Antioxidant and antimicrobial characteristics of ethyl acetate polar fractions from walnut green husk.

Walnut green husk (WGH) is rich in natural compounds and is valued as a potential source of antioxidant and antimicrobial properties. In this study, the antioxidant and antimicrobial activities of petroleum ether polar fraction, dichloromethane polar fraction, ethyl acetate polar fraction (EAPF), and n-butanol polar fraction from WGH were analyzed. The results showed that EAPF exhibited the highest total flavonoid content (65.74 ± 1.01 mg rutin equivalents [RE]/g dry weight [DW]) and total phenol content (48.73 ± 1.09 mg gallic acid equivalent [GAE]/g DW), with the highest 2,2-diphenyl-1-picrylhydrazyl, hydroxyl radical (•OH), and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonate scavenging activity compared with other fractions. EAPF also showed good antibacterial activity against Escherichia coli and Bacillus cereus vegetative cells, with a diameter of inhibition zones of 33.5 and 37.6 mm, respectively, a minimum inhibitory concentration of 31.25 mg/ml and a minimum bactericidal concentration of 62.5 mg/ml, which inhibited the growth of both bacteria. Analysis of the antibacterial mechanism demonstrated that EAPF damaged the integrity of the cell membrane, increased the membrane permeability, and triggered the leakage of intracellular material. In addition, ultrahigh performance liquid chromatography-tandem with mass spectrometry analysis revealed that 8 polyphenols and 14 flavonoids were mainly present in EAPF, such as chlorogenic acid (C16 H18 O9 ), gallic acid (C7 H6 O5 ), vanillic acid (C8 H8 O4 ), ferulic acid (C10 H10 O4 ), epicatechin (C15 H14 O6 ), catechin (C15 H14 O6 ), hesperetin (C16 H14 O6 ), naringenin (C15 H12 O5 ), hyperin (C21 H20 O12 ), luteolin (C15 H10 O6 ), and so on. Therefore, WGH had the potential to be developed as a natural antioxidant and antibacterial material. PRACTICAL APPLICATION: Our work indicates that WGH contains abundant flavonoids and polyphenols compounds. Therefore, the plant byproducts like WGH may have a promising application as a source of antimicrobial and antioxidant additives.

Electron beam irradiation enhanced extraction and antioxidant activity of active compounds in green walnut husk.

Green walnut husk (GWH) contains abundant active compounds and is valued as a potential source of natural antioxidants. This study aimed at assessing the impact of electron beam irradiation (EBI) pretreatment on the extraction yield and antioxidant activity of active compounds in GWH. The ultrasonic extraction of active substances was optimized by response surface method (RSM). Scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction revealed physical structure changes in GWH powder. After EBI pretreatment, the content of polyphenols, flavonoids, and triterpenes in GWH increased by 18.88%, 43.00%, and 11.08%, respectively. Irradiation doses up to 30 kGy, DPPH, OH, and ABTS radical scavenging activity and reducing power of the crude extract were enhanced by 9.56%, 15.62%, 15.60%, and 36.98%, respectively. This was significantly different (P < 0.05) than the non-irradiated GWH. Therefore, EBI is a new pretreatment technology with potential application in the extraction and utilization of GWH.