Optimization of Astaxanthin-producing Fermentation by Phaffia rhodozyma using Okara as Nitrogen Source

Objective  An astaxanthin-producing fermentation by Phaffia rhodozyma using okara for nitrogen was optimized.

Methods  On the conventional fermentation by P. rhodozyma to make astaxanthin, okara was used to replace the commonly applied peptone and yeast extract as the organic nitrogen source for cost reduction. Effects of carbon sources, precursor substances, other nitrogen supply, vitamins, and inorganic salts on yield of astaxanthin were analyzed with the amounts of (NH₄)₂SO₄, vitamin E, glucose, and sucrose optimized by response surface methodology.

Results  When okara was used as a raw ingredient for the fermentation, glucose became the optimal carbon source. The yield of astaxanthin by the P. rhodozyma fermentation could be significantly increased by applying both glucose and sucrose, potassium salts such as KCl, KNO₃, and K₂HPO₄ as well as (NH₄)₂SO₄, VB₂, VE, and zeaxanthin. Hence, the medium was optimized by response surface method on the 4 key ingredients of glucose, sucrose, K₂SO₄, and VE to arrive at a formulation consisting of 10% okara, 0.22% K₂SO₄, 0.6% VE, 1.08% glucose, and 1.50% sucrose to reach a yield of astaxanthin at 32.46 mg·L⁻¹, which was 2.23 folds higher than what obtained by using the YM medium.

Conclusion  Okara could amply be used to replace peptone and yeast extract as the nitrogen source for the astaxanthin production by P. rhodozyma fermentation.