Investigations in ultrasound-induced enhancement of astaxanthin production by wild strain Phaffia rhodozyma MTCC 7536

This work reports ultrasound-induced enhancement of astaxanthin production in batch fermentation using wild strain of P. rhodozyma MTCC 7536. The methodology adopted in this study comprises of statistical optimization of the medium and fermentation parameters, followed by application of sonication at optimized conditions. P. rhodozyma fermentation at conditions of 20 g/L glucose, pH 4.4, temperature 21 °C, 4% v/v inoculum, shaking at 205 rpm with nitrogen sources of (NH4)2SO4 and yeast extract yielded 6.8 mg/L or 1360 μg/g DCW astaxanthin in 84 h. Application of 33 kHz and 140 kPa sonication at 10% duty cycle in final 12 h of fermentation enhanced the astaxanthin yield to 8.6 mg/L or 1728 μg/g DCW, which is higher than several mutant strains reported in literature. These results are essentially manifestations of intense microturbulence generated by sonication in fermentation mixture.