Plant based strategies to improve the nutritional value of beef for the consumer

Project number:             7286

Work Area:                        Product Quality

Lead contractor:            IBERS

Partners:                           University of Bristol, University of Nottingham (LINK)

Start & end date:           01/04/07 – 31/03/12

Actual end date:            August 2013 (final report received)

 

The Problem

Beef is relatively high in saturated fatty acids compared to other meats.  It does contain potentially useful quantities of desirable n-3 fatty acids.  Plants provide the source for these desirable fatty acids to cattle and it may be possible to enhance the fatty acid composition of beef, making it less saturated and/or increasing further the n-3 fatty acid content, by changing the composition of the forage consumed.

This project was linked to the EU project ProSafe Beef.  The project examined the role that forage can play in modifying the fatty acid composition and quality of beef, and the resulting effect on health indicators.

 

Project Aims:

  1. To assess the degree of variation in both total lipid and individual fatty acids in perennial ryegrass and identify associated QTLs.
  2. To examine interactions between plant components and events in the rumen (lipolysis and biohydrogenation) which determine the ability of different plants to manipulate the fatty acid composition of beef.
  3. To assess the ability of plant-based strategies (based on PUFA-rich grasses) to produce beef with a fatty acid composition which is more consistent with current human health recommendations and consumer requirements, containing higher amounts of n-3-PUFA, CLA and lower levels of saturated fatty acids.
  4. To assess the impact of strategies imposed in objective 3 on the fatty acid composition of beef, (including PUFA, CLA, trans-fatty acids) and colour shelf life and sensory attributes of beef and beef products.
  5. To assess the impact of altering the fatty acid profile of beef lipids on plasma lipids and lipoproteins and the development of atherosclerosis in an animal model.

 

Approach:

Grass varieties were identified that are higher in desirable fatty acids.  These were selected and grown, fed to cattle and the resulting meat analysed.  Beef from animals fed the enhanced forage (and other supplemented diets) was fed to animal models to monitor the effect on health.

 

Results:

The extent of genetic variation in perennial ryegrass in total lipid content and the fatty acid composition of this lipid and identifying and mapping QLTs for desirable fatty acids was investigated in a ryegrass mapping population over a 3-year period and 2-cuts per season. The major fatty acid identified in grass were 16:0; 18:0; 18:1n-9; 18:2n-6 and 18:3n-3. As expected 18:3n-3 and 16:0 were the dominant fatty acids.  A significant effect of genotype and of cut, but little evidence of genotype by cut interaction was noted.  Broad sense heritabilities of concentrations of all the fatty acid constituents in the foliage of perennial ryegrass, except oleic acid were 0.5 or above. Such high heritabilities suggest that these traits can indeed be improved genetically. Significant QTLs for individual and and total fatty acids were found. The generation of a dense genetic map has also allowed to pinpoint the genomic regions underlying the traits, and the markers provide interesting leads for further analysis of these traits.

Rumen studies focused on two key areas related to plants (1) fate of plant chloroplasts in the rumen and (2) role of plant secondary components in altering lipolysis and biohydrogenation.  Studies demonstrated that in animals fed on “chloroplast rich feeds such as grass, rumen protozoa relative to bacteria are rich in polyunsaturated fatty acids (PUFA) and that this was related to their ability to engulf chloroplasts.  A study assessed whether increasing intra-protozoal chloroplast resulted in increased throughput of PUFA to the duodenum by comparing flow of protozoa to the duodenum post feeding of a diet low in chloroplast (straw:concentrate) and high in chloroplast (fresh grass). It was found that feeding a fresh grass diet to the steers resulted in a higher protozoal chloroplast content but did not result in their increased contribution to PUFA present at the duodenum. For reasons which are currently unclear, protozoa on grass diet were retained in the rumen. Developing strategies to increase intra-protozoal chloroplast flow to the duodeum would increase flow of beneficial fatty acids to the small intestine and through to muscle.

Studies confirmed that feeding red clover, compared to perennial ryegrass, containing the plant secondary component “polyphenol oxidase (PPO) reduced lipolysis.  However, PPO-containing cocksfoot did not reduce lipolysis, suggesting limited potential for grass PPO relative to red clover PPO to alter lipid profiles in beef.

The effects of plant secondary compounds (Catecholamines, Saponins, polyphenol oxidase (Trifolium pratenses (wildtype red clover) vs. Trifolium pratenses (genetically modified PPO gene 1 silenced red clover) and tannin (Lotus Japonicus (Low tannin) vs. Lotus pedunculatus (High tannin)) on lipolysis, biohydrogenation and the rumen microbial ecosystem were assessed in in vitro batch culture.  The studies demonstrated that (1) saponin (deodorase) was the most effective in reducing biohydrogenation and (2) that for maximum benefit of PPO in red clover it is essential that both the “substrate for the enzyme and the enzyme are present.

Two large scale beef production studies were conducted to assess the ability of plant-based strategies to produce beef with a fatty acid composition which is more consistent with current human health recommendations and consumer requirements. The first study, 40 Belgium Blue steers were fed on grass-based diets from weaning through to commencing a 120 day finishing period.  In this period cattle were fed on either grass silage or barley straw/concentrate with/without a lipid rich plant extract (referred to as PX). The amount of total lipid, neutral lipid, phospholipid, saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) in loin steaks did not vary between dietary treatments, but the amount of PUFA, n-6 and n-3 in the total lipid of meat were differentially affected by diet.  Animals receiving the forage-based diets had the lower amount of n-6 fatty acids, but higher concentrations of n-3 fatty acids (18:3n-3, EPA and DHA), compared to those fed on straw and concentrate.  Addition of PX to concentrate or forage increased the amount of n-3 fatty acids (18:3n-3) in muscle total lipid, with subsequent improvements in the n-6:n-3 ratios.  This study confirmed the benefits of grass feeding relative to concentrate in improving the content of omega-3 fatty acids in beef lipids.

The first, and rate-limiting, step of the conversion of 18:3n-3 to its long chain derivatives, EPA, DPA and DHA, is elongation to 18:4n-3 (stearidonic acid). Provision of a diet rich in 18:4n-3 may further enhance the incorporation of EPA, DPA and DHA in beef. The second beef study, involved 32 Charalois steers, examined the effects of feeding an oil containing stearidonic acid (18:4n-3; source echium oil; Echium plantagineum) relative to linolenic acid (18:3n-3; source linseed oil).  Addition of echium oil or linseed oil had no effect on the concentrations of total lipid, neutral lipid, phospholipid, SFA, MUFA or PUFA, compared to feeding forage alone. Additionally, the ratio of n-6:n-3 fatty acids, P:S were similarly unaffected by diet, as was the concentration of EPA+DHA in the total lipid of M. longissiumus.  In both studies described above, diet had little effect on colour shelf-life or sensory properties of the beef.

A series of studies were conducted to examine the effects of altering the fatty acid profile of beef lipids (beef from forage versus concentrate fed animals) on plasma lipids and lipoproteins and the development of atherosclerosis in an animal model, using the ApoE*3 Leiden mouse.  The effect of adding different oils (linseed oil, fish oil, rapeseed oil or echium oil) to the diet of the mice were also examined.  The differences in the fatty acid composition of forage versus concentrate fed beef were enough to induce some significant differences in mouse tissue fatty acids but had no overall effect on the development of atherosclerosis. Supplementing beef with relatively modest amounts of unsaturated fatty acid markedly reduced plasma cholesterol and development of atherosclerosis.  This effect was seen with all of the oils studied, but surprisingly, rapeseed oil (relatively rich in oleic and linoleic acid) was more potent than any of the n-3 PUFA rich oils studied.  While extrapolation of results in this animal model to humans should be done with caution, the results suggest that reducing the proportion of SFA in beef may be fundamentally more important that the type of fatty acid they are replaced with.

In conclusion, nutritional quality is an increasingly important factor contributing to food product quality. Much attention has been placed on increasing the content of n-3 PUFA in beef and other foods as increased consumption of long chain n-3 PUFA would be beneficial in improving health and well-being and reducing disease in man.  Green forage rich in the 18:3n-3 is an important tool to increasing delivery of n-3 PUFA through the ruminant animal into meat. As the 18:3n-3 is the building block of the long chain n-3 PUFA (EPA and DHA) feeding forage can increase these beneficial PUFA in meat. However, the levels of n-3 PUFA, 18:3n-3, EPA and DHA achieved by forage feeding fall below the level required to be able to claim that beef is either a “source or “rich-in n-3 PUFA (based on recommendations of the European Food Safety Authority).  Hence, it is essential that the two main factors influencing the levels of n-3 PUFA in beef lipids are further addressed, namely (1) strategies to enhance levels of 18:3n-3 in forage and subsequent delivery into the animal and (2) increased ability to reduce lipolysis and/or biohydrogenation in the rumen. Progress in genetic control of lipids in perennial ryegrasses is likely to help significantly. Increased knowledge of the fate of the lipid rich chloroplast in the rumen represents a very exciting opportunity to deliver more beneficial n-3 PUFA from rumen through to the small intestine and hence to meat lipids.

 

Planned activity:

This project has informed future research, and provided targets for plant breeders.  There are no direct messages for communication to producers.