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Yak butter is one of the most important foods for the Tibetan people. Of note, its production yields waste yak milk as a by-product. In this work, waste yak milk protein hydrolysates made via Pepsin hydrolysis were shown to have antimicrobial activity. Furthermore, an innovative method of magnetic liposome adsorption combined with reversed-phase high performance liquid chromatography (RP-HPLC) was developed to screen for and purify the antimicrobial peptides. Two antimicrobial peptides were obtained and their amino acid sequences were determined by N-sequencing, namely Arg-Val-Met-Phe-Lys-Trp-Ala and Lys-Val-Ile-Ser-Met-Ile. The antimicrobial activity spectra of Arg-Val-Met-Phe-Lys-Trp-Ala included Bacillus subtilis, Staphylcoccus aureus, Listeria innocua, Escherichia coli, Enterobacter cloacae and Salmonella paratyphi, while the Lys-Val-Ile-Ser-Met-Ile peptide shows not only bacterial growth inhibition but also of fungi. Haemolytic testing suggested that these two antimicrobial peptides could be considered to have no haemolytic effect at their minimum inhibitory concentrations (MICs).
Yak milk cheese is one of the most important foods for the Tibetan people. <b>Lactobacillus plantarum</b> SLG1 isolated from yak cheese was shown to produce a novel bacteriocin, plantaricin SLG1. Production of plantaricin SLG1 in MRS medium was maximized after 24 h incubation at 37 °C (the stationary phase of growth). An innovative method, namely magnetic liposome adsorption combined with reversed-phase high performance liquid chromatography (RP-HPLC), was developed to screen for and efficiently purify bacteriocin compounds from the cell free supernatants from <b>Lb. plantarum</b> SLG1. The molecular mass of plantaricin SLG1 is 1083.25 Da and its amino acid sequence Tyr-Gly-Asn-Gly-Val-Phe-Ser-Val-Ile-Lys was determined by N-sequencing. Analyses by Circular dichroism (CD) spectra and predicted 3D structure suggested that the peptide maintains a well-defined conformation. Plantaricin SLG1 exhibited a wide range of antimicrobial activity against many food-borne spoilage and pathogenic bacteria, as well as some fungi. Results using scanning electron microscopy indicated that the mode of action was bactericidal and plantaricin SLG1 was able to damage the cell membrane integrity ultimately causing pathogen lethality.<br>• Bacteriocin-producer <b>Lb. plantarum</b> SLG1 isolated from yak cheese. • Bacteriocin, plantaricin SLG1, was obtained. • Magnetic liposomes adsorption & RP-HPLC were used to purification. • The active spectrum include Gram-positive and negative bacteria and fungi.
Highland barley is one of the most important industrial crops in Tibetan plateau. Previous research indicated that highland barley has many medical functions. In this work, the antibacterial abilities of highland barley were investigated. The protein solutions hydrolyzed by trypsin for 4 h exhibited the highest antibacterial activity. An antibacterial peptide, barleycin, was screened and purified by magnetic liposome extraction combining with the protein profiles of reversed-phase high-performance liquid chromatography (RP-HPLC). Structure, characterization, and safety evaluation of barleycin were further investigated. Amino acids sequence was determined as Lys-Ile-Ile-Ile-Pro-Pro-Leu-Phe-His by N-sequencing. Circular dichroism spectra indicated the a-helix conformation of barleycin. The activity spectrum included <i>Bacillus subtilis, Staphylcoccus aureus, Listeria innocua and Escherichia coli</i> and the MICs were from 4 to 16 μg/mL. Safety evaluations with cytotoxicity and hemolytic suggested this antibacterial peptide could be considered as safe at MICs. Finally, mode of action of barleycin on sensitive cells was primarily studied. The results suggested the damage of cell membrane.