5-dimethyl-4-

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hydroxy-3(2H)-furanone, evidently synthesized from fructose (Figure 7a). D-glucose, D-fructose, D-fructose 6-

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phosphate and D-fructose 1,6-diphosphate have been later confirmed as intermediates of the precursor

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pathway of DMHF formation in strawberries.47-49 It has further been shown that in ripening strawberries DMHF

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is the substrate of methylation, and S-methyl-14C-adenosyl-L-methionine was the methyl donor in biosynthesis

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of mesifurane (DMMF).50 The responsible locus in variation of mesifurane in strawberry is the Fragaria x

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ananassa O-methyltransferase gene (FaOMT), and the partially purified enzyme has a molar mass of 80 kDa.51-

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54

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DMHF accumulation during ripening of strawberries.56 Zabetakis and Holden suggested already in 1996 that

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glucoside of DMHF is the evident precursor of the free aglycone, based on studies of strawberry callus

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cultures.57 A detailed review of the topic was published later.58 Glycosidic forms of both DMHF and DMMF are

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known to exist in strawberries.59 Recently, Fu et al. (2017) revealed in more details several genes to be related

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to aroma formation of strawberries and in post-harvest ripening.60 Development of free DMHF and DMMF was

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much higher at 25 °C than at 15 °C and also light had a significant effect on the progress60

Repression of FaOMT results in loss of DMMF.55 An enoneoxidoreductase gene FaQR is also required for the

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Chidley et al. found the corresponding methyltransferase MiOMTS in Alphonso mango, one of the early-known

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sources of DMMF, to show substrate specificity towards furaneol, analogous to strawberries.61 Quantitative

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real-time PCR displayed ripening-related expression of MiOMTS in skin and soft parts of mango and this was in

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accordance with development rate of DMMF. No analogous investigations on arctic bramble have been carried

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out so far and the details were not even proposed in 1975.

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In arctic bramble the content of mesifurane increased exponentially during ripening (Figure 7b). The behavior

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of DMHF could not be defined reliably due to the extremely low content in distillate.62 According to Pérez et al.,

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unripe strawberries did not contain mesifurane at all30 but at the final ripening stage an intense increase was

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observed, like in the studies of Vandendriessche et al..63 Ubeda et al. showed active enzymatic liberation of

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mesifurane from its glycosidic precursors in strawberry, more effectively than by acidic hydrolysis.64 Sen,

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Schieberle and Grosch (1991) recognized already earlier effective enzymatic liberation of DMHF from

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strawberries but the increase of DMMF was not determined.65

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It is worth to notice that both furaneol® and mesifurane are chiral compounds and their isomers have been

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verified in e.g. strawberries, pineapples and grape wine.66 After biosynthesis of DMMF in the ripening berries,

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the pH-dependent racemization starts66 and transformation towards equilibrium between the two

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enantiomers, R-mesifurane, [(+)-(2R)-2,5-dimethyl-4-methoxy-3(2H)-furanone] and S-mesifurane [(-)-(2S)-2,5-

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dimethyl-4-methoxy-3(2H)-furanone] depends on time and physical conditions. Isomerization occurs via the

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enol structure, but the rate is unknown (Figure 6b). It is possible that in the isolated aroma fractions,

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enantiomers of mesifurane may typically not be in the ratio existing in the berries, even though natural

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racemization takes place in the intact fruits. The most proper way to mimic the situation in berries or juice for

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sensory analyses, both orthonasal and rertonasal, might be direct headspace analysis of DMMF. Also solvent

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assisted flavor evaporation of DMMF is worth to be tested.67 An elegant method for quantitative analysis of

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both DMMF and DMHF in e.g. strawberries is stable isotope dilution assay (SIDAs) introduced by Sen,

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Schieberle and Grosh (1991). The procedure has been applied in berries, juices, jams and candies.65 The

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method was later used successfully for quantitation of enantiomers of DMMF with deuterated racemic

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reference compounds with chiral gas chromatography.67,68 A thorough review of GC analysis of enantiomeric

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aroma compounds was compiled by Mosandl alredy 25 years ago, and the article has been a guideline for next

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generations.69

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Bruche et al. showed clear differences between the aroma properties of the enantiomers of both mesifurane

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and furaneol® by GC-sniffing of the resolved enantiomers from pineapples, strawberries and reference

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compounds by using HPLC and cyclodextrin-based GC columns.66,70 They described the racemic mesifurane as

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sweet, spicy, cherry and earthy-like. After chromatographic separation of the antipodes, the first enantiomer

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had a sweet, almost odorless note and the later eluting had the same characteristics as the racemate.70 Fischer

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and Hammerschmidt described in chiral column GC-sniffing analysis the first enantiomer of DMMF as weak,

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sweet, malty, roasty and the second one as strong, fruity, sweet, malty, earthy, roasty. 71 They revealed even

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1000-fold intensity difference between the enantiomers. In all these investigations DMMF was in fruits a

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racemic mixture of enantiomers, practically in ratio 1:1 and Bruche et al. proposed this to be due to

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racemization via keto-enol tautomerism.66 Emura et al. resolved the structures of the enantiomers of both

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furaneol® and mesifurane by enantioselective carbon dioxide supercritical fluid chromatography and the

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structures were defined by chemical relay reactions and vibrational circular dichroism technique.72 The (R)-(+)

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isomer of mesifurane had intensive flavor characteristics of burnt caramel72 representing the later eluting

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enantiomer in the chiral GC analyses of Bruche et al.70 and Fisher and Hammerschmidt.71 Isotope ratio mass

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spectrometry after chiral GC (GC-IRMS) may be used to reveal the origin of the compounds, e.g. for

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authentication of the sample.70 The early chromatographic methods based on FFAP glass capillary columns did

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naturally not resolve the enantiomers of mesifurane in arctic bramble (Figures 3 and 7b) and proportions of the

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isomers in the berry are still unknown. 15,21, 62

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After Pyysalo synthesized DMMF for research on artic bramble and strawberry using the method of Willhalm

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and Thomas,73 a patent (Kuulutusjulkaisu 51890) was applied in Finland on September 19th 1974 and granted

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on May 10th 1977.74 The topic as translated was “A method to give arctic bramble–like aroma to foods or

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drinks, especially to liqueurs, by adding flavorings which give the products aroma/taste of arctic bramble”. In

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Finland, it was not allowed to add flavorings in berry liqueurs, but in some other countries it was and it is. By

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knowing this, the patent application was sold to a traditional Finnish liqueur company. Whether the company

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ever used the information for anything remains unknown. More than 20 international patents have been

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granted on the topic of DMMF after 1989. Our goal in the future is to investigate the kinetics of racemization of

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mesifurane in vivo in Nordic arctic bramble during ripening and storage.

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Commercial use and international trade of mesifurane

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There are several market analyses of mesifurane available in electronic publications in 2016-2017. According

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to PubChem, October 22nd 2017, at least 38 companies from six countries are vendors of this flavor ingredient.

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More than half of them are Chinese, one fourth from USA and the rest typically from Europe and Japan.

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The price level of mesifurane/DMMF has commonly been one to two USD a gram. It is estimated that the

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global mesifurane market size was 6,000 tons in 2015 of which USA produced 23 %. The growth is rated at

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around 5 % a year until 2025 reaching a value USD 154 million.75 Food and beverage area cover 65 % of the

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whole consumption and pharmaceuticals around one fourth. Also animal feeds seem to form an expanding

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market segment.

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References

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(1) Saastamoinen, S. Mesimarja (Rubus arcticus L.) Suomessa. Die nordische Himbeere (Rubus arcticus L.) in

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Finnland. Ann. Soc. Zool. –Bot. Fenn. Vanamo, 1930, 13, 355- 414.

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(2) Vaarama, A. Rubus arcticus L. – Mesimarja. Suuri kasvikirja II, J. Jalas (ed.), Helsinki, Finland, Otava 1965, p.

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750.

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(3) Mäkinen, Y.; Laine, U.; Heino, S.; Iso-Iivari, L.; Nurmi, J. Vaskular flora of Inari Lappland. 8. Rosaceae and

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Fabaceae. Rep Kevo Subarctic Res. Stat., 2011, 24, 3-126.

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(4) Tammisola, J. Incompatibility classes and fruit set in natural populations of arctic bramble (Rubus arcticus L.)

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in Finland. J. Agric. Sci. Finl. 1988, 60, 327-446.

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(5) Kostamo, K.; Toljamo, A.; Antonius, K.; Kokko, H.; Kärenlampi, S.O. Morphological and molecular

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identification to secure cultivar maintenance and management of self-sterile Rubus arcticus. Ann. Bot., 2013,

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111, 713–721.

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(6) Larsson, E.G.K. Development and cultivation of northern small fruits in the genus Rubus L. Acad. Diss.

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Landbrukshögskolan, Uppsala, Sweden, 1970. 19 pp and 6 publications.

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(7) Ryynänen, A. Arctic bramble (Rubus arcticus L.), a new cultivated plant. Ann. Agric. Fenn. 1972, 11, 170-173.

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(8) Ryynänen, A. Rubus arcticus L. and its cultivation. Ann. Agric. Fenn. 1973, 12, 1-76.

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(9) Vaarama, A. Cytological studies of some Finnish species and hybrids of the genus Rubus L. J. Agric. Sci. Finl.

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1939, 11, 72-85.

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(10) Vaarama, A. Om artkorsningsförädling inom släktet Rubus. Nord. Jordbr. Forskn. 1951, 33, 412-417.

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(11) Hiirsalmi, H. Breeding of berries and fruits at the Department of Horticulture. Ann. Agric. Fenn. 1969, 8,

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133-148.

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(12) Kallio, H.; Linko, R. R. Volatile monocarbonyl compounds of arctic bramble (Rubus arcticus L.) at various

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stages of ripeness. Z. Lebensm. Unters. -Forsch. 1973, 153, 23-30.

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(13) Grob, K. Glaskapillaren für die Gas-Chromatographie. Verbesserte Erzeugung und Prüfung stabieler

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Trennflüsigkeitsfilme. Helv. Chim. Acta. 1968, 51, 718-737.

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(14) Kallio, H. Mesimarjan (Rubus arcticus L.) aromiaineista. Ph Lic. Thesis, University of Turku, Finland, 1973,

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94 pp.

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(15) Kallio, H. Identification of vacuum steam-distilled aroma compounds in the press juice of arctic bramble,

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Rubus arcticus L. J. Food Sci. 1976, 41, 555-562.

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(16) Kallio, H.; Honkanen, E. An important major aroma compound in arctic bramble, Rubus arcticus L. In: Proc.

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IV Int. Congress Food Sci. Technol., Madrid, Spain, September 23-27, 1974, Selegraf, Valencia, pp. 84-92.

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(17) Honkanen, E.; Kallio, H.; Pyysalo, T. Tutkimuksia eräiden Rubus-suvun marjojen aromiainekoostumuksesta

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II. Tutkimus ja Tekniikka, 1973, 10, 51-53.

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(18) Heilbron, I.M.; Jones, E.R.H.; Weedon, B.C.L. Studies in the polyene series. Part XVIII. The formation of

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ethers from propenylethynylcarbinol and related compounds. J. Chem. Soc. 1945, 81-84.

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(19) Crout, D.H.G; Hassal, C.H.; Jones, T.L. Cardenolides. Part VI. Uscharidin, calotropin and calotoxin. J. Chem.

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Soc. 1964, 2187-2194.

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(20) Kallio, H.; Honkanen, E. An important major aroma compound in arctic bramble, Rubus arcticus L. In:

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ABSTRACTS of the Proc. IV Int. Congress Food Sci. Technol., Madrid, Spain, September 23-27, 1974, Selegraf,

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Valencia, pp. 6-7.

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development during the ripening of the berry, with special reference to Rubus stellatus Sm. Ph. D. Thesis.

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(23) Kallio, H. Chemical constituents of the volatile aroma compounds in Rubus arcticus L. subsp. stellatus

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(Sm.) Boivin, with reference to Rubus arcticus L. subsp. arcticus. Rep. Kevo Subarctic Res. Stat. 1975, 12, 60-65.

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(Fragaria vesca) volatile composition. Plant Physiol. Biochem. 2017, 121, 99-117.

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(48) Pérez, A.G.; Olías, R.; Olías, J.M.; Sanz, C. Biosynthesis of 4-hydroxy-2,5-dimethyl-3(2H)-furanone and

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biosynthesis in strawberry: S-Adenosylmethionine:Furaneol O-methyltransferase in ripening fruits. J. Agric.

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(52) Wein, M.; Lavid, N.; Lunkenbein, S.; Lewinsohn, E.; Schwab, W.; Kaldenhoff, R. Isolation, cloning and

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furanone, one of the key aroma compounds in strawberry fruits. Plant J. 2002, 31, 755–765.

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I. Genetic analysis of strawberry fruit aroma and identification of O-Methyltransferase FaOMT as the locus

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controlling natural variation in mesifurane content. Plant Physiol. 2012, 159, 851–870.

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metabolism. J. Exp. Bot. 2006, 57, 2445–2453.

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(56) Raab, T.; Lopez-Raez, J. A.; Klein, D.; Caballero, J. L.; Moyano, E.; Schwab, W.; Munoz-Blanco, J. FaQR,

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responses of four biosynthetic pathways of aroma compounds in postharvest strawberry (Fragaria x ananassa

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Stereodifferentiation of chiral furanones. Possibilities and limits to origin assignment of aroma compounds. Z.

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(67) Engel, W.; Bahr, W.; Schieberle, P. Solvent assisted flavour evaporation - a new and versatile technique for

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the careful and direct isolation of aroma compounds from complex food matrices. Eur. Food Res. Technol.

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of aroma-active dihydrofuranones. Z. Lebensm. Unters. -Forsch. 1995, 201, 249–252.

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(72) Emura, M.; Yaguchi, Y.; Nakahashi, A.; Sugimoto, D.; Miura, N.; Monde, K. Stereochemical studies of

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odorours 2-substituted -3(2H)-furanones by vibrational circular dichroism. J. Agric. Food Chem. 2009, 57, 9909-

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9915.

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United States Patent No 3,455,702 (July 15, 1969).

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(74) Kallio, H.P.T.; Pyysalo, T.; Honkanen, E.J. Menetelmä mesimarjatyyppisen aromin antamiseksi

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elintarvikkeille tai juomille, etenkin likööreille. Finnish patent No 51890 (May 10, 1977).

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(75) Anonym. Mesifurane market analysis by application (food & beverages, pharmaceuticals, animal feed), by

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region (North America, Europe, Asia Pacific, Central & South America, MEA), competitive landscape and

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segment forecasts, 2014 – 2025. Grand View Research, 2017, April 17th, pp. 65

388 389 390 391 392 393 394 395 396

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Legends of Figures

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Figure 1. Natural distribution of arctic bramble, Rubus arcticus L. in Inari-Lappland, Finland.3 (With the

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permission of Kevo Subarctic Research Institute)

400 401

Figure 2. Packed column GC-FID sniffing analysis of aroma compounds of arctic bramble (Rubus arcticus L.)

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isolated from press juice by vacuum steam distillation with a climbing film evaporator at 22 °C at 10 torr

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pressure. The distillate was collected in a 2-litre receiving flask chilled in a mixture of NaCl and ice. The flask

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was connected to a vacuum pump by two cold traps chilled with liquid nitrogen. The combined distillate was

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saturated with purified NaCl and extracted for 24 hours with pentane-diethyl ether (1:2, v/v) in a Kutscher-

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Steudel continuous extractor. 5 mL of dichloromethane was added to remove water as azeotrope. The aroma

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extract was concentrated with a Widmer column at 35 °C to the final volume 250 µL. Analysis: Perkin-Elmer F-

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11 GC, 180 cm steel column, i.d. 6.5 mm, filled with Chromosorb W (60-80 mesh, acid washed, DMCD treated)

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coated with 11 % (w/w) GE-SF-96 liquid phase. Glass-liner injector at 220 °C, oven program 50-210 °C, 4

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°C/min. After column, flow between FID and the sniffing port 1:80.14

411 412

Figure 3. Analysis of aroma compounds of arctic bramble (Rubus arcticus L.) isolated from press juice by

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vacuum steam distillation. See Figure 1. Analysis: Varian Aerograph 20100-20 with FFAP glass capillary column,

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140 m, 0.32 mm i.d. prepared with a static coating procedure at 23 °C after CH2Cl2 pyrolysis treatment (2 x 30

415

seconds at 720 °C). Oven temperature 60-230 °C, 2 °C/min, injector split 1:100, nitrogen carrier 0.7 mL/min,

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injector 245 °C, FID 255 °C. Mass spectra (EI, 70 eV) were obtained with the same column with LKB-900

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instrument with a Ryhage-type jet separator, sweep time 1.5 s/decade.15 (With the permission of Wiley Global)

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Figure 4. Collecting device of the unknown compound No 137. Conditions of the GC run as in Figure 2. After

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isolation via the heated (230 °C) CG exit and the 0.5 mm i.d. needle, the collection capillary was removed from

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liquid nitrogen, centrifuged in a special adapter to the tip and sealed as separate ampoules. The compound was

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collected from several GC runs for HR-MS, 1H NMR, UV, IR and sensory analyses (A).13 Capillary GC-FID analysis

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of the isolated unknown arctic bramble compound No. 137 with MW 142 verified the > 98 % purity which was

424

enough for all the further analyses (B).16 (With the permission of Instituto de Agroquímica y Tecnología de los

425

Alimentos )

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Figure 5. An estimated mass spectrometric cleavage of 4-methoxy-4-hexene-2,3-dione, the hypothesized

428

structure of the unknown arctic bramble volatile No. 137, MW 142. The structure was shown after the oral

429

presentation in IV Int. Congress Food Sci. Technol.20 to be incorrect.

430 431

Figure 6. The 1H NMR analysis was carried out with 100 MHz Jeol JNP-PS-100 in CCl4 with a droplet of

432

deuterated CHCl3 with TMS as the reference (A).16 UV analyses with Perkin-Elmer 402 UV-vis

433

spectrophotometer with scan speed 40 nm/min, slit width 25 µm and cell path 1 cm (B).16 (With the permission

434

of Instituto de Agroquímica y Tecnología de los Alimentos )

435 436

Figure 7. Postulated biosynthetic pathway of mesifurane in arctic bramble (A)21 and development of

437

mesifurane and some other volatiles during ripening of the berries UR = unripe, HR = half ripe, R = ripe and OR

438

= over ripe (B).62 (With the permission of Wiley Global)

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