Significance of fat supplemented diets on pork quality – Connections between specific fatty acids and sensory attributes of pork

MEAT SCIENCE Meat Science 77 (2007) 275–286 www.elsevier.com/locate/meatsci

Significance of fat supplemented diets on pork quality – Connections between specific fatty acids and sensory attributes of pork Kaja Tikk a, Meelis Tikk a, Margit D. Aaslyng b, Anders H. Karlsson c, Gunilla Lindahl d, Henrik J. Andersen e,* a

c

Department of Food Science, Faculty of Agricultural Sciences, University of Aarhus, P.O. Box 50, DK-8830 Tjele, Denmark b Danish Meat Research Institute, Maglegaardsvej 2, DK-4000 Roskilde, Denmark Department of Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark d Department of Food Science, Swedish University of Agricultural Sciences, P.O. Box 7051, SE-75007 Uppsala, Sweden e Arla Foods amba, Corporate R&D, Skanderborgvej 277, DK-8260 Viby J, Denmark Received 5 December 2006; received in revised form 6 March 2007; accepted 14 March 2007

Abstract The influence of two diets with different fatty acid compositions has been studied with regard to overall pork quality and significance of specific fatty acids on sensory attributes in fried chops and oven roasts. Twenty castrates and 20 females were in a balanced experimental set-up fed with a standard diet supplemented with a-tocopherol (200 mg/kg feed) where the fat source was either 3% of palm oil or 3% rapeseed oil. After slaughter, despite differences in lipid composition and sensory attributes, no significant difference in overall meat quality parameters and flavour precursors was found. Comparison of the two diets showed that supplementation with rapeseed oil resulted in a significantly higher content of C18:3n-3 (polar lipid (PL), neutral lipid (NL)), C18:2n-6c (NL) and C20:2 (NL) in LD and C18:1n-9c, C18:2n-6c, C18:3n-3, C20:3n-3, C22:5n-3 in backfat, while supplementation with palm oil resulted in a higher content of C16:0 (NL), C16:1 (PL), C18:1n-9t (NL) in LD and C16:0, C17:0, C18:0, C16:1, C20:4n-6 in backfat. A positive and significant correlation between the contents of C18:2n-6c, C20:3n-6 in the PL fraction and the sensory attributes fried meat odour and sweet odour were found in fried pork chops from female pigs. Likewise, positive correlations were seen between the content of C18:1n-9c in the PL fraction and sensory attributes such as sourish odour, piggy odour and piggy flavour in whole oven roasts. These data substantiate the view that specific fatty acids in the PL fraction influences flavour attributes in pork.  2007 Elsevier Ltd. All rights reserved. Keywords: Pork; Diet; Fatty acid composition; PL fraction; NL fraction; Sensory attributes

1. Introduction Carcass composition, technological quality and eating quality of pork are important factors in pork production. Feeding of the animals has proved to be important for controlling overall meat quality (Andersen, Oksbjerg, Young, & Therkildsen, 2005). The role of fat in meat flavour has been the subject of an extensive number of studies (Cameron & Enser, 1991; *

Corresponding author. Tel.: +45 2095 1241; fax: +45 8999 1564. E-mail address: [email protected] (H.J. Andersen).

0309-1740/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2007.03.019

Cameron et al., 2000; Mottram, 1996; Nuernberg et al., 2005; Teye et al., 2006; Wood et al., 1999, 2003). Unlike ruminants, in which most of the dietary unsaturated fatty acids are hydrogenated in the rumen (Jenkins, 1993), dietary fatty acids are incorporated directly into tissue lipids in pigs (Mourot & Hermier, 2001; Wood et al., 2003). Consequently, any feed that influences the concentration of flavour precursors or deposits unique components in the fat will affect the cooked meat flavour (Melton, 1990). Lipids may contribute to the meat flavour of cooked meat in several ways. They may either undergo thermal oxidation which results in flavour active compounds that

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contribute directly to meat flavour (Mottram, 1991; Mottram, 1996; Mottram, 1998a), or react further with other components within the lean tissue resulting in other flavour compounds (Whitfield, Mottram, Brock, Puckey, & Salter, 1988). Additionally, lipids may also act as a solvent for several aroma compounds accumulated during production, processing and cooking of meat (Elmore, Campo, Enser, & Mottram, 2002; Mottram, 1996; Wasserman & Spinelli, 1972). The phospholipids are believed to contribute to aroma development in meat whereas triglycerides do not appear to be as important (Mottram, 1996; Mottram & Edwards, 1983). Correlations between sensory attributes of the meat and fatty acids from PL and NL fractions have been reported (Cameron et al., 2000). Especially the degree of unsaturation of fatty acid has been reported to have significant influence on flavour attributes with high levels of unsaturated lipids contributing to desirable flavours (Mottram, 1996, 1998a). In contrast, other studies did not find connections between lipid composition and flavour in pork meat (Rhee, Davidson, Cross, & Ziprin, 1990; van Oeckel, Casteels, Warnants, van Damme, & Bouque, 1996). However, it is well established that reheated pork containing high levels of unsaturated lipids gives rise to oxidised offflavours (Romans, Wulf, Johnson, Libal, & Costello, 1995; Shackelford, Reagan, Haydon, & Miller, 1990; Skibsted, Mikkelsen, & Bertelsen, 1998; Willemot, Poste, Salvador, Wood, & Butler, 1985). Focus on the nature of the fat source in pig diets is essential to ensure production of high quality meats. In the past, a vast number of studies have focused on the fat source in pig diets in relation to (i) high pig performance (Warnants, van Oeckel, Boucque, & de Paepe, 1995; Warnants, van Oeckel, & Boucque, 1996), (ii) high technological quality including shelf-life (Cameron & Enser, 1991; Sheard et al., 2000; Wood et al., 2003), (iii) elimination of off-flavour (Willemot et al., 1985; Ahn, Lutz, & Sim, 1996) and (iv) fulfillment of legislation and/or improvement of the nutritional value of pork (Kouba, Enser, Whittington, Nute, & Wood, 2003; Sheard et al., 2000). The objective of the present study was to investigate the influence of diets containing two different fat sources, characterised by either an increased level of saturated (palm oil) or unsaturated fatty acids (rapeseed oil) on meat quality including fatty acid profiles, several flavour precursors and sensory characteristics of the cooked meat from both castrates and females. Moreover, potential relationships between specific fatty acids and meat flavour characteristics were explored. 2. Materials and methods 2.1. Animals and treatments The pigs were reared at the experimental farm at the University of Aarhus, Research Centre Foulum. Forty crossbreed pigs (Duroc boars and Danish Landrace · Dan-

ish Yorkshire sows) originating from 10 litters with two females and two castrates in each pen were included in the study. The littermates were distributed uniformly between the diets and genders. The diet of the pigs was based on barley, wheat, soybean meal and vegetable fat (Table 1). Twenty pigs were given a diet including 3% palm oil, and 20 pigs were given a diet including 3% rapeseed oil. This resulted in a 2 (diet) · 2 (sex) experimental design. As seen in Table 1, the feed mixture was changed during the experiment, with the first diet being provided from 20 to 55 kg live weight, and the second diet from 55 kg live

Table 1 Feed composition of the diets used in the experiment Ingredients, %

20–55 kg

55 kg until slaughter

Barley Wheat Wheat bran Soybean meal Vegetable fatb Molasses Lysine, 40% Methionine, 40% Threonine, 50% Monocalcium phosphate Calcium carbonate Sodium chloride Mineral and vitamin premixa E-vitamine (Evisol 25000) Analysed chemical composition; % Dry matter Crude protein Crude fat Ash Fibre

47.58 20.00 – 25.21 3.00 1.00 0.39 0.17 0.11 0.88 0.53 0.37 0.20 0.56

45.43 20.00 5.00 21.84 3.00 2.00 0.15 0.07 – 0.57 0.84 0.34 0.20 0.56

88.40 17.76 5.53 5.28 4.67

88.14 16.73 5.56 5.10 4.69

a Solivit Mikro 106 containing 2,500,000 IU vitamin A, 500,000 IU vitamin D3, 30,000 mg vitamin E, 1100 mg vitamin K3, 1100 vitamin B1, 2000 mg vitamin B2, 1650 mg vitamin B6, 5500 mg D-pantothenic acid, 11,000 mg niacin, 27.5 mg biotin, 11 mg vitamin B12, 25,000 mg Fe, 40,000 mg Zn, 13,860 mg Mn, 10,000 mg Cu, 99 mg J and 150 mg Se per kg. b The vegetable fat source of the diet was either palm oil or rapeseed oil. The fatty acid composition of oils is given according to Gunstone et al. (1994).

Fatty acid

Rapeseed oil (%)

Palm oil (%)

C12:0
– nd <0.2 3.3–6.0 0.1–0.6 1.1–2.5 52.0–66.9 16.1–24.8 6.4–14.1 0.2–0.8 0.1–3.4 0.0–0.1 0.0–0.5 0.0–2.0 0.0–0.1 0.0–0.2 0.0–0.4

0–0.4 – 0.5–2.0 40.1–47.5 0–0.6 3.5–6.0 36–44 6.5–12 0–0.5 0–1.0 – – – – – – –

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weight until slaughter. All pigs were slaughtered at approximately 110 kg live weight with a fasting period of 24 h, during which time the animals had free access to water.

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packed and stored for 2 days at 4 C before freezing at 20 C. 2.4. Chemical analysis

2.2. Slaughtering procedure On the day of slaughter, the pigs were transported (200 m) to the slaughterhouse where they were brought up to the stunner individually. The pigs were stunned by 80% CO2 for 3 min, exsanguinated, scalded at 62 C for 3 min, cleaned and eviscerated within 30 min. pH (pH45 min) and temperature (T45 min) inside M. longissimus dorsi (LD) (at the last rib) and in the deep portion of M. semimembranosus (SM) was measured 45 min postmortem. Subsequently, the carcasses were placed in a chill room at 4 C. The temperature was measured with a Testo 110 thermometer (Testo Gmbh & Co, Germany), and the pH was measured with a PHM201 pH meter (Radiometer, Denmark) equipped with Metrohm LL combined pH penetration electrode (Metrohm, Switzerland). The pH electrode was calibrated in pH 4.01 and 7.00 IUPAC buffers equilibrated at 35 C for the measurements on the warm carcasses at 45 min postmortem and at 4 C for the measurements on the cold carcasses at 24 h postmortem. 2.3. Meat quality traits 24 h post mortem and sampling The day after slaughter, pH (pH24 h) and temperature (T24 h) from LD and SM were measured as described for measurements taken 45 min postmortem. The colour of the meat was measured on LD and SM samples. LD and SM were removed from the carcass, and a 2 cm thick sample across the fibre direction (30– 32 cm from the last rib in the cranial direction) from each LD and SM was cut and bloomed for 1 h at 4 C. Five colour measurements were carried out across the individual sample surfaces, and mean values were used for statistical analysis. Colour was measured using a Minolta Chroma Meter CR-300 (Osaka, Japan) calibrated against a white tile (L* = 93.30, a* = 0.32 and b* = 0.33). The aperture was 8 mm, illuminant D65 and 10 Standard Observer. Water-holding capacity as drip loss was measured from the LD sample taken 5 cm from the last rib in the cranial direction. This was done by weighing the approximately 100 g muscle sample taken out from the LD, hanging it in a net and suspending the net in a plastic bag for 24– 72 h after slaughter at 4 C (Honikel, 1998). Drip loss is expressed as a percentage of the initial weight. For chemical analysis, a 5 cm thick sample (30–35 cm from the last rib in the cranial direction) was cut out from LD, vacuum-packed and stored for 2 days at 4 C before freezing at 20 C. The first layer of backfat from the top of LD (1–5 cm from the last rib in the cranial direction) was removed and frozen for determination of fatty acid composition. For sensory analysis, a 25 cm thick sample (5–30 cm from the last rib in the cranial direction) was cut from the LD, trimmed to a 3 mm fat layer, vacuum-

Intramuscular fat content (%) was determined by the gravimetric method according to SBR (Schmid–Bodzinski–Ratzlaff, NMKL No. 131, 1989). The method was modified to Soxtec equipment (Foss, Hillerod, Denmark). Fatty acids of the intramuscular fat (IMF) of LD were separated into neutral (NL) and polar/phospholipids (PL) fractions and analysed according to a slightly modified method of Kalunzy, Duncan, Merritt, and Epps (1985). Minced lean meat of LD (2 g) was homogenised in 4 g methanol. Subsequently, 0.6 g homogenate was mixed with 4 g of chloroform, 1 g of methanol and 2 g of water and homogenised. After homogenising (10 min at 1400g) the lipids were obtained from the chloroform phase by evaporation of the chloroform using a steam of nitrogen. Subsequently, the lipid fraction was dissolved in 1.2 ml heptane and applied to an amino-propyl column pre-conditioned with heptane under vacuum. The neutral lipids were eluted from the column with 11 ml of chloroform–propanol (2:1), phospholipids were eluted with 12 ml of methanol and charged unesterified fatty acids with 6 ml 2% acetic acid in diethylether, which were discarded. Finally, the NL and PL fractions were redissolved in chloroform and dried under the nitrogen. The extracted fat was methylated in 1 ml natrium methylat. After methylation, 4 ml saturated NaCl and 1 ml heptane were added, and the samples were centrifuged for 10 min at 1400g. Heptane phase containing fatty acids was applied to the GC. Fatty acids in backfat were analysed according to a slightly modified method described by Jakobsen et al. (1995). Backfat (300 mg) was placed in an oven at 50 C for 24 h (to facilitate the homogenisation) and subsequently added to 4 g of chloroform, 4 g of methanol and 3 g of water before homogenisation. The homogenate was centrifuged for 10 min at 1400g. Then the extracted fat fraction was obtained by evaporation of the chloroform phase under a steam of nitrogen. 10 mg of the extracted fat was methylated in 1 ml sodium methylat. After methylation, 4 ml saturated NaCl and 1 ml heptane was added, and the samples were centrifuged 10 min for 1400g. The heptane phase containing fatty acids was applied to the GC. The composition of fatty acids was determined by gas chromatography using a FFAP column (25 m · 32 · 5 lm; Hewlett–Packard). One microliter was applied to the column using splitless injection, helium as carrier gas (8 mL/min), an injector temperature of 275 C and a detector temperature of 300 C. The initial column temperature was 50 C, which was kept for 2 min, whereafter the temperature was raised by 10 C/min to 240 C and then maintained for 15 min. Quantification was based on comparison of retention times and peak areas with external standards (Supelcoe 37 Component FAME Mix, Supelco PUFA-1

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Mix), and calculations were carried out in the included software (HP Chemstation). The concentration of tocopherols in 1 g of meat was analysed by HPLC after saponification and extraction into heptane using a slightly modified method described by Jensen, Engberg, and Hedemann (1999), with a saponification time of 1.5 h at 70 C. The results were expressed as lg/g of muscle. Inosine 5 0 -monophosphate, inosine and hypoxanthine were determined according to Tikk et al. (2006). Muscle glycogen, lactate and glucose-6-phosphate content were determined in duplicate 50 mg muscle samples according to the method of Passonneau and Lowry (1993). Thiamine determination was carried out according to a slightly modified method by Ha¨gg (1994). Five grams of minced muscle was hydrolyzed with 30 ml of 0.1 M HCl for 30 min at 121 C, and cooled to ambient temperature. The pH was adjusted to 4.0–4.5 with approximately 2.5 ml of sodium acetate (2 M), and 5 ml of 6% freshly prepared clara-diastase solution was added before incubation at 50 C for 3 h. Subsequently, the protein was precipitated by addition of 1 ml of 50% trichloracetic acid and heating in waterbath at 100 C for 15 min. Subsequently, the samples were cooled to ambient temperature, and the sample volume was brought up to 50 ml with water before centrifugation at 3000 rpm for 5 min. Five milliliters supernatant was mixed with 2.5 ml potassium ferricyanide in 15% sodium hydroxide, and mixed for 10 s to ensure derivatisation of thiamine to thiochrome. Subsequently, the derivatisation solution was brought up to 10 ml with 3.75 M HCl before sample clean-up with C18 solid phase extraction columns and analysis of thiochrome using the method of Sims and Shoemaker (1993). Finally, 10 ll of thiochrome sample was injected into a ZORBAX Exlipse XDB-C18 USP L1 Column 4.6 · 150 mm, particle size 5 lm from which thiochrome was separated by isocratic elution using a buffer solution (72% of 0.005 M NH4OAC and 28% of methanol, pH 5.0) at a flow rate of 1.5 ml/min. Thiamine as the thiochrome derivative was determined with a fluorescence detector at an excitation wavelength of 370 nm and 435 nm emission wavelength. Quantification was based on a standard curve using external standards and calculations carried out in the included software (HP Chemstation), and the results were expressed as mg/100 g of muscle. 2.5. Sensory analysis Two centimeter thick pork chops from the left LD were fried in a pan at 160 C and turned every 2 min, until an end point temperature of 70 C was reached. The temperature was determined in each chop by a handheld thermometer (Testo 926, Testotherm, Buhl and Bundsoe, Virum, Denmark). The whole roasts from the right LD were cooked in roasting bags in a convection oven at a 90 C, until the end point temperature inside the roast was 65 C. For sensory assessment, the meat was sliced in 1½ cm thick slices. From both cooking methods, two slices each measuring

5 · 5 · 1½ cm were served to each assessor immediately after cooking on hot plates with a three-digit number in a randomized design. The panel for the sensory assessments had received a basic training based on ISO 4121, ASTM-MNL 13, DIN 10964. All assessors were familiar with assessment of pork. For evaluation of the fried chops, the panel consisted of four assessors – two males and two females aged between 44 and 59 years. The fried chops were evaluated on a 15 cm unstructured scale from nothing to very intense for the following attributes: fried meat colour (surface), fried meat odour, sweet odour, sourish odour, sourish taste, bitter taste, sweet taste, metal taste, piggy flavour, fried meat flavour, hardness at first bite, crumbleness, fibrousness, tenderness and juiciness after 3–4 chews. For evaluation of the oven roasts, the panel consisted of eight assessors, all females and aged between 48 and 63 years. The oven roasts were evaluated on a 15 cm unstructured scale from nothing to very intense for the following attributes: boiled meat odour, sweet odour, sourish odour, piggy odour, pores, boiled meat flavour, piggy flavour, sourish taste, metal taste, rancid flavour in the fat layer, hardness at first chew, juiciness after 3–4 chews, fibrousness, crumbleness and tenderness. 2.6. Statistical analysis The statistical analyses were carried out with the statistical analyses system version 8.2 (SAS Institute Inc., Cary, NC, USA). The MIXED procedure was applied when least-squares means (LSM), and standard errors of the LSMs (SEM) of all variables were calculated. Leastsquares means were considered to be significantly different if p < 0.05. The statistical model for analysing all meat quality attributes and chemical data included fixed effects of diet and gender as well as their interaction and the random effect of slaughter date and litter within slaughter date. The results of the sensory profile were analysed in a MIXED model as well, with gender, diet and their interaction as fixed effects, and assessor and animal as random effects. In order to determine significant correlations, the CORR procedure was applied, where both gender and cooking methods were analysed separately. The set of the variables included all fatty acid (PL and NL fraction) and sensory variables of the fried chops and oven roasts. The correlations were considered significant if p < 0.05 and as a tendency if p < 0.1 (Pearson’s correlation coefficients are shown in brackets). Moreover, to visualise the results and to get an overall overview of potential connections between fatty acids and sensory attributes, a multivariate analysis was performed using the Unscrambler 9.1 software (Camo ASA, Oslo, Norway). Partial least square regression (PLSR) was used to investigate the ability to predict the sensory data from the chemical data. A full cross-validation and an uncertainty test were performed where X-variables contained fatty acids (not standardised) and Y-variables sensory attri-

K. Tikk et al. / Meat Science 77 (2007) 275–286

butes (standardised). Female and castrate pigs were analysed separately in the exploration of possible correlations and differences between specific fatty acids and sensory attributes in pork from two genders.

3. Results 3.1. Meat quality and chemical analysis With the exception of fatty acid composition (Tables 4– 6), there were no notable, significant differences in meat quality traits (Table 2) including flavour precursors (Table 3), neither between feeding groups nor between genders. Only in SM, the a*-value was found to be higher from pigs fed a diet supplemented with palm oil compared with pigs fed a diet supplemented with rapeseed oil. A feed and sex interaction was found with regard to muscle lactate level, which was higher in castrates fed rapeseed oil. Moreover, the c-tocopherol content in LD was higher from castrates fed rapeseed oil, compared with the other groups. Feeding and gender gave rise to significant differences in PL and NL composition of IMF of LD (Tables 4 and 5). Comparison of the two diets showed that supplementation with rapeseed oil resulted in a significantly higher content of C18:3n-3 (PL, NL), C18:2n-6c (NL), C20:2 (NL) and C20:3n-3 (NL), while supplementation with palm oil resulted in a higher content of C16:0 (NL), C16:1 (PL), C18:1n-9t (NL). Female pigs showed a higher content of C16:0 in the PL and C18:1n-9c and C18:2n-6c in the NL fraction compared with castrates, while castrates had a significantly higher content of C16:0 in the NL fraction. Moreover, interactions between feeding and gender in the

279

content of C17:0 and C22:6n-3 in the PL fraction was found. The effect of feeding and gender on the total fatty acid composition of backfat is shown in Table 6. As expected, the relative content of saturated fatty acids was significantly higher, and the content of unsaturated fatty acids, especially polyunsaturated fatty acids, was significantly lower in pigs fed a palm oil-supplemented diet compared with pigs fed a rapeseed oil-supplemented diet. Comparison of the two diets showed that feeding with rapeseed oil significantly increased the content of C18:1n-9c, C18:2n-6c, C18:3n-3, C20:3n-3 and C22:5n-3, while feeding with palm oil raised the content of C16:0, C17:0, C18:0, C16:1 and C20:4n-6. Castrates had a significantly higher content of saturated fatty acids such as C14:0, C16:0, C18:0, C20:0 and a lower content of polyunsaturated fatty acids such as C18:2n-6c, C18:3n-3, C20:4n-6, C22:5n-3, C22:6n-3 in their backfat compared with female pigs. Regarding feeding regime, pigs fed a diet supplemented with rapeseed oil had a significantly lower n6:n3 ratio in the PL and NL fractions of LD and in backfat and a significantly higher P:S ratio in the NL fraction of LD and backfat compared with pigs fed a diet supplemented with palm oil. 3.2. Sensory analysis The sensory results of fried pork chops and whole oven roasts are shown in Table 7. A sensory analysis of the pork loins fried as chops in a pan or prepared as whole roasts in an oven showed only minor difference in meat flavour attributes in relation to the feeding regime. Pork from pigs fed rapeseed oil had higher scores for sourish odour compared

Table 2 Meat quality parameters of M. longissimus dorsi (LD) and M. semimembranosus (SM) from pigs fed the diet containing either rapeseed oil or palm oil* Parameter

Liveweight, kg Hot carcass weight, kg Intramuscular fat in LD, % Driploss in LD, % LD pH45 min pH24 h T45 min, C T24 h, C L* a* b* SM pH45 min pH24 h T45 min, C T24 h, C L* a* b* *

Rapeseed oil

Palm oil

SEM

Female

Castrate

Female

Castrate

107.33 84.35 2.59 7.29

104.63 83.74 2.5 5.51

107.11 83.92 2.52 6.48

107.68 84.6 2.92 7.04

6.41 5.51 40.16 3.55 55.32 6.91 5.75

6.48 5.51 40.05 3.58 56.45 6.58 5.92

6.37 5.53 40.35 3.51 55.95 7.05 5.99

6.45 5.56 40.58 4.73 55.32 8.53 7.23

6.52 5.59 40.28 4.77 55.37 8.29 6.95

6.46 5.6 40.48 4.49 54.19 9.14 7.23

Least squares means and SEM are shown.

P (difference) Feed

Sex

1.38 1.17 0.23 0.77

ns ns ns ns

6.44 5.52 40.34 3.64 56.08 6.78 6.01

0.04 0.04 0.33 0.13 0.65 0.32 0.28

ns ns ns ns ns ns ns

ns ns ns ns ns ns ns ns ns ns ns ns

6.43 5.62 40.68 4.94 54.64 8.79 7.18

0.08 0.03 0.18 0.18 0.79 0.39 0.29

ns ns ns ns ns 0.041 ns

ns ns ns ns ns ns ns

280

K. Tikk et al. / Meat Science 77 (2007) 275–286

Table 3 The results of chemical analysis in M. longissimus dorsi (LD) from pigs fed the diet containing either rapeseed oil or palm oilA Rapeseed oil

Hypoxantine, nmol/mg Inosine monophosphate, nmol/mg Inosine, nmol/mg Thiamine, mg/100 g Glycogen, lmol/g Lactate, lmol/g Glucose-6-P, lmol/g Tocopherols, lg/g Alpha Gamma ab A

Palm oil

Female

Castrate

Female

Castrate

0.30 4.38 1.99 0.79 29.50 121.86b 11.69

0.19 4.62 1.94 0.84 28.49 136.35a 11.40

0.32 4.68 2.06 0.75 27.88 134.27ab 10.64

0.27 4.74 1.93 0.76 27.98 124.77ab 10.84

3.96 0.042

3.98 0.062

3.90 0.032

3.94 0.038

SEM

P (difference) Feed

Sex

Feed * Sex

0.05 0.12 0.09 0.04 2.02 5.05 0.71

ns ns ns ns ns ns ns

ns ns ns ns ns ns ns

ns ns ns ns ns 0.023 ns

0.31 0.005

ns 0.015

ns 0.042

ns ns

Means with different letters on the same row show significant differences. Least squares means and SEM are shown.

Table 4 The composition of PL fraction (% of total fatty acids) and ratios of saturated and unsaturated fatty acids in the intramuscular fat of LD from females and castrates fed diet containing rapeseed oil or palm oilA Fatty acid

C14:0 C16:0 C17:0 C18:0 C22:0 C24:0 C16:1 C18:1n-9c C20:1 C18:2n-6c C18:3n-6 C20:2 C20:3n-6 C20:4n-6 C22:4n-6 C18:3n-3 C22:5n-3 C22:6n-3 P PSFA MUFA P PUFA P:S ratio n6:n3 ratio

Rapeseed oil

Palm oil

SEM

Female

Castrate

Female

Castrate

0.27 26.81 0.29b 7.57 0.22 1.37 0.75 15.64 0.05 35.11 0.66 0.31 0.77 4.56 0.26 1.99 0.56 2.78a 36.63 16.47 46.76 1.29 7.88

0.24 26.17 0.41a 7.66 0.36 1.06 0.64 15.37 0.13 35.02 0.72 0.32 1.01 4.27 0.32 2.06 0.62 2.47ab 35.81 16.13 47.88 1.34 8.56

0.27 27.78 0.31b 7.77 0.25 1.05 0.92 16.37 0.19 34.96 0.75 0.29 0.58 4.44 0.25 1.55 0.41 2.42b 37.54 17.52 44.76 1.19 9.45

0.36 26.55 0.27b 7.01 0.29 1.12 1.04 15.74 0.08 36.45 0.72 0.29 0.91 4.53 0.31 1.59 0.51 2.66ab 35.62 16.91 47.25 1.33 9.21

0.05 0.64 0.03 0.26 0.05 0.23 0.11 0.55 0.06 0.69 0.25 0.03 0.17 0.33 0.06 0.18 0.21 0.18 0.52 0.63 0.85 0.04 0.49

P (difference) Feed

Sex

Feed * Sex

ns ns ns ns ns ns 0.013 ns ns ns ns ns ns ns ns 0.022 ns ns ns ns ns ns 0.021

ns 0.031 ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns 0.012 ns 0.032 0.023 ns

ns ns 0.021 ns ns ns ns ns ns ns ns ns ns ns ns ns ns 0.024 ns ns ns ns ns

ab

Means with different letters on the same row show significant differences. C20:3n-3 and C20:5n-3 were detected below 0.1% and are considered as traces. C20:0 and C18:1n-9t were not detected. A Least squares means and SEM are shown.

with palm oil fed pigs independent of gender and cooking method. However, some flavour and texture differences between females and castrates were found in the sensory profiles. Castrates had higher scores for the attributes associated with the Maillard reaction such as fried meat odour and fried meat colour compared with females when the meat was fried as chops. Likewise, the texture attributes hardness at first bite, fibrousness and tenderness differed between genders with pork from the castrates being more tender, less hard and less fibrous. As expected, differences between different cooking methods were evident in relation to flavour and texture attributes. Fried pork chops had

higher intensity scores for sweet odour and metal taste compared with oven roasted pork, whereas piggy flavour and sourish taste were more associated to oven roasted pork compared with fried pork chops. In relation to texture attributes oven roasted pork was less hard, less juicy, less fibrous, but more tender and more crumbly compared with fried pork chops. 3.3. Correlations between fatty acids and sensory attributes Significant positive and negative correlations between sensory attributes and specific fatty acids in PL and NL

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Table 5 The composition of NL fraction (% of total fatty acids) and ratios of saturated and unsaturated fatty acids in the intramuscular fat of LD from females and castrates fed diet containing rapeseed oil or palm oila Fatty acid

C14:0 C16:0 C17:0 C18:0 C20:0 C16:1 C18:1n-9c C18:1n-9t C20:1 C18:2n-6c C20:2 C20:4n-6 C18:3n-3 C20:3n-3 P PSFA MUFA P PUFA P:S ratio n6:n3 ratio

Rapeseed oil

Palm oil

SEM

Female

Castrate

Female

Castrate

1.37 25.64 0.12 14.26 0.17 3.11 47.51 0.26 0.71 5.11 0.22 0.13 0.94 0.13 41.61 51.55 6.34 0.15 5.11

1.36 26.42 0.12 14.51 0.17 3.14 46.82 0.26 0.72 4.81 0.22 0.11 1.01 0.13 42.54 50.92 6.08 0.14 4.61

1.25 26.09 0.12 14.59 0.13 3.23 47.86 0.34 0.69 4.61 0.19 0.14 0.43 0.05 42.43 52.11 5.21 0.12 10.28

1.39 27.31 0.12 15.32 0.16 3.42 46.26 0.31 0.71 4.19 0.18 0.12 0.39 0.05 44.31 50.76 4.72 0.11 10.13

0.05 0.37 0.01 0.44 0.01 0.14 0.55 0.03 0.06 0.21 0.01 0.01 0.07 0.01 0.63 0.61 0.3 0.01 0.26

P (difference) Feed

Sex

ns 0.006 ns ns ns ns ns 0.022 ns 0.002 0.0002 ns <0.0001 <0.0001 0.043 ns <0.0001 <0.0001 <0.0001

ns 0.0003 ns ns ns ns 0.031 ns ns 0.022 ns ns ns ns 0.021 ns 0.051 0.011 ns

a

Least squares means and SEM are shown. C24:0, C18:3n-6, C20:3n-6, C22:4n-6 and C22:5n-3 were detected below 0.1% and are considered as traces. C22:0 and C20:5n-3 were not detected.

Table 6 Total fatty acid composition (% of total fatty acids) and ratios of saturated and unsaturated fatty acids in back fat from females and castrates fed diet containing rapeseed oil or palm oila Fatty acid

C14:0 C16:0 C17:0 C18:0 C20:0 C16:1 C18:1n-9c C18:1n-9t C20:1 C18:2n-6c C20:2 C20:4n-6 C18:3n-3 C20:3n-3 C22:5n-3 C22:6n-3 P PSFA PMUFA PUFA P:S ratio n6:n3 ratio

Rapeseed oil

Palm oil

SEM

Female

Castrate

Female

Castrate

1.01 20.05 0.33 11.44 0.19 1.49 43.32 0.19 0.79 15.93 0.64 0.21 3.45 0.44 0.17 0.11 32.96 45.79 20.91 0.64 3.86

1.05 21.33 0.31 12.23 0.22 1.61 43.57 0.19 0.87 13.93 0.73 0.15 3.03 0.41 0.15 0.11 35.09 46.24 18.59 0.54 3.87

1.01 23.52 0.38 13.56 0.18 1.71 42.21 0.21 0.77 13.63 0.62 0.23 1.25 0.17 0.11 0.14 38.43 44.92 16.11 0.42 8.01

1.11 24.53 0.37 14.76 0.21 1.83 41.68 0.18 0.79 12.38 0.51 0.19 1.17 0.16 0.09 0.08 40.85 44.51 14.57 0.36 8.27

0.02 0.51 0.02 0.47 0.01 0.08 0.53 0.01 0.04 0.51 0.07 0.01 0.11 0.03 0.01 0.01 0.84 0.59 0.69 0.02 0.13

P (difference) Feed

Sex

ns <0.0001 0.011 <0.0001 ns 0.021 0.009 ns ns <0.0001 ns 0.006 <0.0001 <0.0001 <0.0001 ns <0.0001 0.031 <0.0001 <0.0001 <0.0001

0.006 0.021 ns 0.006 0.031 ns ns ns ns 0.0002 ns <0.0001 0.0009 ns 0.004 0.041 0.003 ns 0.0003 0.0001 ns

a

Least squares means and SEM are shown. C22:0, C24:0, C18:3n-6, C20:3n-6, C22:4n-6 and C22:5n-3 were detected below 0.1% and are considered as traces. C20:5n-3 was not detected.

fractions were established. To visualise the results and get a better overall understanding of how the specific fatty acids could explain the variation in the sensory properties, PLSR and a correlation analysis were performed. The correlations were most pronounced in the PL fraction of females compared with castrates.

The correlation analyses (Person’s correlation) of the specific fatty acids in the PL fraction and the flavour attributes of fried pork chops from female pigs showed that C18:2n-6c had a significant and positive correlation with the sensory attribute fried meat odour (r = 0.53) and sweet odour (r = 0.52), C20:3n-6 with sweet odour

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Table 7 Average intensity scores (Least squares means) from the sensory profiling of fried pork chops and whole oven roasts from females and castrates fed diet containing rapeseed oil or palm oil Fried chops

Odour Fried meat Boiled meat Piggy Sweet Sourish Flavour Meat Piggy Rancid Taste Sweet Sourish Metal Bitter Texture Hardness Juiciness Fibrous Crumbleness Tenderness Fried meat colour Pores

Oven roasts

Rapeseed oil

Palm oil

Castrate

Female

Castrate

9.02 – – 4.46 2.11

8.17 – – 4.24 2.55

8.31 2.45 –

SEM

Rapeseed oil

Palm oil

Female

Castrate

Female

Castrate

Female

8.64 – – 4.16 1.87

7.77 – – 3.71 1.96

– 6.59 4.31 1.27 2.61

– 6.73 4.18 1.43 2.33

– 6.58 4.04 1.33 2.09

– 7.24 4.31 1.65 2.39

7.83 1.71 –

7.95 1.94 –

7.19 2.02 –

7.73 3.71 1.82

7.59 3.29 1.83

7.49 3.51 1.39

3.42 5.08 3.62 0.98

3.03 5.77 3.66 1.17

3.02 5.58 3.19 0.82

2.73 5.32 3.74 1.48

– 5.76 2.26 –

– 5.77 2.26 –

5.71 8.51 3.79 6.51 8.59 9.31 –

6.51 8.21 3.92 6.11 7.85 7.85 –

6.03 8.41 3.81 6.09 8.67 8.89 –

6.43 7.93 4.06 6.71 8.09 8.53 –

3.87 7.23 1.55 8.72 10.85 – 5.02

5.21 6.62 2.66 7.82 9.53 – 4.49

(r = 0.45), C22:4n-6 tended to correlate with sourish odour (r = 0.39), while C18:2n-6c, C18:3n-6 were negatively correlated with piggy flavour (r = 0.45, r = 0.37, respectively). C17:0 and C18:0 were significantly and positively correlated with piggy flavour (r = 0.44 and r = 0.69, respectively) while those fatty acid were significantly and negatively correlated with sweet odour (r = 0.64 and r = 0.63, respectively). In general, a higher level of polyunsaturated fatty acids had a positive and significant correlation with sweet odour (r = 0.53) and had a tendency to correlate with fried meat odour (r = 0.41). In oven roasts from female pigs, the monounsaturated fatty acids of the PL fraction, C16:1 and C18:1n-9c were significantly and positively correlated with sourish odour (r = 0.59, r = 0.70, respectively), C17:0 and C18:1n-9c with piggy odour (r = 0.59, r = 0.50) and with piggy flavour (r = 0.56, r = 0.72). Moreover, C18:2n-6c was significantly and negatively correlated to sourish odour (r = 0.70) and piggy flavour (r = 0.54), and C18:3n-6 to sourish taste (r = 0.58) in females. Therefore, polyunsaturated fatty acids were significantly and negatively correlated to sourish odour (r = 0.49), piggy odour (r = 0.45) and piggy flavour (r = 0.53). Likewise, the same patterns can be seen in the graphical presentation of the correlation loadings (Fig. 1), which shows overall possible relations between specific fatty acids in the PL fraction and flavour attributes of fried pork chops and whole oven roasts from female pigs. In addition, C18:3n-6 and C22:6n-3 were associated with fried meat odour and sweet odour. Moreover, boiled

P (difference) Feed

Sex

Cooking method

0.7 0.5 1.1 0.3 0.2

ns ns ns ns 0.021

0.051 0.071 ns ns ns

– – – <0.0001 ns

7.37 3.52 1.92

0.3 0.4 0.6

ns ns ns

ns ns ns

ns <0.0001 –

– 5.89 2.08 –

– 6.01 2.12 –

0.6 0.3 0.3 0.3

ns ns ns ns

ns ns ns ns

– 0.021 <0.0001 –

4.58 7.67 2.31 7.95 10.12 – 3.81

5.29 6.56 2.95 7.85 9.36 – 5.42

0.3 0.4 0.3 0.3 0.4 0.6 0.8

ns ns ns ns ns ns ns

0.004 0.061 0.008 ns 0.011 0.061 ns

<0.0001 0.0002 <0.0001 <0.0001 <0.0001 – –

meat odour and meat flavour were positively correlated with C18:2n-6c and with polyunsaturated fatty acids. Interestingly, the correlations between specific fatty acids from the PL fraction and sensory attributes of meat from castrated pigs were less pronounced with both cooking methods. However, in oven-roasts from castrates, the tendency towards significant correlations between C17:0 and C18:3n-3 of the PL fraction and sourish odour (r = 0.39, 0.43, respectively) were found. Moreover, the fatty acid C22:4n-6 tended to correlate with the sensory attribute meat flavour (r = 0.39). The correlations in the NL fraction were less evident compared with the PL fraction. Fatty acid C18:3n-3 from the NL fraction tended to correlate with sourish taste (r = 0.37), sourish odour (r = 0.44) and meat flavour (r = 0.38) from female pigs fried as chops. C18:2n-6 showed significant positive correlations to fried meat odour (r = 0.44) and fried meat colour (r = 0.54) in fried chops from castrates. C20:0 was only found in the NL fraction of LD. Even though it did show significant correlations with the sensory attributes boiled meat odour (r = 0.56) and meat flavour (r = 0.53) in oven-roasts from castrates, as well as significant positive correlations with the sensory attributes sweet taste (r = 0.47), tendency to meat flavour (r = 0.41), and a significant negative correlation to metal taste (r = 0.46) and bitter taste (r = 0.49) in fried chops from castrates, the level of C20:0 was so low that these correlations are probably not relevant. Moreover, the fatty acids in the NL fraction C18:3n-3 showed a significant positive tendency and C18:2n-6c only

K. Tikk et al. / Meat Science 77 (2007) 275–286

283

Fig. 1. An overview of the correlation loadings from partial least squares regression (PLSR) analyses with fatty acids from PL fraction as X-variable (not standardised) and sensory variables of the fried pork chops (shown as variable name and ‘‘_f’’) and oven-roasted pork (shown as variable name and ‘‘_o’’) from female pigs as Y-variables (standardised).

a tendency to correlate with the sensory attribute sourish odour (r = 0.52 and r = 0.39, respectively) of oven-roasts from castrates, therefore the more PUFA, the more sourish odour (r = 0.45). C18:1n-9c tended to correlate with sourish taste (r = 0.42) in oven roasts from castrates. Finally, no significant correlations between specific fatty acids in either the PL or NL fractions and texture attributes were found. 4. Discussion With the exception of fatty acid composition, no significant differences using 3% rapeseed oil or 3% palm oil as fat source in the feed were found on meat quality parameters, including flavour precursors. However, the a*-value of SM was found to be slightly higher, but without any practical importance, when pigs were fed the diet containing palm oil (Table 2). Moreover, the c-tocopherol content in LD was higher when pigs were fed rapeseed oil, which most probably reflects a higher content of c-tocopherol in rapeseed oil compared with palm oil. The limited effect of the fat source on overall meat quality parameters has been reported in other studies (De la Llata et al., 2001; Teye et al., 2006; Warnants et al., 1996). Consequently, as the amounts of palm oil and rapeseed oil did not give rise to inferior quality attributes, they are both suitable fat sources that can be recommended for inclusion, at these levels, in diets with no detrimental effects on meat quality. As expected, the fatty acid composition of the meat was affected by the diets with the changes in the PL fraction being minor (Table 4), while significant differences between

feeding regimes and level of specific fatty acids were found in the NL fraction of LD and in total fatty acids in backfat (Tables 5 and 6). The feed containing rapeseed oil significantly increased the proportion of PUFA in backfat and in the NL fraction of LD. Moreover, female pigs had more PUFA compared with castrates, independent of feeding. The observed gender effect is in agreement with previous studies (Ho¨gberg, Pickova, Dutta, Babol, & Bylund, 2001; Nuernberg et al., 2005; Warnants et al., 1996), showing a higher PUFA level in female pigs compared with castrates and particularly in the NL fraction and the backfat while not reflected in the PL fraction (Warnants et al., 1996). Moreover, feeding pigs with a rapeseed oil diet has been reported to raise the concentration of all the C18 unsaturated fatty acids, particularly a-linolenic acid (C18:3) (Wood & Enser, 1997), which is supported by present findings. The difference in the degree of unsaturation of the lipids and fatty acids in different feeding groups has been suggested to produce different flavouring compounds and flavour characteristics (Larick & Turner, 1990) in the final product due to difference in the formation of oxidation products. Formation of oxidation products are affected by the temperatures used during preparation (Mottram, 1985; Mottram, 1998b; Satyanarayan & Honikel, 1992; Smith, Salih, & Morgan, 1987) i.e. pan frying (high surface temperature) versus cooking in an oven (low surface temperature) in the present study. However, dietary treatment resulted in notable differences in the formation of the flavour attributes in the sensory results, except the higher scores for sourish odour from pigs fed rapeseed oil com-

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pared with palm oil. In a study by Sheard et al. (2000), grilled loin chops from male pigs received significantly higher abnormal flavour scores compared with females; however, the sensory panel was unable to discern differences between diets. Our study showed some gender effects, more pronounced in relation to texture attributes than to flavour. The fact that the two diets resulted in notable differences in flavour attributes might be explained by the relatively small difference obtained in the fatty acid composition using the two diets in combination with the high level of vitamin E within the muscles, which limits oxidative reactions (Lauridsen, Nielsen, Henckel, & Sørensen, 1999). In contrast, cooking method influenced the intensity of the sensory scores. A more intense sweet odour in pan fried pork compared with oven prepared pork can be related to the formation of Maillard reaction-derived compounds, while the more intense piggy flavour and sourish taste in oven roasted pork can be related to lipid oxidation-derived compounds (Mottram, 1985). The higher tenderness scores for oven roasted pork compared with fried pork can be explained by the difference in water content due to the different temperatures used in cooking. The fatty acid composition of the LD muscle has been suggested to influence the eating quality of pork, with saturated and monounsaturated fatty acids being positively correlated and polyunsaturated fatty acids negatively correlated with pork flavour (Cameron & Enser, 1991). Increased PUFA levels have often been reported to give rise to off-flavour problems after reheating because of their greater susceptibility to oxidative breakdown and the formation of unwanted volatile compounds during cooking (Larick, Turner, Schoenherr, Coffey, & Pilkington, 1992; Shackelford et al., 1990). This has especially been found to be associated with a high level of n  3 PUFA (Coxon, Peers, & Griffiths, 1986; Romans et al., 1995). Wood and Enser (1997) suggested that a high n  3 fatty acid concentration in meat is associated with fishy flavours, which have also been reported in other studies with bacon (Coxon et al., 1986; Romans et al., 1995). These findings are supported by model system findings, thus the study by Campo et al. (2003), found that C18:1 was characterised by oily odour, C18:2 by cooking oil odour and C18:3 by fishy and linseed odours. However, contrary results have been reported. In some consumer studies, it has been found that elevated levels of C18:2 make pork flavour more acceptable (Theunissen, Kouwenhoven, & Blauw, 1979), and they are associated with sweet taste (Campo et al., 2003). The sensory results obtained were correlated to the fatty acids in the PL fraction. Interestingly, correlations in pork from female pigs were more evident compared to castrates independent of cooking method. The polyunsaturated fatty acids C18:2n-6c, C18:3n-6 and C20:3n-6, which were found in higher levels in the PL fraction compared with the NL fraction of LD, were found to be significantly and positively correlated with the sensory attributes fried meat odour and sweet odour and not to be associated to piggy flavour. In contrast, C17:0, C18:0 and C18:1n-9c were sig-

nificantly, positively correlated with piggy flavour and inversely associated with sweet odour and fried meat odour in female pigs. This is partly in agreement with the study by Cameron et al. (2000), who found positive correlations between C18:2n-6, C20:4n-6 and C22:4n-6 with pork flavour, flavour liking and overall acceptability in the PL fraction of LD, and consistent with data found in aqueous model systems showing that PLs are associated with meaty/pleasant cooked chicken aroma (Farmer & Mottram, 1990, 1992). Thus specific fatty acids in the PL fraction might be associated with positive sensory attributes, while this could not be established between NL fatty acids and specific sensory attributes. Rhee et al. (1990) reported significantly increased taste panel scores for tenderness and juiciness with a higher concentration of C18:1 in muscle lipids. Cameron et al. (2000) found positive correlations with pork flavour, flavour liking and overall acceptability in the NL fraction. However, some other studies by Shackelford et al. (1990), St. John et al. (1987) and Miller et al. (1990) did not find improved eating quality with a higher concentration of C18:1. In the present study, no relationships between C18:1n-9c and texture attributes were found. 5. Conclusions This study has demonstrated significant correlations between specific fatty acids and explicit sensory attributes, and shows that control of lipid composition in pork might be useful in the production of high quality fresh pork. Particularly the poly- and monounsaturated fatty acids in the PL fraction of LD seem to be important, even though some of them are only present at low levels in the pork. However, further studies are needed to investigate the threshold values of specific fatty acids to specific flavour attributes before any general conclusions can be drawn. Acknowledgements Acknowledgements are given to the Directorate for Food, Fisheries and Agri Business, Ministry of Food, Agriculture and Fisheries, Denmark, and to Danske Slagterier for financial support. The authors thank Camilla Bjerg Kristensen and Jens Askov Jensen for technical assistance in the slaughterhouse and for help with analysis. We thank Camilla Bejerholm, Maiken Baltzer and Jonna Andersen at the Danish Meat Research Institute, Roskilde, Denmark, for technical assistance during the sensory profiling. Finally, we thank Jana Pickova at the Swedish University of Agricultural Sciences for the consultation regarding fatty acid. References Ahn, D. U., Lutz, S., & Sim, J. S. (1996). Effects of dietary linoleic acid on the fatty acid composition, storage stability and sensory characteristics of pork loin. Meat Science, 43, 291–299.

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