G.R. Nute

Manipulating meat quality and composition.

Meat quality describes the attractiveness of meat to consumers. The present paper focuses on two major aspects of meat quality, tenderness and flavour. Both aspects of quality can be influenced by nutrition, principally through its effects on the amount and type of fat in meat. In several countries, high levels of intramuscular fat (marbling fat), i.e. above 30 g/kg muscle weight in longissimus, are deemed necessary for optimum tenderness, although poor relationships between fat content and tenderness have generally been found in European studies, where fat levels are often very low, e.g. below 10 g/kg in UK pigs. Muscle lipid may be a marker for red oxidative (type 1) muscle fibres which are found at higher concentrations in tender muscles and carcasses. Nutritional treatment can be used to manipulate the fatty acid content of muscle to improve nutritional balance, i.e. increase the polyunsaturated (PUFA): saturated fatty acid value and reduce the n-6:n-3 PUFA value. Increasing PUFA levels may also change flavour because of their greater susceptibility to oxidative breakdown and the generation of abnormal volatile compounds during cooking. This situation particularly applies to the n-3 PUFA which are the most unsaturated meat lipids. In pigs, a concentration of 3 mg alpha-linolenic acid (18:3)/100 mg in muscle and fat tissue fatty acids can easily be achieved by including whole linseed in the diet. This level has led to abnormal odours and flavours in some studies, but not in others. In cattle and sheep, feeding whole linseed raised 18:3 concentrations in muscle fatty acids from about 0.7 mg/100 mg to > 1 mg/100 mg. As with pigs, this diet also increased levels of long-chain n-3 PUFA formed from 18:3, including eicosapentaenoic acid (20:5). Although this increase led to greater oxidative breakdown of lipids during storage and the generation of large quantities of lipid-derived volatile compounds during cooking, there were no deleterious effects on odour or flavour. When 18:3 levels are raised in lamb and beef because of grass feeding, the intensity of the flavours increases in comparison with grain-fed animals which consume and deposit relatively more linoleic acid (18:2). In ruminants, very high levels of 18:2 produced by feeding protected oil supplements cause the cooked beef to be described as oily, bland or pork-like.

Flavour perception of oxidation in beef.

Lipid oxidation is a major factor in meat quality. In order to relate human perceptions of lipid oxidation, as determined by a trained taste panel, to a chemical measurement of oxidation, we studied meat from animals with a wide range of potential oxidation through differences in their PUFA composition and by displaying the meat in high oxygen modified atmosphere packs for varying lengths of time. Meat was obtained from 73 Angus- and Charolais-cross steers from different trials that had been raised on 10 different diets: grass silage (high in C18:3, n-3), cereal concentrate (high in C18:2, n-6), three diets with 3% added fat consisting of three levels of protected lipid supplement (high in C18:2, n-6 and C18:3, n-3, ratio 1:1), a control with Megalac(®) (relatively saturated), three diets with three levels of inclusion of protected fish oil (high in C20:5 n-3 and C22:6 n-3) plus a constant amount of unprotected fish oil and a final diet with an unprotected fish oil control. The longissimus dorsi muscle was excised from the left carcass side, aged vacuum packaged for 10-13 days depending on the projects and frozen for less than eight months. TBARS and sensory analyses were performed on steaks displayed for 0, 4 or 9 days under simulated retail conditions, exposed to light in modified atmosphere packaging (CO(2):O(2); 25:75). Meat oxidation increased throughout display for each of the diets, as shown by a rise in TBARS values. This increase was not linear, differences between 0 and 4 days of display were smaller than between 4 and 9 days of display. The lowest TBARS and lowest increment occurred in the two control diets and the grass-fed animals, probably due to the more saturated fat of meat from animals fed the control diets and the higher content of vitamin E. Sensory attributes were also influenced by time of display. Positive attributes, such as beef flavour or overall liking, decreased throughout display, whereas negative attributes, such as abnormal and rancid flavours, increased. The correlations between sensory and analytical attributes were high. TBARS were a good predictor of the perception of rancidity (Spearmans rho=0.84). Panellist preferences were related to the presence of beef flavour (rho=0.93) and to the absence of abnormal (rho=-0.88) and rancid flavours (rho=-0.83). Under the experimental conditions used, a TBARS value of around 2 could be considered the limiting threshold for the acceptability of oxidised beef.

Fatty acid composition and sensory characteristics of lamb carcasses from Britain and Spain

Fatty acid composition of intramuscular fat in M. Longissimus was measured in four groups of lambs representing two Spanish breeds: Rasa Aragonesa (RA) and Merino (ME) and two British lamb types: the Welsh Mountain breed (WM), whose carcasses were purchased in Spain and typical early lambs (EL) purchased in Britain. The lambs grown in Spain were concentrate fed and slaughtered at a lighter weight and lower age than those grown in Britain. The British lamb carcasses purchased in Spain were of a similar weight to the Spanish lambs but were lighter than the lamb carcasses purchased in Britain. The British lambs were grass fed. Relationships between fatty acid (FA) composition and sensory attributes were examined following sensory testing of all lambs by both British and Spanish taste panels. The production system was shown to be more important than breed in determining FA composition. British lambs had higher percentages, within total fatty acids, of 18:0, 18:3 (n-3) and long chain polyunsaturated n-3 FA and lower percentages of 18:2 (n-6) and long chain polyunsaturated n-6 FA than Spanish lambs. These differences were due to the different feeding systems used. The amounts of these FA in muscle (mg/100 g) were also different between the British and Spanish groups, not only because the British lambs had more total fat. For both taste panels, odour and flavour intensity were positively correlated with the amounts and percentages of 18:0 and 18:3 and negatively correlated with those of 18:2. This was explained by the fact that both panels gave higher odour and flavour intensity scores to the grass-fed British lamb with high 18:3 levels and lower scores to the concentrate-fed Spanish lamb with high 18:2 levels. However, 18:0 and 18:3 were positively correlated with flavour quality and overall appraisal for the British panel and negatively for the Spanish panel. Conversely, 18:2 was a positive contributor to flavour and overall preference for the Spanish panel and was negative for the British panel. The results show that the production system affects muscle fatty acid composition and the flavour of lamb. However, peoples preference is determined to a large extent by their past experience.

Fatty acid composition and eating quality of lamb types derived from four diverse breed production systems

Carcass composition, muscle fatty acids and eating quality of loin chops were examined in ram lambs from four diverse breed × production system groups: pure Welsh Mountain off upland flora, pure Soays off lowland grass, Suffolk crosses off lowland grass and Suffolk crosses off concentrates. The two Suffolk groups had heavier and better muscled carcasses than the others and Soays were particularly lean. Fatty acid composition was different between the groups. The forage-fed lambs all had high concentrations of n-3 polyunsaturated fatty acids (PUFA) including 18:3 (α-linolenic acid) and 20:5 (eicosapentaenoic acid) compared with Suffolks-concentrates which had high concentrations of the n-6 PUFA 18:2 (linoleic acid) and 20:4 (arachidonic acid). Soays were high in both n-3 and n-6 PUFA. Flavour characteristics in grilled chops were similar in Welsh Mountain and Suffolks-grass which differed from Soays and Suffolks-concentrates. The latter two groups had low scores for lamb flavour and overall liking and high scores for abnormal lamb flavour, metallic, bitter, stale, and rancid. Soays had the highest score for livery. These results extend previous findings of the association between feed, PUFA composition and lamb flavour profile and confirm that forage-fed lamb is preferred by UK taste panellists. They also identify a specific breed effect on the quality of meat from lambs raised on forage. These findings suggest that possibilities exist for the production of meat with specific quality characteristics.

Influence of dietary oils and protein level on pork quality. 1. Effects on muscle fatty acid composition, carcass, meat and eating quality.

This study evaluated the effects of three dietary oils - palm kernel (PKO), palm (PO) and soyabean (SBO) - and two protein levels - high (HP) and low (LP) in a 3×2 factorial design involving 60 pigs on growth performance, muscle fatty acid composition and content, carcass, meat and eating qualities. Oil type did not have a significant effect on growth and carcass quality. PKO significantly reduced the polyunsaturated (PUFA) to saturated (SFA) fatty acid (P:S) ratio in longissimus muscle (P<0.001). PKO increased the concentrations of lauric (12:0), myristic (14:0), palmitic (16:0) and stearic (18:0) fatty acids and decreased linoleic acid (18:2). The LP diet increased intramuscular fat (IMF) from 1.7g/100g muscle in HP to 2.9g/100g (P<0.001), increased tenderness by 0.6 units (P<0.01) and juiciness by 0.5 units (P<0.01) on the 1-8 scale, but at the expense of lower daily weight gain (P<0.01), lower feed conversion efficiency (P<0.01), reduced P:S ratio (P<0.001) and increased lipid oxidation (P<0.01). The results suggest that PKO and PO could be used in tropical developing countries as cheaper alternatives to SBO for the production of good quality and healthy pork, but their limits of inclusion need to be determined.

Effects of breed, feed level and conditioning time on the tenderness of pork

This study of 80 pigs compared the effects of breed (Duroc vs Large White), feed level (High vs 0.8 High, termed Low) and conditioning time (1 vs 10 days at 1 °C) on the tenderness and other aspects of the eating quality of pork. Conditioning time had the biggest effect (increase of 1.0 units on 1-8 taste panel scale between 1 and 10 days) and this was associated with an increase in the myofibrillar fragmentation index (MFI) from 19 to 24 units. Tenderness was not different between the two breeds although pork flavour intensity and overall liking scores were higher in Durocs. Durocs had higher concentrations of total lipid (marbling fat) in muscle (13.7 and 5.4 mg/g) and most polyunsaturated fatty acids except α-linolenic (C18:3 n-3) were at lower concentrations in Durocs, reflecting dilution of phospholipid fatty acids within a larger total lipid pool. Pigs fed at the high level were fatter than those fed restrictedly in terms both of P2 fat thickness and marbling fat. There was also a tendency, although not significant, for the meat to be more tender. When the data from all pigs were pooled, MFI was shown to correlate well with tenderness (r = 0.45) and marbling fat with juiciness (r = 0.36).

Genotype with nutrition interaction on fatty acid composition of intramuscular fat and the relationship with flavour of pig meat.

The effects of genotype, diet and the genotype with diet interaction on fatty acid composition of neutral lipid and phospholipid of intramuscular fat in pigs were examined. Pigs from four selection lines and a control line were fed isoenergetic diets, which differed in ileal digestible lysine:digestible energy (A: 0.40, C: 0.76 and E: 1.12 g lysine/MJ DE). The selected lines resulted from seven generations of selection for high daily food intake (DFI), lean food conversion ratio (LFC) and lean growth rate on ad-libitum (LGA) or restricted feeding regimes in a Large White population. During performance test, from 30 to 90 kg, pigs were fed on either ad-libitum or restricted (0.75 g/g ad-libitum daily food intake) feeding regimes. A trained sensory panel assessed intensities of pork flavour and abnormal flavour and the hedonic characteristics of flavour liking and overall acceptability. The proportion of neutral lipid in the LGA line was lower (0.64 v 0.75, s.e.d. 0.03) while the polyunsaturated:saturated (P:S) ratio of the LFC line (0.53 v 0.41, s.e.d. 0.05) was higher than the control line and other selection lines. The DFI line had a higher phospholipid n-6:n-3 ratio than other selection lines (14 v 11, s.e.d. 1.0). Diets C and E resulted in lower neutral lipid:phospholipid ratio (0.7 v 0.8, s.e.d. 0.01), n-6:n-3 ratios for both neutral lipid (5 v 13, s.e.d. 0.8) and phospholipids (7 v 20, s.e.d. 0.6) and a higher P:S ratio (0.5 v 0.3, s.e.d. 0.03) for neutral lipid than diet A. Neutral lipid fatty acids C18:2 n-6, C18:3 n-3, C20:3 n-6, C20:4 n-6, C20:5 n-3, C22:5 n-3 and C22:6 n-3 were negatively correlated with pork flavour (-0.30, s.e.d. 0.10), flavour liking (-0.33) and overall acceptability (-0.30). In contrast, the fatty acids C16:1, C18:1 ω9 and C18:1 ω11 were positively correlated with pork flavour (0.36), flavour liking (0.39) and overall acceptability (0.40). However, correlations for fatty acids in the phospholipid class were positive for C18:2 n-6, C20:4 n-6 and C22:4 n-6 with pork flavour (0.33), flavour liking (0.23) and overall acceptability (0.23). The proportion of neutral lipid had non-significant correlations with flavour traits; pork flavour (0.01), abnormal flavour (0.08), flavour liking (-0.03) and overall acceptability (0.03). The selection lines responded in a similar manner to the different diets, such that there was little evidence for genotype with nutrition interactions for fatty acid concentrations of neutral lipids and phospholipids. Selection for high lean growth will reduce intramuscular fat, but the increased relative amount of phospholipid and concentration of polyunsaturated fatty acids are unlikely to reduce eating quality. Nutritional effects on intramuscular fat characteristics were greater than genetic effects, such that nutritional approaches to feeding pigs will provide effective methods of reducing the n-6:n-3 fatty acid ratio of human dietary fat from pigmeat and improving human health.

Shelf life and quality of pork and pork products with raised n-3 PUFA

Pork chops, liver, bacon and sausages from 80 pigs fed on a control or a linseed-rich test diet were assessed for their sensory qualities and oxidative stability after conditioning and storage, either frozen or under simulated retail display. There was no significant effect of diet on lipid oxidation as assessed by the TBA test (P>0.05) for pork, liver and sausages, values being less than 0.2 throughout the display period, lower than the threshold of 0.5 mg MDA/kg at which consumers may detect rancidity. Nor was there any significant effect of diet on colour changes of pork chops, sausages and bacon under simulated retail display conditions. Grilled loin chops, bacon and sausages from male pigs received significantly higher abnormal flavour scores than those from females but panellists were unable to discern any major differences between control and test diets, even though they could detect this relatively small sex effect. The test diet resulted in higher α-linolenic acid (18:3) levels, with major increases in total n-3 PUFA content, but the concentrations were generally lower than reported values that have resulted in stability problems. The n-6 PUFA content was also reduced by the test diet. The results demonstrate that the nutritional value of pigmeat can be improved by using an 18:3-enriched diet without adversely affecting normal eating quality parameters.

Consumer perceptions: pork and pig production. Insights from France, England, Sweden and Denmark.

Consumer focus groups in France, England, Sweden and Denmark were used to obtain insights into the decision-making involved in the choice of fresh pork and attitudes towards todays pig production systems. Many positive perceptions of pork meat were evoked. Negative images of the production systems in use today were expressed, but rationalised in terms of consumer demands, market competition and by comparisons to previous systems of production. Knowledge of production systems appeared of little consequence in terms of any meat market potential as several groups freely remarked that there was no link between the negative images of production methods and their purchase behaviour. The groups were clearly confused and mistrusted the limited information available at the point of purchase. Careful consideration should be given to meat labelling, in particular taking account of the evident consumer ethnocentrism, to assure that such information is targeted to enhance consumer confidence.

Assessment of commercial lamb meat quality by British and Spanish taste panels

Trained sensory panels in Britain and Spain assessed loin meat from commercial lambs purchased in Spain, which included Welsh lamb (imported from Britain) and two Spanish breeds (Merino and Rasa Aragonesa). The British panel also assessed British lamb purchased in local butcher shops and supermarkets. Sensory panels, in each country, received meat from the same lambs and used their local methods of cooking and assessment. Spanish panels used unstructured line scales to measure lamb odour intensity, tenderness, juiciness, lamb flavour intensity and two hedonic scales of flavour liking and overall liking. The British panel used 8 point category scales with the same attributes. Results from both panels in objective parameters were in agreement, hence showing that different trained sensory panels may arrive at the same conclusion. However, when panellists were allowed to make hedonic judgements (preference), the British panel preferred British lamb and the Spanish panel preferred Spanish lamb. This finding has important consequences for lamb producers who export their lambs and demonstrates that the underlying reasons for different preferences should be investigated. Production variables are discussed in relation to their influence on lamb eating quality and as a way to tailor lamb eating quality attributes familiar to consumers in the importing country.