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Effect of Substrate Concentration on Production of Ethanol from Corn Cob

Research Article ºÚÁÏÍø
Rahul Salve1, Vedprakesh Surve1, Girish Marotirao Machewad1* and Pravin Ghatge2
1Department of Food and Industrial Microbiology, College of Food Technology, Marathwada Krishi Vidyapeeth, Parbhani–431 402, India
2Department of Food Chemistry and Nutrition, College of Food Technology, Marathwada Krishi Vidyapeeth, Parbhani–431 402, India
*Corresponding authors: Girish Marotirao Machewad
Department of Food and Industrial Microbiology
College of Food Technology, Marathwada Krishi Vidyapeeth Parbhani–431402, India
Tel: +91-02452-234150
Fax: +91-02452-234150
Email: gmachewad@rediffmail.com
 
Received September 04, 2012; Published September 12, 2012
 
Citation: Salve R, Surve V, Machewad GM, Ghatge P (2012) Effect of Substrate Concentration on Production of Ethanol from Corn Cob 1: 289. doi:10.4172/scientificreports.289
 
Copyright:© 2012 Salve R, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
 
Abstract
 
The ethanol was produced from corn cob (CC) by using Saccharomyses cerevisiae (2%) (3090) strain. The chemical characteristics of CC (variety PMH-19) were found to contain significantly (P<0.05) higher amount of carbohydrate, fat, ash and hemicellulose than the CC (variety Surya) but less than that of sweet corn. The particle size (0.5 mm) was yielded significantly (P < 0.05) higher amount of ethanol. The particle size of corn cob was inversely proportion to the yield of ethanol. Further the substrate concentration (100 g), hydrolyzed (60 h) at constant enzyme concentration (20FPU), particle size (0.5 mm) and fermented (78 h) yielded higher amount of ethanol (24.79%) than the other substrate concentration. Finally it can be concluded that the maximum yield of ethanol in laboratory condition was obtained from the CC by using Saccharomyses cerevisiae and can be utilized as an alternative source of energy.
 
Keywords
 
Corn cob; Particle size; Acid hydrolysis; Enzyme hydrolysis; Ethanol
 
Introduction
 
Maize (Zea mays) is known as corn and contains high amount of carbohydrates, lipids and proteins. The corn cob (CC) is preferred over other agricultural by-products due to its composition which is easily converted to bioethanol [1]. A viable alternative of bio-fuel can be pursued by utilization of CC due to suitable lignocellulosic waste for bioethanol production with chemical pre-treatments [2]. The lignocellulosic bio mass comprises of cellulose, hemicellulose and lignin [3]. Now-a-day the demand of bioethanol has increased considerably because of its use as a gasohol in addition to the other application in industries which need production of alcohols on large scale [4]. The lignifications and crystallinity of cellulose is major barriers in the process of conversion of lignocellulosic biomass into bioethanol. Further it is essential to alter or remove structural and compositional impediments to hydrolyzed by pre-treatments to improve the rate of hydrolysis. Enzymatic methods have advantages to being eco-friendly besides applicable under mild condition of hydrolysis [5]. Recently the importance of alternative energy resource has become more necessary not only due to the continuous depletion of limited fossil fuel stock but also for the safe and better environment with inevitable depletion of the world energy supply there has been increasing worldwide interest in alternative sources of energy [6].
 
The cellulosic ethanol is chemically identical to ethanol from other sources such as corn starch or sugar but has been advantage of lignocelluloses raw material is abundant and diverse. However it differs in the requirement of greater amount of processing to make sugar monomer available to the microorganisms that are typically used to produce ethanol by fermentation [7]. Bioethanol is an attractive alternative fuel because of renewable bio-based resource and oxygenated thereby provides the potential to reduce particulate emission in compression ignition engines [8]. It has higher octane number, flame speeds, broader flammability limits and heat of vaporization than gasoline. These properties allow for a higher compression ratio, shorter burn times and linear burn engine which lead to theoretical efficiency advantages over gasoline in an internal combustion engine [4]. The most popular blend of ethanol for light duty vehicles is known as E85 and contains 85% bioethanol and 15% gasoline. In Brazil, bioethanol for fuel is derived from sugar cane and is used pure or blended with gasoline in a mixer called gasohol (24% bioethanol and 76% gasoline) [9]. Bioethanol production from the variety PMH- 19 of corn was taken 66 for investigation due to its surplus quantity. Further the particle size and substrate concentration for the production of bioethanol from the corn cob were standardized.
 
Materials and Methods
 
The corn cobs were procured from Sorghum Research Station, Marathwada Krishi Vidyapeeth, Parbhani, Maharashtra.
 
Preparation of corn cob
 
The corn cobs were sundried and ground to fine particle size in hammer mill (Milcet Mill, Ahmadabad, India). The powder of corn cob was sieved to obtain the particle size (0.5, 1.0 and 1.5 mm). The fine powder of corn cob was packed in polythene bags (250 gauge).
 
Microbial innoculum
 
The microbial culture (Saccharomyces cerevisiae 3090) was procured from National Chemical Laboratory, Pune, Maharashtra and subcultures were made on MGYP media to test its viability. Further the Saccharomyces cerevisiae (3090) stain was stored in the refrigerator until it is used.
 
Physical analysis
 
The ethanol content was determined by specific gravity bottle. The empty specific gravity bottle was weighed later filled the ethanol and again weighed. The same procedure was repeated by filling distilled water. The difference in weight was divided by the weight of an equal volume of distilled water to determine the specific gravity of ethanol.
 
Chemical analysis
 
The moisture, carbohydrate, protein, fat, ash, reducing sugar of corn cob were determined [10]. The cellulose and hemicellulose of the corn cob were determined [11]. The hydrolysis yield of reducing sugar was determined [12].
 
Acid hydrolysis
 
The concentrated 2.5N sulphuric acid was added in corn cob (100g). The hydrolysate was boiled at 90-950C for 4 h and centrifuged the slurry at 5000 rpm. The supernatant was collected for alkali hydrolysis at pH (6) with 2N NaOH for neutralization of acid. Finally reducing sugars dissolve in the hydrolysate was subjected to fermentation [13] (Figure 1).
 
Figure 1: Flow diagram for production of ethanol using acid hydrolysis
 
Enzyme hydrolysis
 
Pre-treatment: The ground sample of corn cob (0.5, 1.0 and 1.5 mm) was treated with 0.5N NaOH at the ration of 1:6. The mixture allowed standing 60-90 min at room temperature and atmospheric pressure. After definite period, the residues were free from traces of alkali and dried at 50-520C in hot air oven (Labtop, Thane, Maharashtra) and substrate was hydrolyzed by cellulase enzyme (Figure 2).
 
Figure 2: Flow diagram for production of ethanol using cellulase enzyme
 
Hydrolysis: The alkali treated dried corn cob was suspended in citrate buffer of pH 5. The enzyme cellulase (20 FPU) was added and hydrolysis was carried out at 520C in a shaking water bath (Labtop, Thane, Maharashtra) for the period (6-48 h). Finally reducing sugars were determined [11]. The hydrolysate was subjected to fermentation to produce ethanol [12].
 
Fermentation: The hydrolysate was fermented using Saccharomyces cerevisiae (3090) stain. The level of innoculum (2%) of hydrolysate was utilized [14]. The fermentation period was 78 h at ambient temperature. During fermentation free sugars were converted into ethanol [15].
 
Distillation: The supernatant was collected from fermentor flask and distillation (Rivera, Mumbai, Maharashtra) was carried out at temperature (80-820C) for the period (2 h).
 
Statistical Analysis: The data obtained during study were subjected to statistical analysis using complete randomized design [16].
 
Results and discussion
 
The chemical characteristics of corn cob (variety PMH-19) were found to contain significantly (P < 0.05) higher amount of carbohydrate, fat and hemicellulose than the corn cob (variety Surya) but less than that of sweet corn (Table 1). The protein content (2.10%) was highest in the corn cob (variety Surya) than other corn cob varieties. The carbohydrate make up of corn cob were revealed that highest cellulose (43.20%) and hemicellulose (37%) in sweet corn than other varieties [17]. The hydrolysis of corn cob was done by concentrated H2S04 (2.5N) to convert the polymers into simple sugars. The fermentation was done by Saccharomyses cerevisiae (2%) and pH (5) for 78 h to produce ethanol. The particle size (0.5 mm) was yielded significantly (P < 0.05) higher amount of ethanol (24.50%) (Table 2). The particle size of corn cob was inversely proportion to the yield of ethanol [18]. The acid hydrolysis (2.5N H2SO4) converted the complex polymer in to simple sugar and hydrolysed were fermented to produce ethanol. The particle size of the corn cob increased the reducing sugar and ethanol yield were found significantly (P<0.05) decreased along with non-significant decreased in specific gravity of ethanol [19,20].
 
Table 1: Chemical characteristics of corn cobs.
 
Table 2: Effect of particle size of corn cob on the yield of ethanol using acid
 
The hydrolysis of corn cob was done by using cellulase enzymes (20 FPU) for 6 h. Further the fermentation was done by Saccharomyses cerevisiae (2%) and pH (5) for 78 h (Table 3). The significant (P < 0.05) decrease in reducing sugar, hydrolysis yield, ethanol yield and specific gravity of ethanol were found with increase in particle size of corn cobs [12,21]. The particle size (0.5 mm) of the corn cob produced significantly higher amount of ethanol [22]. The substrate quantity (50, 100 and 150 g) on the enzymatic hydrolysis at fixed ratio (20FPU) of cellulase were investigated to produce higher ethanol yield (Table 4). The substrate quantity (100g) resulted in maximum amount of reducing sugar (43.50%), hydrolysis yield (56.33%) and ethanol yield (24.79%) respectively [23].
 
Table 3: Effect of particle size of corn cob on the production of ethanol by using enzyme
 
Table 4: Effect of substrate concentration on the yield of ethanol
 
Conclusions
 
The corn cob (variety PMH-19) can be better utilized for the production of ethanol. The significantly higher amount of ethanol was produced by acid hydrolysis of corn cob of particle size (0.5 mm), using Saccharomyses cerevisiae (2%) (3090) strain for fermentation period (78 h). The enzyme hydrolysis of CC using cellulase (20FPU), particle size (0.5 mm) hydrolysis period (60 h) and fermented (78 h) produced higher amount of ethanol. Further the substrate concentration (100 g), hydrolyzed (60 h) at constant enzyme concentration (20FPU), particle size (0.5 mm) and fermented (78 h) produced higher amount of ethanol. The maximum yield of ethanol in laboratory conditions was obtained from the CC by using Saccharomyses cerevisiae and can be utilized as an alternative source of energy.
 
 
References
 
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