Synopsis

Previously, we have learned that Red meat has a beneficial property for humans, from an evolution’s point of view to the prevention of heart disease, diabetes, and cancer. Awareness as consumers remains a sound objective across numerous disciplines; therefore, as consumers, it is crucial to be informed from different sources. Now, from what do these benefices come from? These benefactors are called fatty acids. We will review their localizations, their variations, and finally, what may affect them.

Commentary

This limited series of the occasional e-letters are comprised of five (5) articles and will appear over a five-month, one per month, which began on the 1 February and will be accessible through Facebook/enhancedexchange. Part (3) three summarizes the biology aspect of fatty acids present in red meat, this collection of (5) five E-letters summarize the biology of each extrinsic trait to set the stage for discussions of production system elements that impact each trait. Because of the pervasive impact of total fat content and fatty acid profile on beef quality, especially aspects concerning appearance, tenderness, juiciness, flavor, and healthfulness, the biological considerations and the production system elements impacting these issues are distributed throughout this text. This third section will focus on the healthy properties that are present as there is from consuming fatty acids contained in red meat. The beneficial total fat content, fatty acids, and nutrients in red meat are considerable, as they are the optimal source for human consumption, exceeding those issues within that of other commercial meat.

Analysis

Subcutaneous Adipose Fatty Acids

Studies affirm the animal gets fatter; the fatty acids profile also changes. Wood et al. (2008) observed an increase in the proportion of C18:1cis_ 9 in subcutaneous adipose tissue of Angus crossbred steers fed a concentrate diet between (14) fourteen and (24) twenty-four months of age. Carcass fat significantly increased during the period as shown by the carcass fat score. The proportion of C18:0 fell during the same period and this allowed the proportion of C18:2n _ 6 to remain constant. Wood et al. (2008) also reported that the proportion of (CLA) increased with fatness. Apparently, as the ruminant animal fattens and ages, subcutaneous fat becomes more unsaturated and, therefore, more flavorful, and healthful.

Intramuscular Fatty Acids

Early work on ruminant animal fatty acid composition focused on subcutaneous adipose tissue since that is where, at least for animals adapted to temperate climates, the bulk of the body’s fatty acids are located. Later work focused on intermuscular and intramuscular fat of different muscles because these depots have greater significance as food. Fat in muscle also contains higher concentrations of the long-chain n _ 6 and n _ 3 fatty acids, now recognized to have import in red meat flavor and human nutrition, as discussed in this text. The overall level of the fatness of the animal (and of the muscle) has an essential impact on fatty acid profile resulting from the different biological roles played by divergent fat components of neutral lipid and phospholipid. Phospholipid plays a vital role in the function of cell membranes and, therefore, it is under homeostatic control being relatively constant in amount and composition regardless of animal fatness. In young, lean animals, genetically lean animals, or animals fed a low energy diet the lower C18:1cis _ 9 and higher C18:2n _ 6 content of phospholipid is a significant component of total muscle fatty acid composition.

But, as body fat increases, neutral lipid predominates in overall fatty acid composition (Wood et al., 2008). Wood et al. (2008) examined the fatty acid profile of neutral lipid and phospholipid in Angus cross and Holstein–Friesian cattle of three ages (14, 19, and 24 months) on two diets (concentrate and grass silage) fed from (6) six months of age. They found that neutral lipid increases in importance as fattening proceeds, although the level of phospholipid remains relatively constant. Next, for Angus, the concentration of phospholipid in total lipid fell from (30%) thirty percent at (14) fourteen months to (12%) twelve percent at (24) twenty-four months and a concurrent increase in C18 accompanied this:1cis _ 9 and a decrease in C18:2n _ 6 in total lipid (Wood et al., 2008). This alteration in unsaturated fatty acid composition as the animal ages provides evidence of the critical role of stearoyl Co-A desaturase as a determinant of ruminant fatty acid composition and not dietary fat consumption as was previously thought.

Muscle Differences

Sexten et al (2012) found that the longissimus had more saturated fatty acids (43.94 vs. 35.76%) and less unsaturated fatty acids (56.90 vs. 66.19%) than the semitendinosis. Percent of total monounsaturated fatty acids was higher in semitendinosis than longissimus (51.05 vs. 41.98%). They attributed these changes to changes in Δ9-desaturase activity. The desaturase index indicated that the semitendinosis has more Δ9-desaturase activity than longissimus.

Genetic Effects on Fatty Acid Profile

Unlike many other traits important in cattle production, individual fatty acids are synthesized in vivo through well-known anabolic pathways. Research finds, it is likely that only a few genes determine the results among-animal variation in fatty acid composition (Kelly et al., 2014). Candidate genome-wide association studies have been performed yielding polymorphisms associated with differences in fatty acid composition, located on the genes fatty acid synthase (FASN) andstearoyl-CoA desaturase (SCD); Zhang et al., 2008, 2010; Mannen, 2011; Matsuhashi et al., 2011; Orru et al., 2011; Uemoto et al., 2011; Li et al., 2012; Uemoto et al., 2012; and Yokota et al., 2012).  Abe et al. (2008) reported an association between a region on chromosome (19) nineteen covering FASN and associations between (5) five fatty acids (C14:0, C14:1, C16:0, C16:1, C18:1c) and (313) three hundred thirteen microsatellite markers on (178) one hundred seventy-eight genotyped animals.

Other workers have found SNP in FASN to be associated with C14:0, C15:0, C16:0, and C18:1c9 in Angus, in crossbred cattle, in Jersey-Limousin,  and Wagyu (Zhang et al., 2008; Li et al., 2012; and Uemoto et al., 2011). Another candidate gene confirmed by Kelly et al. (2014) is SCD. The gene coding for SCD is located on chromosome (26) twenty-six (Chung et al., 2000; Smith et al., 2006; and Kelly et al., 2014), where (87) eighty-seven associations were identified including associations with C14:1c9, C16:1c9, C16:0, and C19:0. Several significant SNP were present across 5.9 Mb. This region has previously been linked to differences in fatty acid composition for Wagyu (Matsuhashi et al., 2011; and Yokota et al., 2012), for Hanoo cattle (Oh et al., 2011), and for Simmental (Orru et al., 2011). Kelly et al. (2014) reported that for both Bos taurus and Bos indicus breeds, the SNP with the lowest P-value within this region (Bovine HD4100017752) explained large proportions of the genetic variance in C14:1c9 (13.16%,) and C19:0 (10.26%).

Animal Diet Effects on Fatty Acid Profile

Several studies have shown that dietary n_6 and n_3 PUFA can be incorporated into subcutaneous and intramuscular fat of ruminants despite the biohydrogenation of dietary fatty acids in the rumen (Wood et al., 2008). Wood et al. (2008) surmised that ruminants preferentially incorporate essential fatty acids, with their crucial metabolic roles, into intramuscular fat rather than storing them in subcutaneous fat. Wood et al. (2008) reported that as the animal fattens, the proportion of C18:2_6 in intramuscular fat decreases in a curvilinear fashion plateauing at 6 g/100 g total lipid, concluding that as the animal fattens, the proportion of intramuscular fat from phospholipid declines. They surmised that, as the animal fattens, the phospholipid fatty acid component of intramuscular fat remains constant, but neutral lipid (having higher proportions of saturated and monounsaturated fatty acids) increases markedly diluting the phospholipid. Wood et al. (2008) also concluded that animals fed a concentrate diet as compared to a grass silage diet had a higher affinity for incorporation into phospholipid molecules in intramuscular fat and reduced biohydrogenation in the rumen. The reduced ruminal biohydrogenation in concentrate diets has been attributed to shorter residence time in the rumen and particularly with small particle size feeds and C18:2n_6-rich concentrate diets (Doreau and Ferlay, 1994; Wood et al, 2008;  and Scollan et al., 2001).

Polyunsaturated Fatty Acids and their Metabolic Products

Body fats are, in part, derived from the diet, but also endogenous synthesis. The considerable variation in dietary influences on body fat composition led Shorland (1950) to classify animals as either heterolipoid (lacking resemblance to dietary fat) or homolipoid (animals that readily incorporate dietary fatty acids into their fat depots). Monogastric animals are uniformly considered to be homolipoid, while ruminants are heterolipoid (Dugan et al., 2011). Since ruminants are vegetarians, they consume mostly unsaturated fatty acids. These UFA are Reduced into saturated fatty acids and a limited amount of unsaturated fatty acids containing trans double bonds through biohydrogenation by rumen microbes (Reiser 1951; and Shorland et al. 1955). The diversity of intermediates produced during biohydrogenation of the significant polyunsaturated fatty acids in feed was subsequently investigated (Shorland et al. 1957), and pathways for linolenic acid (Ward et al. 1964; Wilde and Dawson 1966; and Kepler and Tove 1967) and linoleic acid (Kepler et al. 1966) biohydrogenation were discovered. These workers recognized that the diversity of biohydrogenation intermediates could only be accounted for by the existence of multiple pathways involving multiple ruminal microorganisms (Kepler et al.1966).

Fatty acid metabolism consists primarily of synthesis by elongation and desaturation and degradation by oxidation (Dugan et al., 2011). However, fatty acid metabolism in the rumen is dependent primarily on a diet, but is also given an animal signature in that individual animals vary as to prevalent rumen conditions giving rise to among-animal differences in predominant species of lipid-metabolizing microorganisms. Because of the importance of different animal microbial signatures associated with individual animal ruminal conditions, the findings of one experiment might not be applicable to other experiments or production situations unless feeding, management, and resulting rumen conditions are similar. Even at this, individual animal variation can be considerable (Kraft et al. 2008; and Aldai et al. 2011). Apparently, variation in rumen digestive kinetics, including the rate of digestion and residence time in the rumen associated with both the feedstuff and the physiology and behavior of the animal, impacts the fatty acid profile in intramuscular fat and can impact both flavor and healthfulness of the red meat.

Current knowledge of polyunsaturated fatty acid biohydrogenation in the rumen has been reviewed by  Harfoot and Hazelwood (1997), Jenkins et al. (2008), Lourenco et al. (2010), and Dugan et al. (2011). Rumen bacteria were originally thought to saturate PUFA because, under ruminal anaerobic conditions, PUFA could act as terminal electron acceptors and maintain oxidation/reduction cycling of nucleotides required for substrate-level phosphorylation (i.e., adenosine triphosphate synthesis). This process aids the efficiency of ruminal fermentation by providing a productive electron sink instead of the alternative of methane production embodying an energy loss to the animal as well as a greenhouse gas to the environment. Although there may be merit in this hypothesis (in that the mechanism is physiologically useful to the ruminant), a more recent and now widely accepted explanation is that polyunsaturated fatty acids are toxic to bacteria, and biohydrogenation neutralizes their effects in the rumen (Dugan et al., 2011).

Conjugated Linoleic Acid

Pariza et al. (1979) were the first to discover an extract from pan-fried ground beef that reduced the rate of mutagenesis. The active compound in the extract was later determined to be a conjugated linoleic acid (Ha et al. 1987). Thus, the consumption of beef could result in a positive health effect. Dietary conjugated linoleic acid has been associated with the prevention of tumor development in rats (Cesano et al., 1998). Beef is a relatively good source of conjugated linoleic acid (Chin et al., 1992). These discoveries led to considerable scientific activity designed to enrich concentrations of conjugated linoleic acid in beef (Dugan et al., 2011). The conjugated linoleic acid enrichment of beef has, however, been difficult to accomplish (Dugan et al., 2011).

It is widely known that beef is a natural source of conjugated linoleic acid and that it is derived from dietary polyunsaturated fatty acids (Dugan et al., 2011). However, because conjugated linoleic acid is an intermediate and not the resulting end or by-product of polyunsaturated fatty acid ruminal biohydrogenation, attempts to increase its concentrations presents challenges (Dugan et al., 2011). The concentration of conjugated linoleic acid in beef is usually less than (1%) one percent of total fatty acids (Dugan et al., 2011).

Vaccenic and Rumenic Acids

Bertram (1928) first reported the occurrence of trans double bonds in ruminant products; he found small amounts of an unsaturated fatty acid in beef and mutton fat and in butterfat. This finding indicated the presence of the trans isomer of an unsaturated fatty acid in ruminant products. Bertram (1928) characterized this fatty acid as 9, t11-18:1, which he named vaccenic acid. Booth et al. (1935) reported a seasonal change in butterfat with an increased absorbance at 230 nm in the summer, a wavelength now known to be indicative of conjugated linoleic acid (Dugan et al., 2011). Griinari et al. (2000) found that rumenic acid (9, t11-18:2), the primary natural isomer of conjugated linoleic acid in ruminant products, does not originate directly from the rumen. Instead, only small amounts of conjugated linoleic acid escape the rumen, and trans-C18:1 fatty acids are the primary biohydrogenation intermediates available at the animal tissue level. These absorbed fatty acids are subsequently desaturated in the tissues of ruminants by Δ 9-desaturase.

Therefore, challenges to increase conjugated linoleic acid in beef are reduced to methods conducive to providing the rumen conditions favorable for bacterial species that synthesize vaccenic acid, while preventing conditions leading to complete biohydrogenation to stearic acid (C18:0). As shown in the section, Increasing, The Healthfulness of Red Meat Through the Enhancement of Production System Elements section, Part (4!) feeding cattle sunflower seeds or flaxseed enhances the levels of linoleic and linolenic acids in beef (Kronberg et al., 2006; and Nassu et al., 20 07, 2011). Ruminal bacterial biohydrogenation of linoleic acid produces vaccenic and rumenic acids, whereas biohydrogenation of linolenic acid produces these as well as t11, c15-18:2, and conjugated linolenic acid. Intramuscular fat content and fatty acid profile, however, can vary among animals consuming the same diet (Dugan et al., 2011). Duckett, Pratt, and Pavan (2009 ) fed either supplemental corn oil or corn grain to steers grazing endophyte-free tall fescue pasture. They reported that steers finished on pasture with no supplement had (2.82%) two-point eight two percent vaccenic acid in their backfat. Supplementation with corn yielded subcutaneous fat with (2.28%) two-point two eight percent vaccenic acid while supplementing corn oil had (6.19%) six-point one nine percent. Subcutaneous rumenic acid concentrations were parallel to the results with vaccenic acid in those concentrations for pasture alone was (0.74%) point seven four percent supplemented with corn, (0.72%) point seven two and corn oil, (1.14%) one-point one four percent.

Challenge at hand is the equation to accomplish increased concentrations of ruminal biohydrogenation intermediates in beef such as rumenic and vaccenic acids, the final step of biohydrogenation from trans-18:1 to 18:0 must be halted. Reducing rumen pH by feeding grain has been demonstrated to inhibit ruminal lipolysis and biohydrogenation in dairy cattle (Chilliard et al. 2007). Since lipolysis is the first step that enables biohydrogenation, reducing the extent of lipolysis also has the potential to promote ruminal bypass of dietary lipids allowing them to be absorbed in the lower tract (Dugan et al., 2011). Biohydrogenation of dietary PUFA by rumen microbes usually results in the formation of a broad spectrum of intermediates, including monounsaturated cis- and trans-fatty acids (cis- and trans-18:1) and CLA isomers (Scollan et al., 2014). Understanding the mechanisms underlying the biosynthesis of single CLA and trans-18:1 isomers in the rumen is essential because the fatty acids flowing out of the rumen are the substrates for incorporation and de novo biosynthesis in the different adipose depots (Chilliard et al., 2007; Shen et al., 2011; Shingfield et al., 2013; and Scollan et al., 2014).

The primary CLA isomer in ruminant muscle is cis-9, trans-11 CLA which accounts for more than (80%) eighty percent of the total CLA while trans-10, cis-12 CLA comprises (3–5%) three to five percent of the total CLA. Even though most of the bioactive fatty acid isomers in these depots are those produced by biohydrogenation by rumen microbes, the diet also plays a role (Dannenberger et al., 2005; and Mapiye et al., 2013). A comparison of feeding a mix of barley and silage to animals grown entirely on pasture has shown an increase in beef CLA from (3) three to (14) fourteen mg/g fat (Poulson et al., 2004). Research with both animal models and humans have indicated that two CLA isomers, cis-9, trans-11 CLA and trans-10, cis-12 CLA, show biological activity including prevention of different types of cancer, cardiovascular health, decreasing body fat, and improved immune response (Dilzer and Park, 2012; and Mitchell et al., 2012). These effects were predominantly observed in animal models but were inconsistent in human studies (Dilzer and Park, 2012; and Mitchell et al., 2012).

Trans Polyunsaturated Fatty Acids

Trans fatty acids are fatty acids with a double bond in a trans configuration whereas the cis configuration is more common. Trans-octadecenoic acids are the most common trans fatty acids found in industrially processed partially hydrogenated vegetable oil. Some of these fatty acids have been reported to have detrimental effects on human health and are the basis for the perceived detrimental effect of trans fatty acids on health (Gebauer et al., 2007; and Mozaffarian et al., 2009). This prompted the requirement for the mandatory listing of trans FA content on food labels. However, trans FA in ruminant-derived milk and meat products are known to have greater proportions of trans-11 vaccenic (C18:1 trans-11) acid and cis-9, trans-11 CLA than trans-octadecenoic acids. These ruminant-sourced trans fatty acids may have potential health benefits (Lock and Bauman, 2004). For example, cis-9, trans-11 CLA is synthesized endogenously by Δ9-desatuarase of vaccenic acid in ruminant adipose tissue and is known to have anticarcinogenic properties suggesting both of these trans fatty acids may be beneficial for human health (Lock et al., 2004).

Similarly,  beef is a source of other trans-fatty acids such as trans-16:1, trans-18:1 isomer, and trans containing CLA, few of which have been examined for bioactive properties (Leth et al., 1999; Precht et al., 2001; and Kadegowda et al., 2010). Palmitelaidic (C16:1 trans-9) acid that is found in beef fat has also been reported to have beneficial health effects (Mozaffarian et al., 2010). Mozaffarian et al. (2010) found that circulating palmitelaidic acid in adult humans was related to a favorable metabolic profile characterized as decreased adiposity, greater high-density lipoprotein cholesterol concentrations, decreased triacylglycerol, decreased insulin resistance, and reduced incidence of diabetes. They also reported that increased whole-fat dairy product consumption had a positive effect on circulating palmitelaidic acid, giving rise to the author’s suggestion that previously observed metabolic benefits of dairy product consumption could have been due to its impact on palmitelaidic acid content. In a companion study, Smit et al. (2010 ) reported that adipose palmitelaidic acid consumption was associated with reduced waist circumference, an index of visceral adiposity, but also was associated with increased skinfold thickness, an index of subcutaneous adiposity.

Kadegowda et al. (2013) hypothesized that the reported effects of palmitelaidic acid (Mozaffarian et al., 2010; and Smit et al., 2010)  could be due to altered lipogenesis and lipid cell viability, and those red meats could also be sources of palmitelaidic acid in the human diet. Kadegowda et al. (2013) reported that beef longissimus contained palmitelaidic acid (10–17 mg/100 g longissimus). The animals fed forage diets had higher concentrations of palmitelaidic acid in longissimus than those fed high concentrate diets. About (50%) fifty percent of palmitelaidic acid taken up by the adipocytes was elongated to trans-11 vaccenic acid, and about (8%) eight percent was desaturated to cis-9, trans-11 CLA, suggesting that cis-9, trans-11 conjugated linoleic acid was endogenously synthesized from palmitelaidic acid. As similar mechanisms of fatty acid elongation and desaturation exist in human adipocytes, the implication from the study of Kadegowda et al. (2013) is that dietary palmitelaidic acid content should be considered in addition to trans-11 vaccenic acid as sources of cis-9, trans-11 CLA in the human diet.

Conclusion

The older and fattened an animal gets, the healthier and increasingly, more savory the meat will become. In addition, the neutral lipid concentration increases as the animal grows, while the amount of phospholipid stays the same. This explains why stearoyl Co-A desaturase plays a significant role in determining the composition of ruminant fatty acids rather than dietary fat, as previously believed. To resume in few words, Δ9-desaturase activity influences the amount of saturated and unsaturated fatty acids present in red meat. Moreover, we know that potential targeted Genetic modifications, animal diet and digestive kinetics alter the fatty acid profile. Furthermore, one of the significant processes in the ruminant’s digestion is the biohydrogenation. It is a defensive response against dietary PUFA’s toxic effects on rumen bacteria. This mechanism is possible thanks to the presence of multiple ruminal microorganisms but this variability also makes studies more complicated as a successful case might fail to be repeated on other cattle if we are not in similar conditions.

Additionally, beef is a natural source of linoleic acid which has been associated with the prevention of rats’ tumor development. Accordingly, scientists tried to enhance the production of this beneficial molecule. One way that has been found is by inhibiting lipolysis (through a pH reduction in the rumen). Last but not least, it is essential to know that not all trans fatty acids are detrimental for our health (such as cis-9, trans-11 CLA, Palmitelaidic, etc.) However, is it the only way to change the red meat’s properties? Would we be able to change these characteristics if we made modifications to the production system? We want to proceed further, more in-depth on this controversial subject. Therefore, Please join us on the (1) first of of next month for Part (4!) four in order to learn more about Increasing the Healthfulness of Red Meat Through the Enhancement of Production System Elements. Thereafter, each month for our montly delivery of insightful, informative must-reads from some of the world’s scientific thinkers. Selected by our editors.

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