Durbha et al.

sp., Neocallimastix sp., Trichoderma reesei and Fusarium oxysporum (Xu et al.,

2009); and C. phytofermentans has the ability use more number of carbohydrates

(Cantarel et al., 2009) and the feasibility of it’s industrial use is under study

(Christian et al., 2010). However, bacteria produce less ethanol in large-scale

fermentation, by-products, susceptible to high ethanol concentrations, can only

grow at narrow and neutral pH range of 6.0 to 8.0 (Bothast et al., 1999) and are

prone to more viral infections (Jones et al., 2000). Zymomonas mobilis isolate

can only ferment glucose, fructose and sucrose. On the other hand, genetically

engineered S. cerevisiae can consume more xylose than genetically engineered

bacteria (Lau et al., 2010).

Commercialethanolproductionwithengineeredmicroorganismshasnotsucceeded

so far (Laluce et al., 2012). Among these, S. cerevisiae is the most preferred

organism for industrial ethanol production. Therefore, though yeasts were isolated

from number of sources, still search for new yeasts or S. cerevisiae strains is on

involving various carbon sources of ethanol production such as fruit juices (low

glucose), starch (high initial glucose and high ethanol), lignocelluloses (multiple

sugars). Moreover, high initial sugar level is vital to get more ethanol accumulation

and to reduce production costs (Gírio et al., 2010). Therefore, industrial strains

should possess characters such as high tolerance towards carbohydrate, ethanol

and salt, be able to produce ethanol from various sugars, good yield and so on. Two

newly isolated strains (RPDPMP and R3DSC5) of S. cerevisiae were subjected to

experiments involving the effect of inoculum density, glucose concentration, initial

pH and temperature on their ethanol producing efficiencies and to determine the

optimum conditions for maximizing ethanol yields from these strains.

materials and methods

All the chemicals were purchased from Merck and Sigma. The two S. cerevisiae

strains, RPDPMP and R3DSC5, were isolated from palm juice and sugar cane

juice and identified in our laboratory.

Standard graphs

Determination of cell number using optical density was carried out following

American Brewer’s Guild http://www.abgbrew.com/pdf/haemocytometer.pdf)

protocol and that of reducing sugar by dinitrosalicylate (DNS) method (Miller,

1959). Cell density was determined by measuring turbidity of small amount of the

sample at 600 nm in a spectrophotometer. Three independent replications were

used for each experiment.

Optimization

Inoculum of palm juice strain was developed on yeast extract peptone and dextrose

(YEPD) medium (Leao and van Uden, 1982) slants. Three production flasks

72

Int. J. Bioinformatics and Biological Sci.: v.2 n.1&2, p. 71-83. March & June 2014