US3847739A

US3847739A - Cultivation of micro-organisms on a feedstock consisting at least in part of straight chain hydrocarbons

Info

Publication number: US3847739A
Application number: US00362063A
Authority: US
Inventors: A Champagnat; B Laine
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1970-09-03
Filing date: 1973-05-21
Publication date: 1974-11-12
Anticipated expiration: 1991-11-12

Abstract

The present invention is directed to an improved hydrocarbon fermentation process which comprises cultivating a straight chain paraffinic hydrocarbon consuming micro-organism in the presence of a feedstock consisting at least in part of a straight chain hydrocarbon, recovering a fraction comprising the micro-organism and at least some aqueous medium and residual hydrocarbon, adding a surface active agent and subjecting the resulting mixture to phase separation to recover (a) a treated fraction comprising the micro-organism together with an aqueous phase and some residual hydrocarbon fraction and (b) a hydrocarbon fraction and subjecting the treated fraction to solvent extraction to remove lipids and associated hydrocarbons from said microorganism.

Description

United States Patent [191 Champagnat et al.

[111 3,847,739 1 Nov. 12, 1974 CULTIVATION OF MICRO-ORGANISMS ON A FEEDSTOCK CONSISTING AT LEAST IN PART OF STRAIGHT CHAIN HYDROCARBONS v [75] Inventors: Alfred Champagnat, Courbevoise;'

Bernard Maurice Laine, Lavern, both of France [73] Assignee: The British Petroleum Company Limited, London, England [22] Filed: May 21, I973 [21] Appl. No.: 362,063 i Related U. S. Application Data [63] Continuation of Ser. No. 69,474, Sept. 3, I970, abandoned, which is a continuation of Ser. No.

845,662, July l0, i969. abandoned, which is a continuation of Ser. No. 546,607, May 2, 1966,

abandoned. v

5 2 U.S..Cl. 195/28 195/82 [51] Int. Cl Cl2b 1/00 [58] Field of Search 195/28 R, 3

[56] References Cited UNITED STATES PATENTS 3,186,962 6/1965 Champagnat et al 195/82 OTHER PUBLICATIONS Raymond R. L., Microbial Oxidation of n-Paraffine Hydrocarbons, Developments In Industrial Microbiology, Vol. 2, pp. 23-32.

Primary Eraminer-Lionel M. Shapiro Assistant ExaminerR. B. Penland Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine [57] ABSTRACT The present invention is directed to an improved hydrocarbon fermentation process which comprises cultivating a straight chain paraffinic hydrocarbon con- 19 Claims, No Drawings This is a continuation of applicationSer. No. 69,474

filed Sept. 3, 1970, abandoned; which isacontinuation The cultivation of yeasts on hydrocarbons, andfin' particular on petroleum hydrocarbons, as the carbonaceous substratum, generally gives yeasts-which after washing and drying-possess a peculiar-taste which is sharp and rancid and which-may interfere with their use in foods for human consumption. The traditional yeasts, cultivated on molasses, residuary liquors or bisulphite liquors, alsohave apeculiar taste, different from that of yeasts cultivated on hydrocarbons, and certain processes have been proposed for attenuating this taste notabl-yto attenuate their bi'tterness, bu-t none of these has succeeded completely.

It has now been found thatyeasts cultivated with hydrocarbons as the sole source of carbon have a distinctly higher lipid contentthanyeasts cultivated .on the traditional substrata: molasses, residuary liquors, bisulphite liquors. Lipids consist-essentially of fatty acids, esters (with greater or lesser degrees of oxidation) including fats and sterols. It has now beenfound that extraction-of theselipids, wholly or in part, leads to a sub.-

stantial reduction in this characteristic taste of yeasts cultivated on hydrocarbons, or totheelimination ofthis taste.

It is an object of this invention to provide animproved process for the productionof micro-organisms. [t is a further object to provide aprocess for the production of a yeast. It is a further object to provide a process for theremoval of straight chainhydrocarbons, wholly or in part, from .mixtures of said hydrocarbons .with other hydrocarbons. Other objects will appear hereinafter.

According to one aspect of this invention there is provided a process which comprises cultivating a micro-organism capable of growing on a feedstock consisting wholly orin part of straight'chain hydrocarbons with formation of lipids, said micrmorganism beingqcultivated in the. presence of said feedstock, separating from the product a fraction comprising the micro-v organism and extractingsaidfraction by means of-a solvent to removelipids in thexextractphase.

Suitably, in accordance with the invention, straight chain hydrocarbons are removed from a petroleum fraction with production of a micro-organism, wherein the feedstock employedfor the growth of the microorganism is a petroleum fraction consisting inipartof straight chain hydrocarbonswherein there is recovered from the product of the growth ofthe micro-organism I, a petroleum fraction having a. reduced proportioniof straight chain hydrocarbons or which is free of said straight chain hydrocarbons. The process of the invention is particularly suitable for the removal, wholly or in part, of waxes from a wax-containing petroleum gas oil, wherein the feedstockisja wax-containingpetroleum gas oil and wherein thereisrecovered, from the productof the: growth of the micro-organism,'a-gas oil of reducedcontent of wax.

Solvents which maybe employed in the solvent extraction stage in-accordance with theinvention include ethyl alcohol, iso-propanol, light hydrocarbons,including benzene andlightplatformatefractions, ethyl ether, acetone, chlorinatedsolvents and-liquefied petroleum gases such as butane and propane.

Within the term micro-organism" used herein we include mixtures of micro-organisms.

Micro-organisms which are-cultivated; as ,herein described may beyeasts, -moulds orbacteria capable of growing on-astraight-chain@hydrocarbon.

Preferably :when-a-yeast: is employed this is of the family ,Cryptococcaceae and particularly of the subfamilyCryptococcoideae; however, if desired there may be-used; foryexample, ascosporogeneous yeasts of the .-su-b-famil y Saccharom-ycoideae. Preferred genera of "the Cryptococcoideae familyare Torulopsis (also known as Torula) ,:;Can di.d.a.and'Mycoderma. Preferred strainsof ,yeastare asfollows. In particular it is preferred toluse IhC SpCGll' lCQSIOCk of indicated reference number; these referencev numbers refer-to CBS stock heldby the CentfiaalBure-au vor ,Schimmelculture, Baarn, Hollandandto lNR-Astock heldby thelnstitut Nationalv de la Recherche Agronomique, Paris, France.

cancoillule Of the above Candida lipolytica is particularly preferred.

If desired, the micro-organism .may be a mould. A suitable strain is Penicillium expansum.

lf desired, the micro-organismimay be a bacterium.

uitably the acteria. are of :one of the orders: Paeudomonales,Eubacterialesand-Actinomycetales.

Rreferably the. bacteria which are employed are of the, familyBacillaeeae and Pseudomonadaceae. ,Rreferred species are-Bacillus me gaterium, Bacillus subtllis and ,Pseudomonas 'aeruginosa. Other strains which may be,emloy e d.include:

Bacillus amylobacler Pseudanzonas' narriegens Arrhrebacrer sp. Micrococcus sp. Coryaebacterium mic/rigauemre Pseudomonas syringae Xamlwmrmas beguniae Flavobacteriumdevoranx Avewbacler .\'[J. Aclononrw'cr sp. Agruhacl 'rium .i'p. Aplanobai'lcr .rp.

For the growth of the micro-organism it will be necessary to provide, in addition to the feedstock, an aqueous nutrient medium and a supply of oxygen, preferably in the form of air.

A suitable nutrient medium for yeasts (and moulds) 5 has the composition:

Diammonium phosphate 2 grams Potassium chloride l.l5 grams Magnesium sulphate, 7H O 0.65 grams 10 Zinc sulphate 0.17 grams Manganese sulphate, IH O 0.045 grams Ferrous sulphate, 7H O 0.068 grams Tap water 200 grams Yeast extract 0.025 grams Distilled water (to make up to l000 mls.)

A typical nutrient medium for the growth of Necardia, a genus in the Actin omycetales order, has the following composition:

Ammonium sulphate 1 gram Magnesium sulphate 0.20 grams Ferrous sulphate, 7H O 0.005 grams Manganese sulphate, lH O 0.002 grams Monopotassium phosphate 2 grams Disodium phosphate 3 grams Calcium chloride 0.1 grams Sodium carbonate 0.1 grams Yeast Extract 0 008 grams Distilled water (to make up to 1000 mls.)

For other bacteria a suitable nutrient medium has the composition:

Monopotassium phosphate 7 grams Magnesium sulphate, 7H O 0.2 grams Sodium chloride 0.1 grams Ammonium chloride 2.5 grams Tap water (trace elements) 100 mls Yeast extract 0.025 grams Made up to I000 mls, with distilled water Another suitable nutrient medium for the growth of bacteria has the composition:

NH Cl 0 5 grams NaCl 4 grams MgSO, 0.5 grams Na HPO, 0 5 grams KH PO 0 5 grams Water to make up to: I000 mls Micro-organisms, and in particular yeasts, when first cultivated with the use of hydrocarbon fractions as feedstock sometimes grow with difficulty and it is sometimes necessary to use an inoculum of a microorganism which has previously been adapted for growth on the hydrocarbon fraction which it is intended to use. Furthermore the micro-organism although cultivated in the presence of an aqueous mineral medium containing the appropriate nutrient elements may grow with difficulty, because the hydrocarbon fraction does not contain the growth factors which exist in carbohydrate feedstocks, unless these growth factors are added.

In batch operation, the micro-organism will usually grow initially at a low rate of increase in cellular density. (This period of growth is referred to as the lag phase). Subsequently the rate of growth will increase to a higher rate of growth; the period at the higher rate of growth is referred to as the exponential phase and subsequently again the cellular density will become constant (the stationary.phase).

A supply of the micro-organism for starting the next batch will preferably be removed before the termination of the exponential phase.

The growth operation will usually be discontinued before the stationary phase.

At this stage, the micro-organism will usually be separated from the bulk of the aqueous nutrient medium and from the bulk of the unused feedstock fraction.

The growth of the micro-organism used is favoured by the addition to the culture medium of a very small proportion of extract of yeast (an industrial product rich in vitamins of group B obtained by the hydrolysis of a yeast) or more-generally of vitamins of group B and/or biotin. This quantity is preferably of the order of 25 parts per million with reference to the aqueous fermentation medium. It can be higher or lower according to the conditions chosen for the growth.

The growth of the micro-organism takes place at the expense of the feedstock fraction with the intermediate production of bodies having an acid function, principally fatty acids, in such manner that the pH of the aqueous mineral medium progressively diminishes. If one does not correct it the growth is fairly rapidly arrested and the concentration of the micro-organism in the medium, or cellular density, no longer increases so that there is reached a so-called stationary phase.

Preferably therefore the aqueous nutrient medium is maintained at a desired pH by the step-wise or continuous addition of an aqueous medium of high pH value. Usually, when using moulds or yeasts and in particular when using Candida lipolytica, the pH of the nutrient medium will be maintained in the range 3-6 and preferably in the range 4-5. (Bacteria require a higher pH usually 6.5-8). Suitable alkaline materials for addition to the growth mixture include sodium hydroxide, potassium hydroxide, disodium hydrogen phosphate and ammonia, either free or in aqueous solution.

The optimum temperature of the growth mixture will vary according to the type of micro-organism employed and will usually lie in the range 2535 C. When using Candida lipolytica the preferred temperature range is 2832 C.

The take-up of oxygen is essential for the growth of the micro-organism. The oxygen will usually be provided as air. In order to maintain a rapid rate of growth the air, used to provide oxygen, should be present in the form of fine bubbles under the action of stirring. The air may be introduced through a sintered surface.

' However there may be used the system of intimate aeration known as vortex aeration.

It has been found that by the use of yeast of the strain Candida lipolytica in a process according to the invention in which aeration is effected by vortex aeration, a high growth rate is achieved whereby the generation time lies in the range 2-5 hours and the cell concentration is increased by a factor of up to 12 in 2 days.

The micro-organism is preferably separated from the bulk of the liquid phase when possible by centrifuging and may be recovered as a cream or paste. However, in some cases separation will be accomplished by filtration or to some extent by decantation.

This cream or paste which contains aqueous material may be treated by continuous solvent extraction or by successive washings with solvent followed by phase separation. Suitably the extraction is carried out in a stationary vessel equipped with paddle stirrer s, preferably rotating at less than revs per minute or in'a vessel which rotates on a horizontal axis. When operating a continuous solvent extraction, the extract is withdrawn continuously and distilled, continuously or batchwise, at atmospheric or reduced pressure, and solvent continuously fed back to the extractor. Under these conditions the yeast may be introduced and withdrawn continuously or batchwise.

Preferably the solvent extraction. is effected while feeding solvent to the extractor at a periodically varying rate to create pulsations in the. flow of said liquid stream.

The pulses of the liquid passing throughthe solid: material bring about oscillations and. limited displacements of each. grain of solid material in relation to its neighbours, and this is equivalent to a mechanical agitation of the whole. For this'reason the whole of the products to be extracted is much. more rapid and complete.

Suitably there is arranged in. the feed of the liquid stream a device which imparts to it pulses whose amplitude and frequency are regulated experimentally at the most favourable value for each particular case. These pulses are produced by any suitable processes already known, and preferably an alternating pump is used whose valves have been removed.

Preferably the number of pulses lies between 1 and 60 per minute. The operation of the process under the action of pulses is further described in British Patent Application 2234/63..-

Suitable solvents for use in the process have been described hereinbefore. If desired a first extraction stage can be operated using a polar solvent, for example an alcoholic solvent, for example ethanol or isopropanol and then the partially purified micro-organism can be further treated in a second. extraction stage using a hydrocarbon. solvent, for example normal hexane or a light platformate fraction or benzene.

Preferably in the second stage there is used as solvent a mixture of a hydrocarbon in major amount with a polar solvent in minor amount. Preferably there is used the azeotropic mixture of hexane with isopropanol or ethanol. If desired both extraction stages can be operated in' continuous manner.

When using a solvent consisting of a mixture of a hydrocarbon and a polar solvent, it is believed that the function or onefunction of the polar solvent is to weaken the bonding of the material to be extracted (even the bonding of hydrocarbons which are not themselves soluble in the polar solvent).

By the use of any alcohol in the first stage of a two stage extraction as hereinbefore described, the water content of the micro-organism cream or paste is considerably reduced. As a result the micro-organism containing material which is fed to the'second stage has a sufficiently low content of water to ensure that the nonaqueous contaminants which are still present are miscible with the solvent used in the second extraction stage. Each extraction stage may consist of either one or more sub-stages consisting of washing with the solvent used in the stage followed by separation.

If a single washing is employed in the first stage the amount of ethanol or isopropanolwhich is used should be 1.5 3 times the volume of water which is present in the cream or. paste of the micro-organism. However if desired two washings with ethanol or isopropanol may be employed using in the first washing a volume of solvent equal to the volume of water in the. cream or paste and in the second washing a smaller amount of ethanol or isopropanol for example, one half of the amount used in the first washing.

Between washings of each stage or sub-stage the cream or paste is allowed to drain, for example by filtering and part of the residual solvent is then preferably removed, by vacuum filtration.

In the second stage the amount of solvent used in the (or each) washing will usually be 2-20 times the volume of the resulting dry micro-organism;

Preferably the final stage employed for the removal of solvent is evaporation, suitably under reduced pressure and suitably in a stream of inert gas, for example, nitrogen or super-heated steam.

By the use in the second extraction stage of a solvent whichis a mixture of a hydrocarbon and a polar solvent the composition of the second stage solvent, which will in any case acquire polar solventfrom the first stage extraction, can be-stabilised. Build up of polar solvent can be avoided. in the course of a distillation stage, in which the second stage solvent is recovered by the removal of separate streams consisting of (a) polar solvent for recycle to the first extraction stage and (b) a mixture of a hydrocarbon and polar solvent for recycle to the second stage. Suitably in a distillation stage the extract obtained by thesecond extraction stage is distilled to recover (a) overhead a mixture of a hydrocarbon, polar solvent and water for recycle to the second extraction stage and (b) a bottoms fraction containing polar solvent, water and the extracted materials; this fraction is preferably blendedwiththe extract obtained in the first extraction stage before this is fed to distillation whereby all contaminants recovered by solvent extraction are removed as a bottoms fraction in this distillation stage. Suitably ,the polar solvent is ethanol or isopropanol. Suitably the second stage solvent is an azeotropic mixture.

In accordance with preferred procedure the microorganism containing fraction is treated in a first stage consisting of one or more sub-stages, in each sub-stage the fraction being washed with a polar solvent and the extract separated, one or more extract fractions being blended with a second stage recycle fraction and the blend distilled to recover first stage solvent which is recycled and a residue fraction, the raffinate product of the first stage being passed to. a second stage treatment, consisting of one or more substages, in each sub-stage the fraction being washed with a mixture of a hydrocarbon solvent and a polar solvent and the extract separated, one or more second stage fractions being distilled with recovery of a. a first stage solvent which is recycled to the first stage,

b. a fraction containing hydrocarbon solvent and polar solvent which is recycled to the second solvent extraction stage and c. a bottoms fraction containing extracted materials which constitutes the said second stage recycle fraction.

Optimum contact time will usually vary inversely with thetemperature of extraction. It will usually be undesirable to use a temperature above C since higher temperatures will lead to some degradation of the product.

If the cream or paste of micro-organism is subjected to partial drying before solvent extraction it will then usually be possible to operate the first extraction stage with only a single washing with an alcoholic solvent and with the use of a smaller amount of solvent than would be required if no drying had taken place. If the extent of drying is considerable a first extraction stage using a polar solvent, for example an alcoholic solvent, is not necessary; in this case the single stage extraction process can be operated by the use of a solvent which is entirely hydrocarbon or which is a mixture of a hydrocarbon and polar solvent, for example an alcohol ketone or chlorinated hydrocarbon.

In general it is desirable to avoid drying under drastic conditions since this will lead to partial decomposition of the micro-organism, for example by destruction of vitamins and oxidation of unsaturated compounds; furthermore the products of decomposition will be soluble in the solvent used in extractive distillation thus being lost from the product or requiring further stages for their recovery.

A yeast which has been freed from the whole or part of its lipids and the contaminating hydrocarbons by one of the methods described hereinbefore and whose taste has been improved is a new industrial product of value for human nutrition.

The lipid extract which has been recovered by the evaporation of the solvent is also a new industrial product which can be used either as such or as a raw material for the separation of its sterols, fatty acids (either before saponification or after) or of its other constituents.

The invention is illustrated but not limited by the following Examples 1-6. Experiments 1 and 2 which do not constitute operation according to the invention are provided for purposes of comparison.

EXAMPLE 1 litres of the following aqueous mineral medium was introduced into a litre stirred fermenter; parts are by weight:

Sodium phosphate, tribasic 3.4 Potassium chloride 0.6 Magnesium sulphate 0.3

Ammonium sulphate 2. Made up to 1000 parts with soft water containing trace elements.

A suitable alternative medium has the composition:

Diammonium phosphate 2 Potassium chloride l.l5 Magnesium sulphate, 7H O 0.65 Zinc sulphate 0.17 Manganese sulphate, 1 H O 0.045 Ferrous sulphate, 7 H O 0.068 Tap water 200 Yeast extract 0.025

Distilled water (to make up to I000 parts).

To the fermenter was added a few parts per million of yeast extract and then 50 grams of Candida lipolytica in the form of an aqueous cream containing percent by wt. of dry material and then 150 grams of a heavy gas oil of petroleum origin containing 20 percent by wt. of normal paraffms.

When the culture reached the desired concentration of yeast cells for continuous operation, the continuous feed, to the fermenter, of aqueous mineral medium and petroleum oil was started up. The temperature was maintained at 30 C and the pH of the medium was maintained regulated at pH 4 by the addition of aqueous ammonia.

This emulsion was fed to a centrifugal separator from which were recovered three phases, being, in increasing order of density; (a) an oil phase containing the yeast cells, (b) an aqueous mineral medium phase (which may contain traces of oil and yeast) and (c) a yeast cream containing approximately 1 part of yeast, 4 parts of aqueous medium and a certain quantity of oil adhering to the yeast cells.

The yeast cream together with an aqueous solution of a surface active agent, for example a non-ionic detergent having, in the molecule, a condensed ethylene oxide chain, was fed continuously to a mixer and the mixture so obtained was centrifuged to obtain three fractions: in increasing order of density: (a) an oil phase, (b) an aqueous phase containing the surfactant product which was recycled to the mixer and (c) a second yeast cream containing 1 part by wt. of yeast (which was still slightly contaminated by the oil) with 4 parts by wt. of aqueous liquid containing the surfactant.

This second yeast cream was passed with water to a mixer and the mixture so obtained was centrifuged to obtain: (a) an oil phase, (b) an aqueous phase and (c) a thick yeast cream containing 20 percent by wt. of yeast (estimated as dry yeast) and percent by wt. of water and which contained only a very small quantity of oil.

This thick yeast cream contained 44 percent by wt. of proteins and 18.5 percent by wt. of lipids. lt possessed a sharp and rancid taste. The lipids with residual oil were extracted from the yeast by solvent extraction using a mixture of 80 percent of hexane and 20 percent of ethyl alcohol.

After evaporating the solvent, a yeast containing 52 percent of proteins and 3 percent of lipids was obtained.

(From gms. of yeast there was obtained by solvent extraction 16 gms. of extract consisting principally of oxidised and unoxidised fatty acids, esters and sterols.)

The yeast which had thus been freed from the major part of its lipids possessed a neutral taste.

EXAMPLE 2 Solvent was drawn off, finally under vacuum. There was thus obtained a mixture of 2 parts of yeast and 2 parts of solvent which consisted of /a water and of ethanol, together with some remaining contaminants.

This mixture was treated with 10 parts by weight of a solvent mixture consisting of:

Normal Hcxane Ethanol 80% by Wt. 207: by wt.

The mixture was maintained at 60 C for 15 minutes and solvent drawn off, finally under vacuum. The wash- Table Yeast cream Yeast product Nitrogen, by wt. of 7% 7.8% dry yeast Total wt. of Lipids 0.5% based on wt. of dry yeast EXAMPLE 3 The yeast cream described in Example 2 was continuously extracted in a'drum havingits axis vertical and having a paddle stirrer which rotated at 10 revs/minute.

In separate runs the solvent'was respectively ethanol; ethanol followed by normal hexane; and isopropanol.

The extractwas continuously distilled forthe recovery of lipids and hydrocarbons andthe solvent recycled to the extractor. V

Conditions and results obtained were as shown in the dium containing 0.5 grams/litre of a non'ionic surface active agent consisting'ofthe condensation productof 1 mole of lauric alcohol with'8.75 mole of ethyleneoxide. The mixture isfed to aSharples Super centrifuge (of tubular type).

The micro-organism containing fraction obtained from the centrifuge is afterwards washed withtap-water only. The cream containing 1 part by weight'of yeast (estimated as dry yeast after dryingat 120 C) and 3.5 parts by weight of water is charged to a solvent extrac tor drum with 8 parts by :weight of isopropanol. The mixture is maintainedat 60 C for minutes while rotating the drum.

Solvent is drawn off finallyunder vacuum. There is thus obtained a mixture of 1 part of dry matter and 1 part of solvent which consists of /a of water and /3 of isopropanol together with some remaining contaminants.

This mixture is treated with 10 parts by weight of a solvent mixture consisting of 80% by wt. of normal hexane 20% by wt. of isopropanol This mixture is maintained at 60 C for 15 minutes and solvent is drawn off, finally under vacuum.

The washingwith this solvent mixture is repeated several times. Finally the yeast product is dried in sufollowing Table: 30 perheated steam.

TABLE Run No. 4 7 8 Solvent and- Ethanol (20 hours) Period of treatment Ethanol (ll hours) Hexane 9 hours) lsogropanol hours) Rate of Feed of Solvent 600 whr. 600 mls/hr. 600 ml L hr. Temperature C 60C 60C Weight of Yeast Paste (grams) 1000 I000 1000 Analysis Before After Before After Before After Treatment Treatment Treatment Treatment Treatment Treatment Dry Yeast Wt. (grams) 210 140 210 200 210 200 Nitrogen 6.0t 9.0 5.65 7.45 5.65 8.50 Total wt. of

Lipids in Yeast 41.2 5.0 42.9 4.2 42.9 6.9 Extract Wt. (grams) 72 200 EXAMPLE 4 EXAMPLE 5 A yeast of the strain Hansenulasuaveolens is grown in continuous culture at a dilution rate of 0.2 vol/vollhour on paraffinic gas oil asfeedstock using a concentration of said gas oil of grams/litre, a temperature of 30 C and a nutrient medium (containing sodium phosphate, potassium chloride, magnesium sulphate and ammonium sulphate) as described in Example 1. Start-up procedure using the said strain of yeast is otherwise as described in Example 1.

The pH is maintained at a value of 4 by continuous addition of controlled amounts of aqueous ammonia.

The growth rate is ofthe order of 10 grams/litre. The broth thus obtained, containing yeast contaminated with some unmetabolised feedstock and aqueous nutrient, is centrifuged in order to obtain a yeast cream. This yeast cream is then treated with an aqueous me- The process described in Example 4 was repeated using a strain of Candida utilis and a satisfactoryyeast product recovered.

EXAMPLE 6 l.6 grams NaCl 0.02 grams MgSO .7H,O 0.48 grams NH C| 4.6 grams hard water containing minerals in trace amounts l00 mls mls mgm.

' The growth rate is of the order of grams/litre. The broth thus obtained, containing bacteria contaminated with some unmetabolised feedstock and aqueous nutrient, is submitted to centrifuging. The fraction containing the micro-organism is subjected to treatment with an aqueous treating medium containing a surface active agent, using 0.5 grams/litre of a surface active agent consisting of 1 mole of lauric alcohol condensed with 8.75 moles of ethylene oxide. The mixture was subjected to centrifuging in a Sharples Supercentrifuge (of tubular type) and the micro-organism fraction so obtained is afterwards washed with tap water. The cream containing 1 part by weight of bacteria (estimated at dry weight after drying at 120 C) and 3 to 4 parts of water is charged to a solvent extraction drum with 8 parts of isopropanol. The mixture is maintained at 60 C for 30 minutes while rotating the drum.

Solvent is drawn off, finally under vacuum. There is thus obtained a mixture of 2 parts of dry matter and 2 parts of solvent which consisted of /a water and of isopropanol together with some remaining contaminants.

This mixture was treated with 10 parts by weight of a solvent mixture consisting of 80% by wt. by wt.

Normal hexane lsopropanol EXPERIMENT l The process described in Example 1 was repeated except that the yeast employed was a yeast Saccharomyces cerevisiae cultivated in the known manner on a substratum of beet molasses. It is found that no perceptible improvement in the characteristic taste of this yeast is obtained.

EXPERIMENT 2 A similar experiment is carried out starting off from a yeast Torula cultivated in a known manner on cellulose bisulphite liquor. It is found in like manner that no perceptible improvement in the characteristic taste of this yeast is obtained.

We claim:

1. A process which comprises cultivating a straight chain paraffinic hydrocarbon-consuming microorganism in the presence of a feedstock consisting at least in part of a straight chain hydrocarbon, recovering a fraction comprising the micro-organism and at least some aqueous medium and residual hydrocarbon, mixing said fraction with a surface active agent and treating the mixture to recover (a) a washed fraction comprising the micro-organism together with an aqueous phase and some residual hydrocarbon fraction and (b) a hydrocarbon fraction of reduced content of straight chain paraffins or which is free of normal paraffins; the said washed fractionbeing treated by solvent extraction for the removal, at least in part, from the microorganism of lipids together with hydrocarbons associated with said micro-organism.

2. A process which comprises cultivating a straight chain paraffinic hydrocarbon-consuming microorganism in the presence of a feedstock consisting at least in part of a straight chain hydrocarbon, recovering a fraction comprising the micro-organism and at least some aqueous medium and residual hydrocarbon, mixing said fraction with a surface active agent and treating the mixture to recover (a).a washed fraction comprising the micro-organism together with an aqueous phase and some residual hydrocarbon fraction and (b) a hydrocarbon fraction of reduced content of straight chain paraffins or which is free of normal paraffins and thereafter a micro-organism containing fraction derived from said washed fraction being treated by solvent extraction for the removal, at least in part, from the micro-organism of lipids together with hydrocarbons associated with said micro-organism.

3. A process according to claim 1 in which the straight chain paraffinic hydrocarbon-consuming micro-organism is a yeast.

4. .A process according to claim 3 in which the yeast is of the family Cryptococcaceae.

5. A process according to claim 4 in which the yeast is of the subfamily Cryptococcoideae.

6. A process accordingto claim 5 in which the yeast is of the genus Torulopsis.

7. A process according to claim 5 in which the yeast is of the genus Candida.

8. A process according to claim 7 in which the yeast is Candida lipolytica.

9. A process according to claim 1 in which the microorganism is a bacterium.

10. A process according to claim 1 in which the solvent extraction is effected by means of a solvent comprising a hydrocarbon.

11. A process according to claim 10 in which the solvent comprising a hydrocarbon is a mixture of a hydrocarbon and a polar solvent.

12. A process according to claim 11 in which the polar solvent is an alcohol.

13. A process according to claim 12 in which the polar solvent is ethanol.

14. A process according to claim 12 in which the polar solvent is isopropanol.

15. A process according to claim 11in which the hydrocarbon is normal hexane.

16. A process according to claim 11 in which the hydrocarbon is benzene.

17. A process according to claim 11 in which the hydrocarbon is a light platformate fraction.

18. A process according to claim 11 in which the mixed hydrocarbon and polar solvent is an azeotropic mixture.

19. A process which comprises cultivating a straight chain paraffinic hydrocarbon-consuming yeast in the presence of a feedstock consisting at least in part of a straight chain hydrocarbon, recovering a fraction comprising the yeast and at least some aqueous medium and residual hydrocarbon, mixing said fraction with a surface active agent, subjecting the mixture to a phase separation to recover (a) a treated fraction comprising the yeast together with an aqueous phase and some residual hydrocarbon fraction and (b) a hydrocarbon fraction and subjecting the said treated fraction to solvent extraction to remove a part of the lipids and associated hydrocarbons from said yeast.

Claims

1. A PROCESS WHICH COMPRISES CULTIVATING A STRAIGHT CHAIN PARAFFINIC HYDROCARBON-CONSUMING MICRO-ORGANISM IN THE PRESENCE OF A FEEDSTOCK CONSISTING AT LEAST IN PART OF A STRAIGHT CHAIN HYDROCARBON, RECOVERING A FRACTION COMPRISING THE MICRO-ORGANISM AND AT LEAST SOME AQUEOUS MEDIUM AND RESIDUAL HYDROCARBON, MIXING SAID FRACTION WITH A SURFACE ACTIVE AGENT AND TREATING THE MIXTURE TO RECOVER (A) A WASHED FRACTION COMPRISING THE MICRO-ORGANISM TOGETHER WITH AN AQUEOUS PHASE AND SOME RESIDUAL HYDROCARBON FRACTION AND (B) A HYDROCARBON FRACTION OF REDUCED CONTENT OF STRAIGHT CHAIN PARAFFINS OR WHICH IS FREE OF NORMAL PARAFFINS; THE SAID WASHED FRACTION BEING TREATED BY SOLVENT EXTRACTION FOR THE REMOVAL, AT LEAST IN PART, FROM THE MICRO-ORGANISM OF LIPIDS TOGETHER WITH HYDROCARBONS ASSOCIATED WITH SAID MICRO-ORGANISM.

2. A process which comprises cultivating a straight chain paraffinic hydrocarbon-consuming micro-organism in the presence of a feedstock consisting at least in part of a straight chain hydrocarbon, recovering a fraction comprising the micro-organism and at least some aqueous medium and residual hydrocarBon, mixing said fraction with a surface active agent and treating the mixture to recover (a) a washed fraction comprising the micro-organism together with an aqueous phase and some residual hydrocarbon fraction and (b) a hydrocarbon fraction of reduced content of straight chain paraffins or which is free of normal paraffins and thereafter a micro-organism containing fraction derived from said washed fraction being treated by solvent extraction for the removal, at least in part, from the micro-organism of lipids together with hydrocarbons associated with said micro-organism.

4. A process according to claim 3 in which the yeast is of the family Cryptococcaceae.

6. A process according to claim 5 in which the yeast is of the genus Torulopsis.