Single-step ethanol production from raw cassava starch using a combination of raw starch hydrolysis and fermentation, scale-up from 5-L laboratory and 200-L pilot plant to 3000-L industrial fermenters

Challenges and prospects of microbial α-amylases for industrial application: a review

α-Amylases are essential biocatalysts representing a billion-dollar market with significant long-term global demand. They have varied applications ranging from detergent, textile, and food sectors such as bakery to, more recently, biofuel industries. Microbial α-amylases have distinct advantages over their plant and animal counterparts owing to generally good activities and better stability at temperature and pH extremes. With the scope of applications expanding, the need for new and improved α-amylases is ever-growing. However, scaling up microbial α-amylase technology from the laboratory to industry for practical applications is impeded by several issues, ranging from mass transfer limitations, low enzyme yields, and energy-intensive product recovery that adds to high production costs. This review highlights the major challenges and prospects for the production of microbial α-amylases, considering the various avenues of industrial bioprocessing such as culture-independent approaches, nutrient optimization, bioreactor operations with design improvements, and product down-streaming approaches towards developing efficient α-amylases with high activity and recyclability. Since the sequence and structure of the enzyme play a crucial role in modulating its functional properties, we have also tried to analyze the structural composition of microbial α-amylase as a guide to its thermodynamic properties to identify the areas that can be targeted for enhancing the catalytic activity and thermostability of the enzyme through varied immobilization or selective enzyme engineering approaches. Also, the utilization of inexpensive and renewable substrates for enzyme production to isolate α-amylases with non-conventional applications has been briefly discussed.

Production and characterization of intracellular invertase from Saccharomyces cerevisiae (OL629078.1), using cassava-soybean as a cost-effective substrate

The growing global market for industrial enzymes has led to a constant search for efficient, cost-effective methods for their production. This study reports the production of invertase using inexpensive and readily available agro-materials. Starch-digesting enzymes extracted from malted unkilned sorghum were used to hydrolyze cassava starch supplemented with 2% whole soybean. The production of intracellular invertase by Saccharomyces cerevisiae OL629078.1 in cassava-soybean and yeast sucrose broth was compared. The purification and characterization of invertase produced using the low-cost medium were also reported. The results showed that there was a 4.1-fold increase in the units of invertase produced in cassava-soybean medium (318.605 U/mg) compared to yeast sucrose broth medium (77.6 U/mg). The invertase produced was purified by chromatographic methods up to 5.53-fold with a recovery of 62.6%. Estimation of the molecular weight with gel filtration indicated a molecular weight of 118 kDa. The enzyme demonstrated its maximum activity at 50 °C and there was no decrease in its activity following a 1-h incubation at this temperature. At a pH of 5.0, the enzyme demonstrated optimal activity and it maintained over 60% of its activity in the acid range (pH 3-6). The Michalis-Menten constants Km and Vmax of intracellular invertase were 5.85 ± 1.715 mM and 6.472 ± 2.099 U/mg, respectively. These results suggest that Saccharomyces cerevisiae grown on cassava-soybean is a viable, cost-effective alternative for commercial invertase production, which can be explored for biotechnological processes.

Pilot-scale bioethanol production from the starch of avocado seeds using a combination of dilute acid-based hydrolysis and alcoholic fermentation by Saccharomyces cerevisiae

BACKGROUND

A processing methodology of raw starch extraction from avocado seeds (ASs) and a sequential hydrolysis and fermentation bioprocess in just a few steps was successfully obtained for the bioethanol production by a single yeast Saccharomyces cerevisiae strain and this research was also to investigate the optimum conditions for the pretreatment of biomass and technical procedures for the production of bioethanol. It successfully resulted in high yields and productivity of all the experiments from the laboratory scale and the pilot plant. Ethanol yields from pretreated starch are comparable with those in commercial industries that use molasses and hydrolyzed starch as raw materials.

RESULTS

Before the pilot-scale bioethanol production, studies of starch extraction and dilute sulfuric acid-based pretreatment was carefully conducted. The amount of starch extracted from dry and fresh avocado seed was 16.85 g ± 0.34 g and 29.79 ± 3.18 g of dry starch, representing a yield of ∼17% and 30%, respectively. After a dilute sulfuric acid pretreatment of starch, the released reducing sugars (RRS) were obtained and the hydrolysate slurries containing glucose (109.79 ± 1.14 g/L), xylose (0.99 ± 0.06 g/L), and arabinose (0.38 ± 0.01 g/L). The efficiency of total sugar conversion was 73.40%, with a productivity of 9.26 g/L/h. The ethanol fermentation in a 125 mL flask fermenter showed that Saccharomyces cerevisiae (Fali, active dry yeast) produced the maximum ethanol concentration, p_max at 49.05 g/L (6.22% v/v) with a yield coefficient, Y_p/s of 0.44 g_Ethanol/g_Glucose, a productivity or production rate, r_p at 2.01 g/L/h and an efficiency, Ef of 85.37%. The pilot scale experiments of the ethanol fermentation using the 40-L fermenter were also successfully achieved with essentially good results. The values of p_max,Y_p/s, r_p, and Ef of the 40-L scale were at 50.94 g/L (6.46% v/v), 0.45 g_Ethanol/g_Glucose, 2.11 g/L/h, and 88.74%, respectively. Because of using raw starch, major by-products, i.e., acetic acid in the two scales were very low, in ranges of 0.88-2.45 g/L, and lactic acid was not produced, which are less than those values in the industries.

CONCLUSIONS

The sequential hydrolysis and fermentation process of two scales for ethanol production using the combination of hydrolysis by utilizing dilute sulfuric acid-based pretreatment and fermentation by a single yeast Saccharomyces cerevisiae strain is practicable and feasible for realistic and effective scale-up strategies of bioethanol production from the starch of avocado seeds.

High-Gravity Fermentation for Bioethanol Production from Industrial Spent Black Cherry Brine Supplemented with Whey

By-products from different industries could represent an available source of carbon and nitrogen which could be used for bioethanol production using conventional Saccharomyces cerevisiae yeast. Spent cherry brine and whey are acid food by-products which have a high organic matter content and toxic compounds, and their discharges represent significant environmental and economic challenges. In this study, different combinations of urea, yeast concentrations, and whey as a nutrient source were tested for bioethanol production scale-up using 96-well microplates as well as 7.5 L to 100 L bioreactors. For bioethanol production in vials, the addition of urea allowed increasing the bioethanol yield by about 10%. Bioethanol production in the 7.5 L and 100 L bioreactors was 73.2 g·L−1 and 103.5 g·L−1 with a sugar consumption of 81.5% and 94.8%, respectively, using spent cherry brine diluted into whey (200 g·L−1 of total sugars) supplemented with 0.5 g·L−1 urea and 0.5 g·L−1 yeast at 30 °C and a pH of 5.0 after 96 h of fermentation for both systems. The results allow these by-products to be considered low-economic-value alternatives for fuel- or food-grade bioethanol production.

Optimized Spectrophotometry Method for Starch Quantification

Starch is a polysaccharide that is abundantly found in nature and is generally used as an energy source and energy storage in many biological and environmental processes. Naturally, starch tends to be in miniscule amounts, creating a necessity for quantitative analysis of starch in low-concentration samples. Existing studies that are based on the spectrophotometric detection of starch using the colorful amylose–iodine complex lack a detailed description of the analytical procedure and important parameters. In the present study, this spectrophotometry method was optimized, tested, and applied to studying starch content of atmospheric bioaerosols such as pollen, fungi, bacteria, and algae, whose chemical composition is not well known. Different experimental parameters, including pH, iodine solution concentrations, and starch solution stability, were tested, and method detection limit (MDL) and limit of quantification (LOQ) were determined at 590 nm. It was found that the highest spectrophotometry signal for the same starch concentration occurs at pH 6.0, with an iodine reagent concentration of 0.2%. The MDL was determined to be 0.22 μg/mL, with an LOQ of 0.79 μg/mL. This optimized method was successfully tested on bioaerosols and can be used to determine starch content in low-concentration samples. Starch content in bioaerosols ranged from 0.45 ± 0.05 (in bacteria) to 4.3 ± 0.06 μg/mg (in fungi).

A review on the conversion of cassava wastes into value-added products towards a sustainable environment

The solid and liquid wastes generated from cassava-based industries are organic and acidic in nature, which leads to various global concerns-primarily global warming and biodiversity loss. But the conversion of these wastes into value-added products associated with environmental pollution control contributes to sustainable development. Generally, the thermochemical process such as pyrolysis and gasification and biochemical processes such as anaerobic digestion have been applied for the conversion of cassava waste into value-added products. This review addresses the valorization of cassava wastes, which fulfill almost all needs of the hour, such as energy (biofuel), wastewater treatment (adsorbents), bioplastics, starch nanoparticles, organic acid production, and antimicrobial agents. The major aim of this paper is to analyze and provide the disclosure of the efficiency of cassava-based industrial waste as a source to minimize the problem associated with conventional fossil fuels and through which mitigate the impact of global warming and climate change. Furthermore, recent research and achievements in the valorization of cassava waste have been highlighted.

Efficient biosynthesis of exopolysaccharide in Candida glabrata by a fed-batch culture

Polysaccharides are important natural biomacromolecules. In particular, microbial exopolysaccharides have received much attention. They are produced by a variety of microorganisms, and they are widely used in the food, pharmaceutical, and chemical industries. The Candida glabrata mutant 4-C10, which has the capacity to produce exopolysaccharide, was previously obtained by random mutagenesis. In this study we aimed to further enhance exopolysaccharide production by systemic fermentation optimization. By single factor optimization and orthogonal design optimization in shaking flasks, an optimal fermentation medium composition was obtained. By optimizing agitation speed, aeration rate, and fed-batch fermentation mode, 118.6 g L⁻¹ of exopolysaccharide was obtained by a constant rate feeding fermentation mode, with a glucose yield of 0.62 g g⁻¹ and a productivity of 1.24 g L⁻¹ h⁻¹. Scaling up the established fermentation mode to a 15-L fermenter led to an exopolysaccharide yield of 113.8 g L⁻¹, with a glucose yield of 0.60 g g⁻¹ and a productivity of 1.29 g L⁻¹ h⁻¹.

Optimization of Yeast, Sugar and Nutrient Concentrations for High Ethanol Production Rate Using Industrial Sugar Beet Molasses and Response Surface Methodology

Among the various agro-industrial by-products, sugar beet molasses produced by sugar refineries appear as a potential feedstock for ethanol production through yeast fermentation. A response surface methodology (RSM) was developed to better understand the effect of three process parameters (concentration of nutrient, yeast and initial sugar) on the ethanol productivity using diluted sugar beet molasses and Saccharomyces cerevisiae yeast. The first set of experiments performed at lab-scale indicated that the addition of 4 g/L of nutrient combined with a minimum of 0.2 g/L of yeast as well as a sugar concentration lower than 225 g/L was required to achieve high ethanol productivities (>15 g/L/d). The optimization allowed to considerably reduce the amount of yeast initially introduced in the fermentation substrate while still maximizing both ethanol productivity and yield process responses. Finally, scale-up assays were carried out in 7.5 and 100 L bioreactors using the optimal conditions: 150 g/L of initial sugar concentration, 0.27 g/L of yeast and 4 g/L of nutrient. Within 48 h of incubation, up to 65 g/L of ethanol were produced for both scales, corresponding to an average ethanol yield and sugar utilization rate of 82% and 85%, respectively. The results obtained in this study highlight the use of sugar beet molasses as a low-cost food residue for the sustainable production of bioethanol.