Synthesis of carotenoids by Rhodotorula rubra GED8 co-cultured with yogurt starter cultures in whey ultrafiltrate.

Two cultures, a yeast ( Rhodorula rubra GED8) and a yogurt starter ( Lactobacillus bulgaricus 2-11+ Streptococcus thermophilus 15HA), were selected for associated growth in whey ultrafiltrate (WU) and active synthesis of carotenoids. In associated cultivation with the yogurt culture L bulgaricus 2-11+S. thermophilus 15HA under intensive aeration (1.3 l(-1)min(-1) air-flow rate) in WU (45 g lactose l(-1)), initial pH 5.5, 30 degrees C, the lactose-negative strain R. rubra GED8 synthesized large amounts of carotenoids (13.09 mg l(-1 )culture fluid). The carotenoid yield was approximately two-fold higher in association with a mixed yogurt culture than in association with pure yogurt bacteria. The major carotenoid pigments comprising the total carotenoids were beta-carotene (50%), torulene (12.3%) and torularhodin (35.2%). Carotenoids with a high beta-carotene content were produced by the microbial association 36 h earlier than by Rhodotorula yeast species. No significant differences were notd in the ratio between the pigments synthesized by R. rubra GED8+ L. bulgaricus 2-11, R. rubra GED8+ S. thermophilus 15HA, and R.rubra GED8+yogurt culture, despite the fact that the total carotenoid concentrations were lower in the mixed cultures with pure yogurt bacteria.