Quality of pork meat and its nutritional value
Authors: Martha Elba Gutiérrez Vargas, Roberto Jiménez Torres, Gabriel Ruiz Castañeda
At the time to define the quality of meat, appreciations change with light shades depending on the view of different links of the chain that goes from livestock farm to the table of consumer. From production to final consumption by the customer, we find elements that will bring as a result one more or less juicy meat, with more or less colour, higher or lower pH and capability in water retention. Factors like the animal genetics, feeding, ante-mortem and post-mortem management, etc., also will influence in an important way the final quality of meat and its products. So it is the matter of this research to find out the properties to be held in meat of good quality and to analize the elements that determine its fine status and at last the great nutritional value that its consomption brings to humans.
It may sound strange that nowadays, in the beggining of XXI century, some forum still exist where people call in doubt the nutritional value of pork meat in human nutrition. Pork meat has been a victim of so many tabooes made by consumers, seen as a nocive product to health, with low nutritional value and able to induce cardiopathy and obesity pathologies. This old idea, coming from far generations, has been anew evaluated, thanks to different scientific studies that show the benefits of pork meat. Pork meat has some nutritional properties between red meat (beef, cattle, lamb) and the white ones (poultry in general), so that’s why it has been named as Pink Meat. According to nutricionist Magnolia Escobar, “pork meat is an excellent source of proteins because their quality is high biological value and has all essential aminoacids to facilitate easy absorption by the organism”. Its meat is more similar to the white meat than the red ones and it has a high degree or rate of digestibility, that goes up to 92%.
Quality of meat is affected by many factors, previous and later to slaughtering of the animals, but feeding plays a determinant role in technologic aptitude (consistence and colour of fat, oxidative stability of lipids and pigments), in nutritional value (proportion of different fatty acids, fats in meat) and in sensorial atributes of meat (colour, flavour, succulence). Nowadays, food security has converted to essential priority for consumers, producers and government; now we can say that pork meat producers have technic and scientific methods to warrant mentioned security, and so we can introduce pork meat into healthy nourishment in all phases of life.
Actually many researches are being carried out and applying some mechanisms that, as time goes by, have reached to improve more the quality of pork meat, to achieve it to bring better nourishment (fat reduction near to 30%) and to give more benefit to human health. For all these arguments exposed, we can say that the consomption of pork meat is so justified in a food context, the nutritional value brought depends directly on the quality of meat.
1. Pork meat
1.1 Myths and realities of pork meat
For some cultures like ancient egipcians joint to fenicians, cananeans, cretensis, etiopeans and hindus, the same as jew and musulman religions, refuse this animal as a nourishment, not only for symbolic reasons, but also for safety and health. This animal is considered for those cultures as dirty animal per excellence. For such many years most myths have been built around pork meat, placing it as a greasy meat with a high calorie level and relating it to several diseases. However, these established beliefs are so far from reality. According to the Federal Commission of Risks against Health, no case of cisticercus has been rapported in the last 20 years related to pork meat consomption.
Until few years ago experts in nutrition recommended a limited consomption and even occasional of pork meat. But, researches in the last years have shown that this meat is as healthy as the others, and have discovered that its fat is the richest in monoinsaturated fatty acids. Pork meat does not have calories excess and has appropiate values to modern human needings. Thus, pork meat provides an offer of healthy and pleasant products, combination of both allows an inclusion of pork meat into a healthy nutrition and so bring it in nutritional recommendations to population.
1.2 Organoleptic attributes of meat
Muscular colour, normal colour of pork meat goes between red and pink. The uniformity in colour is usually found in individual muscles; when we look at muscles as a group, colour may considerably change. This variation in colour may appear due to the following matters: most dark colour may appear as a result of an oximioglobin increase (colour pigment) due to an advanced age of the animal, or a group of muscles with higher physiologic activity (flexor and extensor muscles), bacteria contamination, lack of lactic acid accumulation after slaughter, pale pink colour near to grey may appear as a consequence of a fast conversion of muscular glicogen to lactic acid (low muscular pH=acidity).
Tenderness of meat is determined essentially by muscular fibres and connective tissue, composed mainly by collagen. It also will be conditioned by fat quantity and the quantity and type of the enzymes present in muscle. This way, the presence of infiltrated fat contributes positively to tenderness sensation. Tenderness in an important factor to determine global quality of fresh pork meat products and it is usually pointed by customers as an important part of pleasant experience of its consomption. Talking about senses, tenderness is more related to general approval than other sensory properties, like juicity or flavour.
Juicity of meat is determined by the quantity of water held in muscle and the quantity of fat contained. Thus, juicity involves two sensations: first of all, the “initial juicity”, because of the juice produced during mastication and in second place, the sensation of “maintained juicity” due to infiltrated fat that melts. Factors that influence in juicity will be those ones related to the way water keeps held in muscle among muscular fibres or directly joined to proteins and also those ones that affect intramuscular fat quantity.
The smell and flavour of meat are so valued features by consummers. They are valued simultaneously, and so, smell and flavour together are called “flavor”. Ther exists a basic flavor “of meat” common to all animal species due to hydrosoluble compounds present in muscle. Specific flavor of meat in each specie is determined by lyposoluble compounds present in fat. During meat cooking, many changes happen in all these compounds and new products are origined, that bring characteristic colour and flavor of cooked meat.
Texture ( Humidity condition): In the United States 5 ranks exist to work with:
Rank 1: very soft and wet (open texture muscle), accumulation of fluid on surface, present in pale meat. Rank 2: Soft and wet. Rank 3: Not much firm and juicy. Rank 4: Firm and moderate dry. Rank 5: Very firm and dry, closed and rigid structure (without fluids on surface), related to dark meat.
Intramuscular fat is the adipous deposit found in association with membrane of muscular fibres (intercellular) or drops in muscular fibres (intracellular). Quantity and quality of this infiltration fat are related elements to smell, flavour and tenderness of meat. Bejerholm and Barton-Grade (1986) determined that a minimum of 2% in intramuscular fat is needed to reach an optimum sensory quality in fresh meat. However, this level may change depending on markets priorities and the destination of the product. Quantities between 3 and 4% may be more suitable for meat destined to cured products.
2. Quality of pork meat
2.1 Expectations of the consumer
Nowadays the market of pork meat is demanding a product required by consumers that joins several characteristics or factors combination, as it follows: eatable, nutritive and healthy. The quality of any product must be consistent and specially when it is about meat, taking into account that the product must have attractive appearance, tasty and palatably. Quality is a complex matter, this means that the customer is requiring not only high levels of lean in swine dressed carcasses and specially in the most expensive pieces like hams and loins, but also that the product (meat) must join several characteristics to allow production of the most satisfactory quality with the best results. The concept of meat quality is built on sensory, nutritional, sanitary and technological factors.
The importance of different qualitative points of view differs depending on the part of the meat industry chain which analyzes. For fresh meat, attributes like colour, fat quantity, tenderness, juicity and flavour are essential to decide and fidelize buying. For processed meat, the attention focus in factors as pH, water retention, oxydative stability and absence of anomalous flavours. The importance of each of them also will depend on the final destination of the manufactured product, cooked or cured.
Using physical and chemical methods or sensory analysis also, it is possible to evaluate objective characteristics of meat quality. However, the final approval is determined by consumers, so we should make difference between “objective quality” and “quality noticed by the consumer”. So consumers require, in general, a lean meat, to satisfy their organoleptic expectations, giving great importance to colour when buying and tenderness when time to eat.
2.2 Meat quality and swine nutrition
In swine production, nutrition is one of the most important factors when trying to find quality meat, fresh or to elaborate such big quantity of meat industry products. Nutrition affects in different ways the deposition of meat tissues and so will have a changing incidence depending on which one of them we are working on. In case of lean tissue, because of biochemical nature of protein synthesis in swine, basically by nutrition management quantitative modifications will get reached. It ain’t no sense to include important quantities of aminoacids in animal’s diet, all that will be retained is genetically determined. Every pig has a maximum capability to depose lean tissue, once this point is reached, one extra supply of feed only will contribute to increase the deposition of fat. Even below that point of maximum deposition of muscular tissue, an increase in feed intake goes together with an increase in fat tissue deposition.
The nutricionist or the professional in charge to formulate or making a diet, does not matter the kind of animal, is interested to know the chemical compositions of the ingredients at his disposal and, also, the digestibility of their nutrients. This last matter is more important even than the value of the absolute chemical determination and depends on lots of factors, some related to the animal (type, age, sex, physiological status, feed intake level, health, etc.) and others that depend on raw materials or ingredients (type, chemical composition, technological treatment, antinutritional factors, presentation, etc.). So pigs must receive from feed all the nutrients to face up not only their maintaining demands but also the ones used in: body growth, reproductive processes, health preservation and environment.
In some aspects, nutrition plays a determinant role but, in most cases, we must consider its interelation with other aspects of productive process: genetics, management and slaughter. Every treatment before slaughter (when fattening in farms, feeding, management, loading method, transport or slaughter, dazing method) that has an incidence in energy reserves of muscles at the moment of slaughtering may be determinant to meat quality. Pigs fattened ad libitum produce meat with more tenderness and juicity than the ones submitted to a restricted diet. In general, systems of controlled feeding bring animals with less recovering fat and higher proportion of lean meat in comparison to ad libitum systems. This management needs the use of rationing scales based in sex or body weight and, once is known that we sacrifice growing speed, we can see that feed conversion is better and also the percentage of lean tissue.
Fasting before slaughter affects quality of meat in several aspects. First of all, long fastings (>16 hours) may be effective to decrease the incidence of Pale, Soft and Exudative meat (PSE meat) in animals with genetic predisposition. Fasting before slaughter may reduce the quantity of muscular glicogent present in skeletal muscle due to its mobilization with energetical purposes during that period. Thus, the final result should be a less production of lactic acid and a higher final pH.
2.3 Porcine Stress Syndrome and its effect on quality
Intensity in management when pigs are submitted to, during loads, transports and arrivals in slaughterhouses, are the main factors to cause incidence in stress previous to slaughter. In case of stress next to slaughtertime, itmay exist an increase in PSE meat production, response to the temperature increase in muscles (>38ºC), lactic acid accumulation and increase in metabolic rate, that origines a fast decrease of pH (<6) before the cooling of dressed carcasses, at the same time denatures muscular proteins. This reduces capability in water retention and increases meat paleness, one thing that causes consumers refusal and serious economical consequences to the sector and industry.
2.4 Genetics and meat quality
All the efforts done to improve pigs genetics since decades ago have been made to increase relationship between muscle and fat in porcine dressed carcasses. Several researches have studied the corporal composition of pigs emphazising in properties.
Thus, genetics improvement has today a new challenge: quantity and quality in pork meat. At the same time, characters involved in meat quality got worse. The genetic progress in production characters brought also a turning back in objective and subjective attributes of quality, both fresh consomption and industry.
The effects of simple genes like Halothane gene and RN gene, with bigger effects, well known for their harmful actions over different quality characters. There is a high frequence of these genes in some breeds. Researches in poligenic or quantitative heredity have shown that most of the quality characters have low or moderate heredibility, except for intramuscular lipides contents.
Halothane gene: it is one of the most important genes with pleiotropic effects on some production characters discovered in pigs. The locus, called Hal, has two alleles: the normal one, N, and a mutation, n. Pigs with nn genotype show, when exposed to Halothane, the disease called Malignant Hyperthermia Reaction. Today it is known that the basic metabolic defect is found in a protein (a receptor) from sarcoplasmic reticulum, called ryanodine, that regulates calcium entrance and exit in muscular fibres. So, halothane gen, related to muscular hypertrophy, is responsible for the differences in the type and metabolism of muscular fibres which promote a bad adaptation of the animal to stress situations. The result is that, in situations of stress, a higher liberation of calcium is produced from sarcoplasmic reticulum.
Moreover than Porcine Stress Syndrome, halothane gene has several more pleiotropic effects. First of all, it reduces growth speed, also litter size (these are undesirable effects). On the other hand, the content of lean tissue in carcasses in increased. Halothane gen also produces seriour problems in meat quality, traduced in PSE deffect, english acronym to describe pale, soft and exudative meats, with very low capability in water retention. One of the principal features of meats with this deffect is the evolution of post-mortem acidity. The same as the loss of liquid, that means a reduced capability in water retention. To make things worse, PSE hams frequently show the two-colour condition: some muscles are pale and others are dark.
RN gene: two alleles are known of this locus located in chromosome 15: RN- and m+. The allele RN- produces a big increase of glycogen contain (about 70%) in “white” muscular fibres or glycolitic. This effect is evaluated in both homozygotes and heterozygotes (RN / -). The consequence is an increase in GP (glycolitic potential) with normal rate of post-mortem pH decrease, but falling nearly rock bottom. In the end, we find meat even more acide than the ones origined by halothane gene and, in consequence, with a reduced capability to retain water and low proportion in intramuscular protein. Moreover, pigs with RN- gene show harder meat, less juicy and flavoured than the ones of pigs with genotype m+/m+.
Apart from effects of “main” genes, most of quality characters in meat show poligenic heredity. Researches in poligenic or quantitative heredity have shown that most of quality characters have low to moderate heredibility, except for intramuscular lipides contents.
2.5 Scientific and technological methods to improve quality in pork meat.
Nutrition: quality control in feed processing is the first step in pig chain to reach good quality meat. That’s why cleaning and disinfection are done in feedback, conditionning and treatment silos with antifungal in grain, and also humidity and temperature in long-term stored materials are followed up, so we obtain quality food and mycotoxin free. Pigs are traceable, it means that we are able to know, moreover than the feed they had eaten, the raw materials constituted it. This is reached by batching all raw materials purchased in the plant and the filling for each manufactured feed, for one production order, where raw materials are detailed, incorporated quantity and batch.
Although cholesterol quantity is difficult to decrease, quality and quantity of lipides in meat, specially those coming from monogastric like pigs, are able to handle through dietary lipides and throw them to more healthy nutritional profiles. Pigs deposite fats from feed with very low modifications and this has allowed, for instance, to increase the MFA (mono-unsaturated fatty acids) and to decrease SFA (saturated fatty acids).
Nutritional value of meat is able to be improved and using antioxidants the product may preserve its technological quality. The use of antioxidants helps to correct hydroelectrolytic and oxidative damage. Inclusion of vegetal oils increases the presence of alphatocopherol in tissues and decreases susceptibility of lipides peroxydation. Seeds supplies or oils rich in 18:3-3 like linus allow to increase furnishing with PUFA (poli-unsaturated fatty acids) n-3 decreasing noticeably the rate n-6/n-3.
Stress: there exist some nutritional alternatives to reduce previous stress before slaughter and processing, one of them is the use of synthetic tryptophan added to ration of pigs in the end of fattening. Improvement in meat quality with the addition of this aminoacid occurs due to the competition of tryptophan with tyrosine to reach the joining site in haematoencephalic barrier. In this way, products of tyrosine, mainly epinephrine responsible to manifestation of stress to processing, they are not liberated in enough concentrations to the animal to show stress. Another benefit of using tryptophan in 9 feed for pigs is the fact that this aminoacid is the predecessor of serotonin, hormone involved in the stimilus of feed intake and in the decrease previous to slaughter and processing. In this way, researchers explained that tryptophan supply in stressed pigs during slaughter provided a serotonin concentration of 28%, less than they were compared to pigs with a low degree of stress.
Genetics: genetics improvement has used knowledge in quantitative genetics, and the information coming from phenotypic and genealogical in populations, but, conceptually, selects the animals with a more suitable genetic composition to selection purposes. The development in molecular genetics is going to stir up the patterns of genetics improvement because provides of direct information according to genetic heritage of individuals. Some methods in pork meat improvement are:
a) Using neutral molecular markers in selection assisted by markers. These neutral markers, usually microsatellites, allow to draw which one of both alleles from an ancestor of this marker has been transmitted to descendants. If this microsatellite is physically located in the proximity of a gene or a genome region related to a character of interest (QTL), we shall know the probability for the individual to have received the “favourable” or “disfavourable” allele from this gene, increasing the precission in genetics valuation of individuals and thus, the speed in response to selection.
b) Another chance is by direct detection of genes with a bigger effect in phenotypic expression of the character. The best example in this type of genes is the gene RYR1, that determines sensibility to stress, and its known repercussions. Once these genes with big effect are detected, their use in selection is direct, through removal of individuals the ones which are the carriers of disfavourable alleles.
c) A third possibility to act over the use of molecular information is to detect genes of interest in different populations. If we breed in the same farm, same environmental conditions, a group of Pietrain, Iberian and Meishan pigs, the first ones will grow more, the second ones will reach a better meat quality and the third ones will produce bigger litters. In consequence, these breeds have genes or combinations of them that determine their higher efficiency for several characters. Molecular genetics should be used, in F2 experimental crossbreedings, to locate these distinctive genes of these breedinglines and, later, introduce them in commercial lines with high potential through introgression. In the last years a lot of trials have been carried out all over the world to detect genes in several populations.
3. Nutritional value of pork meat
3.1 Nutrients in pork meat
Proteins: pork meat has a complete protein composition, because they contain all essential aminoacids in enough quantity and proportion to cover corporal needings. It has high nutrition value, with a protein contain between 19 and 20% in lean meats.
Vitamins: pork meat is an important source of complex B group, among them: thiamin, riboflavin, niacin, B6 and B12 vitamins and specially of B1 vitamin (0,95mg). Moreover is an important source of E vitamin. The quantity of thiamin is so high in pork meat (0,6mg/100 g), thiamin together with other complex B vitamins promotes and regulates a lot of necessary chemical reactions for growth and health to the body. Also pork meat is an important source of niacin, working in enzymatic intracellular systems to produce energy.
Iron: food from animal origin, like pork, they are important sources of essential minerals (iron, zinc, copper, iodine, magnesium, etc.) among them emphazising iron. Iron is involved in respiratory transport of oxygen and carbon dioxide and also in enzymes related to cellular respiration, specially in oxidative production of ATP in mitochondria. Iron is also related to immunitary system. Pork meat contains heminic iron, that is so efficiently used in human organism, allowing to cover with simplicity iron needings in humans. Iron is essential to brain operation and to reach a good physical performance.
Zinc: pork meat is a source of zinc, 100 grams of pork lean meat provide of 20% the recommended quantity of this mineral for one day, what makes it an excellent source of this mineral so necessary to grow, DNA synthesis, genetic expression, skin health, taste sense and spermatozoon formation. Like in case of iron, zinc from animal origin is helpful to reach a better use of that other zinc coming from a vegetal origin.
Fat: pork fat is a mix of saturated and unsaturated fatty acids, and also contains essential fatty acids to protect from cardiovascular diseases. In pork fat the most found fatty acids are oleic acid, palmitic acid and stearic acid in similar diets to ruminants. The ones the less found are miristic acid (aprox.1%), palmitoleic acid (2-3%), lauric acid and the unsaturated. Composition in fats depends on corporal region, age and diet composition. With regard to corporal region, dorsal, back and streaky bacon contain aproximately 10% more quantity of oleic and linoleic acids than intestinal and abdominal fats, which presents big quantity of palmitic and stearic acids. Age mainly influences having a straight relationship with linoleic acid.
Phosphorus: pork meat is an excellent source of phosphorus, in only 100 grs of pork lean meat we obtain: more than 70% of B1, more than 16% of B2 vitamin, 25% of B6 vitamin, 50% of B12 vitamin and more than 25% of niacin needings per one day. With this contain in vitamins from B group, we have benefits in energetic metabolism, nervous system operation, circulatory system operation and preventing from anemia and depression.
3.2 Nutrition and human health
Swine is nowadays among the most efficient meat production animals; its particular features, like great precocity and prolificity, short reproductive cycle and high capability to nutrients transformation, make it specially attractive as a food source. The nutritional value of pork meat emphatizes it as one of the most complete food to satisfy human needings, and its consomption may contribute to improve the quality of human life from both physical and intellectual performances points of view.
Humans need to intake nutrients in quantity and quality enough to cover functions required in different phases of life. To keep a good health status is essential to have a correct nutrition. Diet must be well-balanced, enough, varied, healthy and tasty. Pork meat is an excellent ally of health inside of a well-balanced and varied nutrition, as it is shown in different scientific researches that define its composition and nutrients. It is basically composed of muscular tissue containing water, mineral salts, several vitamins, proteins and some carbohydrates, lipides and connective tissue.
Porcine meat has nutritional properties between red meats (beef, cattle, lamb) and white ones (poultry in general) this is why it has been classified as “pink meat”. We can say it is a very complete food in nutritional contain. For instance a 120 grs ration is containing 22 grs of high biological value protein, all essential aminoacids required to good organism development and these quantity of grams are nearly 100% of daily totals.
Pork meat constitutes a source of excellent quality proteins, this evidence suggests that consomption of pork lean meat, joined to healthy life style patterns ( healthy diet, moderate physical activity), may collaborate in weight control in diabetes mellitus type2. At the same time pork meat helps to balance diet in persons with hypertension., because when compared with bovine and broiler meat, pork meat has less levels of sodium and, to take advantage, the highest level of potasium.
Pork meat has a low fat contain in lean parts, as tenderloin (with a 3,4% of fat) or sirloin (3,2%), and its lipidic profile detaches due to monounsaturated fatty acids contain (1,5g/100g, mainly in oleic acid form, typical for olive oil) and poliunsaturated (0,3g/100g, linoleic and linolenic acids) with a cardioprotective effect, opposite to saturated fat, in low quantity in pork meat. Moreover, this meat does not contain trans fatty acids and its cholesterol contain is similar to chicken and a little bit higher than cattle; from which 70-80% is found esterificated with palmitic, stearic or oleic acid.
That is why lean pork meat is an excellent food to be recommended and included in a varied and well-balanced diet for children and youth, in pregnant women, old people, sport practice, to treat and prevent from anemia, in weight control diets, prevention from hypercholesterolemia and protection from cardiovascular diseases, because as it has been mentioned, its composition in fatty acids may help to reduce LDL levels (bad cholesterol) and to maintain HDL levels (good cholesterol).
Daily values of each food appear in food labels. This shows the quantity of different nutrients we should intake daily. The following information is based on a pork portion of 3 ounces weight. As it noticed, these key nutrients make pork meat a very nutritive food.
3.3 Effect of cooking method in meat nutritional value
To improve digestibility, appearance, tenderness and hygienic status, meat is submitted to culinary preparation, which usually includes a direct termic treatment or using fluids (water or fat). Culinary methods, empirically developed through centuries have the aim to develop tasty organoleptic characters, by action of heat over different compounds of meat, favours substances transfers between distinct ingredients in one preparation and warrant a good hygienic and healthy status.
At the same time, cooking may affect nutritve value of meat in a degree that basically depends on intensity (temperature and time) of the termic treatment being used. In general, effects of heat over nutrients are more caused by time of exposition than the intensity of the treatment, so, when it’s time to maintain nutritive value, it is convenient to choose the fastest cooking methods, it means, microwave ovens , vapour, grill.
Some studies show that cooking methods do not change proteic value, however, high temperature cooking may decrease the biological value of meat proteins. In case of fat, its quantity may change depending on the cooking method used. Water cooking reduces final fat quantity because the method allows fat to drain and melt.
In case of minerals, iron and zinc are termostables, however, water cooking promotes iron solution in liquid. To avoid what we mentioned above it is recommended to cook with little liquid, small recipients and avoid overcooking.
4. Pork meat nowadays
It has low fat and low calories also, several studies support this affirmation. One of the most taken into account is tho one from United States Agriculture Department, it shows that from 1963 to 1990, the quantity of fat in cooked pork loin decreased 77% and the quantity of calories 53%. In the last 31 years improvement in genetics and nutrition have transformed old pork meat into the Light pork nowadays. Modern pork meat has cholesterol levels similar to bovine and chicken meat, without skin. It is also submitted to rules of the American Heart Association, which provides a maximum of 300 mg of daily cholesterol intake. When consomption of 100 grs of cooked pork loin, humans intake of cholesterol is about 72,8 mg, less than the 25% of maximum provided.
Modern pork meat agrees the American Heart Association requirements according to saturated fat levels, because when consomption of 100 grs of cooked loin, humans are intaking only 2,4 grams of this fat. This quantity represents less than 10% of the maximum provided in daily intake. Modern porcine meat agrees the american Heart Association requirements according to calories, because when consomption of 100 grs of cooked pork loin, humans are intaking only 188 kcal. ( it means less than 9% of the maximum provided). In consequence porcine meat does not have calories excess and it has the correct values for modern human needings.
Modern porcine meat has a suitable level of protein (19 to 20% in thin meat), with a good combination of all essential aminoacids, presented in a disposal biological way. It has tenderness and nice taste, that is the reason for its great welcome. Whwn 85 grs of pork meat are intaken, one person reaches the following percentages in its daily nutrient needings: 53% tiamin, 33% B12 vitamin, 22% phosphorus, 20% niacin, 19% riboflavin, 18% B6 vitamin, 15% zinc, 11% potasium, 7% iron and 6% magnesium.