02 Aug 2017 15 Sep 2017
Red meat as a source of protein
Meat and processed meat products are a vital source of protein, lipids and other nutritionally important functional constituents which are essential components in a human diet. The two main categories of meat are red and white meat. As per nutritional concepts, the red meat is referred to as the one which is reddish in appearance in raw state and has an elevated myoglobin content in it. Red meat category which is highly consumed by humans include beef, lamb, pork and processed meat products. White meat is the one with a pale appearance and mainly includes poultry, veal and rabbit.
Protein are macromolecules which are composed of long chains of amino acids and are referred to as the building block of the body as it is present in every single cell in the human body. It is vital to include protein containing food in the diet as it essential for major functions include growth and repair and is a major energy source of the body. Among the different food stuffs meat and meat products supplies the necessary protein in human diet. Protein is present in both the vegetarian and non-vegetarian food. As per the New Zealand nutrition foundation animal food as well as plant sources such as soya and quinoa supplies the essential amino acids which are important for the body functions. This essay specifically focusses on analysing the importance of "Red meat as a source of protein".
Nutrient profile of meat
A critical analysis on the nutritional composition of any food is essential for any study on human nutrition. Meat has become an integral part of human diet. Meat is a complex structured food which includes components of biological value such as micronutrients (minerals and vitamins), proteins, fats and low level of carbohydrates. As Per the Food Standards Australia New Zealand the meat includes the flesh with skeletal muscle and fat as well as offal which include the internal organs of the animal. Meat comprises about 75 % moisture content 20 % protein, 3 % lipid and 2 % soluble non-proteinaceous compounds (Briggs & Schweigert, 1990). Meat serves as a vital source of proteins, vitamins such as vitamin B6, B12 and vitamin D, Omega-3 unsaturated fatty acids and minor levels of trace elements such as zinc, iron, phosphorus, bioactive compounds like carnitine, carnosine, ubiquinone and several antioxidant compounds. All these nutritional contents of meat make it an essential component of human diet (Williams, 2007).
Importance of Protein in human diet
Proteins are nitrogenous compounds which are constituted of amino acids. There are about twenty aminoacids which are vital for the growth and other cellular functions. Amino acids are mainly categorised in two: essential and non-essential aminoacids. Non-essential aminoacids are those which can be synthesized by the body and those which cannot be synthesized by the human body and supplied via the diet are essential amino acids (Hoffman & Falvo, 2004).Animal protein is the appropriate source of protein as it includes the essential amino acid content in it and hence it is essential to in include animal based food in the diet. Animal based food include meat and meat products (Pighin et al., 2016).
Red Meat protein
Meat is composed of higher concentration of proteins which includes the "structural proteins such as myofibrillar protein, sarcoplasmic proteins and proteins that are present in connective tissue such as collagen and elastin (Pighin et al., 2016). Meat is a complete source of protein as it includes all essential amino acids such as lysine, threonine, methionine, phenylalanine, tryptophan, leucine, isoleucine, valine. Protein concentration differs in both raw and cooked meat as the nutrients get more concentrated during cooking process due to the depletion of water content in the meat and the meat proteins exhibit higher digestibility ratio. As per the studies, 100g of raw red meat contain about 20-25% of protein whereas in 100g of cooked red meat the protein content is about 28-36% as the protein profile is modified after the cooking process. Beef and pork are considered to have the highest protein content in them. The U. S Dietary Reference Intake (USDRI) recommend a daily intake of 0.8g/kg of protein for adults which is the basic requirement for the proper functioning of the body and this prescribed intake rate of protein by USDRI lowers the incidence of cardiovascular diseases, osteoporosis and diabetes particularly type-2 diabetes (McNeill, 2014).
Evaluation of meat protein quality
Protein digestibility corrected amino acid score(PDCAAS) is a standard methodology recommended by world health organization and food and agriculture organization (FAO/WHO) to estimate the protein quality. In this method the protein quality is estimated by "expressing the content of the first limiting essential amino acid of the test protein as a percentage of the content of the same amino acid content in a reference pattern of essential amino acids" (FAO/WHO, 1990). The resultant value obtained by this method was taken as the protein digestibility corrected amino acid score (PDCAAS) and highest possible score in this method is 1.0. As per the PDCAAS method the protein quality score of red meat is estimated to be 0.9 whereas the protein quality score is between 0.5-0.7 for plant based food. According to Schaafsma, the protein digestibility corrected amino acid score is considered to the reliable method for estimating the quality of proteins consumed in the human diet (Williams, 2007).
Table showing the protein quality rankings according to FAO/WHO (Williams, 2007).
Near infrared reflectance (NIR) spectroscopy is an ultra- sensitive, rapid and less complicated analytical technique that aids in the assessment of chemical constituents present in the meat sample (Osborne, Fearn, & Hindle, 1993).Near infrared spectroscopy is an advanced method that is widely employed in the quantitative analysis of fat, protein and moisture content in meat and meat products. The differentiation between various classes such as beef and kangaroo meat, chilled and non-chilled beef was possible by the near-infrared spectroscopy method. Sample preparation has a vital role in this method as the non-homogenised muscles absorb bulk amount of energy and generating a less accurate reflectance pattern in comparison with the non-homogenised muscle sample. Inaccurate preparation of meat samples adversely affected the clarity of the prediction of chemical composition of meat sample is equivalent to the protein quantity of the food sample.(Prieto, Roehe, Lavín, Batten, & Andrés, 2009)
Other nutritional constituents of red meat
Fat is considered as the important repository of energy that supplies the necessary fatty acids and serves as precursors for various metabolic mechanism in the body. The fatty acid content in red meat are saturated in nature because the unsaturated fatty acid is transformed to saturated form by the microbes present in the rumen. The major saturated fatty acids present in red meat are palmitic and stearic acid. The fatty acid content varies when the fat is trimmed off from the meat.(Gerber, 2007)
Vitamins are organic compounds that are present in minor concentration in food and are important for metabolic functions. The major vitamins present in meat and meat products include vitamin B12, B1 (thiamine), B6 and vitamin D. vitamin B6 acts as a coenzyme for several chemical reactions in the human body such as gluconeogenesis. The vitamin B6 concentration are expected to be in the range between 0.40-0.6mg/100g of meat. Vitamin B12 which is commonly known as riboflavin. The vitamin B12 involved in human metabolic process includes the Methyl cobalamin and 5-deoxyadenosyl cobalamin (Rivlin & Pinto, 2001). Vitamin B1 is vital for normal cellular functions and serves as a coenzyme in various chemical process in the body. (Gerber, 2007)
Minerals and trace elements
The major minerals which are prevalent in red meat are the iron and zinc. The highest concentration of these minerals is observed in beef and pork meat(Williams, 2007).The iron content present in red meat is the heme iron rather than the non-heme iron contained in plant based foods. The heme iron is readily absorbed by the human body and this absorption rate is enhanced by the protein present in red meat. In meat, the factors such as phytate, tannin, oxalate and fibres are absent in red meat which can adversely affect the iron absorption rate. Similarly, the zinc absorption from animal based food is relatively higher than that from plant based food stuffs. The vital trace element found in meat is the selenium which are an integral part of selenoproteins which includes enzymes that are involved in important process such as anti-oxidative defence mechanism, synthesis of thyroid hormone and nucleic acid (DNA), fertility and reproduction.(Gerber, 2007)
Emergence in the research of red meat as a source of high bioavailable irons, high grade protein and other essential nutrients is on high as great importance is given in the improvement of stamina and vitality. Middle age and beyond requires more consumption of high grade protein which is essential for the maintenance quality of life associated with the required muscle strength and mass. Protein causes a stimulation effect on the anabolism of muscle protein. (McAfee et al., 2010)Amino acids present in red meat are branched chain amino acids, which are necessary for the synthesis of protein. Red meat contains the highest amount of branched chain amino acids. (Ford & Caspersen, 2012)
Previous studies reveal people with excess intake of red meat have been found to have higher cholesterol and higher plasma concentration of total cholesterol and Low-density lipoprotein (LDL) cholesterol and triglycerides(TG) as compared to low and medium consumer of red meat as well as vegans and vegetarians. There have also been studies showing significant relation between red meat and risk of colon cancer. Cooking red meat at higher temperature leads to the development of mutagenic compounds such as HCAs and polycyclic aromatic hydrocarbons (PAHs) which are responsible for various cancers. There are also evidences that show the saturated fatty acid content in red meat can be linked with chronic heart diseases. (McAfee et al., 2010)
Red meat is a rich source of nutritionally rich compounds which are essential in a human diet. Meat is a potent source of protein and it supplies the major amino acids that cannot be synthesized by the body termed as essential amino acids. The nutrient composition of meat includes fat, essential amino acids, vitamins, minerals and trace elements that makes it an inevitable part of human diet. Certain studies do show red meat is harmful when consumed in higher amounts and when cooked at higher temperatures, hence a proper monitoring on the cooking practices and consumption of red meat is essential to maintain a healthy diet.
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Ford, E. S., & Caspersen, C. J. (2012). Sedentary behaviour and cardiovascular disease: a review of prospective studies. International journal of epidemiology, dys078.
Gerber, N. (2007). The role of meat in human nutrition for the supply with nutrients, particularly functional long-chain n-3 fatty acids. ETH.
Hoffman, J. R., & Falvo, M. J. (2004). Protein-Which is best. Journal of Sports Science and Medicine, 3(3), 118-130.
McAfee, A. J., McSorley, E. M., Cuskelly, G. J., Moss, B. W., Wallace, J. M., Bonham, M. P., & Fearon, A. M. (2010). Red meat consumption: An overview of the risks and benefits. Meat science, 84(1), 1-13.
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Osborne, B. G., Fearn, T., & Hindle, P. H. (1993). Practical NIR spectroscopy with applications in food and beverage analysis: Longman scientific and technical.
Pighin, D., Pazos, A., Chamorro, V., Paschetta, F., Cunzolo, S., Godoy, F., . . . Grigioni, G. (2016). A Contribution of Beef to Human Health: A Review of the Role of the Animal Production Systems. The Scientific World Journal, 2016.
Prieto, N., Roehe, R., Lavín, P., Batten, G., & Andrés, S. (2009). Application of near infrared reflectance spectroscopy to predict meat and meat products quality: A review. Meat science, 83(2), 175-186. doi:http://dx.doi.org/10.1016/j.meatsci.2009.04.016
Rivlin, R. S., & Pinto, J. T. (2001). Riboflavin (vitamin B2). Handbook of vitamins. 3rd ed. New York: Marcel Dekker, 255-273.
Williams, P. (2007). Nutritional composition of red meat. Nutrition & Dietetics, 64(s4), S113-S119.
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