Optimization of fermentation parameters for production of ethanol from kinnow waste and banana peels by simultaneous saccharification and fermentation

Bioethanol Production Optimization from KOH-Pretreated Bombax ceiba Using Saccharomyces cerevisiae through Response Surface Methodology

The present study was based on the production of bioethanol from alkali-pretreated seed pods of Bombax ceiba. Pretreatment is necessary to properly utilize seed pods for bioethanol production via fermentation. This process assures the accessibility of cellulase to the cellulose found in seedpods by removing lignin. Untreated, KOH-pretreated, and KOH-steam-pretreated substrates were characterized for morphological, thermal, and chemical changes by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Hydrolysis of biomass was performed using both commercial and indigenous cellulase. Two different fermentation approaches were used, i.e., separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). Findings of the study show that the maximum saccharification (58.6% after 24 h) and highest ethanol titer (57.34 g/L after 96 h) were observed in the KOH-steam-treated substrate in SSF. This SSF using the KOH-steam-treated substrate was further optimized for physical and nutritional parameters by one factor at a time (OFAT) and central composite design (CCD). The optimum fermentation parameters for maximum ethanol production (72.0 g/L) were 0.25 g/L yeast extract, 0.1 g/L K2HPO4, 0.25 g/L (NH4)2SO4, 0.09 g/L MgSO4, 8% substrate, 40 IU/g commercial cellulase, 1% Saccharomyces cerevisiae inoculum, and pH 5.

Fatty acid ethyl ester from Manilkara zapota seed oil: a completely renewable biofuel for sustainable development

This article reports the deliverables of the experimental study on the production of a completely renewable biofuel from Manilkara zapota fruit and seed oil. It was attempted to synthesis ethyl ester from Manilkara zapota seed oil using bioethanol synthesized from decayed Manilkara zapota fruit. Bioethanol was produced through fermentation of decayed Manilkara zapota fruit, waste skin, and pulp with Saccharomyces cerevisiae and then distilled at 72°C. The bioethanol yield was noted as 10.45% (v/w). The 95.09% pure bioethanol and 4.9% water molecules were present in the distilled sample. Mechanically extracted raw Manilkara zapota seed oil was used for ethyl ester conversion. The molar ratio of bioethanol to oil, the quantity of KOH, and process temperature were investigated for the maximum yield of Manilkara zapota ethyl ester. A 9:1 molar ratio of bioethanol to oil, 1.5% (w/w) KOH, and 70°C process temperature were identified as enhanced ethanolysis process parameters. The maximum yield of ethyl ester was identified as 93.1%. Physicochemical characteristics of Manilkara zapota oil, bioethanol, and ethyl ester were measured as per the corresponding ASTM standards. It was found that both Manilkara Zapota ethyl ester and bioethanol synthesized from decayed Manilkara zapota fruit could be promising substitutes for fossil diesel and gasoline.

Enzymatic processing of Citrus reticulata (Kinnow) pomace using naringinase and its valorization through preparation of nutritionally enriched pasta

Citrus fruits are consumed either as whole fruits or as juice after processing. Processing of fruits yields a significant number of by-products in the form of pulp, peel and seeds, which are often discarded and major cause of environmental concern. Bitterness in the waste residue of citrus products is one of the leading hindrance in its valorization and supplementation in other food products. Aim of this study was to reduce the bitterness of Citrus reticulata (kinnow) pomace using enzymatic method and its supplementation in production of nutritionally rich pasta. Under optimized conditions (1U/mg enzyme naringinase concentration, temperature 50 °C, at pH 4.5 and treatment time 4 h), the maximum reduction (65.95%) of naringin (bitterness causing compound) was observed coupled with increase (60.13%) in naringenin (non-bitter compound). The debittered kinnow pomace has been further characterized for physio-chemical changes and morphological changes before and after treatment. The debittered kinnow pomace was then supplemented for the preparation of antioxidant and nutrient enriched pasta.

Comparative study of various processes used for removal of bitterness from kinnow pomace and kinnow pulp residue

The current study was focused on new approaches for debittering of by-products like kinnow pomace and kinnow pulp residue by using various food grade mild chemical methods, such as alkali treatment, acid treatment, and solventogenesis. Whereas in the studied various chemical treatments, the solventogenesis method with acetone resulted in maximum extraction of naringin and limonene from kinnow pomace and pulp residue and showed high acceptability for food product development. The acetone treatment was further optimized by RSM for the maximum extraction of naringin and limonene. Under optimized conditions, the maximum amount of naringin and limonene extracted were found to be 8.955, 2.122 mg/g from kinnow pomace and 9.971, 3.838 mg/g from pulp residue, respectively. This process can not only result in the effective utilization of agro-industrial by-product but also provide a sustainable solution to the environmental pollution caused by kinnow juice industry.

Production and purification of laccase by Bacillus sp. using millet husks and its pesticide degradation application

Lignocellulosic agricultural bi-products, pearl millet (PM) and finger millet (FM) husks, were used for the production of laccase using Bacillus sp. PS under solid-state fermentation (SSF). Abiotic variables such as substrate (PM, FM) concentration (1-5%), incubation time (24-96 h) and pH (5-10) were optimized using Response surface methodology (RSM) to maximize the laccase production. The predicted model showed maximum laccase activity of 402 U/mL appearing after 96 h of incubation with PM 2.0 g/L and FM 1.5 g/L at pH 7.0. Single protein band on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) confirmed homogeneity of the laccase with a molecular weight of 63-75 kDa. The partially purified laccase effectively degraded the pesticides (Tricel, 71.8 ± 3.5 and Phoskill 77.3 ± 3.4%) within 5 days of incubation (40 °C) in pH 7.0. The pesticide degradation was further confirmed by high-performance liquid chromatography (HPLC) and the chromatograms showed the single dominant peaks at retention time 2.482 (tricel) and 2.608 (phoskill) min, respectively. Pesticide-degrading laccase was produced by Bacillus sp. PS under SSF reveals the utilization of low-cost bi-substrates for enhanced laccase production.

An overview of the recent trends on the waste valorization techniques for food wastes

A critical and up-to-date review has been conducted on the latest individual valorization technologies aimed at the generation of value-added by-products from food wastes in the form of bio-fuels, bio-materials, value added components and bio-based adsorbents. The aim is to examine the associated advantages and drawbacks of each technique separately along with the assessment of process parameters affecting the efficiency of the generation of the bio-based products. Challenges faced during the processing of the wastes to each of the bio-products have been explained and future scopes stated. Among the many hurdles encountered in the successful and high yield generation of the bio-products is the complexity and variability in the composition of the food wastes along with the high inherent moisture content. Also, individual technologies have their own process configurations and operating parameters which may affect the yield and composition of the desired end product. All these require extensive study of the composition of the food wastes followed by their effective pre-treatments, judicial selection of the technological parameters and finally optimization of not only the process configurations but also in relation to the input food waste material. Attempt has also been made to address the hurdles faced during the implementation of such technologies on an industrial scale.

Value additon of kinnow industry byproducts for the preparation of fiber enriched extruded products

In the present study dietary fiber enriched vermicelli from wheat flour supplemented with debittered kinnow industry by-products (pulp residue and pomace) has been developed. Functional, cooking and textural properties of both supplemented and unsupplemented vermicelli were evaluated. Vermicelli containing 15% debittered kinnow pulp residue and pomace showed minimum cooking loss (18.5, 20.0%) but higher swelling index (2.06, 1.87), water absorption capacity (153, 202 g/100 g) and optimal cooking time (9.34, 9.02 min). Firmness and fracturability of vermicelli supplemented debittered pulp residue (10.0 and 21.5) and pomace (16.7 and 16.1) was higher as compared to control sample (6.1 and 2.1) respectively. Further, redness, firmness, TPC, DPPH activity and water absorption capacity of vermicelli got increased with addition of debittered kinnow pulp and pomace. The utilization of debittered kinnow pulp and pomace in vermicelli can provide dual benefit like production of healthy food products along with solving the problem of solid waste disposal of kinnow industry byproducts.

Evaluación de la producción de Etanol por dos cepas recombinantes y una comercial de <i>Saccharomyces cerevisae</i> (Fungi: Ascomycota) en melaza de caña de azúcar de y mostos de banano de rechazo de Urabá, Colombia

La producción de bioetanol a partir de Saccharomyces cerevisiae (Fungi: Ascomycota) está influenciada por la concentración de azúcares y el sustrato de fermentación. Por ello, en este trabajo se evaluaron las cinéticas de producción de biomasa, azúcares residuales y producción de etanol de cuatro cepas de S. cerevisiae en dos medios de fermentación (melaza de caña de azúcar y banano de rechazo) a dos concentraciones de azúcares (100 y 170 g/l). Las cepas Ethanol Red® y GG570-CIBII presentaron mayor producción de etanol con pico de producción de 119,74 (35 h) y 62 g/l (15 h), Yps 0,75 y 0,43 g/g y Qp 3,42 y 2,61 g/l/h, respectivamente a 170 g/l de azúcares en melaza de caña de azúcar. Adicionalmente, la cepa GG570-CIBII mostró un incremento de 37,1 g/l de etanol con respecto a la cepa control.

Evaluación de la producción de etanol por dos cepas recombinantes y una comercial de <i>Saccharomyces cerevisiae</i> (Fungi: Ascomycota) en melaza de caña de azúcar y mostos de banano de rechazo de Urabá (Antioquia), Colombia

La producción de bioetanol a partir de Saccharomyces cerevisiae (Fungi: Ascomycota) está influenciada por la concentración de azúcares y el sustrato de fermentación. Por ello en este trabajo se evaluaron las cinéticas de producción de biomasa, azúcares residuales y producción de etanol de cuatro cepas de S. cerevisiae en dos medios de fermentación (melaza de caña de azúcar y banano de rechazo) a dos concentraciones de azúcares (100 y 170 g/l). Las cepas EthanolRed® y GG570-CIBII presentaron mayor producción de etanol con pico de producción de 119,74 (35 h) y 62 g/l (15 h), Yps 0,75 y 0,43 g/g y, Qp 3,42 y 2,61 g/l/h, respectivamente a 170 g/l de azúcares en melaza de caña de azúcar. Adicionalmente, la cepa GG570-CIBII mostró un incremento de 37,1 g/l de etanol con respecto a la cepa control.

Comparison of physicochemical pretreatments of banana peels for bioethanol production

Pretreatments with different concentrations of sulfuric acid (0, 0.5, and 1% v/v) and temperatures (28 and 121 °C at 103 kPa in an autoclave) were performed on banana peels (BP) milled by mechanical grinding and grinding in a blender as well as without grinding. Cellulose, hemicellulose, lignin, ash, and total and reducing sugar contents were evaluated. The highest yields of cellulose enzymatic hydrolysis (99%) were achieved with liquefied autoclaved BP treated with 0.5 and 1% acid after 48 h of hydrolysis. Ethanol production by Kluyveromyces marxianus fermentation was assayed using hydrolyzed BP at 10, 15, and 20% (w/w). The highest ethanol level (21 g/L) was reached after 24 h of fermentation with 20% (w/w) BP. Kinetics of the consumption of reducing sugars under this fermentation condition demonstrates the presence of a lag period (about 8 h). Thus, BP are a good source for ethanol production.

High temperature alcoholic fermentation of orange peel by the newly isolated thermotolerant Pichia kudriavzevii KVMP10

This work explores the potential for the development of orange peel based ethanol bioprocesses through isolation of the thermotolerant Pichia kudriavzevii KVMP10. A model solution of hydrolysed Valencia orange peel was employed to determine the ethanologenic potential of the yeast, which was maximized at 42°C producing 54 g l(-1) of ethanol. The effect of orange peel oil on bioethanol formation was investigated at 30 and 42°C confirming that the minimum inhibitory peel oil content was 0·01% (v/v). Pichia kudriavzevii KVMP10 demonstrated significant technological advantages for the production of sustainable bioenergy, such as utilization of both hexoses (glucose, sucrose, fructose and galactose) and pentoses (xylose) at high temperatures, exemplifying its great potential for application in orange peel based biorefineries for ethanol production.

SIGNIFICANCE AND IMPACT OF THE STUDY

Citrus peel waste is one of the most underutilized and geographically diverse residues in the planet. In attempt to develop a citrus peel based biorefinery we report here the isolation of a yeast which exhibited favourable technological characteristics for the production of ethanol through utilization of the specific food waste. Pichia kudriavzevii KVMP10 was highly thermotolerant and utilized both hexoses and pentoses for ethanol production, which was achieved at elevated rates, highlighting its great potential for application in ethanol production processes from citrus peel.

Enhanced ethanol production from pomelo peel waste by integrated hydrothermal treatment, multienzyme formulation, and fed-batch operation

Pomelo peel is an abundant pectin-rich biomass waste in China and has the potential to serve as a source of fuels and chemicals. This study reports a promising way to deal with pomelo peel waste and to utilize it as raw material for ethanol production via simultaneous saccharification and fermentation (SSF). An integrated strategy, incorporating hydrothermal treatment, multienzyme formulation, and fed-batch operation, was further developed to enhance the ethanol production. The results show that hydrothermal treatment (120 °C, 15 min) could significantly reduce the use of cellulase (from 7 to 3.8 FPU g(-1)) and pectinase (from 20 to 10 U g(-1)). A multienzyme complex, which consists of cellulase, pectinase, β-glucosidase, and xylanase, was also proven to be effective to improve the hydrolysis of pretreated pomelo peel, leading to higher concentrations of fermentative sugars (36 vs 14 g L(-1)) and galacturonic acid (23 vs 9 g L(-1)) than those with the use of a single enzyme. Furthermore, to increase the final ethanol concentration, fed-batch operation by adding fresh substrate was employed in the SSF process. A final solid loading of 25% (w/v), which is achieved by adding 15% fresh substrate to the SSF system at an initial solid loading of 10%, produced 36 g L(-1) ethanol product in good yield (73.5%). The ethanol concentration is about 1.73-fold that at the maximum solid loading of 14% for batch operation, whereas both of them have a closed ethanol yield. The results indicate that the use of the fed-batch mode could alleviate the decrease in ethanol yield at high solid loading, which is caused by significant mass transfer limitation and increased inhibition of toxic compounds in the SSF process. The integrated strategy demonstrated in this work could open a new avenue for dealing with pectin-rich biomass wastes and utilization of the wastes to produce ethanol.

Biorefinery of instant noodle waste to biofuels

Instant noodle waste, one of the main residues of the modern food industry, was employed as feedstock to convert to valuable biofuels. After isolation of used oil from the instant noodle waste surface, the starch residue was converted to bioethanol by Saccharomyces cerevisiae K35 with simultaneous saccharification and fermentation (SSF). The maximum ethanol concentration and productivity was 61.1g/l and 1.7 g/lh, respectively. After the optimization of fermentation, ethanol conversion rate of 96.8% was achieved within 36 h. The extracted oil was utilized as feedstock for high quality biodiesel conversion with typical chemical catalysts (KOH and H2SO4). The optimum conversion conditions for these two catalysts were estimated; and the highest biodiesel conversion rates were achieved 98.5% and 97.8%, within 2 and 3h, respectively. The high conversion rates of both bioethanol and biodiesel demonstrate that novel substrate instant noodle waste can be an attractive biorefinery feedstock in the biofuels industry.

Pretreatment of banana agricultural waste for bio-ethanol production: individual and interactive effects of acid and alkali pretreatments with autoclaving, microwave heating and ultrasonication

Banana agricultural waste is one of the potential lignocellulosic substrates which are mostly un-utilized but sufficiently available in many parts of the world. In the present study, suitability of banana waste for biofuel production with respect to pretreatment and reducing sugar yield was assessed. The effectiveness of both acid and alkali pretreatments along with autoclaving, microwave heating and ultrasonication on different morphological parts of banana (BMPs) was studied. The data were statistically analyzed using ANOVA and numerical point prediction tool of MINITAB RELEASE 14. Accordingly, the optimum cumulative conditions for maximum recovery of reducing sugar through acid pretreatment are: leaf (LF) as the substrate with 25 min of reaction time and 180°C of reaction temperature using microwave. Whereas, the optimum conditions for alkaline pretreatments are: pith (PH) as the substrate with 51 min of reaction time and 50°C of reaction temperature using ultrasonication (US).

Scale up and efficient bioethanol production involving recombinant cellulase (Glycoside hydrolase family 5) from Clostridium thermocellum

Background

Lignocellulose degrading fungal enzymes have been in use at industrial level for more than three decades. However, the main drawback is the high cost of the commercially available Trichoderma reesei cellulolytic enzymes.

Results

The hydrolytic performance of a novel Clostridium thermocellum cellulolytic recombinant cellulase expressed in Escherichia coli cells was compared with the naturally isolated cellulases in different modes of fermentation trials using steam explosion pretreated thatch grass and Zymomonas mobilis. Fourier transform infrared (FT-IR) spectroscopic analysis confirmed the efficiency of steam explosion pretreatment in significant release of free glucose moiety from complex lignocellulosic thatch grass. The recombinant GH5 cellulase with 1% (w v-1) substrate and Z. mobilis in shake flask separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) trials demonstrated highest ethanol titre (0.99 g L-1, 1.2 g L-1) as compared to Bacillus subtilis (0.51 g L-1, 0.72 g L-1) and Trichoderma reesei (0.67 g L-1, 0.94 g L-1). A 5% (w v-1) substrate with recombinant enzyme in shake flask SSF resulted in a 7 fold increment of ethanol titre (8.8 g L-1). The subsequent scale up in a 2 L bioreactor with 1 L working volume yielded 16.13 g L-1 ethanol titre implying a 2 fold upturn. The rotary evaporator based product recovery from bioreactor contributed 94.4 (%, v v-1) pure ethanol with purification process efficiency of 22.2%.

Conclusions

The saccharification of steam exploded thatch grass (Hyparrhenia rufa) by recombinant cellulase (GH5) along with Z. mobilis in bioethanol production was studied for the first time. The effective pretreatment released substantial hexose sugars from cellulose as confirmed by FT-IR studies. In contrast to two modes of fermentation, SSF processes utilizing recombinant C. thermocellum enzymes have the capability of yielding a value-added product, bioethanol with the curtailment of the production costs in industry.

Lignocellulosic fermentation of wild grass employing recombinant hydrolytic enzymes and fermentative microbes with effective bioethanol recovery

Simultaneous saccharification and fermentation (SSF) studies of steam exploded and alkali pretreated different leafy biomass were accomplished by recombinant Clostridium thermocellum hydrolytic enzymes and fermentative microbes for bioethanol production. The recombinant C. thermocellum GH5 cellulase and GH43 hemicellulase genes expressed in Escherichia coli cells were grown in repetitive batch mode, with the aim of enhancing the cell biomass production and enzyme activity. In batch mode, the cell biomass (A_600 nm) of E. coli cells and enzyme activities of GH5 cellulase and GH43 hemicellulase were 1.4 and 1.6 with 2.8 and 2.2 U·mg⁻¹, which were augmented to 2.8 and 2.9 with 5.6 and 3.8 U·mg⁻¹ in repetitive batch mode, respectively. Steam exploded wild grass (Achnatherum hymenoides) provided the best ethanol titres as compared to other biomasses. Mixed enzyme (GH5 cellulase, GH43 hemicellulase) mixed culture (Saccharomyces cerevisiae, Candida shehatae) system gave 2-fold higher ethanol titre than single enzyme (GH5 cellulase) single culture (Saccharomyces cerevisiae) system employing 1% (w/v) pretreated substrate. 5% (w/v) substrate gave 11.2 g·L⁻¹ of ethanol at shake flask level which on scaling up to 2 L bioreactor resulted in 23 g·L⁻¹ ethanol. 91.6% (v/v) ethanol was recovered by rotary evaporator with 21.2% purification efficiency.

Microencapsulation of Banana Juice from Three Different Cultivars

In order to effectively process and utilize surplus bananas and those without the quality for export, in this research it is proposed to microencapsulate the banana juice by means of spray drying and using maltodextrin as the covering material. Three cultivars Enano gigante (Musa AAA, subgroup Cavendish), and the tetraploids hybrids (AAAA), FHIA-17 and FHIA-23 were selected for this research. Being Enano gigante, the cultivar shows the highest glass transition temperature. The drying parameters were established, depending upon the ratio of juice/maltodextrin and the drying air temperature. The optimal drying air temperature was 220°C for the three cultivars with a 20% juice/maltodextrin ratio for both the Enano Gigante and the FHIA-23, while in the FHIA-17 there were no significant differences between the juice/maltodextrin ratios. The morphology and size distribution of the microcapsules were observed by a scanning electron microscopy. The number of particles is directly proportional to the temperature and inversely proportional to the juice/maltodextrin ratio. A Weibull particle size distribution was common to all treatments. There is a correlation between the principal components and clustering analyses with the optimization of the system. The principal components analysis considers three Weibull parameters (obtained from the particle size distribution) and the powders moisture percentage.

Design and optimization of ethanol production from bagasse pith hydrolysate by a thermotolerant yeast Kluyveromyces sp. IIPE453 using response surface methodology

Ethanol production from sugarcane bagasse pith hydrolysate by thermotolerant yeast Kluyveromyces sp. IIPE453 was analyzed using response surface methodology. Variables such as Substrate Concentration, pH, fermentation time and Na2HPO4 concentration were found to influence ethanol production significantly. In a batch fermentation, optimization of key process variables resulted in maximum ethanol concentration of 17.44 g/L which was 88% of the theoretical with specific productivity of 0.36 g/L/h.

An economic and ecological perspective of ethanol production from renewable agro waste: a review

Agro-industrial wastes are generated during the industrial processing of agricultural products. These wastes are generated in large amounts throughout the year, and are the most abundant renewable resources on earth. Due to the large availability and composition rich in compounds that could be used in other processes, there is a great interest on the reuse of these wastes, both from economical and environmental view points. The economic aspect is based on the fact that such wastes may be used as low-cost raw materials for the production of other value-added compounds, with the expectancy of reducing the production costs. The environmental concern is because most of the agro-industrial wastes contain phenolic compounds and/or other compounds of toxic potential; which may cause deterioration of the environment when the waste is discharged to the nature. Although the production of bioethanol offers many benefits, more research is needed in the aspects like feedstock preparation, fermentation technology modification, etc., to make bioethanol more economically viable.

Bioconversion of Agricultural Waste to Ethanol by SSF Using Recombinant Cellulase from Clostridium thermocellum

The effect of different pretreatment methods, temperature, and enzyme concentration on ethanol production from 8 lignocellulosic agrowaste by simultaneous saccharification and fermentation (SSF) using recombinant cellulase and Saccharomyces cerevisiae were studied. Recombinant cellulase was isolated from E. coli BL21 cells transformed with CtLic26A-Cel5-CBM11 full-length gene from Clostridium thermocellum and produced in both batch and fed-batch processes. The maximum cell OD and specific activity in batch mode were 1.6 and 1.91 U/mg, respectively, whereas in the fed-batch mode, maximum cell OD and specific activity were 3.8 and 3.5 U/mg, respectively, displaying a 2-fold increase. Eight substrates, Syzygium cumini (jamun), Azadirachta indica (neem), Saracens indica (asoka), bambusa dendrocalmus (bamboo), Populas nigra (poplar), Achnatherum hymenoides (wild grass), Eucalyptus marginata (eucalyptus), and Mangifera indica (mango), were subjected to SSF. Of three pretreatments, acid, alkali, and steam explosion, acid pretreatment Syzygium cumini (Jamun) at 30°C gave maximum ethanol yield of 1.42 g/L.

Ethanol production from banana peels using statistically optimized simultaneous saccharification and fermentation process

Dried and ground banana peel biomass (BP) after hydrothermal sterilization pretreatment was used for ethanol production using simultaneous saccharification and fermentation (SSF). Central composite design (CCD) was used to optimize concentrations of cellulase and pectinase, temperature and time for ethanol production from BP using SSF. Analysis of variance showed a high coefficient of determination (R(2)) value of 0.92 for ethanol production. On the basis of model graphs and numerical optimization, the validation was done in a laboratory batch fermenter with cellulase, pectinase, temperature and time of nine cellulase filter paper unit/gram cellulose (FPU/g-cellulose), 72 international units/gram pectin (IU/g-pectin), 37 °C and 15 h, respectively. The experiment using optimized parameters in batch fermenter not only resulted in higher ethanol concentration than the one predicted by the model equation, but also saved fermentation time. This study demonstrated that both hydrothermal pretreatment and SSF could be successfully carried out in a single vessel, and use of optimized process parameters helped achieve significant ethanol productivity, indicating commercial potential for the process. To the best of our knowledge, ethanol concentration and ethanol productivity of 28.2 g/l and 2.3 g/l/h, respectively from banana peels have not been reported to date.

Cost-effective approach to ethanol production and optimization by response surface methodology

Food wastes disposed from residential and industrial kitchens have gained attention as a substrate in microbial fermentations to reduce product costs. In this study, the potential of simultaneously hydrolyzing and subsequently fermenting the mixed carbohydrate components of kitchen wastes were assessed and the effects of solid load, inoculum volume of baker's yeast, and fermentation time on ethanol production were evaluated by response surface methodology (RSM). The enzymatic hydrolysis process was complete within 6h. Fermentation experiments were conducted at pH 4.5, a temperature of 30°C, and agitated at 150 rpm without adding the traditional fermentation nutrients. The statistical analysis of the model developed by RSM suggested that linear effects of solid load, inoculum volume, and fermentation time and the quadratic effects of inoculum volume and fermentation time were significant (P<0.05). The verification experiments indicated that the developed model could be successfully used to predict ethanol concentration at >90% accuracy. An optimum ethanol concentration of 32.2g/l giving a yield of 0.40g/g, comparable to yields reported to date, was suggested by the model with 20% solid load, 8.9% inoculum volume, and 58.8h of fermentation. The results indicated that the production costs can be lowered to a large extent by using kitchen wastes having multiple carbohydrate components and eliminating the use of traditional fermentation nutrients from the recipe.

Enhanced ethanol production from Kinnow mandarin (Citrus reticulata) waste via a statistically optimized simultaneous saccharification and fermentation process

Dried, ground, and hydrothermally pretreated Kinnow mandarin (Citrus reticulata) waste was used to produce ethanol via simultaneous saccharification and fermentation (SSF). Central composite design was used to optimize cellulase and pectinase concentrations, temperature, and time for SSF. The D-limonene concentration determined with high-performance liquid chromatography (HPLC) for fresh, dried, and pretreated biomass was 0.76%, 0.32%, and 0.09% (v/w), respectively. Design Expert software suggested that the first-order effect of all four factors and the second-order effect of cellulase and pectinase concentrations were significant for ethanol production. The validation experiment using 6 FPU gds(-1) cellulase and 60 IU gds(-1) pectinase at 37 °C for 12 h in a laboratory batch fermenter resulted in ethanol concentration and productivity of 42 g L(-1) and 3.50 g L(-1) h(-1), respectively. Experiments using optimized parameters resulted in an ethanol concentration similar to that predicted by the model equation and also helped reduce fermentation time.

Ethanol production from orange peels: two-stage hydrolysis and fermentation studies using optimized parameters through experimental design

Orange peels were evaluated as a fermentation feedstock, and process conditions for enhanced ethanol production were determined. Primary hydrolysis of orange peel powder (OPP) was carried out at acid concentrations from 0 to 1.0% (w/v) at 121 degrees C and 15 psi for 15 min. High-performance liquid chromatography analysis of sugars and inhibitory compounds showed a higher production of hydroxymethyfurfural and acetic acid and a decrease in sugar concentration when the acid level was beyond 0.5% (w/v). Secondary hydrolysis of pretreated biomass obtained from primary hydrolysis was carried out at 0.5% (w/v) acid. Response surface methodology using three factors and a two-level central composite design was employed to optimize the effect of pH, temperature, and fermentation time on ethanol production from OPP hydrolysate at the shake flask level. On the basis of results obtained from the optimization experiment and numerical optimization software, a validation study was carried out in a 2 L batch fermenter at pH 5.4 and a temperature of 34 degrees C for 15 h. The hydrolysate obtained from primary and secondary hydrolysis processes was fermented separately employing parameters optimized through RSM. Ethanol yields of 0.25 g/g on a biomass basis (YP/X) and 0.46 g/g on a substrate-consumed basis (YP/S) and a promising volumetric ethanol productivity of 3.37 g/L/h were attained using this process at the fermenter level, which shows promise for further scale-up studies.