Greece is considered a leader country in the production of small ruminants in European Union. It possesses 35% of goat production and 8.98% of sheep population of the EU (FAO, 2010). The quality of sheep meat is a main concern for producers and consumers. For the production of preferred lambs by producers and processors, the importance of interactions among breeds, age at slaughter and carcass weight, sex and diet practices should be recognized (Hoffman et al. 2003). Quality is a multifaceted dynamic concept that can be studied from a variety of aspects (process, market, nutrition, animal develop or genetic, etc) (Sañudo et al. 1998; Joo et al. 2013). Karlsson (1992) suggested that when there is a large number of a related factor in evaluating quality then these factors can be replaced by a smaller number without any important loss of information. Consumer’s preferences and subjective quality of perception is difficult to be determined. There is a tendency to evaluate the retail quality of meat by its tender ness, juiciness and flavor (Schönfeldt et al. 1993; Rubino et al. 1999; De Backer and Hudders, 2015) having as auxiliary criteria its chemical components. Among these three components of eating quality, tenderness is the most important (Miller et al. 1990), while the best indicator of tenderness is the total collagen content in the meat (Seideman et al. 1987; Okeudo and Moss, 2005). As the level of collagen content decrease, muscle tenderness increase (Field et al. 1990). The decrease in tenderness with increasing age is due to the changing nature of collagen, the connective tissue protein found in the meat. Juiciness as well as tenderness is directly related with the intramuscular fat content and with the level of moisture in the meat (Schönfeldt et al. 1993; Hedrick et al. 1994). However, the sensation of juiciness is mainly determined by the ability of meat to hold its water capacity (Hedrick et al. 1994). Moreover, it is widely accepted that the amount and type of fat in the meat influence the two major quality components of tenderness and flavor (Wood et al. 2008). The nutritional content is also regarded as a significant quality aspect of meat (Damez and Clerjon, 2008) and plays a substantial role in the diet of modern consumers providing the necessary quantity of protein and vitamins (Grunert, 2006; Binnie et al. 2014). Among many components of the muscle, protein is the most important and it can influence the tenderness of meat (Therkildsen et al. 2002; Sazili et al. 2004). The meat of younger animals is tenderer since protein synthesis is decreased as the animal gets older (Therkildsen et al. 2002; Sazili et al. 2004). The objective of the present study was to investigate the effect of carcass weight, age at slaughter and sex on the chemical composition of lamb meat of Boutsiko sheep breed.
MATERIALS AND METHODS
Experimental design and animal management
The study was carried out using a sample of twenty-two lambs (twelve females and ten males) of Boutsiko sheep, a native breed of Greek sheep, in the mountainous area of Metsovo, Greece. The measurement of lambs’ weight was carried out every 7 days from their birth. Animal body weights were measured before slaughter and carcasses were weighed after the slaughter. The average age of lambs at slaughter was 47.8 ± 4 days. During the suckling period lambs were fed supplementary unchopped lucerne hay and concentrated mixture (corn, barley, soy flour, sunflower flour, cotton pie, salt, limestone powder and nutrition supplement, Table 1).
Sampling procedure and analysis
The dissection of the lamb carcasses was carried out within 24 hours after the slaughter in the following cuts: shoulder, leg, racks, loin, rear flank, breast ribs, scrag-end. Measurement of weight for each cut was done with an electronic scale of type Angel A (model no-15A). Lamb carcass cuts were stored in a deep freezer (-40 ˚C) for two weeks. All frozen samples were defreezed and about 100 g from each sample were ground in a small miller (SEVERIN 3781, 700w) and then passed twice through a mesh screen to obtain higher homogeneity.
Table 1 The supplementary concentrated feed
Measurements were made using an NIRS instrument (FOSS Foodscan Lab, Type78810, Denmark) using the FOSS CIS software according to the method of the association of official analytical chemists (AOAC, 2006). Each sample was scanned twice and an average spectrum was used for calibration. Spectra were stored in a log (1/R) format (Cao, 2013). These units represent the quantity of infrared energy absorbed by the sample during a reflex sampling. The analyses were carried out at room temperature of 22-24 ˚C and humidity of 75%.
Statistical analysis was conducted using SPSS (SPSS, 2011). To identify relationships, regression analysis was adopted. The dependent variable was represented by the quality components (fat, protein, moisture and collagen) and the independent by age, sex and carcass weight. Initially, regressions were estimated for the average of all seven cuts (shoulder, leg, racks, loin, rear flank, breast ribs, scrag-end) and then for each cut, separately. In total 32 equations were estimated.
RESULTS AND DISCUSSION
On average the percentage for fat content amounted to 25.35%, for protein to 16.70% for moisture to 57.96% and for collagen to 1.77%. The estimated regression equations for the total number of cuts are presented in the equations 1 to 4. Results indicate that carcass weight is the most significant factor in explaining fat, protein, and moisture content, while the age at slaughter in explaining collagen content. The sex did not appear to be a significant interpretive factor to any of the four chemical components. The impact of carcass weight, age at slaughter and sex was also examined in relation to each cut of lamb meat (Tables 2, 3, 4 and 5).
Table 2 Regression results for fat content per anatomical carcass cut
CW: carcass weight.
Table 3 Regression results for protein content per anatomical carcass cut
CW: carcass weight.
Table 4 Regression results for moisture content per anatomical carcass cut
CW: carcass weight.
Table 5 Regression results for collagen content per anatomical carcass cut
CW: carcass weight.
The results agree to a large extent with the above findings regarding the total number of cuts. Carcass weight is the dominant explanatory variable for fat, protein and moisture, while age at slaughter for collagen. The only exception is found in collagen regarding the equation of rack in which both age and weight were found statistically significant. Carcass weight on its own appears to explain a significant portion of the variation of the three chemical components for most of the cuts. Values of R2range between 0.09 to 0.49 with the lowest values found in the leg equations (0.09-0.13) and the highest in the shoulder equations (0.40-0.49). As to the collagen, age at slaughter explained 74% of its content in the scrag-end and only 13% in the shoulder.
Υfat= -2.397 + 0.003 ΧCW + e (1)
ΧCW= 0.716 and e= 0.000
Υprotein= 21.866 - 0.001 ΧCW + e (2)
ΧCW= 0.000 and e= 0.001
Υmoisture= 80.045 – 0.002 ΧCW + e (3)
ΧCW= 0.000 and e= 0.000
R2adj = 0.44
Υcollagen= -1.220 + 0.063 Χage + e (4)
Χage= 0.049 and e= 0.000
The average content of protein for all pieces amounted to 16.70% which can be regarded as normal since it is in the range of 15-20% and is not distant from the values found in other studies (Loest et al. 1997; Brzostowski et al. 2006; Abdullah and Qudsieh, 2008). Although a value of protein content up to 20% could be considered more satisfactory, the figure of 16.70% is near the value of 16.88% which according to United States Department of Agriculture (USDA, 2001) is the percentage contained in an edible portion of lamb. Similar comments can be made about moisture which is almost 57.7 %. According to USDA (2001) moisture in lamb meat should be approximately 60%. It is worth mentioning that lambs with the well known Callipyge gene contain moisture just below 60%, while normal lambs contain above 50% (Field et al. 1990). As to collagen content, the average value of 1.77% found in the present study is higher from the corresponding normal lamb measurement of 1.68% (Field et al. 1990), but still it is in the range of the standard levels set by Food Safety Authority of Ireland (2003). Results of regression analysis appeared to be similar with the findings of other studies which shown that fat content can be affected from carcass weight and that there is a positive relation between them (Abdullah and Qudsieh, 2008; Sobrinho et al. 2003; Pérez et al. 2002). Moreover, higher age at slaughter and carcass weight are correlated with higher levels of fat (Field et al. 1990; Zygoyiannis et al. 1990; Aziz et al. 1993; Schönfeldt et al. 1993; Vipond et al. 1993) although differences are not significant sometimes (Alfonso and Thompson, 1996). However, in the present study, age was not found a significant factor in affecting fat and protein content. It is not unlike that age at slaughter may act as a mediator since a grown lamb is expected to have larger weight. This view of the impact of age at slaughter through carcass weight can also be expressed for the content of moisture. Previous studies have shown that loss of moisture is related to an increase (Rashid and Faidhi, 1990; Schönfeldt et al. 1993) or a decrease (Aziz et al. 1993; Failla et al. 1996) of age at slaughter. The results from the present study indicated that as carcass weight increase then moisture decrease which is in agreement with previous findings for lambs (Sañudo et al. 1996). In relation to collagen content, only age at slaughter had significant impact. This finding is in line with the results of other studies where the increase in age at slaughter involves higher levels of collagen content and reduction of its solubility leading to less tenderness (Devine et al. 1993; Lawrie, 1998; Gerrard and Grant, 2003). It should be noted that carcass weights in this study may not have been high enough for there to be a restructuring of the interconnections in the muscle collagen, although it is possible that a reduction in tenderness consequent to an increase in muscle fat content counteracts any increase with age at slaughter (Miller et al. 1990). However, Ablikim et al. (2016) found differences in tenderness, assessed by a taste panel, between Lacha and Rasa Aragonesa lambs slaughtered at 12 and 24 kg live weight. The meat from 24 kg lambs was harder, mealier, more cohesive and more difficult to swallow than meat from the milk-fed lambs. According to regression coefficients a reduction of 1 kg in carcass weight can reduce fat content on the average by 3%. At the same time, this reduction in weight will increase protein and moisture content by 1 and 2%, respectively, which is a more desirable level for Boutsiko lamb. Further balance can be reached by cutting down the average age at slaughter of lambs. A reduction of 2 days, from 47.8 to 45.8, will decrease the amount of collagen content from 1.77 to 1.66. In general females are the sexual type that contain higher amount of fat (Field et al. 1990; Sainz et al. 1990; Notter et al. 1991; Alfonso and Thompson, 1996; Teixeira et al. 1996). The results of this study indicated that sex does not have an impact on fat which agrees with the findings of Sainz et al. (1990). Different authors have found males’ meat to be tougher because collagen accumulation may be stimulated by testosterone (Dransfield et al. 1990; Miller et al. 1990; Beermann et al. 1995). However, the present study showed that sex does not have important influence not only in collagen and in protein, but also in the content of moisture, a result which is consistent with the findings of Horcada et al. (1998).
The results of this study show that carcass weight had significant effect on the content of fat, protein and moisture of Boutsiko lamb meat, while age at slaughter was the only factor which has an impact on the value of collagen. The significant positive relation of carcass weight with fat content and its negative relation with moisture and protein is an indication that lessening the weight by a small amount will have comparatively favorable results in the chemical quality of meat.
The authors thank the technician Apostollos Dollpatsis for the help in the slaughter of lambs and carcass dissection.