• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.2
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• pp.89-94
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• 2002

The continuous production of citric acid from dairy wastewater was investigated using calcium-alginate immobilized Asrergillus niger ATCC 9142. The citric acid productivity and yield were strongly affected by the culture conditions. The optimal pH, temperature, and dilution rate were 3.0, 30$^{\circ}C$, and 0.025 h$\^$-1/, respectively. Under optimal culture conditions, the maximum productivity, concentration, and yield of citric acid produced by the calcium-alginate immobilized Aspergillus niger were 160 mg L$\^$-1/ h$\^$-1/, 4.5 g/L, and 70.3%, respectively, The culture was continuously perfored for 20 days without any apparent loss in citric acid productivity. Conversely, under the same conditions with a batch shake-flask culture, the maximum productivity, citric acid concentration, and yield were only 63.3 mg L$\^$-1/h$\^$-1/, 4.7 g/L and 51.4%, respectively, Therefore, the results suggest that the bioreactor used in this study could be potentially used for continuous citric acid production from dairy wastewater by applying calcium-alginate immobilized Aspergillus niger.

• Journal of the Korean Society of Food Science and Nutrition
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• v.27 no.2
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• pp.201-206
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• 1998

The antibrowning effcts of cysteine, citric acid and ascorbic acid on the browning reaction of enzymatic garlic hydrolyzate were investigated at 37$^{\circ}C$ for 12 days. Cysteine was the most effective antibrowning agent followed by citric acid. The antibrowning effects of cysteine and citric acid were greater as concentrations increased, and the optimal concentration of both cysteine and citric acid as antibrowning agents was 0.3%. Ascorbic acid itself contributed to the browning reaction and showed an accelerating effect as the concentration increased. The addition of 0.1% ascorbic acid as synergist either to 0.3% cysteine or 0.3% citric acid did not enhance significantly the antibrowning effect of cysteine or citric acid. When stored at 3$0^{\circ}C$, 4$0^{\circ}C$ and 5$0^{\circ}C$, the browning reaction was accelerated as the temperature increased, especially at 5$0^{\circ}C$. Even though the effects of citric acid and cysteine as inhibitors on the browning reaction decreased as temperature increased, cysteine was more effective in decreasing browning reaction than citric acid.

• Tribology and Lubricants
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• v.34 no.6
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• pp.226-234
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• 2018

Copper chemical mechanical planarization (CMP) has become a key process in integrated circuit (IC) technology. The results of copper CMP depend not only on the mechanical abrasion, but also on the slurry chemistry. The slurry used for Cu CMP is known to have greater chemical reactivity than mechanical material removal. The Cu CMP slurry is composed of abrasive particles, an oxidizing agent, a complexing agent, and a corrosion inhibitor. Citric acid can be used as the complexing agent in Cu CMP slurries, and is widely used for post-CMP cleaning. Although many studies have investigated the effect of citric acid on Cu CMP, no studies have yet been conducted on the interfacial friction characteristics and step height reduction in CMP patterns. In this study, the effect of citric acid on the friction characteristics and step height reduction in a copper wafer with varying pattern densities during CMP are investigated. The prepared slurry consists of citric acid ($C_6H_8O_7$), hydrogen peroxide ($H_2O_2$), and colloidal silica. The friction force is found to depend on the concentration of citric acid in the copper CMP slurry. The step heights of the patterns decrease rapidly with decreasing citric acid concentration in the copper CMP slurry. The step height of the copper pattern decreases more slowly in high-density regions than in low-density regions.

• Journal of Soil and Groundwater Environment
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• v.27 no.3
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• pp.41-49
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• 2022

This study utilized citric acid as a floating agent in biological denitrification process and assessed its role under different carbon supplying conditions. Several microcosm tests including citric acid active (CAA), precipitating tablet release active (PTRA) and floating tablet release active (FTRA) were conducted to evaluate nitrate denitrification efficacy. In CAA reactors, nitrate removal was accompanied by the formation of denitrification by-products such as nitrite and nitrous oxide, with the extent of nitrate removal being proportional to citric acid concentration. These results suggest that citric acid induced heterotrophic biological denitrification. PTRA reactor that incorporated CAA and the same electron donor showed a similar denitrification efficiency to CAA reactor. FTRA reactor, which contained the same amount of fumarate as PTRA, enhanced denitrification by 7% as compared to the PTRA reactor. The overall results of this work indicate that surplus citric acid can be efficiently utilized in heterotrophic denitrification.

• Journal of Ginseng Research
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• v.33 no.3
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• pp.194-198
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• 2009

The changes that would occur in a content of five phenolic ingredients and eight ginsenosides in acid-treatedred ginseng extracts were measured in this study. Acid-treated-red ginseng was prepared by treating with 1 M ascorbic acid or citric acid for 20 min. As a result, the contents of esculetin and quercetin in citric acid-treated-red ginseng increased by 3.5 times and 2.0 times, respectively, compared with control red ginseng. However, all phenolic ingredients decreased after treatment with ascorbic acid. In addition, the contents of ginsenoside Rg$_3$, Rh$_2$, Rd increased but those of Rb$_1$, Rc, Re, Rf, Rg$_1$ decreased after acid treatment. Although these tendency of results are similar, the rate of change of ginsenosides in citric acid-treated-red ginseng was higher than in ascorbic acid-treated-red ginseng. These results indicated that citric acid is more effective in the conversion of ginseng ingredients than ascorbic acid.

• Food Science of Animal Resources
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• v.24 no.3
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• pp.266-272
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• 2004

The objective of this study was to investigate the physicochemical characteristics of gelatin extracted from pork skin under soaking in various acid solutions (lactic acid, acetic acid, and citric acid). Gelatin sol was extracted at 8$0^{\circ}C$, frozen at -2$0^{\circ}C$ and lyophilized it for 3 days to be completely dried in freeze drying unit. In the evaluation of gelatin quality, gelatin soaked in citric acid showed higher L- and a-values than those of any other gelatin (p<0.05). Gelatin treated by acetic acid showed the highest gel strength, cohesiveness, and brittleness. The content of hydroxyproline amino acid in gelatin treated by acetic acid was larger than one of gelatin treated in lactic and citric acid in order. From the experimental results, the highest quality of gelatin in all of period, which was soaked in acetic acid and lactic acid, has a more good quality than gelatin soaked in citric acid.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.56 no.2
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• pp.253-258
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• 2023

This study was conducted to inhibit histamine formation in salt-fermented anchovy Engraulis japonicus fish sauce, by lowering the pH using 1% citric acid as food additive during the initial fermentation stage. The fish sauce samples were prepared with fresh anchovies used immediately after being caught (F), and left at ambient temperature for 4 h, and 24 h with 25% salt, 1% citric acid, and without citric acid for a 6-month fermentation period. The content of ammonia nitrogen, total nitrogen, and glutamic acid in fish sauce was unaffected by the addition of citric acid during the fermentation period. The histamine content of F and 4 h samples were 20.5-30.6 and 77.4-119.3 mg/kg, respectively. The histamine content of F and 4 h samples with 1% citric acid was 4.1-8.7 and 50.4-56.1 mg/kg, respectively. Furthermore, addition of citric acid did not inhibit histamine formation in 24 h sample that had lower freshness quality. Additionally, effective inhibition of histamine is observed during manufacturing of salt-fermented anchovy fish sauce on an industrial scale, suggesting that lowering the initial pH using 1% citric acid does not alter the taste and flavor of the fish sauce.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.7
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• pp.1307-1318
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• 2000

The purpose of this study is to investigate the degradation characteristics of oxalic acid and citric acid by $UV/H_2O_2$ oxidation. For this purpose, the effects of pH, $H_2O_2$ dosage and the concentration of each compounds on the degradation of oxalic acid and citric acid by $UV/H_2O_2$ were investigated. Oxalic acid was effectively degraded at the wavelength of 254 nm, while the degradation efficiency of citric acid was very low at the same wavelength. It was also found that both organic substances were not degraded by the injection of $H_2O_2$ only. The optimum pH of degradation of oxalic acid and citric acid was 4 and 4 to 6, respectively. In the case of $UV/H_2O_2$ oxidation, the degradation efficiency was increased by increasing $H_2O_2$ dosage. The degradation efficiency decreased when the dose of $H_2O_2$ exceeds 200 mg/L. From these results, it can be concluded that the optimum reaction conditions for the degradation of oxalic acid and citric acid by $UV/H_2O_2$ oxidation were pH 4 and 200mg/L of $H_2O_2$.

• KSBB Journal
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• v.25 no.2
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• pp.137-141
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• 2010

Citric acid is a natural preservative and is used to add a sour taste to foods and soft drinks. For the preparation of stable food additives of citric acid, a coating process using vegetable oil was developed. Coating materials used were purified soy bean oil and carnauba wax. The yield of coated citric acid was up to 95% in both cases. The contents of coating materials was 20~33% in the total composition and the coating efficiency was 95.2 ${\pm}$ 0.01%. The surface of coated citric acid was much smoother and more homogeneous than that of original citric acid according to SEM data. The coated citric acid can be used to as a stable food additive and also would be applied to nutraceuticals and cosmetic ingredients.

• Journal of Periodontal and Implant Science
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• v.32 no.4
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• pp.697-709
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• 2002

The present study was performed to evaluate the effect of citric acid on the change of implant surface microstructure according to application time. Implants with pure titanium machined surface, titanium plasma-sprayed surface, and sand-blasted, large grit, acid etched surface were utilized. Implant surface was rubbed with pH 1 citric acid for $\frac{1}{2}$ min., 1 min., 1 $\frac{1}{2}$ min., 2 min., and 3min, respeaively in the test group and implant surface was not treated in the control group. Then, the specimens were processed for scanning electron microscopic observation. The following results were obtained. 1. Both test and control group showed a few shallow grooves and ridges in pure titanium machined surface implants. There were not significant differences between two groups. 2. In titanium plasma-sprayed surfaces, round or amorphous particles were deposited irregularly. The irregularity of titanium plasma-sprayed surfaces conditioned with pH 1 citric acid was lessened and the cracks were increased relative to the application time of pH 1 citric acid. 3. Sand-blasted, large grit, acid etched surfaces showed the macro/micro double roughness. The application of pH 1 citric acid didn't change the characteristics of the sand-blasted, large grit, acid etched surfaces. In conclusion, the application of pH 1 citric acid to titanium plasma-sprayed surface is improper. And pure titanium machined surface implants and sand-blasted, large grit, acid etched surface implants can he treated with pH 1 citric acid for peri-implantitis treatment if the detoxification of these surfaces could be evaluated.