Isolation and Molecular Characterization of Yeast Strains from Kenyan Cheese Industries and their Potential Utilization in Bioethanol Production from Whey

Abstract

The use of Bio-wastes like whey as raw materials for production of ethanol is gaining importance due to the environmental impact and exhaustion of fossil fuel sources making renewable fuel alternatives highly attractive. The objective of the study involved the isolation, characterization and identification of yeast strains from the Kenyan Cheese Industries exhibiting robust whey-lactose fermentation to ethanol and their potential application in bioethanol production from whey, Yeast strains were isolated using PDA and YEPL Medias from samples collected from KCC, Sameer and Browns cheese dairy industries. Genetically, the variable D1/D2 domain of the large subunit (26S) ribosomal DNA of the isolates were amplified by the polymerase chain reaction (PCR), sequenced and compared with known 26S rDNA sequences in the GenBank database, the rDNA fragment containing the internal transcribed spacers (ITS1 and ITS2) and 5.8S-ITS rDNA were PCR-amplified, sequenced and the PCR product digested with the enzymes HinfI, and HaeIII. Twenty eight out of forty two pure isolates were found to have fermentative ability. The sequence analysis of the variable D1/D2 domain of the 26S rDNA, showed that the isolates belonged to Kluyveromyces, Yarrowia, Pichia and Candida. In addition, the unique variability in the size and profiles of the amplified product and in the restriction patterns enabled differentiation between the isolates. The assessment of fermentative performance of 4 yeast strains showed that K. marxianus strain BM4, K. marxianus strain BM9 and K. lactis strain P41 had higher ethanol productivity of 5.52, 4.92 and 5.05% w/v, XVIII respectively, from whey at pH 4.5 and 30oC while P. cactophila strain YB2 produced 1.40% w/v ethanol at 10% whey sugar and pH 4.5 at 30oC. It was concluded that molecular methods based on the sequences of the 26S rDNA D1D2 domain and the ITS region were rapid and precise compared with the physiological method for the identification and typing of these species, The yeast strains isolated also showed potential in whey to Bio-ethanol production.