P.R. Sheard

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.

Feeding linseed to increase the n-3 PUFA of pork: fatty acid composition of muscle, adipose tissue, liver and sausages

Eighty pigs, male and female littermate pairs, were fed a control or a test diet from 25 to 95 kg live weight. The diets, as fed, contained 15.5 g/kg linoleic acid (18:2) and 1.9 g/kg α-linolenic acid (18:3) (control) or 10 g/kg linoleic acid and 4 g/kg α-linolenic acid (test). The test diet, with added linseed, was, therefore, high in the main n-3 polyunsaturated fatty acid (PUFA) 18:3 and low in the main n-6 PUFA 18:2. Making this relatively small change led to a 56% increase in the content of 18:3 in muscle and major increases in the contents of the beneficial longer chain PUFAs EPA (20:5n-3) (100% increase) and DHA (22:6n-3) (35% increase) which are synthesised from 18:3n-3. Levels of EPA and DHA in pigmeat adipose tissue were also increased by the test diet. In liver, the test diet resulted in an 18:3 level 4× higher than in muscle, with 10× more EPA and 20× more DHA. Sausages, analysed after 6 months frozen storage also had high n-3 PUFA levels, due to the contribution of these fatty acids from both muscle and adipose tissue. From a health perspective these results confirm the potential of pigmeat to supply valuable n-3 PUFA to the human diet. The test diet produced a PUFA:saturated FA ratio in muscle of 0.4, close to the minimum recommended value for the diet as a whole and an n-6:n-3 ratio of 5, a significant improvement on the current average for pigmeat (7). It is estimated that the test diet would provide 12 g of long chain n-3 PUFA to the human diet per annum at current pigmeat consumption levels in the UK, about a third of that from oily fish.

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.

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.

Injection of salt, tripolyphosphate and bicarbonate marinade solutions to improve the yield and tenderness of cooked pork loin

Several marinade solutions were tested for their effects on pork tenderness. Paired loins were removed from eight Large White crossbred pigs. Each pair was cut to give eight pieces and injected to a target of 110% of original weight with one of the following eight solutions (g/100 g water): uninjected (A, control), 5% salt (B), 5% sodium tripolyphosphate (C), 3% sodium bicarbonate (D), 5% salt and 5% sodium tripolyphosphate 5% (E), 5% salt and 3% sodium bicarbonate (F), 5% sodium tripolyphosphate and 3% sodium bicarbonate (G), 5% salt, 5% sodium tripolyphosphate and 3% sodium bicarbonate (H). Samples were left overnight to equilibrate, cooked and assessed for tenderness using a Volodkevich shear force method. Mean pHs for meat injected with phosphate and/or bicarbonate (C-H) ranged from 5.75 to 5.97, compared to 5.45 for the control. All injected loins, had a significantly higher yield than the control (p<0.05), except salt alone which, though higher, did not differ significantly (p>0.05) from the control. Treatment H increased the yield from 70% (control) to 85%. All marinades significantly reduced the shear force (p<0.05), some treatments (D and F) by up to a half compared to the control (5150 g). Individual animal results suggest that marination could be used to good effect even in the toughest samples, whilst improving tender samples still further. Samples treated with bicarbonate had an usual porous structure, probably due to carbon dioxide produced during cooking which may have contributed to the reduced toughness.

The effect of cooking on the chemical composition of meat products with special reference to fat loss

The chemical composition and energy content of four product categories (sausages, restructured steaks, burgers and minced beef) were determined before and after cooking. Two cooking methods were used for each product category: sausages and burgers were fried or grilled, restructured steaks were grilled or cooked in an oven whilst mince was either boiled or lightly fried and then boiled to simulate domestic practice. Based on an initial 100 g of product and excluding the low fat products included in the survey, the average weights after cooking were 78, 73, 72 and 70 g for the sausages, restructured steaks, burgers and minced beef, respectively; average fat contents before and after cooking were 22 and 17 g for the sausages, 17 and 14 g for the restructured steaks, 25 and 16 g for the beef burgers, and 19 and 7 g for the mince; and average energy contents before and after cooking were 1215 and 1016 kJ for the sausages, 958 and 815 kJ for the restructured steaks, 1244 and 906 kJ for the burgers and 1009 and 544 kJ for the mince. For a given product type, cooking method was relatively unimportant; the cooking loss, fat loss and energy content of the cooked product being more dependent on product formulation and manufacturing process. The survey included a low fat sausage, a low fat burger, a lean mince and an extra lean mince with fat contents of 8.7, 7.5, 12.4 and 5.2%, respectively. Overall weight losses during cooking were similar to standard products, though low fat products lost proportionally more water and less fat. Frying resulted in a slight gain in fat content for the low fat sausages and burgers, based on an initial 100 g of product, though fried low fat products still had lower fat and energy contents than standard products. It is argued that national consumption figures should take into account the losses that occur during cooking to avoid overestimating fat and energy intake levels.

Effects of breed and marination on the sensory attributes of pork from Large White and Hampshire-sired pigs

The effects of breed and marination were tested for their effects on meat pH, water holding (marinade uptake and losses) and eating quality (tenderness, juiciness and flavour). Loins were removed from one side of 20 Large White-sired and 20 Hampshire-sired pigs after slaughter, cut into four pieces and injected to 112% of their initial weight with water, a polyphosphate-containing marinade (pH 7.7) or a high pH marinade (pH 10.3). An uninjected piece of loin served as control. Samples were left overnight and then frozen before being thawed, cooked and assessed by a trained ten member sensory panel using 1-8 category scales. Hampshires had higher intramuscular fat (0.95%) than Large Whites (0.62%) but otherwise the effects of breed were small compared with marination. Both marinades significantly increased meat pH from 5.5 (control) by 0.2U, significantly reduced the cooking loss and increased the meat yield from about 80% to 90%. Water-injected samples lost large amounts of added water as drip after thawing and had a yield (76%) similar to the control. Marinaded samples retained more water post-cooking. Both marinades significantly increased tenderness (p<0.001) and juiciness (p<0.001) by about 1.0U compared with the control (4.4 for tenderness and 4.2 for juiciness). Pork flavour, however, was significantly reduced (p<0.001) and abnormal flavour was significantly increased (p<0.001) by marination. Tenderness was positively correlated with pH after injection (0.83) and yield (0.75); juiciness was also positively correlated with pH after injection (0.78) and yield (0.87). The absence of any significant difference in eating quality between control and water-injected samples, and the relatively large effects of marination, suggest that retained water (after cooking) is crucial in determining perceived tenderness and juiciness in pork.

Influence of dietary oils and protein level on pork quality. 2. Effects on properties of fat and processing characteristics of bacon and frankfurter-style sausages

Palm kernel oil (PKO) and palm oil (PO) are used in tropical countries as cheaper substitutes for conventional feed sources such as soya bean oil (SBO) but little is known about their effects on meat quality. This study, therefore, evaluated the effects of these three dietary oils on the fatty acid composition (FA) of pork fat and the qualities of belly bacon and frankfurter sausage. The 3×2 factorial design also included high and low dietary protein. Total cooking loss, water loss and fat losses were determined in frankfurter sausages at chopping temperatures from 2 to 24°C. PKO resulted in a poor P:S ratio (0.34) and a relatively hard fat (slip point 32.8°C), but resulted in bacon with a higher tensile cohesive force and more high quality slices, judged subjectively. PO had a fatty acid composition closer to the SBO control, a better P:S ratio than PKO (0.48) and softer fat. There was a trend for total cooking losses and fat losses to be higher in PKO compared with PO and SBO at all chopping temperatures, suggesting that the firmest, most saturated fat (PKO) was least suitable for frankfurter production. The low protein diet increased the concentration of saturated fatty acids and increased fat firmness but its effect on fatty acid composition and other properties were less marked than those of oil type.

Effect of pelvic suspension on three major leg muscles in the pig carcass and implications for ham manufacture

Thirty-two female pigs were slaughtered and their left sides suspended conventionally by the Achilles tendon whilst right sides were suspended from the pelvic bone. The first 16 pigs were used to measure suspension effects on the characteristics of three major leg muscles (m. gluteobiceps, m. semimembranosus and m. rectus femoris) and to assess their suitability for ham manufacture. The remaining pigs were used for the production of hams, made from tunnel- boned whole legs injected to a target 10% weight gain, then tumbled and cooked. Compared with conventional hanging, pelvic suspension resulted in significantly (P<0.01) lower weight loss from the sides during chilling (2.8 and 2.5%). There were major changes in the shape of all three muscles, with pelvic suspension producing marked increases in the width of the m. gluteobiceps (24%) and length of the m. semimembranosus (34%), and a small reduction in the length of the m. rectus femoris (2%). It also resulted in the two former muscles having a relatively higher brine retention, lower drip losses after storage and lower instrumental texture values (Volodkevitch shear force). Cooking loss was reduced in the pelvic-suspended m. semimembranosus. Similarly, whole gammon hams made from pelvic-suspended sides had greater injection gains than hams from conventionally-hung sides (13.6 and 12.3%), with lower cooking losses (16.7 and 19.0%). Instrumental texture values (punch and die peak force) made on the individual muscles in 3-mm thick slices were lower for the m. gluteobiceps (5914 and 9085 g) and m. semimembranosus (6163 and 7600 g) as a result of pelvic suspension. There were minor but significant effects on some colour parameters which probably have little commercial impact. The results demonstrate the advantages of pelvic suspension in terms of brine uptake and retention, and hence increased yield, as well as reduced toughness, for at least two of the major leg muscles, m. gluteobiceps and m. semimembranosus, with no disadvantage for the m. rectus femoris. Together, these three muscles constitute about half of the trimmed leg weight.

Eating quality of UK-style sausages varying in price, meat content, fat level and salt content

Thirty-six brands of pork sausage were purchased from a total of 10 retailers over a 4 months period and assessed for eating quality. The brands included 5 of the 10 most popular sausages in the UK, 4 basic, 14 standard, 10 premium and 8 healthy eating brands. The average price, meat content, fat content and salt content was 3.31 pounds/kg, 62%, 17% and 1.6%, respectively, but there were wide differences in price (1.08 pound/kg-5.23 pounds/kg), meat content (32-97%), fat content (2.1-29.1%) and salt content (0.5-2.5%). Sausages were assessed by a trained sensory panel using 100mm unstructured line scales and 14 descriptors (skin toughness, firmness, juiciness, pork flavour, fattiness, meatiness, particle size, cohesiveness, saltiness, sweet, acidic, bitter and metallic) including overall liking. The declared meat content was positively correlated with price, skin toughness, firmness, pork flavour, meatiness, particle size and perceived saltiness (r=0.5 or better). The declared fat content was positively correlated with fattiness and sweetness (r=0.42 or better) but not juiciness. There was no significant correlation between declared salt content and perceived saltiness. A principal component analysis showed that the first two principal components accounted for 51% of the variability in the data. Products could be separated into four quadrants according to their price, meat content, fat content and their associated eating quality attributes.