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Background: Postbiotics are an emerging research interest in recent years and are fairly advanced compared to prebiotics and probiotics. The composition and function of postbiotics are closely related to fermentation conditions. Methods: In this study, we developed a solid-state fermentation preparation method for postbiotics with antimicrobial, antioxidant, and anti-inflammatory activities. The antibacterial activity was improved 3.62 times compared to initial fermentation conditions by using optimization techniques such as single factor experiments, Plackett-Burman design (PBD), steepest ascent method (SAM), and central composite design (CCD) methods. The optimized conditions were carried out with an initial water content of 50% for 8 days at 37°C and fermentation strains of Bacillus amyloliquefaciens J and Lactiplantibacillus plantarum SN4 at a ratio of 1:1 with a total inoculum size of 8%. The optimized SSF medium content ratios of peptide powder, wheat bran, corn flour, and soybean meal were 4, 37.4, 30, and 28.6%, respectively. Results: Under these optimized conditions, postbiotics with a concentration of 25 mg/mL showed significant broad-spectrum antibacterial capabilities against Escherichia coli, Salmonella, and Staphylococcus aureus and strong antioxidant activity against ABTS, DPPH, and OH radicals. Moreover, the optimized postbiotics exhibited good anti-inflammatory ability for reducing nitric oxide (NO) secretion in RAW 264.7 macrophage cells in response to LPS-induced inflammation. Furthermore, the postbiotics significantly improved intestinal epithelial wound healing capabilities after mechanical injury, such as cell scratches in IPEC-J2 cells (p < 0.05). Conclusion: In brief, we developed postbiotics through optimized solid-state fermentation with potential benefits for gut health. Therefore, our findings suggested that the novel postbiotics could be used as potential functional food products for improving body health.
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BACKGROUND: 10-Hydroxy-cis-12-octadecenoic acid (10-HOE, 10-OH C18:1), an emerging functional fatty acid, has anti-fungal and anti-inflammatory effects. 10-HOE is synthesized by bacterial 10-linoleic acid hydratase (10-LHT) with linoleic acid as the substate. However, the characterization of 10-LHT and its targeted synthesis of 10-HOE have been rarely reported. In this study, the recombinant 10-LHT from Lactiplantibacillus plantarum ZS2058 was characterized, and the biocatalysis of 10-HOE using crude enzyme was optimized. RESULTS: The recombinant 10-LHT catalyzed the conversion of linoleic acid (C18:2) to 10-HOE as identified using gas chromatography-mass spectrometry (GC-MS). It showed a molecular weight of about 70 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and was a flavin adenine dinucleotide (FAD)-dependent enzyme. The activity of 10-LHT was optimal at pH 6.5 and 25 °C, and it was pH-stable but thermo-sensitive. The optimal condition for the 10-HOE biosynthesis using crude enzyme was 5 g L-1 linoleic acid (C18:2), 148.0 U mL-1 10-LHT, 0.05 mmol L-1 FAD, 2% methanol and 100 mmol L-1 sodium chloride at 25 °C and pH 6.5. A conversion yield of 47.8 ± 1.5% and the corresponding 10-HOE concentration of 2.4 ± 0.1 g L-1 were achieved at 48 h under the optimal reaction conditions. CONCLUSION: This work achieved the highest conversion yield of 10-HOE with the highest substrate concentration, and provides some useful information for the industrial production of 10-HOE. © 2021 Society of Chemical Industry.
