Method for obtaining a lipid-containing composition from microbial biomass

Abstract

Methods are provided for pelletizing a microbial biomass, extracting a refined lipid composition from the pelletized biomass under supercritical conditions and distilling the refined lipid composition, at least once under short path distillation conditions, to obtain a lipid-containing fraction. Also disclosed are methods of making lipid-containing oil concentrates therefrom, by transesterifying and enriching the lipid-containing fraction.

1 . A method comprising
 pelletizing a microbial biomass having a moisture level and comprising oil-containing microbes,   wherein said pelletizing comprises:   (1) mixing the microbial biomass and at least one grinding agent capable of absorbing oil to provide a disrupted biomass mix;   (2) blending the disrupted biomass mix with at least one binding agent to provide a fixable mix capable of forming a solid pellet; and   (3) forming said fixable mix into solid pellets to provide a pelletized microbial biomass.   
     
     
         2 . The method of  claim 1 , wherein the oil-containing microbes are selected from the group consisting of yeast, algae, fungi, bacteria, euglenoids, stramenopiles, and oomycetes. 
     
     
         3 . The method of  claim 1 , wherein the oil-containing microbes comprise at least one polyunsaturated fatty acid. 
     
     
         4 . The method of  claim 1 , wherein the moisture level of the microbial biomass is in the range of about 1 to 10 weight percent. 
     
     
         5 . The method of  claim 1 , further comprising extracting the pelletized microbial biomass to produce an extracted oil. 
     
     
         6 . The method of  claim 1 , wherein the mixing of step (1) is done in a twin screw extruder comprising:
 (a) a total specific energy input (SEI) of about 0.04 to 0.4 KW/(kg/hr);   (b) a compaction zone using bushing elements with progressively shorter pitch length; and   (c) a compression zone using flow restriction;   wherein the compaction zone is prior to the compression zone within the extruder.   
     
     
         7 . The method of  claim 1 , wherein:
 (a) said at least one grinding agent:
 (i) comprises a particle having a Moh hardness of 2.0 to 6.0 and an oil absorption coefficient of 0.8 or higher as determined according to ASTM Method D1483-60; 
 (ii) comprises silica or silicate; or 
 (iii) is present at about 1 to 20 weight percent, based on the summation of the weights of microbial biomass, grinding agent and binding agent in the solid pellets; 
 and/or 
   (b) said at least one binding agent:
 (iv) comprises water or a carbohydrate selected from the group consisting of sucrose, lactose, fructose, glucose, and soluble starch; or 
 (v) is present at about 0.5 to 10 weight percent, based on the summation of the weights of microbial biomass, grinding agent and binding agent in the solid pellets. 
   
     
     
         8 . The method of  claim 1 , wherein:
 steps (1) and (2) are performed in an extruder, are performed simultaneously, or are performed simultaneously in an extruder; and/or   step (3) comprises a step selected from the group consisting of:
 (i) extruding said fixable mix through a die to form strands, 
 (ii) drying and breaking said strands, and 
 (iii) a combination of step (i) and step (ii). 
   
     
     
         9 . The method of  claim 1 , wherein said solid pellets:
 have an average diameter of about 0.5 to about 1.5 mm and an average length of about 2.0 to about 8.0 mm,   have a moisture level of about 0.1 to 5.0 weight percent, or   comprise about 70 to about 98.5 weight percent of microbial biomass comprising oil-containing microbes, about 1 to about 20 weight percent of at least one grinding agent capable of absorbing oil, and about 0.5 to 10 weight percent of at least one binding agent, based on the summation of the weights of microbial biomass, grinding agent and binding agent in the solid pellets.   
     
     
         10 . The method of  claim 5 , wherein said extracting is performed with an organic solvent and said extracted oil is degummed and optionally bleached. 
     
     
         11 . The method of  claim 5 , wherein said extracting comprises:
 processing the pelletized microbial biomass with a solvent comprising liquid carbon dioxide or supercritical fluid carbon dioxide, wherein said pelletized microbial biomass further comprises at least one polyunsaturated fatty acid, to obtain:
 (i) an extract comprising a lipid fraction substantially free of phospholipids; and 
 (ii) a residual biomass comprising phospholipids. 
   
     
     
         12 . The method of  claim 11 , wherein said extracting further comprises:
 fractionating the extract comprising the lipid fraction substantially free of phospholipids at least once to obtain an extracted oil having a refined lipid composition comprising at least one polyunsaturated fatty acid, wherein the refined lipid composition is enriched in triacylglycerols relative to the oil composition of pelletized microbial biomass that is not processed with a solvent.   
     
     
         13 - 15 . (canceled) 
     
     
         16 . The method of  claim 2 , wherein the oil-containing microbes are  Yarrowia  yeast. 
     
     
         17 . The method of  claim 16 , wherein the  Yarrowia  yeast are recombinantly engineered for the production of a polyunsaturated fatty acid selected from the group consisting of: linoleic acid, gamma-linolenic acid, eicosadienoic acid, dihomo-gamma-linolenic acid, arachidonic acid, docosatetraenoic acid, omega-6 docosapentaenoic acid, alpha-linolenic acid, stearidonic acid, eicosatrienoic acid, eicosatetraenoic acid, eicosapentaenoic acid, omega-3 docosapentaenoic acid, and docosahexaenoic acid. 
     
     
         18 - 19 . (canceled) 
     
     
         20 . The method of  claim 11 , wherein the residual biomass comprising phospholipids is further extracted to isolate the phospholipids. 
     
     
         21 . The method of  claim 17 , wherein the recombinant  Yarrowia  yeast are engineered for production of eicosapentaenoic acid. 
     
     
         22 . The method of  claim 21 , wherein at least 20% of the dry cell weight of said  Yarrowia  yeast is eicosapentaenoic acid.