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Meat and fat colour as a tool to trace grass-feeding systems in light lamb production
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MEAT SCIENCE Meat Science 80 (2008) 239–248 www.elsevier.com/locate/meatsci
Meat and fat colour as a tool to trace grass-feeding systems in light lamb production G. Ripoll, M. Joy *, F. Mun˜oz, P. Albertı´ Unidad de Tecnologı´a en Produccio´n Animal, CITA, Apdo. 727, 50080 Zaragoza, Spain Received 22 March 2007; received in revised form 25 October 2007; accepted 27 November 2007
Abstract Ninety-five lambs were fed as follows: lambs and dams grazing alfalfa (Gr); As Gr but lambs had access to concentrate (Gr+S); ewes grazed and lambs received milk and concentrate until weaning and thereafter concentrate and straw (Rat-Gr); ewes and lambs were stallfed (Ind). Lambs were slaughtered at 22–24 kg of live-weight and fat and M. rectus abdominis colour measured. Visual appraisal scores of Gr and Ind were significantly different. The absolute value of the integral of the translated spectrum (SUM) was greater in Gr and GR+S. A discriminate analysis was able to discriminate between grass-fed and indoor-fed lambs. A logistic regression including SUM and b* classify correctly 99.1% of carcasses. A equation is proposed to calculate the probability of one carcass to do not belongs 1 to Gr or Gr+S group (PNA): PNA ¼ 1þeð1:953þ1:320b 0:115SumÞ . Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Alfalfa; Rectus abdominis colour; Subcutaneous caudal fat colour; Reflectance spectrophotometry
1. Introduction Traditional lamb meat production in Spain is based on light lambs (22–24 kg of body weight, less than 90 days old). The ‘‘Ternasco de Arago´n” protected geographical indication is a typical light lamb, usually fattened indoors. The conventional feeding system is suckling lambs supplemented with concentrate until weaning (45–50 days old) and thereafter only concentrate and straw. Lamb meat coming from this production system is characterized by a pale pink meat colour and white fat, without important variations between farms, with the breed and slaughter weight as exclusive factors of differentiation among other labelled lamb meat. The constantly increasing price of cereals, demand for healthy and safe meat products and the EU Common Agricultural Policy that favours extensive grazing systems for ruminants are stimulating the interest in pasture-based production system. Grazing lambs are often
*
Corresponding author. Tel.: +34 976 716442; fax: +34 976 716 335. E-mail address: [email protected] (M. Joy).
0309-1740/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2007.11.025
˚ dnøy et al., considered to be of a higher general quality (A 2005), mainly in northern European countries, because of the increasing interest that has arisen in sustainable and socially acceptable food production methods (Zervas, Hadjigeorgiou, Zabeli, Koutsotolis, & Tziala, 1999). Previous studies have shown good prospects for animal performance in spring lambing ewes raising lambs on pastures (Alvarez-Rodriguez, Sanz, Delfa, Revilla, & Joy, 2007; Joy, Albertı´, Tort, & Delfa, 2004). The main traits taken into account by consumers are fat and meat colour. Yellow fat is generally not appreciated by consumers (Priolo, Micol, Agabriel, Prache, & Dransfield, 2002a) particularly Spanish consumers, with a clear preference for lamb meat from the light animals (Font i Furnols et al., 2006) with a muscle colour classified as pale (San˜udo et al., 2007). Any feeding systems that effect fat or muscle colour need to be studied in order to avoid consumer rejection of the meat due to changes on colour. Carcass and meat quality of lambs and cattle raised on concentrate or grass systems are different, mainly with regard to muscle and fat colour (Chestnutt, 1994; Dunne, O’Mara, Monahan, & Moloney, 2006;
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French et al., 2000; Prache & Theriez, 1999; Priolo et al., 2002a; Schroeder, Cramer, Bowling, & Cook, 1980; Yang, Brewster, Lanari, & Tume, 2002) and fatty acid composition (Nozie`re et al., 2006; Priolo et al., 2002a). Different studies have demonstrated that muscle from grass-fed ruminants has greater amount of n3 fatty acids than concentrate-fed animals, improving their value for human nutrition (Enser et al., 1998; Nu¨rnberg, Wegner, & Ender, 1998). Consumers increasingly demand clear information regarding production systems, especially animal feeding and management. Recently efforts have been made to trace feeding systems in herbivores in order to implement food safety. One of the major challenges for scientists is to develop analytical tools to quantify compounds in the animal tissue that can not be synthesized endogenously and, therefore, can act as tracers of animals diet (Prache, Cornu, Berdague´, & Priolo, 2005). As the carotenoids can only be biosynthesized by plants and microorganisms (Goodwin, 1955; Prache et al., 2005; Zalokar, 1954), their presence in animal tissues is attributed to ingestion in food (Olson, 1964; Schieber & Carle, 2005). Their content in adipose tissues is responsible for differences in carcass fat colour since these pigments generate yellow (lutein), orange (b-carotene) and red colours. In sheep and goats lutein is the only carotenoid stored in the adipose tissue (Prache, Priolo, & Grolier, 2003; Yang, Larsen, & Tume, 1992), and its concentration in fat is usually very low in most breeds (Hill, 1962). The concentration of carotenoid pigments is high in fresh pastures, such as alfalfa or grass, and low in grains, which means that these compounds can be used as biomarkers or tracers to develop techniques for the authentication of products from grazing lambs. Prache and Theriez (1999) proposed an index based on the reflectance spectrum of adipose tissue to trace grass-feeding, but results were certain only for 81%. Ripoll, Joy, Mun˜oz, Albertı´, and Delfa (2006) added to that index the trichromatic coordinates of the CIELab space to obtain 100% discrimination between forage- and concentrate-fed lambs. These same authors concluded that the reflectance spectrum of adipose tissue as well as the trichromatric coordinates of the CIELab are fast, non-destructive, on-line and readily available methods as opposed to other tracer techniques, such as fatty acid composition or vitamin E. The aim of this study was to assess the influence of the lamb feeding system on muscle and fat colour, and to ascertain the capability of reflectance spectrophotometry to discriminate between carcasses from forage- and concentrate-fed lambs. 2. Materials and methods 2.1. Animal management and diets This experiment was conducted at the experimental facilities of a Research Centre in Zaragoza (Spain) and involved 95 single, spring-born, male Rasa Aragonesa
lambs. The experiment was repeated in two consecutive years (50 animals in the 1st year and 45 in the 2nd year). Lambs and dams were randomly allocated to four experimental lots according to their future feeding system: 1. Grazing (Gr): Ewes and lambs were continuously stocked on alfalfa pasture. No concentrate was available to dams or lambs. Lambs suckled their mothers and grazed until slaughter (n1st year = 13; n2nd year = 11). 2. Grazing with supplement for lambs (Gr+S): Management was the same as for Gr, and additionally the lambs received concentrates ad libitum in lamb creep feeders (n1st year = 12; n2nd year = 11). 3. Rationed grazing (Rat-Gr): This treatment is the most usual livestock system in the area. Ewes grazed on alfalfa pasture for seven hours a day without their lambs and thereafter remained indoors, receiving a mixed ration. Lambs were kept permanently indoors and were fed with ewe milk and concentrate ad libitum until weaning. From this time up to slaughter lambs had free access to concentrate and barley straw. After weaning, ewes were removed from the trial (n1st year = 12; n2nd year = 12). 4. Indoors (Ind): Ewes and lambs were kept permanently indoors with ad libitum access to a total mixed ration and lambs fed with ewe milk and concentrate ad libitum until weaning. Thereafter, lambs had access to concentrate only (n1st year = 13; n2nd year=11). Composition of feeds is presented in Table 1. A meadow of Alfalfa cv. Arago´n sown at a rate of 25 kg per hectare in spring of 2003 was used to graze ewes and lambs of Gr and Gr+S treatments. The alfalfa pasture was divided into five paddocks of 843 m2 each, and grass-fed animals rotationally grazed on one paddock each week. The stocking rate was 17 ewes (plus lambs) per hectare per year. The alfalfa offered was always green vegetative and had an averages of 234 g CP/kg DM, 338 g NDF/kg DM and 2.61 Mcal/kg DM. Lambs and ewes were supplied with fresh water and mineral-vitamin ad libitum. The lambs from Ind and RatGr treatments were weaned at 45 days old, whereas lambs from Gr+S and Gr remained with their dams in meadows until slaughter. 2.2. Slaughter and sampling procedures Ewe and lamb live-weight (LW) was recorded at weekly intervals during the experimental period. When lambs reached 22–24 kg LW they were slaughtered according to specifications of Ternasco de Arago´n protected geographical indication (Regulation (EC) No. 1107/96) that stipulate lambs of 22–24 kg LW and less than 90 days old. Lambs were slaughtered using standard commercial procedures and carcasses were hung by the Achilles tendon and were chilled 24 h at 4 °C in total darkness to preserve carotenoid pigments. A visual appraisal (VA) of the M. rectus abdominis colour was made according to the Colomer-Rocher scale
G. Ripoll et al. / Meat Science 80 (2008) 239–248
241
Table 1 Feedstuff composition, kg/100 kg Lamb concentrate
Ewes mixed ration
Corn grain Barley grain Soybean meal, 44% Wheat grain Soya oil Vegetal powdered serum Vitamin and mineral supplement Calcium carbonate Sodium chloride Ammonium chloride
20 40.3 21 10 1.2 2.5 1.6 2.4 0.5 0.5
Crude protein (g/kg DM) NDF (g/kg DM) Metabolic energy (MJ/kg DM)
185 190 13.2
(Colomer-Rocher, Delfa, & Sierra, 1988) for light carcasses (<13 kg). This scale is divided into pink, pale red and red, expanded to nine points. M. longissimus thoracis was removed and ultimate pH was measured at the 4th vertebral region with pH-meter equipped with a Crison 507 penetrating electrode (Crison Instruments S.A., Barcelona, Spain). 2.3. Instrumental colour Fat and muscle colour were measured at 24 h at 4 °C after slaughter using a Minolta CM-2006 d spectrophotometer (Konica Minolta Holdings, Inc, Osaka, Japan) in the CIELAB space (CIE, 1986) with a measured area diameter of 8 mm, specular component included and 0% UV, standard illuminant D65 which simulates daylight (colour temperature 6504 K), observer angle 10° and zero and white calibration. The lightness (L*), redness (a*) and yellowness (b*) were recorded, and hue angle (H*) and chroma (C*) indices were calculated as H*=tan1(b*/a*)*57.29, expressed in degrees and C*=(a*2 + b*2)0.5. Chroma is related to the quantity of pigments and high values represent a more vivid colour and denote lack of greyness (Miltenburg, Wensing, Smulders, & Breukink, 1992). Hue is the attribute of a colour perception denoted by blue, green, yellow, red, purple, etc. (Wyszecki & Styles, 1982), and it is related with the state of pigments (Renerre, 1982). Caudal subcutaneous fat from the tail root (Diaz et al., 2002) and kidney fat colour values were recorded from three locations randomly selected but avoiding blood spots, discolorations and less covered areas. Besides trichromatic coordinates, the proportion of reflected light each 10 nm between 450 and 510 nm was collected and the absolute value of the integral of the translated spectrum (SUM) was calculated according to Priolo, Prache, Micol, and Agabriel (2002b). The reflectance spectrum was translated to make reflectance value at 510 nm equal to zero (TR). On the translated spectrum, the integral value was calculated as follows: SUM ¼ ðTR450 =2 þ TR460 þ TR470 þ TR480 þ TR490 þ TR500 þ TR510 =2Þ 10
Cereal straw Gluten feed Palmkernel Barley Soybean hulls Citrus pulp Cotton seeds Calcium carbonate Sodium chloride Fatty acids salt Urea
Barley straw 40 22.8 10.8 8.1 6 6 3.4 1 0.6 0.6 0.7 120 253 12.2
49 835 4.5
where TRi was the reflectance value at i nm. An extensive explanation of the baselines of the method is exposed in Prache and Theriez (1999). Rectus abdominis muscle colour was measured at two locations on the internal face of each piece randomly selected to obtain a mean value representative of the surface colour, after having removed the covering fascia (Eikelenboom, Hoving-Bolink, & Hulsegge, 1992; Klont et al., 2000). 2.4. Statistical analysis Statistical analyses were performed with SAS v.9.1. A two-way ANOVA (4 feeding systems 2 fat locations) was used for fat colour variables and SUM. When non-significant interactions (p < 0.05) were found, models were reduced to main effects only. A Bonferroni test was used to compare means, with a significance of p < 0.05. Feeding system and fat location were included as fixed effects and the effect of year as blocking factor since there were no significant interactions with fixed effects. Pearson’s r was used to correlate M. rectus abdominis visual appraisal with instrumental colour variables. Because the normality assumption was rejected, a base 10 logarithmic transformation was applied to the absolute value of the integral of the translated spectrum (SUM) before the analysis of variance. Means and standard errors shown are not transformed. A forward stepwise discriminant analysis was carried out for subcutaneous caudal and kidney fat, with L*, a*, b*, C*, H* and SUM as the variables evaluated. Selected variables were included in a binary logistic regression to calculate the probability of a carcass does not belong to a Gr or Gr+S group (PNA). 3. Results and discussion Age, slaughter live-weight and ADG from birth to slaughter were not affected by feeding systems (p > 0.05), with a general mean (mean ± s.e.) of 70 ± 0.9 d, 23.14 ± 0.09 kg and 285 ± 3.8 g/d, respectively. Cold car-
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cass weight was 11.3 ± 0.08 kg without there being differences among treatments (p > 0.05). 3.1. M. rectus abdominis colour and ultimate pH Mean pH values are shown in Table 2. There were no significant differences between feeding systems, ranging from 5.56 to 5.59, which is the normal pH in light lamb meat and did not reveal any differences among treatments. The lack of effect of the treatment on pH values may be due to the fact that lambs were weighed weekly and the slaughtering procedure was carried out on the property thus avoiding stress. Grazing animals are not used to being managed frequently and human presence prior to slaughter can cause stress which leads to lower glycogen reserves, and usually to higher values of the ultimate pH (Bowling, Smith, Carpenter, Dutson, & Oliver, 1977; Coulon & Priolo, 2002; Priolo, Micol, & Agabriel, 2001; Vestergaard, Oksbjerg, & Henckel, 2000). The ultimate pH of the light lamb meat in the present study was in agreement with results obtained by Diaz et al. (2002) and Ripoll et al. (2005) but it was slightly lower than the results of Priolo et al. ˚ dnøy et al. (2005). However in both studies (2002b) and A the slaughter weight of lambs was greater than that of the present study. Table 2 shows the instrumental colour and visual appraisal of M. rectus abdominis. Differences were observed between grazing lamb groups (Gr and Gr+S) and indoor lamb groups (Ind and Rat-Gr) in redness (a*) but not in L*, b*, hue and chroma. Diaz et al. (2002) did not find any significant differences between Talaverana lambs raised on pasture or stall-fed in L*, a*, b*, C* or hue of rectus abdominis, although in both treatments all animals had free access to concentrate from birth to weaning. Treatment affected the visual appraisal scores, although only Gr and Ind showed significant differences between each other (p < 0.05); the rest of treatments were similar (p > 0.05). This result is in accordance with the differences (p < 0.001) observed in
Table 2 Instrumental colour and visual appraisal of M. rectus abdominis and M. longissimus thoracis ultimate pH
pHu L* a* b* Hue Chroma Visual appraisal
Gr1
Gr+S
Ind
Rat-Gr
s.e.
Sig.
5.57 47.99 8.93a 9.51 45.96 13.47 5.79a
5.57 49.15 9.40a 10.48 46.07 14.31 5.30ab
5.59 49.28 8.04b 10.59 51.81 13.46 4.83b
5.56 49.95 7.29b 9.31 50.23 11.98 4.92ab
0.078 0.577 0.313 0.721 2.170 0.650 0.226
ns ns *** ns ns ns *
Different superscript (a,b) indicate significant difference (p < 0.05) among feeding systems. ns = P P 0.05; *=P < 0.05; **=P < 0.01; ***=P < 0.001. 1 Gr, grazing lambs on alfalfa pasture; Gr+S, grazing lambs on alfalfa pasture supplemented with concentrate; Ind, grazing dams and lambs fed with milk and concentrate; Rat-Gr, dams permanently indoors and lambs fed with milk and concentrate.
instrumental redness values (Table 2). Ind treatment showed the palest colour of muscle followed by RatGr, Gr+S and Gr, with values of 4.83, 4.92, 5.30 and 5.79, respectively, and all treatments were classified as pale red colour. Beriain et al. (2000) and Horcada, Beriain, Purroy, Lizaso, and Chasco (1998) concluded that concentrate-fed Rasa Aragonesa lambs, slaughtered at the same live-weight, were classified as pale red colour as is the case with the present results. In grazing systems, the effect of physical activity is often confused with the effect of feeding level and/or feed ration (Vestergaard et al., 2000). The muscle of lambs raised on pasture is darker in relation to stall-fed lambs due to greater concentration of haem pigments in muscles as a result of exercise (Renerre, 1986). However, in light lamb carcasses, Colomer-Rocher et al. (1988) reported that M. rectus abdominis colour was influenced by diet and age, but not by physical activity. Hopkins, Beattie, and Pirlot (1998) and Young, Daly, Graafhuis, and Moorhead (1997) concluded that there was no consistent diet effect on muscle colour. The differences in muscle colour among treatments observed in the present study were not due to the final muscle pH (Hopkins et al., 1998), and may be due to the diet, according to Colomer-Rocher et al. (1988). Muscle colour in light lamb carcasses may be influenced by different factors to those reported by Hopkins et al. (1998) and Young et al. (1997) in heavy lamb carcasses. Low but highly significant correlations (p < 0.01) between M. rectus abdominis visual appraisal and instrumental colour variables were found (rva-L* = .42, rva-hue* = .42, rva-b* = .32), which are in agreement with Klont et al. (1999) for veal colour. There was no correlation between visual appraisal and redness values, in spite of the significant differences of a* observed among treatments (p < 0.05). This controversial result could be explained because evaluators are not able to appreciate individual L*, a*, b* coordinates, but are able to understand real colour (hue) and lightness (L*). It is advisable to define colour in terms of lightness, chroma and hue (Wyszecki & Styles, 1982) rather than L*, a* and b*. In fact, Albertı´ et al. (2005) advise that the separate use of a* or b* is a simplification of reality and can lead to errors in interpretation. Rigg (1987) also recommended C* values in fat instead b* because they represent adipose tissue colour more accurately, as it is perceived visually by consumers or meat graders (Dunne, O’Mara, Monahan, & Moloney, 2006). 3.2. Fat colour Table 3 shows the effects of feeding management, fat location on the carcass, and its interaction in fat colour. No interaction was observed between feeding system and fat location in L*, a* and H*. These variables are significantly affected by the location (p < 0.001), while the feeding system had an effect on all variables (p < 0.001), except redness (p > 0.05).
G. Ripoll et al. / Meat Science 80 (2008) 239–248
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Table 3 Effects of feeding system and fat location on lamb fat colour (F values) and significance L*
a* ***
System Location System Location
15.50 18.84*** ns
0.67ns 19.43*** ns
b*
C* ***
6.64 3.39ns 3.81*
H* **
5.44 1.34ns 3.86*
SUM *
3.16 35.09*** ns
70,55*** 18,92*** ns
a
a
Gr
ns = P P 0.05. * =P < 0.05. ** =P < 0.01. *** =P < 0.001.
When the kidney and subcutaneous caudal fat depots were compared, it was observed that kidney fat had greater values of L* and a*, and lower hue values in the four feeding systems studied (Table 4). However, b* and C* values varied according to fat depots in lambs in the concentrate-fed groups (Ind and Rat-Gr; Fig. 1). Kidney fat had lower b* and C* than those observed in grazing treatment groups (Gr and Gr+S). In contrast, caudal fat did not show any differences between treatments for the colour attributes. According to Priolo et al. (2002b), when carotenoid concentrations are high, as occurs in grazing lambs, the yellowness and chroma values are similar in all fat depots. However, when they are low, as in indoor lambs, they are accumulated in a greater amount in subcutaneous caudal fat (Priolo et al., 2002b). Higher values of b* were observed in grass- and stall-fed lambs slaughtered at 35 kg in subcutaneous and perirenal fat (Priolo et al., 2002b; Priolo et al., 2002a). Carotenoid content of herbage (Knight, Death, Muir, Ridland, & Wyeth, 1996; McDonald, Edwards, Greeenhalgh, & Morgan, 1995), the grass intake (Priolo et al., 2002b), breed (Baker, Steine, Vabeno, & Breines, 1985) and weight at slaughter might influence b* and C* values. Fig. 2 shows the individual redness and yellowness values of each treatment. The averages of caudal fat colour according to feeding systems were placed more closely among them than those observed in kidney fat. This latter depot presented high chroma values (far from the coordinate origin) in Gr and Gr+S treatments. Ind and Rat-Gr had lower hue angles (near to x-axis) with a colour closer to red. Furthermore, in both fat depots, individual points
14 13
n.s.
Gr+S
12
b
b
Ind Rat-Gr
b* 11
10 9 8 Caudal 14
Kidney a
a
n.s.
13 b
12
b
C* 11 10 9 8 Caudal
Kidney
Fig. 1. Yellowness (b*) and Chroma (C*) means and standard error (error bars) of kidney and caudal subcutaneous fat of four feeding systems: Grazing lambs on alfalfa pasture (Gr), grazing lambs on alfalfa pasture supplemented with concentrate (Gr+S), grazing dams and lambs fed with milk and concentrate (Ind) and dams permanently indoors and lambs fed with milk and concentrate (Rat-Gr).
were mixed, not allowing easy interpretation or discrimination between feeding systems or between grazing and nongrazing systems. Hence, colour coordinates (b* and a*, and
Table 4 Subcutaneous caudal and kidney fat lightness (L*), redness (a*) and Hue (H*) (mean ± s.e.) GrB *
L
a* Hue
A
SCF KF SCFA KF SCFA KF
Gr+S ay
73.6 ± 0.55 74.6ax ± 0.69 1.9by ± 0.20 3.2x ± 0.25 81.5ax ± 0.89 76.4y ± 0.96
ay
74.2 ± 0.62 75.6ax ± 0.67 2.3aby ± 0.24 3.3x ± 0.28 79.9abx ± 0.90 76.2y ± 0.80
Ind
Rat-Gr by
69.4 ± 0.98 72.2bx ± 0.57 2.4aby ± 0.27 3.1x ± 0.24 78.9abx ± 1.00 74.2y ± 0.99
70.7by ± 0.63 73.6bx ± 0.45 2.7by ± 0.27 2.9x ± 0.25 77.7bx ± 1.15 75.1y ± 1.01
Different superscript (a,b) indicate significant differences (P < 0.05) among feeding systems. Different superscript (x,y) indicate significant differences (P < 0.05) between fat locations. A SCF = Subcutaneous caudal fat; KF = kidney fat. B Gr, grazing lambs on alfalfa pasture; Gr+S, grazing lambs on alfalfa pasture supplemented with concentrate; Ind, grazing dams and lambs fed with milk and concentrate; Rat-Gr, dams permanently indoors and lambs fed with milk and concentrate.
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18
Yellowness (b*)
16
14
Gr+S
12
Gr
Ind
Rat-Gr
10
8
6
0
1
2
3
4
5
6
Redness (a*) 18
Yellowness (b*)
16
14
Gr+S Gr
12
Ind
10
Gr
Rat-Gr
Gr+S Ind
8
Rat-Gr Mean value
6
0
1
2
3
4
5
6
Redness (a*) *
*
Fig. 2. Relation between redness (a ) and yellowness (b ) of individual values of subcutaneous caudal fat (above) and kidney fat (below) of four feeding systems: Grazing lambs on alfalfa pasture (Gr), grazing lambs on alfalfa pasture supplemented with concentrate (Gr+S), grazing dams and lambs fed with milk and concentrate (Ind) and dams permanently indoors and lambs fed with milk and concentrate (Rat-Gr).
indirectly C* and H*) of both fat depots, are insufficient to discriminate between carcasses, probably due to the influence of other factors in fat colour, apart from the concentration of carotenoids. 3.3. Absolute value of the integral of the translated spectrum Values of SUM (Fig. 3) were greater (p < 0.001) in Gr and GR+S in both fat depots, the difference being more than twofold among grazing- and indoor- lambs. The mag-
nitude and direction of these differences is in agreement with those reported by Priolo et al. (2002b), who found in subcutaneous caudal and kidney fat, greater values for grass-fed lambs with values within a range of 400–300 units, while the stall-fed lambs had values lower than 200 units. The lower values observed in the present study may be due to the lower slaughter weight of lambs in relation to that used in the study cited above, as well as to different food sources. The present values observed were 200– 250 for grass-fed and 75–125 for concentrate-fed lambs, in
G. Ripoll et al. / Meat Science 80 (2008) 239–248
a
250
Gr+S
a, 1 a
200
Rat-Gr
SUM
175 150
b
125 100
0
Ind
b
b
-2 % reflectance
225
2
Gr
a
245
b
-4 -6 -8 -10 -12
75
-14
50
440
Caudal
450
460
Kidney
470
480
490
500
510
520
500
510
520
Wavelength (nm)
Fig. 3. Absolute value of the integral of the translated spectrum (SUM) of subcutaneous caudal and kidney fat at 24 h of slaughter.
2
keeping with Prache et al. (2005), who defined a limit of 152 units to separate grass-fed from stall-fed lambs. Kidney fat had greater SUM values than caudal fat (Fig. 3) in accordance with Atti, Ben Salem, and Priolo (2003). These authors reported that subcutaneous fat is a late maturing fat depot and pigments have still not been deposited in light lambs. Priolo et al. (2002b) also reported that the difference between treatments was higher for perirenal than for subcutaneous caudal fat, validating that in light lambs pigments are accumulated first in the kidney fat depot. Furthermore, lutein absorbs blue light and therefore appears yellow at low concentrations and orange–red at high concentrations, which agrees with the greater values of a* in kidney fat explained above (Table 4). Carotenoids absorb light between 450 and 510 nm, and a greater concentration implies a lower translated reflectance. The translated spectrum of the subcutaneous caudal and kidney fat, between 450 and 510 nm, was always negative and below the grazing group (Gr and Gr+S) for any wavelength, except at 510 nm (Fig. 4). Differences between feeding systems were similar in both fat depots studied, whereas Priolo et al. (2002b) reported a greater difference in perirenal adipose tissue compared to subcutaneous caudal fat. Differences in SUM, C* and b* between kidney and subcutaneous, and the different magnitude and direction of differences of SUM and b* within a fat location could result from other chemical and structural components of the adipose tissue contributing to perception of colour (Dunne, O’Mara, Monahan, & Moloney, 2006). Irie (2001) found that absorbance of deoxy- and met-haemoglobin from the peripheral adipose tissue affected spectrophotometer reflectance, while b* would be less affected. Moreover, differences in the concentrations of carotenoids could be related to adipose cellularity (Strachan, Yang, & Dillon, 1993), such as adipocyte volume differences in kidney and subcutaneous fat depots (Nozie`re et al., 2006). Distribution of feeding systems into classes of SUM for each fat depot is shown in Fig. 5. Ind and Rat-Gr overlapped within the range of 0–150 units of SUM in subcuta-
% reflectance
0 -2 -4 -6 -8 -10 -12 -14 440
450
460
470
480
490
Wavelength (nm) Gr
Gr+S
Ind
Rat-Gr
Fig. 4. Averaged translated reflectance spectrum of subcutaneous caudal fat (a) and kidney fat (b).
neous caudal fat. Two carcasses belonging to the Gr and Gr+S feeding systems had values above 350 and the others were symmetrically distributed around the <200 class, from 50 to 300 units. Gr and Gr+S carcasses overlapped 50% with Ind and Rat-Gr in the <150 class and also were mixed in the <100 class. Ind and Rat-Gr carcasses were placed in the fourth first classes while Gr and Gr+S carcasses were spread over seven classes, from <150 to <450. There was just one important overlapping of the four treatments in the <200 class of the kidney fat. 3.4. Discriminant analysis Discriminant analysis selected C* and SUM for subcutaneous caudal fat, and b* and SUM for kidney fat as the variables which explained the greatest amount of variation correctly classifying 43.15% and 50.53% of carcasses, respectively. The inclusion of C* instead b* in the subcutaneous caudal fat is in accordance with Fig. 2, in which grazing and non-grazing treatments are poorly discriminated by b* but are discriminated by a*. Consequently, both b* and a* are necessary, and they were included as C*, which is related to the quantity of pigments (Renerre, 1982) of any colour. The analysis was able to discriminate between grass-fed lambs (Gr and Gr+S) and indoor-fed
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a
G. Ripoll et al. / Meat Science 80 (2008) 239–248 Table 5 Discriminant classification, expressed on percent of carcasses rightly classified, for caudal subcutaneous fat (SCF) and kidney fat (KF)
40
Number of lambs
35 30
Gr
Gr+S
Ind
Rat-Gr
Origin
Predicteda Gr
25 20 15 10 5
Gr+S
Ind
Rat-Gr
Fat depot
SCF
KF
SCF
KF
SCF
KF
SCF
KF
Grb Gr+S Ind Rat-Gr
37.5 43.5 0.0 0.0
45.8 43.5 0.0 0.0
58.3 43.5 12.5 8.3
45.8 43.5 0.0 4.2
4.2 8.7 41.7 41.7
0.0 0.0 50.0 33.3
0.0 4.3 45.8 50.5
8.4 13.0 50.0 62.5
a
0 <50 <100 <150 <200 <250 <300 <350 <400 <450 500 SUM
b
30
Number of lambs
25
Gr
Gr+S
Ind
Analysis for subcutaneous caudal fat included C* and SUM; analysis for kidney fat included b* and SUM. b Gr, grazing lambs on alfalfa pasture; Gr+S, grazing lambs on alfalfa pasture supplemented with concentrate; Ind, grazing dams and lambs fed with milk and concentrate; Rat-Gr, dams permanently indoors and lambs fed with milk and concentrate.
Rat-Gr
Table 6 Estimate and standard error of logistic regression for caudal subcutaneous fat and kidney fat
20 15
Caudal subcutaneous fat 10 5
Intercept b* SUM
0
Kidney fat 2
Estimate
s.e.
P>v
Estimate
s.e.
P > v2
1.953 1.320 0.115
2.583 .400 .032
** ***
6.475 1.037 0.111
4.020 .523 .030
* ***
<50 <100 <150 <200 <250 <300 <350 <400 <450 500 SUM
Fig. 5. Distribution of lambs in the classes of absolute value of the integral of the translated reflectance spectrum (SUM) of subcutaneous caudal fat (a) and kidney fat (b).
ones (Ind and Rat-Gr) (Table 5). However, it is not clear when the classification has to be carried out within one of the two main groups of treatments: grazing (Gr vs. Gr+S) and indoor (Ind vs. Rat-Gr). For kidney fat, 13.0% of Gr+S and 8.3% of Gr carcasses were classified into Rat-Gr. For caudal fat variables, 8.7% and 4.3% of Gr+S were classified into Ind and Rat-Gr, respectively, while 4.2% of Gr were classified into Ind. Inclusion of concentrate in grazing lambs diet induced an increase of the cases erroneously classified. Milk from grazing ewes could have an influence on pigment depots in Rat-Gr lambs (Nozie`re et al., 2006). A logistic regression (Table 6) was applied to determine the probability of a carcass belonging to a non-alfalfa-fed (PNA) treatment. This system classified carcasses into grazing lambs (Gr and GR+S) or concentrate-fed lambs (Ind and Rat-Gr). When only SUM was entered into the regression, 93.9% and 98.4% of carcasses were correctly classified for subcutaneous caudal and kidney fat, respectively. Prache and Theriez (1999) discriminated 81% of the carcasses using subcutaneous caudal fat SUM. Discrimination using kidney fat SUM value was correct only in 78.1% cases in the Priolo et al. (2002b) study, and they pointed to the shape of kidney fat as the main factor hindering correct
measurements. This difficulty was taken account in our study and the correct classifications were 20 percent higher. When SUM and b* were included, the proportions of correct classifications increased to 97.9% and 99.1% for subcutaneous caudal and kidney fat, respectively, and the inclusion of C* in the regression did not improve results. Although logistic binary regression using kidney fat variables classified slightly better than when using subcutaneous fat variables, when lambs are slaughtered, kidney fat becomes bloodied and is less easy to measure on-line than subcutaneous caudal fat. Furthermore, the measuring surface of the spectrophotometer is not in perfect contact with the hard kidney fat, thus affecting measurements. Consequently, to be practical and for simplicity it is proposed to use the b* and SUM variable of subcutaneous caudal fat 1 according to the expression: PNA ¼ 1þeð1:953þ1:320b 0:115SumÞ . This expression could be easily implemented in a slaughterhouse to quickly trace the feeding system of lamb production. 4. Conclusions Alfalfa grazing with or without supplement allows similar lamb performance to that of concentrate-fed lambs. M. rectus abdominis, kidney fat and subcutaneous caudal fat colour were affected by the main feeding groups (alfalfa vs. concentrate-fed), but there was no effect within those (Grazing vs. grazing plus concentrate; indoors vs. rationed grazing). M. rectus abdominis of grazing lambs had higher values of redness and visual appraisal classified it as slightly
G. Ripoll et al. / Meat Science 80 (2008) 239–248
darker than muscle of indoor lambs. Fat colour was influenced in a different way by the effect of feeding system and location of fat depot. Kidney fat of grazing lambs showed the highest values of yellowness and chroma in relation to that of indoor-fed lambs. Subcutaneous caudal fat in all feeding systems had a narrower range of yellowness and chroma values than kidney fat. The absolute value of the integral of the translated spectrum was higher for grazing lambs in both fatty depots, and it was also higher in kidney fat because it is an early maturing tissue. Logistic regression with fat colour variables plus the absolute value of the integral of the translated spectrum is a suitable method to accurately discriminate between both feeding systems. Measurements in subcutaneous caudal fat are proposed for the practical on-line use of this technique. Acknowledgements The authors wish to thank the staff of CITA for their collaboration. Special thanks to Alessandro Priolo for his suggestions. This study was funded by the Ministry of Education and Science of Spain and European Union Regional Development funds (INIA RTA-03-031). The present study is dedicated to the memory of Rafael Delfa. References ˚ dnøy, T., Haug, A., Sørheim, O., Thomassen, M. S., Varszegi, Z., & Eik, A L. O. (2005). Grazing on mountain pastures – does it affect meat quality in lambs?. Livestock Production Science 94, 25–31. Albertı´, P., Panea, B., Ripoll, G., San˜udo, C., Olleta, J. L., Negueruela, I., et al. (2005). Medicio´n del color. In Monografı´as INIA: Ganadera n°1 (255 pp). MICYT-INIA Madrid, Espan˜a. Alvarez-Rodriguez, J., Sanz, A., Delfa, R., Revilla, R., & Joy, M. (2007). Performance and grazing behaviour of Churra Tensina sheep stocked under different management systems during lactation on Spanish mountain pastures. Livestock Science, 107, 152–161. Atti, N., Ben Salem, H., & Priolo, A. (2003). Effects of polyethylene glycol in concentrate or feed blocks on carcass composition and offal weight of Barbarine lambs fed Acacia cyanophylla Lindl foliage. Animal Research, 52, 363–375. Baker, R. L., Steine, A., Vabeno, A. W., & Breines, D. (1985). The inheritance and incidence of yellow fat in Norwegian sheep. Acta of Agricultural Scandinavian, 35, 389–397. Beriain, M. J., Horcada, A., Purroy, A., Lizaso, G., Chasco, J., & Mendizabal, J. A. (2000). Characteristics of Lacha and Rasa Aragonesa lambs slaughtered at three live weights. Journal of Animal Science, 78, 3070–3077. Bowling, R. A., Smith, G. C., Carpenter, Z. L., Dutson, T. R., & Oliver, W. M. (1977). Comparison of forage-finished and grain-finished beef carcasses. Journal of Animal Science, 45, 209–215. CIE. (1986). Commission Internationale de L’Eclairage. Colorimetry, 2nd ed. Viena. Colomer-Rocher, F., Delfa, R., & Sierra, I. (1988). Me´todo normalizado para el estudio de los caracteres cuantitativos y cualitativos de las canales ovinas producidas en el a´rea mediterra´nea, segu´n los sistemas de produccio´n. Programa AGRIMED-CIHEAM: ‘‘Les carcasses d’agneux et de chevreaux me´diterrane´ens”. 9–10 December. Zaragoza. Published in French: EEC (1988), Rapport EUR 11479 FR. Published in Spanish: Cuadernos INIA (1988) 17, 19–41.
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MEAT SCIENCE Meat Science 80 (2008) 239–248 www.elsevier.com/locate/meatsci
Meat and fat colour as a tool to trace grass-feeding systems in light lamb production G. Ripoll, M. Joy *, F. Mun˜oz, P. Albertı´ Unidad de Tecnologı´a en Produccio´n Animal, CITA, Apdo. 727, 50080 Zaragoza, Spain Received 22 March 2007; received in revised form 25 October 2007; accepted 27 November 2007
Abstract Ninety-five lambs were fed as follows: lambs and dams grazing alfalfa (Gr); As Gr but lambs had access to concentrate (Gr+S); ewes grazed and lambs received milk and concentrate until weaning and thereafter concentrate and straw (Rat-Gr); ewes and lambs were stallfed (Ind). Lambs were slaughtered at 22–24 kg of live-weight and fat and M. rectus abdominis colour measured. Visual appraisal scores of Gr and Ind were significantly different. The absolute value of the integral of the translated spectrum (SUM) was greater in Gr and GR+S. A discriminate analysis was able to discriminate between grass-fed and indoor-fed lambs. A logistic regression including SUM and b* classify correctly 99.1% of carcasses. A equation is proposed to calculate the probability of one carcass to do not belongs 1 to Gr or Gr+S group (PNA): PNA ¼ 1þeð1:953þ1:320b 0:115SumÞ . Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Alfalfa; Rectus abdominis colour; Subcutaneous caudal fat colour; Reflectance spectrophotometry
1. Introduction Traditional lamb meat production in Spain is based on light lambs (22–24 kg of body weight, less than 90 days old). The ‘‘Ternasco de Arago´n” protected geographical indication is a typical light lamb, usually fattened indoors. The conventional feeding system is suckling lambs supplemented with concentrate until weaning (45–50 days old) and thereafter only concentrate and straw. Lamb meat coming from this production system is characterized by a pale pink meat colour and white fat, without important variations between farms, with the breed and slaughter weight as exclusive factors of differentiation among other labelled lamb meat. The constantly increasing price of cereals, demand for healthy and safe meat products and the EU Common Agricultural Policy that favours extensive grazing systems for ruminants are stimulating the interest in pasture-based production system. Grazing lambs are often
*
Corresponding author. Tel.: +34 976 716442; fax: +34 976 716 335. E-mail address: [email protected] (M. Joy).
0309-1740/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2007.11.025
˚ dnøy et al., considered to be of a higher general quality (A 2005), mainly in northern European countries, because of the increasing interest that has arisen in sustainable and socially acceptable food production methods (Zervas, Hadjigeorgiou, Zabeli, Koutsotolis, & Tziala, 1999). Previous studies have shown good prospects for animal performance in spring lambing ewes raising lambs on pastures (Alvarez-Rodriguez, Sanz, Delfa, Revilla, & Joy, 2007; Joy, Albertı´, Tort, & Delfa, 2004). The main traits taken into account by consumers are fat and meat colour. Yellow fat is generally not appreciated by consumers (Priolo, Micol, Agabriel, Prache, & Dransfield, 2002a) particularly Spanish consumers, with a clear preference for lamb meat from the light animals (Font i Furnols et al., 2006) with a muscle colour classified as pale (San˜udo et al., 2007). Any feeding systems that effect fat or muscle colour need to be studied in order to avoid consumer rejection of the meat due to changes on colour. Carcass and meat quality of lambs and cattle raised on concentrate or grass systems are different, mainly with regard to muscle and fat colour (Chestnutt, 1994; Dunne, O’Mara, Monahan, & Moloney, 2006;
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French et al., 2000; Prache & Theriez, 1999; Priolo et al., 2002a; Schroeder, Cramer, Bowling, & Cook, 1980; Yang, Brewster, Lanari, & Tume, 2002) and fatty acid composition (Nozie`re et al., 2006; Priolo et al., 2002a). Different studies have demonstrated that muscle from grass-fed ruminants has greater amount of n3 fatty acids than concentrate-fed animals, improving their value for human nutrition (Enser et al., 1998; Nu¨rnberg, Wegner, & Ender, 1998). Consumers increasingly demand clear information regarding production systems, especially animal feeding and management. Recently efforts have been made to trace feeding systems in herbivores in order to implement food safety. One of the major challenges for scientists is to develop analytical tools to quantify compounds in the animal tissue that can not be synthesized endogenously and, therefore, can act as tracers of animals diet (Prache, Cornu, Berdague´, & Priolo, 2005). As the carotenoids can only be biosynthesized by plants and microorganisms (Goodwin, 1955; Prache et al., 2005; Zalokar, 1954), their presence in animal tissues is attributed to ingestion in food (Olson, 1964; Schieber & Carle, 2005). Their content in adipose tissues is responsible for differences in carcass fat colour since these pigments generate yellow (lutein), orange (b-carotene) and red colours. In sheep and goats lutein is the only carotenoid stored in the adipose tissue (Prache, Priolo, & Grolier, 2003; Yang, Larsen, & Tume, 1992), and its concentration in fat is usually very low in most breeds (Hill, 1962). The concentration of carotenoid pigments is high in fresh pastures, such as alfalfa or grass, and low in grains, which means that these compounds can be used as biomarkers or tracers to develop techniques for the authentication of products from grazing lambs. Prache and Theriez (1999) proposed an index based on the reflectance spectrum of adipose tissue to trace grass-feeding, but results were certain only for 81%. Ripoll, Joy, Mun˜oz, Albertı´, and Delfa (2006) added to that index the trichromatic coordinates of the CIELab space to obtain 100% discrimination between forage- and concentrate-fed lambs. These same authors concluded that the reflectance spectrum of adipose tissue as well as the trichromatric coordinates of the CIELab are fast, non-destructive, on-line and readily available methods as opposed to other tracer techniques, such as fatty acid composition or vitamin E. The aim of this study was to assess the influence of the lamb feeding system on muscle and fat colour, and to ascertain the capability of reflectance spectrophotometry to discriminate between carcasses from forage- and concentrate-fed lambs. 2. Materials and methods 2.1. Animal management and diets This experiment was conducted at the experimental facilities of a Research Centre in Zaragoza (Spain) and involved 95 single, spring-born, male Rasa Aragonesa
lambs. The experiment was repeated in two consecutive years (50 animals in the 1st year and 45 in the 2nd year). Lambs and dams were randomly allocated to four experimental lots according to their future feeding system: 1. Grazing (Gr): Ewes and lambs were continuously stocked on alfalfa pasture. No concentrate was available to dams or lambs. Lambs suckled their mothers and grazed until slaughter (n1st year = 13; n2nd year = 11). 2. Grazing with supplement for lambs (Gr+S): Management was the same as for Gr, and additionally the lambs received concentrates ad libitum in lamb creep feeders (n1st year = 12; n2nd year = 11). 3. Rationed grazing (Rat-Gr): This treatment is the most usual livestock system in the area. Ewes grazed on alfalfa pasture for seven hours a day without their lambs and thereafter remained indoors, receiving a mixed ration. Lambs were kept permanently indoors and were fed with ewe milk and concentrate ad libitum until weaning. From this time up to slaughter lambs had free access to concentrate and barley straw. After weaning, ewes were removed from the trial (n1st year = 12; n2nd year = 12). 4. Indoors (Ind): Ewes and lambs were kept permanently indoors with ad libitum access to a total mixed ration and lambs fed with ewe milk and concentrate ad libitum until weaning. Thereafter, lambs had access to concentrate only (n1st year = 13; n2nd year=11). Composition of feeds is presented in Table 1. A meadow of Alfalfa cv. Arago´n sown at a rate of 25 kg per hectare in spring of 2003 was used to graze ewes and lambs of Gr and Gr+S treatments. The alfalfa pasture was divided into five paddocks of 843 m2 each, and grass-fed animals rotationally grazed on one paddock each week. The stocking rate was 17 ewes (plus lambs) per hectare per year. The alfalfa offered was always green vegetative and had an averages of 234 g CP/kg DM, 338 g NDF/kg DM and 2.61 Mcal/kg DM. Lambs and ewes were supplied with fresh water and mineral-vitamin ad libitum. The lambs from Ind and RatGr treatments were weaned at 45 days old, whereas lambs from Gr+S and Gr remained with their dams in meadows until slaughter. 2.2. Slaughter and sampling procedures Ewe and lamb live-weight (LW) was recorded at weekly intervals during the experimental period. When lambs reached 22–24 kg LW they were slaughtered according to specifications of Ternasco de Arago´n protected geographical indication (Regulation (EC) No. 1107/96) that stipulate lambs of 22–24 kg LW and less than 90 days old. Lambs were slaughtered using standard commercial procedures and carcasses were hung by the Achilles tendon and were chilled 24 h at 4 °C in total darkness to preserve carotenoid pigments. A visual appraisal (VA) of the M. rectus abdominis colour was made according to the Colomer-Rocher scale
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241
Table 1 Feedstuff composition, kg/100 kg Lamb concentrate
Ewes mixed ration
Corn grain Barley grain Soybean meal, 44% Wheat grain Soya oil Vegetal powdered serum Vitamin and mineral supplement Calcium carbonate Sodium chloride Ammonium chloride
20 40.3 21 10 1.2 2.5 1.6 2.4 0.5 0.5
Crude protein (g/kg DM) NDF (g/kg DM) Metabolic energy (MJ/kg DM)
185 190 13.2
(Colomer-Rocher, Delfa, & Sierra, 1988) for light carcasses (<13 kg). This scale is divided into pink, pale red and red, expanded to nine points. M. longissimus thoracis was removed and ultimate pH was measured at the 4th vertebral region with pH-meter equipped with a Crison 507 penetrating electrode (Crison Instruments S.A., Barcelona, Spain). 2.3. Instrumental colour Fat and muscle colour were measured at 24 h at 4 °C after slaughter using a Minolta CM-2006 d spectrophotometer (Konica Minolta Holdings, Inc, Osaka, Japan) in the CIELAB space (CIE, 1986) with a measured area diameter of 8 mm, specular component included and 0% UV, standard illuminant D65 which simulates daylight (colour temperature 6504 K), observer angle 10° and zero and white calibration. The lightness (L*), redness (a*) and yellowness (b*) were recorded, and hue angle (H*) and chroma (C*) indices were calculated as H*=tan1(b*/a*)*57.29, expressed in degrees and C*=(a*2 + b*2)0.5. Chroma is related to the quantity of pigments and high values represent a more vivid colour and denote lack of greyness (Miltenburg, Wensing, Smulders, & Breukink, 1992). Hue is the attribute of a colour perception denoted by blue, green, yellow, red, purple, etc. (Wyszecki & Styles, 1982), and it is related with the state of pigments (Renerre, 1982). Caudal subcutaneous fat from the tail root (Diaz et al., 2002) and kidney fat colour values were recorded from three locations randomly selected but avoiding blood spots, discolorations and less covered areas. Besides trichromatic coordinates, the proportion of reflected light each 10 nm between 450 and 510 nm was collected and the absolute value of the integral of the translated spectrum (SUM) was calculated according to Priolo, Prache, Micol, and Agabriel (2002b). The reflectance spectrum was translated to make reflectance value at 510 nm equal to zero (TR). On the translated spectrum, the integral value was calculated as follows: SUM ¼ ðTR450 =2 þ TR460 þ TR470 þ TR480 þ TR490 þ TR500 þ TR510 =2Þ 10
Cereal straw Gluten feed Palmkernel Barley Soybean hulls Citrus pulp Cotton seeds Calcium carbonate Sodium chloride Fatty acids salt Urea
Barley straw 40 22.8 10.8 8.1 6 6 3.4 1 0.6 0.6 0.7 120 253 12.2
49 835 4.5
where TRi was the reflectance value at i nm. An extensive explanation of the baselines of the method is exposed in Prache and Theriez (1999). Rectus abdominis muscle colour was measured at two locations on the internal face of each piece randomly selected to obtain a mean value representative of the surface colour, after having removed the covering fascia (Eikelenboom, Hoving-Bolink, & Hulsegge, 1992; Klont et al., 2000). 2.4. Statistical analysis Statistical analyses were performed with SAS v.9.1. A two-way ANOVA (4 feeding systems 2 fat locations) was used for fat colour variables and SUM. When non-significant interactions (p < 0.05) were found, models were reduced to main effects only. A Bonferroni test was used to compare means, with a significance of p < 0.05. Feeding system and fat location were included as fixed effects and the effect of year as blocking factor since there were no significant interactions with fixed effects. Pearson’s r was used to correlate M. rectus abdominis visual appraisal with instrumental colour variables. Because the normality assumption was rejected, a base 10 logarithmic transformation was applied to the absolute value of the integral of the translated spectrum (SUM) before the analysis of variance. Means and standard errors shown are not transformed. A forward stepwise discriminant analysis was carried out for subcutaneous caudal and kidney fat, with L*, a*, b*, C*, H* and SUM as the variables evaluated. Selected variables were included in a binary logistic regression to calculate the probability of a carcass does not belong to a Gr or Gr+S group (PNA). 3. Results and discussion Age, slaughter live-weight and ADG from birth to slaughter were not affected by feeding systems (p > 0.05), with a general mean (mean ± s.e.) of 70 ± 0.9 d, 23.14 ± 0.09 kg and 285 ± 3.8 g/d, respectively. Cold car-
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G. Ripoll et al. / Meat Science 80 (2008) 239–248
cass weight was 11.3 ± 0.08 kg without there being differences among treatments (p > 0.05). 3.1. M. rectus abdominis colour and ultimate pH Mean pH values are shown in Table 2. There were no significant differences between feeding systems, ranging from 5.56 to 5.59, which is the normal pH in light lamb meat and did not reveal any differences among treatments. The lack of effect of the treatment on pH values may be due to the fact that lambs were weighed weekly and the slaughtering procedure was carried out on the property thus avoiding stress. Grazing animals are not used to being managed frequently and human presence prior to slaughter can cause stress which leads to lower glycogen reserves, and usually to higher values of the ultimate pH (Bowling, Smith, Carpenter, Dutson, & Oliver, 1977; Coulon & Priolo, 2002; Priolo, Micol, & Agabriel, 2001; Vestergaard, Oksbjerg, & Henckel, 2000). The ultimate pH of the light lamb meat in the present study was in agreement with results obtained by Diaz et al. (2002) and Ripoll et al. (2005) but it was slightly lower than the results of Priolo et al. ˚ dnøy et al. (2005). However in both studies (2002b) and A the slaughter weight of lambs was greater than that of the present study. Table 2 shows the instrumental colour and visual appraisal of M. rectus abdominis. Differences were observed between grazing lamb groups (Gr and Gr+S) and indoor lamb groups (Ind and Rat-Gr) in redness (a*) but not in L*, b*, hue and chroma. Diaz et al. (2002) did not find any significant differences between Talaverana lambs raised on pasture or stall-fed in L*, a*, b*, C* or hue of rectus abdominis, although in both treatments all animals had free access to concentrate from birth to weaning. Treatment affected the visual appraisal scores, although only Gr and Ind showed significant differences between each other (p < 0.05); the rest of treatments were similar (p > 0.05). This result is in accordance with the differences (p < 0.001) observed in
Table 2 Instrumental colour and visual appraisal of M. rectus abdominis and M. longissimus thoracis ultimate pH
pHu L* a* b* Hue Chroma Visual appraisal
Gr1
Gr+S
Ind
Rat-Gr
s.e.
Sig.
5.57 47.99 8.93a 9.51 45.96 13.47 5.79a
5.57 49.15 9.40a 10.48 46.07 14.31 5.30ab
5.59 49.28 8.04b 10.59 51.81 13.46 4.83b
5.56 49.95 7.29b 9.31 50.23 11.98 4.92ab
0.078 0.577 0.313 0.721 2.170 0.650 0.226
ns ns *** ns ns ns *
Different superscript (a,b) indicate significant difference (p < 0.05) among feeding systems. ns = P P 0.05; *=P < 0.05; **=P < 0.01; ***=P < 0.001. 1 Gr, grazing lambs on alfalfa pasture; Gr+S, grazing lambs on alfalfa pasture supplemented with concentrate; Ind, grazing dams and lambs fed with milk and concentrate; Rat-Gr, dams permanently indoors and lambs fed with milk and concentrate.
instrumental redness values (Table 2). Ind treatment showed the palest colour of muscle followed by RatGr, Gr+S and Gr, with values of 4.83, 4.92, 5.30 and 5.79, respectively, and all treatments were classified as pale red colour. Beriain et al. (2000) and Horcada, Beriain, Purroy, Lizaso, and Chasco (1998) concluded that concentrate-fed Rasa Aragonesa lambs, slaughtered at the same live-weight, were classified as pale red colour as is the case with the present results. In grazing systems, the effect of physical activity is often confused with the effect of feeding level and/or feed ration (Vestergaard et al., 2000). The muscle of lambs raised on pasture is darker in relation to stall-fed lambs due to greater concentration of haem pigments in muscles as a result of exercise (Renerre, 1986). However, in light lamb carcasses, Colomer-Rocher et al. (1988) reported that M. rectus abdominis colour was influenced by diet and age, but not by physical activity. Hopkins, Beattie, and Pirlot (1998) and Young, Daly, Graafhuis, and Moorhead (1997) concluded that there was no consistent diet effect on muscle colour. The differences in muscle colour among treatments observed in the present study were not due to the final muscle pH (Hopkins et al., 1998), and may be due to the diet, according to Colomer-Rocher et al. (1988). Muscle colour in light lamb carcasses may be influenced by different factors to those reported by Hopkins et al. (1998) and Young et al. (1997) in heavy lamb carcasses. Low but highly significant correlations (p < 0.01) between M. rectus abdominis visual appraisal and instrumental colour variables were found (rva-L* = .42, rva-hue* = .42, rva-b* = .32), which are in agreement with Klont et al. (1999) for veal colour. There was no correlation between visual appraisal and redness values, in spite of the significant differences of a* observed among treatments (p < 0.05). This controversial result could be explained because evaluators are not able to appreciate individual L*, a*, b* coordinates, but are able to understand real colour (hue) and lightness (L*). It is advisable to define colour in terms of lightness, chroma and hue (Wyszecki & Styles, 1982) rather than L*, a* and b*. In fact, Albertı´ et al. (2005) advise that the separate use of a* or b* is a simplification of reality and can lead to errors in interpretation. Rigg (1987) also recommended C* values in fat instead b* because they represent adipose tissue colour more accurately, as it is perceived visually by consumers or meat graders (Dunne, O’Mara, Monahan, & Moloney, 2006). 3.2. Fat colour Table 3 shows the effects of feeding management, fat location on the carcass, and its interaction in fat colour. No interaction was observed between feeding system and fat location in L*, a* and H*. These variables are significantly affected by the location (p < 0.001), while the feeding system had an effect on all variables (p < 0.001), except redness (p > 0.05).
G. Ripoll et al. / Meat Science 80 (2008) 239–248
243
Table 3 Effects of feeding system and fat location on lamb fat colour (F values) and significance L*
a* ***
System Location System Location
15.50 18.84*** ns
0.67ns 19.43*** ns
b*
C* ***
6.64 3.39ns 3.81*
H* **
5.44 1.34ns 3.86*
SUM *
3.16 35.09*** ns
70,55*** 18,92*** ns
a
a
Gr
ns = P P 0.05. * =P < 0.05. ** =P < 0.01. *** =P < 0.001.
When the kidney and subcutaneous caudal fat depots were compared, it was observed that kidney fat had greater values of L* and a*, and lower hue values in the four feeding systems studied (Table 4). However, b* and C* values varied according to fat depots in lambs in the concentrate-fed groups (Ind and Rat-Gr; Fig. 1). Kidney fat had lower b* and C* than those observed in grazing treatment groups (Gr and Gr+S). In contrast, caudal fat did not show any differences between treatments for the colour attributes. According to Priolo et al. (2002b), when carotenoid concentrations are high, as occurs in grazing lambs, the yellowness and chroma values are similar in all fat depots. However, when they are low, as in indoor lambs, they are accumulated in a greater amount in subcutaneous caudal fat (Priolo et al., 2002b). Higher values of b* were observed in grass- and stall-fed lambs slaughtered at 35 kg in subcutaneous and perirenal fat (Priolo et al., 2002b; Priolo et al., 2002a). Carotenoid content of herbage (Knight, Death, Muir, Ridland, & Wyeth, 1996; McDonald, Edwards, Greeenhalgh, & Morgan, 1995), the grass intake (Priolo et al., 2002b), breed (Baker, Steine, Vabeno, & Breines, 1985) and weight at slaughter might influence b* and C* values. Fig. 2 shows the individual redness and yellowness values of each treatment. The averages of caudal fat colour according to feeding systems were placed more closely among them than those observed in kidney fat. This latter depot presented high chroma values (far from the coordinate origin) in Gr and Gr+S treatments. Ind and Rat-Gr had lower hue angles (near to x-axis) with a colour closer to red. Furthermore, in both fat depots, individual points
14 13
n.s.
Gr+S
12
b
b
Ind Rat-Gr
b* 11
10 9 8 Caudal 14
Kidney a
a
n.s.
13 b
12
b
C* 11 10 9 8 Caudal
Kidney
Fig. 1. Yellowness (b*) and Chroma (C*) means and standard error (error bars) of kidney and caudal subcutaneous fat of four feeding systems: Grazing lambs on alfalfa pasture (Gr), grazing lambs on alfalfa pasture supplemented with concentrate (Gr+S), grazing dams and lambs fed with milk and concentrate (Ind) and dams permanently indoors and lambs fed with milk and concentrate (Rat-Gr).
were mixed, not allowing easy interpretation or discrimination between feeding systems or between grazing and nongrazing systems. Hence, colour coordinates (b* and a*, and
Table 4 Subcutaneous caudal and kidney fat lightness (L*), redness (a*) and Hue (H*) (mean ± s.e.) GrB *
L
a* Hue
A
SCF KF SCFA KF SCFA KF
Gr+S ay
73.6 ± 0.55 74.6ax ± 0.69 1.9by ± 0.20 3.2x ± 0.25 81.5ax ± 0.89 76.4y ± 0.96
ay
74.2 ± 0.62 75.6ax ± 0.67 2.3aby ± 0.24 3.3x ± 0.28 79.9abx ± 0.90 76.2y ± 0.80
Ind
Rat-Gr by
69.4 ± 0.98 72.2bx ± 0.57 2.4aby ± 0.27 3.1x ± 0.24 78.9abx ± 1.00 74.2y ± 0.99
70.7by ± 0.63 73.6bx ± 0.45 2.7by ± 0.27 2.9x ± 0.25 77.7bx ± 1.15 75.1y ± 1.01
Different superscript (a,b) indicate significant differences (P < 0.05) among feeding systems. Different superscript (x,y) indicate significant differences (P < 0.05) between fat locations. A SCF = Subcutaneous caudal fat; KF = kidney fat. B Gr, grazing lambs on alfalfa pasture; Gr+S, grazing lambs on alfalfa pasture supplemented with concentrate; Ind, grazing dams and lambs fed with milk and concentrate; Rat-Gr, dams permanently indoors and lambs fed with milk and concentrate.
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18
Yellowness (b*)
16
14
Gr+S
12
Gr
Ind
Rat-Gr
10
8
6
0
1
2
3
4
5
6
Redness (a*) 18
Yellowness (b*)
16
14
Gr+S Gr
12
Ind
10
Gr
Rat-Gr
Gr+S Ind
8
Rat-Gr Mean value
6
0
1
2
3
4
5
6
Redness (a*) *
*
Fig. 2. Relation between redness (a ) and yellowness (b ) of individual values of subcutaneous caudal fat (above) and kidney fat (below) of four feeding systems: Grazing lambs on alfalfa pasture (Gr), grazing lambs on alfalfa pasture supplemented with concentrate (Gr+S), grazing dams and lambs fed with milk and concentrate (Ind) and dams permanently indoors and lambs fed with milk and concentrate (Rat-Gr).
indirectly C* and H*) of both fat depots, are insufficient to discriminate between carcasses, probably due to the influence of other factors in fat colour, apart from the concentration of carotenoids. 3.3. Absolute value of the integral of the translated spectrum Values of SUM (Fig. 3) were greater (p < 0.001) in Gr and GR+S in both fat depots, the difference being more than twofold among grazing- and indoor- lambs. The mag-
nitude and direction of these differences is in agreement with those reported by Priolo et al. (2002b), who found in subcutaneous caudal and kidney fat, greater values for grass-fed lambs with values within a range of 400–300 units, while the stall-fed lambs had values lower than 200 units. The lower values observed in the present study may be due to the lower slaughter weight of lambs in relation to that used in the study cited above, as well as to different food sources. The present values observed were 200– 250 for grass-fed and 75–125 for concentrate-fed lambs, in
G. Ripoll et al. / Meat Science 80 (2008) 239–248
a
250
Gr+S
a, 1 a
200
Rat-Gr
SUM
175 150
b
125 100
0
Ind
b
b
-2 % reflectance
225
2
Gr
a
245
b
-4 -6 -8 -10 -12
75
-14
50
440
Caudal
450
460
Kidney
470
480
490
500
510
520
500
510
520
Wavelength (nm)
Fig. 3. Absolute value of the integral of the translated spectrum (SUM) of subcutaneous caudal and kidney fat at 24 h of slaughter.
2
keeping with Prache et al. (2005), who defined a limit of 152 units to separate grass-fed from stall-fed lambs. Kidney fat had greater SUM values than caudal fat (Fig. 3) in accordance with Atti, Ben Salem, and Priolo (2003). These authors reported that subcutaneous fat is a late maturing fat depot and pigments have still not been deposited in light lambs. Priolo et al. (2002b) also reported that the difference between treatments was higher for perirenal than for subcutaneous caudal fat, validating that in light lambs pigments are accumulated first in the kidney fat depot. Furthermore, lutein absorbs blue light and therefore appears yellow at low concentrations and orange–red at high concentrations, which agrees with the greater values of a* in kidney fat explained above (Table 4). Carotenoids absorb light between 450 and 510 nm, and a greater concentration implies a lower translated reflectance. The translated spectrum of the subcutaneous caudal and kidney fat, between 450 and 510 nm, was always negative and below the grazing group (Gr and Gr+S) for any wavelength, except at 510 nm (Fig. 4). Differences between feeding systems were similar in both fat depots studied, whereas Priolo et al. (2002b) reported a greater difference in perirenal adipose tissue compared to subcutaneous caudal fat. Differences in SUM, C* and b* between kidney and subcutaneous, and the different magnitude and direction of differences of SUM and b* within a fat location could result from other chemical and structural components of the adipose tissue contributing to perception of colour (Dunne, O’Mara, Monahan, & Moloney, 2006). Irie (2001) found that absorbance of deoxy- and met-haemoglobin from the peripheral adipose tissue affected spectrophotometer reflectance, while b* would be less affected. Moreover, differences in the concentrations of carotenoids could be related to adipose cellularity (Strachan, Yang, & Dillon, 1993), such as adipocyte volume differences in kidney and subcutaneous fat depots (Nozie`re et al., 2006). Distribution of feeding systems into classes of SUM for each fat depot is shown in Fig. 5. Ind and Rat-Gr overlapped within the range of 0–150 units of SUM in subcuta-
% reflectance
0 -2 -4 -6 -8 -10 -12 -14 440
450
460
470
480
490
Wavelength (nm) Gr
Gr+S
Ind
Rat-Gr
Fig. 4. Averaged translated reflectance spectrum of subcutaneous caudal fat (a) and kidney fat (b).
neous caudal fat. Two carcasses belonging to the Gr and Gr+S feeding systems had values above 350 and the others were symmetrically distributed around the <200 class, from 50 to 300 units. Gr and Gr+S carcasses overlapped 50% with Ind and Rat-Gr in the <150 class and also were mixed in the <100 class. Ind and Rat-Gr carcasses were placed in the fourth first classes while Gr and Gr+S carcasses were spread over seven classes, from <150 to <450. There was just one important overlapping of the four treatments in the <200 class of the kidney fat. 3.4. Discriminant analysis Discriminant analysis selected C* and SUM for subcutaneous caudal fat, and b* and SUM for kidney fat as the variables which explained the greatest amount of variation correctly classifying 43.15% and 50.53% of carcasses, respectively. The inclusion of C* instead b* in the subcutaneous caudal fat is in accordance with Fig. 2, in which grazing and non-grazing treatments are poorly discriminated by b* but are discriminated by a*. Consequently, both b* and a* are necessary, and they were included as C*, which is related to the quantity of pigments (Renerre, 1982) of any colour. The analysis was able to discriminate between grass-fed lambs (Gr and Gr+S) and indoor-fed
246
a
G. Ripoll et al. / Meat Science 80 (2008) 239–248 Table 5 Discriminant classification, expressed on percent of carcasses rightly classified, for caudal subcutaneous fat (SCF) and kidney fat (KF)
40
Number of lambs
35 30
Gr
Gr+S
Ind
Rat-Gr
Origin
Predicteda Gr
25 20 15 10 5
Gr+S
Ind
Rat-Gr
Fat depot
SCF
KF
SCF
KF
SCF
KF
SCF
KF
Grb Gr+S Ind Rat-Gr
37.5 43.5 0.0 0.0
45.8 43.5 0.0 0.0
58.3 43.5 12.5 8.3
45.8 43.5 0.0 4.2
4.2 8.7 41.7 41.7
0.0 0.0 50.0 33.3
0.0 4.3 45.8 50.5
8.4 13.0 50.0 62.5
a
0 <50 <100 <150 <200 <250 <300 <350 <400 <450 500 SUM
b
30
Number of lambs
25
Gr
Gr+S
Ind
Analysis for subcutaneous caudal fat included C* and SUM; analysis for kidney fat included b* and SUM. b Gr, grazing lambs on alfalfa pasture; Gr+S, grazing lambs on alfalfa pasture supplemented with concentrate; Ind, grazing dams and lambs fed with milk and concentrate; Rat-Gr, dams permanently indoors and lambs fed with milk and concentrate.
Rat-Gr
Table 6 Estimate and standard error of logistic regression for caudal subcutaneous fat and kidney fat
20 15
Caudal subcutaneous fat 10 5
Intercept b* SUM
0
Kidney fat 2
Estimate
s.e.
P>v
Estimate
s.e.
P > v2
1.953 1.320 0.115
2.583 .400 .032
** ***
6.475 1.037 0.111
4.020 .523 .030
* ***
<50 <100 <150 <200 <250 <300 <350 <400 <450 500 SUM
Fig. 5. Distribution of lambs in the classes of absolute value of the integral of the translated reflectance spectrum (SUM) of subcutaneous caudal fat (a) and kidney fat (b).
ones (Ind and Rat-Gr) (Table 5). However, it is not clear when the classification has to be carried out within one of the two main groups of treatments: grazing (Gr vs. Gr+S) and indoor (Ind vs. Rat-Gr). For kidney fat, 13.0% of Gr+S and 8.3% of Gr carcasses were classified into Rat-Gr. For caudal fat variables, 8.7% and 4.3% of Gr+S were classified into Ind and Rat-Gr, respectively, while 4.2% of Gr were classified into Ind. Inclusion of concentrate in grazing lambs diet induced an increase of the cases erroneously classified. Milk from grazing ewes could have an influence on pigment depots in Rat-Gr lambs (Nozie`re et al., 2006). A logistic regression (Table 6) was applied to determine the probability of a carcass belonging to a non-alfalfa-fed (PNA) treatment. This system classified carcasses into grazing lambs (Gr and GR+S) or concentrate-fed lambs (Ind and Rat-Gr). When only SUM was entered into the regression, 93.9% and 98.4% of carcasses were correctly classified for subcutaneous caudal and kidney fat, respectively. Prache and Theriez (1999) discriminated 81% of the carcasses using subcutaneous caudal fat SUM. Discrimination using kidney fat SUM value was correct only in 78.1% cases in the Priolo et al. (2002b) study, and they pointed to the shape of kidney fat as the main factor hindering correct
measurements. This difficulty was taken account in our study and the correct classifications were 20 percent higher. When SUM and b* were included, the proportions of correct classifications increased to 97.9% and 99.1% for subcutaneous caudal and kidney fat, respectively, and the inclusion of C* in the regression did not improve results. Although logistic binary regression using kidney fat variables classified slightly better than when using subcutaneous fat variables, when lambs are slaughtered, kidney fat becomes bloodied and is less easy to measure on-line than subcutaneous caudal fat. Furthermore, the measuring surface of the spectrophotometer is not in perfect contact with the hard kidney fat, thus affecting measurements. Consequently, to be practical and for simplicity it is proposed to use the b* and SUM variable of subcutaneous caudal fat 1 according to the expression: PNA ¼ 1þeð1:953þ1:320b 0:115SumÞ . This expression could be easily implemented in a slaughterhouse to quickly trace the feeding system of lamb production. 4. Conclusions Alfalfa grazing with or without supplement allows similar lamb performance to that of concentrate-fed lambs. M. rectus abdominis, kidney fat and subcutaneous caudal fat colour were affected by the main feeding groups (alfalfa vs. concentrate-fed), but there was no effect within those (Grazing vs. grazing plus concentrate; indoors vs. rationed grazing). M. rectus abdominis of grazing lambs had higher values of redness and visual appraisal classified it as slightly
G. Ripoll et al. / Meat Science 80 (2008) 239–248
darker than muscle of indoor lambs. Fat colour was influenced in a different way by the effect of feeding system and location of fat depot. Kidney fat of grazing lambs showed the highest values of yellowness and chroma in relation to that of indoor-fed lambs. Subcutaneous caudal fat in all feeding systems had a narrower range of yellowness and chroma values than kidney fat. The absolute value of the integral of the translated spectrum was higher for grazing lambs in both fatty depots, and it was also higher in kidney fat because it is an early maturing tissue. Logistic regression with fat colour variables plus the absolute value of the integral of the translated spectrum is a suitable method to accurately discriminate between both feeding systems. Measurements in subcutaneous caudal fat are proposed for the practical on-line use of this technique. Acknowledgements The authors wish to thank the staff of CITA for their collaboration. Special thanks to Alessandro Priolo for his suggestions. This study was funded by the Ministry of Education and Science of Spain and European Union Regional Development funds (INIA RTA-03-031). The present study is dedicated to the memory of Rafael Delfa. References ˚ dnøy, T., Haug, A., Sørheim, O., Thomassen, M. S., Varszegi, Z., & Eik, A L. O. (2005). Grazing on mountain pastures – does it affect meat quality in lambs?. Livestock Production Science 94, 25–31. Albertı´, P., Panea, B., Ripoll, G., San˜udo, C., Olleta, J. L., Negueruela, I., et al. (2005). Medicio´n del color. In Monografı´as INIA: Ganadera n°1 (255 pp). MICYT-INIA Madrid, Espan˜a. Alvarez-Rodriguez, J., Sanz, A., Delfa, R., Revilla, R., & Joy, M. (2007). Performance and grazing behaviour of Churra Tensina sheep stocked under different management systems during lactation on Spanish mountain pastures. Livestock Science, 107, 152–161. Atti, N., Ben Salem, H., & Priolo, A. (2003). Effects of polyethylene glycol in concentrate or feed blocks on carcass composition and offal weight of Barbarine lambs fed Acacia cyanophylla Lindl foliage. Animal Research, 52, 363–375. Baker, R. L., Steine, A., Vabeno, A. W., & Breines, D. (1985). The inheritance and incidence of yellow fat in Norwegian sheep. Acta of Agricultural Scandinavian, 35, 389–397. Beriain, M. J., Horcada, A., Purroy, A., Lizaso, G., Chasco, J., & Mendizabal, J. A. (2000). Characteristics of Lacha and Rasa Aragonesa lambs slaughtered at three live weights. Journal of Animal Science, 78, 3070–3077. Bowling, R. A., Smith, G. C., Carpenter, Z. L., Dutson, T. R., & Oliver, W. M. (1977). Comparison of forage-finished and grain-finished beef carcasses. Journal of Animal Science, 45, 209–215. CIE. (1986). Commission Internationale de L’Eclairage. Colorimetry, 2nd ed. Viena. Colomer-Rocher, F., Delfa, R., & Sierra, I. (1988). Me´todo normalizado para el estudio de los caracteres cuantitativos y cualitativos de las canales ovinas producidas en el a´rea mediterra´nea, segu´n los sistemas de produccio´n. Programa AGRIMED-CIHEAM: ‘‘Les carcasses d’agneux et de chevreaux me´diterrane´ens”. 9–10 December. Zaragoza. Published in French: EEC (1988), Rapport EUR 11479 FR. Published in Spanish: Cuadernos INIA (1988) 17, 19–41.
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