90
R. Abdulla et al.
Incubation duration affects the acid hydrolysis significantly as the duration influences the availability of free glucose that is fermentable. In this study, the concentration of extracted glucose was found to be maximum for incubation duration of
30 min. At time above 30 min, the concentration of glucose reduced. The decrease in
glucose yield with increased incubation longer than 30 min is supported by the study
conducted by Chen et al. (2012). In their study, 30 min was proven to be the optimum
incubation time for acid hydrolysis of algal biomass. Besides, the obtained result is
in agreement with Harun and Danquah (2011b). They reported that pretreating the
microalgae cells for a duration longer than 30 min resulted in lower sugar yield and
thus lower bioethanol production.
Similar incubation duration was proven to be optimal as reported by earlier studies.
Sarkar and Aikat (2013) reported that 30 min was the optimum duration for acid
hydrolysis when they were working with rice straw. In their study, the maximum
sugar yield of 19.35 g/L was obtained when the rice straw waste was pretreated with
0.24 mol/l sulphuric acid for 30 min. Apart from that, Saucedo-Luna et al. (2010)
reported that acid hydrolysis of the bagasse of Agave tequilana Weber had their
maximum yield of 15.0 g/l fermentable sugars for the duration of 30 min. Most of
the related studies stated that higher incubation duration might result in a reduction
of sugar yield. Higher duration tends to prolong the acid hydrolysis process and
under the condition of high temperature and high sulphuric acid concentration, this
will enhance the production of furfural, HMF and organic acids. Hence, a lower
concentration of extracted glucose or sugar will be obtained (Saucedo-Luna et al.
2010; Talukder et al. 2012; Wang et al. 2014).
Despite the studies highlighted above, some studies had reported very different
ranges of the optimum incubation period. Markou et al. (2013) reported that the
maximum reducing sugars yield was achieved after the incubation period of 30 h
when they were working with cyanobacteria Arthrospira platensis. Other than that,
Laopaiboon et al. (2009) suggested the incubation period of hours for acid hydrolysis when they were working with sugarcane bagasse. The incubation period for acid
hydrolysis is believed to be correlated to the temperature and sulphuric acid concentration. If relatively high acid concentration and high temperature are used in the
acid hydrolysis, shorter duration is preferred to prevent the formation of inhibitors.
4 Yeast Inoculum for Fermentation
Yeast inoculum was prepared by dissolving 1.0 g of dry Saccharomyces cerevisiae
powder in 20 ml of warm water at room temperature. The solution was left for 30 min
with shaking and stirring uniformly to suspend the yeast cells (Harun et al. 2010).
The yeast cells were inoculated on Yeast Extract–Peptone–Dextrose (YPD) agar
plates using streaking method for single colony isolation purpose. The agar plates
were incubated at 30 °C for 24 h. After incubation, the yeast colony was aseptically
transferred from the YPD agar plate into 100 ml of sterilized YPD medium containing
R. Abdulla et al.
Incubation duration affects the acid hydrolysis significantly as the duration influences the availability of free glucose that is fermentable. In this study, the concentration of extracted glucose was found to be maximum for incubation duration of
30 min. At time above 30 min, the concentration of glucose reduced. The decrease in
glucose yield with increased incubation longer than 30 min is supported by the study
conducted by Chen et al. (2012). In their study, 30 min was proven to be the optimum
incubation time for acid hydrolysis of algal biomass. Besides, the obtained result is
in agreement with Harun and Danquah (2011b). They reported that pretreating the
microalgae cells for a duration longer than 30 min resulted in lower sugar yield and
thus lower bioethanol production.
Similar incubation duration was proven to be optimal as reported by earlier studies.
Sarkar and Aikat (2013) reported that 30 min was the optimum duration for acid
hydrolysis when they were working with rice straw. In their study, the maximum
sugar yield of 19.35 g/L was obtained when the rice straw waste was pretreated with
0.24 mol/l sulphuric acid for 30 min. Apart from that, Saucedo-Luna et al. (2010)
reported that acid hydrolysis of the bagasse of Agave tequilana Weber had their
maximum yield of 15.0 g/l fermentable sugars for the duration of 30 min. Most of
the related studies stated that higher incubation duration might result in a reduction
of sugar yield. Higher duration tends to prolong the acid hydrolysis process and
under the condition of high temperature and high sulphuric acid concentration, this
will enhance the production of furfural, HMF and organic acids. Hence, a lower
concentration of extracted glucose or sugar will be obtained (Saucedo-Luna et al.
2010; Talukder et al. 2012; Wang et al. 2014).
Despite the studies highlighted above, some studies had reported very different
ranges of the optimum incubation period. Markou et al. (2013) reported that the
maximum reducing sugars yield was achieved after the incubation period of 30 h
when they were working with cyanobacteria Arthrospira platensis. Other than that,
Laopaiboon et al. (2009) suggested the incubation period of hours for acid hydrolysis when they were working with sugarcane bagasse. The incubation period for acid
hydrolysis is believed to be correlated to the temperature and sulphuric acid concentration. If relatively high acid concentration and high temperature are used in the
acid hydrolysis, shorter duration is preferred to prevent the formation of inhibitors.
4 Yeast Inoculum for Fermentation
Yeast inoculum was prepared by dissolving 1.0 g of dry Saccharomyces cerevisiae
powder in 20 ml of warm water at room temperature. The solution was left for 30 min
with shaking and stirring uniformly to suspend the yeast cells (Harun et al. 2010).
The yeast cells were inoculated on Yeast Extract–Peptone–Dextrose (YPD) agar
plates using streaking method for single colony isolation purpose. The agar plates
were incubated at 30 °C for 24 h. After incubation, the yeast colony was aseptically
transferred from the YPD agar plate into 100 ml of sterilized YPD medium containing