WO1991013997A1

WO1991013997A1 - Process for the production of natural long-chain alcohols

Info

Publication number: WO1991013997A1
Application number: PCT/US1991/001598
Authority: WO
Inventors: Gregory V. Page; Robert G. Eilerman
Original assignee: BASF K&F Corp
Current assignee: BASF K&F Corp
Priority date: 1990-03-09
Filing date: 1991-03-08
Publication date: 1991-09-19
Anticipated expiration: 1992-09-09
Also published as: EP0520027A1; EP0520027A4; AU7567091A; JPH05506983A

Abstract

A process for the preparation of primary alcohols containing four to twenty carbon atoms from organic acids or derivatives thereof is disclosed. The process comprises cultivating, under anaerobic conditions, a fungus of the genus Mucor in suitable medium containing the carboxylic acid or a derivative thereof.

Description

PROCESS FOR THE PRODUCTION OF NATURAL LONG-CHAIN ALCOHOLS

TECHNICAL FIELD

The present invention relates to a process for the preparation of primary alcohols containing about 4 to about 20 carbon atoms from organic acids or their derivatives. The process is carried out by cultivating a fungus of the genus Mucor in a suitable medium which contains a carboxylic acid or a derivative thereof. BACKGROUND OF THE INVENTION

Long-chain primary alcohols, such as octanol and hexanol, have useful organoleptic properties and have long been employed as fragrance and flavor materials. Hexanol has important uses in coconut and various berry complexes in fruit flavor compositions, while octanol is used primarily in citrus flavors as well as peach, pineapple, coconut and chocolate flavorants. Hexanol occurs naturally in several essential oils such as strawberry, Java citronella, Bourbon geranium, lavender and bitter orange. Octanol is found in green tea, grapefruit, and several types of oranges.

Although these alcohols have been identified in various fruits or herbaceous materials, their isolation by extraction or distillation is often impractical or impossible due to the extremely low concentrations present in these products. Consequently, synthetic reactions are often used to manufacture these long-chain alcohols for use as flavor and fragrance materials. The microbial production of primary alcohols with chain lengths in excess of 4 carbons (i.e., butanol) , has been described in very few reports. Aspergillus flavus has been reported by Kaminski, E. et al., Appl. Microbiol. , 24:721-726 (1972) to produce both octanol and hexanol when grown on moistened wheat meal. However, less than 1 mg of alcohol was recovered from 2 kg of meal after 4 days of incubation. Similarly, Kaminski, E. et al., Appl. Microbiol. , 24:1001-1004 (1974) reported various species of Penicillium, Aspergillis and some species of Fungi imperfecti to produce aliphatic alcohol, but with the same low yields.

Extracts of various dried mushrooms, e.g. , Boletus eduljs, have also been reported in J. Agr. Food Chem. 21: 955-958 (1973) to contain trace amounts of hexanol and octanol. It has recently been reported in Acta Biotechnol, 2:209-219 (1987) that strains of Zymomonas are capable of producing trace amounts of hexanol. Additional reports have also been made regarding the production of low levels of long-chain alcohols by yeasts during the fermentation of wine and beer. These chemicals are generally considered undesirable in these products.

However, as is the case with processes utilizing plant extraction to obtain the desired long-chain alcohols, the microbial processes described in the above references suffer from extremely poor yields and produce only a very specific chain-length alcohol rather than alcohols having the range of chain-lengths required for inclusion in flavor formulations. Thus, none of the references disclose a microbial process for the production of long-chain alcohols in high yields and in the hydrocarbon chain-lengths needed for use in various flavor formulations.

It is therefore one object of the present invention to provide a process for the microbial production of such alcohols in yields that are economical for alcohol manufacture.

Another object of the invention is to provide a microbial process for the production of primary alcohols of variable carbon chain length.

It is yet another object of this invention to provide alcohols from corresponding saturated or unsaturated carboxylic acids or derivatives thereof.

SUMMARY OF THE INVENTION

A microbial process for the production of various long- chain alcohols is disclosed, wherein a Mucor fungal culture, or an enzyme extract thereof, is incubated with a substrate comprising a carboxylic acid having at least four carbon atoms or a derivative thereof, including a salt, an alkyl ester, a mono-, di- or triglyceride or an unsubstituted, monoalkyl or dialkyl amide thereof, to produce the desired alcohol through fermentation. The organic carboxylic acid or its derivative used as the substrate for the microbiological process of this invention may be substituted with any functional group that does not interfere with the formation of a terminal hydroxyl group by the reduction of the carboxylic acid moiety.

It is preferred to use as a substrate a saturated carboxylic acid of from 4 to 20 carbons in length or a derivative thereof, to produce a C. - C_2Q primary alcohol.

DETAILED DESCRIPTION OF THE INVENTION

The following invention is directed to a microbial process useful for the production, in unexpectedly high yields, of long-chain primary alcohols from an organic carboxylic acid of at least 4 carbons or a derivative thereof. The organic carboxylic acid is preferably a C. - C_2Q alkanoic or alkenoic acid and the corresponding primary alcohols will be the same number of carbon atoms in length.

As used herein, the term "organoleptic" refers to compounds of the invention which stimulate the sense of smell or taste, and are thus perceived as having a characteristic odor and/or flavor.

The terms "odor", "fragrance" and "smell" are used interchangeably whenever a compound is intended to stimulate the sense of smell. The terms "flavor", "flavoring" and "flavorant" are also used interchangeably whenever an organoleptic compound is referred to which is intended to stimulate the sense of taste.

As used herein, alkyl refers to a branched or linear saturated carbon chain containing 1 to 20 carbon atoms, and alkenyl refers to branched or linear carbon chains containing one or more double bonds.

The long-chain primary alcohols produced by the process of the present invention are organoleptic compounds which possess useful, characteristic flavor and fragrance properties. By including effective amounts of one or more of the alcohols produced according to this invention, it is possible to augment or enhance the flavor or fragrance of consumable materials. These alcohols are particularly useful in certain flavor compositions where wholly natural ingredients are required.

Primary alcohols of varying molecular weight can be prepared, based upon the fermentative incubation of a fungus of the genus Mucor, in conjunction with an appropriate substrate, to obtain a high yield of the desired alcohol. The

Mucor fungus reduces the carboxylic acid moiety of the substrate to form an alcohol.

Favorable results have been obtained with members of the dimorphic fungus genera Mucor. Examples of preferred species used in the process described herein include: M. substillissimus, M. mucedo, M. miehei, M. circinelloides, M. luteus, M. flavus, M. corticolus, and M. albo-ater.

The organic carboxylic acid or its derivative used as the substrate for the microbiological process of this invention may be substituted with 1 or more functional groups that do not interfere with the formation of a terminal hydroxyl group. Preferred substrates include compounds of the formula:

R^ώC(0)Z

wherein is alkyl or alkenyl of 3 to 19 carbons;

Z is -OX, -OCH₂CHOR³CHOR⁴ or -NR⁵R⁶ where X is hydrogen, alkyl of 1 to 6 carbons, an alkali or alkaline earth metal cation or an ion exchange resin; R 3 and R4 are independently hydrogen, alkyl of 1 to 6 carbons or R 2C(0) with R2 as defined above; and

R and R independently are hydrogen or alkyl of 1 to 6 carbons.

It is preferred that the alpha carbon is unsubstituted and unbranched. Another preferred substrate group is C to C_ straight chain saturated aliphatic carboxylic acids, i.e., R is alkyl and X is hydrogen.

Another preferred substrate for use in the process described herein is where R 2 represents R²' (CH₂)₄

and R 2 ' i .s hydrogen, C , ₁₅ alkyl, or alkenyl of 1 to 15 carbon atoms.

The substrate acid may be added to the fungus directly as the free acid or in the form of a salt, e.g., sodium, potassium, calcium, magnesium, ammonium, and the like.

Alternatively, any of the acid derivatives (e.g., ester, amide, anhydride, and the like) may be employed. In the case of ester substrates, the alcohol portion preferably contains up to 6 carbon atoms. Glycerol esters can also be employed.

The nutrient broth used according to the process of the invention includes the usual sources of nitrogen, carbohydrates and minerals. Incubative fermentation conditions used according to the process may include any pH, temperature, substrate concentration and substrate feed rate which will maintain the viability of the culture. The process of the present invention may be conducted in batch or continuous mode operations. In a batch fermentation, the nutrient medium, culture and substrate are combined and fermented until the alcohol concentration becomes constant. In a continuous process, the substrate or nutrient medium may be continuously recirculated through a fermentation reactor. The substrate is continuously added and product is similarly removed from the recirculating medium.

According to the process of the present invention, cultivation and fermentative incubation of the fungus are accomplished in an aqueous medium in the presence of the usual nutrient substances for an effective length of time and at an effective temperature. A suitable medium is one which contains carbon sources, nitrogen sources, inorganic salts and growth factors. Suitable carbon sources include, glucose, fructose, xylose, sucrose, maltose, lactose, mannitol, sorbitol, glycerol, corn syrup and corn syrup solids. Examples of suitable nitrogen sources include organic and inorganic nitrogen-containing substances such as peptone, corn steep liquor, meat extract, yeast extract, casein, urea, amino acids, ammonium salts, nitrates and mixtures thereof. Phosphates, sulfates, magnesium, sodium, calcium, and potassium are examples of inorganic salts which may be used in the aqueous medium of the process of the present invention. Suitable growth factors include one or more vitamins of the B group, and one or more trace minerals, such as iron, manganese, cobalt or copper.

When used as a nitrogen source, peptone is preferably utilized at a concentration of about 0.1 to about 3 weight percent. It is preferable to utilize peptone at a concentration, relative to the total weight of the broth, of about 0.01 to about 1.0 weight percent.

Yeast extract, when used as a vitamin source in the aqueous medium, is preferably utilized at a concentration of about 0.1 to 2 weight percent. It is more preferable to utilize yeast extract at a concentration, relative to the total weight of the broth, of about 0.2 to about 1 weight percent. The nutrients may be supplemented with various vitamins and minerals, such as one or more B vitamins and trace minerals, such as iron, manganese, cobalt and copper and the like.

It is also preferred to employ B vitamins either as a separate supplement or in the form of a yeast extract.

Dextrose may optionally be included in the nutrient medium, preferably at a concentration, for example, of about 1 to about 20 weight percent, and more preferably from about 2 to about 10 weight percent. The most preferred concentration is from about 2 to 5 weight percent. The kind and amount of the above mentioned additives to the aqueous medium may be determined based upon the specie selected and the time and temperature of incubation.

In a typical procedure, a Mucor fungus is cultivated in innoculum quantities to produce a mature culture. The culture is innoculated into a fermenter and allowed to incubate. The substrate is then added and fermentation is carried out continuously until a steady concentration of alcohol is present.

The cultivation and fermentative incubation of the fungus can be carried out as a stationary culture or as a submerged culture (e.g., shake-flask, fermentor) under anaerobic conditions. Cultivation and incubation may proceed at any suitable pH range, e.g., from about 3 to about 9, more preferably in the range of from about 4 to about 8, and most preferably from about 6 to about 7. The pH may be adjusted b the addition of organic or inorganic acids or bases, such as hydrochloric acid, acetic acid, sodium hydroxide, calcium carbonate, ammonia, ion-exchange resins, or by the addition o a buffer such as phosphate, phthalate or Tris^®.

The incubation temperature is suitably maintained at between about 18°C and about 31°C, with a preferred range of from about 20°C to about 28"C and a particularly preferred range from about 24°C to about 27°C. While anaerotic conditions are preferable, the cultivation and fermentative incubation of the fungus may be carried out in an atmosphere containing up to about 100% dissolved oxygen.

Alternatively, the substrate is added to the culture medium at the outset under anaerobic conditions. The substrate may be added either alone or in combination with another carbon source, such as glucose, during fermentative incubation or after cultivation is complete. It is preferable to add the substrate to the culture medium during the period from about 7 to 24 hours after growth of the culture in the fermentative broth has commenced. The substrate may be continuously added during fermentation, after the first 7 to 12 hours. A preferred continuous feed rate for this addition is about 0.001 to 2 g/hour/liter of medium. A more preferred feed rate is about 0.01 to 1 g per hour per liter, and the most preferred feed rate is 0.1 to 0.3 g per hour per liter.

The steady state concentration of the substrate in the medium may vary depending on the conditions.

In practice, the concentration of the substrate in the medium may conveniently vary, relative to the total weight of the nutrient broth, from about 0.01% to about 10%, preferably about 0.1% to about 5%, more preferably 0.1 to about 0.5%, consistent with the manner in which it is added to the culture. The reaction period will vary according to the specific incubation parameters, such as the strain of microorganism employed, the composition of the culture medium and type of substrate present. In general, shake-flask culture techniques require from between 2 hours and about 10 days to reach steady state depending upon the microbial strain and substrate utilized. When a fermenter is used, however, the fermentation period may be reduced to about 90 hours .or less.

The fermentative incubation of the fungus is carried out under anaerobic conditions, wherein the dissolved oxygen content in the incubation broth is maintained at 0% by sparging nitrogen gas into the vessel. The substrate is preferably maintained in continuous contact with the aqueous phase and the microorganism. Generally, vigorous stirring or shaking is satisfactory, but a surface active agent, such as Tween 80, can be added to aid in the dispersion of the substrate if desired. Conventional antifoam agents such as silicone oils, polyalkylene glycol derivatives, or soya oil can be used to control foaming. The fermentation may be carried out using cells isolated from the culture solution, or with an enzyme extract isolated from the cells in a manner known in the art. When an enzyme extract is used, the reaction can be conveniently carried out in aqueous solution. Examples of such aqueous solutions include buffer solutions and water. The isolated cells or an enzyme extract thereof may be immobilized on a solid support and the desired transformation conducted separately. It is convenient to employ the immobilized form of the enzyme extract in a continuous process. The fermentation of the substrate may also be effected by mutants of the fungus. The progress of the fermentative production of the alcohol can be monitored by assaying for alcohol concentrations using standard analytical techniques such as chromotography (gas-liquid, thin layer or high pressure liquid) and spectroscopy such as IR and NMR. Fermentation can also be followed by measuring the consumption of substrate, e.g., fatty acid or derivative thereof, or carbohydrate, e.g., glucose, or by measuring pH changes. The fermentative production of the alcohol is generally terminated when all of the substrate has been consumed, or when no further increase in the alcohol concentration is observed.

The final products containing four to twenty carbon atoms, can be isolated and purified by solvent extraction, distillation, chromatographic separation, high pressure liquid chromatography and the like.

The present invention produces a generally high yield of such primary alcohols, e.g., from about 50 to 100 mgs. to about 2 to 3 grams of primary alcohol per liter of medium. Conventional fermentation methods, on the other hand, result in alcohol yields at best on the order of only several milligrams per liter.

The following examples demonstrate certain preferred embodiments of the invention. It is understood that these examples are illustrative only, and that the invention is not restricted thereto.

All parts, proportions, percentages, and ratios used herein are by weight unless otherwise indicated. EXAMPLE 1 MUCOR CIRCINELLOIDES FERMENTATION FOR HEXANOL PRODUCTION

Ten ml of a stationary culture of Mucor circinelloides (ATCC no. 20983) can be inoculated into a two liter fermentor containing IL of a sterile broth composed of 1% peptone, 0.5% yeast extract, and 5% dextrose dissolved in IL of water (herein after referred to as PYE-5 broth) . After inoculation, 1.5% (15g) of 2-methylbutyl hexanoate (2MBH) is added to the vessel. No gases are added to the mixture and after 5 days of incubation, the broth is extracted with methylene chloride. The extract weighs 8g and the major components are 15% hexanol, 15% methyl hexanoate, 15% hexanoic acid and 40% 2MBH. This represents a hexanol yield of 1.2 g/L broth. Some results obtainable through the use of varying media, substrate concentrations and growth conditions are shown in Table I.

TABLE I

-

% Compc >sition (Extract)

Methyl Yield

Substrate Incubation Hexanoic Hexa¬ (g hexanol (cone.) E Period Hexanol 2MBH Acid noate L broth)

2MBH (1.5%)^A 6.8 3 days 12 65 10 12 1.2

2MBH (0.5%)^B 5.5 5 days 45 13 trace 35 NM B 2MBH (0.5%) 6.8 2 days 37 10 trace 30 NM

2MBH (0.5%)^B 6.5 7 days 40 15 2 30 1.5 Ethyl (0.5%)^C 5.0 3 days 20 10 25 20 1.0 Hexanoate

B,G

2MBH (0.5%) 5.0 3 days 30 20 25 1.0

A Medium used was PYE-10 (1% peptone, 0.5% yeast extract, 10% dextros B Medium used was PYE-10 with 1.5% malt extract.

C Medium used was PYE-5.

D Nitrogen gas was bubbled into the reactor during the entire incubation period.

E Nitrogen gas was bubbled into the reactor during the first 5h of incubation. F Carbon dioxide gas was bubbled into the reactor during the entire incubation period.

G Added after a 24 hour preincubation period. NM Not measured due to very low weight of extract. EXAMPLE 2

FERMENTATION WITH MUCOR CIRCINELLOIDES FOR OCTANOL PRODUCTI

M. circinelloides (ATCC no. 20983) was grown in 10 ml of PYE broth containing 10% dextrose and 2.5% ethyl octanoate at 27°C and 250 rpm on a rotary shaker. The pH wa periodically adjusted to 7.0 over the course of the next 4 d after which the broth was extracted. The extract weighed 1. and contained 60% ethyl octanoate, 20% octanol, 2% methyl caproate and 4% octanoic acid.

EXAMPLE 3 FERMENTATION WITH MUCOR CIRCINELLOIDES FOR OCTANOL PRODUCTI 15L of PYE-5 may be inoculated with 100 ml of a stationary culture of M. circinelloides (ATCC no. 20983) . T pH should be maintained at 7.0 and the temperature at 27°C. gases are added to the reactor. After 24 hours, ethyl octanoate is pumped into the culture at a rate of 2 mL/h for hours (total of 48 ml ester added) . The broth is extracted with organic solvent after a total of 36 hours of incubation The extract weighs 35 g and contains 55% ethyl octanoate, 23 octanoic acid and 3% octanol.

EXAMPLE 4 FERMENTATION OF VARIOUS STRAINS OF MUCOR FOR HEXANOL PRODUCT M. circinelloides, ATCC Deposit Nos. 27649, 8540 a 42258, were grown in PYE-2 containing 1.5% malt extract as described in Example 1. After a 24 hour preincubation perio 0.5% 2MBH was added to each culture. After 3 days, the cultures were extracted, and the extracts contained 2 to 3% hexanol, which represented a yield of less than O.lg hexanol broth.

5 Other strains tested include M. hiemalis, ATCC No.

24435 (0.5% hexanol), M. hiemalis ATCC Nos. 28841 and 22840

(trace of hexanol but not quantifiable) , and M. leuteus, ATC

No. 28932 (trace) . M. sps. 5607 and M. corticolus 18358 bot grew very poorly under anerobic conditions and were not assa

10 for hexanol production. However, the yields obtained with these Mucor species are surprisingly higher than those obtai with other systems, which typically yield only a few milligr of hexanol/several liters of broth.

15 EXAMPLE 5

LARGE SCALE FERMENTATION WITH

M. CIRCINELLOIDES FOR HEXANOL PRODUCTION

16L of PYE-10 may be inoculated with 300 ml of a 2 hour stationary culture of M. circinelloides (ATCC no. 20983)

20 After 2 hours, ethyl hexanoate is pumped into the reactor at rate of 1 ml/h, which is increased to 2 ml/h after 17 hours.

The ester is fed for 72 hours (total ester added was 161 ml) .

The total volume of broth was then extracted with methylene chloride. The resulting extract weighs 27 g and contains 64 25 hexanol (17.4 g) representing a yield of 1.1 g/L.

Claims

1. A process for the production of a C. to C₂₀ lo chain primary alcohol comprising: incubating in a nutrient medium a Mucor fungus and substrate comprising a carboxylic acid, a salt or an alkyl ester of a carboxylic acid; maintaining the fungus and the nutrient medium at a temperature and for a time effective for fermentatively producing a C to C__Q long chain alcohol in high yield; and extracting the alcohol from the nutrient medium.

2. A process for the production of a C to C_2Q lo chain primary alcohol which comprises: incubating in a nutrient medium a Mucor fungal enz extract with a C. to C_₀ substrate comprising a carboxylic acid, a salt or an alkyl ester of a carboxylic acid for a ti and at a temperature effective for fermentatively producing C to C_2Q long chain alcohol in high yield; and extracting the alcohol from the nutrient medium.

3. The process according to Claim 1 wherein said fungus is of the genus Mucor.

4. The process according to Claim 2 wherein the carboxylic acid or its corresponding derivative is of the formula: R²C (0) Z

wherein R represents an alkyl or alkenyl of 3 to 19 carbon atoms in length;

Z represents -OX, -OCH₂CHOR³CH₂OR⁴ or NR⁵R⁶;

X represents hydrogen, alkyl of 1 to 6 carbons, an alkali or alkaline earth metal cation or an ion exchange res R 3 and R4 represent independently hydrogen, alkyl 1 to 6 carbon atoms or R 2C(O) where R2 is as defined above; R 5 and R6 i.ndependently are hydrogen or alkyl of 1

6 carbon atoms.

5. The process according to Claim 2 wherein said enzyme extract is from a fungus of the genus Mucor.

6. The process according to Claim 1 wherein said long chain alcohol is a C to C₂ primary alcohol.

7. The process according to Claim 2 wh-.rein said long chain alcohol is a C. to C_2Q primary alcohol.

8. The process according to Claim 1 wherein said derivative of said carboxylic acid or derivative thereof is selected from the group consisting of a salt, an alkyl este mono- di- or triglyceride, or an unsubstituted, monoalkyl o dialkyl amide thereof.

9. The process according to Claim 6 wherein said long chain alcohol has the formula:

R-(CH₂)₄-OH

wherein R represents C, ₁₆ alkyl,

10. The process according to claim 4 wherein the substrate has the formula R 2C(0)Z and R2 represents

^R (CH₂)₄-

wherein R 2' represents hydrogen, C, ._ alkyl or an alkenyl group of 1 to 15 carbon atoms.

11. The process according to Claim 1 wherein said incubation is conducted at

(a) a pH of about 3 to about 9;

(b) a temperature of about 18°C to 31°C; and (c) and the nutrient medium contains nitroge and carbohydrate.

12. The process according to Claim 1 wherein

(a) said substrate concentration ranges from about 0.01% to about 10% by weight;

(b) said substrate is continuously added at feed rate ranging from about 1 mg to about 2 g per hour per liter; and (c) the incubation period is about 1 to abou 10 days.

13. The process of claim 11 wherein the source of nitrogen is a peptone.

14. The process of claim 13 further comprising adding a yeast extract to the nutrient medium.

15. The process according to Claim 14 wherein

(a) said substrate is present from about 0.0 to about 10 percent;

(b) said peptone is present at a concentrati of about 0.01 to about 3 percent; (c) said yeast extract is present at a concentration of 0.1 to 2%;

(d) dextrose is present at a concentration o about 2 to about 20 percent;

(e) said substrate is added at a feed rate ranging from about 1 mg to about 2 g per hour per liter; and

(f) the incubation period is about 1 to 10 days.

16. The process according to Claim 14 wherein

(a) the pH of the media is about 4 to about

(b) the temperature is about 20.C to about 28°C; (c) the yeast extract concentration is from about 0.1 to about 2%;

(d) said peptone has a concentration from a 0.1 to about 2%; (e) said dextrose has a concentration from about 1% to about 15%;

(f) the atmosphere contains from about 0% t about 80% oxygen;

(g) said substrate is present in said nutri broth at a concentration from about 0.1% to about

(h) said feed rate ranges from about 0.01 g about 1 g per hour per liter; and,

(i) said incubation period is about 2 to 8 days.

17. The process according to Claim 14 wherein

(a) the pH is about 6 to about 7;

(b) the dextrose concentration is about 2%;

(c) B vitamins are added as a supplement or the yeast extract;

(d) said substrate feed rate is about 0.1 g about 1.2 g per hour per liter; and

(e) the atmosphere is about 0% dissolved oxygen.

18. The process according to Claim 1 further comprising monitoring the alcohol concentration in the nutr broth, and terminating the incubation when the concentratio alcohol remains about constant.

19. The process according to Claim 8 wherein said substrate is an alkyl ester.

20. The process according to Claim 18 wherein the alkyl group is 1 to 3 carbons in length.

21. The process according to Claim 8 wherein said substrate is an unsubstituted amide.

22. The process according to Claim 1 wherein a mixture of various carbon-length alcohols is produced.

23. The process according to Claim 21 wherein sai alcohol produced comprises hexanol.

24. The process according to Claim 21 wherein sai alcohol produced comprises octanol.

25. The process according to Claim 8 wherein said substrate is ethyl octanoate.