Introduction

Bioethanol production from sugarcane was started in Brazil and the United States in the early 1970 (Classen et al. 1999). Feasibility of lignocellulosic materials for ethanol production has been explored around the world depending upon availability (Shindo and Tachibana 2006). At present, the fermentation of sugars to ethanol is the best established process for conversion of biomass to energy (Classen et al. 1999). Bioethanol is currently commercially produced from raw materials such as sugar cane, sugar beet or starch from cereals (Gable et al. 2005). The polysaccharides, cellulose and hemicellulose, are degraded slowly by enzymes as their structure is compact and stringent (Chandrakant and Bisaria, 1998). The cellulose cannot be enzymatically hydrolysed to glucose without physical and chemical pretreatment. High concentration of cellobiose and glucose inhibits the activity of cellulase enzymes and reduces the efficiency of the saccharification. One of the methods used to decrease this inhibition is to ferment the reduced sugars along their release (Gnansounou and Dauriat 2005). Simultaneous saccharification and fermentation (SSF) involves the enzymatic hydrolysis of cellulose to glucose and the conversion of fermentable sugars to ethanol in the same vessel (Eklund and Zacchi 1995).

SSF of lignocellulosics leading to the production of biofuels, animal feed, human food and chemicals is economical and should be practiced in developing countries (Sharma et al. 2006). Apple pomace is the residue left after juice extraction and constitutes about 25-35% of the weight of fresh fruit (Smock and Neubert 1956). It contains a large amount of water and sugar, a small amount of protein, and has a low pH. More than 500 food processing plants in the United States produce a total of about 1.3 million metric tons of apple pomace per years. Two main biologiocal fermentation processes could be applied to apple pomace for energy recovery: ethanol alcohol production and biogas generated via anaerobic digestion. Hang et al (1982) have documented the potential for ethanol production from fresh wet pomace and this represents a 20% of energy recovery from the total energy in pomace (Jewell and Cummings 1984). In the present study waste apple pomace left after juice extraction which is generally dumped is used as a substrate for ethanol production in solid state fermentation (SSF) system.

Materials and methods

Sample and microorganism

Ethanol production

Recovery and ethanol and analysis

Results and discussion

Waste apple pomace obtained from the fruit processing unit of HPMC contained 76% moisture and the same is maintained in the pomace before its fermentation. S. cerevisiae MTCC 173 (ethanol production), A. foetidus MTCC 117 (pectinase producer) and F. oxysporum MTCC 1755 (cellulose producer) were obtained from MTCC, Institute of Microbial Technology, Chandigarh, India and were maintained respectively on YEPD, Czapek yeast extract and Potato dextrose agar at pH 6.5 and 30oC (Fig. 1).

Figure 1

Figure 1: Plate culture of microorganisms used for solid state fermentation (SSF) of waste apple pomace a) b) c) and d) fermentation in synthetic medium and with apple pomace.

Temperature had a profound influence on the rate of alcoholic fermentation of waste apple pomace. Ethanol production was carried out at different temperature to verify the best temperature for ethanol production with waste apple pomace (Fig. 2). The result showed 30°C as best temperature for ethanol production as compared with 25°C and 40°C. Similar results were observed earlier by Hang et al (1982) with apple pomace with out juice extraction.

Figure 2

Preliminary studies have revealed that the apple pomace fermented by the yeast (S. cerevisiae) at 30°C for 4 days (Fig. 3) contained only a small amount of ethanol (3.43% v/w). It was thus necessary to inoculate the apple pomace with consortia of microorganisms to accelerate the fermentation process. After the inoculation of apple pomace with combination of A. foetidus and F. oxysporum (Fig. 4) and yeast (S. cerevisiae) plus A. foetidus and F. oxysporum (Fig. 5) the sugar present in the apple pomace is further released with simultaneous saccharification by A. foetidus (pectinase) and F. oxysporum (cellulase) and subsequent fermentation with S. cerevisiae and converted into ethanol. Simultaneous saccharification and fermentation involves the enzymatic hydrolysis of lignocellulose to glucose and the conversion of fermentable sugars to ethanol in the same vessel (Eklund and Zacchi, 1995).

Figure 3

Figure 4

Figure 5

The initial sugar concentration present in waste pomace after juice extraction was 3.21 % (w/w). During the fermentation process the sugar level decreased at different time intervals up to 96 h however the maximum ethanol production was observed at 72 h after this there was a decrease in ethanol production at 96 h of incubation in all combinations (Fig. 3-5). This could be due to inhibition of enzyme activity by high concentrations of cellobiose and glucose during saccharification. One of the method used to decrease this inhibition is to ferment the reduced sugar along their release (Gnansounou and Dauriat 2005 ).The amount of ethanol produced varied apparently dependent upon the initial amount of sugar concentration of the apple pomace fermented.

Conclusion

A solid state fermentation process has been reported for the production of ethanol from apple pomace using consortia of cultures viz., S. cerevisiae, A. foetidus and F. oxysporum. This process yielded as high as 16.09 % (v/w of apple pomace) ethanol from fermented apple pomace with a residual sugar of 0.15 % (w/w of apple pomace). The present study indicates that the alcoholic fermentation of apple pomace might be an efficient method for alleviating waste disposal with the concomitant production of ethanol. The economical potential of this solid state fermentation process remain to be assessed.