Ultimate pH, colour characteristics and proximate and mineral composition of edible organs, glands and kidney fat from Saanen goat male kids

ABSTRACT Ultimate pH value and instrumental colour (CIEL*a*b* values) characteristics, proximate (moisture, protein, total fat and total ash) and mineral composition (K, P, Na, Mg, Ca, Zn, Fe, Cu, Ni and Mn) were determined in 10 (heart, tongue, lungs, spleen, liver, kidney, brain, testicle, thymus and kidney fat) edible by-products of Saanen goat male kids. Many significant or numerical differences were found in the mean values of quality characteristics among the edible by-products. Among edible organs and glands, liver had the lowest surface CIEL* value (darkest colour), and the highest levels of protein, Zn, Cu and Mn. Furthermore, the highest pH24h, total ash, K, P and Mg levels were determined in the thymus. The testicle had the highest moisture, Ca and Ni levels. The spleen had the lowest fresh cut cross-section CIEL* value (darkest colour), and the highest Fe level. The highest total fat content and Na level were determined in the brain and kidney, respectively. Among all the edible by-products, kidney fat had the highest pH24h, surface CIEL* value (lightest colour) and total fat content, and the lowest moisture, protein, total ash, K, P, Na, Mg, Ca, Zn, Fe, Cu, Ni and Mn levels.


Introduction
Goats, the earliest ruminant to be domesticated, are traditional sources of meat, milk, fibre, leather, related products of animal origin and are used as draught and pack animals (Casey & Webb 2010;Argüello 2011).
In general, the number of goats, as well as goat meat production, has increased worldwide over past years (Argüello 2011;FAOSTAT 2015). In Serbia, no statistical records were kept concerning the number of goats and their breeding because goat keeping was banned by law after the Second World War for a long period Žujović et al. 2009). This law was, fortunately, never fully implemented, but resulted in a lack of knowledge of the goat population size in the past. In 2014, The Statistical Office of the Republic of Serbia reported the Serbian goat population to be 219,000 head.
The most important category of goat meat in Serbia, as in developed countries, is kid meat (Žujović et al. 2009). The greatest demand for young goats in Serbia occurs seasonally during spring. Production is based on various breeds, more or less locally determined. In some regions, production systems of goats are quite extensive. The number of kids (and goats) that are slaughtered annually in Serbia is considerable. Meat from these animals, however, is not available on the market, since most kids and even adult goats are slaughtered and consumed on the farms where they were raised Žujović et al. 2009).
Traditionally, kids are slaughtered at 3-7 months old and 12-15 kg carcass weight (Peña et al. 2009). According to Serbian legislation (1974), kids are normally slaughtered between 3 weeks and 6 months of age. The carcass weight with head, liver, heart, lungs, kidney and internal fat and without skin and distal parts of the legs should be between 4 and 12 kg.
Over the past decade, farmers in Vojvodina have become interested in goat breeding, especially raising noble, highly yielding breeds. As there were few such goats in the country, they have been imported on several occasions; these imports were Alpine, Saanen and German fawn dairy goats (Krajinović et al. 2011). In farms keeping dairy goats, male kids are considered as a by-product. Therefore, to save the milk for the dairy industry, goat keepers remove the kids from their dams very early in the postnatal period, and the kids are then raised under an intensive system. Goat kids in intensive dairy goat farms are usually reared on milk replacers (Marichal et al. 2003;Argüello et al. 2005Argüello et al. , 2012Zurita-Herrera et al. 2013). It is well known that young animals fed high concentrate diets generally have higher daily gains, dressing percentage and carcass quality than those produced in a forage system. Saanen dairy goats, which originated in the Saanen valley of Switzerland, are very famous for their prolific milk production, as well as for being the largest of the dairy goat breeds (Encyclopedia Britannica 2015).
Meat is the major product of the goat, as all goats can produce meat (Mahgoub et al. 2012). Goldstrand (1988) calculates that organs, fatty tissues, bones and blood represent 39.30% and 35% of the live weight of cattle, pigs and lambs or goats, respectively.
The available scientific literature mainly describes sensory, technological and nutritional quality of goat meat, but little or no information is available for some edible by-products. Edible by-products can be categorized into edible organs, glands, and edible fats (Spooncer 1988;Ockerman & Basu 2004). Edible offal, or variety meat, is also a form of meat which is used as food, but which is not skeletal muscles, and, in general, it possesses higher levels of some micronutrients, especially minerals and vitamins, than muscular tissue (Anderson 1988;Goldstrand 1988;Ockerman & Basu 2004;Lawrie & Ledward 2006;Honikel 2011). Also, edible organs and glands are often different from skeletal tissue in structure, composition, functional and sensory properties (Spooncer 1988;Ockerman & Basu 2004). According to Serbian legislation (1974), the edible organs and glands (edible offal) of a butchered goat that are removed in dressing include brain, tongue, heart, lungs, thymus, liver, spleen, kidneys and testicles.
Animal fat is important for human nutrition for its high energy value, which is more than twice that of carbohydrates (Wood 1984). The ascending order of fat deposition in goats was: subcutaneous, intermuscular, mesenteric, kidney knob and channel and omental fat (Mahgoub et al. 2012).
Edible by-products from goat slaughter are part of the diet in different countries worldwide (Nollet & Toldrá 2011), as a component of kitchen-style food preparations or as processed meat products (Ockerman & Basu 2004;Dalmás et al. 2011;Toldrá et al. 2012;de Queiroz et al. 2013). Therefore, the aim of this study was to determine the ultimate pH and colour characteristics and proximate and mineral composition of 10 edible byproducts (heart, tongue, lungs, spleen, liver, kidney, brain, testicle, thymus and kidney fat) from intensively reared Saanen goat male kids. This is important to provide, update and improve regular nutrient composition data of goat edible by-products.

Materials and methods
This study included 20 Saanen male kids. All kids were raised under identical husbandry, management and feeding conditions. At birth, all kids were removed from their dams and housed individually until they were 10 days old. From the tenth day until slaughter, the kids were housed in pens, with 30 animals per pen. The feeding schedule for the kids is presented in Table 1 (Belanger 2001), and the chemical composition of the diet is presented in Table 2. Age and body weight at slaughter ranged from 67 to 83 days and from 19.5 to 23.9 kg.
At the end of the fattening period, all kids were transported to a commercial abattoir. Kids were held overnight without feed before slaughter. Kids were slaughtered and dressed using standard commercial procedures. After evisceration, kidney fat and the following nine edible organs and glands items were collected from each kid: heart, tongue, lungs, spleen, liver, kidney, brain, testicle and thymus (Spooncer 1988). All items were packed individually in clean polyethylene bags within 1 h of the animal's slaughter, and conventionally chilled overnight in a chiller at 0-4°C. Ultimate pH and colour characteristics were measured on the surface and/or centre cross-section of the fresh offal and kidney fat. After determination of ultimate pH and colour characteristics, the remaining part of each offal item and kidney fat was individually homogenized (Waring 8010ES Blender, USA; capacity 1 l, speed 18,000 rpm, duration of homogenization 10 s, temperature after homogenization <10°C), vacuum packaged in polyethylene bags and stored at −40°C until determination of proximate and mineral composition.
The pH value was measured at 24 h (pH 24h ) post-mortem using a portable pH meter (Consort T651, Turnhout, Belgium) equipped with an insertion glass combination electrode (Mettler Toledo Greifensee, Switzerland). The pH meter was calibrated before and during the readings using standard phosphate buffers (pH value of calibration buffers was 7.00 and 4.01 at 25°C) and adjusted to the expected temperature of measured muscles (ISO 2917(ISO 1999. Six replicate surface and/or centre cross-section colour measurements were performed after 60 min of blooming at 3°C (Honikel 1998). The CIEL* (lightness), CIEa* (redness) and CIEb* (yellowness) colour coordinates (CIE 1976) were determined using a Konica Minolta Chroma Meter CR-400 (Minolta Co., Ltd., Osaka, Japan) using D 65 illuminant, a 2°standard observer angle and an 8-mm aperture in the measuring head. The instrument was standardized with a white plate (Y = 92.9, x = 0.3159 and y = 0.3322), and warmed according to the manufacturer's instructions.
Moisture (ISO 1442(ISO 1997, protein (nitrogen × 6.25; ISO 937 1978), total fat (ISO 1443 1973) and total ash (ISO 9361998) levels in the edible organs, glands and fat were determined according to methods recommended by the International Organization for Standardization.

Ultimate pH and colour characteristics
Results for ultimate pH value and instrumental colour (CIEL*a*b* values) of all edible by-products of Saanen goat male kids are presented in Table 3. In this study, ultimate pH and colour were significantly affected by the type of byproduct (P < .05).
According to Florek et al. (2012), the distinction made between offal as derived mainly from organ tissue and those originating from muscular tissue is crucial because of differences in their potential to sustain quality.
The post-mortem pH of meat is determined by the amount of lactic acid produced from glycogen during anaerobic glycolysis (Lawrie & Ledward 2006). With the exception of liver, offal contains low levels of carbohydrates, being quite similar to, or lower than, levels in lean meat. The liver normally has about 5.3% carbohydrate, mainly as glycogen (Savell & Pearson 1988). The pH is a very important criterion for meat and meat products' quality. An ultimate pH above 5.85 shortens the shelf life (Gill 1988;Honikel 1999;Lawrie & Ledward 2006).
Kidney fat had the highest surface CIEL* value (75.60). There were significant (P < .05) differences in surface CIEL* value among the particular edible organ and gland items, except between heart and spleen, heart and kidney, tongue and testicle, and brain and thymus (P > .05). Among the edible organs and glands, liver had the lowest mean surface CIEL* value (35.76; P < .05), that is, darkest colour, while brain and thymus had the highest mean surface CIEL* value (P < .05), that is, lightest colour (64.45, 64.65, respectively; P > .05). Lungs had the highest mean surface CIEa* value (27.47; P < .05). The lowest mean surface CIEa* value (6.28; P < .05) was determined in kidney fat, followed by tongue (8.23), with a significant (P < .05) difference between them. The mean surface CIEb* value was numerically the highest for the kidney (12.57), while the lowest mean surface CIEb* value (0.94; P < .05) was determined in the spleen. Except between the heart and kidney, mean fresh cut cross-section CIEL* values differed significantly (P < .05) among all investigated edible organs and glands, being the lowest (darkest colour) in the spleen (26.48; P < .05), and the highest (lightest colour) in the thymus (66.57; P < .05) (fresh cut cross-section colour, CIEL*a*b* values, for the brain and kidney fat were not determined). The mean fresh cut crosssection CIEa* value differed significantly (P < .05) among all investigated edible organs and glands, except for the liver and kidney. Lungs had the highest (26.26; P < .05) and the thymus had the lowest (8.85; P < .05) mean fresh cut crosssection CIEa* value. The mean fresh cut cross-section CIEb* value was highest (P < .05) in the lungs and liver (11.47, 10.60, respectively, P > .05) and the lowest in the testicle (−0.59; P < .05). The difference between surface and fresh cut crosssection colour parameters (CIEL*a*b* values) was not significant (P > .05) for the heart (CIEb* value), lungs (CIEa*and CIEb* values), liver (CIEL* and CIEa* values), testicle (CIEa* values) and thymus (CIEL* and CIEa* values).

Proximate composition
Moisture, protein, total fat and total ash contents of all edible by-products of Saanen goat male kids are presented in Table 4. The proximate composition was significantly influenced by the type of by-products. Among all investigated edible by-products, kidney fat had the highest mean total fat content (89.66 g/100 g; P < .05) and   the lowest mean moisture (8.88 g/100 g; P < .05), protein (1.28 g/100 g; P < .05) and total ash (0.04 g/100 g; P < .05) levels.
The testicle had the highest mean moisture level of all edible organ and gland items (85.01 g/100 g; P < .05), while the tongue and liver (74.99 and 74.40 g/100 g, respectively; P > .05) had the lowest mean moisture level (P < .05). Furthermore, the spleen and liver had the highest mean protein content (18.26 and 18.43 g/100 g, respectively; P > .05), and the brain had the lowest mean protein content (9.69 g/100 g; P < .05). The mean total fat content was highest in the brain (7.13 g/100 g; P < .05), while numerically the lowest mean total fat content was in the testicle (1.57 g/100 g). The thymus had the highest mean total ash level (2.02 g/100 g; P < .05), while the lowest mean total ash levels (P < .05) were found in the tongue and testicle (0.95 and 0.99 g/100 g, respectively, P > .05). There is a lack of information about proximate composition of by-products from goat kids. Levels of moisture and total fat for goat heart, liver and kidney obtained in this study are in agreement with the results of Park et al. (1991).

Mineral composition
Mineral (K, P, Na, Mg, Ca, Zn, Fe, Cu, Ni and Mn) levels of all edible by-products of Saanen goat male kids are presented in Table 5(a) and (b). The mineral composition was significantly influenced by the type of by-product.
Among all investigated edible organs and glands, the highest mean K level (P < .05) was in the thymus (444 mg/ 100 g), while the lowest mean K level was in the kidney (235 mg/100 g; P < .05). The highest level of P was found in the thymus (516 mg/100 g; P < .05) and the lowest (P < .05) in the heart and tongue (226 and 220 mg/100 g, respectively, P > .05). The kidney had the highest Na level (167 mg/100 g; P < .05), while the lowest Na levels (P < .05) were determined in the spleen, liver and thymus (64.6, 63.5 and 59.6 mg/100 g, respectively, P > .05). The level of Mg was highest in the thymus (21.7 mg/100 g; P < .05) and lowest in the brain (11.2 mg/100 g; P < .05). Numerically, the highest mean Ca level occurred in the testicle (17.6 mg/100 g) and the lowest mean Ca level was in the heart (10.7 mg/100 g; P < .05). Furthermore, Zn, Cu and Mn levels were highest in the liver (4.78, 2.62 and 0.21 mg/100 g, respectively; P < .05), while Fe and Ni levels were highest in the spleen and testicle (12.8 mg/100 g and 0.046 mg/100 g; P < .05, respectively). The brain had numerically the lowest mean Zn level (1.10 mg/100 g), while the thymus had numerically the lowest mean Fe, Cu and Ni levels (0.89, 0.57 and 0.12 mg/100 g, respectively). Finally, the level of Mn was numerically the lowest for the heart (0.015 mg/ 100 g). Compared to the mineral composition of goat liver, kidney, heart, spleen and brain reported by Webb et al. (2005), the Ca level in the brain, Fe levels in the spleen and kidney, Cu levels in the spleen and liver, and Mn level in the same type of organs in the present study were lower, while K and P levels in the same type of organs were slightly higher. In the present study, compared to the mineral composition of goat kid liver and kidney obtained by Mioč et al. (1998), levels of P and Fe were higher, levels of Mg were slightly higher and levels of Mn were lower for both organs, while the level of Na in the liver was lower. The mineral composition (P, K, Ca, Mg and Na) of goat liver presented by Park (1990) is similar to the results found in the present study.
In conclusion, the present study provides data on the quality of fresh edible by-products from Saanen goat male kids raised under an intensive farming system. Many significant differences were found in the mean values of quality traits among the edible by-products studied. Nevertheless, more studies are necessary to provide better knowledge of the characteristics of edible by-products from Saanen goat male kids, especially the quality of cooked edible by-products intended for human consumption.