Improved Production of Poly-γ-Glutamic Acid by Bacillus subtilis D7 Isolated from Doenjang, a Korean Traditional Fermented Food, and Its Antioxidant Activity

Abstract

The objectives of this study was to improve poly-γ-glutamic acid (γ-PGA) production by Bacillus subtilis D7 isolated from a Korean traditional fermented food and to assess its antioxidant activity for applications in the cosmetics and pharmaceutical industries. Strain D7 produced γ-PGA in the absence of L-glutamic acid, indicating L-glutamic acid-independent production. However, the addition of L-glutamic acid increased γ-PGA production. Several tricarboxylic acid cycle intermediates and amino acids could serve as the metabolic precursors for γ-PGA production, and the addition of pyruvic acid and D-glutamic acid to culture medium improved the yield of γ-PGA markedly. The maximum yield of γ-PGA obtained was 24.93 ± 0.64 g/l in improved medium, which was about 5.4-fold higher than the yield obtained in basal medium. γ-PGA was found to have 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (46.8 ± 1.5 %), hydroxyl radical scavenging activity (52.0 ± 1.8 %), 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS) radical scavenging activity (42.1 ± 1.8 %), nitric oxide scavenging activity (35.1 ± 1.3 %), reducing power (0.304 ± 0.008), and metal chelating activity (91.3 ± 3.5 %). These results indicate that γ-PGA has a potential use in the food, cosmetics, and biomedical industries for the development of novel products with radical scavenging activity. As far as we are aware, this is the first report to describe the antioxidant activityof γ-PGA produced by bacteria.

Properties of Poly-γ-Glutamic Acid Producing-Bacillus Species Isolated From Ogi Liquor and Lemon-Ogi Liquor

“…ACE inhibitory activities have been reported in a variety of fermented food, including cereal-based products (Hernández-Ledesma et al, 2004; Wang et al, 2016; Wu et al, 2018) and γPGA extracted from Bacillus spp. (Weng and Chen, 2012; Lee et al, 2014a,b). In addition to peptides that may be present in γPGA, ACE-inhibitory activity might be due to oligosaccharides and protease inhibitor that are associated with hydroxyl groups to establish hydrogen bonds with ACE (Pihlanto et al, 2008).…”

Bioavailability of Isoflavone Metabolites After Korean Fermented Soybean Paste (Doenjang) Ingestion in Estrogen‐Deficient Rats

“…Future studies of nutrikinetics for nonphytochemicals will also be needed. For example, the sticky poly‐gamma‐glutamic acid (PGA), an amino acid polymer, produced during the DJ process is a representative fermentation product (Lee et al., ) and these properties make it of interest for application in the food and medical industries (Ogunleye et al., ).…”

Bacillus subtilis HJ18‐4 from Traditional Fermented Soybean Food Inhibits Bacillus cereus Growth and Toxin‐Related Genes

“…The typical mucilaginous slime of fermented soybean food inhibited the growth of harmful yeasts and Gram‐positive and Gram‐negative bacteria by damaging the membrane of pathogenic bacteria cells (Schallmey and others ). Lee and others () reported that the poly‐γ‐glutamic acid (γ‐PGA) produced by B. subtilis D7 isolated from Korean traditional fermented food, Doenjang had novel functionalities such as angiotensin‐converting enzyme (ACE) inhibition and antimicrobial activity against some pathogenic bacteria; these findings suggest that γ‐PGA is a candidate antimicrobial agent and therapeutic drug in the pharmaceutical and food industries. Thus, the stringy and mucilaginous substance produced by B. subtilis HJ18‐4 may be a candidate antimicrobial agent.…”