8. ANÁLISIS DE RESULTADOS
8.2 METANARRATIVA SOBRE LA EVALUACIÓN DE LA IMPLEMENTACIÓN
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2.1 Introduction
Meat flavour is influenced by compounds contributing to the sense of taste and smell. Other sensations like mouth-feel and juiciness will also affect the overall flavour sensation, but the volatile compounds of cooked meat mainly determine its aroma attributes and flavour characteristics. There have been over 1000 volatile compounds isolated from meat (Mottram, 1991).
Meat flavour is thermally derived as raw meat possesses little odour and a mild serum-like taste, which is described as salty, metallic and bloody, with a sweet aroma (Wasserman, 1972; Hornstein and Wasserman, 1987). Much research has been aimed at understanding the chemistry of meat aroma and the nature of the reacting compounds. The major precursors of meat flavour can be divided into the two categories of water- soluble components (amino acids, peptides, carbohydrates, nucleotides, thiamine, etc.) and lipids. The Maillard reactions between amino acids and reducing sugars, and the thermal degradation of lipids result in many aroma volatiles forming during the cooking process (deRoos, 1992; Kramlich & Pearson, 1960; MacLeod & Seyyedain-Ardebili, 1981). Also lipid-derived volatiles have an important part to play in desirable meat aromas both directly as aroma compounds and as intermediates to other aroma compounds (Nawar, 1969; Mottram, 1991). In this literature review the chemistry of pork flavour is covered first, followed by a consideration of factors affecting pork flavour with a particular emphasis on pre-slaughter factors.
2.2 Chemistry of pork flavour
Raw pork meat tissue consists of water, proteins, amino acids, nucleotides, sugars, lipid, vitamins, and other compounds. All these components act as potentially important flavour compounds, flavour enhancers and aroma precursors (Mottram, 1991).
During the cooking process, various non-volatile compounds in pork undergo degradation or reaction with each other to produce numerous volatile compounds to form multiple volatiles and non-volatiles that give the characteristic pork flavour (Chen
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& Ho, 1998). Flavour formation is thus closely related to the amount and nature of precursors present in the raw pork at the time of cooking (Mottram, 1991). A number of factors may influence the presence of flavour precursors, such as feed (Koutsidis et al., 2007a; Mottram, Koutsidis, Oruna-Concha, Ntova, & Elmore, 2004; Rosenvold et al., 2001), pre-slaughter stress (D´ Souza, Dunshea, Warner, & Leury, 1998; Wiklund, Andersson, Malmfors, & Lundström, 1996) and ageing (Koutsidis, Mottram, Elmore, & Oruna-Concha, 2003; Koutsidis et al., 2007b; Parrish et al., 1969; Tikk et al., 2006).
The types of volatile compounds found in pork flavour have been identified as hydrocarbons, alcohols, carbonyls, carboxylic acids, esters, lactones, ethers, sulphur- containing compounds as well as different classes of heterocyclic compounds, including furans, pyridines, pyrazines, oxazoles, thiazoles and thiophens (Table 2.1). Shahidi, Rubin & D’Souza (1986) noted that the number of volatiles present in cured pork is about one third of those in uncured pork.
Table 2.1
Classification of volatile compounds found in uncured and cured pork (modified from Shahidi et al. 1986)
Class of compound Number of compounds
Pork (uncured) Pork (cured)
Hydrocarbons 45 4 Aldehydes 35 29 Ketones 38 12 Alcohols 24 9 Phenols 9 1 Carboxylic acids 5 20 Esters 20 9 Lactones 2 - Furans 29 5 Pyridines 5 - Pyrazines 36 -
Other nitrogen compounds 24 3
Sulphur compounds 31 31
Halogenated compounds 4 1
Miscellaneous compounds 7 11
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Generally the characteristic species-associated flavours and aromas that occur in pork, beef, lamb and poultry are located in the lipid fraction (Hornstein and Wasserman, 1987; Macy et al., 1964), while the water-soluble fraction contains components contributing to the development of ‘meaty’ flavour (Macy et al., 1964). Differences in the fatty acid composition in animals may contribute to characteristic species flavour differences. It is also known that lipids alone are not responsible for these characteristic aromas (Mottram, Edwards & MacFie, 1982). A study has shown that regardless of the source (beef or pork) of the fat added to lean meat, the inclusion of 10% subcutaneous fat allowed panellists to more easily correctly differentiate minced pork and beef patties (Mottram, 1979).
During cooking, lipids decompose to create a myriad of volatiles. The main reactions involved are oxidation and degradation of both unsaturated and saturated fatty acids. The primary oxidation products, known as the monohydroperoxides, decompose via an intermediate alkoxy radical, thus forming a range of aroma volatiles. Such decompositions include many aliphatic hydrocarbons, alcohols, aldehydes, ketones, acids, lactones, esters and long chain alkyl-substituted heterocyclic compounds (Macleod and Ames, 1986). Lipid derived volatile compounds dominate the flavour profile of pork cooked at temperatures below 100oC. Table 2.2 lists some of the volatile compounds generated from lipid degradation in cooked pork volatiles.
Aldehydes are the major components identified in the volatiles of cooked pork. Octanal, nonanal and 2-undecenal are oxidation products of oleic acid, hexanal, 2- nonenal and 2,4-decadienal are major volatiles products of linoleic acid. Oleic and linoleic acids are the two most abundant unsaturated fatty acids in pork (Schliemann, Wolm, Schrodter & Ruttloff, 1987). 1-octen-3-ol may be derived from the 12- hydroperoxide of arachidonic acid in cooked pork (Mottram, 1985; Chou and Wu, 1983). 2-pentyfuran, which has been identified in cooked pork, is an autooxidation product of linoleic acid (Ho, Smagula & Chang 1978).
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Table 2.2
Examples of volatile lipid oxidation products identified in cooked pork (Ramarathnam , Rubin & Diosady, 1993; Chou & Wu, 1983; Mottram, 1985)
Compounds Aldehydes
Hexanal Heptanal 3-methylhexanal Octanal Nonanal Dodecanal Tridecanal Tetradecanal Hexadecanal Octadecanal 2-hexenal 2-heptanal 2-octenal 2-nonenal 4-decenal 2-undecenal 2-dodecenal 2-tridecenal 2-tetradecenal 17-octadecenal 16-octadecenal 15-octadecenal 9-octadecenal 2,4-nonadienal 2,4-decadienal 2,4-undecadienal
Ketones
2-heptanone 2-tetradecanone 2-hexadecanone 2,3-octanedione
Alcohols
1-pentanol 1-hexanol 1-heptanol 1-octanol 2-heptenol 1-octen-3-ol 1-nonanol 1-nonen-3-ol
Alkyfurans
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2.3 Factors affecting pork flavour
The flavour development of pork following standard cooking procedures depends on the amount and nature of precursors present in meat, which, in turn, depends on several factors including feed (Mottram, Koutsidis, Oruna-Concha, Ntova, & Elmore, 2004), post mortem treatments such as aging (Koutsidis, Mottram, Elmore, & Oruna-Concha, 2003; Parrish et al., 1969), and genetic variations (Lawrie, 1991). Some of the factors that may influence the flavour of pork at different stages of animal production and meat processing were outlined as follows (adapted from Ngapo and Gariépy (2008)):
Pre-slaughter factors Genetic factors
1. Breed and genetic lines
Gender effects and Nutrition effects
1. Direct transfer of aroma active components
2. Changes in the fatty acid composition
3. Diet effects on hind gut digestion
4. Diet effects on liver metabolism
Post-slaughter factors
Post-mortem and pre-cooking factors
1. Patterns of temperature change
2. Conditioning or ageing
3. Storage before cooking
Preparation before consumption
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In this review, only the preslaughter factors as set out in Figure 2.1 will be reviewed in detail as they are of most relevance for the project reported in this thesis.
They are:
1. Genetic effects 2. Gender effects 3. Nutrition effects
2.3.1 Genetic effects on pork flavour
2.3.1.1 Breeds
The genetic background of pigs plays an important role in the eating quality of pork (Casteels, Van Oeckel, Bosschaerts, Spincemaille & Boucqué, 1995; de Vries, Van der wal, Eikelenboom, Merks, 1992) due at least in part to genetic effects on the level of intramuscular fat (IMF). Casteels et al. (1995) compared three genotypes for eating quality in a preference test and showed lower preference scores for taste intensity, tenderness and juiciness for pork from Belgian Landrace pigs relative to pork from Large Whites and hybrids which had the highest IMF levels and also scored best for intrinsic and sensory meat quality parameters.
Positive relationships between IMF levels and eating quality of pork were reported by Kirkegaard, Mǿller, & Wismer-Pedersen (1979); Bejerholm & Barton-Gade (1986); Gandemer et al. (1990); Jakobsen (1992) and Hovenier, Kanis, and Verheven (1993), with recommended IMF levels being from 1 to more than 4%. It should be possible to modify the IMF content by selection as the heritability of IMF is in the range of 0.4 – 0.6 (Cameron, 1990; de Vries, Hovenier, Brascamp, & Westerink, 1992; Lo et al., 1992; Schwörer, Blum, & Rebsamen, 1986; Sellier, 1988; Touraille & Monin, 1982; Touraille & Monin, 1984). The pork from 100% Duroc pigs which was juicier, had a higher IMF content compared with 0 and 50% Duroc pigs (Channon et al., 2004). The intramuscular neutral lipid was higher in saturated fatty acids 14:0 and 16:0 and polyunsaturated fatty acids (PUFA) in the meat of Duroc and Large White pigs compared to that from Berkshire and Tamworth pigs (Wood et al., 2004).
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Other examples of where increased IMF level has resulted in better sensory qualities in pork have been from pig crosses (Touraille, Monin & Legault (1989) for Large White (LW) and MeiShan x Large White (MS x LW) pork. The half-Chinese crossbred pigs gave a meat of higher palatability than the corresponding purebred European pigs. MS x LW meat was evaluated as being tastier, more tender and more juicy as compared to the LW.
Sellier (1988) and Warriss, Brown, Franklin, & Kestin (1990) suggested that increased IMF levels can be achieved without having carcasses with an undesirable amount of subcutaneous fat that has to be trimmed, thereby decreasing the yield of saleable meat.
Correlations reported by Casteels, Van Oeckel, Bosschaerts, Spincemaille & Boucqué (1995) between the IMF level and daily gain and back fat thickness indicated that it was possible to increase the IMF level by selection programs, without negative consequences for the growth and back fat thickness of the animals.
2.3.1.2 Individual gene effects
It has been shown that cooked pork from carriers of the RN- allele has significantly higher levels of both glucose and glucose 6-phosphate, and that the fatty acid composition in this pork includes more unsaturated fatty acids compared with that from non-carriers (Meinert, Andersen, Bredie, Bjergegaard, & Aaslyng, 2006). The lipid of pork from RN- carrier pigs had more polyunsaturated phospholipids and more monounsaturated triglycerides than non-carriers in the study of Enser, Hallett, Hewett, Fursey, and Wood (1996). In the studies by Johansson et al. (1999) and Lundström et al (1996, 1998), the RN- allele in Hampshire crosses had significant effects on the sensory properties of pork loin, with RN- meat more acidulous in taste (due to low pH) than meat from non-carriers, and having a more intense meat taste (Johansson, et al., 1999; Jonsall et al., 2001, 2002; Lundström et al., 1996). Le Roy et al. (1996) obtained better sensory scores for flavour, but worse scores for tenderness, juiciness and mellowness for RN-carriers than for non-carriers. RN- carriers have also been found to have lower protein content (Estrade et al., 1993; Enfält et al., 1997), higher drip and cooking losses, and higher internal reflectance values (Lundstrom et al., 1996).
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The halothane gene can affect the quality of pork. The most obvious quality defect associated with the halothane gene is the high incidence of pale, soft exudative (PSE) meat Means, McCormick & Du, 2007 showed that the presence of the halothane gene induced early energy depletion, which could be the main change causing the adenosine monophosphate-activated protein kinase (AMPK) activation that leads to accelerated glycolysis and an increased incidence of PSE meat.
In conclusion, the genetic influence on pork quality comprises differences among breeds as well as differences among animals within the same breed. These differences can be caused by a large number of genes with small effects, known as polygenic effects, and in principle most traits of interest for meat quality like flavour and texture have a multifactorial background (Andersson, 2001). A comprehensive list of genetic markers for carcass and meat quality in pigs has been published by Garnier, Klont, and Plastow (2003).
2.3.2 Gender effects on pork flavour
Growing entire male pigs for meat production offers economical advantages in production costs as well as the advantage of increased carcass leaness (Malmfors & Lundstrom, 1983; Cliplef, Grinwich & Castell, 1984; Diestre, Oliver, Gispert, Arpa & Arnau, 1990; Bekaert, Casteels, Eexkhout, & Buyssee, 1974; Van Oeckel, Casteels, Warnants, De Boever, et al., 1996).
However, boar meat sometimes has a boar taint, which can reduce consumer acceptability (Bañón, Andreu, Laencina & Garrido, 2004; De Kock, Heinze, Potgieter, Dijksterhuis & Minnaar, 2001). A recent international study involving seven EU countries (Bonneau et. al., 2000) showed that a higher proportion of consumers were not satisfied with pork from entire males when compared with gilt pork (31.9 vs 26.0% for odour; 21.5 vs 18.5% for flavour). The major causes of the taint have been recognised as andronstenone (Patterson, 1968) together with other 16-androstene steroids (García-Regueiro & Diaz, 1989) produced by testes, and skatole (Vold, 1970),
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which is produced by bacteria in the gut. These compounds accumulate in fats and generate offensive off-odours and off-flavours of meat when it is heated (Babol, Squires & Gullett, 1999).
In the U.K., pigs are slaughtered at relatively light weights and young ages compared to most other countries, which reduces the likelihood of boars developing high levels of androstenone or skatole (Malmfors & Lundstrom, 1983). The main limiting factor with regard to the use of heavier entire males is boar taint in unprocessed meat, but this defect is better tolerated in processed meat products, so pork from heavier males may be best used for processed products (Banón, Costa, Gil, & Garrido, 2003; Bonneau, Denmat, Vaudelet, Veloso-Nunes, Mortensen & Mortensen 1992; Diestre, Oliver, Gispert, Arpa, & Arnau, 1990).
Another study by Gullett, Partlow, Fisher, Halina & Squires (1993) compared the consumer acceptability of fresh and cured pork from gilt, intersex, cryptorchid, and intact male pigs. The intersex pigs used in the study were pseudo-hermaphrodites possessing a female external morphology and an internal morphology of male, male/female or female. Cryptorchidism is either a developmental defect where the testes fail to descend into the scrotum, or it can be induced. Consumer rating of pork chops from intact males received the lowest score, followed by the cryptorchid while the gilts and the intersex pigs received the highest. Castration reduces androstenone and skatole in meat (Bañón, Andreu, Laencina, & Garrido, 2004), but it also slows down the growth of pigs and makes them fatter, thereby increasing production costs (Bonneau, 1998). Castration of male pigs has been the traditional method of preventing boar odors since boars are the main source of the problem. Skatole concentrations in adipose tissues of boars can vary between 0.0 and 1.5 ppm, whereas for gilts and barrows the concentration seldom reaches 0.3 ppm. The acceptable limit for skatole was 0.25 ppm (Mortensen et al., 1986; Bejerholm & Barton-Gade,1993).
Not everyone is necessarily sensitive to boar taint and some people are more affected by it than others genetically determined ( Only 56% of men can detect androstenone, compared with 92% of women. The odour
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was shown to be more unpleasant to women than to men by however, is highly offensive to most people to note the eating quality differences between animals of differing gender, there will always be both male and female animals producing pork for the market. The ratios of different sexual groups very much depends on the demand in the market and may be influenced by criteria other than production efficiencies or eating quality, such as, the ethical debate of castration of boars.
The findings on effects of boar taint on pork and its products are summarised in Table 2.3. Based on the six studies summarised in Table 2.3, it can be concluded that:
1. Boar taint is associated with androstenone, skatole and indole.
2. The presence of boar taint in pork is undesirable among a variable proportion of consumers.
3. Pork acceptance has been shown to be better for pork from castrated males than entire males.
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Table 2.3
A summary of the results from the studies showing the effects of boar taint on chemical and sensory properties of fat, pork meat and pork products with emphasis on effects on flavour
Animal and Experimental design Measurements made and methods used Results and Conclusions References
40 entire males (EM) and 40 castrated males (CM) received feed made from cereals (corn, barley and wheat), molasses and soya ad libitum.
Androstenone and skatole content of the fat was determined using HPLC.
8 trained judges evaluated five attributes in cooked loin using 5-point scales from 1 (minimum) to 5 (maximum).
68 untrained consumers assessed preference and acceptability of cooked loin samples on a scale of 1 (very poor) to 5 (very good).
• Castration caused a considerable reduction in androstenone, skatole and indole levels in subcutaneous fat.
• Androstenone was reduced by more than 70% by castration, while the fall in skatole and indole was less pronounced.
• Increased meat fatness and reduced boar taint, aroma and taste for pork from castrated pigs.
• Pork acceptance was better in castrated males than in entire ones. Castrated ones were preferred by 75% of consumers.
Bañón et al., 2004
Back fat samples and samples of the corresponding L. dorsi and fat covering L. dorsi were obtained from 12 boars and three gilts.
Indolic compounds were determined using HPLC.
• A correlation was observed between the concentration of indole and skatole in the back fat and fat covering the L. dorsi samples (p<0.001, r=0.99).
• No significant correlation was obtained in L. dorsi samples, between skatole and indole levels.
• The mean concentrations of these indolic compounds were significantly higher (P<0.05) in the back fat samples than fat covering the L.dorsi samples.
Rius et al., 2001
Pork fat samples from loins from boars with low, medium or high skatole and androstenone concentrations were obtained from a commercial abattoir.
300 pork consumers evaluated the pork using a nine-point scale with word anchors (dislike extremely and like extremely) at the extreme ends.
• Majority of consumers were less willing to consume pork meat exhibiting detectable levels of boar odour. • Most of them were dissatisfied with pork meat with
detectable levels of skatole.
• More females compared with males responded more negatively towards samples with detectable levels of androstenone.
De Kock et al., 2001
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Table 2.3 (continued)
718 meat samples with 646 from entire male pigs and 72 from gilts.
Trained analytical sensory panels in seven European countries assessed pig meat with known levels of androstenone and skatole.
• Sensory panels in general were able to differentiate between the two compounds and between different levels of the compound.
• Androstenone was found to relate mostly to the urine attribute, while skatole related mostly to manure and, to a lesser extent, to naphthalene
Bonneau et al., 1996
48 cooked loins and 48 dry-cured hams from entire males and castrates were studied.
8 trained panellists evaluated the sensory attributes of dry-cured ham. The scale ranged from 1 (minimum) to 5 (maximum) for intensity of boar odour , boar flavour, saltiness, graininess, toughness , juiciness and marbling . 268 randomly chosen consumers
carried out a preference and acceptability test using a scale of 1 (very poor) to 5 (very good).
• The dry cured ham from castrates was scored as more flavoured, more marbled and softer. It has less grainy, less salty and had less boar odour and flavour. • Dry-cured ham from castrated males was more
accepted by consumers, especially women and habitual consumers.
• Castration of male pigs improved the quality of dry- cured ham.
Bañón et al., 2003
Model and commercial type Swedish fermented sausage products based on low or high levels of boar tainted fat, three different starter cultures and two different levels of smoking were studied.
The sensory panel consisted solely of women (21–56 years of age) using a 15-cm unstructured line scale anchored from “none” to “extreme” for odour, flavour and texture of pork.
• The perception of boar taint was significantly negatively correlated to the overall positive impression of the commercial sausages.
• Liquid smoke masked the perception of boar taint.
Stolzenbach et al., 2009
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2.3.3 Nutrition effects on pork flavour
Many reports have shown that the diet fed to pigs can influence the flavour quality of pork. The reasons for modifying the diets are mainly to improve pig performance, but this can also influence the sensory quality of pork (Warnants, Van