Method for producing a biomass which can be easily broken down and which has an increased content of polyunsaturated fatty acids
According to the invention, it has been found that when the amount of sulfate used in the culturing of PUFAs-producing cells is selected such that the sulfate concentration drops to zero in the last phase of the growth phase of the cells, an easily disruptable biomass is obtained which has an increased proportion by mass of polyunsaturated fatty acids (PUFAs) in the final product.
1 . A process for producing a biomass containing polyunsaturated fatty acids (PUFAs) by fermentation, said fermentation comprising: a) a growth phase wherein Thraustochytriaceae cells are incubated in a fermentation medium comprising sulfate and nutrients needed for cell growth other than sulfate; b) an oil-production phase that begins after sulfate in the growth phase falls below 0.05 g per kg of fermentation medium and that is initiated by limiting at least one of said nutrients needed for cell growth other than sulfate; wherein sulfate in the fermentation medium is at a concentration that remains below 0.05 g/kg throughout the oil-production phase; and at the beginning of the growth phase a concentration of sulfate is present in an amount such that there is a sulfate concentration of 7.5 to 9.5 g per kg of biomass at the end of the oil-production phase.
2 . The process of claim 1 , wherein sulfate at the beginning of the growth phase is present in an amount such that there is a sulfate concentration of 7.5 to 9.5 g per kg of biomass at the end of the oil-production phase.
3 . The process of claim 1 , comprising as a further step, a mechanical disruption of the biomass obtained at the end of the oil-production phase, using a mechanical force of up to 12 Watt-hours per kilogram (Wh/kg).
4 . The process of claim 1 , comprising, as a further step, a mechanical disruption of the biomass obtained at the end of the oil-production phase, using a mechanical force of 1 to 10 Wh/kg.
5 . The process of claim 1 ; wherein the sulfate concentration in the fermentation medium falls to below 0.05 g per kg of fermentation medium in the second half of the growth phase.
6 . The process of claim 1 , wherein the fermentation produces a broth that is concentrated and further processed to give a feedstuff.
7 . The process of claim 1 , wherein, in the growth phase, cells are cultured to a biomass density of at least 50 g per litre of fermentation medium.
8 . The process of claim 7 , wherein, in the growth phase, sulfate concentration in the medium falls below 0.05 g per kg after a biomass density of at least 50 g per litre of fermentation medium has been reached.
9 . The process of claim 1 , wherein the cells are cultured in the growth phase to a biomass density of at least 100 g per litre of fermentation medium.
10 . The process of claim 9 , wherein the limiting nutrient is nitrogen.
11 . The process of claim 1 , wherein the fermentation medium contains a chloride content of not more than 2 g per kg during the entire fermentation.
12 . The process of claim 1 , wherein the fermentation medium contains a chloride content of not more than 500 mg/L during the entire fermentation.
13 . The process of claim 1 , wherein the fermentation medium contains a chloride content of not more than 250 mg/L during the entire fermentation.
14 . The process of claim 1 , wherein the cells are of the genus Thraustochytrium, Schizochytrium, Aurantiochytrium or Oblongichytrium.
15 . The process of claim 1 , wherein the concentration of sulfate at the beginning of the growth phase is adjusted using sodium sulfate.
16 . The process of claim 15 , wherein the oil production phase is initiated by limiting nitrogen.
17 . The process of claim 1 , wherein the cells in the biomass obtained contain at least 40% by weight of PUFAs, based on dry biomass.
18 . The process of claim 17 , wherein the cells are Schizochytrium or Aurantiochytrium cells.
19 . A process for producing a biomass containing polyunsaturated fatty acids (PUFAs) by fermentation, said fermentation comprising: a) a growth phase wherein Thraustochytriaceae cells are incubated in a fermentation medium comprising sulfate and nutrients needed for cell growth other than sulfate wherein: i) the sulfate concentration at the beginning of the growth phase is chosen, at least in part, to optimize purity based on grams of docosahexaenoic acid (DHA) per kg of dry biomass in cells when an oil-production phase is complete; and ii) the cells are cultured in the growth phase up to a biomass density of 50 to 250 g per litre of fermentation medium; and b) an oil-production phase, wherein said oil-production phase begins after sulfate in the growth phase falls below 0.05 g per kg of fermentation medium and that is initiated by limiting nitrogen or phosphate; wherein sulfate in the fermentation medium is at a concentration that remains below 0.05 g/kg throughout the entire oil-production phase and there is a chloride content of not more than 250 mg/L during the entire fermentation; and at the beginning of the growth phase a concentration of sulfate is present in an amount such that there is a sulfate concentration of 7.5 to 9.5 g per kg of biomass at the end of the oil-production phase.