Effects of pH and fermentative substrate on ruminal metabolism of fatty acids during short-term in vitro incubation

New research development on trans fatty acids in food: Biological effects, analytical methods, formation mechanism, and mitigating measures

The trans fatty acids (TFAs) in food are mainly generated from the ruminant animals (meat and milk) and processed oil or oil products. Excessive intake of TFAs (>1% of total energy intake) caused more than 500,000 deaths from coronary heart disease and increased heart disease risk by 21% and mortality by 28% around the world annually, which will be eliminated in industrially-produced trans fat from the global food supply by 2023. Herein, we aim to provide a comprehensive overview of the biological effects, analytical methods, formation and mitigation measures of TFAs in food. Especially, the research progress on the rapid, easy-to-use, and newly validated analytical methods, new formation mechanism, kinetics, possible mitigation mechanism, and new or improved mitigation measures are highlighted. We also offer perspectives on the challenges, opportunities, and new directions for future development, which will contribute to the advances in TFAs research.

Effects of diet fermentability and supplementation of 2-hydroxy-4-(methylthio)-butanoic acid and isoacids on milk fat depression: 1. Production, milk fatty acid profile, and nutrient digestibility

The objectives of this experiment were to determine the effects of increased diet fermentability and polyunsaturated fatty acids (FA) with or without supplemental 2-hydroxy-4-(methylthio)-butanoic acid (HMTBa), isoacids (IA; isobutyrate, 2-methylbutyrate, isovalerate, and valerate) or the combination of these on milk fat depression (MFD). Ten Holstein cows (194 ± 58 DIM, 691 ± 69 kg BW, 28 ± 5 kg milk yield) were used in a replicated 5 × 5 Latin square design. Treatments included a high-forage control diet (HF-C), a low-forage control diet (LF-C) causing MFD by increasing starch and decreasing neutral detergent fiber (NDF), the LF-C diet supplemented with HMTBa at 0.11% (28 g/d), the LF-C diet supplemented with IA at 0.24% of dietary dry matter (60 g/d), and the LF-C diet supplemented with HMTBa and IA. Preplanned contrasts were used to compare HF-C versus LF-C and to examine the main effects of HMTBa or IA and their interactions within the LF diets. Dry matter intake was greater for LF-C versus HF-C, but milk yield remained unchanged. The LF-C diet decreased milk fat yield (0.87 vs. 0.98 kg/d) but increased protein yield compared with HF-C. As a result, energy-corrected milk was lower (28.5 vs. 29.6 kg/d) for LF-C versus HF-C. Although the concentration of total de novo synthesized FA in milk fat was not affected, some short- and medium-chain FA were lower for LF-C versus HF-C, but the concentrations of C18 trans-10 isomers were not different. Total-tract NDF apparent digestibility was numerically lower (42.4 vs. 45.6%) for LF-C versus HF-C. As the main effects, the decrease in milk fat yield observed in LF-C was alleviated by supplementation of HMTBa through increasing milk yield without altering milk fat content and by IA through increasing milk fat content without altering milk yield so that HMTBa or IA, as the main effects, increased milk fat yield within the LF diets. However, interactions for milk fat yield and ECM were observed between HMTBa and IA, suggesting no additive effect when used in combination. Minimal changes were found on milk FA profile when HMTBa was provided. However, de novo synthesized FA increased for IA supplementation. We detected no main effect of HMTBa, IA, and interaction between those on total-tract NDF digestibility. In conclusion, the addition of HMTBa and IA to a low-forage and high-starch diet alleviated moderate MFD. Although the mechanism by which MFD was alleviated was different between HMTBa and IA, no additive effects of the combination were observed on milk fat yield and ECM.

Effects of supplemental plant oils on rumen bacterial community profile and digesta fatty acid composition in a continuous culture system (RUSITEC)

Lipid supplementation of ruminant diets may trigger changes in the ruminal microbiota and in anaerobic digestion. Changes in the bacterial community composition and in the fatty acid hydrogenation caused by the addition of different supplemental plant oils to a high concentrate diet were investigated in vitro using RUSITEC (rumen simulation technique) fermenters. The control (CTR) diet was a high-concentrate total mixed ration for dairy sheep, with no supplementary oil. The other experimental diets were supplemented with olive (OLV), sunflower (SFL) or linseed (LNS) oils at 6% (dry matter basis). Four RUSITEC fermenters were used for each experimental diet, all inoculated with rumen digesta of sheep. Extent of dry matter and fat degradation, composition of the bacterial community and long-chain fatty acids in digesta were determined. The addition of plant oils increased (P < 0.001) apparent degradation of fat in the fermenters, whereas fermentation kinetics (gas production and average fermentation rate) were lower (P < 0.05) with the LNS than with the CTR diet. Hydrogenation of C18 unsaturated fatty acids (P < 0.05), in particular that of oleic acid (P < 0.001), and stearic acid proportion (P < 0.001) were reduced, and oleic acid proportion was increased (P < 0.001) with all oil supplements. Addition of OLV decreased linoleic and LNS increased α-linolenic (P < 0.001), whereas conjugated linoleic was increased with SFL oil (P = 0.025) and vaccenic increased with both SFL and LNS oils (P = 0.008). Addition of 6% OLV and LNS reduced (P < 0.05) microbial community diversity and quantity of total bacteria relative to the control. Some specific microbial groups were affected (P < 0.001) by oil addition, with less relative abundance of Clostridiales and Actinobacteria and increased Bacteroidales, Aeromonadales and Lactobacillales species. In conclusion, the supplementation of high-concentrate ruminant diets with plant oils, in particular from sunflower or linseed, causes shifts in the rumen microbiota and fatty acid hydrogenation in the rumen increasing the formation of vaccenic and conjugated linoleic acids.

Culture pH interacts with corn oil concentration to affect biohydrogenation of unsaturated fatty acids and disappearance of neutral detergent fiber in batch culture

Effects of culture pH and corn oil (CO) concentration on biohydrogenation (BH) of unsaturated fatty acids and disappearance of neutral detergent fiber (NDF) in batch culture were evaluated in a 2 × 3 factorial design experiment. Culture vessels (100 mL; 4 replicates/treatment per time point) included ground alfalfa hay plus CO at 0, 1, or 2% dry matter inclusion rate and were incubated at pH 5.8 (low pH) or 6.2 (high pH) for 0, 6, 12, 18, or 24 h. Effects of culture pH, CO, time, and their interactions were determined. Adding CO increased total fatty acid concentration in substrates to 1.01, 2.31, and 3.58% dry matter for 0, 1, and 2% CO, respectively. Corn oil concentration interacted with culture pH and resulted in different effects on BH of cis-9,cis-12 18:2 at low or high culture pH. After 24 h of incubation, low pH, compared with high pH, reduced disappearance of NDF by 35% and BH extent of cis-9,cis-12 18:2 by 31%. Increasing CO increased disappearance of NDF across pH treatments and decreased BH extent of cis-9,cis-12 18:2 at low pH and increased it at high pH over 24 h. Compared with high pH, low pH reduced concentrations of 18:0 by 31% and increased concentrations of trans-10,cis-12 18:2 and trans-10 18:1 by 110 and 79% after 24 h, respectively. Adding CO at low pH had greater effect on BH intermediates of cis-9,cis-12 18:2 compared with adding oil at high pH. In particular, increasing CO to 1 and 2% DM at low pH, compared with at high pH, resulted in a 36 and 46% reduction in the concentration of 18:0, an 84 and 131% increase in the concentration of trans-10,cis-12 18:2, and an 81 and 129% increase in the concentration of trans-10 18:1, respectively. Despite the interactions between culture pH and CO concentration, main effects across time were also significant for the response variables of interest. In conclusion, culture pH interacted with CO concentration to affect BH of UFA and disappearance of NDF in batch culture, as the effects were greater at low culture pH than at high culture pH.