Safety evaluation of Bacillus cereus isolated from smelly mandarin fish

Integrated one-dimensional CuO-nanowire arrays/Cu-foam nanoarchitecture for ultrahigh sensitive and non-enzymatic electrochemical determination of histamine levels in different-bacteria fermented mandarin fish

Integrated one-dimensional CuO-nanowire arrays/Cu-foam (CuO-NWAs/Cu-foam) nanostructure, which was fabricated by oxidation and calcination, has been newly utilized as non-enzymatic electrocatalytic electrode for exploring histamine level. Under optimal condition of pH at 13 and potential at 0.55 V (vs Ag/Ag/Cl), the sensitivity of CuO-NWAs/Cu-foam electrode towards non-enzymatic electrochemical histamine determination presented as high as 12.94 mA mM^-1 cm^-2, linear range spanned between 0.5 and 1046 μM, a detection limit (S/N = 3) was about 44 nM. The unprecedented causes of ultrahigh sensitivity were physically contributed to enhancing active surface area and declining charge transfer resistance. More crucially, the outstanding selectivity, stability and reproducibility facilitated its practical capacity on evaluating histamine levels in different-bacteria fermented mandarin fish, which triggered the potential feasibility for commercializing non-enzymatic electrochemical determination of histamine with high sensitivity, reliable precision and low expenditure.

The relationship between flavor formation, lipid metabolism, and microorganisms in fermented fish products

Traditional fermented fish products are favored due to their unique flavors. The fermentation process of fish is accompanied by the formation of flavor substances through a complex metabolic reaction of microorganisms, especially lipolysis and lipid oxidation. However, it is difficult to precisely control the reaction of microorganisms during the fermentation process in modern industrial production, and fermented fish products have lost their traditional characteristic flavors. The purpose of this review is to summarize the different kinds of fermented fish, core microorganisms in it, and flavor formation mechanisms, providing guidance for industrial cultural starters. Future research on the flavor formation mechanism is necessary to confirm the relationship between flavor formation, lipid metabolism, and microorganisms to ensure stable flavor and safety, and to elucidate the mechanism directly toward industrial application.

Isolation of a Highly Efficient Antigenic-Protein-Degrading Bacillus amyloliquefaciens and Assessment of Its Safety

Simple Summary

Soybean meal (SBM), a byproduct of soybean oil extraction, is a commonly used dietary protein in the poultry and swine feed industries because of its high quality protein and relatively well-balanced amino acids. However, major antigenic proteins in SBM, glycinin and β-conglycinin, can trigger allergic reactions, including intestine villus atrophy and other malabsorption syndromes, in newborn animals. Microbial fermentation is considered an economically viable processing technique to reduce the content of antigenic proteins, and improve the nutritional quality of SBM. The kind of microorganism used in fermentation is one of the major factors affecting the nutritional value of SBM. In this study, a highly efficient Bacillus. amyloliquefaciens strain was successfully isolated with convenient and effective plate tests, and used in a fermentation experiment. Fermentation with B. amyloliquefaciens for 24 h effectively degraded the glycinin and β-conglycinin in SBM, significantly improved the crude protein content and acid soluble protein concentration, and increased the total amino acid content. Furthermore, B. amyloliquefaciens had no adverse effects on animal health. These results indicate that the B. amyloliquefaciens strain isolated in this study is safe for animal use and can be widely used in SBM fermentation.

Abstract

The aims of this study were to screen and isolate a highly efficient strain from the rumen of a cow that can degrade the antigenic soy proteins in soybean meal (SBM) and improve the nutritional value of SBM by fermenting it with this strain. The safety of this strain was investigated with an acute oral toxicity test. A Bacillus amyloliquefaciens strain was successfully screened with plate tests and fermentation. After solid state fermentation of SBM with B. amyloliquefaciens for 24 h, the amounts of glycinin and β-conglycinin, two major antigenic proteins in SBM, decreased by 92.32% and 85.05%, respectively. The crude protein content in the fermented soybean meal (FSBM) increased by 17.54% compared with that in SBM. Notably, the trichloroacetic-acid-soluble protein (TCA-SP) content, particularly small peptides and free amino acids, was 9.97-fold higher in FSBM than in SBM. The in vitro dry matter digestibility and digestible energy of SBM increased from 62.91% to 72.52% and from 10.42 MJ/kg to 13.37 MJ/kg (dry matter basis), respectively, after fermentation. The acute oral toxicity test suggested that the strain exerted no harmful effects on the relative organ weights, the morphological tissue structure, or the health of mice. These results indicate that the B. amyloliquefaciens strain isolated in this study is a safe strain for animals, and could be used to improve the nutritional quality of SBM by solid-state fermentation.

Recombinant Expression of Serratia marcescens Outer Membrane Phospholipase A (A1) in Pichia pastoris and Immobilization With Graphene Oxide-Based Fe3O4 Nanoparticles for Rapeseed Oil Degumming

Enzymatic degumming is an effective approach to produce nutritional, safe, and healthy refined oil. However, the high cost and low efficiency of phospholipase limit the application of enzymatic degumming. In this study, an 879 bp outer membrane phospholipase A (A1) (OM-PLA1) gene encoding 292 amino acid residues was isolated from the genome of Serratia marcescens. The recombinant OM-PLA1 profile of appropriately 33 KDa was expressed by the engineered Pichia pastoris GS115. The OM-PLA1 activity was 21.2 U/mL with the induction of 1 mM methanol for 72 h. The expression efficiencies of OM-PLA1 were 0.29 U/mL/h and 1.06 U/mL/OD600. A complex of magnetic graphene oxide (MGO) and OM-PLA1 (MGO-OM-PLA1) was prepared by immobilizing OM-PLA1 with graphene oxide-based Fe3O4 nanoparticles by cross-linking with glutaraldehyde. The content of phosphorus decreased to 5.1 mg/kg rapeseed oil from 55.6 mg/kg rapeseed oil with 0.02% MGO-OM-PLA1 (w/w) at 50°C for 4 h. MGO-OM-PLA1 retained 51.7% of the initial activity after 13 times of continuous recycling for the enzymatic degumming of rapeseed oil. This study provided an effective approach for the enzymatic degumming of crude vegetable oil by developing a novel phospholipase and improving the degumming technology.

Shortening Fermentation Period and Quality Improvement of Fermented Fish, Chouguiyu, by Co-inoculation of Lactococcus lactis M10 and Weissella cibaria M3

Chouguiyu, a Chinese traditional fermented fish, is famous for its uniquely strong odor and desirable taste. However, traditional spontaneous fermentation often resulted in contamination and unstable quality of products. In this study, individual or conjunctive inoculation of two indigenous lactic acid bacteria (LAB), Lactococcus lactis M10 and Weissella cibaria M3, was tested for their effect on improving Chouguiyu's quality. It was shown that inoculation would not affect the system's pH, while increased the total bacteria count and lactic acid bacteria amounts. Matrix-assisted laser desorption/ionization time-of-flight mass (MALDI-TOF) analysis results revealed that Lactoc. lactis M10 and W. cibaria M3 could quickly occupy a dominant position in the ecosystem, and Lactoc. lactis M10 played an important role in the control of spoilage bacteria. Volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), and biogenic amines results also showed that Lactoc. lactis M10 had a positive effect on improving the product's quality. Co-inoculation of Lactoc. lactis M10 and W. cibaria M3 could promote the formation of flavor according to the E-nose and gas chromatography-mass spectrometer (GC-MS) analyses, especially for the aroma-active and key volatile compounds. PCA plots of E-nose and hierarchical clustering analysis of GC-MS profiles revealed that the co-inoculation sample at the fifth day (LW5) was the most similar to the natural fermentation sample at the seventh day (C7). The overall acceptance of LW5 was also the closest to that of C7 in sensory evaluation. In conclusion, mixed starter culture was shown to have a good effect on improving product quality and enhancing flavor with fermentation time shortened by 29%.

Genomic Characterization and Probiotic Potency of Bacillus sp. DU-106, a Highly Effective Producer of L-Lactic Acid Isolated From Fermented Yogurt

Bacillus sp. DU-106, a newly isolated member of Bacillus cereus group, exhibits the predominant ability to produce L-lactic acid. The probiotic potency of test strain revealed its survivability at acidic pH, bile salts and viability in simulated gastric juice in vitro. The acute oral toxicity test indicated its no toxicity to laboratory mice in vivo. We further determined the complete genome of strain DU-106 to understand genetic basis as a potential probiotic. It has a circular chromosome and three plasmids for a total genome 5,758,208 bp in size with a G + C content of 35.10%. Genes associated with lactate synthesis were found in the DU-106 genome. We also annotated various stress-related, bile salt resistance, and adhesion-related domains in this strain, which likely provide support in exerting probiotic action by enabling adhesion to host epithelial cells and survival under gastrointestinal tract. Moreover, strain DU-106 genome lacks the virulence genes encodes cereulide synthetase, enterotoxin FM, and cytotoxin K. These phenotypic and genomic probiotic potencies facilitate its potential candidate as probiotic starter in food industry.