A comparison of the carcass and meat quality of Martina Franca donkey foals aged 8 or 12 months

Meat Science 106 (2015) 6–10

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A comparison of the carcass and meat quality of Martina Franca donkey foals aged 8 or 12 months Paolo Polidori a,⁎, Stefania Pucciarelli b, Ambra Ariani b, Valeria Polzonetti b, Silvia Vincenzetti b a b

Scuola di Scienze del Farmaco e dei Prodotti della Salute, Università di Camerino, Via Circonvallazione 93, 62024 Matelica, MC, Italy Scuola di Bioscienze e Medicina Veterinaria, Via Circonvallazione 93, 62024 Matelica, MC, Italy

a r t i c l e

i n f o

Article history: Received 13 November 2014 Received in revised form 19 March 2015 Accepted 22 March 2015 Available online 28 March 2015 Keywords: Donkey meat Donkey carcass Meat quality Fatty acids Amino acids

a b s t r a c t The effects of slaughter age (8 vs 12 months) were investigated on meat and carcass quality obtained from Martina Franca donkey foals. Sixteen male foals were used, eight were slaughtered at 8 months of age with a mean (± s.e.) final body weight of 101 ± 18 kg and the remaining 8 foals slaughtered at 12 months of age with a mean final body weight of 122 ± 13 kg. Carcass weight and dressing percentage were higher (P b 0.05) in older foals. Shear force value was lower (P b 0.05) in donkeys slaughtered at 8 months of age (54.03 N) compared to the same muscle Longissimus Thoracis et Lumborum (LTL) collected in older animals (62.66 N). Muscle glycogen content was higher (P b 0.05) in foals slaughtered at 12 months of age. Donkey foal meat showed an interesting content of essential amino acids and a notable percentage of unsaturated fatty acids in both groups of animals, giving a high nutritional value to this alternative red meat. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Donkey (Equus asinus, Perissodactyla) is a domestic animal belonging to the equine family, its progenitor was the small grey donkey of northern Africa (Equus africanus) domesticated around 4000 BC on the shores of the Mediterranean Sea (Aganga, Aganga, Thema, & Obocheleng, 2003). Despite the increase in mechanization throughout the world, donkeys have an important role to play in transport of people and goods in arid and semi-arid areas where roads are poor or non-existent. Donkeys are therefore easy to manage and not too demanding in terms of feeding: they can almost survive on poor quality feeds and thrive under adverse climatic conditions, in fact they can tolerate considerable heat and dehydration (Smith & Pearson, 2005). In working donkeys, it has been recommended that castration should be performed between 6 months and 1 year of age (Jones, 1994), as then the donkey still has the comfort of its mother to aid recovery. However, an important problem with castration at this young age involves testicles: they may be undescended and difficult to locate. For this reason, donkey castration is often performed after 12 months of age. In recent years, in the south of Europe there is an increasing interest in raising donkeys for their use in leisure activities and onotherapy, a type of animal assisted treatment that involves the use of donkeys. ⁎ Corresponding author. Tel.: +39 0737 403426; fax: +39 0737 403402. E-mail address: [email protected] (P. Polidori).

http://dx.doi.org/10.1016/j.meatsci.2015.03.018 0309-1740/© 2015 Elsevier Ltd. All rights reserved.

Also, research and market interest in donkey milk has increased with the results of several studies indicating this milk as the best replacer for human milk when it is not possible to use cow's milk in children allergic to milk proteins (Carroccio et al., 2000; Monti et al., 2007; Vincenzetti et al., 2014). Donkey meat has recently (Lorenzo et al., 2014) been recognized as a nutritive food for human consumption with good quality proteins, vitamins and minerals. The acceptance of donkey meat as an appealing food for humans has changed along the centuries: in the past this kind of meat was obtained from animals that were slaughtered at the end of their working lives, and was considered unacceptably tough. Consequently the meat was mostly destined for salami production or other salted horse meat-based products (Lorenzo & Carballo, 2015). Today's consumers require leaner meat, with less fat and a consistent quality (Franco et al., 2011), and thus donkey meat is mainly produced from young animals (Polidori & Vincenzetti, 2013) to avoid undesirable characteristics such as the lack of tenderness. Factors such as Equine breed, sex, live weight and their interactions have been shown to affect carcass and meat quality, as well as fat deposition and fatty acid composition (Juárez et al., 2009). The Martina Franca donkey is an autochthonous breed in the south of Italy, where these animals were used for transport and to work on farms. The aim of the present study was to determine the effect of two different slaughter ages (8 vs 12 months) established taking into consideration the possibility of avoiding castration, that is normally necessary for adult males, on meat and carcass quality from 16 male

P. Polidori et al. / Meat Science 106 (2015) 6–10

donkeys not destined for breeding, in order to characterise a new product, donkey foal meat. The study was conducted in compliance with the requirements of the Animal Ethics Committee of the University of Camerino. 2. Materials and methods 2.1. Sample collection The trial involved 16 entire donkey male foals of the Martina Franca breed; 8 animals were slaughtered at 8 months of age with a mean final body weight of 101 ± 18 kg, and the remaining 8 foals were slaughtered at 12 months of age with a mean final body weight of 122 ± 13 kg. Animals were slaughtered according to the European Union Regulations (Council Directive 93/119 EEC) at an approved abattoir. All procedures involving animals were conducted according to the Italian law on animal welfare in scientific experiments. Foals were reared with their dams on pasture until 6–7 months of age, according to the local natural weaning system. For the following 6–7 months the animals were reared on the same farm and were fed the same diet, based on polyphyte hay (Lolium perenne, Festuca arundinacea and Trifolium repens) given ad libitum in the evening and the same pasture of the previous months (Dactylis glomerata, Taraxacum officinale and F. arundinacea) in the rest of the day. The donkeys were slaughtered on different days according to their birth dates. The animals were fasted (only water was available) for 18 h before slaughter; transport of the donkeys to the slaughter house took 60 min. The animals were slaughtered using a conventional captive bolt and rolled out onto a cradle where the carotid arteries and jugular veins were severed, resulting in bleeding out of the animal causing rapid heart failure and death. All the carcasses were skinned and eviscerated, then were stored in a cold room at +1 °C plusminus, suspended by both their hind legs. Carcass weight and carcass dressing percentage were calculated 1 h post-mortem. To determine the dressing percentage from each carcass we eliminated skin and coat, head (cut at the occipital–atlantoidal articulation), neck (cut at the last cervical and at the first thoracic articulation) and feet (cut at tarsal–metatarsal and carpal–metacarpal articulations), liver, heart, spleen, lungs, kidneys, trachea and all the digestive tracts. Carcasses were chilled for four days, then from the left side of the carcasses approximately 400 g of muscle sample was taken from Longissimus Thoracis et Lumborum (LTL), between the 12th and the 13th ribs. Each sample was placed into bags and placed on ice in a cooler for transport to the laboratory, where each sample was divided into two parts, one was used immediately for colorimetric determination, the second half was repackaged in labelled vacuum-packaged bags and stored at −20 °C until further analysis.

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was performed on a Chrompack (model CP 9003, Agilent Technologies, California, USA) gas chromatograph with a flame ionization detector and a fused-silica capillary column and a film thickness of 0.2 μm, packed with CP Sil 88 (50 m × 0.25 mm i.d.). Helium was used as the carrier gas and the column temperature was held at 80 °C for 4 min, and then increased at 10 °C/min from 80 °C to 140 °C, then at 5 °C/ min from 140 °C to a final temperature of 210 °C (held for 14 min). Fatty acid identification was made by comparing gas chromatographic retention times with the anti-oxidant standard butylated hydroxytoluene (BHT). The amino acid levels were determined by acid hydrolysis: 10 g of each sample was homogenised (Ultra Turrax T25, Ika, Germany) with sulphosalicylic acid 5% (w/v); after centrifugation the liquid phase was brought to a known volume, as described by Paleari, Moretti, Beretta, Mentasti, and Bersani (2003). For amino acid determination 100 μl was injected into an Amino Acid Analyser (model 3A30, Carlo Erba, Milano, Italy). The analytical conditions were: a cation exchange resin column (150 × 4.6 mm i.d.) with a four step lithium buffer gradient pH 2.80–5.40, the flow rate was 30 ml/min with a temperature gradient of 43–73 °C; derivatisation was post-column with ninhydrin; detection was by a colorimeter at 570 and 440 nm; and data were acquired by an integrator (model C-R6A, Shimadzu, Kyoto, Japan). The muscle colour parameters were measured using a Minolta CR200 colorimeter (Minolta Camera Co., Osaka, Japan), with the HunterLab method. After placing the measuring lens on the meat surface, it was turned through 0, 45 and 90° (clockwise) to obtain three different reflectance measurements that were later averaged. Using these spectra, the D65 Illuminant source and the CIE 1964 (10°) Standard Observer, measurements were taken with the camera set at maximum zoom, repeated 3 times in 3 different places, to determine L* (lightness), a* (redness) and b* (yellowness). The instrument was calibrated to a standard tile before analysis. The colorimetric parameters were measured five days after slaughter, on a fresh surface of muscle LTL. Samples designated for shear force determination were removed from the carcasses four days post-mortem. Steaks (each 2.5 cm thick) were obtained from the mid-region of each sample, and roasted on a metal tray at an oven temperature of 180 °C to an internal temperature of 73 °C (monitored with thermocouples), according to the procedures of Polidori, Antonini, Torres, Beghelli, and Renieri (2007). Steaks were cooled to room temperature (25 °C) for 30 min. From each sample, eight cores (1.3 cm in diameter) were removed, and shear force determination was obtained using an Instron apparatus 4411 (Instron, High Wycombe, UK) with a Warner-Bratzler shear device and crosshead speed set at 200 mm/min (AMSA, 1995). The considered parameter was the maximum shear force in N.

2.2. Chemical and physical analyses

2.3. Statistical analysis

Chemical composition and cholesterol content of the LTL muscle of the animals were determined using the methods described by Babiker, El Khidir, and Shafie (1990). Residual glycogen was determined spectrophotometrically (340 nm) using a commercial kit from Sigma (Glucose HK 16-50) which is based on a NAD-linked assay catalysed by hexokinase and glucose-6-phosphate dehydrogenase, as described by Immonen, Kauffman, Schaefer, and Puolanne (2000). Fatty acid composition was determined for all the samples. Total lipids were extracted from the meat as described by Bligh and Dyer (1959); for the preparation of fatty acid methyl esters the lipid sample (20 mg) was dissolved in 0.1 ml of tetrahydrofuran in a test tube and 10% methanolic hydrogen chloride (2 ml) were added (Sukhija & Palmquist, 1988). The sample was sealed and heated at 100 °C for 1 h. To each sample 2 ml of 1 M potassium carbonate solution was added. The fatty acid methyl esters were extracted with 2 × 2 ml of hexane and 1 μl was injected into a gas-chromatograph. Fatty acid analysis

Data were analysed by the method of least squares using the general linear model procedures of SAS (2001) with age as the main effect and results were expressed as least square means. Significant differences between means were indicated when P b 0.05.

Table 1 Donkey carcass characteristics (means ± s.e.). Slaughter age (months)

Final body weight (kg) Carcass weight (kg) Dressing percentage (%)

8

12

(n = 8)

(n = 8)

101 ± 18 49.7 ± 3.22 49.2 ± 0.88

122 ± 13 65.7 ± 4.16 53.9 ± 3.31

P-value

b0.01 0.024 0.032

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P. Polidori et al. / Meat Science 106 (2015) 6–10

3. Results and discussion The final body weights and carcass characteristics' data are shown in Table 1. Carcass weight differed (P b 0.05) between foals slaughtered at 8 months (49.7 ± 3.22 kg) compared to animals slaughtered at 12 months of age (65.7 ± 4.16). Dressing percentage differed (P b 0.05) between the two groups, too; 8 month old foals had 49.2% dressing percentage compared to 53.9% obtained in older animals. The values from this study were lower than those obtained by Polidori, Vincenzetti, Cavallucci, and Beghelli (2008) on donkeys belonging to the same Martina Franca breed; the difference can possibly be attributed to the older slaughter age (15 months) of animals used in that experiment. The chemical composition of the LTL is shown in Table 2; slaughter age had no influence on any of the chemical components measured. The chemical composition determined in this study was similar to that obtained on horse-meat samples by Lanza, Landi, Scerra, Galofaro, and Pennisi (2009) for fat and protein content, and by Lorenzo and Pateiro (2013) for cholesterol content. The donkey foal meat analysed in this study is characterised by a low fat and cholesterol content and a good protein content (Table 2), confirming the similarity with horse meat obtained by foals slaughtered at 15 months of age (Franco & Lorenzo, 2014). Residual glycogen content was determined 12 h after the samples were collected; the level obtained in foals slaughtered at 12 months of age (0.38%) was significantly higher (P b 0.05) than that of the younger foals (0.22%). The presence of glycogen in horse and donkey meat has been demonstrated in previous studies, as reviewed by Lorenzo et al. (2014), with significant differences between different muscles (Tateo, De Palo, Ceci, & Centoducati, 2008). The colorimetric characteristics of donkey meat showed no significant differences in lightness (L*) and redness (a*) in the LTL muscle collected from foals slaughtered at 8 and 12 months of age, respectively 33.57 versus 32.34 for L* and 12.24 versus 11.49 for a* (Table 2). Similarly, the age of the animals did not affect the colorimetric characteristics, according to the previous results obtained in horse meat (Sarriés & Beriain, 2006), confirming therefore that feeding systems play an important role in differentiating between meat samples on the basis of colour. Meat colour is also influenced by the myoglobin content, and the myoglobin content within a species varies with age (Lawrie, 1985). A possible explanation of the results obtained in the present study could be that haemoglobin contents in LTL muscle did not differ between foals slaughtered at 8 and 12 months of age. Shear force values (Table 2) determined for LTL muscles were significantly lower (P b 0.05) in donkey foals slaughtered at 8 months of age (54.03 ± 9.47 N) compared to animals slaughtered at 12 months of age (62.66. ± 11.38 N). In horse meat (Tateo et al., 2008) shear force values Table 2 Chemical and physical characteristics (means ± s.e.) of the LTL muscle of donkeys slaughtered at different ages. Slaughter age (months) 8

12

(n = 8)

(n = 8)

P-value

Chemical composition Moisture (%) Fat (%) Protein (%) Ash (%) Residual glycogen (%) Cholesterol (mg/100 g)

77.3 ± 2.26 1.76 ± 0.23 19.8 ± 0.24 1.11 ± 0.25 0.22 ± 0.05 62.4 ± 2.33

75.8 ± 1.64 1.87 ± 0.18 21.0 ± 2.32 1.33 ± 0.22 0.38 ± 0.02 63.9 ± 3.08

0.284 0.754 0.215 0.772 0.031 0.783

Colour parameters L* a* b* Shear force values (N)

33.57 ± 2.94 12.24 ± 0.48 8.76 ± 0.22 54.03 ± 9.47

32.34 ± 2.36 11.49 ± 0.83 7.87 ± 0.13 62.66 ± 11.38

0.782 0.764 0.662 0.025

of 51.38 N were obtained 10 days post-mortem using 11 month old stallion foals. The ageing period is a very important factor in determining meat tenderness (Lawrie, 1985; Thompson, 2002); the values obtained in this study 4 days post-mortem could be improved with a longer ageing period, or using appropriate finishing diets. In fact, as indicated by Destefanis, Brugiapaglia, Barge, and Dal Molin (2008), Warner-Bratzler shear forces higher than 52.68 N are perceived as “tough” by most consumers; this is an aspect that warrants further research, in order to obtain tender meat from donkey. The fatty acid composition of the intramuscular fat did not show significant differences between the two groups of animals (Table 3). Interestingly, a high content of polyunsaturated fatty acids (PUFA) was found in both foals slaughtered at 8 and at 12 months of age, with 26.36 and 26.43 g/100 g total fatty acids, respectively. PUFA content is normally smaller in ruminant meats (ranging from 4.3 to 5.0 g/100 g of total fatty acids) and in pork (about 8.3 g/100 g total fatty acids), as reviewed by Chan (2004). The two most abundant fatty acids were oleic acid (18:1cis9) and palmitic acid (C16:0), as was previously found in Sanfratellano and Haflinger horse foals (Lanza et al., 2009), and in donkey meat (Polidori, Cavallucci, Beghelli, & Vincenzetti, 2009). Saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) contents were similar in both the two groups of animals used in this study (Table 3); data on the same muscles from Italian Heavy Draft horses had higher amounts of SFA (Tateo et al., 2008). The ratio between PUFA/SFA was basically identical between the two groups of animals (Table 3). These results agree with the study conducted by Lorenzo, Fuciños, Purriños, and Franco (2010), where the SFA, MUFA and PUFA contents in meat obtained from Galician Mountains foals were not influenced by slaughter age (9 vs 12 months). Stearic acid (C18:0) decreased in intramuscular fat of older foals, in agreement with results obtained in horse meat (Sarriés, Murray, Troy, & Beriain, 2006). This result can be attributed to an increase in desaturase activity giving rise to oleic acid (C18:1), as described by Smith (1995). In equids, short-chain fatty acids are produced by microbial fermentation in the hindgut in considerable amounts (Sneddon & Argenzio, 1998), as confirmed in this study. Other authors found SFA as the predominant fatty acids also in horse meat (Sarriés et al., 2006; De Palo, Maggiolino, Centoducati, & Tateo, 2013). Finally, the Σn−6/Σn−3 ratios (Table 3) were higher compared to the results obtained on horse meat by Franco, Crecente, Vázquez,

Table 3 Fatty acid composition (% total fatty acids) determined in LTL muscle of donkeys slaughtered at different ages (means ± s.e.). Slaughter age (months) 8

12

Fatty acid

(n = 8)

(n = 8)

C12:0 C14:0 C15:0 C16:0 C16:1 C17:0 C18:0 C18:1n−9 C18:2n−6 C18:3n−3 C20:1n−9 C20:2n−6 C20:3n−6 C20:4n−6 C20:5n−3 SFA MUFA PUFA PUFA/SFA Σn−3 Σn−6 Σn−6/Σn−3

0.19 ± 0.01 3.68 ± 0.51 0.37 ± 0.18 27.93 ± 2.68 3.46 ± 0.46 0.45 ± 0.12 7.53 ± 0.88 28.87 ± 4.11 19.76 ± 1.47 4.32 ± 0.89 0.33 ± 0.03 0.20 ± 0.01 0.19 ± 0.02 2.28 ± 0.27 0.15 ± 0.01 40.15 ± 1.99 33.20 ± 1.87 26.36 ± 2.32 0.66 4.47 22.43 5.02

0.21 ± 0.02 3.81 ± 0.44 0.40 ± 0.21 28.14 ± 2.11 3.51 ± 0.47 0.53 ± 0.18 6.88 ± 0.91 29.10 ± 3.18 20.24 ± 2.01 3.89 ± 0.76 0.32 ± 0.07 0.21 ± 0.4 0.18 ± 0.01 2.23 ± 0.18 0.20 ± 0.03 39.97 ± 1.21 33.45 ± 1.46 26.43 ± 1.87 0.66 4.09 22.68 5.55

P-value

0.827 0.826 0.816 0.882 0.822 0.663 0.669 0.812 0.823 0.689 0.941 0.935 0.926 0.842 0.311 0.756 0.855 0.902 0.931 0.657 0.879 0.723

P. Polidori et al. / Meat Science 106 (2015) 6–10 Table 4 Amino acid composition (g/100 g muscle) determined in LTL muscle of donkeys slaughtered at different ages (means ± s.e.). Slaughter age (months) 8

12

P-value

(n = 8)

(n = 8)

Essential Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

1.22 ± 0.27 0.74 ± 0.19 0.85 ± 0.23 1.44 ± 0.56 1.53 ± 0.26 0.51 ± 0.24 0.85 ± 0.26 0.86 ± 0.23 0.33 ± 0.17 1.03 ± 0.45

1.33 ± 0.12 0.81 ± 0.18 0.90 ± 0.32 1.55 ± 0.28 1.59 ± 0.37 0.57 ± 0.27 0.92 ± 0.24 0.99 ± 0.24 0.28 ± 0.10 1.11 ± 0.52

0.722 0.717 0.656 0.547 0.589 0.568 0.431 0.529 0.568 0.554

Non-essential Alanine Aspartic acid Cystine Glutamine Glycine Proline Serine Tyrosine

1.08 ± 0.14 1.65 ± 0.33 0.17 ± 0.04 2.53 ± 0.86 0.88 ± 0.47 0.84 ± 0.47 0.74 ± 0.32 0.48 ± 0.25

1.22 ± 0.32 1.81 ± 0.48 0.21 ± 0.06 2.99 ± 0.87 0.93 ± 0.56 0.91 ± 0.33 0.82 ± 0.31 0.66 ± 0.38

0.448 0.391 0.678 0.489 0.392 0.386 0.472 0.284

Total AA Essential AA (%)

17.73 ± 3.21 9.36 ± 2.86 (52.80%)

19.60 ± 3.32 10.05 ± 2.64 (51.28%)

0.269 0.476

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essential amino acids is an important factor in determining the nutritional quality of donkey meat. Donkey meat tenderness was influenced by the age of the animals; the choice of an appropriate ageing period or alternative post-mortem intervention to enhance tenderness warrants further research, in order to improve the final meat tenderness. The potentiality of Martina Franca foals to produce meat with favourable dietetic characteristics is demonstrated in this study, but could be improved further by, for example, studying the effects of a longer pasture feeding period with a short stall finishing period. The results of this study confirm that donkey meat may serve as a suitable meat source for consumers seeking an alternative to traditional red meats, the reduced production cost of donkey breeding can contribute to obtain a cheap red meat compared to the traditional ones, with many similarities with the better known horse meat. References

Gómez, and Lorenzo (2013) and by Franco and Lorenzo (2014), but similar to those obtained by Lanza et al. (2009) and by De Palo et al. (2013). Eicosapentaenoic acid (EPA; C20:5n − 3) was determined to be in higher amounts (0.20 ± 0.03 g/100 g total fatty acids) in older donkeys, while docosahexaenoic acid (DHA; C22:6n − 3) was not detected in this study. The amino acid content of the LTL is shown in Table 4; the two groups of animals used in this study did not show statistically significant differences in amino acid contents. Arginine was included as an essential amino acid, as it is considered a conditionally essential amino acid (Franco & Lorenzo, 2014). Donkey meat appears to be an important source of high biological value proteins as it contains essential amino acids in good amounts. A study conducted by Paleari et al. (2003) compared the amino acid content determined in deer, boar, horse, beef and goat meat; beef meat had a significantly lower content (47.4%), while in that study both deer and goat meat showed higher proportions of essential amino acids, respectively 58.8% and 54.8%. The results obtained for donkey meat in the present study can be considered close to horse (54.5%) and boar meat (50.0%). The highest concentrations of essential amino acids (Table 4) were determined for lysine (1.53 g/100 g muscle at 8 months, 1.59 g/100 g muscle at 12 months) followed by leucine (1.44 g/100 g muscle at 8 months, 1.55 g/100 g muscle at 12 months) and arginine (1.22 g/100 g muscle at 8 months, 1.33 g/100 g muscle at 12 months). Glutamine, aspartic acid and alanine were the most abundant amino acids in the non-essential fraction, as has also been observed in previous studies on horse meat (Lorenzo et al., 2014). The ratio between essential/non-essential amino acids was larger than 50%, both at 8 months of age (52.8%) and at 12 months of age (51.3%) confirming the high biological values of donkey meat proteins. 4. Conclusions The total number of animals used in this study was limited to 16 foals, therefore the results obtained must be considered as preliminary indications. Slaughter age significantly influenced meat tenderness and carcass dressing percentage. Martina Franca foals showed low fat and cholesterol contents and a balanced distribution between SFA and MUFA, in addition to a high amount of PUFA. The high content of

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