Abstract
This research aimed at the production of bioethanol from a cheap and renewable resource (spoilage dates) by nonconventional yeasts to reduce total cost of the production. Chemical, physical or biological pretreatment of the spoilage date juice (SDJ) did not affect the availability of fermentable sugars significantly. The isolated osmotolerant yeast strains: Pichia kudriavzevii KKUY-0034, Hanseniaspora opuntiae KKUY-0152 and H. uvarum KKUY-0078, which were genetically identified based on sequences of D1/D2 domain 26S rRNA gene and phylogenetic analysis, were tested for their fermentability of the SDJ. The fermentation conditions were adjusted to induce the maximum production of ethanol. Results showed that the highest quantities of ethanol were obtained when the yeasts were grown on 20% of date juice at 30 degrees C and when the pH was adjusted at 4-6 for 60 h. Addition of either Zn or Mg (0.4 g/L) and NH4H2PO4 (4 g/L) had a good impact on the ethanol productivity by the three species, however, H. uvarum KKUY-0078 was the leader that produced 60 g/L of ethanol. In 7-L fermentor, when the optimum conditions were kept constant, ethanol production reached to 80 g/L after 60 h. The study concludes that SDJ is a promising and costless substrate for production of the bioenergy and using the osomtolerant yeasts is an economic strategy. The partial 26S rRNA gene sequences of P. kudriavzevii KKUY-0034, H. uvarum KKUY-0078 and H. opuntiae KKUY-0152 were deposited in the DDBJ, EMBL, and GenBank database under the accession Nos. JQ690250, JQ690236 and KC110834, respectively. (C) 2017 Friends Science Publishers