4.4 Article

Metabolism of α-linolenic acid during incubations with strained bovine rumen contents: products and mechanisms

Journal

BRITISH JOURNAL OF NUTRITION
Volume 115, Issue 12, Pages 2093-2105

Publisher

CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0007114516001446

Keywords

Biohydrogenation; Conjugated linoleic acid; Conjugated linolenic acid; Linolenic acid; Rumen bacteria

Funding

  1. Finnish Ministry of Agriculture and Forestry
  2. Scottish Government Rural and Environment Science and Analytical Services Division
  3. Raisio Science Foundation
  4. August Johannes Agricultural Science Foundation
  5. Aino Tiura Agricultural Science Foundation

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Description of alpha-linolenic acid (cis-9, cis-12, cis-15-18 : 3, ALA) metabolism in the rumen is incomplete. Ruminal digesta samples were incubated with ALA and buffer containing water or deuterium oxide to investigate the products and mechanisms of ALA biohydrogenation. Geometric Delta 9,11,15-18 : 3 isomers were the main intermediates formed from ALA. An increase in the n + 1 isotopomers of Delta 9,11,15-18 : 3 was due to H-2 labelling at C-13. Isomers of Delta 9,11,13-18 : 3, cis-7, cis-12, cis-15-18 : 3 and cis-8, cis-12, cis-15-18 : 3 were also formed. No increase in n + 1 isotopomers of Delta 7,12,15-18 : 3 or Delta 8,12,15-18 : 3 was detected. Enrichment in n + 2 isotopomers of 18 : 2 products indicated that ALA metabolism continued via the reduction of 18 : 3 intermediates. Isomers of Delta 9,11,15-18 : 3 were reduced to Delta 11,15-18 : 2 labelled at C-9 and C-13. ALA resulted in the formation of Delta 11,13-18 : 2 and Delta 12,14-18 : 2 containing multiple H-2 labels. Enrichment of the n + 3 isotopomer of Delta 12,15-18 : 2 was also detected. Metabolism of ALA during incubations with rumen contents occurs by one of three distinct pathways. Formation of Delta 9,11,15-18 : 3 appears to be initiated by H abstraction on C-13. Octadecatrienoic intermediates containing cis-12 and cis-15 double bonds are formed without an apparent H exchange with water. Labelling of Delta 9,11,13-18 : 3 was inconclusive, suggesting formation by an alternative mechanism. These findings explain the appearance of several bioactive fatty acids in muscle and milk that influence the nutritional value of ruminant-derived foods.

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