Production and stability analysis of yellowish pink pigments from Rhodotorula rubra MTCC 1446

摘要

Rhodotorula rubra MTCC1446 is a good source of yellowish pink pigment. Submerged fermentation, whey sugar lactose, coconut water, complex nitrogen sources viz. yeast extract and peptone have stimulatory effect on growth as well as yields of intracellular pigments of Rhodotorula rubra MTCC 1446. Physicochemical analysis of the extracted pigments indicated its stability near neutral pH, but the pigment is relatively heat sensitive. Introduction Rhodotorula is a carotenoid biosynthetic yeast, part of the Basidiomycota phylum, easily identifiable by distinctive yellow, orange/red colonies (Postgate, 1994). The main carotenoids produced were identified as torularhodin, torulene, γ-carotene, and minute β-carotene in Rhodotorula species. Aside from being natural pigments, carotenoids also have important biological activities including vitamin A biosynthesis, enhancement of the immune system and reduction of the risk for degenerative diseases such as cancer, cardiovascular diseases, macular degeneration and cataract. Thus, carotenoids constitute one of the most valuable class of food additives, potential pharmaceutical ingredients and as SCP for aquacultured animals. Feed supplement with a Rhodotorula cell mass has been found to be safe and nontoxic in animals (Krinsky, 2001; Costa et al., 2005; Iriani et al., 2005).As color is an important attribute to gain consumer acceptance, thus adding color to processed foods has become a common practice in recent years. The huge international market for carotenoids has been met mainly by synthetic carotenoids with similar structures as natural carotenoids. However due to the possible toxicity of synthetic colors natural coloring alternatives have been increasingly sought. Traditionally, carotenoids have been marketed as dried powder or extracts of plants like annatto, paprika and saffron. Natural plant extracts, however suffer from unstable supply of raw materials, subject to climatic conditions, varying colorant level with plant variety and diminished quality of the final product due to chemical extraction (Iriani et al., 2005).To increase yield of these pigments and improve biomass production, attempts were being made to obtain color pigment by strain improvement, mutation (Sakaki et al., 2000); by optimizing C: N ratio and culture conditions (Tinoi et al., 2005); by cultivating the yeast culture in various liquid substrates namely whey filtrate, glucose broth and potato extract (Natarajan et al., 2007). Synthetic media with addition of complex substrates (fermented radish brine, glycerol, hydrolyzed mung bean, waste flour from glass noodle production, sweet potato extract, yogurt, peat hydrolysate supplemented with peptone, yeast extract) could enhance Β-carotene production (Suntornsuk, 2004). In the present study a yellowish pink pigment producing strain of Rhodotorula rubra MTCC1446 was employed to study effect of culture conditions on pigment production and to analyze stability of the extracted pigment towards heat and pH. Materials and methods Microbial Strain and culture conditions Rhodotorula rubra MTCC 1446 was employed in the study. Culture was maintained on malt yeast extract agar (MYEA) containing (malt extract-3g/l, peptone-5g/l, yeast extract-3g/l, glucose-10g/l, agar-15g/l) at 25°C for 3 days as per specification provided by MTCC, Chandigarh. Preparation of spore suspension R. rubra was streaked on MYEA plates and incubated at 25oC for 3 days. R. rubra cultures were then transferred to 40C for 30 days. Yeast cells were harvested using sterile distilled water and the suspension was refrigerated at 40C for 2 to 3 days to obtain teliospores of R. rubra as per the methodology described by Newell and Hunter (1970). Preparation of coconut water An average sized coconut was broken carefully and the liquid inside was collected in a beaker. Small pieces of coconut were blended with water, filtered with cheesecloth and then clarified by centrifugation for 20 min. The clear filtrate was th