Abstract
Not only the needs and demand of the meat industry sponsor research on quality factors of beef products, but also investigation tasks that determine, above all, the possibility of scientific knowledge of the cow’s body. Beef is the most valuable meat products consumed by humans. Due to the complexity of the composite structure of the cow, it is difficult to argue that only one of the traits can affect the quality of products, but the role of fatty tissue in this context is irreplaceable. Fatty or adipose tissue is traditionally defined as the structure of the organism, consisting of small cells, lipocytes, with fatty inclusions. The chemical composition of these lipocytes varies not only between different animals but also between different organ systems of the same mammal. It is important to note that a thicker animal has not more lipocytes but their larger volume. Fat tissue performs a variety of functions, supporting homeostasis of the animal body. It was shown that the quality of beef in the context of the formation of adipose tissue is determined both genetically and by environmental factors. In this work, some breeds of cows were considered, and it was shown what their difference is. The official classification of steaks of beef depending on the degree of marbling is also given. Marbling as a determining factor in the quality of meat products is formed both on the molecular-genetic level and on the level of an adult animal. It was shown that cows of grain breeds have a large total content of fatty tissue. In addition, the age characteristics of the animal also influenced fat deposits.
Introduction
As a consumer, a human is interested in research to identify factors that directly or indirectly affect the quality of meat. Basically, it is the production characteristics — beef class, breeding method, type and quantity of feed, or genetic predisposition — that determine the taste, smell, and color of the meat product. Thus, it is the internal desire of researchers to make their contribution to the improvement of the quality of the created products that become the reason for the emergence and intensification of knowledge areas devoted to this problem.
However, it would be wrong to believe that only the consumer motives of the authors are responsible for the development of meat sciences. On the contrary, a deep understanding of the interrelationship between organic processes and the nature of their manifestations, the study of hereditary causes of the formation of the pathology of adipose tissue, as well as the definition of organoleptic characteristics of the product, determine the depth of case studies. In other words, the scientific value of such works is reduced not only to determining how to make more delicious meat but also to establishing the cause-and-effect relationships within the body. Moreover, it is possible that the effects discovered in the course of research will also be fair to the human body, which literally means the continuity of biological traits.
The value of this research work is to generalize the available information in the context of the extent to which adipose tissue affects the quality of beef. Taking into account the subjectivity of taste characteristics of meat products, the qualities will be understood as mechanical and organoleptic properties of the piece, such as juiciness, structurality, and value. Moreover, the author of this work has further developed the research topic and answered the questions concerning the factors of formation or pathology of adipose tissue, mutational processes in responsible proteins, and this tissue’s nature.
The Nature of Adipose Tissue
As a representative of a class of vertebrate mammals, cows have a complex multifunctional organism that defines the differentiated system’s integrity. Without focusing on other tissues and organ systems of cows, it should be noted that adipose tissue is an important component of the animal’s protective, humoral, and regulatory mechanisms. In terms of classical biology, it should be recognized that adipose tissue is traditionally understood as a cluster of fat cells separated by loose connective materials (Jiang et al., 2018). The structural unit of such tissue is the lipocyte, whose cell can reach a size of 100-150 microns. Moreover, it should be noted that larger animals have not more lipocytes, but their larger total volume. Most fat is deposited in the natural depot of the body: subcutaneous tissue, in the abdominal cavity, near the kidneys, intestines, and, for some breeds of cattle, in the tail area. In cattle of meat and dairy breeds, the fat is also located in the endomysium, perimysium, and epimysium, forming the fatty marbling of the meat, which is highly appreciated by cooks. On the contrary, in wild and elderly animals, fat deposits are mainly located in the fat depots and in very small amounts between the muscles.
It should be noted that the marbling of a piece of meat is understood as a special characteristic, laid, as a rule, on the genetic level. From the point of view of this meat is an ordinary veal but speckled with white mesh fat: it is a light and very soft fat with a very low melting point. Its chemical composition includes many monounsaturated fats, omega-3, and omega-6 fatty acids.
The multiplicity of localization of the genesis of adipose tissue inside the body determines its functions. Thus, the tissue of the animal’s back contains the remains of subcutaneous muscle tissue and often ingrown hair follicles: the main task of this layer is thermal regulation and protection against mechanical damage of the body. Fat kidney tissue consists of lipocytes surrounding the ureter and provides water and salt exchange, as well as protection of the organ. Cattle subcutaneous fat tissue contains many collagen fibers, which determines the structure and elasticity of the layer. Other functions of this tissue are redundant (because the body stores energy, which is consumed when not fed enough), endocrine, and immune.
The structure of adipose tissue is classically defined as a set of lipocytes, each of which contains a fatty drop. In such cells, the cytoplasm is poorly developed, and the nucleus is located at the periphery of the cell (Adipose Tissue, n.d.). In this case, between the cells, there are collagen, nerve, reticular, and elastic fibers, blood capillaries, which determine the nutrition and saturation of tissue. The chemical composition of the fat drop inside the lipocyte includes neutral fat with an admixture of saturated or unsaturated fatty acids combined with cholesterol molecules.
Beef-Cow Breeds
The hereditary signs of individual livestock populations cause a seemingly external difference between them. Furthermore, individual breeds of cows differ not only in appearance: it was observed that cows from different breeds are characterized by individual behavior patterns, metabolic processes, and chemical compositions of meat products (Hausman et al., 2016). In other words, the evaluation of the class of meat cows allows determining the most valuable and nutritious breed of animals. Some of the common cow varieties will only be briefly discussed here, after which beef classes will be evaluated.
Usually, Angus cows are monochrome: either black or red. Such cattle have a light head on a short, inconspicuous neck, and they do not have horns. The structure of animal bones is quite light and rarely exceeds 20% of the total body weight. The high nutritional value of this breed is determined by fatty and voluminous hips, and the meat yield, SMY, is relatively high (Aberdeen Angus, 2020). The Shorthorn breed of cow has tender and loose meat, and the animal itself usually has a reddish color. The SMY of this breed is the same or slightly higher than that for Angus one (How much meat, 2020; Beef Shorthorn, 2020). Next, Limousin cows are also highly valued by farmers, as they demonstrate advanced musculature and fine bone structure (Limousin, 2020). However, in terms of fat saturation, this breed is not very important because, although it has a relatively high SMY, the product is almost devoid of the fat layer. On the contrary, a group of cows called Wagyu has a high content of unsaturated fatty acids or marbling. This includes four different subgroups differentiated by SMY (Gotoh et al., 2018). All over the world, such meat is considered a delicacy and is expensive.
Marble Beef Classes
An important criterion of quality and nutritional value of meat products is the quantity and nature of the distribution of fat in it. Being a source of vital lipid components representing a complex mixture of compounds different in structure, playing their specific role in nutrition, fat determines the taste, species, and composition properties of meat. There are several classes of beef that differ from each other by the degree of marbling, which is determined experimentally. The standard practice is to cut steak in the area of the 12th rib and compare it with the standard. As a result of this procedure, the meat is given a marbling category: the higher the number, the better the quality of the meat.
Table 1. Classification of beef according to the degree of marbling or adipose tissue content (Hale et al., 2013)
Beef Quality
In the context of the task, it is important to determine the nature of adipose tissue’s influence on the quality of beef. Manipulated variables can be the chemical composition of lipocytes because it is known that unsaturated and saturated fatty acids affect the meat product’s final profile in different ways. Although meat fats are composed primarily of saturated fatty acids that do not demonstrate a double-bond connection in the molecule, some unsaturated fat content may also be detected. It should be recognized that there is no consensus in the literature about the nature of the influence of specific fat molecules on the taste of meat. Thus, for example, some authors believe that the content of unsaturated fatty acids should be reduced because they do not have taste characteristics and only create the form and type of fine meat (Lee et al., 2019). More specifically, the increase in omega-3 and omega-6 fatty acids was the reason for the reduction in the shelf life of products, as well as the creation of rancid taste and color (Wood et al., 2004).However, other researchers believe that when the level of mono- and polyunsaturated fatty acids in muscle tissue increases, the general organoleptic properties of beef increases (da Silva Martins et al., 2018). In search of a compromise, some authors point to the need for a balance between the two types of acids, believing that the degree of conformity between saturated and unsaturated fats should reach 1:0.4.
The cause of high or low-fat content in a cow’s body during life is largely determined by two factors: nutritional composition and genetic predisposition. PCR analysis has revealed differential genetic differences between high and low marbling in Korean Hanwoo livestock (Shin and Chung, 2016). More than a hundred differences in marbling- responsible genes were found, several dozens of which were strongly pronounced in the group with high marbling, while about a hundred in the group with low marbling. Among them, eight differences were selected, expressing the largest difference in expression levels between the two degrees of marbling. These genes can be classified as five candidate genes, homologous with known genes and biological functions: ATP6, TPI1, ACTA1, TNNT1, and MDH2.
At the same time, it should be recognized that similar work has been done on Limousin, Hereford, and Holstein cattle breeds. The purpose of this article was to identify genes associated with marbling compared to global gene expression in a semi-dry muscle (Sadkowski et al., 2014). Beef from the Limousin breed was low in intramuscular fat (0.53%), unlike the other two breeds, Hereford and Holstein (1.10% and 0.81% respectively). A comparison of molecular-genetic patterns for marble and fat-free beef muscles revealed significant differences in the expression of several hundred genes. This result suggests that the development of adipocytes and their precursors is related to the genetic patterns of the cow’s body. Therefore, an artificial increase in the percentage of adipose tissue can be studied at the genotypic level. The Sadkowski et al.’s results showed a high correlation between the presence of these genes and the content of intramuscular fat.
In this regard, it is necessary to discuss further the mutational effect of myostatin, an important protein that inhibits the growth and differentiation of muscle tissue. In natural conditions, the content of this substance in the body is limited, but in the case of hereditary mutations, a sharp increase in muscle mass is possible. An unfavorable effect for the consumer from this mutation is increased dryness of muscle meat and almost no fat layer. In addition, it has been shown that this mutation is not beneficial to the body because the mortality rate of these animals is higher (Wiener et al., 2009). This determines the need to find protective mechanisms that prevent myostatin from blocking and thus maintain beef quality.
An important factor in the formation of beef composition is the feed taken by animals during their life. Low levels of feeding young cows not only reduce their live weight but also dramatically reduces meat productivity while delaying the growth of muscle and fat tissue (Moisá et al., 2017). The result is a decrease in the yield of meat, protein, and fat (Mwangi et al., 2019). Therefore, feeding the young generation grown for meat should be biologically complete. These are just some of the differences that have been noticed and scientifically proven for two lines of cows fed on cereals (A) and on herbs (B).
- The color of beef fat B is always saturated yellow or even orange, while beef fat A is pale or white;
- Beef A’s actual meat fiber color is lighter, pinkish, while beef B, which grew on the grass, has a darker meat color, rich darker red.
- Beef A is fattier than beef B. The fatness of beef A is much higher. In other words, the grains of cows are more valuable than those of grasses (Hwang and Joo, 2017). Therefore, the marbling indicator is a clear sign of the presence of grain in the diet of a cow. In addition, some types of beef, such as Wagyu, are exclusively fed with grains to give the maximum meat marbling.
In addition, the age of the animal at the time of slaughter is an essential factor in the formation of fatty tissue. In the process of growth and development of animals, there are significant quantitative and qualitative changes associated with the increase in weight and change in the morphological composition of the carcass (Mancuso and Bouchard, 2019). Thus, as animals age, their slaughter weight and slaughter yield increase, the yield of individual cuts changes, and although muscle tissue growth slows down, the process of fat deposition increases (Bown et al., 2016). In other words, slaughtering a more mature animal will bring farmers more fat-enriched products. However, it should be considered that not only the presence of fat affects the taste of meat, but also the quality of muscle tissue: thus, slaughtering an older animal may not be an appropriate measure, and a compromise must be sought.
Conclusion
Summing up, it should be noted that in-depth research into the quality of meat products, and more importantly, the factors affecting this quality are the main purpose of the meat sciences. In this paper, the relationship between the formation of adipose tissue and its composition in the body of the cow and the resulting consumer value of the product was discussed in detail. It was shown that the composition of fatty molecules could include both saturated and unsaturated fatty acids, which affects the organoleptic properties. Although there is no unified academic opinion on the nature of this relationship, two sides of the discussion were presented, and the balance between the two types of acids was shown to be sufficient. Moreover, the relationship between animal nutrition type and fatty tissue formation has been demonstrated. Thus, if a cow has more cereals in its daily diet, then its body will be richer in fat. For consumers, this is interpreted as the marbling of beef, which is highly valued in the market. Finally, the work discussed several breeds of cows and emphasized the difference in meat yield, as well as the classification of marbled steaks.
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