Purification and characterization of a naringinase from Aspergillus aculeatus JMUdb058

Amination of naringinase to improve citrus juice debittering using a catalyst immobilized on glyoxyl-agarose

A naringinase complex was chemically aminated prior to its immobilization on glyoxyl-agarose to develop a robust biocatalyst for juice debittering. The effects of amination on the optimal pH and temperature, thermal stability, and debittering performance were analyzed. Concentration of amino groups on catalysts surface increased in 36 %. Amination reduced the β-glucosidase activity of naringinase complex; however, did not affect optimal pH and temperature of the enzyme and it favored immobilization, obtaining α-l-rhamnosidase and β-d-glucosidase activities of 1.7 and 4.2 times the values obtained when the unmodified enzymes were immobilized. Amination favored the stability of the immobilized biocatalyst, retaining 100 % of both activities after 190 h at 30 °C and pH 3, while its non-aminated counterpart retained 80 and 52 % of α-rhamnosidase and β-glucosidase activities, respectively. The immobilized catalyst showed a better performance in grapefruit juice debittering, obtaining a naringin conversion of 7 times the value obtained with the non-aminated catalyst.

Production of Prunin and Naringenin by Using Naringinase from Aspergillus oryzae NYO-2 and Their Neuroprotective Properties and Debitterization

Naringin is a flavanone glycoside in citrus fruits that has various biological functions. However, its bitterness affects the quality, economic value, and consumer acceptability of citrus products. Deglycosylation of naringin using naringinase decreases its bitterness and enhances its functional properties. In this study, eight microbial strains with naringinase activity were isolated from 33 yuzu-based fermented foods. Among them, naringinase from Aspergillus oryzae NYO-2, having the highest activity, was used to produce prunin and naringenin. Under optimal conditions, 19 mM naringin was converted to 14.06 mM prunin and 1.97 mM naringenin. The bitterness of prunin and naringenin was significantly decreased compared to naringin using the human bitter taste receptor TAS2R39. The neuroprotective effects of prunin and naringenin on human neuroblastoma SH-SY5Y cells treated with scopolamine were greater than that of naringin. These findings can widen the potential applications of deglycosylation of naringin to improve sensory and functional properties.

Naringinase Biosynthesis by Aspergillus niger on an Optimized Medium Containing Red Grapefruit Albedo

This study aimed to develop a method of naringinase biosynthesis by Aspergillus niger KMS on an optimized culture medium. The concentration of the six medium components in shake flasks was optimized by the Box and Wilson factor gradient method. Naringinase's substrate, naringin, powdered albedo, flavedo, and red grapefruit segment membranes were used to stimulate naringinase biosynthesis. Rhamnose was chosen as the carbon source, while the nitrogen source was yeast extract and sodium nitrate. Naringinase biosynthesis was most favorable in the culture medium with the following composition (g 100 mL): 3.332-NaNO₃; 3.427-yeast extract; 0.184-KH₂PO₄; 0.855-red grapefruit albedo; 0.168-naringin; 2.789-rhamnose. The obtained Aspergillus niger KMS culture fluid was concentrated, thereby precipitating the protein. As a result, a naringinase preparation with high activity, equal to 816 µmol × min^-1 × g^-1, was obtained.

Simultaneous production and sustainable eutectic mixture based purification of narringinase with Bacillus amyloliquefaciens by valorization of tofu wastewater

The current investigation is being executed for sustainable one-pot production and purification of naringinase using natural deep eutectic solvent-based extractive fermentation. Five natural deep eutectic solvents were prepared and their physicochemical properties were determined as a function of temperature. Tofu wastewater was used as a low-cost substrate for naringinase production and simultaneous in-situ purification of the enzyme was accomplished by employing NADES. Optimal conditions of influential factors like concentrations of NADES (74.5% w/w), Na₂SO₄ (15% w/v) and tofu wastewater (1.5% w/w) resulted in an effective yield of naringinase (249.6 U/ml). Scale-up of naringinase production with a 3 l custom made desktop bioreactor was accomplished and effective regeneration of NADES was established. NADES exhibits selectivity during extraction even after the fifth cycle proving it to be tailor-made. The resulting active enzyme was quantified by size exclusion chromatography (736.85 U/mg). Ultrapure enzyme fraction was obtained with anion exchange chromatography yielding maximum purity of (63.2 U/ml) and specific naringinase activity of (3516 U/mg). The in-vitro debittering activity of the resulting ultrapure enzyme fraction was determined with grape juice resulting in naringin and limonin removal of [23.4% (w/w)] and [64.3% (w/w)] respectively.

Purification and Characterization of a Novel α-L-Rhamnosidase from Papiliotrema laurentii ZJU-L07 and Its Application in Production of Icariin from Epimedin C

Icariin is the most effective bioactive compound in Herba Epimedii. To enhance the content of icariin in the epimedium water extract, a novel strain, Papiliotrema laurentii ZJU-L07, producing an intracellular α-L-rhamnosidase was isolated from the soil and mutagenized. The specific activity of α-L-rhamnosidase was 29.89 U·mg⁻¹ through purification, and the molecular mass of the enzyme was 100 kDa, as assayed by SDS-PAGE. The characterization of the purified enzyme was determined. The optimal temperature and pH were 55 °C and 7.0, respectively. The enzyme was stable in the pH range 5.5–9.0 for 2 h over 80% and the temperature range 30–40 °C for 2 h more than 70%. The enzyme activity was inhibited by Ca²⁺, Fe²⁺, Cu²⁺, and Mg²⁺, especially Fe²⁺. The kinetic parameters of K_m and V_max were 1.38 mM and 24.64 μmol·mg⁻¹·min⁻¹ using pNPR as the substrate, respectively. When epimedin C was used as a nature substrate to determine the kinetic parameters of α-L-rhamnosidase, the values of K_m and V_max were 3.28 mM and 0.01 μmol·mg⁻¹·min⁻¹, respectively. The conditions of enzymatic hydrolysis were optimized through single factor experiments and response surface methodology. The icariin yield increased from 61% to over 83% after optimization. The enzymatic hydrolysis method could be used for the industrialized production of icariin. At the same time, this enzyme could also cleave the α-1,2 glycosidic linkage between glucoside and rhamnoside in naringin and neohesperidin, which could be applicable in other biotechnological processes.

Grapefruit Debittering by Simultaneous Naringin Hydrolysis and Limonin Adsorption Using Naringinase Immobilized in Agarose Supports

Naringin and limonin are the two main bitter compounds of citrus products such as grapefruit juice. The aim of this investigation was to evaluate the reduction in both bitter components simultaneously using a combined biochemical and physical approach. The proposed strategy was based on the use of heterofunctional supports with glyoxyl groups that allow for the covalent immobilization of naringinase, which hydrolyses naringin and alkyl groups that allow for the adsorption of limonin. The supports were butyl-glyoxyl agarose (BGA) and octyl-glyoxyl agarose (OGA), which were characterized in terms of aldehyde group quantification and FTIR analysis. The optimal pH and temperature of free and immobilized enzymes were assessed. The maximum enzyme loading capacity of supports was analyzed. Debittering of grapefruit juice was evaluated using soluble enzyme, enzyme-free supports, and immobilized catalysts. Enzyme immobilized in BGA reduced naringin and limonin concentrations by 54 and 100%, respectively, while the use of catalyst immobilized in OGA allowed a reduction of 74 and 76%, respectively, obtaining a final concentration of both bitter components under their detection threshold. The use of OGA biocatalyst presented better results than when soluble enzyme or enzyme-free support was utilized. Biocatalyst was successfully applied in juice debittering in five repeated batches.

Screening and characterization of a GH78 α-l-rhamnosidase from Aspergillus terreus and its application in the bioconversion of icariin to icaritin with recombinant β-glucosidase

In this study, a GH78 α-L-rhamnosidase AtRha from Aspergillus terreus CCF3059 was screened and expressed in Pichia pastoris KM71H. The maximum enzyme activity of AtRha was 1000 U/mL after 12 days. AtRha was most active at 65 °C and pH 6.5, displaying excellent thermal stability and pH stability. The kinetic parameters Km, Vmax, kcat and kcat/Km values for pNPR were 0.481 mM, 659 μmol/min·mg, 1065 s-1 and 2214 s-1mM-1, respectively. AtRha could be inhibited by Fe2+, Hg2+ and Cu2+. Moreover, it displayed good tolerance to organic reagents with 52.6% activity in 15%(w/v) methanol. AtRha can hydrolyze icariin containing the α-1 rhamnoside linkage. Furthermore, AtRha and β-glucosidase TthBg3 showed excellent selectivity to cleave the rhamnose at the 3rd position and the glucosyl at the C-7 group of icariin, which established an effective and green method to produce the more pharmacological active icaritin. In addition, the optimal enzyme addition schemes and the reaction conditions were screened and optimized. After a two-stage transformation under optimized conditions, 0.5 g/L of icariin was transformed into 0.25 g/L of icaritin, with a corresponding molar conversion rate of 91.2%. Our findings provide a new, specific and cost-effective method for the production of icaritin in the industry.

Microorganisms, the Ultimate Tool for Clean Label Foods?

Clean label is an important trend in the food industry. It aims at washing foods of chemicals perceived as unhealthy by consumers. Microorganisms are present in many foods (usually fermented), they exhibit a diversity of metabolism and some can bring probiotic properties. They are usually well considered by consumers and, with progresses in the knowledge of their physiology and behavior, they can become very precise tools to produce or degrade specific compounds. They are thus an interesting means to obtain clean label foods. In this review, we propose to discuss some current research to use microorganisms to produce clean label foods with examples improving sensorial, textural, health and nutritional properties.

Novel Strategy of Mussel-Inspired Immobilization of Naringinase with High Activity Using a Polyethylenimine/Dopamine Co-deposition Method

Mussel-inspired surface chemistry is recognized as a simple, efficient, and mild surface modification method and has become a research hotspot in many fields. In this study, polyethylenimine/dopamine was coated on the surface of SBA-15 using a co-deposition method, making it possible to immobilize naringinase with high activity and operation stability. The optimal modification and immobilization conditions as well as enzyme properties were investigated. The naringinase activity can reach up to 753.78 U/g carrier, which was much higher than those of the previous works. Besides, the residual naringinase activity still kept 78.91% of the initial activity after one month of storage and maintained 60.79% after 8 cycles. Therefore, the strategy of mussel-inspired enzyme immobilization could be recognized as a promising and universal enzyme immobilization method, with the advantages of high relative enzyme activity, enzyme carrying rate, enzyme activity recovery rate, and good reusability and storage stability.

Solid-State Fermentation of Aspergillus niger to Optimize Extraction Process of Isoliquiritigenin from Glycyrrhiza uralensis

We successfully extracted isoliquiritigenin from Glycyrrhiza uralensis via fermentation with Aspergillus niger and ultrasonic-assisted extraction. In brief, we used A. niger fermentation to culture G. uralensis powder, and we optimized some key parameters such as reaction conditions of pH, inoculation concentration of A. niger, fermentation time, and solid-liquid ratio. Based on a single-factor experiment, we utilized the response surface methodology (RSM) approach to optimize this extraction procedure. Using the RSM approach, optimized conditions of pH = 3.694, the solid-liquid ratio = 1 : 2.155, and the inoculation concentration of A. niger = 1466745 were selected. Optimized conditions resulted in an extraction efficiency of 1.525 mg/g. These results showed that the extraction of isoliquiritigenin was most affected by pH and then the time of fermentation and the solid-liquid ratio. Overall, the developed extraction technique yielded 5 times the amount of isoliquiritigenin when compared to traditional methods.

Recent developments in enzyme immobilization technology for high-throughput processing in food industries

The demand for food and beverage markets has increased as a result of population increase and in view of health awareness. The quality of products from food processing industry has to be improved economically by incorporating greener methodologies that enhances the safety and shelf life via the enzymes application while maintaining the essential nutritional qualities. The utilization of enzymes is rendered more favorable in industrial practices via the modification of their characteristics as attested by studies on enzyme immobilization pertaining to different stages of food and beverage processing; these studies have enhanced the catalytic activity, stability of enzymes and lowered the overall cost. However, the harsh conditions of industrial processes continue to increase the propensity of enzyme destabilization thus shortening their industrial lifespan namely enzyme leaching, recoverability, uncontrollable orientation and the lack of a general procedure. Innovative studies have strived to provide new tools and materials for the development of systems offering new possibilities for industrial applications of enzymes. Herein, an effort has been made to present up-to-date developments on enzyme immobilization and current challenges in the food and beverage industries in terms of enhancing the enzyme stability.

Changes in bitterness, antioxidant activity and total phenolic content of grapefruit juice fermented by Lactobacillus and Bifidobacterium strains

Four strains of Lactobacillus and Bifidobacterium including L. plantarum 01, L. fermentum D13, L. rhamnosus B01725, and B. bifidum B7.5 exhibiting naringinase production were applied in grapefruit juice fermentation. All investigated strains grew well in grapefruit juice without nutrition supplementation. In all cases, cell counts were 108–109 CFU ml−1 after 24 hours of fermentation. The highest lactic acid and acetic acid productions were observed in the case of strain L. plantarum 01. The L. plantarum 01 and L. fermentum D13 strains prefer glucose over fructose and sucrose, whereas fructose was the most favoured sugar for L. rhamnosus B01725 and B. bifidum B7.5. At the end of the fermentation process, antioxidant activity and total polyphenol content of grapefruit juice decreased in all cases, but the changes were not significant. Significant decrease of naringin was observed in the case of L. plantarum 01, 28% naringin in grapefruit juice was removed after fermentation. This result is promising for development of technology for production of probiotic grapefruit juice.

Comparison between irradiating and autoclaving citrus wastes as substrate for solid-state fermentation by Aspergillus aculeatus

Agricultural or food processing wastes cause serious environmental burden and economic losses. Solid-state fermentation using these wastes is an attractive option to valorize these wastes. However, conventional autoclaving of substrate may degrade nutrients and generate toxins. Unsterilization of the substrate will cause undesired microbial contamination. Therefore, we compared irradiation with autoclaving to treat citrus wastes as substrate for solid-state fermentation by Aspergillus aculeatus. By comparing microbial growth, enzymes tested and medium consumption, irradiated substrate had higher biomass and extracellular protein, more sugar consumption and higher enzyme production than those with autoclaved substrate. Irradiation prevented the generation of cell-inhibiting components such as 5-hydroxymethylfurfural (5-HMF) whereas preserved the flavonoids well that are often enzyme inducers. These findings suggest that irradiation of agricultural and food processing wastes as substrate has advantages over autoclaving for solid-state fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: This study proposes irradiation as an alternative to sterilize agricultural residues rich in nutrients and thermosensitive compounds, such as citrus wastes for fungal solid-state fermentation and production of enzymes.

Heterologous Expression and Characterization of a New Clade of Aspergillus α-L-Rhamnosidase Suitable for Citrus Juice Processing

α-L-Rhamnosidase is a glycoside hydrolase capable of removing naringin from citrus juice. However, α-L-rhamnosidases always have broad substrate spectra, causing negative effects on citrus juice. In this study, a α-L-rhamnosidase-expressing fungal strain, JMU-TS529, was identified, and its α-L-rhamnosidase was characterized. As a result, JMU-TS529 was identified as Aspergillus tubingensis via morphological and molecular characteristics. The predicted protein sequence shared an amino acid identity of less than 30% with previously characterized α-L-rhamnosidases. The optimal pH and temperature were 4.0 and 50-60 °C, respectively. Most importantly, the α-L-rhamnosidase showed a strong ability to hydrolyze naringin but scarcely acted on other substrates. Furthermore, the enzyme could efficiently remove naringin from pomelo juice without changing its attractive aroma. These results indicate that the present enzyme represents a new clade of Aspergillus α-L-rhamnosidase that is desirable for debittering citrus juice, providing a better alternative for improving the quality of citrus juice.

Purification and Characterization of a Naringinase from Cryptococcus albidus

Naringinase which was extracted from the fermented broth of Cryptococcus albidus was purified about 42-folds with yield 0.7% by sulfate fractionation and chromatography on Toyopearl HW-60, Fractogel DEAE-650-s, and Sepharose 6B columns. Molecular weight of protein determined by gel filtration and SDS-PAGE was 50 kDa. Naringinase of C. albidus includes high content of the dicarbonic and hydrophobic amino acids. Enzyme contains also carbohydrate component, represented by mannose, galactose, rhamnose, ribose, arabinose, xylose, and glucose. The enzyme was optimally active at pH 5.0 and 60 °C. Naringinase was found to exhibit specificity towards p-nitrophenyl-α-L-rhamnose, p-nitrophenyl-β-D-glucose, naringin, and neohesperidin. Its K _m towards naringin was 0.77 mM and the V _max was 36 U/mg. Naringinase was inhibited by high concentrations of reaction product-L-rhamnose. Enzyme revealed stability to 20% ethanol and 500 mM glucose in the reaction mixture that makes it possible to forecast its practical use in the food industry in the production of juices and wines.

Development and evaluation of an HPLC method for accurate determinations of enzyme activities of naringinase complex

An HPLC method that can separate naringin, prunin, and naringenin was used to help accurately measure the activities of naringinase and its subunits (α-L-rhamnosidase and β-D-glucosidase). The activities of the naringinase and β-d-glucosidase were determined through an indirect calculation of the naringenin concentration to avoid interference from its poor solubility. The measured enzymatic activities of the naringinase complex, α-L-rhamnosidase, and β-D-glucosidase were the as same as their theoretical activities when the substrates' (i.e., naringin or prunin) concentrations were 200 μg/mL, and the enzyme concentrations were within the range of 0.06-0.43, 0.067-0.53, and 0.15-1.13 U/mL, respectively. The β-D-glucosidase had a much higher Vmax than either naringinase or α-L-rhamnosidase, implying the hydrolysis of naringin to prunin was the limiting step of the enzyme reaction. The reliability of the method was finally validated through the repeatability test, indicating its feasibility for the determinations of the naringinase complex.