Shunxi Wang

Condensed tannins affect bacterial and fungal microbiomes and mycotoxin production during ensiling and upon aerobic exposure

ABSTRACT Purple prairie clover (PPC; Dalea purpurea Vent.) containing 84.5 g/kg dry matter (DM) of condensed tannin (CT) was ensiled without (control) or with polyethylene glycol (PEG) for 76 days, followed by 14 days of aerobic exposure. Changes in fermentation characteristics were determined, and the composition of bacterial and fungal communities were assessed using metagenomic sequencing. The addition of polyethylene glycol (PEG) that deactivated CT at ensiling increased (P < 0.05 to ∼0.001) soluble N, nonprotein N, lactic acid, total volatile fatty acids, ammonia N, deoxynivalenol (DON), and ochratoxin A (OTA) but decreased (P < 0.001) pH and water-soluble carbohydrates. The concentrations of DON and OTA increased (P < 0.001) for both silages, with the extent of increase being greater for control than for PEG-treated silage during aerobic exposure. The PEG-treated silage exhibited higher (P < 0.01 to ∼0.001) copy numbers of total bacteria, Lactobacillus, yeasts, and fungi than the control. The addition of PEG decreased (P < 0.01) bacterial diversity during both ensiling and aerobic exposure, whereas it increased (P < 0.05) fungal diversity during aerobic exposure. The addition of PEG at ensiling increased (P < 0.05) the abundances of Lactobacillus and Pediococcus species but decreased (P < 0.01) the abundances of Lactococcus and Leuconostoc species. Filamentous fungi were found in the microbiome at ensiling and after aerobic exposure, whereas Bacillus spp. were the dominate bacteria after aerobic exposure. In conclusion, CT decreased protein degradation and improved the aerobic stability of silage. These desirable outcomes likely reflect the ability of PPC CT to inhibit those microorganisms involved in lowering silage quality and in the production of mycotoxins. IMPORTANCE The present study reports the effects of condensed tannins on the complex microbial communities involved in ensiling and aerobic exposure of purple prairie clover. This study documents the ability of condensed tannins to lower mycotoxin production and the associated microbiome. Taxonomic bacterial community profiles were dominated by Lactobacillales after fermentation, with a notable increase in Bacillus spp. as a result of aerobic exposure. It is interesting to observe that condensed tannins decreased bacterial diversity during both ensiling and aerobic exposure but increased fungal diversity during aerobic exposure only. The present study indicates that the effects of condensed tannins on microbial communities lead to reduced lactic acid and total volatile fatty acid production, proteolysis, and mycotoxin concentration in the terminal silage and improved aerobic stability. Condensed tannins could be used as an additive to control unfavorable microbial development and maybe enhanced feed safety.

Characterization of Condensed Tannins from Purple Prairie Clover (Dalea purpurea Vent.) Conserved as either Freeze-Dried Forage, Sun-Cured Hay or Silage

Conservation methods have been shown to affect forage nutrient composition and value, but little information is available about the effect of forage conservation on plant condensed tannins (CT). The objective of this study was to assess the effects of conservation method on the concentration, chemical composition and biological activity of CT. Whole-plant purple prairie clover (PPC, Dalea purpurea Vent.) was harvested at full flower and conserved as freeze-dried forage (FD), hay (HAY) or silage (SIL). Concentration of CT in conserved PPC was determined by the butanol-HCl-acetone method. Structural composition, protein-precipitation capacity and anti-bacterial activity of CT isolated from conserved forage were determined by in situ thiolytic degradation followed by HPLC-MS analysis, a protein precipitation assay using bovine serum albumin and ribulose 1,5-disphosphate carboxylase as model proteins and by an Escherichia coli (E. coli) growth test, respectively. Conservation method had no effect on concentration of total CT, but ensiling decreased (p < 0.001) extractable CT and increased (p < 0.001) protein- and fiber-bound CT. In contrast, hay-making only increased (p < 0.01) protein-bound CT. Regardless of conservation method, epigallocatechin (EGC), catechin (C) and epicatechin (EC) were the major flavan-3-ol units, and gallocatechin (GC) was absent from both terminal and extension units of PPC CT. The SIL CT had the lowest (p < 0.001) EGC, but the highest (p < 0.01) EC in the extension units. Similarly, SIL CT exhibited a lower (p < 0.001) mean degree of polymerization (mDP), but higher (p < 0.001) procyanidins (PC) than FD or HAY CT. The protein-precipitating capacity of CT in conserved PPC ranked (p < 0.001) as FD > HAY > SIL. E. coli growth n M9 medium was inhibited by 25–100 µg/mL of CT isolated from FD, HAY and SIL (p < 0.05), but preservation method had no effect on the ability of CT to inhibit bacterial growth. The results demonstrated that ensiling decreased the extractability and protein-precipitating capacity of CT by increasing the proportions of PC. Purple prairie clover conserved as hay retained more biologically active CT than if it was conserved as silage.

Achievements of Fresh Keeping Techniques of Grapes

Abstract. Abstract: Based on the analysis of the main problems existed in the storage period, the effect and the research status of 14 species main preservation technologies had been reviewed world-wildly, which focused on describing and prospecting researches such as ozone processing, gas adjustable storage technology, biological control coated film technology etc. This paper aims to provide a theoretical review on the storage technology of grapes harvest.

A Cooperative Method for Detemination of Aflatoxin B1 in Tea by Immunoaffinity Column Purification and HPLC-FLD with Post-Column Photochemical Derivatization

Abstract. A method for determination of aflatoxin B 1 in tea by using HPLC-FLD with photochemical derivatization after immunoaffinity column purification was developed, and the determination conditions of sample were optimized in this paper. The sample was purified by immunoaffinity column using the mobile phase composed of methanol and water (60:40, v/v), then quantified with fluorescence detection after photochemical derivatization. The results showed that this method to determine aflatoxin B 1 was finished within 12.5 min under the optimum conditions. The standard curve had a good linearity when the aflatoxin B 1 was in the range of 0.2i½ž20 I¼g/L. The correlation coefficient, the limits of detection and quantification, the recovery rate and the relative standard deviation of the method were 0.9999, 0.03 ng/g (S/N=3), 0.11ng/g (S/N=10), 80%i½ž90% and 1.4%i½ž2.4% (n=5), respectively. This is a very simple method and it has high sensitivity and good repeatability, which is applicable to determine the content of aflatoxin B 1 in tea sample.