A factorial approach for a sugarcane juice-based low cost culture medium: increasing the astaxanthin production by the red yeast Phaffia rhodozyma

A sugarcane juice-based low cost culture medium was previously explored to produce the carotenoid pigment astaxanthin in liquid culture by the red yeast Phaffia rhodozyma (1300 mu g astaxanthin/g of dry yeast and 6500 mu g/l whole culture medium). Two peculiar limitations in Phaffia are growth temperature (<26 degrees C) and lack of sugar osmotolerance. Two advantages are the wide biochemical ability for the assimilation and metabolization of disaccharides and the prompt utilization of simple nitrogen sources. For instance, the sucrolytic/ureolytic enzymatic activities deserves exploration. In order to improve the culture medium composition and the conditions of fermentation for highly oxygenated carotenoids (e.g., astaxanthin) a study was carried out with a factorial design in two steps. As a first step, the production of astaxanthin was studied as a function of the nutrient concentration levels and their interactions. The production increase (mu g/l) obtained was 23.0% but at the expense of 16.0% pigment content decrease (mu g/g). In the second step, the variables pH and agitation level (OTR, oxygen transfer rate) were optimized and then, both goals were attained: the increase of pigment content (418 mu g astaxanthin/g of yeast) as well as the absolute pigment production enhancement (1987 mu g/l).