Field of the invention

[0001 ] The present invention relates to a process for the preparation of 5-methylhept- 2-en-4-one, also known as filbertone, as well as the 5-methylhept-2-en-4-one obtained by said method. In addition, the invention pertains to the use of said 5-methylhept-2- en-4-one as aroma/flavor or odorant or in the preparation of aroma/flavor compositions and/or fragrance compositions. Additionally, the present invention relates to the intermediary formed 3-methylpentan-2-one and its use. Finally, the present invention relates to food-products comprising said 5-methylhept-2-en-4-one and/or 3- methylpentan-2-one.

State of the art

[0002] 5-Methylhept-2-en-4-one (CSHHO), also known as filbertone, is the key flavor compound in the fruits of hazelnut trees Corylus maxima and C. avellana. Because of its typical strong nutty, roasted, fruity odor impression and taste, it is widely used for the modification and improvement of flavor compositions (DE 3345784 A1 , WO 2018202311 A1 , CN 105919892 A). Moreover, several applications in the pharmaceutical field have been published recently (WO 2016195355 A1 , KR 2019000612 A, KR 1558476 B1 ).

[0003] 5-Methylhept-2-en-4-one exists in the form of four isomers ( 2Z,5R , 2Z,5S, 2E,5R, und 2E,5S). All four isomers have a characteristic nutty odor impression and taste. However, the odor threshold value of the (2E,5S)-isomer is approximately ten times lower than that of the (2E,5R)-isomer, and three times lower than that of the (2Z,5S)-isomer. Therefore, based on its low odor threshold value the (2E,5S)-isomer is the most valuable isomer of filbertone for imparting, enhancing or modifying a nutty odor and taste. Investigations on the isomer ratio of filbertone in different nuts showed, that the (2E,5S)-isomer is the main isomer, however, only with an enantiomeric excess of from 54 to 73%. In addition, the enantiomeric excess decreases to 43 to 45% during the roasting process of hazelnuts.

[0004] The flavor industry is continuously searching for materials, which can be isolated or produced by green, environmentally friendly methods, utilizing readily available, renewable raw materials and reactants. However, the low levels of naturally occurring filbertone (1 to 5 mg/L in unroasted hazelnut oil and 32 to 36 mg/L in roasted samples) in nuts make the isolation of filbertone not reasonable for large-scale production. Therefore, new sustainable and cost-effective approaches towards filbertone are clearly required.

[0005] To date, many methods for the preparation of filbertone as flavoring substance have been published. Also, the synthesis starting from 2-butanone is already known. For example, CN 101597223 A discloses a three-step process involving the aldol- condensation between 2-butanone and acetaldehyde catalyzed by hydrochloric acid, subsequent reduction of the double bond using hydrogen catalyzed by Raney Nickel or palladium, followed by a second aldol-condensation with acetaldehyde catalyzed by zinc acetate. The limitations of this process for large-scale production are difficult handling of hydrochloric acid, possible corrosion, and the use of heavy metals. In particular, the use of the difficult-to-handle, highly reactive and/or toxic reagents of said process pose major challenges to the manufacturer in terms of safety, sustainability and large-scale production (including cost efficiency).

[0006] Another synthetic strategy for the preparation of filbertone is based on the so- called Knoevenagel-condensation of b-keto esters with acetaldehyde, followed by decarboxylation and water elimination. This procedure provides very good yields for racemic filbertone; however, firstly the starting material must be synthesized from ethyl acetoacetate and 2-methylbutyric acid chloride (CN 102030626 A). In addition, based on this strategy, a complex five-step chemoenzymatic synthesis starting from chiral 2- methylbutyric acid towards chiral filbertone was developed. However, this procedure is less suitable for large-scale production due to a multitude of synthesis steps and reactants required. In addition, the amount of waste is increased, recyclability reduced and (thus) the overall costs increased, simultaneously making the process less sustainable.

[0007] Other methods for the preparation of filbertone include either the addition of organometallic compounds to carbonic acid derivatives (JP 2006096721 A, CN 106045833 A) or to aldehydes (DE 3345784 A1 ), followed by oxidation, or fragmentation of potassium dihomoallylic alkoxides in HMPA (hexamethylphosphoramide). However, these strategies either require strictly anhydrous conditions or the use of stoichiometric amounts of oxidizing agents or carcinogenic reagents, or generate toxic waste, thus, severely limiting their industrial potential. Consequently, a sustainable, environmentally friendly, and cost-effective approach towards the large-scale synthesis of filbertone is clearly required.

[0008] Therefore, it was the primary object of the present invention to provide a process for preparing 5-methylhept-2-en-4-one, i.e. filbertone that at least partially overcomes one or more of the above disadvantages.

[0009] The object of the present invention is furthermore to provide a sustainable, environmentally friendly, and cost-effective process for the preparation of 5- methylhept-2-en-4-one, i.e. filbertone.

[0010] Additionally, it is an object to provide a new and preferably facilitated process (preferably with a reduces number of process steps) for the preparation of 5- methylhept-2-en-4-one based on green, environmentally-friendly methods, avoiding the use of difficult-to-handle, highly reactive and/or toxic or hazardous reagents, which is simultaneously suitable for large-scale production. Thus, the process should also be safer than the available state-of-the-art processes by reducing health and environmental risks.

[0011] Surprisingly, it was found that the synthesis of filbertone starting from 2- butanone can be achieved without the use of any heavy metal catalysis or the use of corrosive mineral acids based on organic acids and yeast fermentation as presented herein.

[0012] The process to which this invention relates is particularly advantageous to the flavor industry, because it is based on green, environmentally friendly methods, using sustainable, naturally occurring or fermentatively produced starting materials, without using any halogenated or toxic chemicals, oxidation reagents or metal catalysts. In addition, the use of solvents for the aldol reaction can be reduced or completely avoided, allowing for a significant reduction in the waste production.

[0013] Moreover, the process according to the invention does not require elaborate reaction conditions such as very high or low temperatures or strictly anhydrous conditions, so that the process can be easily realized in large scale.

[0014] Furthermore, based on the reduced number of chemicals required, the reduced amount of waste as well as the low number of process steps it was possible to reduce the overall costs.

Summary of the invention

[0015] The present invention relates to a process for the preparation of 5-methylhept- 2-en-4-one (filbertone), and preferably (E)-5-methylhept-2-en-4-one (formula (I)), starting from 2-butanone via an acid-catalyzed aldol condensation with acetaldehyde, with subsequent reduction of the double bond by means of a biocatalyst such as yeast and a subsequent second acid-catalyzed aldol condensation with acetaldehyde.

(E)-5-methylhept-2-en-4-one

(filbertone)

Formula (!)

[0016] More specifically, in a first aspect, the present invention relates to a process for the preparation of 5-methylhept-2-en-4-one, and preferably (E)-5-methylhept-2-en- 4-one, comprising the steps of:

(a) acid-catalyzed aldol-condensation between 2-butanone and acetaldehyde to obtain 3-methylpent-3-en-2-one;

(b) reaction of the 3-methylpent-3-en-2-one from step (a) with a biocatalyst to obtain 3-methylpentan-2-one; and

(c) acid-catalyzed aldol-condensation between the 3-methylpentan-2-onefrom step (b) and acetaldehyde to obtain 5-methylhept-2-en-4-one, and preferably (E)-5- methylhept-2-en-4-one.

[0017] In a second aspect, the present invention relates to 5-methylhept-2-en-4-one, and preferably (E)-5-methylhept-2-en-4-one, obtained or obtainable by the process according to the invention, preferably wherein the S-isomer of said 5-methylhept-2-en- 4-one is comprised in an amount of at least 50 % by weight, further preferred in an amount of at least 51 % by weight, most preferred in an amount of at least 70 % by weight.

[0018] Moreover, the present invention relates to the intermediary formed 3- methylpentan-2-one obtained or obtainable in step (b) or (b.2) of the process according to the invention, preferably in its enantioenriched form. [0019] Additionally, 3-methylpentan-2-one is disclosed, wherein the S-isomer of said 3-methylpentan-2-one is comprised in an amount of at least 70 % by weight, further preferred in an amount of at least 80 % by weight and most preferred in an amount of at least 90 % by weight relative to the total weight of 3-methylpentan-2-one. Preferably, said enantioenriched 3-methylpentan-2-one is obtained or obtainable by the process according to the invention.

[0020] In another aspect, the present invention relates to the use of said 5- methylhept-2-en-4-one and/or 3-methylpentan-2-one according to the invention as aroma/flavor and/or odorant or in the preparation of aroma/flavor compositions and/or fragrance compositions as well as the preparation of foodstuff, luxury food, food supplements, semi-finished products for the preparation of foodstuff or foods supplements, pet food.

[0021] Finally, the present invention relates to aroma/flavor compositions, fragrance compositions, and food-related products such as foodstuff, luxury food, food supplements, semi-finished products for the preparation of foodstuff or foods supplements, pet food comprising the 5-methylhept-2-en-4-one and/or 3- methylpentan-2-one according to the invention.

Detailed description of the invention

[0022] In accordance with the present invention, the above object is achieved by a process for the preparation of 5-methylhept-2-en-4-one (i.e. filbertone), and preferably (E)-5-methylhept-2-en-4-one, comprising the following steps of:

(a) acid-catalyzed aldol-condensation between 2-butanone and acetaldehyde to obtain 3-methylpent-3-en-2-one;

(b) reaction of the 3-methylpent-3-en-2-one from step (a) with a biocatalyst to obtain 3-methylpentan-2-one by biocatalytic reduction of the double bond formed in step (a); and (c) acid-catalyzed aldol-condensation between the 3-methylpentan-2-onefrom step (b) and acetaldehyde to obtain 5-methylhept-2-en-4-one, and preferably (E)-5- methylhept-2-en-4-one.

[0023] The specific synthetic methods followed for preparing 5-methylhept-2-en-4- one according to the present invention are based on the application of conventional discrete reaction steps. The details of these process steps are given in the following description. Reagents or reaction conditions may be modified from those given below, the originality of the process described being the specific choice of the different reaction steps and in particular the substances catalyzing these reaction steps.

[0024] Thereby, preferably, the process according to the invention relates to the preparation of (E)-5-methylhept-2-en-4-one.

[0025] In a preferred embodiment of the process according to the present invention, 2-butanone, 2-butanone containing mixtures or extracts (for example from fermentation) and acetaldehyde or acetaldehyde containing mixtures or extracts (for example from orange oil) can be used as the starting materials for step (a).

[0026] In step (a) of the process according to the present invention, the 2-butanone is reacted with acetaldehyde in an acid-catalyzed aldol condensation to obtain 3- methylpent-3-en-2-one as product of process step (a).

[0027] The aldol condensation according to the present invention and step (a) is a condensation reaction in which the 2-butanone as enol or as an enolate ion reacts with a further carbonyl compound, here acetaldehyde, to form a b-hydroxyketone, followed by dehydration to give a conjugated enone (3-methylpent-3-en-2-one and preferably (E)-3-methylpent-3-en-2-one).

[0028] Thereby, in this reaction step (a), preferably (E)-3-methylpent-3-en-2-one is formed. This isomer is thermodynamically clearly preferred according to the process. [0029] For the reaction, pure 2-butanone or 2-butanone-containing mixtures can be used as indicated above. However, preferably pure 2-butanone is provided. Moreover, either pure acetaldehyde or acetaldehyde-containing mixtures can be used as the other starting material of step (a). However, preferably pure acetaldehyde is used as the reactant. Therefore, the use of single substances is preferred. This is advantageous as side-reaction and wastes can be minimized allowing for higher selectivities and yields as well as reduced costs.

[0030] Preferably, the molar ratio of the 2-butanone to the acetaldehyde used in step (a) is ranging from 10:1 to 1 : 10 and preferably from 5: 1 to 1 :5 and even more preferred from 1 :1.1 to 1 :4.

[0031] Thereby, preferably an excess of acetaldehyde is used allowing for a more efficient process as excess 2-butanone would have to be removed by extraction and/or distillation resulting in increased extraction/distillation times rendering the process less efficient.

[0032] In addition, if the reagents are employed within said molar range high yields and high product purities can be achieved in step (a) in an efficient manner highly suitable for a green large-scale preparation.

[0033] Therefore, in a preferred variant of the present invention, a process for the preparation of 5-methylhept-2-en-4-one, and preferably (E)-5-methylhept-2-en-4-one, is disclosed, wherein the molar ratio of the 2-butanone to the acetaldehyde is in the range of from 10:1 to 1 :10 in step (a), and preferably wherein the molar ratio is in the range of from 5:1 to 1 :5 and even more preferred from 1 :1.1 to 1 :4 in step (a) of the process according to the invention.

[0034] The aldol-condensation according to step (a) and/or step (c) can generally be catalyzed by an acid or base or a corresponding mixture of acids or bases. However, acid catalyzed aldol reactions with reactive aldehydes are mentioned in literature only few times. The self-condensation of the aldehyde is a big limitation of this reaction. That is why, usually instead of reactive aldehydes, protected intermediates, which slowly release the aldehyde in the reaction media, are used. For example, paraldehyde is used. The use of free acetaldehyde in acid catalyzed aldol condensation was reported using hydrochloric acid or sulfuric acid, strong, inorganic acids belonging to the group of the so-called mineral acids, i.e. acids being derived from one or more inorganic compounds. However, the use of hydrochloric acid or sulfuric acid for large- scale production is limited due to difficult handling of the chemicals and their strong corrosive effect.

[0035] Further examples of mineral inorganic acids are hydrochloric acid, phosphoric acid, sulfuric acid, and mixtures thereof. As indicated above, these substances can be used for the aldol condensation according to step (a) and/or step (c). However, due to their strength, their corrosive properties as well as the high storage and handling precautions required, it is preferred to avoid the use of such mineral or inorganic acids in the process according to the present invention. In addition, these substances do not have any biological origin.

[0036] Surprisingly, it was now found that the aldol condensation of step (a) and/or step (c) can be efficiently catalyzed using organic acids. The use of these organic acids in aldol condensation reactions was not published until now.

[0037] Organic acids are organic compounds with acidic properties which are usually weaker than inorganic acids, which are soluble in organic solvents and which are less corrosive and usually have a biological origin, e.g. most of the carboxylic acids are frequently found in nature. Moreover, they are often used in the production of food and beverages or food additives, for example in food preservation. Organic acids can be found in nature amongst others as normal constituents of plants or animal tissues or are formed through microbial fermentation of carbohydrates.

[0038] Therefore, in a preferred variant of the present invention the aldol condensation in step (a) and/or step (c) is catalyzed using organic acids. Preferably, carboxylic acids, i.e. organic acids that comprise or contain at least one carboxyl group are used as the organic acid(s) within the process according to the present invention in steps (a) and/or (c).

[0039] As indicated above, preferably carboxylic acids are used to catalyze the aldol condensation of step (a) and/or step (c). These carboxylic acids are preferably either monocarboxylic acids (comprising one carboxylic group or carboxyl functional group, - COOH) such as formic acid, acetic acid, lactic acid and the like, dicarboxylic acids (comprising two carboxylic groups) such as oxalic acid, malonic acid, tartaric acid, malic acid and the like, or tricarboxylic acids (comprising three carboxylic groups) such as citric acid and the like. Thereby, the use of dicarboxylic acids and tricarboxylic acids is particularly preferred for an efficient catalyzation of the aldol reactions according to the present invention.

[0040] Suitable organic acids which can be used in step (a) and/or step (c), are preferably carboxylic acids, such as oxalic acid, tartaric acid, citric acid, lactic acid, malic acid, malonic acid, formic acid and acetic acid and mixtures thereof. Generally, single acids can be used within the process according to the invention or mixtures of two or more of said organic acids.

[0041] Therefore, according to a preferred variant of the process according to the invention the organic acid(s) used in steps (a) and/or (c) is/are selected from the group consisting of: oxalic acid, tartaric acid, citric acid, lactic acid, malic acid, malonic acid, formic acid, acetic acid, or mixtures thereof.

[0042] Further preferred within the scope of the present invention is the use of oxalic acid, tartaric acid, citric acid, formic acid or mixtures thereof. Particularly preferred are oxalic acid, tartaric acid, citric acid or mixtures thereof. Most preferred are tartaric acid and/or citric acid.

[0043] These organic acids allow for an efficient aldol-condensation between the starting materials for the formation of 3-methylpent-3-en-2-one in high yields and purities in step (a), and preferably its (E)-isomer ((E)-3-methylpent-3-en-2-one). Also the reaction in step (c) is efficiently catalyzed allowing for the formation of high quality filbertone (and preferably its (E)-isomer).

[0044] In a further preferred variant, the pKa-value of the organic acids, and preferably carboxylic acids, used in step (a) and/or step (c) is in the range of from 1 to 5, preferably in the range of from 1 .2 to 4 and even more preferred in the range of 2 to 3.2 in order to achieve an efficient reaction.

[0045] The use of such naturally occurring acids is especially advantageous for the preparation of flavor compounds, because the resulting products can be used for food production without any concerns. In addition, the problems faced in the large-scale production caused by using hydrogen chloride or hydrochloric acid or sulfuric acid, such as difficult handling of gaseous or highly reactive/acidic chemicals and possible corrosions, or other rather harmful reagents can be avoided. Moreover, the use of such reagents allows for the additional reduction of costs and is particularly beneficial in terms of environmental aspects, without negatively influencing the efficacy of the aldol reaction or the quality of the as-obtained reaction products in terms of yield, purity and the like.

[0046] Thus, according to a preferred variant of the inventive process, the organic acid(s) used in steps (a) and/or (c) is a/are naturally occurring acid(s).

[0047] Moreover, these naturally occurring organic acids specified above are preferred for the preparation of 5-methylhept-2-en-4-one because the resulting products do not contain or cause any chemical side-products and can be used for food production without any concerns. Moreover, they are easy to handle, less toxic and thus allow for a considerable reduction in health and environmental impacts. In addition, they are less corrosive and can be suitably used for large-scale production.

[0048] In addition, it is preferred to avoid the use of the heavy metal salts. [0049] According to the invention, the organic acid(s) can be used either in catalytic amounts, in equimolar amounts, or in equivalent amounts or in excess relative to the amount of 2-butanone.

[0050] In the context of the present invention, “equimolarity” or “equimolar amount” describes a condition in which the different individual components or reactants are present in the same molar ratio.

[0051] In a preferred embodiment for the condensation in step (a) the use of 0.2 eq. to 3 eq. (equivalents) of organic acid relative to the 2-butanone is preferred and even more preferred an amount of 0.5 to 2.0 eq. and most preferred of 0.5 to 1.5 eq. of acid relative to the 2-butanone are used.

[0052] Therefore, according to a preferred variant, the organic acid(s) is/are used in an amount of 0.2 eq. to 3 eq. relative to the 2-butanone in step (a) and even more preferred in an amount of 0.5 eq. to 2.0 eq. relative to the amount of 2-butanone.

[0053] Moreover, according to the present invention the acid can be added as pure substance or can be used in the form of aqueous solutions. Using aqueous solutions, the concentration of the acid may vary from about 20 % by weight up to 100 % by weight with a preferred concentration of acid being about from 50 % by weight, and preferably from 70 % by weight to 100 % by weight.

[0054] In step (a) of the process according to the invention it is beneficial to add water in order to facilitate the mixing of reagents and thus to increase the efficacy of the reaction in a uniform manner, thereby also causing a dilution of the concentrated acid. Thereby, the concentrated acid can either be directly added to the reaction mixture comprising water, or alternatively an aqueous solution of the acid is prepared which is then added to the reactants/starting materials. Therefore, in step (a) of said process preferably aqueous solutions of the acids specified above are added, wherein the final concentration of the acid in the reaction mixture is preferably in the range of from 10 % by weight to 70 % by weight and even more preferred in the range of from 20 % by weight to 50 % by weight.

[0055] As indicated above, according to another preferred variant of the process according to the present invention, the reaction mixture of step (a) can be subsequently diluted with water in order to simplify the stirring. Thereby, up to 90 % by weight of water, preferred up to 50 % by weight of water, particularly preferred up 10 % by weight of water, relative to the total weight of all reagents in the reaction mixture of step (a), can be used.

[0056] In a preferred variant of the process according to the present invention, the aldol condensation of step (a) is carried out without the addition of any additional organic solvent to the reaction mixture. This is especially favorable for the development of a sustainable, environmentally friendly processes. In addition, it is thereby possible to facilitate the process and reduce the overall costs as less reactants are required, and less waste will be produced which might require additional recycling and/or disposal. Moreover, the isolation and/or purification of the resulting product is facilitated e.g. via distillation if no further reactants are used.

[0057] In accordance with a preferred variant of the present invention, the aldol condensation of step (a) can be carried out at a temperature ranging from 80 °C to 180 °C and preferably for a reaction time ranging from 8 h to 24 h, particularly preferred at a temperature ranging from 100 °C to 150 °C for preferably a reaction time ranging from 10 h to 16 h. Because of the low boiling points of the reagents the reaction is preferably carried out in an autoclave (preferably at a pressure ranging from 1 bar to 10 bar).

[0058] Therefore, according to a preferred variant of the process according to the invention, the aldol condensation of step (a) is carried out at a temperature ranging from 80 °C to 180 °C and preferably at a temperature ranging from 100 °C to 150 °C. [0059] The acid-catalyzed aldol-condensation between 2-butanone and acetaldehyde according to process step (a) results in a mixture comprising the intermediate 3-methylpent-3-en-2-one.

[0060] Thereby, as indicated above, in the process according to the invention preferably the E-isomer of said 3-methylpent-3-en-2-one ((E)-3-methylpent-3-en-2- one) is formed in reaction step (a). This is the thermodynamically preferred isomer of said intermediate compound.

[0061] Preferably, after the reaction of step (a) is completed, the 3-methylpent-3-en- 2-one, and preferably the (E)-3-methylpent-3-en-2-one obtained in step (a) is isolated and/or purified in a subsequent step (a.2), preferably by extraction (isolation) in combination with subsequent distillation (purification).

[0062] Thus, according to a preferred embodiment, the isolation and purification of the intermediate 3-methylpent-3-en-2-one from step (a) is carried out using extraction, followed by distillation.

[0063] After the completion of the reaction of step (a), the reaction mixture comprising the intermediate 3-methylpent-3-en-2-one is thus preferably diluted with water and washed with a basic solution to remove the acid.

[0064] Suitable basic solutions are for example NaOH or KOH solutions (concentration: 5 % or 10 %) or saturated NaHCCb solutions.

[0065] After washing, the product can be isolated using simple phase separation or extraction methods with organic solvent(s). Particularly preferred is the extraction with low-boiling solvents such as methyl fe/f-butyl ether (2-methoxy-2-methylpropane). Afterwards, these low-boiling substances can easily be separated.

[0066] Subsequently, the solvent is preferably removed at 30 °C under reduced pressure which is preferably ranging from 150 mbar to 400 mbar. According to a preferred embodiment, the removed solvent can be re-used for the extraction of further intermediate 3-methylpent-3-en-2-one, making the process more sustainable and environmentally friendly.

[0067] Finally, the as-obtained product can be distilled, preferably at a pressure ranging from 20 mbar to 150 mbar and at a temperature which is ranging from 60 °C to 120 °C, and preferably at a pressure ranging from 30 mbar to 100 mbar and at a temperature ranging from 70 °C to 100 °C in order to achieve high purities.

[0068] In a subsequent process step (b), the 3-methylpent-3-en-2-one from step (a) (or step (a.2)) is reacted with a biocatalyst or a biocatalytic system to obtain 3- methylpentan-2-one by biocatalytic reduction of the carbon-carbon double bond formed in step (a) and thus to obtain the biologically or biochemically generated intermediate product 3-methylpentan-2-one.

[0069] Therefore, according to a preferred variant of the process according to the invention a biocatalyst or a biocatalytic system is used in step (b) of the process.

[0070] Catalytically active biomolecules (such as enzymes, ribozymes, hormones, vitamins, growth substances) or whole, active or deactivated cells (such as microorganisms, plant and animal cells) or microorganisms applied to carriers can be used for biotechnical conversions (see biocatalysis and immobilized biocatalysts) and are formally considered as catalysts. Thus, a biocatalyst is a substance, i.e. a catalyst of natural origin, that initiates or increases the rate of a (bio)chemical reaction, and more specifically relates to the use of (biological) systems such as enzymes and microorganisms such as bacteria, yeasts or fungi in order to catalyze chemical reaction or transformations.

[0071] The biocatalyst which is favorably used for the process according to the invention is selected from the group consisting of enzymes and yeast. According to the present invention the biocatalytic reduction of the carbon-carbon double bond in step (b) can be preferably realized using yeast. [0072] Therefore, preferably said biocatalyst or biocatalyst system shows enoyl- reductase activity suitable for the reduction of the double bond in a,b-unsaturated ketones formed in process step (a).

[0073] The use of biocatalysts for the generation of aroma compounds has a long history in flavor industry or for example in the preparation of beer, cheese, wine and the like, and can be used for food production without any concerns. For example, the use of yeast for biocatalysis is especially advantageous, as the use of additional cofactors or gene modified organisms can be avoided.

[0074] In addition, biocatalysts such as yeasts are highly selective and allow for an enantioselective conversion and high yields. Additionally, this type of catalyst is fully biodegradable.

[0075] Therefore, preferably said biocatalyst is yeast.

[0076] According to the present invention different Saccharomyces species (Baker’s yeast, wine yeast or beer yeast) can be used for the transformation of 3-methylpent-3- en-2-one (from step (a) or (a.2)) into 3-methylpentan-2-one (microbial conversion or bioconversion). Preferably, yeast of the Saccharomyces species, selected from the group consisting of baker’s yeast, beer yeast and wine yeast is used as the biocatalyst. This type of yeast is even used as a probiotic in humans and animals.

[0077] Preferred is the use of Baker’s yeast, whereby said yeast can be used in fresh form or as (freeze) dried culture.

[0078] Yeast from the Saccharomyces- type shows enoyl-reductase activity and allows for the enoyl-reductase-catalyzed enantioselective conversion of 3-methylpent- 3-en-2-one from step (a) into 3-methylpentan-2-one. Thereby, preferably, the corresponding S-isomer is formed. Consequently, yeast is an efficient, green biocatalyst and is therefore particularly suitable in view of providing a more environmentally friendly, but simultaneously highly efficient process for the preparation of sustainable filbertone, wherein the process can be applied in large-scale and avoids the use of dangerous or harmful substances to the greatest possible extent.

[0079] The present process therefore provides a new green approach towards the large-scale production of filbertone by using commercially available biocatalysts which are neither harmful to health nor to the environment. Based on the present approach it is efficiently possible to reduce safety and environmental concerns, especially in view of the growing demand for safer and more sustainable production processes. In addition, biocatalyst such as yeast are environmentally benign, being fully degraded in the environment. Moreover, the microorganism and enzymes are used under milder, i.e. , biological conditions allowing for the reduction of undesired side-reactions and allowing for the reduction of costs as well as equipment wear. Furthermore, as surprisingly found, they allow for the enantioselective formation of 3-methylpentan-2- one.

[0080] The process according to the present invention is relatively simple, efficient, inexpensive, and simultaneously highly environmentally friendly. Therefore, the present approach is highly suitable for green large-scale productions.

[0081] According to a preferred embodiment the biocatalytic reduction is carried out under the following conditions: to a yeast solution containing from 10 g/L to 300 g/L, and preferably from 150 to 250 g/L of yeast calculated on a dry matter basis 3- methylpent-3-en-2-one from step (a) (and preferably from step (a.2)) is added to obtain a substrate concentration from 0.5 g/L to 5 g/L, preferably from 1 .0 g/L to 2.5 g/L.

[0082] In accordance with the present invention, the yeast solution is preferably prepared by suspending yeast in normal tap water, in a NaCI solution (0.9 % w/v) or in a buffer such as a potassium phosphate buffer. Therefore, firstly the dry weight of the yeast is calculated in order to adjust the correct concentration. [0083] Therefore, in accordance with a preferred variant of the inventive process, 3- methylpent-3-en-2-one obtainable or obtained from steps (a) or (a.2) is treated with a yeast solution containing 10 g/L to 300 g/L yeast, and preferably with a yeast solution containing 150 g/L to 250 g/L yeast.

[0084] According to a preferred embodiment, the concentration of the 3-methylpent- 3-en-2-one from step (a) or step (a.2) in step (b) may vary from 0.5 g/L to 5.0 g/L, preferably from 1 .0 g/L to 2.5 g/L.

[0085] If the biocatalyst is used within said amounts relative to the 3-methylpent-3- en-2-one, it is possible to achieve an efficient conversion, i.e. reduction of the carbon- carbon double bond with high selectivity. In addition, high yields can be achieved and the subsequent reduction into the corresponding alcohol can be suppressed.

[0086] Preferably the bioconversion is carried out at a temperature ranging from 15 °C to 40 °C for preferably 8 h to 48 h, particularly preferred at a temperature ranging from 20 °C to 35 °C for preferably 20 h to 30 h in order to achieve full and efficient conversion into the 3-methylpentan-2-one.

[0087] Thus, according to a preferred variant, a process is disclosed, wherein the reaction of step (b) is carried out at a temperature ranging from 15 °C to 40 °C, and preferably at a temperature ranging from 20 °C to 35 °C.

[0088] These mild reaction conditions are beneficial in terms of sustainability. In addition, side-reactions are considerably reduced.

[0089] During the process, the suspension is preferably stirred with a velocity of approximately 500 rpm in order to prevent the sedimentation of the yeast and to facilitate a homogenous distribution of the substrate 3-methylpent-3-en-2-one and thus to achieve an efficient reaction. Furthermore, the reaction can be performed with aeration of the suspension with compressed air or without any additional gassing. To prevent a critical foam formation an antifoam agent such as silicone oil (10 g/L to 25 g/L) can be added.

[0090] Based on said process for the reduction of the carbon-carbon double bond of 3-methylpent-3-en-2-one the use of hard-to-handle reagents, heavy metal-based catalysts or toxic and harmful catalysts can be fully avoided. In addition, the reaction conditions are considerably milder reducing potential side-reactions, and a more enantioselective conversion can be achieved allowing for the formation of enantioenriched 3-methylpentan-2-one in step (b).

[0091] Preferably, after the reaction of step (b) is completed, the 3-methylpentan-2- one from step (b) is isolated from the reaction mixture obtained in step (b) and/or purified in a subsequent step (b.2), preferably by distillation and even more preferred by water steam distillation combined with subsequent extraction.

[0092] According to a preferred embodiment of the invention, the isolation of 3- methylpentan-2-one in step (b.2) is preferably carried out using distillation. Preferably, the reaction mixture from step (b) can be directly distilled, preferably however by using water steam distillation at a temperature ranging from 100 °C to 120 °C under normal pressure.

[0093] Subsequently, the as-obtained product can be isolated using simple phase separation or extraction with organic solvents. Particularly preferred is the extraction with low-boiling solvents such as methyl fe/f-butyl ether, followed by the removal of the solvent at 30 °C under reduced pressure preferably ranging from 400 mbar to 200 mbar. Preferably, the removed solvent can be re-used for further extractions, making the process more sustainable and environmentally friendly.

[0094] Thereafter, the product is preferably distilled under a pressure ranging from 200 mbar to 600 mbar and at a temperature ranging from 50 °C to 150 °C, preferably under a pressure ranging from 300 mbar to 450 mbar and at a temperature ranging from 80 °C to 120°C, to obtain the isolated and purified 3-methylpentan-2-one. [0095] In a further aspect, thus, the present invention also relates to 3-methylpentan- 2-one obtained or obtainable by the process according to the present invention, and more specifically in step (b) or (b.2) of the process according to the invention.

[0096] Therefore, in a further variant, the present invention relates to biocatalytically obtained or obtainable 3-methylpentan-2-one and more specifically, 3-methylpentan- 2-one obtained or obtainable according to process steps (a) and (b) of the process according to the present invention.

[0097] The 3-methylpentan-2-one obtained in step (b) or as isolated in step (b.2) com prises a chiral center and, thus, can occur in different stereoisomeric forms as indicated above, and thus as such may exist in its corresponding enantiomerically pure forms or in any mixture of its stereoisomers, in particular enantiomers.

[0098] Consequently, whenever reference is made in the present description to 3- methylpentan-2-one, this is deemed to refer to all stereoisomers, in particular to all enantiomers.

[0099] Thus, the 3-methylpentan-2-one obtained in step (b) and/or (b.2) according to the inventive process is preferably present in the form of:

(i) a pure optically active enantiomer;

(ii) a racemic mixture of the enantiomers; or

(iii) an optically active mixture of the enantiomers.

[0100] The same applies to the final product, i.e. 5-methylhept-2-en-4-one.

[0101] Preferably, in step (b) the intermediary formed 3-methylpentan-2-one is ob tained or obtainable in its racemic form or in its enantiomerically enriched form (enan- tioenriched form, (iii)), whereby the 3-methylpentan-2-one can occur as S-isomer or as R-isomer ((3S)-3-methylpentan-2-one and (3R)-3-methylpentan-2-one or simply (S)- or (R)-3-methylpentan-2-one). [0102] Alternatively, particularly preferred is that the 3-methylpentan-2-one is present in its enantioenriched form, wherein one of said enantiomers is prevailing in amount, preferably the S-isomer. Thus, preferably, said substance is present in its enantiomeri- cally enriched form based on the use of a biocatalyst such as yeast for its synthesis.

[0103] A substance is considered to be enantioenriched or enantiomerically enriched if one of its enantiomeric isomers constitutes the major component with respect to the other enantiomeric isomer, i.e. if the mixture of enantiomers comprises more than 50 % by weight of one of the isomers.

[0104] In the present case, the enantioenriched form of the 3-methylpentan-2-one obtainable or obtained in step (b) or (b.2) preferably comprises or consists of more than 50 % by weight of the corresponding S-isomer. It was surprisingly found that said such enantioenriched 3-methylpentan-2-one shows intense sensory properties which can be described as being fresh, fruity, ethereal, nutty, somewhat fermented. These advantageous sensory properties have not been reported until now and are highly suit able for imparting, enhancing or modifying a nutty but fresh and fruity odor and taste.

[0105] Therefore, in another aspect, the present invention relates to 3-methylpentan- 2-one obtained or obtainable according to the process defined above and more spe cifically in step (b) or (b.2) of the process according to the invention in its enantioen riched form, i.e. in its enantiomerically enriched form.

[0106] Thereby, the 3-methylpentan-2-one obtained or obtainable in step (b) or step (b.2), respectively, of the process according to the present invention preferably comprises or consists of at least 50 % by weight of the S-isomer of 3-methylpentan-2- one (3S)-3-methylpentan-2-one, or at least 51 % by weight of said S-isomer and preferably of at least 60 % by weight, more preferred of at least 70 % by weight, even more preferred of at least 80 % by weight and most preferred of at least 90 % by weight of said S-isomer, relative to the total weight of the 3-methylpentan-2-one present in the product of step (b) or step (b.2), respectively. [0107] Preferably, the S-isomer is comprised in the enantioenriched form in the amounts specified above. This has the advantage of providing a suitable substrate for preparing (5S)-5-methylhept-2-en-4-one, by natural procedures. In addition, the compound (3S)-3-methylpentan-2-one is useful in its own right for flavor products due to its beneficial olfactory and gustatory and/or olfactory properties which were surprisingly found.

[0108] Enantioenriched 3-methylpentan-2-one, comprising said S-isomer within the ratios specified above, is therefore suitable as aroma/flavor and/or odorant or for the preparation of aroma/flavor compositions and/or fragrance compositions as well as for the preparation of food products.

[0109] In a preferred variant, the present invention therefore relates to 3- methylpentan-2-one comprising or consisting of at least 51 % by weight of the S-isomer of 3-methylpentan-2-one, preferably at least 60 % by weight, more preferred at least 70 % by weight, even more preferred at least 80 % by weight and most preferred at least 90 % by weight of said S-isomer, relative to the total weight of the 3- methylpentan-2-one obtained or obtainable in step (b) or step (b.2), respectively.

[0110] As indicated above, it was surprisingly found, that such an enantioenriched product shows beneficial olfactory and gustatory and/or olfactory properties, which can be described as being fresh, fruity, ethereal, nutty, somewhat fermented. It is assumed, that the S-isomer of 3-methylpentan-2-one particularly contributes to the particularly fresh, fruity and nutty impression of the 3-methylpentan-2-one as specified herein.

[0111] In another variant, in the enantioenriched form the ratio of the S-isomer to the R-isomer is preferably ranging from 95:5 to 55:45 and even more preferred from 90:10 to 60:40 and further preferred from 90:10 to 70:30 and most preferred form 90:10 to 80:20. Especially, preferred the ratio of the S-isomer to the R-isomer of the 3- methylpentan-2-one in the product obtained or obtainable in step (b) or (b.2) is prefer ably more than or equal to 7: 1 , even more preferably more than or equal to 9: 1 . [0112] Thus, another aspect of the present invention relates to 3-methylpentan-2-one as such, wherein the S-isomer of 3-methylpentan-2-one is comprised in an amount of at least 70 % by weight, further preferred in an amount of at least 80 % by weight and most preferred in an amount of at least 90 % by weight relative to the total weight of 3- methylpentan-2-one based on its extraordinary sensory properties.

[0113] Subsequently, in a following process step (c), the 3-methylpentan-2-one from step (b) (or step (b.2)) as specified above, is reacted with acetaldehyde in an acid- catalyzed aldol-condensation to obtain 5-methylhept-2-en-4-one, and preferably (E)-5- methylhept-2-en-4-one.

[0114] Thereby, in accordance with process step (a), the aldol condensation in step (c) is preferably catalyzed by using organic acids and even more preferred, using carboxylic acids as specified above for process step (a).

[0115] Preferably, said organic acid(s) used in step (c) is a/are naturally occurring acid(s), which are preferably selected from the group consisting of: oxalic acid, tartaric acid, citric acid, lactic acid, malic acid, malonic acid, formic acid, acetic acid, or mixtures thereof.

[0116] The acid or acids used in step (c) can be the same or different from those used in step (a). The advantages described in the context of reaction step (a) in view of said acids also apply to their use in reaction step (c).

[0117] As specified above, the acid(s) used in step (c) is/are preferably selected from the group comprising or consisting of: oxalic acid, tartaric acid, citric acid, lactic acid, malic acid, malonic acid, formic acid, acetic acid, or mixtures thereof. Particularly preferred are oxalic acid, tartaric acid and citric acid and even more preferred are oxalic acid and citric acid. [0118] In addition, also in step (c), the use of the salts of said organic or carboxylic acids such as zinc acetate, which is a substance being classified as dangerous on the basis of its health and/or environmental effects, should be avoided.

[0119] Preferably, the molar ratio the 3-methylpentan-2-one to the acetaldehyde used in step (c) is ranging from 1 :1 to 1 :15 and preferably from 1 :2 to 1 :8 and even more preferred from 1 :3 to 1 :5.

[0120] If the reagents are employed within said molar range improved yields and high product purities can be achieved.

[0121] Therefore, in a preferred variant of the present invention, a process for the preparation of 5-methylhept-2-en-4-one is disclosed, wherein the molar ratio of the 3- methylpentan-2-one to the acetaldehyde is from 1 :1 to 1 :15 in step (c), and preferably wherein the ration is from 1 :2 to 1 :8 and even more preferred from 1 :3 to 1 :5.

[0122] Additionally, in a preferred embodiment for the condensation in step (c) the use of 0.2 to 5 eq. (equivalents) of organic acid relative to the 3-methylpentan-2-one is preferred, and even more preferred amounts in the range of 0.2 to 4 eq. of acid and most preferred amounts in the range of 1 eq. to 2 eq. of acid relative to the 3- methylpentan-2-one are used.

[0123] Therefore, according to preferred variant, the organic acid(s) is/are used in an amount in the range of 0.2 eq. to 5 eq. relative to the 3-methylpentan-2-one in step (c), further preferred in an amount in the range of 0.2 eq. to 4 eq. relative to the 3- methylpentan-2-one and even more preferred in an amount of 1 eq. to 2 eq. relative to the 3-methylpentan-2-one.

[0124] According to a further preferred variant, the aldol-condensation of step (c) of the process according to the present invention for the preparation of 5-methylhept-2- en-4-one is preferably carried out in an autoclave (at a pressure in the range of 3 bar to 15 bar). Thereby, preferably, 1 eq. of 3-methylpentan-2-one from step (b) and preferably from step (b.2) is reacted with 1 eq. to 15 eq. of acetaldehyde and preferably, with 2 eq. to 8 eq. of acetaldehyde, and particularly preferred with 3 eq. to 5 eq. as specified above.

[0125] Again, the addition of acetaldehyde in excess amounts is preferred in terms of process efficiency and allows for the preparation of a high-quality product with improved properties at large scale.

[0126] Thus, preferably, the acetaldehyde is used in excess in step (c) of the process according to the invention.

[0127] Moreover, as indicated above, preferably, relative to 1 eq. of 3-methylpentan- 2-one from step (b), and preferably from step (b.2), 0.2 eq. to 4 eq. of the acid(s) specified above is/are added, and preferably 0.5 eq. to 3 eq. of acid and even more preferred 1 eq. to 2 eq. of acid.

[0128] Thereby, the reaction temperature is preferably ranging from 80 °C to 180 °C, and the reaction time is preferably ranging from 8 h to 45 h, and even more preferred the temperature is ranging from 100 °C to 150 °C and the reaction time form 20 h to 35 h.

[0129] Therefore, according to a preferred variant of the process according to the invention, the acid-catalyzed aldol condensation of step (c) is carried out at a temper ature ranging from 80 °C to 180 °C and preferably at a temperature ranging from 100 °C to 150 °C.

[0130] It was surprisingly found that the selectivity of the aldol-reaction according to step (c) can be improved by stepwise addition of the aldehyde.

[0131 ] The addition of acetaldehyde in step (c) of the process according to the inven tion to the 3-methylpentan-2-one obtained in the previous process step in 2 to 8 distinct and even additions or steps, particularly preferred in 3 to 5 steps, was found to be especially beneficial.

[0132] In addition, in the aldol-condensation of step (c), a stepwise addition of the acid was found to be particularly advantageous to reduce the formation of side prod ucts and to improve the yield. In a preferred embodiment, the acid can be added in 2 to 8 distinct additions or steps, particularly preferred in 2 to 4 additions or steps.

[0133] Therefore, in a preferred variant the present invention relates to a process according to the invention, wherein the organic acid and/or the acetaldehyde is/are added stepwise to the reaction mixture in step (c).

[0134] Thereby, the use of concentrated acids was found to be particularly advantageous to selectively prepare the desired product and achieve high conversion rates. A dilution with water or the addition of water was not required and was found to be rather disadvantageous in step (c).

[0135] Preferably, after the reaction of step (c) is completed, the 5-methylhept-2-en- 4-one from step (c) is isolated from the reaction mixture obtained in step (c) and/or purified in a subsequent step (c.2), preferably by extraction combined with subsequent distillation.

[0136] According to a preferred embodiment, the isolation of the product in step (c.2) is carried out using extraction techniques, followed by distillation. Therefore, after the reaction according to step (c) is completed, the reaction mixture is diluted with water and washed with a basic solution to remove the acid as specified above for step (a.2).

[0137] Suitable basic solutions are for example NaOH solutions (concentration: 5 % or 10 %), KOH solutions (concentration: 5 % or 10 %) or saturated NaHCCb solutions.

[0138] After washing, the product can be isolated by using simple phase separation or extraction techniques with organic solvent(s). Particularly preferred is the extraction with low-boiling solvents such as ethyl acetate or methyl tert- butyl ether, followed by removal of the solvent at preferably 30 °C under reduced pressure which is preferably in the range of from 100 mbarto 400 mbar. According to a preferred embodiment, the removed solvent can be re-used for further extractions, making the process more sustainable and environmentally friendly.

[0139] Finally, the as-obtained product can be distilled preferably at a pressure ranging from 5 mbar to 80 mbar and at a temperature which is ranging from 80 °C to 150 °C, and preferably at a pressure ranging from 10 mbar to 30 mbar and at a temperature ranging from 90 °C to 120 °C.

[0140] According to a further preferred embodiment, the conversion of the reaction in step (c) is approximately 30 %; however, the starting material 3-methylpentan-2-one can be re-isolated and re-used in the aldol-condensation of step (c) again.

[0141] Thereby, in the process according to the invention preferably the E-isomers of 5-methylhept-2-en-4-one are formed (i.e. (2 E)- 5-methylhept-2-en-4-one or simply (E)- 5-methylhept-2-en-4-one). These are the thermodynamically but also gustatory and/or olfactory preferred isomers of filbertone.

[0142] As indicated above, the 5-methylhept-2-en-4-one is a chiral compound and thus, the 5-methylhept-2-en-4-one (and preferably the (E)-5-methylhept-2-en-4-one) obtained in step (c) and/or (c.2) is preferably present in the form of:

(a) a pure optically active enantiomer;

(b) a racemic mixture of the enantiomers; or

(c) an optically active mixture of the enantiomers.

[0143] In a further aspect the present invention therefore also relates to 5-methylhept- 2-en-4-one obtained or obtainable by the process according to the present invention as a green alternative to other commercially available synthetic filbertone products having remarkable gustatory and/or olfactory properties highly suitable for use as aroma/flavor and/or odorant. [0144] Thereby, it is preferably present in its racemic form or in its enantioenriched form, wherein the enantioenriched form is especially preferred.

[0145] Therefore, in another variant, the present invention relates to 5-methylhept-2- en-4-one and preferably (E)-5-methylhept-2-en-4-one, obtained or obtainable accord ing to the process according to the invention in its enantioenriched form, i.e. in its en- antiomerically enriched form.

[0146] As indicated above, it was found that the S-isomers of filbertone show im proved gustatory and/or olfactory properties and a considerably reduced odor thresh old value. Therefore, these S-isomers of filbertone (i.e. the (2E,5S)- and (2Z,5S)-iso- mers) are highly valuable in terms of their olfactory and gustatory properties. There fore, increased amounts of said isomers in the final product are preferred.

[0147] Preferably, according to the present invention, the 5-methylhept-2-en-4-one or filbertone obtained in step (c) or step (c.2) comprises or consists of at least 50 % by weight of the S-isomers of filbertone or preferably of at least 51 % by weight of said S- isomers and more preferred of at least 60 % by weight, and most preferred of at least 70 % by weight, relative to the total weight of filbertone present in the product.

[0148] Among the S-isomers the (2E,5S)-isomer shows even better gustatory and/or olfactory properties. Therefore, even more preferred the highly valuable 2E,5S-isomer is the predominant isomer within the ranges specified above. This provides a composition, analogous to the natural mixture, especially in the enantioenriched form (comprising or consisting of > 51 % by weight of the 2E,5S-isomer), which also has the advantage of being bio-based as described above. Said compositions shows remarkable gustatory and/or olfactory properties superior to those of commercially available synthetic filbertone, closely resembling the gustatory and/or olfactory properties of naturally occurring filbertone. Therefore, said composition is highly suitable for the use aroma/flavor and/or odorant or for the preparation of aroma/flavor compositions and/or fragrance compositions and/or flavored food-products. [0149] Thus, preferably the 5-methylhept-2-en-4-one or filbertone obtained in step (c) or step (c.2) comprises or consists of at least 51 % by weight of the corresponding S- isomers, and preferably the (2E,5S)-isomer, relative to the total weight of 5-methylhept- 2-en-4-one present in the product and therefore in its enantiomerically enriched form.

[0150] These isomers show the best odor threshold values and are therefore especially preferred for use as aroma/flavor and/or odorant or in aroma/flavor and/or fragrance compositions.

[0151] Therefore, in another aspect, the present invention therefore also relates to enantiomerically enriched 5-methylhept-2-en-4-one comprising or consisting of at least 51 % by weight of the S-isomers of 5-methylhept-2-en-4-one, preferably at least 60 % by weight, more preferably at least 70 % by weight, relative to the total weight of 5- methylhept-2-en-4-one preferably obtained in step (c) or (c.2). Even more preferred the enantioenriched form of filbertone comprises or consists of the (2E,5S)-isomer in the ratios specified above.

[0152] This enantiomerically enriched product closely resembles naturally occurring 5-methylhept-2-en-4-one in terms of its composition and properties such as its gustatory and/or olfactory properties which are superior to commercially available synthetic 5-methylhept-2-en-4-one.

[0153] However, also the racemic form is highly valuable as a green alternative to other commercially available synthetic filbertone products as it is obtainable via a green, environmentally friendly and sustainable large-scale process in an efficient manner with improved product quality (yield, purity etc.) while simultaneously allowing for a considerable reduction in costs, waste and the use of difficult-to-handle or harmful reagents.

[0154] The as-filbertone is mainly based on natural occurring and less harmful reagents further reducing potential health concerns. [0155] In addition, also the racemic filbertone obtained or obtainable by the process according to the present invention shows remarkable gustatory and/or olfactory properties highly suitable for use as aroma/flavor and/or odorant, especially since all of its isomers show the desired taste and odor of hazelnuts.

[0156] Therefore, the use of said 5-methylhept-2-en-4-one obtained or obtainable by the process according to the present invention is excellently suitable as aroma/flavor and/or odorant in a variety of formulations, closely resembling the aroma/flavor and odor of natural filbertone. Also the 3-methylpentan-2-one obtained or obtainable in step (b) of the process can be used as aroma/flavor and/or odorant or in the corresponding formulations.

[0157] Thus, another aspect of the present invention relates to the use of the 5- methylhept-2-en-4-one and/or 3-methylpentan-2-one according to the invention as aroma/flavor and/or odorant or for the preparation of aroma/flavor compositions and/or fragrance compositions as well as the preparation of foodstuff, luxury food, food supplements, semi-finished products for the preparation of foodstuff or foods supplements, pet food.

[0158] Moreover, these aromas/flavors and/or odorants as well as the corresponding compositions may be incorporated into products which are flavored or perfumed or are intended to be flavored or perfumed, preferably foodstuff, luxury food, food supplements, semi-finished products for the preparation of foodstuff or food supplements, pet food, fragrance or formulations serving for personal hygiene such as cleaning agents, laundry agents.

[0159] Thus, the present invention also relates to the flavored or perfumed products such as aroma/flavor compositions, fragrance compositions, foodstuff, luxury food, food supplements, semi-finished products for the preparation of foodstuff or foods supplements, pet food comprising the 5-methylhept-2-en-4-one and/or 3- methylpentan-2-one according to the invention. [0160] In the following the process according to the invention is exemplarily shown based on the conversion with yeast in step (b).

O acetaldehyde butan-2-one ethylpent-3-en-2-one

O fermentation with yeast

(b) ethylpent-3-en-2-one 3-methylpentan-2-one

3-methyl pe ntan-2 -o ne aceta Ide hyd e

Reaction scheme 1

[0161] As indicated above, preferably the process according to the invention for the preparation of 5-methylhept-2-en-4-one comprises additional isolation and/or purification steps (a.2), (b.2) and/or (c.2) after steps (a), (b) and/or (c), respectively.

[0162] Therefore, in addition, a process is disclosed, wherein the process according to the invention comprises additional isolation and/or purification steps (a.2), (b.2) and/or (c.2) after steps (a), (b) and/or (c), respectively. [0163] Preferably, step (a.2) comprises the subsequent isolation and/or purification of 3-methylpent-3-en-2-one from step (a), preferably by extraction in combination with subsequent distillation.

[0164] Preferably, step (b.2) comprises the subsequent isolation and/or purification of 3-methylpentan-2-one from step (b), preferably by distillation and even more preferred by water steam distillation combined with subsequent extraction.

[0165] Preferably, step (c.2) comprises the subsequent isolation and/or purification of 5-methylhept-2-en-4-one from step (c), preferably by extraction in combination with subsequent distillation.

[0166] Therefore, in a preferred embodiment the process for the preparation of 5- methylhept-2-en-4-one comprises the following steps of:

(a) acid catalyzed aldol-condensation between 2-butanone and acetaldehyde to obtain 3-methylpent-3-en-2-one;

(a.2) isolation and/or purification of 3-methylpent-3-en-2-one from step (a), preferably by extraction in combination with subsequent distillation;

(b) reaction of the 3-methylpent-3-en-2-one from step (a) with a biocatalyst to obtain 3-methylpentan-2-one;

(b.2) isolation and/or purification of 3-methylpentan-2-one from step (b), preferably by distillation and even more preferred by water steam distillation combined with subsequent extraction;

(c) acid catalyzed aldol-condensation between the 3-methylpentan-2-one from step (b) and acetaldehyde to obtain 5-methylhept-2-en-4-one; and

(c.2) isolation and/or purification of 5-methylhept-2-en-4-one from step (c), preferably by extraction in combination with subsequent distillation.

[0167] The process according to the present invention therefore provides for a new and green approach towards the sustainable preparation of the aroma/flavor and odor substances, and more specifically of 5-methylhept-2-en-4-one or filbertone in large scale, respectively. Based on the use of less harmful, and rather common ingredients used in food processing or substances which are naturally occurring and/or biodegradable in combination with a more environmentally friendly process it was possible to provide for an aroma/flavor and odor substance which is uncritical for consumption and which closely resembles naturally occurring filbertone in terms of its composition. Simultaneously the present 3-step process allows for a reduction in costs as all reagents used within the process can efficiently be recycled, no complicated waste disposal is required, and overall milder reaction conditions can be applied which in addition reduces the formation of side-products. This has also a beneficial effect on the equipment used. Moreover, the intermediate compounds as well as the final product can easily be isolated using common techniques. In addition, the use of reagents harmful in view of health and environmental aspects (such as heavy-metal containing substances) as well as difficult-to-handle reagents could be avoided and no strict reaction conditions such as anhydrous reaction conditions are required. Moreover, the present process can be suitably applied to the large-scale manufacturing of filbertone in a sustainable, i.e. green, environmentally friendly manner. Thereby, the overall number of process steps is generally reduced.

[0168] The 5-methylhept-2-en-4-one or (E)-5-methylhept-2-en-4-one, respectively, obtained or obtainable by the process according to the invention can be prepared in a sustainable but simultaneously efficient manner.

[0169] In the context of the present invention, the terms “aroma” or “flavor” are used in an equivalent sense.

[0170] In the above description, whenever reference is made to 5-methylhept-2-en- 4-one and/or 3-methylpentan-2-one, this is deemed to refer to the pure enantiomers thereof, and any mixtures of said enantiomers, similarly, as long as not described oth erwise.

[0171] The present invention shall now be described in detail with reference to the following examples, which are merely illustrative of the present invention, such that the content of the present invention is not limited by or to the following examples. [0172] Examples

[0173] The following examples have the purpose of clarifying the invention, without limiting it thereby.

[0174] Example 1 (aldol reaction - process step (a))

[0175] 30.0 g (1.0 eq.) of 2-butanone was treated under stirring with 15.0 g water, 60.6 g (1.0 eq.) of tartaric acid and subsequently with 33.8 ml_ (1.5 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 16 h in a closed autoclave (at a pressure of 6 bar). After 16 h the reaction mixture was cooled to room temperature and washed with water and NaOH solution (5-%) to remove the acid. The product was extracted with 200 ml_ methyl fe/f-butyl ether (MTBE). Finally, the organic phase was concentrated under reduced pressure and the as-obtained product was distilled (at 30 mbar, at 90 °C) to give 21.6 g of (E)-3-methylpent-3-en-2-one. The yield was 55 %.

[0176] Example 2 (aldol reaction - process step (a))

[0177] 30.0 g (2.0 eq.) of 2-butanone was treated under stirring with 30 g water, 31 .2 g (1.0 eq.) of tartaric acid and subsequently with 11.6 ml_ (1.0 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 14 h in a closed autoclave (pressure = 6 bar). After 14 h the reaction mixture was cooled to room temperature and washed with water and NaOH solution (5-%) to remove the acid. The product was extracted with 200 ml_ MTBE. Finally, the organic phase was concentrated under reduced pressure and the as-obtained product was distilled (at 30 mbar, at 90 °C) to give 10.6 g of (E)-3-methylpent-3-en-2-one. The yield was 52 %.

[0178] Example 3 (aldol reaction - process step (a))

[0179] 15.0 g (1.0 eq.) of 2-butanone was treated under stirring with 30.0 g water, 40.0 g (1 .0 eq.) of citric acid and subsequently with 12.9 ml_ (1 .1 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 14 h in a closed autoclave. After 14 h the reaction mixture was cooled to room temperature and washed with water and NaHCCb solution to remove the acid. The product was distilled under reduced pressure (at 30 mbar, at 90 °C) to give 7.14 g of (E)-3-methylpent-3-en-2-one. The yield was 35 %.

[0180] Example 4 (aldol reaction - process step (a))

[0181] 30.0 g (1 .0 eq.) of 2-butanone was treated under stirring with 20 g water, 19.1 g (1.0 eq.) of formic acid and subsequently with 25.6 ml_ (1.1 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 14 h in a closed autoclave. After 14 h the reaction mixture was cooled to room temperature and washed with water and NaHCCb solution to remove the acid. The as-obtained product was distilled under reduced pressure (at 30 mbar, at 90 °C) to give 7.75 g of (E)-3-methylpent-3-en-2-one. The yield was 19 %.

[0182] Example 5 (reduction of the double bond with baker’s yeast - process step (b))

[0183] To a Baker’s yeast solution (750 ml_ of 200 mM KPI buffer, i.e. a potassium phosphate buffer (pH 7.0), containing 235 g/L yeast) 1.5 g of 3-methylpent-3-en-2-one were added. The resulting reaction mixture was stirred at room temperature for 24 h. After 24 h the reaction mixture was steam distilled at 120 °C under normal pressure. The resulting water-product mixture was extracted with MTBE. After the removal of solvent, the as-obtained product was distilled under reduced pressure (at 400 mbar, at 80 °C) to give 0.56 g of 3-methylpentan-2-one (R/S =11 :70; [a] ^{25 7} D = 7.95°, c = 0.1785 g/L in Ethanol). The yield was 37 %.

[0184] Example 6 (reduction of the double bond with baker’s yeast - process step (b)) [0185] To a Baker’s yeast solution (750 mL water, containing 235 g / L yeast) 1 .5 g of 3-methylpent-3-en-2-one were added. The resulting reaction mixture was stirred at room temperature for 24 h. After 24 h the reaction mixture was distilled at 120 °C under normal pressure. The resulting water product mixture was extracted with MTBE. After the removal of solvent, the as-obtained product was distilled under reduced pressure (at 400 mbar, at 80 °C) to give 0.67 g of 3-methylpentan-2-one. The yield was 45 %.

[0186] Example 7 (aldol reaction - process step (c))

[0187] 20.0 g (1.0 eq.) of 3-methylpentan-2-one was treated under stirring with 19.2 g (0.5 eq.) of citric acid, and subsequently with 22.5 ml (2.0 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 8 h in an autoclave. After 8 h the reaction mixture was cooled to room temperature, treated with 19.2 g (0.5 eq.) of citric acid and subsequently with 22.5 ml (2.0 eq.) of acetaldehyde and then heated to 120 °C for 8 h in an autoclave. After 8 h the reaction mixture was cooled to room temperature, treated with 19.2 g (0.5 eq.) of citric acid and subsequently with 22.5 ml (2.0 eq.) of acetaldehyde and then heated to 120 °C for 8 h in an autoclave. After 8 h the reaction mixture was cooled to room temperature, treated with 19.2 g (0.5 eq.) of citric acid and subsequently with 22.5 ml (2.0 eq.) of acetaldehyde and then heated to 120 °C for 8 h in an autoclave. After 8 h the reaction mixture was cooled to room temperature and washed with water and a 10-% KOH solution to remove the acid. The as-obtained product was extracted with 400 mL MTBE. Finally, the organic phase was concentrated under reduced pressure and the resulting product was distilled under reduced pressure (at 10 mbar, at 90 °C) to give 3.28 g of (E)-5-methylhept-2-en-4-one (filbertone). The yield was 13 %.

[0188] Example 8 (aldol reaction - process step (c))

[0189] 20.0 g (1.0 eq.) of 3-methylpentan-2-one was treated under stirring with 19.2 g (0.5 eq.) of citric acid and subsequently with 16.9 ml (1.5 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 10 h in an autoclave. After 10 h the reaction mixture was cooled to room temperature and treated with 19.2 g (0.5 eq) of citric acid and subsequently with 16.9 ml (1.5 eq.) of acetaldehyde. The resulting reaction mixture was then heated to 120 °C for 15 h in an autoclave. After 15 h the reaction mixture was cooled to room temperature and washed with water and a 10-% KOH solution to remove the acid. The as-obtained product was extracted with 400 ml_ MTBE. Finally, the organic phase was concentrated under reduced pressure and the resulting product was distilled under reduced pressure (at 10 mbar, at 90 °C) to give 2.77 g of (E)-5-methylhept-2-en-4-one (filbertone). The yield was 11 %.

[0190] Example 9 (aldol reaction - process step (c))

[0191] 20.0 g (1.0 eq.) of 3-methylpentan-2-one was treated under stirring with 19.2 g (0.5 eq.) of citric acid and subsequently with 11 .2 ml (1.0 eq.) of acetaldehyde. The resulting reaction mixture was heated to 120 °C for 8 h in an autoclave. After 8 h the reaction mixture was cooled to room temperature and treated with 11 .2 ml (1 .0 eq.) of acetaldehyde. The resulting reaction mixture was then heated to 120 °C for 8 h in an autoclave. After 8 h the reaction mixture was cooled to room temperature and treated with 19.2 g (0.5 eq.) of citric acid and subsequently with 11.2 ml (1.0 eq.) of acetaldehyde. After 8 h the reaction mixture was cooled to room temperature and treated with 11 .2 ml (1 .0 eq.) of acetaldehyde. After 8 h the reaction mixture was cooled to room temperature and washed with water and a 10-% KOH solution to remove the acid. The as-obtained product was extracted with 400 ml_ MTBE. Finally, the organic phase was concentrated under reduced pressure and the resulting product was distilled under reduced pressure (at 10 mbar, at 90 °C) to give 3.0 g of (E)-5- methylhept-2-en-4-one (filbertone). The yield was 12 %.