Deaeration process

Abstract

A process for producing an oil, or a polyunsaturated fatty acid (PUFA), is described where an aqueous liquid comprising cells is deaerated, and the oil or PUFA is obtained from the cells. Deaeration can be performed by a wide variety of techniques, including the application of a vacuum (or reduced pressure), mechanical deaeration or degassing by reduced stirring or subjecting the broth to centrifugal forces, reducing viscosity (by dilution or heating), reduction in the supply of oxygen or air during fermentation or a reduction in stirring rate, lowering the pH (to lower the solubility of CO 2 ), filtration using PTFE capillaries, gas displacement (by bubbling in nitrogen or helium) or chemical deaeration (using oxygen scavengers).

1 . A process for producing an oil or a polyunsaturated fatty acid (PUFA), the process comprising: 
 (a) deaerating an aqueous liquid comprising cells; and    (b) obtaining the oil or PUFA from the cells.    
     
     
         2 . A process according to  claim 1 , wherein the cells are microbial cells.  
     
     
         3 . A process according to  claim 1 , wherein the cells are heated or pasteurised after deaeration in (a) but before stage (b).  
     
     
         4 . A process according to  claim 1 , wherein the aqueous liquid is a fermentation broth.  
     
     
         5 . A process according to  claim 1  which further comprises: 
 (c) extracting, purifying or isolating the oil or one or more PUFAs.    
     
     
         6 . A process according to  claim 1  wherein deaeration comprises: 
 a) application of vacuum (or reduced pressure);    b) mechanical deaeration/de-gassing (stirring, vibration, use of accelerative or g-force, such as in a centrifuge or a cyclon;    c) viscosity change (either by dilution with water or other liquid, or by increase in temperature);    d) change in fermentation conditions, for example a reduction in airlift, air sparging or the supply of oxygen or air during fermentation, or a reduction in stirring rate;    e) pH change, for example by lowering the pH or acidification;    f) filtration, for example by using a filter or membrane preferably comprising an (inert) polymer, for example PTFE;    g) gas displacement, with an inert gas such as nitrogen, a noble gas such as helium, or steam;    h) chemical deaeration, for example using an oxygen scavenger, for example sodium sulphite or hydrazine;    i) time, where the aqueous liquid is allowed to rest under conditions such that oxygen or air diffuses out of the liquid;    or a combination of one or more of the methods in (a) to (i).    
     
     
         7 . A process according to  claim 1  wherein the deaeration is effected by reduced stirring and/or gas displacement.  
     
     
         8 . A process according to  claim 7  wherein gas displacement is performed using a gas comprising either no oxygen or oxygen at a concentration level below atmospheric air.  
     
     
         9 . A process according to  claim 7  wherein the gas is, or comprises, nitrogen.  
     
     
         10 . A process according to  claim 1  wherein deaeration comprises subjecting the aqueous liquid to reduced pressure.  
     
     
         11 . A process according to  claim 10 , wherein said reduced pressure is a pressure of no more than 800 mbara, preferably no more than 600 mbara.  
     
     
         12 . A process according to  claim 10 , wherein the aqueous liquid is deaerated using a vacuum or degassing pump, a parasol deaerator or an umbrella nozzle.  
     
     
         13 . A process according to  claim 1 , wherein deaeration results in an O 2  content in the aqueous liquid of less than 20 ppm, preferably less than 10 ppm.  
     
     
         14 . A process according to  claim 1 , wherein deaeration results in a concentration of dissolved oxygen of less than 10 ppm, preferably less than 5 ppm, more preferably less than 2 ppm.  
     
     
         15 . A process according to  claim 1 , wherein the process comprises subjecting the deaerated aqueous liquid to 
 (i) a pressure of above 1 bara, preferably above 1.5 bara, more preferably above 2 bara; and/or    (ii) a temperature above 60° C., preferably above 80° C., more preferably above 100° C.    
     
     
         16 . A process according to  claim 1 , wherein the cells are heated or pasteurised at a temperature above 80° C., preferably above 90° C., preferably above 100° C.  
     
     
         17 . A process according to  claim 1  wherein the PUFA comprises, or oil comprises a PUFA which, is a C18, C20 or C22 Ω-3 or Ω-6 PUFA (optionally ARA, EPA, DHA and/or GLA).  
     
     
         18 . A process according to  claim 1 , wherein the cells are yeast, bacterial, fungal or algal cells.  
     
     
         19 . A process according to  claim 1 , wherein the oil is a microbial or single cell oil.  
     
     
         20 . A process according to  claim 1 , wherein (b) comprises obtaining an oil comprising a PUFA from the cells, said oil having a POV of less than 12 and/or an AnV of less than 20.  
     
     
         21 . An oil comprising a PUFA, or a PUFA, obtained by a process according to  claim 1 .  
     
     
         22 . An oil according to  claim 21 , wherein the oil is a microbial or single cell oil.  
     
     
         23 . Apparatus for producing an oil or a PUFA from microbial cells, comprising: 
 (a) means for culturing or fermenting microbial cells;    (b) means for deaerating an aqueous liquid comprising the microbial cells; and    (c) optionally, means for obtaining the oil or PUFA from the microbial cells.    
     
     
         24 . Apparatus according to  claim 23  wherein (a) comprises a fermenter vessel, (b) comprises a deaerator (optionally able to apply reduced pressure) and/or (c) comprises a homogeniser and/or a centrifuge.  
     
     
         25 . Apparatus according to  claim 23  wherein (b) comprises a vacuum or degassing pump, parasol deaerator or umbrella nozzle.  
     
     
         26 . Apparatus according to  claim 1 , wherein (b) comprises a deaerator able to apply a pressure of less than 800 mbara, preferably less than 600 mbara.