Studies on a new strain of Rhodotorula rubra isolated from yogurt

Hari, Ravinder Pal Kaur (1994) Studies on a new strain of Rhodotorula rubra isolated from yogurt. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

A new strain of red yeast was isolated from yogurt and identified as Rhodotorula rubra TP 1. Studies were conducted on its pigment production, morphology, sexuality, growth kinetics and possible use in aquaculture. -- Studies on the sexuality indicated a basidiomycetous affinity of the isolate and hence the first report of a sexual stage in Rhodotorula rubra. -- The isolate showed good growth on different substrates. It grew readily on a molasses and wort medium. Peat hydrolysate also supported a satisfactory growth of the yeast. The pH profiles were also studied and growth was found within a broad pH zone of 3 to 10. -- Studies on the genetics of the isolate included mutagenesis with nitrosoguanidine. One of the two mutants obtained utilized additional substrates for growth and pigmentation. This mutant also showed a higher value for productivity, yield coefficient and economic coefficient. -- The kinetics of growth and pigment formation of the isolate showed pigmentation in the exponential phase, like Phaffia rhodozvma. The isolate was grown in a 1500 L batch fermenter using molasses and wort as the growth medium and the influence of various kinetic parameters on the yield coefficient and specific growth rate was observed. The fermenter culture showed a higher value for the specific growth rate and productivity than that of the shake flask cultures. -- Studies on aquaculture involved a feeding trial for 9 weeks using rainbow trout. The new yeast was found to be a good source of pigments as well as nutrients for the fish when fed as intact cells. Though the commercial astaxanthin containing diet induced better pigmentation than that containing the test yeast, the total color difference between the fish fed with the two diets declined to almost one-third at the end of the feeding trial. The test yeast fed fish had higher growth rates than those fed with the commercial pigment. The proximate analysis of the fish was done wherein the test yeast-fed fish showed an increase in the protein amount at the end of the feeding trial while the synthetic astaxanthin-fed fish showed a decrease. The lipid levels of both groups decreased at the end of the experiment.

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