Investigating the Hepatoprotective Properties of Mulberry Leaf Flavonoids against Oxidative Stress in HepG2 Cells.

Oxidative stress significantly contributes to ageing and disease, with antioxidants holding promise in mitigating its effects. Functional foods rich in flavonoids offer a potential strategy to mitigate oxidative damage by free radicals. We investigated the protective effects of mulberry leaf flavonoids (MLF) against H2O2-induced oxidative damage in HepG2 cells. It assessed the inhibitory effect of MLF (62.5-500 µg/mL) on H2O2-induced oxidative damage by analyzing cellular morphology and oxidative stress markers, including ROS production, mitochondrial membrane potential, antioxidant enzyme levels, MDA, and apoptosis-related proteins. The results demonstrated that MLF prevented spiny cell formation triggered by 750 µM H2O2 and significantly reduced ROS levels, restored mitochondrial membrane potential, decreased lactate dehydrogenase and alanine transaminase leakage, and reduced MDA content induced by H2O2. MLF also modulated antioxidant enzymes and attenuated oxidative damage to HepG2 cell DNA, as confirmed by staining techniques. These findings indicate the potential of MLF as a hepatoprotective agent against oxidative damage in HepG2 cells.

Protective Effect of Flavonoids from Mulberry Leaf on AAPH-Induced Oxidative Damage in Sheep Erythrocytes.

To evaluate the antioxidant activity of flavonoids extracted from Chinese herb mulberry leaves (ML), flavonoids from mulberry leaves (FML) were extracted and purified by using ultrasonic-assisted enzymatic extraction and D101 macroporous resin. Using LC-MS/MS-Liquid Chromatography with tandem mass spectrometry analysis, hesperidin, rutoside, hyperoside, cyanidin-3-o-glucoside, myricitrin, cyanidin, and quercetin were identified, and NMR and UV were consistent with the verification of IR flavonoid characteristics. The antioxidant activity of FML has also been evaluated as well as the protective effect on 2,2 0-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidative stress. The results showed that FML exhibited powerful antioxidant activity. Moreover, FML showed dose-dependent protection against AAPH-induced sheep erythrocytes' oxidative hemolysis. In the enzymatic antioxidant system, pretreatment with high FML maintained the balance of SOD, CAT, and GSH-Px; in the non-enzymatic antioxidant system, the content of MDA can be effectively reduced after FML treatment. This study provides a research basis for the development of natural products from mulberry leaves.

Water-in-Oil Pickering Emulsions Stabilized Solely by Water-Dispersible Phytosterol Particles.

Water-in-oil (W/O) Pickering emulsions were successfully synthesized by water-dispersible phytosterol (PS) particles formed through simple antisolvent precipitation. The effects of the organic/aqueous ratio on the particle morphology, crystallinity, and contact angle were investigated. Sheet-like PS particles with reduced crystallinity were further used as W/O Pickering emulsion stabilizers. The properties of the formed W/O emulsions could be transformed by changing the oil type, water-phase fraction, or particle contents. Results showed that emulsions with 80% water fraction could be stabilized by 3% particles in the aqueous phase, where dodecane was used as the oil phase. W/O Pickering emulsions stabilized by PS particles showed temperature responsiveness. When dried, PS particles could be well dispersed either in the water or oil phase to stabilize W/O Pickering emulsions. Therefore, this kind of PS particles could not only enrich the family of food-grade Pickering stabilizers, especially the W/O type, but also provide a smart Pickering stabilizer to fabricate environmental-responsive emulsion products.

Novel caffeine degradation gene cluster is mega-plasmid encoded in Paraburkholderia caffeinilytica CF1.

The widespread use of caffeine in food and drug industries has caused great environmental pollution. Herein, an efficient caffeine-degrading strain Paraburkholderia caffeinilytica CF1 isolated from a tea garden in China can utilize caffeine as its sole carbon and nitrogen source. Combination of chromatographic and spectrophotometric techniques confirmed that strain CF1 adopts N-demethylation pathway for caffeine degradation. Whole genome sequencing of strain CF1 reveals that it has two chromosomes with sizes 3.62 Mb and 4.53 Mb, and a 174-kb mega-plasmid. The plasmid P1 specifically harbors the genes essential for caffeine metabolism. By analyzing the sequence alignment and quantitative real-time PCR data, the redundant gene cluster of caffeine degradation was elucidated. Genes related to catalyzing the N1-demethylation of caffeine to theobromine, the first step of caffeine degradation were heterologously expressed, and methylxanthine N1-demethylase was purified and characterized. Above all, this study systematically unravels the molecular mechanism of caffeine degradation by Paraburkholderia. KEY POINTS: • Caffeine degradation cluster in Paraburkholderia caffeinilytica CF1 was located in mega-plasmid P1. • The whole genome and the caffeine degrading pathway of P. caffeinilytica CF1 were sequenced and elucidated, respectively. • This study succeeded in heterologous expression of methylxanthine N1-demethylase (CdnA) and Rieske oxygenase reductase (CdnD) and illuminated the roles of CdnA and CdnD in caffeine degradation of P. caffeinilytica CF1.

Effect of atmospheric cold plasma treatment on antioxidant activities and reactive oxygen species production in postharvest blueberries during storage.

BACKGROUND: Blueberry is universally acknowledged as a kind of berry rich in antioxidants. Cold plasma, an emerging non-thermal treatment technology, has been proved to be able to maintain or improve the antioxidant level while inactivating the microorganisms on the surface of fruits and vegetables. Postharvest blueberries were treated with atmospheric cold plasma (ACP; 12 kV, 5 kHz) for 0 s (Control), 30 s (ACP-30), 60 s (ACP-60), and 90 s (ACP-90) in this study, and the effects of ACP on the antimicrobial properties, antioxidant activities, and reactive oxygen species (ROS) production were investigated during storage at 4 ± 1 °C for 40 days. RESULTS: Total aerobic bacteria and mold populations on ACP-treated blueberries decreased significantly in a time-dependent manner (P < 0.05), and decreased by 0.34-1.24 and 0.57-0.87 log10 CFU g-1 respectively on ACP-60-treated blueberries during storage. The decay rate of blueberries was decreased by 5.8-11.7% and the decrease of blueberry firmness was slowed down by ACP-60. But the total phenol, anthocyanin, and ascorbic acid contents increased, and superoxide dismutase, catalase, and peroxidase activities were enhanced in ACP-treated blueberries. The free radical scavenging activity and total antioxidant capacity (T-AOC) were enhanced. Hydrogen peroxide (H2 O2 ) and superoxide anion (O2 - ) production rates declined by 27.3% and 41.3% at day 40 of storage, respectively. CONCLUSION: It is suggested that ACP may be a promising non-thermal treatment technology for postharvest sterilization and preservation of blueberry under suitable conditions. © 2020 Society of Chemical Industry.

Preparative Purification of Total Flavonoids from Sophora tonkinensis Gagnep. by Macroporous Resin Column Chromatography and Comparative Analysis of Flavonoid Profiles by HPLC-PAD.

For the full development and utilization of Sophora tonkinensis Gagnep., this study was primarily intended to established a simple and efficient approach for the preparative purification of total flavonoids from S. tonkinensis by macroporous resin column chromatography (MRCC). The adsorption and desorption characteristics of the total flavonoids on ten macroporous resins were first studied, and AB-8 resin was chosen as the most suitable, and the adsorption data were best fitted to the pseudo-second-order kinetics model and Langmuir isotherm model. Furthermore, the technological parameters for the purification of the total flavonoids were optimized using column chromatography. After a sample one-step purification procedure, the content of the total flavonoids increased by about 4.76-fold from 12.14% to 57.82%, with a recovery yield of 84.93%. In addition, the comparative analysis of the flavonoid extracts before and after purification was performed by high-performance liquid chromatography coupled with photodiode-array detection (HPLC-PAD). The results showed that the contents of six major flavonoids in the purified product were all higher than before the purification. Therefore, the AB-8 MRCC established in this work was a promising method for the industrial-scale purification of the total flavonoids from S. tonkinensis.

Optimization of Ultrasonic-Assisted Extraction of Total Phenolics from Citrus aurantium L. Blossoms and Evaluation of Free Radical Scavenging, Anti-HMG-CoA Reductase Activities.

The objective of this study was to develop an ultrasonic-assisted procedure for the extraction of total phenolics from Citrus aurantium L. blossoms (CAB) and evaluate the free radical scavenging activity and anti-HMG-CoA reductase activity of the total phenolics. In this work, a Box- Behnken design based on single-factor experiments was used to explore the optimum extraction process. Under the optimum conditions (extraction solvent 70.31% ethanol, extraction temperature 61.94 °C, extraction time 51.73 min, and liquid-to-solid ratio 35.63 mL/g), the extraction yield of total phenolics was 95.84 mg gallic acid equivalents (GAE)/g dry matter (DM), which was highly consistent with the theoretical value (96.12 mg GAE/g DM). The higher contents of total phenolics and five main phenolic compounds obtained from the optimized ultrasonic-assisted extraction (UAE) proved its efficiency when compared with conventional heat reflux extraction (HRE). The total phenolic extract showed excellent free radical scavenging properties against 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·), 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) radical (ABTS+·), hydroxyl radical (·OH) and superoxide anion radical (·O2-), with IC50 values of 197.007, 83.878, 218.643, and 158.885 µg/mL, respectively; the extracts also showed good inhibition of ß-hydroxy-ß-methylglutaryl-CoA reductase (HMG-CoA reductase) activity, with an IC50 value of 117.165 µg/mL. Total phenolics from CAB could be a potential source of natural free radical scavenger and HMG-CoA reductase inhibitor.

Effect of Methyl Jasmonate on Phenolic Accumulation in Wounded Broccoli.

In order to find an efficient way for broccoli to increase the phenolic content, this study intended primarily to elucidate the effect of methyl jasmonate (MeJA) treatment on the phenolic accumulation in broccoli. The optimum concentration of MeJA was studied first, and 10 µM MeJA was chosen as the most effective concentration to improve the phenolic content in wounded broccoli. Furthermore, in order to elucidate the effect of methyl jasmonate (MeJA) treatment on phenolic biosynthesis in broccoli, the key enzyme activities of phenylpropanoid metabolism, the total phenolic content (TPC), individual phenolic compounds (PC), antioxidant activity (AOX) and antioxidant metabolism-associated enzyme activities were investigated. Results show that MeJA treatment stimulated phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarin coenzyme A ligase (4CL) enzymes activities in phenylpropanoid metabolism, and inhibited the activity of polyphenol oxidase (PPO), and further accelerated the accumulation of the wound-induced rutin, caffeic acid, and cinnamic acid accumulation, which contributed to the result of the total phenolic content increasing by 34.8% and ferric reducing antioxidant power increasing by 154.9% in broccoli. These results demonstrate that MeJA in combination with wounding stress can induce phenylpropanoid metabolism for the wound-induced phenolic accumulation in broccoli.

Effect of ethanol treatment on the quality and volatiles production of blueberries after harvest.

BACKGROUND: Blueberries are appreciated by consumers for their rich natural antioxidants and their good nutritional and health functions. However, blueberries are very perishable due to microbial infection and metabolic aging after harvest. Ethanol has been shown to have the effect of controlling postharvest microorganisms and improving storage quality of fruits and vegetables. This study aimed to clarify the effects of ethanol on the appearance quality and flavor attributes of postharvest blueberries. Blueberries were treated with ethanol (250, 500, and 1000 µL L-1 ) and stored at 0 ± 0.5 °C, 90% relative humidity (RH), for 40 days. RESULTS: The results indicated that ethanol treatment could slow the decline of blueberry firmness and reduce the decay rate significantly in a dose-dependent manner. The soluble solids content (SSC) and titratable acidity (TA) of ethanol-treated blueberries increased significantly (P < 0.05), improving the taste of the blueberries. The activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) were stimulated with the accumulation of ethanol in blueberries, which catalyzed the conversion of ethanol, acetaldehyde, and pyruvate, increasing their levels in blueberries. More volatiles, especially esters, were detected in ethanol-treated blueberries, e.g. methyl acetate, ethyl acetate, ethyl propanoate, ethyl isobutyrate, ethyl 2-methylbutanoate, ethyl isovalerate, ethyl 3-methyl-2-butenoate, diethyl sebacate, and isopropyl myristate. CONCLUSION: The preservative effect of ethanol on blueberry was significantly affected by ethanol concentration. In this study, the effect of 500 µL L-1 ethanol fumigation on blueberry was the best in terms of appearance quality (firmness and decay rate) and flavor attributes (SSC, TA, and volatiles). © 2019 Society of Chemical Industry.

Effect of thyme oil-alginate-based coating on quality and microbial safety of fresh-cut apples.

BACKGROUND: Food preservation is critical for keeping fresh-cut products fresh, nutritious, safe, attractive and available for consumers. To improve the safety and quality of fresh-cut fruits, 15 essential oils (EOs) were screened to test the antimicrobial activity against Listeria monocytogenes (LM), Salmonella typhimurium (ST), Staphylococcus aureus (SA) and Escherichia coli O157:H7 (EC O157:H7). The effect of alginate-based edible coating (EC) incorporating different concentrations thyme oil on fresh-cut 'Red Fuji' apples was investigated. RESULTS: Results showed that thyme oil, cinnamon oil and oregano oil were more effective in inhibiting the microbes than other EOs. The result showed that the combined usage of 0.5 µL mL-1 thyme oil incorporated with alginate-based EC could significantly inhibit the microbial growth, respiration, weight loss, firmness and browning of fresh-cut 'Red Fuji' apples. CONCLUSION: The edible coating and natural additives like thyme oil could be used to preserve the quality of fresh-cut fruits. It revealed that EC incorporated with 0.5 µL mL-1 thyme oil can be a safe preservative for fresh-cut apples. © 2017 Society of Chemical Industry.

Effects of hydrogen sulfide on the surface whitening and physiological responses of fresh-cut carrots.

BACKGROUND: The effect of hydrogen sulfide (H2 S) on the inhibition of the surface whitening of fresh-cut carrots was investigated. Whitening index; H2 O2 and malondialdehyde (MDA) contents; activities of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD); and antioxidant capacities were evaluated. RESULTS: H2 S treatment significantly inhibited the surface whitening of fresh-cut carrots (P < 0.05), reduced the accumulation of H2 O2 and MDA, and enhanced antioxidant enzymes (CAT, APX and GR) activities and antioxidant capacities (P < 0.05). The PAL, PPO and POD activities of fresh-cut carrots were inhibited by treatment with H2 S (P < 0.05). Furthermore, correlation analysis revealed that whitening index was significantly positively correlated with H2 O2 content, lipid peroxidation, PPO and POD activities. CONCLUSION: H2 S inhibited the surface whitening of fresh-cut carrots by reducing H2 O2 accumulation and lipid peroxidation, and also inhibited PPO and POD activities. © 2018 Society of Chemical Industry.

Franconibacter daqui sp. nov., a facultatively alkaliphilic species isolated from a Daqu sample.

A novel bacterium, designated strain DL503T, was isolated from a Daqu sample and its taxonomic position determined using a polyphasic taxonomy. Strain DL503T was a Gram-stain-negative, facultatively anaerobic, non-sporulating, motile and coccoid-rod-shaped bacterium. Optimum growth occurred at 20-45 °C, pH 5.0-10.0 and 1.5 % (w/v) NaCl. Comparative analysis of the 16S rRNA gene sequence showed that the isolate belongs to the genus Franconibacter, showing highest levels of similarity with respect to Franconibacter pulveris JCM 16471T (98.94 %) and Franconibacter helveticus DSM 18396T (98.39 %). Cells contained the quinones Q-8 and MK-8, and the polar lipid profile consisted of a mixture of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, three unidentified polar lipids and three unidentified amino lipids. The DNA G+C content was 53.3 mol% and the major fatty acids were C16 : 0, C17 : 0 cyclo, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), summed feature 4 (C17 : 1 iso I and/or C17 : 1 anteiso B) and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The DNA-DNA relatedness values between strain DL503T and its close relatives, including F. pulveris JCM 16471T and F. helveticus DSM 18396T, were 51.5±0.5 % and 45.2±1.1 %, respectively. Based on phylogenetic analysis, phenotypic and genotypic data, it is concluded that the isolate represents a novel species of the genus Franconibacter, for which the name Franconibacter daqui sp. nov. is proposed. The type strain is DL503T (=LMG 29914T=CGMCC 1.15944T).

Growth of Salmonella spp. and Escherichia coli O157:H7 on Fresh-Cut Fruits Stored at Different Temperatures.

The objective of this work was to determine the growth potential of Salmonella spp. and Escherichia coli O157:H7 on fresh-cut honeydew melon, cantaloupe, watermelon, pitaya, mango, papaya, and pineapple stored at 5°C, 13°C, and 25°C. The results showed that both pathogens were able to grow on fresh-cut fruits except fresh-cut pineapple at 13°C and 25°C. Salmonella spp. grew more rapidly on fresh-cut honeydew melon, cantaloupe, watermelon, and mango than did E. coli O157:H7 at 13°C. The growth of both species was inhibited on fresh-cut pineapple, with that of Salmonella spp. being particularly pronounced. Naturally occurring microbiota populations on fresh-cut fruits increased significantly at 13°C and 25°C, but no significant changes in growth were observed for Salmonella spp., E. coli O157:H7, or natural microbiota species at 5°C. The study therefore emphasizes the importance of strict temperature control from processing to consumption, including transportation, distribution, storage, and handling in supermarkets and by consumers.

Cytotoxic diterpenoids from Pteris ensiformis.

Phytochemistry investigation on Pteris ensiformis led to the isolation of a new ent-kaurane diterpenoid, ent-kaurane-6ß,16α-diol-3-one (1), along with five known diterpenoids (2-6) and three known sesquiterpenes (7-9). Their structures were established by means of spectroscopic methods. The ethanol extract and the isolated compounds (1-9) were evaluated for their antitumor activity against three cancer cell lines.

Dihydrochalcones and Diterpenoids from Pteris ensiformis and Their Bioactivities.

Two new dihydrochalcone enantiomers (+)-1 and (-)-1, along with eight known compounds 3-10, were obtained from Pteris ensiformis. The planar structures were determined on the basis of extensive 1D and 2DNMR and HRESIMS. The resolution of (+)-1 and (-)-1 was achieved by chiral HPLC analysis. The absolute configurations of (+)-1 and (-)-1 were established by the bulkiness rule using Rh2(O2CCF3)4-induced circular dichroism (ICD) method. Compounds (+)-1, (-)-1, 8, 9 and 10 exhibited the inhibitory assay of NO production in mouse macrophages stimulated by LPS, with IC50 values of 2.0, 2.5, 8.0, 9.5 and 5.6 µM, respectively. Otherwise, compound 10 showed moderate cytotoxic activity against HCT-116, HepG-2 and BGC-823 cell lines with IC50 values of 3.0, 10.5 and 6.3 µM, respectively.

Anti-Inflammatory Triterpene Glycosides from the Roots of Ilex dunniana Levl.

A new triterpene glycoside ilexdunnoside A (1) and a new sulfated triterpene derivative ilexdunnoside B (2), together with five known analogues 3-7 were isolated from the roots of Ilex dunniana Levl. The structures were established by NMR spectroscopic analysis and acid hydrolysis. Results of an in vivo study of the biological activity showed that 75% ethanol and n-butanol extracts of the plant displayed anti-inflammatory activities against ear edema in mice, with inhibition rates of 23.5% and 37.5%, respectively, at a dose of 50 mg/kg. Furthermore, Compounds 1, 2 and 3 exhibited moderate indirect inhibitory effects on lipopolysaccharide-induced NO production in BV2 microglial cells in vitro, with IC50 values of 11.60, 12.30 and 9.70 µM, respectively.

[Chemical constituents from Pteris multifida and cytotoxic activity].

The materials were extracted by 95% ethanol, and the extracting solution was isolated by kinds of chromatographic columns including polyamide, MCI, preparative MPLC, and preparative HPLC. Eight diterpenes and two sesquiterpenes were isolated from the plant. On analysis of ESI-MS and NMR spectroscopic data, the structures were established as ent-3ß-hydroxy-kaur-16-en-19-al (1), 4-epi-kaurenic acid (2), mitrekaurenone (3), 7ß,16α,17-trihydroxy-ent-kauran-19-oic acid (4), crotonkinin E (5), crotonkinin F (6), pterisolic acid A (7), pterisolic acid C (8), (2R)-pterosin P (9), and dehydropterosin B (10). Compounds 1-6 were obtained from Pteris for the first time, and compounds 7-10 were obtained from P. ensiformis for the first time. Compounds 5-8 showed moderate activity against HCT-116, HepG2 and BGC-823 cell lines, separately.

[Bioactive quinolizidine alkaloids from Sophora tonkinensis].

Twelve quinolizidine alkaloids were isolated from Sophora tonkinensis by means of silica gel, preparative MPLC, and preparative HPLC. On analysis of NMR spectroscopic data, their structures were established as 3-(4-hydroxyphenyl)-4-(3-methoxy-4-hydroxyphenyl)-3,4-dehydroquinolizidine(1), lanatine A(2), cermizines C(3), senepodines G(4), senepodines H(5), jussiaeiines A(6), jussiaeiines B(7),(+)-5α-hydroxyoxysophocarpine(8),(-)-12ß-hydroxyoxysophocarpine(9),(-)-clathrotropine(10),(-)-cytisine(11), and (-)-N-methylcytisine(12), respectively. Compounds 1-7 were first isolated from Sophora L. plant. In the in vitro assays,the isolated compounds 1, 3, 6-10 exhibited potent activity against CVB3 with IC50 of 6.40, 3.25, 4.66, 3.21, 0.12, 0.23 and 1.60, and with selective index values(SI=TC50/IC50)of 12.0, 5.6, 13.0, 15.1, 50.1, 26.2, and 23.6, respectively. Compounds 1, 3, and 7 exhibited activity against staphylococcus aureus(ATCC 29213)with MICvalues of 8.0, 3.5, 6.0 g•L⁻¹, respectively. Compounds 1, 3, 7, and 12 exhibited activity against staphylococcus aureus(ATCC 33591)with MIC values of 18.0, 7.5, 8.0, 12.0 g•L⁻¹, respectively. Compounds 2, 6, 7 exhibited activity against Escherichia coli(ATCC 25922) with MIC values of 1.0, 3.2, 0.8 g•L⁻¹.

New insight into transmembrane topology of Staphylococcus aureus histidine kinase AgrC.

Staphylococcus aureus accessory gene regulator (agr) locus controls the expression of virulence factors through a classical two-component signal transduction system that consists of a receptor histidine protein kinase AgrC and a cytoplasmic response regulator AgrA. An autoinducing peptide (AIP) encoded by agr locus activates AgrC, which transduces extracellular signals into the cytoplasm. Despite extensive investigations to identify AgrC-AIP interaction sites, precise signal recognition mechanisms remain unknown. This study aims to clarify the membrane topology of AgrC by applying the green fluorescent protein (GFP) fusion technique and the substituted cysteine accessibility method (SCAM). However, our findings were inconsistent with profile obtained previously by alkaline phosphatase. We report the topology of AgrC shows seven transmembrane segments, a periplasmic N-terminus, and a cytoplasmic C-terminus.

Partial purification and characterization of a novel histidine decarboxylase from Enterobacter aerogenes DL-1.

Histidine decarboxylase (HDC) from Enterobacter aerogenes DL-1 was purified in a three-step procedure involving ammonium sulfate precipitation, Sephadex G-100, and DEAE-Sepharose column chromatography. The partially purified enzyme showed a single protein band of 52.4 kD on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH for HDC activity was 6.5, and the enzyme was stable between pH 4 and 8. Enterobacter aerogenes HDC had optimal activity at 40°C and retained most of its activity between 4 and 50°C. HDC activity was reduced in the presence of numerous tested compounds. Particularly with SDS, it significantly (p < 0.01) inhibited enzyme activity. Conversely, Ca(2+) and Mn(2+) showed prominent activation effects (p < 0.01) with activity increasing to 117.20% and 123.42%, respectively. The Lineweaver-Burk plot showed that K m and V max values of the enzyme for L-histidine were 0.21 mM and 71.39 µmol/min, respectively. In comparison with most HDCs from other microorganisms and animals, HDC from E. aerogenes DL-1 displayed higher affinity and greater reaction velocity toward L-histidine.