Abstract
The aim of this work was to research a bioprocess for bioethanol production at laboratory scale from raw sweet potato using Saccharomyces cerevisiae MTCC-170. In order to obtain maximum conversion of starch into fermentable sugar, optimum parameters for the liquefaction were determined as 104 to 105°C, 0.15% v/w of α-amylase enzyme solution (300 U/ml) and 30 g dry-weight sweet potato mash/100 ml distilled water, respectively with a 74.38% loss in dry weight during the process. For saccharification process, the optimum dose of amyloglucosidase was 0.25% v/w (300 U/ml) with 16.82% glucose production at pH 5.0 and temperature 60°C after 1 h. The fermentation parameters like inoculum size, temperature, pH and different concentrations of nutrients were also determined. The maximum ethanol concentration, that is, 7.95% (v/v) was obtained with 10% inoculum size at pH 6.0 after 48 h. Furthermore, out of the three nitrogen sources (yeast extract, peptone and ammonium sulphate) tested for ethanol production, peptone at a concentration of 1.5 g/L was found to be best (7.93%). From the present study, it may be concluded that sweet potato can be an attractive feedstock for bioethanol production from both the economic stand points and environment friendly. Key words: Sweet potato starch, ethanol, liquefaction, saccharification, Saccharomyces cerevisiae MTCC-170.
Highlights
Petroleum is the source of about 170 quads of energy out of the total of more than 460 quads used by the world which is far more than derived from other sources (IPCC, 2007)
According to the results in terms of liquefaction, the process conducted at 105°C using 30 g flour of sweet potato and 0.10% v/w α-amylase for 1 h was found to be the most suitable, considering higher liquefaction yield, and when saccharified with glucoamylase (20.5 GA U/g starch) at 60°C for 2 h the maximum amount of fermentable sugar was released from sweet potato flour that is, 16.84 g/100 ml
Experimental conditions were tested for liquefaction and saccharification, revealing the higher performance of α-amylase and amyloglucosidase
Summary
Petroleum is the source of about 170 quads of energy out of the total of more than 460 quads used by the world which is far more than derived from other sources (IPCC, 2007). Industrial sweet potatoes are not intended for use as a food crop They are bred to increase its starch content, significantly reducing its attractiveness as a food crop when compared to other conventional food cultivars (visual aspect, color, taste etc.). They offer potentially greater fermentable sugar yields from a sweet potato crop for industrial conversion processes. It has been reported that some industrial sweet potatoes breeding lines developed could produce ethanol yields of 4500 to 6500 L/ha compared to 2800 to 3800 L/ha for corn (Duvernay et al, 2013; Ziska et al, 2009). Sweet potato has several agronomic characteristics that determine its wide adaptation to marginal lands such as drought resistant, high multiplication rate and low degeneration of the propagation material, short grow cycle, low illness incidence and plagues, cover the soil rapidly and protect it from the erosive rains and controlling the weed problem (Cao et al, 2011; Duvernay et al, 2013)
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