Maximum Citric Acid Research Articles

Stimulation of citric acid production by heat shock promoting <i>Aspergillus niger</i> using nitrogen enriched <i>Dioscorea bulbifera</i>

High cost of substrate and how to stimulate citric acid are among the factors that mitigate citric acid production. Exploiting a cheap substrate for citric acid production will be a viable alternative in order to reduce the cost of citric acid production. Therefore, the aim of this research was to evaluate the potential of wild Dioscorea bulbifera tubers for citric acid production. Experimental procedures were designed to determine the effect of different concentrations of wild Dioscorea bulbifera, different nitrogen sources and effect of different concentrations of nitrogen sources on citric acid production. The data obtained were analyzed using one- way analysis of variance (ANOVA). The results of the experiment showed that wild Dioscorea bulbifera tuber was able to produce citric acid. The concentration of acid produced increased from 5 % to 20 % citric acid up to 8.5 ±1.0 g/lafter 96 hours of fermentation. Among the different nitrogen sources used to supplement wild Dioscorea bulbifera, the medium with ammonium nitrate produced the highest citric acid concentration of 10.5 ±1.5 g/l after 96 hours of fermentation. Meanwhile, when the concentration of the amonium nitrate were varied, 0.4 % was the optimum for the maximum citric acid concentration of 14.8 ±2.0 g/l after 96 hours of fermentation (P< 0.05). In conclusion, Dioscorea bulbifera tubers is suitable for citric acid production and supplementation of the medium with ammonium nitrate as a nitrogen source had a positive effect on the yield.

Assessing Waste Sunflower Oil as a Substrate for Citric Acid Production: The Inhibitory Effect of Triton X-100

In this study, waste sunflower oils were evaluated as substrates for citric acid (CA) production by Yarrowia lipolytica IFP29 (ATCC 20460). This strain was selected based on its capacity to produce organic acids in a selective medium. Attempts were made to optimize the process using the Taguchi statistical method in terms of the oil polarity, oil concentration, fermentation time, and Triton X-100 concentration. The results indicated that Y. lipolytica IFP29 utilized waste sunflower oil as a substrate and produced a maximum CA of 32.17 ± 1.44 g/L. Additionally, Triton X-100 inhibited the production of CA. For this reason, this process could not be optimized. These results were obtained by periodically adjusting the pH with NaOH during the fermentation period. On the other hand, a new experimental design was created without Triton X-100. As a buffering agent, 2-morpholinoethanesulfonic acid monohydrate (MES) was used to prevent a drop in pH; the maximum concentration of CA was found to be 20.31 ± 2.76. The optimum conditions were as follows: 90 g/L of waste sunflower oil with a polarity of 16 and 12 days of fermentation. According to the analysis of variance results, the effects of factors other than polarity on CA production were found to be significant (p < 0.05).

Improving dietary citric acid production by the wild-type Aspergillus niger ASP26 strain isolated from date by-product.

This research investigates citric acid (CA) synthesis using the indigenous strain Aspergillus niger ASP26, which was isolated from date by-products. The study initially involved isolating fungi capable of CA production and identifying the most potent strain based on its characteristic enzymatic activity. A. niger ASP26 was acknowledged in a previous study for its remarkable ability to produce extracellular enzymes, such as cellulase and amylase, which enable it to degrade organic materials effectively. After the identification phase, these isolates were screened for CA production using a modified Czapek-Dox medium. The research identified significant factors affecting CA production in submerged fermentation, including pH, carbon source, inoculum size, and fermentation time. Optimal conditions were determined for A. niger ASP26, resulting in a maximum CA yield of 16.89 g/L. These conditions included a 2.5% spore suspension at 2 × 107 spores/mL, an initial glucose concentration of 125 g/L, and incubation at 30°C for 144 h. Notably, A. niger ASP26 demonstrated the ability to produce CA under stress conditions as well. Citric acid is essential for various biological processes, such as cellular respiration, and is naturally present in citrus fruits. It also serves as a preservative and flavor enhancer in processed foods and beverages. The ability of A. niger ASP26 to produce CA from agricultural residues positions it as a viable candidate for sustainable CA production, harnessing the value from organic waste materials.

Costly effective bioleaching of valuable metals from low grade ore using Aspergillus nidulans

This research investigated the feasibility of employing organic acids, like citric acid, produced by Aspergillus nidulans MT355567 in a bioleaching process to recover uranium (U) from a low-grade rock sample. The optimal conditions for fungal growth and maximum citric acid (CA) synthesis across three distinct media were determined. The maximum citric acid concentration was produced on medium made from wheat bran (83%) and tea waste (77%). An investigation was carried out to see how citric acid and, by consequence, uranium bioleaching affinity, were affected by varying carbon sources, nitrogen sources, pH, temperature, incubation period, ore particle size, and the solid–liquid ratio. At 25 °C and a pH of 5.0, media containing 100 g/L of sucrose as a carbon source and peptone as a nitrogen source made the highest yield of citric acid and U bioleaching. Higher U bioleaching was achieved with ore particles 0.075 mm at a ratio of 2 g/L after only 30 min of contact with the fungal filtrate. Iron interference has a negative impact on uranium extraction. Interestingly, none of the conditions applied to enhance CA synthesis and U-bioleaching caused iron (Fe) dissolution. Based on these findings, it appears that bioleaching using A. nidulans MT355567 metabolic products is a promising economic and ecofriendly technology for extracting uranium from low-grade ore that might be adopted on a pilot scale.Graphical abstractsummarizing the experimental workflow for bioleaching of uranium from low-grade ore using citric acid produced by Aspergillus nidulans. The process involved optimizing A. nidulans growth and citric acid biosynthesis, evaluating factors influencing bioleaching activity of the acid metabolite solutions, and finally applying the optimized conditions to bioleach uranium from the ore sample. The schematic illustrates the key steps and the optimal condition for Aspergillus nidulans growth medium preparation using agricultural wastes, downstream application of metabolite synthesized for uranium bioleaching

Investigating the Usefulness of Wild Dioscorea esculenta (Wild Yam) Flour as Substrate for Citric Acid Biosynthesis

Background and Objective: The cost of substrate represents a significant percentage of the total biosynthesis cost of citric acid. There is need to continue searching for better and cheap underutilize starchy raw material for citric acid biosynthesis. Therefore, the objective of this research was to biologically synthesis citric acid in submerged fermentation of Aspergillus niger using wild Dioscorea esculenta (wild yam) tubers.
 Methodology: Submerged fermentation was conducted and the effect of Dioscorea esculenta concentrations, combined pretreatment and membrane permeability induction on citric acid biosynthesis were carried out.
 Results: Citric acid concentration increased as the concentration of the wild yam increased with maximum citric acid production of 10.5 ± 0.9 g/ l after 96 hours of fermentation. The overnight combined pretreatment with 0.3 % NaOH before pretreatment at 121oC for 20 minutes as one time combined pretreatment yielded 15. 0 ±1.2 g/l citric acid. Calcium chloride membrane induction produced 24.5 ± 1.3 g/l citric acid concentration respectively after 96 hours of fermentation.
 Conclusion: The result showed that wild Dioscorea esculenta tubers can be used as a substrate for the biosynthesis of citric acid. The biosynthesis of citric acid from Dioscorea esculenta tubers was enhanced by increased in concentration, combined pretreatment and membrane permeability induction.

Use of Pressurized and Airlift Bioreactors for Citric Acid Production by Yarrowia lipolytica from Crude Glycerol

Citric acid production is generally carried out in an aqueous medium in stirred tank reactors (STR), where the solubility of oxygen is low and the oxygen demand of microbial cultures is high. Thus, for this bioprocess, providing adequate oxygen mass transfer rate (OTR) from the gas phase into the aqueous culture medium is the main challenge of bioreactor selection and operation. In this study, citric acid production by Yarrowia lipolytica W29 from crude glycerol, in batch cultures, was performed in two non-conventional bioreactors normally associated with high mass transfer efficiency: a pressurized STR and an airlift bioreactor. Increased OTR was obtained by raising the total air pressure in the pressurized STR and by increasing the aeration rate in the airlift bioreactor. An improvement of 40% in maximum citric acid titer was obtained by raising the air pressure from 1 bar to 2 bar, whereas, in the airlift bioreactor, a 30% improvement was attained by increasing the aeration rate from 1 vvm to 1.5 vvm. Both bioreactor types can be successfully applied for the citric acid production process using alternative ways of improving OTR than increasing mechanical stirring power input, thus leading to important operating saving costs.

Optimisation of Rice Husks’ Lignocellulose Pre-Treatment Methods and Use of Central Composite Design in Citric Acid Fermentation: A Review

In today’s industry, about 80% to 90% of citric acid (C6H8O7) production is carried out using submerged fermentation method and Aspergillus niger as citric acid producing microorganism. The use of fermentation method provides advantages, including the utilization of agricultural waste as substrate. Rice husks can be used as substrate in citric acid fermentation because they contain high cellulose and hemicellulose. However, agricultural waste also contains lignin which can interfere with the hydrolysis of cellulose and hemicellulose into reducing sugars, therefore optimisation of pre-treatment process is needed to separate lignin in rice husk. In addition to the optimisation of pre-treatment process, optimisation of fermentation parameter variations to obtain maximum citric acid yield is necessary. Therefore, the aim of this narrative review is to desribe various pre-treatment methods that can be done to remove lignin from rice husks, and to provide information on the benefits of using the Central Composite Design method in the optimisation of various fermentation parameters.

Simultaneous saccharification and citric acid production from paper wastewater pretreated banana pseudostem: Optimization of fermentation medium formulation and kinetic assessment

This study optimized the simultaneous saccharification and citric acid (CA) production from banana pseudostem (BP). Thereafter, kinetic assessment of Aspergillus brasiliensis growth and CA production were determined for the optimum conditions using fresh water (SSFoptimizedFW) or dairy wastewater (SSFDWW) and compared to Sabouraud Dextrose Emmon’s medium modified with BP (SSFSDEmodified). The optimized conditions gave a CA concentration of 14.408 g/L. Kinetic assessment revealed the same maximum specific growth rates (μmax) (0.05 h−1) for all three bioprocesses, while the SSFSDEmodified process resulted in the highest maximum potential CA concentration (Pm) (13.991 g/L) in comparison to the SSFDWW (Pm = 13.095 g/L) and SSFoptimizedFW (Pm = 12.967 g/L) systems. Findings from this study facilitates the implementation of waste-based lignocellulosic bioprocesses that may eradicate the use of expensive pretreatment chemicals, fermentation medium constituents, and resources, in keeping with the water, energy and food nexus towards developing a circular bioeconomy.

Utilization of Pap processing waste in submerged culture of Aspergillus niger enriched with poultry dropping extract for citric acid production

Determining the potential of pap processing waste for citric acid production was investigated using Aspergillus niger isolated from pap waste. The cost of substrate for citric acid production represents a significant percentage of the total production cost. The aim of this work was therefore, to utilize pap processing waste in submerged culture enriched with poultry dropping extract for citric acid production. The effect of initial pH, inoculums size, poultry dropping extract, pap processing waste concentration and alcohol addition were investigated on citric acid production from pap processing waste. The results show that the initial pH, inoculums size, poultry dropping extract, pap processing waste and methanol had significant effect on citric acid production from pap processing waste (p< 0.05). Citric acid concentration increased as the pH increased. A pH value of 6.0 was the optimum for maximum citric acid concentration of 6.5 ± 0.116 g/l after 96 hours of fermentation. Citric acid concentration also increased as the percentage inoculums increased. A 10 % inoculums size was the optimum with the maximum concentration of 8.0 ± 0.231 g/l citric acid. There is also an increase in citric acid concentration as the percentage poultry dropping extract concentrations increased from 5 % to 15 %. A 15 % poultry dropping extract concentrations was the optimum with the maximum concentration of 11.0 ± 0.251 g/l citric acid. As the concentration of the pap processing waste increased up to 20 % the citric acid concentration of 16.0 ± 0.413 g/l was produced after 96 hours of fermentation. A 3 % methanol addition was the optimum with the maximum citric acid concentration of 26.0 ± 0.351 g/l after 96 hours of fermentation. This research work has established the potential of pap processing waste on citric acid production if well harnessed.

Production of Citric Acid by Aspergillus niger Cultivated in Olive Mill Wastewater Using a Two-Stage Packed Column Bioreactor

For building a sustainable fermentation process, it is essential to reduce dependence on natural resources and lower the amount of pollution that is created. The reuse of agro-industrial wastewater after possible treatment leads to the achievement of these goals concurrently. This study investigates the production of citric acid and the cellulase enzyme by A. niger cultivated in olive mill wastewater (OMW) using a loofa sponge-packed column bioreactor. The process was conducted under batch conditions using a single-stage packed bioreactor and under continuous operation using two-stage packed-column bioreactors. Citric acid and cellulase enzyme production were enhanced when the culture was supplied with cellulose. Employing loofa sponge slices for cell entrapment/immobilization improved the efficiency of the process. The maximum citric acid concentration achieved was 16 g/L with a yield (YCit.A/BOD) of 38.5% and a productivity of 2.5 g/L/day. When the process parameters were translated into continuous operation employing two loofa sponge-packed column bioreactors, citric acid production was improved significantly to 25 g/L in a steady-state period of 5 days at a production rate of 3.6 g/L/day and an allover yield (YCit.A/BOD) of 57.5%. Cellulases and reducing sugars were continuously supplied to the second-stage bioreactor by the first-stage bioreactor, which in turn enhanced fungal growth and citric acid production.

Evaluating the potential of wild cocoyam (Caladium bicolor) for citric acid production in a submerged culture of Aspergillus niger

BackgroundWild cocoyam (Caladium bicolar) is non-edible starchy material which is commonly known as ‘Ede umuagbara’ in the south-east region of Nigeria. Evaluating the potential of wild cocoyam for citric acid production was investigated using Aspergillus niger in a submerged culture.ResultsThis study showed that wild cocoyam flour concentration, pretreatment of wild cocoyam, inoculums size, initial pH of wild cocoyam and incubation temperature of wild cocoyam medium had significant effect on the amount of citric acid produced from wild cocoyam (p < 0.05). Citric acid concentration increased as the concentration wild cocoyam increased up to 15% with the maximum citric acid concentration of 10.0 ± 0.251 g/l after 96 h of fermentation. Also citric acid concentration increased as the pretreatment time of wild cocoyam increased from 5 to 20 min. A 20 min pretreatment time at 121 °C was the optimum with maximum concentration of 14.0 ± 0.325 g/l citric acid after 96 h of fermentation. 15% inoculums was the optimum with the maximum concentration of 16.0 ± 0.431 g/l citric acid. However, the wild cocoyam initial pH value of 5.5 was the optimum for maximum citric acid concentration of 19.0 ± 0.316 after 96 h of fermentation. Moreover, citric acid concentration increased as the incubation temperature of wild cocoyam medium increased from 20 to 30 °C. Incubation of wild cocoyam medium at 30 °C was the optimum with the maximum citric acid concentration of 23.0 ± 0.432 g/l after 96 h of fermentation.ConclusionTherefore, the result revealed that wild cocoyam which is found plenty within the south-east region of Nigeria can be converted to citric acid if well harnessed.

A Novel Endophytic Trichoderma longibrachiatum WKA55 With Biologically Active Metabolites for Promoting Germination and Reducing Mycotoxinogenic Fungi of Peanut.

Plant residuals comprise the natural habitat of the plant pathogen; therefore, attention is currently focusing on biological-based bioprocessing of biomass residuals into benefit substances. The current study focused on the biodegradation of peanut plant residual (PNR) into citric acid (CA) through a mathematical modeling strategy. Novel endophytic Trichoderma longibrachiatum WKA55 (GenBank accession number: MZ014020.1), having lytic (cellulase, protease, and polygalacturonase) activity, and tricalcium phosphate (TCP) solubilization ability were isolated from peanut seeds and used during the fermentation process. As reported by HPLC, the maximum CA (5505.1 μg/g PNR) was obtained after 9 days in the presence of 15.49 mg TCP, and 15.68 mg glucose. GC–MS analysis showed other bioactive metabolites in the filtrate of the fermented PNR. Practically, the crude product (40%) fully inhibited (100%) the growth and spore germination of three mycotoxinogenic fungi. On peanuts, it improved the seed germination (91%), seedling features, and vigor index (70.45%) with a reduction of abnormal seedlings (9.33%). The current study presents the fundamentals for large-scale production in the industry for the sustainable development of PNR biomass as a natural source of bioactive metabolites, and safe consumption of lignocellulosic-proteinaceous biomass, as well. T. longibrachiatum WKA55 was also introduced as a novel CA producer specified on PNR. Application of the resulting metabolite is encouraged on a large scale.

Chemical route for synthesis of citric acid from orange and grape juices

Citrus fruits contain sufficient citric acid, which is the main tricarboxylic acid. The properties of citric acid make it an important additive in various process industries. This experimental study aims to produce citric acid from orange and grape juices. The chemical route for the synthesis of citric acid from citrus juices involves three steps: (i) neutralization to adjust pH (9-11) with a 2.8 M NaOH solution, (ii) addition of CaCl2 solution (40.3-41.1% w/v), and (iii) acidification with an H2SO4 solution (1.5-2.3 M) to produce citric acid. In this study, the fruits were peeled, crushed, filtered, neutralized, added CaCl2 solution, and acidified to obtain citric acid. The experiments were carried out by varying the final pH of the solution and the concentrations of CaCl2 and H2SO4 solutions, maintaining the total volume constant. A maximum citric acid yield of 91.1% and 79.8% were achieved from orange and grapefruits, respectively, at the optimum final pH of the solution and the concentrations of CaCl2 and H2SO4 solutions at 10, 40.7% w/v, and 1.9 M, respectively. Finally, the purified citric acid crystals were characterized using FTIR and XRD. Thus, it could be concluded that orange fruit would be a promising source for citric acid production than grape.

Biological production of citric acid in submerged culture of Aspergillus niger using cassava pulp wastes

Utilization of cassava pulp wastes for citric acid production was investigated using Aspergillus niger in a submerged culture. A series of experiments were designed on various fermentation parameters to establish the optimal conditions for citric acid production from cassava pulp. This study revealed that production parameters such as cassava pulp concentration, initial pH, incubation temperature, agitation, and nitrogen source and fermentation period had effect on the amount of citric acid produced from cassava pulp. Citric acid concentration increased as the concentration of cassava pulp increases up to 20% with maximum citric acid concentration of 14.9 ± 0.413 g/l after 120 hours of fermentation. pH 5.5 was the optimum with maximum citric acid concentration of 16.8 ± 0.23 g/l after 120 hours of fermentation. Incubation temperature at 300 C was the optimum, with citric acid concentration of 19.15 ± 0.43 g/l. Increased in agitation speed from 100 to 225 rpm gave the maximum citric acid concentration of 25.2 ± 0.32 g/l after 120 hours of fermentation. Soybean meal supplementation was the best maximum citric acid concentration of 28.2 ± 0.51 g/l. Evaluating the effect of different concentration of soybean meal shows that 0.3 % supplementation was the optimum with maximum concentration of 31.2 ±0.35g/l from cassava pulp after 120 hours of fermentation. The result suggested that citric acid can be accumulated using cassava pulp by Aspergillus niger in submerged culture during fermentation. Cassava pulp if well harnessed can be used for large scale citric acid production.

Palm dates as a source for isolation of Aspergillus niger to produce citric acid by submerged fermentation; kinetics study

The study discussed here deals with the isolation of Aspergillus niger from palm dates, the formal and the most famous fruit in Iraq, to test and qualify this fungus isolate for its ability to produce citric acid. Submerged fermentation technique was used in the fermentation process. A.niger isolated from “Zahdi” Palme dates was used in the study of the fermentation kinetics to get the production efficiency of citric acid. Kinetics of CA production via fermentation by A. niger S11 was evaluated within 432 h fermentation time and under submerged conditions of 11% (w/v) sucrose, 5% (v/v) inoculum size, pH 4, 30 °C and 150 rpm. The maximum citric acid produced was (37.116 g/l). Kinetic criterions (product, exhaustion and growth rates “Cp/t, Cs/t, Cx/t”, yield coefficients “Yp/s, Yp/x, Yx/s”, and specific fermentation rate constants “qp, qs”) were studied and discussed to reach to a logical explanation of fermentation process.

HPLC based characterization of citric acid produced from indigenous fungal strain through single and Co-Culture fermentation

Agro-based waste materials are primarily composed of complex polysaccharides that strengthen microbial growth to produce industrially relevant value-added products. Therefore, in the present study, solid state fermentation (SSF) was carried out using peanut shell, orange peel and mixture of both with 50:50 ratio as support for SSF to enhance citric acid production from single and co-culture consortia of Rhizopus stolonifera and Aspergillus niger. During initial trial, it was observed that growth media supplemented with orange peel under solid state fermentation (SSF) process of co-culture consortia revealed high yield (1593 μg/mL) of citric acid. On partial optimization of co-culture showed the maximum citric acid yields (7651 μg/mL) in the presence of orange peel base medium at 50% moisture content, 30 °C temperature, 5.5 pH and 25 g substrate concentration after 48th hours of solid-state fermentation. This amount of citric acid produced in the culture was estimated through reversed-phase High Performance Liquid Chromatography (HPLC) technique. Recent research activity revealed that a suitable addition of fermentative substrate to the solid-state fermentation media increased fungal growth, sugar utilization and citric acid production when used in lower concentration.

A biotechnological process for obtaining citric acid through paper cellulose aerobic bioreaction

AbstractThe purpose of this study was to develop a biotechnological process to produce citric acid using paper residues from Urban Solid Waste (USW), like raw material. The selected microorganism to transform degraded cellulose from paper to produce citric acid was Aspergillus niger. The aerobic bioreaction was carried out in a heterogeneous bioreactor. The efficiency of the biotransformation in this study was measured under different operating conditions: 2 and 3 pH levels, 30 and 40 °C temperatures, and high and low concentrations of trace elements: Copper (Cu), Manganese (Mn) and Zinc (Zn). In optimized operation conditions from 20 g of waste paper the maximum citric acid amount obtained was 5.73 g l−1.

Comparison of three culture media for one-step and two-step bioleaching of nickel and cadmium from spent Ni-Cd batteries by Aspergillus niger

Among the biological processes, bioleaching is the most widely employed method for metal extraction from electronic waste (e-waste). The purpose of this research was to evaluate the ability of one-step and two-step bioleaching under different culture media for nickel (Ni) and cadmium (Cd) removed from spent Ni-Cd batteries by the fungus Aspergillus niger. In this result, the concentrations of Ni and Cd in battery scraps from e-waste recycling shops were respectively 578.13 ± 7.02 mg Ni g-1 and 128.35 ± 11.42 mg Cd g-1. During the bioleaching process, both heavy metal removals were higher in Richards’s Broth (RB) followed by the Potato Dextrose Broth (PDB) and Malt Extract Broth (MEB), respectively. The maximum citric acid production (96.99±3.05 mM) and lower pH values were obtained in the RB medium. The bioleaching experiment showed that the recovery for the two-step leaching method was higher than the one-step bioleaching method. Following an incubation period of 21 days between the spent Ni-Cd batteries and RB medium, the two-step bioleaching experiment suggested that the citric acid products of A. niger were the best leaching agent for Ni and Cd bioleaching.

Optimization of Citric Acid Production by Immobilized Cells of Novel Yeast Isolates

Citric acid is a commercially valuable organic acid widely used in food, pharmaceutical, and beverage industries. In this study, 260 yeast strains were isolated from soil, bread, juices, and fruits wastes and preliminarily screened using bromocresol green agar plates for their ability to produce organic acids. Overall, 251 yeast isolates showed positive results, with yellow halos surrounding the colonies. Citric acid production by 20 promising isolates was evaluated using both free and immobilized cell techniques. Results showed that citric acid production by immobilized cells (30–40 g/L) was greater than that of freely suspended cells (8–19 g/L). Of the 20 isolates, two (KKU-L42 and KKU-L53) were selected for further analysis based on their citric acid production levels. Immobilized KKU-L42 cells had a higher citric acid production rate (62.5%), while immobilized KKU-L53 cells showed an ∼52.2% increase in citric acid production compared with free cells. The two isolates were accurately identified by amplification and sequence analysis of the 26S rRNA gene D1/D2 domain, with GenBank-based sequence comparison confirming that isolates KKU-L42 and KKU-L53 were Candida tropicalis and Pichia kluyveri, respectively. Several factors, including fermentation period, pH, temperature, and carbon and nitrogen source, were optimized for enhanced production of citric acid by both isolates. Maximum production was achieved at fermentation period of 5 days at pH 5.0 with glucose as a carbon source by both isolates. The optimum incubation temperature for citric acid production by C. tropicalis was 32 °C, with NH4Cl the best nitrogen source, while maximum citric acid by P. kluyveri was observed at 27 °C with (NH4)2 SO4 as the nitrogen source. Citric acid production was maintained for about four repeated batches over a period of 20 days. Our results suggest that apple and banana wastes are potential sources of novel yeast strains; C. tropicalis and P. kluyveri which could be used for commercial citric acid production.

Valorization of Banana Peel for Citric Acid Production under Solid State Fermentation with Aspergillus niger

Valorization of banana peel (BP) through solid state fermentation (SSF) was aimed&lt;br /&gt; in this research. The appropriate conditions of citric acid (CA) production by SSF of&lt;br /&gt; Aspergillus niger were investigated. Firstly, the optimum initial pH of the BP and the&lt;br /&gt; aeration rate were studied by conducting SSF in a 250-mL flask and 2-L glass column,&lt;br /&gt; respectively. It was found that the initial pH of the BP and aeration rates affected the CA&lt;br /&gt; production. The results showed that the initial pH of 5.0 and 1.0 vvm aeration were appropriate for the CA production of A. niger using BP as a substrate. The problem of rising temperature during SSF was found when applying the optimum condition to the SSF&lt;br /&gt; in the 20-L packed bed bioreactor (PBB), which caused a decrease in the CA production&lt;br /&gt; compared to that of the glass column. The cooling air jacket constructed to the PBB to&lt;br /&gt; remove the heat during the SSF helped increase the CA production from that in the PBB.&lt;br /&gt; The maximum CA production in the 20-L air-jacketed PBB was 124.0±19.2 mg g–1DS.