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Molecules 2018, 23(3), 586; https://doi.org/10.3390/molecules23030586

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

1
Key Laboratory of Animal Nutrition and Feed Science (South China) of Ministry of Agriculture, Guangdong Key Laboratory of Animal Breeding and Nutrition, Institute of Animal Science, Guangdong Academy of Agricultural Science, Guangzhou 510640, China
2
Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, Lethbridge, AB T1J 4B1, Canada
3
College of Engineering, China Agriculture University, Beijing 100083, China
4
College of Animal Science and Technology, Yangzhou University, Yangzhou 225009, China
5
Chemistry and Biochemistry Laboratory, School of Agriculture, Policy and Development, University of Reading, Reading RG6 6AT, UK
*
Author to whom correspondence should be addressed.
Received: 1 February 2018 / Revised: 27 February 2018 / Accepted: 2 March 2018 / Published: 6 March 2018
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Abstract

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. View Full-Text
Keywords: tannin composition; purple prairie clover; conservation method; protein precipitation; Escherichia coli tannin composition; purple prairie clover; conservation method; protein precipitation; Escherichia coli
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Peng, K.; Huang, Q.; Xu, Z.; McAllister, T.A.; Acharya, S.; Mueller-Harvey, I.; Drake, C.; Cao, J.; Huang, Y.; Sun, Y.; Wang, S.; Wang, Y. Characterization of Condensed Tannins from Purple Prairie Clover (Dalea purpurea Vent.) Conserved as either Freeze-Dried Forage, Sun-Cured Hay or Silage. Molecules 2018, 23, 586.

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