High-purity acid-form sophorolipid (SL) containing composition and process for preparing same
The present invention provides a high-purity acid-form sophorolipid (SL)-containing composition characterized by substantially not containing acetic acid. The high-purity acid-form SL-containing composition can be produced, for example, by the following method: (i) adjusting the pH of a partially purified acid-form SL-containing composition to an acidic range; and (ii-a) subjecting an acidified partially purified acid-form SL-containing composition obtained in step (i) to chromatography to acquire a fraction containing an acid-form SL, or (ii-b) leaving the acidified partially purified acid-form SL-containing composition obtained in step (i) to stand under a low-temperature condition to acquire a resulting gelled object.
1. A method for producing an acid-form sophorolipid-containing composition, the method comprising the following steps (i-b) and (ii-b):
(i-b) adjusting the pH of a partially purified acid-form sophorolipid-containing composition to an acidic range of not higher than pH 4; and
(ii-b) leaving the acidified partially purified acid-form sophorolipid-containing composition obtained in step (i) to stand under low-temperature conditions of not higher than 15° C. to acquire a resulting gelled object, and washing the gelled object with a cold solvent selected from water, ethanol, and a mixture thereof;
wherein the composition has properties of the following (1), (2), (3), (6), and (7);
(1) the composition amount of acetic acid contained per ml of a solution obtained by dissolving 1 g of an ethanol soluble matter of the composition in a 5% sulfuric acid aqueous solution to make a total volume of 3 ml being 5 μg/ml or less;
(2) ignition residue: 0 to 10%;
(3) ester value: 0 to 9 mg KOH/g;
(6) ethanol soluble matter: 98 to 100%; and
(7) a 15 mass% aqueous solution of the composition with a pH of 3 becomes a gel when cooled to 4° C.
2. The method according to claim 1 , further comprising the following step before step (i-b):
a step of subjecting a liquid culture of a sophorolipid-producing yeast or a processed product of the liquid culture to alkali hydrolysis to prepare a partially purified acid-form sophorolipid-containing composition with an acid-form sophorolipid content of 78 mass% or more, based on the total amount of sophorolipids.
3. The method according to claim 1 , the method further comprising the following steps:
(iii) distilling a liquid acid-form sophorolipid-containing composition obtained via steps (i-b) and (ii-b), and
(iv) precipitating an acid-form sophorolipid from a residual liquid obtained from the distillation.
4. The method according to claim 3 , wherein step (iv) is a step of spray-drying.
5. The method according to claim 1 , the method further comprising the following steps:
(v) solidifying, through cooling, an acid-form sophorolipid-containing composition obtained via steps (i-b) and (ii-b); and
(vi) drying the cooling-solidified object.
6. The method according to claim 5 , wherein the steps of (v) and (vi) are freeze -drying steps.