Meat Flavor

Broadly, meat flavour is the result of the development of hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, lactones, ethers, furans, pyridines, pyrazines, pyrroles, oxazoles and oxazolines, thiazoles and thiazolines, thiophenes and other sulfur- and halogen-containing substances during chemical reaction with heating.

From: Encyclopedia of Meat Sciences , 2004

The Eating Quality of Meat

Mónica Flores , in Lawrie´s Meat Science (Eighth Edition), 2017

13.7 Conclusions and Future Trends

Meat flavor has been studied for many years, but due to the meat matrix complexity its advancement has been a challenge. Nevertheless, a remarkable progress was made in the last years in the identification and quantification of the characteristic meat aroma compounds. Thousands of volatile compounds were identified as volatile constituents, but the use of olfactometry methodologies and mass spectrometry contributed to increase the knowledge of the main meat odors. Among them, the impact of sulfur containing compounds in meat aroma was of main importance, but the contribution of other aroma compounds should not be underestimated due to possible synergisms among aroma components. Moreover, many different factors affect the generation of flavor, and all of them should be taken into consideration to improve the quality of cooked and processed meat. This meat flavor knowledge is very helpful for the development of savory flavors in flavor creation. Although other features should be taken into account such as the sensory perception of flavor, the effect of meat matrix in flavor interactions, and the online monitoring of flavor release to link in vivo results to consumers attitude. All of these aspects will help in understanding the complexity of flavor perception. Finally, the actual trend to demand natural flavor ingredients in foods makes flavor scientist to look for precursors and biotechnology processes for the production of natural meat flavors.

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CHEMICAL AND PHYSICAL CHARACTERISTICS OF MEAT | Palatability

R.K. Miller , in Encyclopedia of Meat Sciences (Second Edition), 2014

Measuring Meat Flavor

Meat flavor can be detected either chemically or by using humans, defined as 'sensory evaluation.' Sensory evaluation may include either trained or consumer methods. Chemical detection of meat flavor identifies the volatile compounds from meat using gas chromatography. The compounds are separated, usually by molecular weight, and can be identified using mass spectroscopy. Ideally, as compounds come from the gas chromatography to the mass spectrometer, a portion of the compounds are directed to a sniff port. A trained evaluator can smell the compounds as they are eluded and identify the odor characteristics and intensity of volatile compounds. Because all volatile compounds not are detectable by humans, this information can be used to identify compounds that contribute to the flavor of meat. Multivariate techniques, mainly principal component analyses, can be used to identify compounds that contribute toward flavor attributes in the meat.

Flavor attributes in meat are commonly defined by trained sensory panels. Trained sensory panels can use flavor attributes defined in a flavor lexicon. The beef lexicon was developed after an expert panel evaluated beef under a multitude of conditions. The panelist determined descriptors of beef flavor and developed standardized references that could be used to uniformly and consistently identify and quantitate beef flavor attributes. The beef lexicon provides a list of attributes, definition of the attributes, and references to maintain a standard of identify across sensory panelists. Flavor attributes defined by trained, descriptive sensory panelists can then be used in principle component analyses to understand the relationship between chemical volatile compounds and human perception of flavor.

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CHEMICAL AND PHYSICAL CHARACTERISTICS OF MEAT | Palatability

R.K. Miller , in Encyclopedia of Meat Sciences, 2004

Chemical Development and Reactions of Meat Flavour

Cooked meat flavour is the result of chemical reactions that occur within and between the lipid and lean portions of meat during cooking. Raw meat contains very little aroma. Raw meat aroma can be described as blood-like or having a serumy taste, but precursors to cooked meat flavour are contained within raw meat even though in the raw state these precursors are nonvolatile or nondetectable. In general, cooked meat flavour develops as a result of interactions of amino acids, peptides, reducing sugars, vitamins and nucleotides from the lean component, or their breakdown products, during cooking. Lipids also play a role in meat flavour and much of the species-specific flavour of meat is derived from adipose tissue. Lipid degradation and oxidation both contribute to meat flavour, usually negatively by contributing off-flavours.

Broadly, meat flavour is the result of the development of hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, lactones, ethers, furans, pyridines, pyrazines, pyrroles, oxazoles and oxazolines, thiazoles and thiazolines, thiophenes and other sulfur- and halogen-containing substances during chemical reaction with heating. Sulfurous and carbonyl-containing volatile compounds are thought to be mainly responsible for flavour aromatics in meat. These chemical reactions are complex and intermediate reaction products can inter-react with multiple products.

From a sensory standpoint, meat flavour is segmented into multiple components. Aroma or smell prior to consumption is sensed by the olfactory senses. Flavour aromatics are perceived by the olfactory senses during chewing and basic receptors on the tongue. Mouthfeels are identified from the trigeminal receptors in the mouth that provides astringent and metallic sensory attributes and aftertastes are perceived after swallowing. Afterstastes are almost always flavour attributes perceived by the olfactory senses. The underlying chemical components that contribute to these sensory attributes have been studied extensively.

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Improving the quality of meat from ratites

K.W. McMillin , L.C. Hoffman , in Improving the Sensory and Nutritional Quality of Fresh Meat, 2009

18.5.6 Flavor

Meat flavor is a function of the sensory sensations of odor and taste. Odor has many different chemical components due to release of volatiles, while taste is sweet, salty, sour, bitter, and the savory characteristic of meat umami. Peptides, lipids, carbohydrates, nucleic acids and many other compounds contribute to taste ( Miller, 2004).

Ostrich meat has a characteristic aftertaste, which is seldom observed in beef (Harris et al., 1993; Paleari et al., 1995). However, the panelists in those studies also considered ostrich meat to be bland, with the M. gastrocnemius identified as bland more frequently than the M. iliofibularis, M. obturatorius medialis and M. iliotibialis lateralis and the M. obturatorius medialis was described as the most intense in flavor (Harris et al., 1993). The perceived blandness may be attributed to the high ultimate pH and low intramuscular fat content of ostrich meat (Lawrie, 1998; Cooper and Horbaňczuk, 2002). Ostrich muscle type and slaughter age were found to have no effect on meat flavor intensity (Pollock et al., 1997c; Girolami et al., 2003). A consumer panel ranked the hedonic flavor and overall likeness scores of ostrich muscles in order of increased liking as M. fibularis longus, M. oburatorius medialis, M. gastrocnemius, M. iliofibularis, and M. iliofemoralis externus, which was also the same order for sensory tenderness scores (Marks et al., 1998). Beef and ostrich were characterized by relatively strong intensities for most flavor and odor attributes (Kubberød et al., 2002). Interestingly, the evaluation of gender specific preferences and attitudes towards meat indicated that dislike of red meat varieties, including ostriches, was more prevalent in females than in males (Kubberød et al., 2002).

Flavor was highest in the M. iliotibialis cranialis from 10-month-old emus while the M. iliotibialis lateralis muscles from 14-month-old emus were rated higher for flavor compared with other ages of emus (Berge et al., 1997). Feeding fish oil at 43.5 g per day to ostriches had no effect on sensory characteristics of ostrich meat, but did influence flavor of abdominal fat pads (Hoffman et al., 2005). However, feeding fish oil at higher levels might result in undesirable meat sensory attributes.

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Sensory and quality properties of packaged fresh and processed meats

M.G. O'Sullivan , J.P. Kerry , in Advances in Meat, Poultry and Seafood Packaging, 2012

3.4.2 Flavour of fresh and cooked meat

Meat flavour is thermally derived, since uncooked meat has little or no aroma and only a blood-like taste. Only after cooking and a series of thermally induced complex reactions that occur between the many different non-volatile compounds of the lean and fatty tissues does meat become flavoursome (Calkins and Hodgen, 2007; Mottram, 1998). Hundreds of compounds contribute to the flavour and aroma of meat and are very complex attributes of meat palatability. Many of these compounds are altered through storage and cooking, making meat flavour an incredibly complex topic (Calkins and Hodgen, 2007). The main reactions during cooking, which result in aromatic volatile production, are the Maillard reactions between amino acids and reducing sugars, and the thermal degradation of lipid (Mottram, 1998). In general, amino compounds condense with the carbonyl group of a reducing sugar in the presence of heat. This produces gylcosylamine, which is rearranged and dehydrated to form furfural, furanone derivatives, hydroxyketones and dicarbonyl compounds (Calkins and Hodgen, 2007). The broad array of flavour compounds found in meat includes hydrocarbons, aldehydes, ketones, alcohols, furans, thriphenes, pyrrols, pyridines, pyrazines, oxazoles, thiazoles, sulphurous compounds and many others (MacLeod, 1994). Sulphurous compounds occur at low concentrations, but their very low odour thresholds make them potent aroma compounds and important contributors to the aromas of cooked meat (Mottram, 1998). Many of these sulphur compounds contribute sulphurous, onion-like and, sometimes, meaty aromas (Fors, 1983). Roast flavours in foods are usually associated with the presence of heterocyclic compounds such as pyrazines, thiazoles and oxazoles (Mottram, 1998).

A higher proportion of unsaturated fatty acids in the triglycerides of pork and chicken, compared with beef or lamb, produce more unsaturated volatile aldehydes in these meats and these compounds may be important in determining the specific aromas of meat species (Mottram, 1991). Additionally, the effects of dietary ingredients on the sensory attributes of meat are dependent on the type of diet being offered to the meat-producing species in question and also, to a large extent, on the meat species itself (Rødbotten et al., 2004).

In fresh meat the products of fatty acid oxidation produce off-flavours and odours which are usually described as rancid (Gray and Pearson, 1994). The oxidation of fatty acids occurs due to the exposure to O2 and is accelerated in the presence of light and catalysts, such as free iron, and similar to the mechanism described previously for pigment and lipid oxidation. The relationship between rancidity and flavour is unclear. As rancid flavours develop, a subsequent loss in desirable flavour notes occurs (Campo et al., 2006). Greene and Cumuze (1981) reported that oxidized flavour in beef was detected over a broad range of TBARS from 0.6 to 2.0   mg MDA/kg meat, indicating a big variation in the threshold of the panellists. It is difficult to determine the limiting point at which beef can be rejected due to lipid oxidation, based on sensory perceptions (Campo et al., 2006). The general population of meat consumers would not detect oxidation flavours until oxidation products reached levels of at least 2.0   mg/kg tissue (Greene and Cumuze, 1981).

High O2 MAP increases lipid oxidation in meat - Kerry et al. (2000) in lamb; Lund et al. (2007b) in pork; Jakobsen and Bertelsen (2000), Zakrys et al. (2008) and Zakrys-Waliwander et al., (2009, 2010) in beef. The main drawback with using high O2 MAP is the potential for off-flavour development in packs due to lipid oxidation (Jayasingh et al., 2002). Zakrys et al. (2008) found that the sensory quality of MAP beef steaks was best promoted by packaging under atmospheres containing 50% O., followed by 80% O. samples, with TBARS levels below 2   mg MDA/kg. Campo et al. (2006) also indicated that beef would be rejected due to a strong sensory perception of lipid oxidation with TBARS values of 2 or over. The removal of O2 is particularly important with cooked MAP muscle foods. Cooking promotes lipid oxidation, partially due to the release of iron, which acts as a pro-oxidant. The presence of small amounts of O2 accelerates oxidation of cooked MAP meat even further (Smiddy et al., 2002a). The odour of oxidized cooked meats is also referred to as 'warmed over flavour' (WOF) (Pearson et al., 1977). Raw meat is generally considered less susceptible to WOF than heated meat. However, after grinding and exposure to air during processing, odours develop that are similar to those found in oxidized cooked meats (Sato and Hegarty, 1971).

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Volume 2

Siripong Kanokruangrong , ... Alaa El-Din Ahmed Bekhit , in Encyclopedia of Food Chemistry, 2019

Meat Flavor

The majority of meat flavor precursors can be divided into two groups; water-soluble components and lipids. During the heat treatment, many reactions such as Maillard reactions, lipid oxidation, and thiamine degradation contribute to the formation of these compounds. Meat flavor and palatability are influenced by fat content, especially in Intra-muscular fat. Lipid oxidation is a major cause of meat quality deterioration during storage and processing due to generation of rancid and off-flavors but low levels of lipid oxidation can enhance the flavor of the cooked meat. Heterocyclic compounds have been reported to be the main contributors to the volatiles of cooked meat.

The Maillard reaction is a reaction between the carbonyl group of a reducing sugar and the amine group of amino acids. It produces the desirable flavor in the cooked meat, baked bread, coffee and chocolate. In the Maillard reaction, a cascade of reactions occur, and this creates numerous compounds. Primary compounds such as furfural, furanone derivatives, hydroxyketones, and dicarbonyl compounds are created initially. Further reactions with other amines, amino acids, aldehydes, hydrogen sulphide, and ammonia through the Amadori rearrangement, Strecker degradation, and Schiff bases pathways lead to more complex products. The reaction also leads to the formation of melanoidins, brown and high molecular weight polymers, from the condensation of cyclic compounds. The overall reaction scheme is shown in Fig. 1. Different classes of compounds contribute their own characteristics to the meat flavor. The summary and compound examples are shown in Table 1.

Figure 1. Schematic illustration of volatile compounds generated by the Maillard reaction between sugars and amino acids; heat degradation of lipids and thiamin, ∗ refers to Strecker's degradation.

 Source: Bertrand, E., El Boustany, P., Faulds, C.B., Berdagué, J.-L., 2018. The maillard reaction in food: an introduction. Reference Module in Food Science. Elsevier.

Table 1. Flavor compounds generated from the Maillard reaction

Flavor class Characterized flavor/aroma notes Compound example
Alkane Fatty, burnt, pungent Hexane
Aldehyde Green, fatty, sweet, pungent, smoky Hexanal, Butanol, Undecanal
Ketone Musty, fruity, fatty, mouldy 2-Octanone, 1-octen-3-one
Alcohol Roasted, woody, fatty, oily 1-Octen-3-ol
Pyrazine Nutty, roasted, meaty Dimethylpyrazine
Pyridine Cereal-like 2-Isobutyl-3,5-diisopropylpyridine
Furan Sweet, burnt, pungent, caramel-like Pentafuran
Oxazoles Green, nutty, sweet 2,4,5-Trimethyl-1,3-oxazole
Thiophene Meaty 2-Formyl-5-methylthiophene

Adapted from Van Ba et al. (2012) and http://www.flavornet.org/flavornet.html.

The final stage of the MR (Fig. 2) is the most important step for flavor formation and it is often called the Strecker degradation. The intermediate carbonyl compounds react with each other, amino compounds, and amino acid degradation products such as hydrogen sulphide and ammonia. This final stage produces heterocyclic compounds such as pyrazines, pyrroles, furans, oxazoles, thiazoles and thiophenes.

Figure 2. Strecker degradation.

 Source: Mottram, D.S., 2007. The Maillard reaction: source of flavour in thermally processed foods. Flavours and Fragrances. Springer.

The Strecker degradation is very important in flavor generation, as it provides routes by which nitrogen and sulphur can be introduced into heterocyclic compounds in the final stage of the Maillard reaction. The Strecker degradation is initiated by reaction between carbonyl compounds and amino acid forming two important intermediate compounds; α-aminoketones and Strecker aldehyde. The Strecker aldehyde itself contributes to the flavor of the meat. The α-aminoketones are key precursors for heterocyclic compounds, such as pyrazines, oxazoles and thiazoles. In the case of alkylpyrazines, the most direct and important route for their formation is thought to be via self-condensation of α-aminoketones or condensation with other aminoketones.

The Strecker degradation can lead to the production of hydrogen sulphide, ammonia and acetaldehyde if the amino acid is cysteine, whereas methionine will yield methanethiol. These compounds, together with carbonyl compounds produced in the Maillard reaction, provide intermediates for reactions giving rise to important aroma compounds, including sulphur-containing compounds such as thiophenes, thiazoles, trithiolanes, thianes, thienothiophenes and furanthiols and disulphides. The reaction scheme is shown in Fig. 3.

Figure 3. Strecker degradation of cysteine compounds.

 Source: Mottram, D.S., 2007. The Maillard reaction: source of flavour in thermally processed foods. Flavours and Fragrances. Springer.

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Six-membered Rings with Two Heteroatoms, and their Fused Carbocyclic Derivatives

E. Kleinpeter , M. Sefkow , in Comprehensive Heterocyclic Chemistry III, 2008

8.11.9.3.2 Preparation from geminal dithiols or dihalides

Methylenedithiol was used to construct cyclic meat flavor compounds, such as 1,3-dithian-5-one 217 <1998FFJ177>. The reaction of the geminal dithiol with a 1,3-dibromide proceeds with pyridine as base in 44% yield (Equation 81).

(81)

Geminal dihalides have also been applied for the construction of 1,3-dioxanes and congeners. For example, bromochloromethane readily reacted with tetrahydroxynaphthalenes to afford the tetracycle 218 in good yield (Equation 82). Bisdioxane 218 was subsequently used for the synthesis of alkannin and shikonin <1998AGE839, 2000SC1023>.

(82)

An interesting formation of a 1,3-dioxan-4-one from a geminal dichloride and salicylic acid is displayed in Scheme 103 . Langer et al. have found that phthaloyl chloride cleanly reacted with salicylic acid. The product was not the expected nine-membered ring but spirotetracycle 219 in 82% yield. The product formation can be explained by assuming an initial equilibration of phthaloyl chloride and 3,3-dichloro-3H-isobenzofuran-1-one <2001EJO1511>.

Scheme 103.

Dichlorodiphenoxymethane was employed for the synthesis of symmetric <1996AJC1261> and unsymmetric spirobis-1,3-dithianes and congeners <1999AJC657>. The smooth formation of unsymmetrical bis-1,3-dithianes is attributed to the large difference in reactivity between the halide and the phenoxy group, also allowing the preparation of monocyclic intermediates ( Scheme 104 ).

Scheme 104.

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Ingredient Addition and Impacts on Quality, Health, and Consumer Acceptance

Shai Barbut , in Poultry Quality Evaluation, 2017

12.4.3 Flavor Enhancers

Flavor enhancers are compounds that act synergistically with meat flavor compounds to enhance the meaty flavor. A few of the most commonly used ones are 5′-ribonucleotides, hydrolyzed yeast proteins, and MSG. When used at levels in excess of their independent detection thresholds, these compounds contribute to what is called the delicious or umami taste of foods. When used at levels below the independent detection threshold they simply enhance flavors. It is important to recognize that a very small percentage of the population is sensitive to ingredients such as MSG, and therefore, MSG should be clearly marked on the package. Overall, one should remember that meat product's flavor can be affected by many factors (e.g., animal, breed, feed used, aging after slaughter, cooking method) and their interactions (see review by Khan et al., 2015).

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Flavour development in meat

J.S. Elmore , D.S. Mottram , in Improving the Sensory and Nutritional Quality of Fresh Meat, 2009

5.4 Other pre-slaughter factors affecting meat flavour

5.4.1 Breed effect

When compared against dietary effects, breed effects on cooked meat flavour are relatively small. Raes et al. (2003) compared the sensory properties of four beef samples: two from intensively-grown Belgian breeds, an Irish beef sample and an Argentinian sample, the latter two assumed to be extensively reared. The Argentinian and Irish beef samples had a higher flavour intensity, which was probably due to their higher n–3 PUFA content, whereas the two Belgian breeds were not discriminated. Machiels et al. (2004) compared cooked steaks from double-muscled Belgian Blue bulls with those from Limousin and Aberdeen Angus bulls, using GC-MS and GC-olfactometry. Twenty-one volatile compounds were affected by breed. 5-Methyl-2,3-diethylpyrazine was an important aroma compound present at higher levels in the Belgian Blue steaks, while the Strecker aldehyde 2-methylpropanal was at higher levels in the other two steaks (Fig. 5.8). Chambaz et al. (2003) compared four beef breeds for sensory quality. Flavour intensity was unaffected by breed, while juiciness and tenderness were. Campo et al. (1999) noted small effects on flavour and aroma when comparing four beef breeds aged over 21 days, but trends were difficult to ascertain.

Fig. 5.8. Miscellaneous compounds found in meat, including those associated with boar taint.

It is often assumed in beef that the traditional breeds such as Aberdeen Angus have better flavour than dairy breeds such as Holstein–Friesian. Vatansever et al. (2000) compared meat from Welsh Black and Holstein–Friesian cross-breeds. The Welsh Black was significantly tougher than the Holstein–Friesian, but no differences in flavour were noted. Similar results were obtained by Monsón et al. (2005). They compared the sensory properties of four breeds at different conditioning times. This time the Holstein dairy breed was the least tender and the Limousin beef breed was the most tender, although differences were only significant at 7 days or earlier after slaughter. Nuernberg et al. (2005) compared German Holsteins with German Simmentals and found that steaks from Holsteins scored higher for bitter taste but overall liking was not significantly different.

Elmore et al. (2004b) compared the volatile aroma compounds of steaks from Aberdeen Angus and Holstein–Friesian steers. Only four compounds were affected by breed: 1-phytene, 2-phytene and S-methylthioacetate were higher in the Holstein–Friesian steaks, and acetone was higher in the Aberdeen Angus steaks (Fig. 5.8). Koutsidis et al. (2008a) showed that the effects of breed on the water-soluble compounds of these steaks were relatively small. Ribose, arginine and creatinine were slightly higher in Aberdeen Angus than Holstein–Friesian, while glycine and hypoxanthine were higher in the Holstein–Friesian.

The flavour and texture characteristics of Wagyu breed beef are highly regarded. Boylston et al. (1996) showed that lipid-derived volatiles in Wagyu steers were higher than in three common American breeds, but only after storing the cooked meat at 3 °C for 3 days. The higher neutral lipids content of the Wagyu meat may have been responsible for this effect. Larick et al. (1989) compared the flavour of bison steaks with those of Hereford and Brahman steers. Bison steaks scored higher for off-flavour and aftertaste; off-flavours included ammonia, bitter, gamey, liverish, metallic, old, rotten and sour. Off-flavours may have been due to the higher content, and more unsaturated composition, of bison phospholipids, compared to the two cattle breeds.

Wood et al. (2004) compared the sensory properties of cooked meat samples from two traditional (Berkshire, Tamworth) and two modern (Duroc, Large White) pig breeds. The modern breeds were heavier at slaughter with a lower intramuscular fat content, and were lower in pork flavour and desirable flavour than the traditional breeds.

Martinez-Cerezo et al. (2005) compared the flavour of cooked muscle from three lamb breeds, one of which was a dairy breed. Differences were small, with no effect on acceptability. Other workers have also shown little effect of breed on sheep meat flavour (Young et al., 1993). However, when Elmore et al. (2000) compared the aroma volatiles of pressure-cooked steaks of Suffolk lambs with those of Soay, a rare Scottish semi-feral breed, over 50 compounds were present at higher levels in the cooked Soay steaks. Many of these compounds were derived from the Maillard reaction, including sensorially important alkylpyrazines, dimethyl disulphide and dimethyl trisulphide. When the sensory properties of grilled steaks from grass-fed Suffolk lambs were compared with those of grass-fed Soays, Soays scored lower for juiciness, sweetness, normal lamb flavour and overall liking, and higher for abnormal flavour, bitterness, toughness and rancidity (Fisher et al., 2000).

5.4.2 Age/weight at slaughter

When the aroma volatiles of grilled beef steaks from cattle which had been fed either concentrates or grass-based diets were compared, higher levels of the important sulphur compounds dimethyl disulphide and dimethyl trisulphide were present in animals slaughtered at 24 months, compared with those slaughtered at 14 months (Elmore et al., 2006). Differences in volatile composition due to the diets were smaller in the older animals, reflecting smaller differences in the fatty acid composition of the animals at 24 months. Guth and Grosch (1995) showed a linear increase with age of animal in the formation of the character impact compound 12-methyltridecanal from the plasmalogens of beef phospholipids.

Weller et al. (1962) examined lambs slaughtered at three different ages and three different slaughter weights. Roasts were compared and older lambs (over 6 months and 100 lb) were preferred, scoring higher for mildness and typical flavour. Sutherland and Ames (1996) reported higher levels of several fatty acids, including the odour-potent branched chain fatty acids, in the adipose tissue of lambs slaughtered at 30 weeks, compared to those slaughtered at 12 weeks. 4-methyloctanoic acid, in particular, was present at high enough levels to have an impact on lamb flavour. Ames and Sutherland (1999) found higher levels of alkylphenols in the adipose tissue of the same lambs slaughtered at 30 weeks. These compounds may contribute to pastoral flavour in ruminant meat (Young et al., 1999).

Madruga et al. (2000) studied the effect of slaughter age on goat meat flavour. Older animals were tougher with more goaty aroma and less flavour and juiciness, leading to a reduction in overall palatability.

5.4.3 Castration

The use of entire male animals in meat production has been limited, principally due to their aggressive nature, which may also result in glycogen depletion at slaughter, resulting in meat quality defects. In general, however, entire males have a greater lean-to-fat ratio and a better food conversion ratio (Moss, 1992). Boar taint is an off-flavour associated with entire male pigs and castration is seen as a means to minimise its formation.

Ames and Sutherland (1999) showed no effect of castration on the headspace aroma composition of cooked meat from lambs slaughtered at 12 weeks and 30 weeks of age. However, three thiophenols were identified in the adipose tissue of entire lambs, which were absent in castrates. In addition, the faecal-smelling semivolatile compounds indole and skatole were found only in the muscle and adipose tissue of entire lambs, particularly those slaughtered at 30 weeks. Cooked meat with adipose tissue from entire animals was scored much higher for 'farmyard' aroma than meat with adipose tissue from castrates, and also scored higher for 'stale' and 'urine' aromas. Entire animals also scored higher for 'lamby', 'meaty' and 'roasty' notes, as did animals slaughtered at 30 weeks.

Madruga et al. (2000) studied the effect of castration on goat meat flavour. Differences were small but entire animals scored higher for overall palatability. Lipid-derived aldehydes and hydrocarbons were present at higher levels in entire males, while lipid-derived ketones were at higher levels in castrates.

5.4.4 Stress and pH

Under ideal conditions, the pH of meat should be around 5.5 (Lawrie, 1991), and some problems with meat quality can be attributed to pH changes, often caused by animals becoming stressed immediately pre-slaughter. Elevated pH, i.e. ≥ 5.8, due to insufficient lactic acid production in the muscle post-slaughter, leads to a reduction in shelf-life, and at its extreme, results in the phenomenon known as DFD, because the meat appears dark, firm and dry.

Braggins (1996) reported that high-pH (pH ~6.8) cooked lamb mince scored low for overall odour, overall flavour, sheepmeat flavour, and high for foreign odour, compared to ideal pH lamb mince. Nearly all aroma compounds were at lower levels in the high-pH meat, although due to relatively mild cooking conditions, few Maillard reaction-derived compounds were measured. Yancey (2005) found that steaks from high-pH cattle exhibiting DFD had less beef flavour, less brown-roasted flavour, and more rancid flavour than steaks from normal-pH muscle.

Dransfield et al. (1985) examined the relationship between pH post-slaughter and eating quality in pigs fed diets based on soya meal or rapeseed meal. Final pH values ranged from 5.3 to 7.1. Pork became darker as pH increased, with most of the samples being DFD above pH 6.0, while pork flavour was at a maximum and abnormal flavour at a minimum at pH 5.8.

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CANNING

I. Guerrero-Legarreta , in Encyclopedia of Meat Sciences, 2004

See also:

AUTOMATION IN THE MEAT INDUSTRY. COOKING OF MEAT. HACCP AND SELF-REGULATION. HEAT EFFECTS ON MEAT | Flavour development. HURDLE TECHNOLOGY. MICROBIOLOGICAL ANALYSIS | Sampling and testing; MICROBIOLOGICAL ANALYSIS | Standard methods; MICROBIOLOGICAL ANALYSIS | Rapid methods; MICROBIOLOGICAL ANALYSIS | DNA methods; MICROBIOLOGICAL ANALYSIS | Total bacterial count; MICROBIOLOGICAL ANALYSIS | Indicator organisms. MICROBIOLOGICAL SAFETY OF MEAT | Salmonella spp.; MICROBIOLOGICAL SAFETY OF MEAT | Escherichia coli O157:H7; MICROBIOLOGICAL SAFETY OF MEAT | Clostridium botulinum ; MICROBIOLOGICAL SAFETY OF MEAT | Clostridium perfringens ; MICROBIOLOGICAL SAFETY OF MEAT | Thermotolerant Campylobacter ; MICROBIOLOGICAL SAFETY OF MEAT | Listeria monocytogenes ; MICROBIOLOGICAL SAFETY OF MEAT | Yersinia enterocolitica ; MICROBIOLOGICAL SAFETY OF MEAT | Staphylococcus aureus ; MICROBIOLOGICAL SAFETY OF MEAT | Bacillus cereus ; MICROBIOLOGICAL SAFETY OF MEAT | Aeromonas spp; MICROBIOLOGICAL SAFETY OF MEAT | Yeasts and moulds; MICROBIOLOGICAL SAFETY OF MEAT | Prions and viruses. PARASITES | Internal. PROCESSING EQUIPMENT | Tumblers and massagers. SENSORY AND MEAT QUALITY, OPTIMIZATION OF.

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