Mineral analysis in rabbit meat from Galicia (NW Spain)

MEAT SCIENCE Meat Science 73 (2006) 635–639 www.elsevier.com/locate/meatsci

Mineral analysis in rabbit meat from Galicia (NW Spain) M. Hermida a, M. Gonzalez a, M. Miranda b, J.L. Rodrı´guez-Otero

c,*

a Laboratorio de Mouriscade, Diputacio´n Provincial de Pontevedra, 36500 Lalı´n, Galicia, Spain Departamento de Ciencias Clı´nicas Veterinarias, Facultad de Veterinaria, 27002 Lugo, Galicia, Spain Instituto de Investigacio´n y Ana´lisis de Alimentos, Facultad de Veterinaria, Universidad de Santiago, 27002 Lugo, Galicia, Spain b

c

Received 7 April 2005; received in revised form 9 March 2006; accepted 10 March 2006

Abstract A total of 54 rabbits 50, 70 and 90 days old, were taken from farms in Galicia (NW Spain); 18 rabbits of each age were sampled. The minerals in the muscle meat from the back legs of the rabbits were analysed, and the following average concentrations were found: ash 1.21/100 g, potassium 388 mg/100 g; phosphorus 237 mg/100 g; sodium 60 mg/100 g; magnesium 27 mg/100 g; calcium 8.7 mg/100 g; zinc 10.9 mg/kg; iron 5.56 mg/kg; copper 0.78 mg/kg; and manganese 0.33 mg/kg. The high potassium and low sodium concentration may make rabbit meat particularly recommended for hypertension diets. Rabbit meat is rich in phosphorus, and 100 g provides approximately 30% of the recommended daily intake. However, rabbit meat provides less zinc and iron than meats of other species. The Galician rabbit meat analysed in this study, shows higher copper and manganese, and lower calcium contents than those found in the literature for rabbit meat of other origins. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Rabbit meat; Macrominerals; Trace elements

1. Introduction Currently rabbit farming has grown from raising a few rabbits for family consumption to large commercial operations; this fact has led to competitive prices and so rabbit, besides being healthy, is a relatively inexpensive source of meat. At present, Spain is the third largest producer of rabbit meat in the World, after China and Italy (FAOSTAT, 2005). In recent years the consumption of rabbit meat has increased considerably in the World, and in Spain, as in other Mediterranean countries, rabbit meat is common in the diet, and the consumption has increased since 2001 when the first case of BSE was diagnosed, with a subsequent decline in beef consumption. Moreover, due to avian flu the consumption of poultry meat has declined recently also.

*

Corresponding author. Fax: +34 98 225 1611. E-mail address: [email protected] (J.L. Rodrı´guez-Otero).

0309-1740/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2006.03.004

Rabbit meat in comparison to meat of other animal species has a high percentage of protein, and a low fat content. In addition, rabbit fat has a particularly low proportion of cholesterol and high proportion of unsaturated fatty acids (oleic and linoleic). It is also easily digested and very flavourful. These composition characteristics make rabbit meat especially recommended for avoiding cardiovascular diseases (Moreno, 1991). Meat is an important source of both macrominerals and trace elements and greatly contributes to the daily intake of these nutrients in the diet (WHO, 1996); however, some chronic diseases due to deficient intake of trace elements are still observable (Lombardi-Boccia, Aguzzi, Cappelloni, Di Lullo, & Lucarini, 2003). Although surveys to determine the levels of trace elements in cattle have been conducted in many countries (for review see Lo´pez-Alonso et al., 2000), data on the mineral content in rabbit meat are scarce (Combes, 2004; Falandysz, 1991; Falandysz, Kotecka, & Kannan, 1994; LombardiBoccia, Lanzi, & Aguzzi, 2005; Lucker, Failing, Walter, & Bulte, 1998; Moreiras, Carbajal, Cabrera, & Cuadrado,

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2004; Niinivaara & Antila, 1973). In fact, Combes (2004) in a review article about the nutritional value of rabbit meat emphasized that iron and copper content in rabbit meat are not sufficiently established and that he was not aware that the contents of many other trace elements had ever been evaluated. The aims of this work were: (i) to evaluate the contents of some macrominerals such as phosphorus, potassium, sodium, magnesium and calcium, and some trace elements such as zinc, iron, copper and manganese in the meat of rabbits bred in Galicia (NW Spain); (ii) to compare the results of our study with levels found in other studies for either rabbit meat or meat from other species. 2. Materials and methods

Calcium and magnesium were measured in the ash solution by atomic absorption spectroscopy at 422.7 and 285.2 nm respectively; a multi-element (Ca and Mg) hollow cathode lamp and an air-acetylene flame were used. Since for calcium determination chemical interferences due to aluminium, silicon or phosphorus may occur, a solution of lanthanum oxide was added (AOAC, 1995). For magnesium determination a strontium chloride solution was added with the aim of avoiding chemical interferences due to aluminium or silicon (OJEC, 1973). Zinc, iron, copper and manganese were determined by atomic absorption spectroscopy using single element hollow cathode lamps and air-acetylene flame at 213.9, 248.3, 324.7 and 279.5 nm, respectively. For the elements determined below 300 nm a background correction with a deuterium lamp was done (AOAC, 1995).

2.1. Samples 2.4. Statistical analysis A total of 54 rabbits of three different ages, 50, 70 and 90 days old, were taken from farms in Galicia (NW Spain): 18 rabbits of each age being sampled. The carcass weights were approximately 700, 1000 and 1400 g for 50, 70 and 90 day rabbits, respectively. These three rabbit ages were selected since the carcass weights within 700 and 1400 g are those of commercial demand. Rabbits were raised with a feedstuff of the following average composition: moisture 11.2%, crude protein 16.8%, starch 15.5%, cellulose 14.3%, ash 8.2% and ether extract 3.7%. After removing the protective layers of skin and fat, approximately 200 g of meat was sampled from the back legs of the rabbits, chopped into 0.5–1 cm thick pieces and triturated until a homogeneous mixture was achieved. Samples were stored under refrigeration in dry holders (<4 °C), which were entirely full to avoid water evaporation.

Ash content was determined by calcination of 20 g of sample at 550 °C to constant weight.

The limit of detection was set at three times the standard deviation of the mean blank value (Miller & Miller, 2002). The results obtained for the different components analysed were: 3.33 lg/g for phosphorus, 0.868 lg/g for potassium, 2.724 lg/g for sodium, 0.037 lg/g for magnesium, 0.437 lg/g for calcium, 0.120 lg/g for zinc, 0.113 lg/g for iron, 0.021 lg/g for copper and 0.011 lg/g for manganese. The results obtained for all components in all samples were above the limit of detection. The repeatability standard deviations (Sr) of all analytical methods were calculated over 10 duplicated analyses (Miller & Miller, 2002). With the aim of considering the errors of all the steps of sample preparation and analytical methods, all analyses started by meat sampling. The results obtained for the different components analysed were: for ash 0.011 (% w/w), for phosphorus 1.64 (mg/100 g), for potassium 3.27 (mg/100 g), for sodium 1.12 (mg/100 g), for magnesium 0.544 (mg/100 g), for calcium 0.465 (mg/ 100 g), for zinc 0.445 (mg/kg), for iron 0.440 (mg/kg), for copper 0.171 (mg/kg), and for manganese 0.064 (mg/kg). All analyses were performed in duplicate.

2.3. Mineral analysis

3. Results and discussion

For mineral analysis the ash was dissolved in hydrochloric acid, evaporated to dryness, re-dissolved in hydrochloric acid and diluted to 200 ml with Milli-Q water and filtrated. Phosphorus was determined in the ash solution by measuring the yellow colour developed by the reaction, in acid medium, of phosphates with molybdate–vanadate reagent at 430 nm (UV-1603, SHIMADZU) (AOAC, 1995). Sodium and potassium were determined in the ash solution by emission spectroscopy (Spectra AA-220FS, VARIAN) at 589.0 and 766.5 nm respectively, by using an air-acetylene flame. To avoid sodium and potassium ionisation under the flame, a buffer solution of caesium chloride and aluminium nitrate was added (OJEC, 1971).

3.1. Macrominerals

2.2. Ash analysis

Table 1 shows the average, standard deviation and range for ash, phosphorus, potassium, sodium, magnesium and calcium for the three groups of ages and for all the rabbits analysed in this study. With the aim of comparing the values obtained for the rabbits at the three different ages, the analysis of variance was applied: for ash, phosphorus and calcium the null hypothesis was retained. Therefore it can be stated, for p = 0.05, that no statistical differences were found in the results of these minerals between the three different ages of the animals. However for potassium, sodium and magnesium statistical differences (p < 0.05) were detected

M. Hermida et al. / Meat Science 73 (2006) 635–639

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Table 1 Ash (% w/w), phosphorus, potassium, sodium, magnesium and calcium levels (mg/100 g fresh muscle) in rabbit meat from Galicia (NW Spain) Age

Ash

P

K

Na

Mg

Ca

50 days Mean ± SDa Range

1.206 ± 0.024 1.15–1.25

235 ± 6.8 219–246

387 ± 18.4 352–418

66 ± 5.6 57–75

26 ± 2.0 22–29

9.0 ± 1.65 6.5–12.2

70 days Mean ± SD Range

1.218 ± 0.28 1.17–1.26

236 ± 4.8 229–244

401 ± 19.5 371–450

60 ± 3.5 52–65

27 ± 1.2 25–29

8.9 ± 1.94 6.9–15.1

90 days Mean ± SD Range

1.218 ± 0.031 1.17–1.28

239 ± 7.6 223–249

376 ± 16.5 342–406

55 ± 3.2 50–59

28 ± 2.5 24–33

8.3 ± 1.40 6.1–10.9

All animals Mean ± SD Range

1.214 ± 0.028 1.15–1.28

237 ± 6.6 219–249

388 ± 20.6 342–450

60 ± 6.3 50–75

27 ± 2.1 22–33

8.7 ± 1.68 6.1–15.1

a

Results are for 18 animals of each age resulting in a total of 54 for all animals.

between the three different ages. The highest level of potassium was at 70-days; a slight increase in magnesium content from 50- to 90-day rabbits was detected, while the opposite tendency was found for sodium. The highest coefficient of variation was found for calcium (19.2%); while for the other minerals it was much lower, below 10% for phosphorus, magnesium, potassium and sodium at the three ages studied and even lower for ash (2.0%). The average macrominerals and trace element concentrations in tissues depend, in part, on the type of cuts, age of the animals, and various other factors, which are often not reported. Therefore, comparison of data between studies must be considered with some caution. Potassium, accounting on average for 32% of the ash weight, was the most abundant of the elements determined. The mean content of 388 mg/100 g was similar to the values reported previously for rabbits by Niinivaara and Antila (1973), Combes (2004) and Moreiras et al. (2004) with means of 382, 404 and 360 mg/100 g, respectively. Rabbit meat has higher potassium concentrations than meat of other animal species: potassium content in cattle ranged within 150–171 mg/100 g, in swine within 172– 175 mg/100 g, in poultry within 248–259 mg/100 g and in lamb within 295–350 mg/100 g (Moreiras et al., 2004; Niinivaara & Antila, 1973; Price & Schweigert, 1994). The second most abundant mineral was phosphorus, which accounts on average for 19.5% of the ash weight; together with potassium it accounts for about 50% of the ash content. As well as for potassium, the phosphorus content found in this study was similar to the values reported in literature for rabbit meat (224–230 mg/100 g) (Combes, 2004; Niinivaara & Antila, 1973). The levels of phosphorus in rabbit meat were higher than the levels in poultry (200 mg/100 g), cattle (150–171 mg/100 g), swine (172– 175 mg/100 g) and lamb (147–179 mg/100 g) (Niinivaara & Antila, 1973; Price & Schweigert, 1994). Sodium contributed to about 4.9% of the ash. The content of this mineral found in our study was similar to that

reported by Moreiras et al. (2004) with average values of 67 mg/100 g; but higher than that found by Niinivaara and Antila (1973) (47 mg/100 g) and Combes (2004) (49 mg/100 g) for rabbit meat. There is a substantial difference between these studies and our study, probably due to the age of the animals; in fact in our study the mean sodium concentration decreased with the age of the animals. Therefore it is not easy to compare the sodium levels of different studies; maybe the variability of the data found by other authors could be due to the age dependent nature of sodium accumulation in meat; but unfortunately the age of the animals was not described in the other papers. The sodium content in rabbit meat was, in general, lower than the values found for meat of other species: cattle (65– 89 mg/100 g), swine (70–84 mg/100 g), poultry (64–83 mg/ 100 g) and lamb (75–100 mg/100 g) (Moreiras et al., 2004; Niinivaara & Antila, 1973; Price & Schweigert, 1994). The high potassium and low sodium concentration may make the rabbit meat particularly recommended for hypertension diets. The magnesium content accounted for about 2.2% of the ash; there were small differences between the values found in this study and those reported for rabbit meat by Niinivaara and Antila (1973), Combes (2004) and by Moreiras et al. (2004) with means of 29, 29 and 25 mg/ 100g respectively. Rabbit meat, in general, has a high magnesium content in comparison to meat of other species: cattle (18–25 mg/100 g), swine (18–31 mg/100 g), poultry (22– 37 mg/100 g) and lamb (15–22 mg/100 g) (Moreiras et al., 2004; Niinivaara & Antila, 1973; Price & Schweigert, 1994). The calcium concentration found in this study, which accounted for only 0.7% of ash, was very similar to that reported in the literature for meat of other species: cattle (8–11 mg/100 g), swine (8–9 mg/100 g) and lamb (8– 10 mg/100 g) (Moreiras et al., 2004; Niinivaara & Antila, 1973; Price & Schweigert, 1994). However, the calcium content determined in our study showed very small values in comparison with that reported for rabbit meat by Niinivaara and Antila (1973) (14 mg/100 g), and by Moreiras

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Table 2 Zinc, iron, copper and manganese levels (mg/kg fresh muscle) in rabbit meat from Galicia (NW Spain) Age

Zn

Fe

Cu

Mn

50 days Mean ± SDa Range

10.5 ± 1.10 8.5–13.4

5.36 ± 1.65 2.93–9.22

0.89 ± 0.326 0.58–1.71

0.35 ± 0.087 0.21–0.51

70 days Mean ± SD Range

11.2 ± 1.63 9.0–16.5

5.57 ± 1.12 3.23–7.40

0.68 ± 0.427 0.34–2.14

0.35 ± 0.086 0.19–0.46

90 days Mean ± SD Range

11.0 ± 1.39 8.1–13.8

5.74 ± 1.28 3.77–9.11

0.79 ± 0.277 0.41–1.41

0.29 ± 0.108 0.13–0.48

All animals Mean ± SD Range

10.9 ± 1.40 8.1–16.5

5.56 ± 1.35 2.93–9.22

0.78 ± 0.355 0.34–2.14

0.33 ± 0.096 0.13–0.51

a

Results are for 18 animals of each age resulting in a total of 54 for all animals.

et al. (2004) (22 mg/100 g) but very similar to the values reported by Combes (2004); which, like our study, were for rabbit back legs. 3.2. Trace elements Table 2 shows the average, standard deviation and range for zinc, iron, copper and manganese for the three age groups and for all the rabbits combined in this study. Age had no effect on the concentration of any of the trace elements (p > 0.05). The coefficients of variation for the trace elements were higher than those of the macrominerals, with the exception of calcium and zinc. The highest value was found for copper (45%) and the lowest for zinc (13%). Zinc variation and accumulation was small due to the strict homeostatic gastric mechanisms for zinc absorption and excretion (Elinder & Piscator, 1979). In agreement with Falandysz (1991) and with Falandysz et al. (1994), in the meat from Galician rabbits, just like in that from Polish rabbits (17–18 mg/kg), zinc was the most abundant of the trace elements. However, the values for zinc content found in our study were below those of Polish rabbit meat; but about twice that reported by LombardiBoccia et al. (2005) for Italian rabbit meat (5.5 mg/kg). This variation could be due to the type of muscle, since in this study the sample was taken from the whole carcass whereas in our study only the back legs were sampled. Rabbit meat shows lower zinc concentrations than other species reported in the literature like bovines, horse, swine, ostrich, chicken and turkey (Falandysz, 1991, 1993; Falandysz et al., 1994; Lombardi-Boccia et al., 2005; Lo´pez-Alonso et al., 2000; Moreiras et al., 2004; Price & Schweigert, 1994). Iron was the second most abundant trace element in rabbit meat. However, as in the case of zinc, the iron concentration was also lower in our study, about half to a third of the previous values reported for rabbit meat (10–15 mg/ kg) (Combes, 2004; Falandysz, 1991; Falandysz et al., 1994), but similar to that reported by Lucker et al. (1998) for rabbit meat sampled from the back leg muscle

(4.5 mg/kg) and, as in the case of zinc, higher than that reported by Lombardi-Boccia et al. (2005) for Italian rabbit meat (3.8 mg/kg). The iron levels in rabbit meat, as in the case of zinc, were lower than those reported in the literature for meat of other species (Falandysz, 1991; Falandysz et al., 1994; Price & Schweigert, 1994). The iron content in meat varies significantly between the different meat cuts (Lombardi-Boccia et al., 2005; Lucker et al., 1998). Lucker et al. (1998) reported variations in iron content between 3.5 and 7.9 mg/kg in the different parts of the carcass, so the anatomical heterogeneity of iron concentration dominates all of the other sources of variation. The copper concentration found in our study for Galician rabbit meat was higher than the values reported in the literature for rabbit meat of other geographical origins, which ranged from 0.30 mg/kg (Lombardi-Boccia et al., 2005) to 0.58 mg/kg (Falandysz, 1991) but similar to that reported by Combes (2004) for the back legs (0.88 mg/ kg). As for zinc and iron, copper concentration in meat can vary in the different types of muscle. In cattle it has been demonstrated that copper concentrations in muscle are inversely related to muscle lipid concentration (Lo´pez-Alonso et al., 2000). For that reason it is difficult to compare studies since in most of them the type of cut sampled was not clearly described. In the quoted reports of rabbit meat, only Combes (2004) explicitly stated that the origin of meat was, as in our work, the back legs. This explains the closeness of all minerals levels between both studies, with the exception of iron. In relation to manganese, it has to be remarked that the contents determined in our study were much higher than the values reported in the literature either for rabbit meat (0.12 mg/kg) or for meat of swine (0.11 mg/kg) and lamb (0.09 mg/kg) (Falandysz, 1993; Falandysz et al., 1994). 4. Conclusion This study provides baseline data on macro and trace element concentration in rabbit meat. The high potassium and low sodium concentration may make rabbit meat par-

M. Hermida et al. / Meat Science 73 (2006) 635–639

ticularly recommended for hypertension diets. Rabbit meat is rich in phosphorus, and 100 g provides approximately 30 % of the recommended daily intake of this mineral. However, rabbit meat provides less zinc and iron than meats of other species. There is a great variability in trace element content of rabbit meat between the different studies. This fact could be related to the mineral distribution in the carcass, so further studies are needed in order to evaluate the distribution of trace elements in rabbit meat. References AOAC (1995). Official methods of analysis of AOAC International (16th ed.). Arlington: AOAC International. Combes, S. (2004). Nutritional value of rabbit meat: a review. Productions Animales, 17(5), 373–383. Elinder, C. G., & Piscator, M. (1979). Zinc. In L. Friberg, G. F. Nordberg, & V. B. Vouk (Eds.), Handbook on the toxicology of metal (pp. 675–685). Amsterdam: Elsevier. Falandysz, J. (1991). Manganese, copper, zinc, iron, cadmium, mercury and lead in muscle meat, liver and kidneys of poultry, rabbit and sheep slaughtered in the northern part of Poland, 1987. Food Additives and Contaminants, 8(1), 71–83. Falandysz, J. (1993). Some toxic and essential trace metals in swine from the Northern Poland. The Science of the Total Environment, 136, 193–204. Falandysz, J., Kotecka, W., & Kannan, K. (1994). Mercury, lead, cadmium, manganese, copper, iron and zinc concentrations in poultry, rabbit and sheep from the northern part of Poland. The Science of the Total Environment, 141, 51–57.

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