Effects of pH and Concentrations of Linoleic and Linolenic Acids on Extent and Intermediates of Ruminal Biohydrogenation in Vitro

Abstract

Three experiments were conducted by in vitro incubations in ruminal fluid to investigate the effects of pH and amounts of linoleic and linolenic acids on the extent of their biohydrogenation, the proportions of conjugated linoleic acid (CLA) and trans-C18:1 as intermediates, and the ratio trans-10:trans-11 intermediates. The effects of pH and amount of linoleic acid were investigated in kinetic studies, and effects of the amount of linolenic acid were studied with 6-h incubations. With identical initial amounts of linoleic acid, its disappearance declined when the mean pH during incubation was under 6.0 compared with a mean pH over 6.5, and when the amount of linolenic acid increased from 10 to 180 mg/160-ml flask, suggesting an inhibition of the isomerization step of the biohydrogenation. Low pH decreased the ratio of trans-10:trans-11 intermediates. With initial amounts of linoleic acid increasing from 100 to 300 mg, the percentage of linoleic acid disappearance declined, but the amount that disappeared increased, without modification of the trans-10:trans-11 ratio, suggesting a maximal capacity of isomerization rather than an inhibition. Moreover, increasing initial linoleic acid resulted in high amounts of trans-C18:1 and an increase of C18:0 that was a linear function of time, suggesting a maximal capacity for the second reduction step of biohydrogenation. High amounts of initial linolenic acid did not affect the amounts of CLA, trans-C18:1, or the ratio trans-10:trans-11. Based on these experiments, a ruminal pH near neutrality with high amount of dietary linoleic acid should modulate the reactions of biohydrogenation in a way that supports CLA and trans-11C18:1 in the rumen.

In vitro study of dietary factors affecting the biohydrogenation shift from trans-11 to trans-10 fatty acids in the rumen of dairy cows

“…Moreover, when starch was added to the diet or the substrate, the pH was lowered. Although this precludes any definitive separation between the effects of starch and pH, an effect of pH is consistent with the observations of Troegeler-Meynadier et al (2003), and might be related to a decrease in the activity of D12-isomerases produced by B. fibrisolvens, whose optimal pH is 7.0 to 7.2 (Kepler and Tove, 1967). Consequently, to boost the D12-isomerisation, a preliminary selection of a trans-11 BH microflora by a lowstarch diet is necessary, and addition of LA in the culture, both acting as a BH substrate and increasing E1, optimises the trans-11 isomers balance.…”

“…Troegeler-Meynadier et al (2003) showed that increasing LA concentrations (from 100 to 300 mg of LA in 160 ml flasks, carried by soybean oil), decreased the LA BH efficiency, but increased the amount of LA that disappeared, suggesting a limit of the capacity of isomerisation rather than an inhibition. In our case, 90 mg of LA were added to 120 ml cultures as free FA.…”

Production of trans C18:1 and conjugated linoleic acid in continuous culture fermenters fed diets containing fish oil and sunflower oil with decreasing levels of forage

“…Total concentrations of CLA were highest in the HF, intermediate in MF, and least in LF indicating that CLA formation is favoured by high ruminal pH. Troegeler-Meynadier et al (2003) also reported more CLA accumulation in rumen cultures incubated at high than low pH. The predominate CLA isomer detected in the HF and LF were c9t11 CLA and t10c12 CLA, respectively.…”

“…The biohydrogenation of oleic, linoleic and linolenic acids was greater in HF and MF than LF diet. Wang et al (2002) and Troegeler-Meynadier et al (2003) also reported decreased biohydrogenation of linoleic and linolenic acids at low pH in vitro. Under in vivo conditions, Sackmann et al (2003) and Kucuk and Hess (2004) have shown that higher dietary forage levels increase biohydrogenation of dietary C18 unsaturated FA.…”

Effect of grain type and processing method on rumen fermentation and milk rumenic acid production

“…E-mail: john.kennelly@ales.ualberta.ca (Kramer et al, 2004). The concentrations of the intermediates in the rumen depends on the extent to which PUFA substrates are metabolized and are influenced by the initial concentration of dietary PUFA (Harfoot et al, 1973), passage rate, and rumen pH (Troegeler-Meynadier et al, 2003;Qiu et al, 2004). Altered rumen function resulting from a low rumen pH has been demonstrated to reduce the extent of PUFA biohydrogenation both in vitro (Martin and Jenkins, 2002) and in vivo (Kalscheur et al, 1997).…”