Meat Fatty Acid Profile
Of the most important saturated fatty acids for human health, the fatty acids C14:0 and C16:0 are found, considered hypercholesterolemic, and the C18:0 considered as neutral for the influence on the cholesterol content (Dietschy 1998; Grundy and Denke 1990). Menezes et al. (2014) observed that the levels of C14:0 (1.64%), C16:0 (24.40%), and C18:0 (20.35%) in meat were not influenced by the feeding system, and together they represented 95.18% of the total SFA, a value close to that found in the present study. The C18:0, in addition to acting neutrally on human health, is believed to be responsible for many of the desirable characteristics of flavor and texture, that is imparted to long-chain saturated fatty acids (Menezes et al. 2014).
It is known that in grass-fed animals, linolenic acid (C18:3n-3) is the main substrate for biohydrogenation, which by bacterial activity (mainly from Butyrivibrio fibrisolvens) is converted to stearic acid (Kim et al. 2009; Maia et al. 2010; Ramos and Wallace 2010). Possibly, this ruminal biohydrogenation process was lower in the SS-1 group, which contributed to the fact that the meat of animals in this group had a higher content of C18:3n-3. Nevertheless, Duynisveld et al. (2006) did not observe differences between animals on pasture, animals on pasture supplementation, and confined animals, regarding the Myristic and Palmitic acid contents, but they observed higher values of stearic acid for animals grazing, concerning the other groups.
SS-1 showed higher C14:1 content, which may be associated with the concentration of Myristic acid (C14:0) since the amount of this acid influences the denaturation and formation of Myristoleic acid (C14:1) by the enzyme Δ9 desaturase 14 (De Smet et al. 2004). Thus, as the index of the enzyme Δ9 destroys 14 increases, the content of Myristoleic acid also increases. In agreement with what was observed in the present study, the activity of the Δ9 desaturase 14 enzyme was higher in the SS-1 group, likewise, the variation of C18:1n9cis is fundamentally associated with the action of the Δ-9 desaturase 18 enzymes, which was higher in the SS- group, being responsible for the desaturation of C18:0. Menezes et al. (2014), when comparing the oleic acid content of the diet offered to the animal and the meat, found that the meat with the highest oleic acid content did not come from the animal that was fed the diet with the highest oleic acid content, demonstrating that the biohydrogenation process of ruminants interferes with the content of unsaturated fatty acids.
C18:1n9cis is an essential acid in beef, which competes in reactions mediated by desaturases and elongases with linoleic and α-linolenic acids and their intermediate products (Toral et al. 2018; Christie 2014). In vitro research has shown that oleic acid can be isomerized to various C18:1 trans isomers, including vaccenic acid, a precursor to CLA, which makes for higher quality meat for the consumer (Dannenberger et al. 2004). On the other hand, oleic acid provides benefits to human health and has been highlighted as an anticarcinogenic agent, as it suppresses the expression of the Her-2/neu gene, one of those related to breast cancer, in addition to acting as a hypocholesterolemic agent, promoting the reduction of total and LDL cholesterol (Menendez et al. 2005; Mir et al. 2003; Schwingshackl and Hoffmann 2012).
Pasture feeding provides a higher content of n-3 fatty acids, especially C18:3n-3 in beef (Nuernberg et al. 2005; Rossato et al. 2010) what was observed in this work. What may have happened was that even the SS-1 group was fed only on pasture and, possibly, being the group with the highest rate of biohydrogenation, the forage-based feed showed the superiority of these n3 fatty acids (C18:3n3 and C20: 5n3), which allowed the levels to remain higher in the food consumed and this reflected in the final levels of the same in the meat. This same effect was observed by Reis (2017), working with ½Angus-Nelore animals and Nellore animals in the finishing phase on pasture. When comparing the C18:3n-3 content of the SS-1 group on pasture (0.70%) with other studies, the content presented was lower than those observed by Nuernberg et al. (2005) (2.22% in Simmental animals on pasture), Rossato et al. (2010) (1.45% in Nellore animals and 0.89% in Angus on pasture), which suggests that, in addition to diet, the breed can also influence the amounts of polyunsaturated fatty acids in meat.
Among the main important Omega3s in meat are EPA, DPA, and DHA. The values of EPA and DHA observed are between the levels reported in the literature for beef, from 0.05–2.13% for EPA and 0.02–0.20% for DHA, highlighting the influence of the feeding system on the content of these acids in the flesh. Nuernberg et al. (2005), observed EPA, DPA and DHA values of 0.08%, 0.29% and 0.05%, respectively, in animals in confinement vs. 0.94%, 1.32% and 0.17%, respectively in animals fed on pasture.
Arachidonic acid is part of the omega 6 families and is present in beef, characterized by being present in greater amounts in the meat of animals fed diets based on concentrate. In human health, it is of great importance in the first months of life, as it is a fundamental constituent of cellular structures and precursors of inflammatory mediators (Wood et al. 2008). Furthermore, C20:4n-6 is one of the two most important 20-carbon essential fatty acids, formed by desaturation and elongation of linoleic acid; the other is C20:5n-3, EPA, formed by the desaturation and elongation of α-linolenic acid; both are eicosanoid formers.
Conjugated linoleic acid (CLA) is characterized by being present in products of animal origin, it can be present in different forms or isomers, but the C18:2 isomers cis-9 trans-11, or rumenic acid, is of greater importance for presenting 80% of the total content of CLA; in ruminants, it is predominant in meat fat and stands out for being present in greater quantity in animals fed on pasture, in addition to being a fatty acid with multiplex benefits to human health. There are two pathways for the formation of CLA, one of the desaturations of trans-vaccenic acid by the enzyme Δ-9 desaturase and the other by the isomerization of linoleic acid through the fermentation produced by Butyrivibrio fibrisolvens in the rumen (Grinari and Bauman 1999; Jenkins et al. 2008). Values of 0.08–0.1% of CLA were reported in animals with different millet concentrations in taurine and zebu animals (Silva et al. 2014) and values of 0.50% and 0.66% were found in meat from Nelores and Angus animals, respectively fed pasture (Rossato et al. 2010). The levels of CLA observed in the present work are close to those reported. The higher values in the SS-1 group may be associated with the fact of greater biohydrogenation, which led to higher concentrations of this acid in the meat of pasture-fed steers, the same feat recorded by Daley et al. (2010), in a review of the fatty acid profiles of beef from grass-fed and grain-fed cattle.
In general, the beef fat composition can range from 45–55% SFA, 35–45% MUFA and around 5% PUFA. The values of the present work are among those reported in the literature. Lambertucci et al. (2013) found values of 48.15% (SFA); 45.32% (MUFA); and 7.04% (PUFA) in the meat of pasture-finished Nellore × Simmental crossbred steers. The difference observed in the total PUFA content is attributed to the presence of the enzyme delta-12-desaturase in plants, capable of converting oleic acid into linoleic acid and delta-15-desaturase and converting linoleic acid into α − linolenic acid (Darley et al 2010; Dervishi et al. 2010; Total et al. 2018), such that meat from grass-fed animals is characterized by having a higher PUFA content compared to supplemented or confined animals.
The average PUFA/SFA ratio was 0.06%, a lower value than those reported by French et al. (2000) of 0.13%, observed in meat from crossbred steers in different feeding systems.
The mean h: H ratio was 1.46%; in the literature, there are no limits or fixed values recommended, higher values of the ratio are related to healthier products, since they would be products with a higher content of hypocholesterolemic fatty acids beneficial to human health. According to Santos-Silva et al. (2002), 2.0% is considered as a reference value for h: H in beef.
SS-1 has a higher content of n-3, this is related to the fact that grasses have a greater amount of fatty acids from the omega 3 family, which leads to higher concentrations in the meat of animals fed with forage. The consumption of long-chain omega-3 fatty acids can be beneficial for humans, as they have anti-inflammatory action, since they decrease the production of inflammatory eicosanoids, as to replace arachidonic acid. The recommendation for the human diet is that consumption is only 3.59 times more omega-6 than omega-3 (Aferri et al. 2012; Darley et al. 2010). According to the review carried out by the same authors, the average n-6/n-3 meat ratio of the studies they cited ranged from 1.53 and 7.65 for grass-fed and grain-fed animals, respectively. In this work, despite having found a difference between the dietary strategies in the n-6: n-3 ratio, the results observed are within the optimal pattern suggested by nutritionists, since the recommended value is less than 4.0.
Unlike the harmful effects attributed to red meat, these characteristics presented in the nutritional indexes contribute beneficially to human health, to the reduction of the risks of developing cancer or possible coronary complications, the decrease of this ration-6/n-3, as it favors the formation of eicosanoids showing anti-inflammatory effects in addition to allowing reduction of platelet aggregation, blood viscosity, vasospasm and vasoconstriction (Harnack et al. 2009; Simopoulos 2008).
Given the results obtained, it can be concluded that the use of protein or mineral supplementation for grazing steers did not affect the total saturated fatty acid content of the meat. However, steers grazing with mineral supplementation have the meat with the highest composition of polyunsaturated fatty acids, mainly omega-3 and CLA, which provides a reduction in the n-6: n-3 ratio, highly related to human health.