Factors affecting meat quality and the role of fatty acids
This section reviews principles of meat quality with an emphasis on lipids in the production of traditional flavoursome beef. Characteristics of Wagyu beef are outlined.
Meat quality
The superior taste of beef culminates from the balance between tenderness, juiciness, and flavour. A recent survey undertaken by Kansas State University suggests that consumers rate safety from illness after cooking and the expected freshness of livestock products as indicated by expiration date and visual perception at retail ahead of flavour, taste and texture for beef steak. Price per unit and human health and nutritive value are the next values. There were minor variations in ranking for ground beef when compared with steak. Safety had the highest value and health implications to the consumer ranked higher than price.
Hormone/antibiotic free, animal welfare, environment and traceability values were consistently in the bottom half of the values.
Tenderness
Tenderness used to be a limiting factor but much progress has resulted from improvements in pre- and post-harvest techniques.
Tenderness and connective tissue
Intramuscular connective tissue has a major role in determining meat texture. Collagen fibrils and fibres are arranged in intramuscular tissue during the development of muscle. The collagen becomes progressively tougher, more rigid and less easily denatured over time. The association between texture, connective tissue and intramuscular fat in two muscles in Black Wagyu steers was investigated during fattening to 32 months of age (from Nishimura et al., 1999).
The shear force from raw semitendinosus muscle increased rapidly to 24 months of age then slowed thereafter and is represented by the white line in the chart to the left. Fat content rose to 6% and is shown by the solid yellow line. Collagen content decreased gradually from 8 to 32 months to 3.5% of dry weight.
The shear force from raw longissimus muscle increased from 9 to 20 months of age, and then decreased through to 32 months and is shown in the white line in the chart on the right. The shear force of connective tissue increased up to 24 months of age, and then decreased gradually to 32 months. The crude fat increased gradually to 20 months of age then rapidly thereafter to attain 18% of wet weight. The collagen content decreased from 12 to 24 months of age to 1% of dry weight.
Fat deposited in muscle improves texture during the late fattening phase with Black Wagyu. Intramuscular fat in 32 month old longissimus muscle was deposited between muscle bundles within the perimysium. This may have weakened the structure of the connective tissue. A high correlation was observed between crude fat content in longissimus muscle and shear force value in animals aged over 20 months (r = -0.76) when fat content rose from 6 to 18%.
Intramuscular fat may be required to exceed 8% to enable texture to be improved by fat deposition in other breeds. Duckett et al., 1993 reported moderate regression of the effect of fat on texture (r = -0.61) when fat content of Angus x Hereford approached 12%.
Tenderness and fatty acids
Historically there is limited and conflicting information.
Sensory panel results for texture in Longissimus muscle from Angus (n = 1,737) with an average carcase weight of 333 kilogram was analysed (from Garmyn et al., 2011). Texture is shown in yellow and significant differences are bright yellow. Scores for connective tissue is shown in blue and significant differences have a deeper shade. Desirable scores are above the "0" axis.
Stearic acid (18:0), linoleic acid (18:2) and arachidonic acid (20:4) were negatively correlated (P < 0.05) with all the tenderness traits and were positively correlated (P < 0.05) with WB shear force. These readings are consistent with undesirable texture. In contrast, the MUFA were positively correlated (P < 0.05) with panellist tenderness ratings and negatively associated with WB shear force.
Temperament and tenderness
The producer can enhance on-farm factors that influence beef palatability. Good temperament is associated with improved meat quality, feedlot performance, ease of transport and improvements in some reproductive traits under intensive production systems. Animals with good temperament have better gains in the feedlot and this is found across tropically adapted and British breeds. Brahman based steers with the slowest flight time had an average 0.4 kg/day higher daily weight gain than steers with a worse temperament.
Animals with poor temperament are more likely to produce progeny with beef of unacceptable eating quality as temperament is heritable. Better temperament is also associated with better health in the feedlot when measured by number of admissions to the hospital pen (Beef CRC Fact Sheet).
Better temperament was genetically correlated with improved tenderness (r = -0.42 shear force). Selection based on flight time and crush scores can be used to improve temperament, meat tenderness and eating quality in tropically adapted breeds of cattle (Kadel et al., 2006). Stress depletes glycogen prior to slaughter and this can cause dark cutting meat or to reduce the potential l to age after slaughter. Correlations between striploin tenderness, MSA tenderness and MSA Q4 scores have been found with flight time in Brahman, Belmont Red and Santa Gertrudis animals.
The odd animal that is temperamental but is kept for breeding because of its good genetics is likely to produce progeny with the same behavioural problems.
Ageing and tenderness
Ageing improves tenderness, flavour and overall acceptance of beef. Texture of meat is determined by myofibrils and intramuscular connective tissue which break down with time postmortem. The benefits to texture from ageing are greater in muscles which have a high shear force reading a couple of days postmortem.
Semitendinosus muscle in Black Wagyu steers aged 32 months was stored at 4ºC for 35 days post mortem and shear force measured for raw beef and intramuscular connective tissue which had muscle removed (Nishimura et al., 1998).
The rapid decrease of the shear force values in raw beef up to 10 days (white line in the chart) is mainly due to the weakening of the myofibrillar structures. The gradual weakening thereafter is caused chiefly by the structural weakening of the endomysium and the perimysium. The typical honeycomb structure of the endomysium is seen to be unchanged until after the first 14 days. The decrease in shear force of intramuscular connective tissue is linear from 14 days post mortem.
The rate of improvement of texture is greatest during the initial phase of ageing and decreases over time. A longer period of ageing is required at a lower temperature.
Animal welfare
Animal welfare is important for the well being of the animal and the production of the highest quality of beef.
The skillful handling of livestock in a safe, efficient and low-stress manner is one factor. Tips for good handling when moving small groups of animals, not overcrowding animals in pens, understanding flight zone and point of balance, keeping animals calm and quiet and moving cattle comfortably are found in guidelines.
Dark cutting beef is a condition that is caused by prolonged animal stress, usually greater than 12-24 hours, which depletes glycogen from the muscles and leads to undesirable flavour and texture and high pH.
Flavour
Consistency of flavour is paramount for the consumer when purchasing beef. Some premium is usually paid for beef or a steak, so one bad experience can have lasting effects.
Fat is crucial for flavour as a minimum level of 30mg/kg (3%) may be required for acceptable eating quality for beef in UK and USA (Enser et al., 2001). Western palates may plateau at 11 to 14% fat. Wagyu beef, which can exceed 25% fat, caters for the niche market. Properties of the fat are important in determining the overall eating experience.
Flavour - marbling
Marbling is fat that is stored in adipose tissue between muscle fibre bundles within the muscles. IMF is beneficial to flavour, taste and juiciness. IMF develops during growth, together with muscle fibres, but IMF content continues to increase after muscle development is complete. The relationship between carcase weight and IMF is shown in the following chart from Wagyu cross Holstein (from Pethick et al., 2001).
During the early post natal development phase IMF content remains low and constant but is followed by a linear phase at between 200 and 400 kg carcass weight. After mature size is reached at 450 kg the IMF deposition rate is lowered as feed intake and growth rate decline.
For lotfeeding in Australia, cattle at an induction body weight of 400 kg will need 5% fat to be able to reach 15% fat at 400 kg carcase weight in order to grade at mid-range marbling AUS-MEAT 4 (Pethick et al. 2001).
Cattle which have been restricted at some stage before the finishing phase often exhibit compensatory growth but need to be fed for a longer period and to a higher carcase weight so that optimal grades are achieved. A minimum ADG of 0.45 kg on grassland is recommended through the adverse winter in USA.
Flavour - fatty acid composition
A large pool of Angus cattle (n = 1,737) with an average carcase weight of 333 kilogram was analysed (Garmyn et al., 2011). The strongest correlations with juiciness were negative relationships (P < 0.05) with linoleic acid (18:2), linolenic acid (18:3), arachidonic acid (20:4) and PUFA. Correlations with beef flavour were weak, but the strongest was a positive relationship with MUFA (r = 0.13). SFA (r = 0.06) was also positive and PUFA was negatively associated with beef flavour (r = -0.08).
The results of individual fatty acid correlations from the sensory panel are illustrated above. The associations were weaker than in similar trials but were significantly different (P < 0.05) for several acids. They are shown in the chart above in bright yellow for beef flavour and blue for juiciness. The lower colour tones are used for non-significant scores.
Dryden and Marchello, 1970 found that oleic acid had a positive and stronger association with beef flavour (r = 0.67) than above. Correlations of fatty acids which have exhibited associations with beef flavour from Westerling and Hedrick, 1979, Melton et al., 1982 and O'Quinn, 2012 have been gathered. A ranking for fatty acid association with flavour in beef is consolidated:
The five acids in the middle (arachidonic, myristoleic, trans-vaccenic, palmitic and margaric acids) gave conflicting positive and negative correlations in different trials so could be considered "neutral" in the market. The group on the top left only gave significant favourable flavour scores, while those at the bottom to the right gave significant adverse flavour scores.
Contrasting results were obtained from sensory panellists in Korea which evaluated Australian Angus and Korean Hanwoo beef (Cho et al., 2005). Hanwoo had 11.3% intramuscular fat and Angus was 5.7% but the data are pooled for breed. The saturated fatty acids - such as C16:0 palmitic and C18:0 stearic acid - were positively correlated with all sensory traits while the unsaturated fatty acids were negatively correlated with all sensory traits (P < 0.05). In particular, polyunsaturated fatty acids had significant negative correlation with tenderness, flavour, juiciness and overall likeness. The correlations for fatty acid groups SFA were positive, MUFA were negative, and PUFA were significantly negative for all properties.
Flavour - grass finishing or grass fed and grain finished
The most recent forage versus concentrate finishing trial on carcase and meat quality gave typical outcomes (Duckett et al., 2013). Corn and sileage was fed for 134 days to one group. The forage groups were grazed from weaning then were split into three groups for the final 40 days on either mixed pasture, alfalfa or pearl millet. Average daily bodyweight gain was greater (P = 0.001) for grain finishing than from forage finishing. Amongst the forage groups, average daily gain was greater (P = 0.03) for pearl millet. Harvest weight and hot carcase weight were greater for grain finishing versus forage finishing (587 vs 484 kilograms and 252 vs 352 kilograms respectively). Finishing on forages reduced (P = 0.001) total lipid content by 61% for longissimus muscle compared with grain finished cattle. Oleic acid concentration and total MUFA of the longimissus muscle were 21 and 22% less (P = 0.001) than from grain. Concentratations of linolenic acid, eicosadexaenoic (EPA), docosapentaenoic (DPA) and docosadexaenoic (DHA) acids, and total omega-3 fatty acids were greater (P = 0.001) from forage than from grain finishing. Finishing on alfalfa increased (P = 0.017) the concentration of linoleic acid compared with mixed pastures or pearl millet forages.
Beef flavour intensity was greater (P < 0.001) for grain than forage finishing, as was juiciness (P < 0.01). The charts with the individual scores are on the left above (from Duckett et al., 2013). Beef flavour intensity was greater (P < 0.02) for alfalfa and pearl millet than mixed pastures. Off-flavour intensity was greater (P < 0.001) for all forage-fed steaks than for grain finished. The off-flavour tastes are charted to the right above and the lower scores are preferred.
A glimpse of the changes that occur in the microflora population in the rumen when grains replace forages is illustrated (Latham et al., 1972). Rumen bacteria Butyrivibrio fibrisolvens produce CLA as an intermediate substrate of linoleic acid and their population decrease with grain feeding (Ponnampalam et al., 2006).
The effects of pasture finishing versus feedlot finishing over time in Angus crossbred steers were monitored in USA (Fincham et al., 2009). Linoleic acid made up 57% and 2% was linolenic acid of the total fatty acids in the feedlot diet. Linolenic acid comprised 66% and linoleic acid 9% in the feedlot.
In the rumen, SFA were predominant. Stearic acid comprised 56.5% of forage fatty acids and 68.6% of feedlot fatty acids. Palmitic acid decreased to 18.8% of forage and 12.7% of the fatty acids in the feedlot.
In plasma, CLA predominates with 44.6% in the feedlot and 19.3% on forages. Palmitic and stearic acids total 28.8% on grain and 30.2% on pasture.
Deposition in subcutaneous tissue is illustrated in the chart. Both the amount of marbling and the concentration of monounsaturated fatty acids (MUFA) increase with time on feed in grain-fed and pasture-fed cattle, but more dramatically in grain-fed cattle. In this trial, MUFA comprised 46.7% of total fatty acids from pasture and 53.2% from the feedlot. PUFA was 2.63% and 1.96% respectively. SFA was 50.7% (33.6% cholesterol raising SFA) and 44.9% (38.5% C-R SFA) respectively.
In an Australia trial, temperate grasses were compared with grain finishing (barley and/or sorghum were supplemented with whole cotton seed plus cotton seed meal). Bos taurus cattle were slaughtered at 18 months of age after grazing temperate grasses, short fattened for 80 days or long fattened for 150 to 200 days. Fatty acid composition is illustrated (from Ponnampalam et al., 2006):
This chart shows fatty acid levels in muscle to illustrate differences between cuts and method of finishing. There was a significently higher level of omega-3 (n-3) in grass fed beef. Cuts from long grain-feeding had higher levels of SFA, MUFA, omega-6 (n-6) and 18:1 trans. In rump cuts, oleic acid increased from 1,050 from grass finishing to 2,193 mg/100g from long grain finishing. When this is related to fatty acid composition, there was a 7.9% increase of oleic acid in the rump with long-feeding and 4.3% in strip loin compared to grass-fed cattle. Palmitic acid composition increased 1.4% and 0.9% while stearic acid decreased 2.% and was unchanged in rump and strip loin respectively.
When comparisons are made on the carcase from pasture and grain-finishing, muscle colour is invariably darker from forage diets (Wood et al., 2008). Subcutaneous fat is darker with yellow colour from green forages. β-carotene in beef from forage finishing was 0.499 and 0.057 g/100g from 132 day grain finishing (Duckett et. al., 2013). Carotenoid concentrations drop when forages are dried before feeding.
Flavour - sex differences
Sex differences were demonstrated in pure Wagyu and crosses were demonstrated by Zembayashi et al., 1995.
Heifers had higher contents of oleic acid and total MUFA, and higher ratios of MUFA:SFA in subcutaneous and intramuscular neutral lipids than steers of the same carcase fat percentage.
Herefords of both sexes were finished on forages or grain. Steers had higher levels of linoleic and arachidonic acid than heifers (Westerling et al., 1979). Sensory scores for flavour were positively associated with oleic acid (0.67) and negatively associated with palmitic (-0.52), stearic acid (-0.60) and linoleic acid (-0.63). Significent differences (P<0.01) were also observed for correlations between Flavour score in intramuscular fat and Total UFA (0.66) and negative for Total SFA (-0.66) and Flavour score in subcutaneous fat for Total UFA (0.65) and negative for Total SFA (-0.65).
These findings may provide the science behind the awarding of certification to one the most prestigious beef brands in Japan - "Matsusaka beef"- only to heifers.
Effect of site of sampling on fatty acid content
Fatty acid composition of subcutaneous, intermuscular, intramuscular and kidney fat in Black Wagyu is charted on the left (Oka et al., 2002). Bovine tissues near the body surface have higher percentages of MUFA than internal tissues.
A study was conducted on Black Wagyu steers on the rates of intramuscular fat deposition from 24 to 30 months of age. Fattening commenced at 10 months. M. longissimus increased 15% in fat content at 7th to 8th rib and 27% at the 11th to 12th rib. M. latissimus dorsi increased 34% and M. semitendinosus gained 59%. The other major muscles had gains from 6 to 16%.
The forequarter has a higher demand in Asian markets than in Australia. The high level of marbling and tenderness in Wagyu forequarters is opening new opportunities as the grilling value increases. In conventional beef these cuts produce the lower end ground beef.
Flavour - melting and slip points
Fatty acids have different melting points so variation in fatty acid composition has a major influence on the firmness or softness of the fat in meat. SFA and trans fats have highest melting points. They decline with the addition of double bonds and chain length.
High concentrations of SFA cause fat to be hard at room temperature. Stearic acid is one of the main fatty acids that dictate fat hardness (Smith et al., 2012) so any practice that increases the conversion of stearic acid to oleic acid wil increase fat softness. Soft translucent fat, with its relatively low melting point contributes to desired mouth feel and flavour attributes when cooked. Hardness of fat in meat is measured by a slip-point test and some results are tabled:
A slip point of 17.4ºC was noted in Matsusaka branded Black Wagyu. This slip point is below room temperature and is attributed to a MUFA content of 69%. Incidentally, the MUFA:SFA ratio is 2.3.
Melting point was measured from cattle raised on pasture up to 450 kg bodyweight in NSW, Australia. Melting point of subcutaneous fat was significently affected by sire breed, environment, and age. Subcutaneous fat from Brahman sired steers had a lower (P < 0.01) melting point - 37.25ºC - than fat from the Bos taurus steers. Fat from steers grown out at Glen Innis had a lower melting point (38.32ºC) than that from steers at Trangie (39.97ºC). Melting point decreased with increasing age. The error correlation between melting point and the saturation ratio of fatty acids was 0.88. The steers averaged bodyweight gains ranging from 0.31 to 0.53 kg per day through the trial (Perry et al., 1998).
Melting point in Australia was significantly negatively correlated with MUFA (-0.66) in lightly marbled beef from grain feeding (Stephens, 2001).
Simmental slaughtered between 9 and 14 months of age after 36 to 87 days on feed averaged 42.1ºC with a range from 39.6 to 45.1ºC. Wagyu from an Australian feedlot aged an average of 26.3 months after an average of 320 days on feed had an average melting point of 36.0ºC with a range from 32.5 to 39.5ºC. 78.8% of the samples were liquid at 37ºC (Lloyd et al., 2014).
Flavour - breed
Breed differences in flavour in USA have generally not been found when age, carcase weight, fat thickness, marbling and fat trim level were standardized. Both the method of finishing - grain-fed versus grass-fed - and USDA quality grade had the largest effects on beef flavour (O'Quinn, 2012).
Black Wagyu (Japanese Black) has the genetic predisposition for producing lipids containing higher concentrations of monounsaturated fatty acids than Holstein, Red Wagyu or Charolais (Zembayashi et al., 1995).
Smith et al., 2001 report that a trial carried out by Lunt in USA established that BMS - Japanese marbling score - was significantly higher for F2 and F3 Wagyu steers (7.3) than purebred Angus steers (4.5) which were raised under Japanese conditions.
Flavour has a low heritability (<10%), but the heritability of IMF is high. Selection for marbling can improve flavour.
Contribution of Wagyu to improving meat quality
Wagyu, the traditional cattle of Japan, were draught animals for two thousand years. Those beasts with reserves of energy stored within their muscles were able to work for prolonged periods. Intramuscular fat (IMF) is the source of energy stored within muscles so selection for sustained performance indirectly increased IMF in Wagyu.
Heritability estimates for Black Wagyu and Red Wagyu/Akaushi are tabled (Osawa et al., 2008):
Variablity in size within the Wagyu breed results in a medium heritability estimate for carcase weight. It is high for Wagyu cross and in Braham. However, Wagyu Black has high heritability for marble score and it is lower for the other breeds. Individual fatty acid composition heritabilities are tabled (Australian pool data Kelly et al., and Wagyu from Nogi et al., 2010):
Heritability estimates are high for the major fatty acids individually and in groups. It is highest for oleic acid which has a major influence on flavour.
The Wagyu breed is blessed that its strongest attributes for meat quality are highly heritable so progress is assured once it is measured.
Grading and value in the market for marbling
In Japan, marbling - as measured by intramuscular fat % - has been the major driver of value through the BMS marbling score. More recently, marble fineness - as determined by the more robust digital camera - is beginning to exert some influence. The BMS marbling was modified in 2008 and the lowest score of 3 is associated with 21% intramuscular fat.
This IMF% is the equivalent of the highest IMF level of 9 in the AUS-MEAT marble score in Australia. Some graders record an informal 9+ score in kill sheets. 30% of Fullblood Wagyu carcasses are graded AUS-MEAT 9 after conventional grain finishing. Winner of the 2017 Wagyu branded beef competition of a F1 50% Wagyu steer after 375 days on feed had 49% IMF. This is more than double the official score that can be graded by AUS-MEAT.
The limitations of the grading system are even more punishing against Wagyu producers in USA. The highest grade of Prime is awarded to carcasses with intramuscular fat between 8 and 11%. Only 3% of carcasses across the USA grade Prime, but 90% of Wagyu and Wagyu infused carcasses are graded in this category.
