Thermal stability data of juglone from extracts of walnut (Juglans regia) green husk, and technologies used to concentrate juglone

An integrated approach of homogenization-ultrasound-assisted extraction followed by high-speed countercurrent chromatography for rapidly preparative separation naphthoquinones and diarylheptanes from Juglands mandshurica Maxim. exocarp

This research investigated the effectiveness of an integrated method for the extraction and separation of naphthoquinones and diarylheptanes from exocarp of Juglands mandshurica Maxim. (namely, green walnut husks). The target compounds were obtained by ultra-turrax homogenization (UTH) coupled with ultrasound-assisted extraction (UAE) technology followed by high-speed countercurrent chromatography (HSCCC). The UTH-UAE extraction method achieved higher efficiency with 2.49- and 2.36-fold to those by UAE, and 1.39- and 1.34-fold to those by UTH in a short time. HSCCC was adopted for further separation and purification; six target compounds, namely, regiolone (RE), juglone (JU), myricatomento-genin (MG), galleon (GA), 2-oxatrycyclo[13.2.2.13,7]eicosa-3,5,7(20),15,17,18-hexaen-10-16-diol (OE), and juglanin A (JA), were separated with more than 95.37% purities and more than 84.71% final recovery rates, respectively. In this study, the integrated strategy of extraction and separation could get high purity compounds quickly, which would provide time and solvent saved method for the natural products separation from plants.

Whitening Effect of Juglans regia Dry Husk Extract on Primary and Permanent Teeth

Walnut is a common member of the family Juglandaceae. Recently, the evaluation of the phenolic content and antioxidant activity of the parts of walnut has received increased interest. Many reasons are responsible for teeth discolouration because teeth can absorb ingredients from tea, coffee, and food. Stains from these ingredients could stay in the porous enamel layer. Traditional whitening chemicals have some side effects, the most common of which is tooth sensitivity and mild or moderate gingival irritation. The aims of this comparative experimental study were to evaluate the whitening effect of Juglans regia dry husk extract and compare it with that of traditional prophylactic pumice. Forty human teeth were collected. Amongst these teeth, 20 were permanent, and the other 20 were primary. Each group was randomly divided into a study group (treated with dry husk extract) and a control group (treated with traditional pumice). Tooth colour was measured with Easy VitaShade Advanced 4.0, and the readings of lightness, chroma, and hue (a^∗ represents the green to red axis and b^∗ represents the blue to yellow axis) were documented for each tooth before and after polishing. A statistical analysis was performed using the Statistical Package for Social Science (version 22; Chicago, Illinois, USA). Data were analysed using Shapiro-Wilk, Wilcoxon sum rank, and Wilcoxon signed rank tests, and the level of significance was set to 0.05. A normality test was conducted using the Shapiro-Wilk test, and it showed that the colour variables were not normally distributed. With regard to tooth lightness, significant differences were observed in the primary and permanent teeth and Juglans regia exerted a much better whitening effect than pumice at p < 0.05. This study supports the use of Juglans regia dry husk extract in dentistry as a natural product with a whitening effect. It has utilisation potential in dentistry due to its beneficial properties and highly active components.

Antimicrobial and antioxidant activity of phenolic extracts from walnut (Juglans regia L.) green husk by using pressure-driven membrane process

In this study, antioxidant (DPPH and metal chelating), DNA cleavage, biofilm, and antimicrobial properties of extracted phenol from the walnut green husk (WGH) and its different concentrate and permeate samples were evaluated. For maximum phenolic compound extraction from the WGH first, the effects of solvent type (deionized water, methanol, n-hexane, acetone, and ethanol), solvent temperature (25-75 °C), and extraction time (0.5-24 h) were optimized. Then to concentrate phenolic compounds a pressure-driven membrane process was used with four different membrane types. The phenol contents of the concentrate samples were found to be microfiltration (MF) concentrate 4400 mg/L, ultrafiltration (UF) concentrate 4175 mg/L, nanofiltration (NF) concentrate 8155 mg/L, and reverse osmosis (RO) concentrate 8100 mg/L. LC-MSMS was used to determine the quantification of phenolic compounds in permeate and concentrate streams. In addition, all of the concentrate samples with high phenol content showed a high antioxidant activity as 100% with MF concentrate, UF concentrate, NF concentrated and RO concentrated. Likewise, concentrate samples were found to have very high antibiofilm activity as 82.86% for NF concentrate againts S. aureus, 85.80% for NF concentrate against P. aureginosa, 80.95% for RO concentrate against S. aureus, and 83.61% for RO-concentrate against P. aureginosa. When the antimicrobial activity of the extracted phenol from WGH and its different concentrate and permeate samples were evaluated by micro dilution and disk diffusion methods, it was found that the ability of the concentrate samples to inhibit bacterial growth was much higher than permeate ones. In addition, extracted phenol from WGH and its different concentrate and permeate samples showed significant DNA nuclease activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05588-w.

Juglone Inactivates Pseudomonas aeruginosa through Cell Membrane Damage, Biofilm Blockage, and Inhibition of Gene Expression

Due to the strong drug resistance of Pseudomonas aeruginosa (P. aeruginosa), the inhibition effects of conventional disinfectants and antibiotics are not obvious. Juglone extracted from discarded walnut husk, as a kind of plant-derived antimicrobial agent, has the advantages of naturalness, high efficiency, and low residue, with a potential role in the inhibition of P. aeruginosa. This study elucidated the inhibitory effect of juglone on the growth of plankton and the formation of P. aeruginosa biofilm. The results showed that juglone (35 μg/mL) had an irreversible inhibitory effect on P. aeruginosa colony formation (about 10⁷ CFU/mL). The integrity and permeability of the cell membrane were effectively destroyed, accompanied by disorder of the membrane permeability, mass leakage of the cytoplasm, and ATP consumption. Further studies manifested that juglone could induce the abnormal accumulation of ROS in cells and block the formation of the cell membrane. In addition, RT-qPCR showed that juglone could effectively block the expression of five virulence genes and two genes involved in the production of extracellular polymers, thereby reducing the toxicity and infection of P. aeruginosa and preventing the production of extracellular polymers. This study can provide support for the innovation of antibacterial technology toward P. aeruginosa in food.