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Fatty acid composition of goat diets vs intramuscular fat
Meat Science 54 (2000) 313±318
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Fatty acid composition of goat diets vs intramuscular fat K.S. Rhee a,*, D.F. Waldron b, Y.A. Ziprin a, K.C. Rhee c a
Meat Science Section, Department of Animal Science, Texas A & M University, College Station, TX 77843-2471, USA b Agricultural Research and Extension Center, Texas Agricultural Experiment Station, San Angelo, TX 76901, USA c Department of Soil and Crop Sciences, Texas A & M University, College Station, TX 77843, USA Received 2 April 1999; accepted 6 July 1999
Abstract Twenty Boer x Spanish goats, at the age range of 90±118 days, were assigned to two dietary treatments, with 10 animals fed a grain ration (G) and the other 10 grazed in rangeland. The grain ration contained sorghum grain (67.5%), cottonseed hulls, dehydrated alfalfa meal, cottonseed meal, soybean meal, molasses, and mineral and vitamin supplements. Animals were slaughtered at the age range of 206±234 days. Intramuscular fat (IF) and the diet specimens Ð representative samples of G and the parts of range plants (RPs) that goats were expected to have consumed Ð were analyzed for fatty acid composition. The percentage of 16:0 was higher in RPs than in G, but not dierent between IF from range goats and that from grain-fed goats. Total unsaturated fatty acid (UFA) percentage was higher in G than in RPs. The major UFAs were 18:2 and 18:3 in RPs, and 18:1 and 18:2 in G. In IF, 18:1 constituted more than two-thirds of UFAs, regardless of diet type. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Goat meat; Fatty acids
1. Introduction The fat type or fatty acid composition of meat is an important diet/health concern to consumers. It also is a primary factor that determines product shelf-life/storage stability and ¯avor (Rhee, 1992). The fatty acid composition of tissues of ruminants generally is less aected by dietary lipid composition than that of nonruminants (Rhee, 1992). The great disparity between dietary and tissue fat in ruminant arises primarily from hydrogenation of dietary lipids by rumen microbes (Byers & Schelling, 1993). The ruminal conversion (saturation) of dietary unsaturated fatty acids, however, is normally not complete (Byers & Schelling, 1993), and bovine studies (Chilliard, 1993; Marmer, Maxwell & Williams, 1984; Melton, 1983; Westerling & Hedrick, 1979) have shown that dietary fatty acid composition dierences can result in dierences in tissue fatty acid composition. This was true with goats as well (Rhee, Ziprin, Bishop & Waldron, 1997). Speci®cally, the lipid extracts from the lean meat of range goats (raised in * Corresponding author. Tel.: +1-409-845-3936; fax: +1-409-8459454. E-mail address: [email protected] (K.S. Rhee).
rangeland with multiple species of grasses and forbs without any supplement) were more saturated than the corresponding extracts from goats fed a grain-based diet. Accordingly, raw or cooked meat samples from range goats were less susceptible to lipid oxidation (as measured by 2-thiobarbituric acid-reactive substances) than those of grain-fed goats. There has been no research that evaluated the fatty acid composition of diets themselves, along with the fatty acid composition of goat tissues. Our objectives were to conduct such a study and to further understand the relationship between the fatty acid composition of diets and that of intramuscular fat. 2. Materials and methods 2.1. Goat meat samples Animal feeding was done in San Angelo, Texas. Twenty animals (castrated male goats) at the age range of 90±118 days (mean, 105 days) were assigned to two dietary treatments, with 10 animals grazed in rangeland and the other 10 placed on a grain ration. The breed of all sires was Boer-cross and all the dams of the kids
0309-1740/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(99)00094-7
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K.S. Rhee et al. / Meat Science 54 (2000) 313±318
were Spanish goats. The range kids were given access to rangeland/pasture populated with multiple species of native grasses, browses and forbs. The pasture was similar to that documented by Warren (1981). Table 1 shows the common and scienti®c names of the range plants that would have constituted the great majority of the range goat diet during the feeding treatment period (from 16 June 1997 to 9 October 1997). Based on the study by Warren (1981), where the diet composition of the Spanish goats grazing a rangeland similar to that of this study was estimated by microhistological analysis of fecal material, littleleaf sumac (browse) would have constituted more than 50% of the range goat diet (Table 1). For the grain diet treatment, a grain ration was given ad libitum for 116 days before slaughter. It contained sorghum grain (67.5%), cottonseed hulls (12%), dehydrated alfalfa meal (5%), cottonseed meal (4%), soybean meal (4%), molasses (4%), and mineral and vitamin supplements. All goats on the grain diet treatment were kept in a large pen (100100 ft) with shade available. Animals were slaughtered in San Angelo. At the time of slaughter, they were at the age range of 206±234 days (mean, 221 days). On the day of slaughter (10 October 1997) all kids were removed from their diet treatments and live weights were obtained between 10:00 and 10:30 am before the animals were transported for slaughter. Goats were slaughtered at a commercial facility 35 miles from the feeding facility. Transportation time was 45 min. Goats were slaughtered between 12:45 and 1:15 pm. Common commercial slaughter practices were used. Muscle (semimembranosus) samples were removed from carcasses at 60 h postmortem and frozen in Ziploc1 freezer bags. The plant samples were obtained in October, 1997 (toward the end of period when the goats were on the pasture) to be representative of the status of the plants close to the time of slaughter. The parts of each plant that Table 1 Description of dominant range plants and their contribution percentage to the diet of range goats Plant type and common name Grasses Sideoats grama Sand dropseed Common curlymesquite
Scienti®c name
Bouteloua curtipendula 12 Sporobolus cryptandrus (Torr.) Gray 7 Hilaria belangeri (Steud.) Nash 3
Browses Littleleaf sumac Rhus microphylla Engelm. Catclaw acacia Acacia greggii Gray Forb Globe mallow a
Estimated % in the diet of range goatsa
Sphaeralcea spp.
Estimation based on the study by Warren (1981).
60 6 4
goats were expected to have consumed were collected by cutting with a pair of scissors. Samples were placed in airtight plastic bags and frozen. The muscle samples (28 g/animal), range plant samples (250 g/species), and a representative sample (700 g) of the grain ration (sampling done after coarse-grinding of a large amount of the grain ration) were shipped frozen with dry ice from San Angelo to College Station. Upon receiving, the muscle samples were vacuum-packaged, whereas the diet samples were double-bagged in Ziploc1 freezer bags. All samples were kept at ÿ20 C until analyzed 2 months later. 2.2. Analytical methods Total fat was extracted by the procedure of Folch, Lees and Sloane-Stanley (1957). Before fat extraction, the plant samples were cut very ®nely with a pair of scissors (as they were too ®brous to be chopped in a food processor), soaked in distilled water (30 ml for 10 g sample) for 24 h at 4 C, and drained. The grain ration was ®nely chopped in a food processor and was also soaked in distilled water (30 ml for 10 g sample) and drained. The total fat extraction from each muscle sample utilized a 10-g portion of ®nely chopped tissue. Aliquots of lipid extracts were freed of solvent and transmethylated using tetramethylammonium hydroxide in methanol (Metcalfe & Wang, 1981). Fatty acid methyl esters were analyzed using a gas chromatograph (Varian 3400) ®tted with a fused silica capillary column, as described by Rhee, Ziprin, Ordonez and Bohac (1988). Results for each fatty acid were expressed as a percentage of the sum of all identi®ed fatty acids. Analysis of each diet specimen was replicated two times, from the initial fat extraction step to the ®nal gas chromatographic analysis of fatty acid methyl esters. The General Linear Model Procedure of the SAS (SAS, 1990) program was used for data analysis, with means separated by the Student±Newman±Keuls test. The data were analyzed as a completely randomized design, with 2 treatments (grain ration and grazing in rangeland) for goat muscle samples and 7 treatments (grain ration and the 6 range plants) for diet specimens. Signi®cance was de®ned at P40.05. 3. Results and discussion The live weight of animals (3 h prior to slaughter) and hot carcass weight were, on average, 35.11 and 18.55 kg (52.8% of the live weight), respectively, for the grain-fed goats and 26.26 and 12.18 kg (46.4%), respectively, for the range goats. Body wall thickness (average) measured 11 cm from midline, at the separation between the 12th and 13th ribs, was 1.63 cm for the grain-fed goats and 1.01 cm for the range goats.
K.S. Rhee et al. / Meat Science 54 (2000) 313±318
The range plant samples were much higher in the percentage of total saturated fatty acids when compared to the grain ration Ð 27±38% for the range plant samples vs 19% for the grain ration (Table 1). Conversely, the percentage of total unsaturated fatty acids was higher for the grain ration (81% vs 62±73%). In range plants, polyunsaturated fatty acids (18:2 and 18:3) made up the majority (71±87%) of total unsaturated fatty acids, while
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18:1 and 18:2 constituted 37 and 59%, respectively, of the total unsaturated fatty acids in the grain ration. When the range plants and the grain diet were compared for their dierences in 16:0 vs in 18:0 (the two primary fatty acids), the 18:0 dierences were much greater (on average, about 2 times higher in range plants) than the 16:0 dierences (1.4 times higher on average in range plants). However, the 18:1 percentage was 1.7±5.6 times higher in the grain
Table 2 Percentageb fatty acid compositions for range plants and grain rationa Fatty acids
Grain ration
Range plants Grasses
12:0 14:0 15:0 16:0 16:1 17:0 18:0 18:1 18:2 18:3 20:0 21:0 23:0 24:0 Saturated (S) Unsaturated (U) Monounsaturated (M) Polyunsaturated (P) U/S P/S M/S a
Browses
Forb
Sideoats grama
Sand dropseed
Common curlymesquite
Littleleaf sumac
Catclaw acacia
Globe mallow
0.04b (0.01)c 0.17d (0.02) 0.06a (0.01) 15.72d (1.77) 0.68a (0.01) 0.12c (0.01) 2.04d (0.22) 30.21a (0.78) 48.34a (0.56) 2.26d (0.04) 0.20c (0.01) 0.13d (0) 0b (0) 0.10b (0.04)
1.28a (0.27) 1.90b (0.20) 0.28a (0) 23.55a (0.47) 1.06a (0.35) 0.59b (0.02) 5.70b (1.33) 17.82b (4.96) 24.09c (0.33) 21.14c (6.19) 0.62a (0.05) 0.72b (0.07) 0.32a (0.05) 0.72ab (0.04)
1.08a (0.20) 1.84b (0.28) 0.20a (0.02) 22.58ab (0.57) 0.48a (0.49) 0.64b (0.04) 3.26cd (0.15) 9.29cd (0.91) 22.94cd (0.30) 36.00b (1.50) 0.43ab (0.04) 0.50c (0.02) 0.27a (0.01) 0.59ab (0.06)
1.12a (0.01) 2.46a (0.10) 0.36a (0) 22.69ab (0.11) 0.56a (0.59) 3.72a (0.22) 4.82bc (0.04) 14.51bc (0.08) 28.86b (0.71) 18.48c (0.54) 0.54ab (0.06) 0.86ab (0.15) 0.27a (0.04) 0.78ab (0.18)
0.10b (0.04) 1.84b (0.15) 0a (0) 20.18c (0.22) 0.27a (0) 0.66b (0.07) 3.27cd (0.22) 11.57cd (0.81) 10.26f (0.16) 48.82a (0.89) 0.32bc (0.14) 0.94a (0.04) 0.30a (0.09) 1.49a (0.10)
0.37b (0.31) 1.10c (0.19) 0.34a (0.24) 22.62ab (0.59) 0.54a (0.12) 0.77b (0.07) 7.22a (0.48) 7.68d (1.63) 12.88e (0.62) 44.19a (1.77) 0.54ab (0.02) 0.65bc (0.04) 0b (0) 1.13ab (0.78)
0.19b (0.03) 0.94c (0.02) 0a (0) 21.38b (0.80) 0.42a (0.01) 0.29c (0.01 2.31d (0.04) 5.35d (0.07) 21.68d (0.96) 45.61a (0) 0.36bc (0.02) 0.87ab (0.08) 0.22a (0.01) 0.38ab (0.01)
18.58f (0.45) 81.50a (0.16) 30.89a (0.76) 50.60bc (0.60) 4.39a (0) 2.73a (0) 1.66a (0)
35.68b (1.14) 64.10e (1.20) 18.88b (5.31) 45.22c (6.51) 1.80e (0.09) 1.27d (0.22) 0.53b (0.13)
31.38c (0.44) 68.62d (0.41) 9.68cd (1.39) 58.94b (1.80) 2.19d (0.04) 1.88bc (0.08) 0.31c (0.04)
37.60a (0.33) 62.40f (0.33) 15.06bc (0.50) 47.33c (0.17) 1.66e (0.02) 1.26d (0.01) 0.40bc (0.02)
29.08d (0.25) 70.91c (0.24) 11.84cd (0.81) 59.08b (1.05) 2.44c (0.03) 2.03b (0.05) 0.41bc (0.02)
34.72b (0.64 65.27e (0.64) 8.21cd (1.75) 57.06b (2.39) 1.88e (0.05) 1.64c (0.10) 0.24c (0.05)
26.94e (0.91) 73.06b (0.90) 5.77d (0.06) 67.29a (0.96) 2.71b (0.13) 2.50a (0.12) 0.21c (0)
Means within the same row followed by a common letter are not dierent (P>0.05). Each mean represents results of two separate analyses (from the initial fat extraction step to the ®nal analysis). b Percentage based on a total of identi®ed fatty acids listed. c Standard deviation.
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diet, depending on the plant species with which the grain diet was compared. Distinct dierences among the range plant types were found in 18:2 and 18:3. Grasses (sideoats grama, common curlymesquite and sand dropseed) and forb (globe mallow) were about 2 folds higher in the 18:2 percentage when compared to browses (littleleaf sumac and catclaw acacia). The percentage of 18:0, however, was higher in the browses and forb than in the grasses. Table 3 Percentageb fatty acid composition of goat muscle (semimembranosus) samplea Fatty acids
14:0 14:1 16:0 16:1 17:0 17:1 18:0 18:1 18:2 18:3 20:3 20:4 21:0 24:0 Saturated (S) Unsaturated (U) Monounsaturated (M) Polyunsaturated (P) U/S P/S M/S
Muscle samples from Range goats
Grain-fed goats
1.78a (0.69)c 0.30a (0.21) 20.51a (1.52) 1.62b (0.30) 1.29b (0.34) 0.94b (0.26) 16.27a (1.13) 42.43b (3.59) 7.74a (1.88) 1.16a (0.37) 0.21a (0.17) 3.43a (0.99) 1.17a (0.40) 1.17a (0.36)
1.78a (0.29) 0.43a (0.22) 20.99a (1.10) 2.71a (0.63) 1.75a (0.49) 2.32a (0.96) 10.24b (1.96) 51.00a (2.02) 5.74b (1.64) 0.18b (0.12) 0.08b (0.10) 2.27b (0.74) 0.15b (0.17) 0.38b (0.59)
42.19a (1.84) 57.82b (1.84) 45.29b (3.81) 12.54a (3.04) 1.37b (0.10) 0.30a (0.07) 1.07b (0.12)
35.28b (1.75) 64.72a (1.76) 56.46a (3.11) 8.27b (2.37) 1.84a (0.14) 0.23a (0.07) 1.61a (0.15)
a Means within the same row followed by a common letter are not dierent (P>0.05). Each mean represents results from 10 animals. b Percentage based on a total of identi®ed fatty acids listed. c Standard deviation.
Dierences in total fatty acid unsaturation between the intramuscular fat from range goats and that from grain-fed goats (Table 3) were not as large as the dierences observed between the range plants and the grain diet (Table 2). In intramuscular fat, whether from range goats or grain-fed goats, 18:1 constituted more than two-thirds (73% for range goats and 79% for grain-fed goats) of total unsaturated fatty acids. In comparison, 18:1 made up only 7±28% of the total unsaturated fatty acids in range plants and 37% in the grain ration. To further evaluate the relationship between dietary fatty acids and the fatty acids of intramuscular fat, data for range plants were averaged over all six plant species Ð taking into account each plant's estimated contribu-
Fig. 1. Relationships between the fatty acid pro®les of diets (range plants diet and grain diet) Ð with means for the range plants diet weighted for each plant's estimated contribution to the total diet of range goats Ð and the fatty acid pro®les of muscle tissue (intramuscular fat) from goats fed the dierent diets: common individual fatty acids.
K.S. Rhee et al. / Meat Science 54 (2000) 313±318
tion to the total diet of range goats (Table 1). Fig. 1 shows the resultant weighted means for the range diet in comparison to the means of the grain ration, along with comparisons of intramuscular fat from range goats vs the fat from grain-fed goats. Only 16:0, 18:0, 18:1, 18:2 and 18:3 (the most common fatty acids) were included for these comparisons. Apparently, the 16:0 percentage in intramuscular fat was not aected by feeding regimen. Although the dietary 16:0 percentage was higher in the range plant diet than in the grain diet, the 16:0 percentage in muscle tissue (intramuscular fat) was not signi®cantly dierent between range goats and grain-fed goats. A review by Chilliard (1993) has indicated that fatty acid synthesis in ruminants is more sensitive to inhibition by saturated fatty acids. This may partly explain why 16:0 in intramuscular fat was similar (P>0.05) between range goats and grain-fed goats (21% regardless of feeding regimen), while the dietary 16:0 percentage was higher in the range plants than in the grain ration (21% vs 16%). In other words, the de novo 16:0 synthesis could have been less in range goats than in grain-fed goats, because the range plants provided much more exogenous 16:0 (inhibitory to the de novo synthesis of 16:0) than the grain ration. Unlike 16:0, 18:0 may be produced by elongation of 16:0 and/or through ruminal hydrogenation of 18-carbon unsaturated fatty acids (Chang, Lunt & Smith, 1992; Ekeren, Smith, Lunt & Smith, 1992). For 18:0, 18:1 and 18:3, the directional (more or less) dierences between intramuscular fat from range goats and that from grain-fed goats were similar to those between the range plant diet and the grain diet; however, the magnitude of the dierences varied. Such was not the case for 18:2. It is possible that the relative eciency of ruminal hydrogenation of 18:2 may have been similar whether goats had the range plant regimen or the grain ration, but the intramuscular 18:2 produced as a result of ruminal hydrogenation of dietary 18:3 (42.80% in the range diet vs 2.26% in the grain diet) could have been greater in range goats due to the inordinately higher percentage of 18:3 in the range plants. As a result, the directional dierence in 18:2 may have shifted from `grain ration > range plants' to `range goats > grain-fed goats.' It is not certain whether there were digestibility dierences between these fatty acids in the goats on the two dietary treatments. Byers and Schelling (1993), in their review of ruminants in general, stated that ruminants usually digest unsaturated fatty acids to a lower degree when compared to nonruminants, whereas saturated fatty acids are digested more completely in the intestinal tracts of ruminants. There is little published information available on the eect of diet/feeding regimen on fatty acid composition of goat muscles/intramuscular fat. In our previous study (Rhee et al., 1997) on goat meat patties made with knife-separable lean composite (with some, though minimal, visible external fat), patties from grain-fed
317
animals within the same breed type were higher in the 18:1 percentage when compared to the respective patties from animals grazed in rangeland without grain supplementation, while the 18:0 percentage was higher in the latter. As for other ruminants, diet eects on fatty acid composition of beef have been extensively studied, as mentioned previously. For lambs, it has been mentioned that grazing may increase the 18:0 concentration in adipose tissue, while grain concentrates may increase 18:1 and 18:2 (Enser, 1995). Regarding the eects of grain diet vs forage diet on bovine tissue fatty acid composition, some dierences have been found between published studies. Westerling and Hedrick (1979) reported that the 16:0 percentage in intramuscular fat
Fig. 2. Saturated, monounsaturated and polyunsaturated fatty acid percentages for the range plants diet (with means weighted for each plant's estimated contribution to the total diet) vs the grain diet and for muscle tissue from range goats vs that from grain-fed goats: calculated from Fig. 1 data.
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was similar between animals fed an 82.4% corn diet and those grazed on predominantly fescue grass, whereas the 18:1 percentage was greater in grain-fed animals and 18:0, 18:2 and 18:3 percentages were higher in foragefed animals. In the study by Marmer et al. (1984), however, the 18:2 percentage of intramuscular fat was higher in animals fed a 79% corn diet than in animals fed a forage diet (primarily winter wheat). The dierences between these studies may be related to fatty acid composition dierences that could have been present between the two grain diets and/or the two forage diets (fatty acid pro®les of diet samples were not mentioned in these studies). In the present study (of goats), the 18:2 percentage was much higher for the grain ration while the 18:3 percentage was much higher for the range plant diet (Fig. 1). However, the combined percentage of the two fatty acids was not markedly dierent between the range and grain diets (57% vs 51%) (Fig. 2). For intramuscular fat vs diets, the combined percentage was much lower for intramuscular fat (<10% in range goats as well as grain-fed goats) than for the diets (>50% in both diets) (Fig. 2), because much of the dietary 18:2 and 18:3 would have been hydrogenated in the rumen to 18:1 and 18:0. In conclusion, this study has determined that intramuscular fat from Boer x Spanish goats grazed on pasture without any grain supplementation is more saturated than intramuscular fat from goats fed a grain diet. This trend with intramuscular fat seemed to generally re¯ect the fatty acid saturation or unsaturation dierences between the two diets. Further studies are needed on the relationship between the fatty acid pro®les of diet specimens (dierent grain diets and various range plants) and those of tissue samples from goats that have undergone the dietary treatments. In addition, what eect the time-on-feed (grain diet) may have on the composition of goat meat fatty acids needs to be investigated in future studies.
References Byers, F. M., & Schelling, G. T. (1993). Lipid in ruminant nutrition. In: D. C. Church, Ruminant animal: digestive physiology and nutrition (pp. 298±312). Prospect Heights, IL: Waveland Press Inc. Chang, J. H. P., Lunt, D. K., & Smith, S. B. (1992). Fatty acid composition and fatty acid elongase and stearoyl-CoA desaturase activities in tissues of steers fed high oleate sun¯ower seed. Journal of Nutrition, 122, 2074±2080. Chilliard, Y. (1993). Dietary fat and adipose tissue metabolism in ruminants, pigs, and rodents: a review. Journal of Dairy Science, 76, 3897±3931. Ekeren, P. A., Smith, D. R., Lunt, D. K., & Smith, S. B. (1992). Ruminal biohydrogenation of fatty acids from high-oleate sun¯ower seeds. Journal of Animal Science, 70, 2574±2580. Enser, M. (1995). Meat lipids. In R. J. Hamilton, Developments in oils and fats. Bishopbriggs, Glasgow: Blackie Academic and Professional. Folch, J., Lees, M., & Sloane-Stanley, G. H. (1957). A simple method for the isolation and puri®cation of total lipid from animal tissues. Journal of Biological Chemistry, 226, 497±509. Marmer, W. N., Maxwell, R. J., & Williams, J. E. (1984). Eect of dietary regimen and tissue site on bovine fatty acid pro®les. Journal of Animal Science, 59, 109±121. Melton, S. L. (1983). Eect of forage feeding on beef ¯avor. Food Technology, 37(5), 239±248. Metcalfe, L. D., & Wang, C. N. (1981). Rapid preparation of fatty acid methylesters using organic base-catalyzed transesteri®cation. Journal of Chromatographic Science, 19, 530±535. Rhee, K. S. (1992). Fatty acids in meats and meat products. In C. K. Chow, Fatty acids in foods and their health implications (pp. 65±93). New York: Marcel Dekker Inc. Rhee, K. S., Ziprin, Y. A., Bishop, C. E., & Waldron, D. F. (1997). Composition and stability of goat meat patties as aected by breed type and feeding regimen. Journal of Food Science, 62, 949±953, 962. Rhee, K. S., Ziprin, Y. A., Ordonez, G., & Bohac, C. E. (1988). Fatty acid pro®les of the total lipids and lipid oxidation in pork muscles as aected by canola oil in the animal diet and muscle location. Meat Science, 23, 201±210. SAS (1990). SAS user's guide: statistics. SAS Institute Inc., Cary, NC. Warren, L. E. (1981). Diets of various breeds of sheep and goats grazing in common on selected plant communities in west Texas. M.S. thesis. Angelo State University, San Angelo, Texas. Westerling, D. B., & Hedrick, H. B. (1979). Fatty acid composition of bovine lipids as in¯uenced by diet, sex and anatomical location and relationship to sensory characteristics. Journal of Animal Science, 48, 1343±1348.
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Fatty acid composition of goat diets vs intramuscular fat K.S. Rhee a,*, D.F. Waldron b, Y.A. Ziprin a, K.C. Rhee c a
Meat Science Section, Department of Animal Science, Texas A & M University, College Station, TX 77843-2471, USA b Agricultural Research and Extension Center, Texas Agricultural Experiment Station, San Angelo, TX 76901, USA c Department of Soil and Crop Sciences, Texas A & M University, College Station, TX 77843, USA Received 2 April 1999; accepted 6 July 1999
Abstract Twenty Boer x Spanish goats, at the age range of 90±118 days, were assigned to two dietary treatments, with 10 animals fed a grain ration (G) and the other 10 grazed in rangeland. The grain ration contained sorghum grain (67.5%), cottonseed hulls, dehydrated alfalfa meal, cottonseed meal, soybean meal, molasses, and mineral and vitamin supplements. Animals were slaughtered at the age range of 206±234 days. Intramuscular fat (IF) and the diet specimens Ð representative samples of G and the parts of range plants (RPs) that goats were expected to have consumed Ð were analyzed for fatty acid composition. The percentage of 16:0 was higher in RPs than in G, but not dierent between IF from range goats and that from grain-fed goats. Total unsaturated fatty acid (UFA) percentage was higher in G than in RPs. The major UFAs were 18:2 and 18:3 in RPs, and 18:1 and 18:2 in G. In IF, 18:1 constituted more than two-thirds of UFAs, regardless of diet type. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Goat meat; Fatty acids
1. Introduction The fat type or fatty acid composition of meat is an important diet/health concern to consumers. It also is a primary factor that determines product shelf-life/storage stability and ¯avor (Rhee, 1992). The fatty acid composition of tissues of ruminants generally is less aected by dietary lipid composition than that of nonruminants (Rhee, 1992). The great disparity between dietary and tissue fat in ruminant arises primarily from hydrogenation of dietary lipids by rumen microbes (Byers & Schelling, 1993). The ruminal conversion (saturation) of dietary unsaturated fatty acids, however, is normally not complete (Byers & Schelling, 1993), and bovine studies (Chilliard, 1993; Marmer, Maxwell & Williams, 1984; Melton, 1983; Westerling & Hedrick, 1979) have shown that dietary fatty acid composition dierences can result in dierences in tissue fatty acid composition. This was true with goats as well (Rhee, Ziprin, Bishop & Waldron, 1997). Speci®cally, the lipid extracts from the lean meat of range goats (raised in * Corresponding author. Tel.: +1-409-845-3936; fax: +1-409-8459454. E-mail address: [email protected] (K.S. Rhee).
rangeland with multiple species of grasses and forbs without any supplement) were more saturated than the corresponding extracts from goats fed a grain-based diet. Accordingly, raw or cooked meat samples from range goats were less susceptible to lipid oxidation (as measured by 2-thiobarbituric acid-reactive substances) than those of grain-fed goats. There has been no research that evaluated the fatty acid composition of diets themselves, along with the fatty acid composition of goat tissues. Our objectives were to conduct such a study and to further understand the relationship between the fatty acid composition of diets and that of intramuscular fat. 2. Materials and methods 2.1. Goat meat samples Animal feeding was done in San Angelo, Texas. Twenty animals (castrated male goats) at the age range of 90±118 days (mean, 105 days) were assigned to two dietary treatments, with 10 animals grazed in rangeland and the other 10 placed on a grain ration. The breed of all sires was Boer-cross and all the dams of the kids
0309-1740/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(99)00094-7
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were Spanish goats. The range kids were given access to rangeland/pasture populated with multiple species of native grasses, browses and forbs. The pasture was similar to that documented by Warren (1981). Table 1 shows the common and scienti®c names of the range plants that would have constituted the great majority of the range goat diet during the feeding treatment period (from 16 June 1997 to 9 October 1997). Based on the study by Warren (1981), where the diet composition of the Spanish goats grazing a rangeland similar to that of this study was estimated by microhistological analysis of fecal material, littleleaf sumac (browse) would have constituted more than 50% of the range goat diet (Table 1). For the grain diet treatment, a grain ration was given ad libitum for 116 days before slaughter. It contained sorghum grain (67.5%), cottonseed hulls (12%), dehydrated alfalfa meal (5%), cottonseed meal (4%), soybean meal (4%), molasses (4%), and mineral and vitamin supplements. All goats on the grain diet treatment were kept in a large pen (100100 ft) with shade available. Animals were slaughtered in San Angelo. At the time of slaughter, they were at the age range of 206±234 days (mean, 221 days). On the day of slaughter (10 October 1997) all kids were removed from their diet treatments and live weights were obtained between 10:00 and 10:30 am before the animals were transported for slaughter. Goats were slaughtered at a commercial facility 35 miles from the feeding facility. Transportation time was 45 min. Goats were slaughtered between 12:45 and 1:15 pm. Common commercial slaughter practices were used. Muscle (semimembranosus) samples were removed from carcasses at 60 h postmortem and frozen in Ziploc1 freezer bags. The plant samples were obtained in October, 1997 (toward the end of period when the goats were on the pasture) to be representative of the status of the plants close to the time of slaughter. The parts of each plant that Table 1 Description of dominant range plants and their contribution percentage to the diet of range goats Plant type and common name Grasses Sideoats grama Sand dropseed Common curlymesquite
Scienti®c name
Bouteloua curtipendula 12 Sporobolus cryptandrus (Torr.) Gray 7 Hilaria belangeri (Steud.) Nash 3
Browses Littleleaf sumac Rhus microphylla Engelm. Catclaw acacia Acacia greggii Gray Forb Globe mallow a
Estimated % in the diet of range goatsa
Sphaeralcea spp.
Estimation based on the study by Warren (1981).
60 6 4
goats were expected to have consumed were collected by cutting with a pair of scissors. Samples were placed in airtight plastic bags and frozen. The muscle samples (28 g/animal), range plant samples (250 g/species), and a representative sample (700 g) of the grain ration (sampling done after coarse-grinding of a large amount of the grain ration) were shipped frozen with dry ice from San Angelo to College Station. Upon receiving, the muscle samples were vacuum-packaged, whereas the diet samples were double-bagged in Ziploc1 freezer bags. All samples were kept at ÿ20 C until analyzed 2 months later. 2.2. Analytical methods Total fat was extracted by the procedure of Folch, Lees and Sloane-Stanley (1957). Before fat extraction, the plant samples were cut very ®nely with a pair of scissors (as they were too ®brous to be chopped in a food processor), soaked in distilled water (30 ml for 10 g sample) for 24 h at 4 C, and drained. The grain ration was ®nely chopped in a food processor and was also soaked in distilled water (30 ml for 10 g sample) and drained. The total fat extraction from each muscle sample utilized a 10-g portion of ®nely chopped tissue. Aliquots of lipid extracts were freed of solvent and transmethylated using tetramethylammonium hydroxide in methanol (Metcalfe & Wang, 1981). Fatty acid methyl esters were analyzed using a gas chromatograph (Varian 3400) ®tted with a fused silica capillary column, as described by Rhee, Ziprin, Ordonez and Bohac (1988). Results for each fatty acid were expressed as a percentage of the sum of all identi®ed fatty acids. Analysis of each diet specimen was replicated two times, from the initial fat extraction step to the ®nal gas chromatographic analysis of fatty acid methyl esters. The General Linear Model Procedure of the SAS (SAS, 1990) program was used for data analysis, with means separated by the Student±Newman±Keuls test. The data were analyzed as a completely randomized design, with 2 treatments (grain ration and grazing in rangeland) for goat muscle samples and 7 treatments (grain ration and the 6 range plants) for diet specimens. Signi®cance was de®ned at P40.05. 3. Results and discussion The live weight of animals (3 h prior to slaughter) and hot carcass weight were, on average, 35.11 and 18.55 kg (52.8% of the live weight), respectively, for the grain-fed goats and 26.26 and 12.18 kg (46.4%), respectively, for the range goats. Body wall thickness (average) measured 11 cm from midline, at the separation between the 12th and 13th ribs, was 1.63 cm for the grain-fed goats and 1.01 cm for the range goats.
K.S. Rhee et al. / Meat Science 54 (2000) 313±318
The range plant samples were much higher in the percentage of total saturated fatty acids when compared to the grain ration Ð 27±38% for the range plant samples vs 19% for the grain ration (Table 1). Conversely, the percentage of total unsaturated fatty acids was higher for the grain ration (81% vs 62±73%). In range plants, polyunsaturated fatty acids (18:2 and 18:3) made up the majority (71±87%) of total unsaturated fatty acids, while
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18:1 and 18:2 constituted 37 and 59%, respectively, of the total unsaturated fatty acids in the grain ration. When the range plants and the grain diet were compared for their dierences in 16:0 vs in 18:0 (the two primary fatty acids), the 18:0 dierences were much greater (on average, about 2 times higher in range plants) than the 16:0 dierences (1.4 times higher on average in range plants). However, the 18:1 percentage was 1.7±5.6 times higher in the grain
Table 2 Percentageb fatty acid compositions for range plants and grain rationa Fatty acids
Grain ration
Range plants Grasses
12:0 14:0 15:0 16:0 16:1 17:0 18:0 18:1 18:2 18:3 20:0 21:0 23:0 24:0 Saturated (S) Unsaturated (U) Monounsaturated (M) Polyunsaturated (P) U/S P/S M/S a
Browses
Forb
Sideoats grama
Sand dropseed
Common curlymesquite
Littleleaf sumac
Catclaw acacia
Globe mallow
0.04b (0.01)c 0.17d (0.02) 0.06a (0.01) 15.72d (1.77) 0.68a (0.01) 0.12c (0.01) 2.04d (0.22) 30.21a (0.78) 48.34a (0.56) 2.26d (0.04) 0.20c (0.01) 0.13d (0) 0b (0) 0.10b (0.04)
1.28a (0.27) 1.90b (0.20) 0.28a (0) 23.55a (0.47) 1.06a (0.35) 0.59b (0.02) 5.70b (1.33) 17.82b (4.96) 24.09c (0.33) 21.14c (6.19) 0.62a (0.05) 0.72b (0.07) 0.32a (0.05) 0.72ab (0.04)
1.08a (0.20) 1.84b (0.28) 0.20a (0.02) 22.58ab (0.57) 0.48a (0.49) 0.64b (0.04) 3.26cd (0.15) 9.29cd (0.91) 22.94cd (0.30) 36.00b (1.50) 0.43ab (0.04) 0.50c (0.02) 0.27a (0.01) 0.59ab (0.06)
1.12a (0.01) 2.46a (0.10) 0.36a (0) 22.69ab (0.11) 0.56a (0.59) 3.72a (0.22) 4.82bc (0.04) 14.51bc (0.08) 28.86b (0.71) 18.48c (0.54) 0.54ab (0.06) 0.86ab (0.15) 0.27a (0.04) 0.78ab (0.18)
0.10b (0.04) 1.84b (0.15) 0a (0) 20.18c (0.22) 0.27a (0) 0.66b (0.07) 3.27cd (0.22) 11.57cd (0.81) 10.26f (0.16) 48.82a (0.89) 0.32bc (0.14) 0.94a (0.04) 0.30a (0.09) 1.49a (0.10)
0.37b (0.31) 1.10c (0.19) 0.34a (0.24) 22.62ab (0.59) 0.54a (0.12) 0.77b (0.07) 7.22a (0.48) 7.68d (1.63) 12.88e (0.62) 44.19a (1.77) 0.54ab (0.02) 0.65bc (0.04) 0b (0) 1.13ab (0.78)
0.19b (0.03) 0.94c (0.02) 0a (0) 21.38b (0.80) 0.42a (0.01) 0.29c (0.01 2.31d (0.04) 5.35d (0.07) 21.68d (0.96) 45.61a (0) 0.36bc (0.02) 0.87ab (0.08) 0.22a (0.01) 0.38ab (0.01)
18.58f (0.45) 81.50a (0.16) 30.89a (0.76) 50.60bc (0.60) 4.39a (0) 2.73a (0) 1.66a (0)
35.68b (1.14) 64.10e (1.20) 18.88b (5.31) 45.22c (6.51) 1.80e (0.09) 1.27d (0.22) 0.53b (0.13)
31.38c (0.44) 68.62d (0.41) 9.68cd (1.39) 58.94b (1.80) 2.19d (0.04) 1.88bc (0.08) 0.31c (0.04)
37.60a (0.33) 62.40f (0.33) 15.06bc (0.50) 47.33c (0.17) 1.66e (0.02) 1.26d (0.01) 0.40bc (0.02)
29.08d (0.25) 70.91c (0.24) 11.84cd (0.81) 59.08b (1.05) 2.44c (0.03) 2.03b (0.05) 0.41bc (0.02)
34.72b (0.64 65.27e (0.64) 8.21cd (1.75) 57.06b (2.39) 1.88e (0.05) 1.64c (0.10) 0.24c (0.05)
26.94e (0.91) 73.06b (0.90) 5.77d (0.06) 67.29a (0.96) 2.71b (0.13) 2.50a (0.12) 0.21c (0)
Means within the same row followed by a common letter are not dierent (P>0.05). Each mean represents results of two separate analyses (from the initial fat extraction step to the ®nal analysis). b Percentage based on a total of identi®ed fatty acids listed. c Standard deviation.
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diet, depending on the plant species with which the grain diet was compared. Distinct dierences among the range plant types were found in 18:2 and 18:3. Grasses (sideoats grama, common curlymesquite and sand dropseed) and forb (globe mallow) were about 2 folds higher in the 18:2 percentage when compared to browses (littleleaf sumac and catclaw acacia). The percentage of 18:0, however, was higher in the browses and forb than in the grasses. Table 3 Percentageb fatty acid composition of goat muscle (semimembranosus) samplea Fatty acids
14:0 14:1 16:0 16:1 17:0 17:1 18:0 18:1 18:2 18:3 20:3 20:4 21:0 24:0 Saturated (S) Unsaturated (U) Monounsaturated (M) Polyunsaturated (P) U/S P/S M/S
Muscle samples from Range goats
Grain-fed goats
1.78a (0.69)c 0.30a (0.21) 20.51a (1.52) 1.62b (0.30) 1.29b (0.34) 0.94b (0.26) 16.27a (1.13) 42.43b (3.59) 7.74a (1.88) 1.16a (0.37) 0.21a (0.17) 3.43a (0.99) 1.17a (0.40) 1.17a (0.36)
1.78a (0.29) 0.43a (0.22) 20.99a (1.10) 2.71a (0.63) 1.75a (0.49) 2.32a (0.96) 10.24b (1.96) 51.00a (2.02) 5.74b (1.64) 0.18b (0.12) 0.08b (0.10) 2.27b (0.74) 0.15b (0.17) 0.38b (0.59)
42.19a (1.84) 57.82b (1.84) 45.29b (3.81) 12.54a (3.04) 1.37b (0.10) 0.30a (0.07) 1.07b (0.12)
35.28b (1.75) 64.72a (1.76) 56.46a (3.11) 8.27b (2.37) 1.84a (0.14) 0.23a (0.07) 1.61a (0.15)
a Means within the same row followed by a common letter are not dierent (P>0.05). Each mean represents results from 10 animals. b Percentage based on a total of identi®ed fatty acids listed. c Standard deviation.
Dierences in total fatty acid unsaturation between the intramuscular fat from range goats and that from grain-fed goats (Table 3) were not as large as the dierences observed between the range plants and the grain diet (Table 2). In intramuscular fat, whether from range goats or grain-fed goats, 18:1 constituted more than two-thirds (73% for range goats and 79% for grain-fed goats) of total unsaturated fatty acids. In comparison, 18:1 made up only 7±28% of the total unsaturated fatty acids in range plants and 37% in the grain ration. To further evaluate the relationship between dietary fatty acids and the fatty acids of intramuscular fat, data for range plants were averaged over all six plant species Ð taking into account each plant's estimated contribu-
Fig. 1. Relationships between the fatty acid pro®les of diets (range plants diet and grain diet) Ð with means for the range plants diet weighted for each plant's estimated contribution to the total diet of range goats Ð and the fatty acid pro®les of muscle tissue (intramuscular fat) from goats fed the dierent diets: common individual fatty acids.
K.S. Rhee et al. / Meat Science 54 (2000) 313±318
tion to the total diet of range goats (Table 1). Fig. 1 shows the resultant weighted means for the range diet in comparison to the means of the grain ration, along with comparisons of intramuscular fat from range goats vs the fat from grain-fed goats. Only 16:0, 18:0, 18:1, 18:2 and 18:3 (the most common fatty acids) were included for these comparisons. Apparently, the 16:0 percentage in intramuscular fat was not aected by feeding regimen. Although the dietary 16:0 percentage was higher in the range plant diet than in the grain diet, the 16:0 percentage in muscle tissue (intramuscular fat) was not signi®cantly dierent between range goats and grain-fed goats. A review by Chilliard (1993) has indicated that fatty acid synthesis in ruminants is more sensitive to inhibition by saturated fatty acids. This may partly explain why 16:0 in intramuscular fat was similar (P>0.05) between range goats and grain-fed goats (21% regardless of feeding regimen), while the dietary 16:0 percentage was higher in the range plants than in the grain ration (21% vs 16%). In other words, the de novo 16:0 synthesis could have been less in range goats than in grain-fed goats, because the range plants provided much more exogenous 16:0 (inhibitory to the de novo synthesis of 16:0) than the grain ration. Unlike 16:0, 18:0 may be produced by elongation of 16:0 and/or through ruminal hydrogenation of 18-carbon unsaturated fatty acids (Chang, Lunt & Smith, 1992; Ekeren, Smith, Lunt & Smith, 1992). For 18:0, 18:1 and 18:3, the directional (more or less) dierences between intramuscular fat from range goats and that from grain-fed goats were similar to those between the range plant diet and the grain diet; however, the magnitude of the dierences varied. Such was not the case for 18:2. It is possible that the relative eciency of ruminal hydrogenation of 18:2 may have been similar whether goats had the range plant regimen or the grain ration, but the intramuscular 18:2 produced as a result of ruminal hydrogenation of dietary 18:3 (42.80% in the range diet vs 2.26% in the grain diet) could have been greater in range goats due to the inordinately higher percentage of 18:3 in the range plants. As a result, the directional dierence in 18:2 may have shifted from `grain ration > range plants' to `range goats > grain-fed goats.' It is not certain whether there were digestibility dierences between these fatty acids in the goats on the two dietary treatments. Byers and Schelling (1993), in their review of ruminants in general, stated that ruminants usually digest unsaturated fatty acids to a lower degree when compared to nonruminants, whereas saturated fatty acids are digested more completely in the intestinal tracts of ruminants. There is little published information available on the eect of diet/feeding regimen on fatty acid composition of goat muscles/intramuscular fat. In our previous study (Rhee et al., 1997) on goat meat patties made with knife-separable lean composite (with some, though minimal, visible external fat), patties from grain-fed
317
animals within the same breed type were higher in the 18:1 percentage when compared to the respective patties from animals grazed in rangeland without grain supplementation, while the 18:0 percentage was higher in the latter. As for other ruminants, diet eects on fatty acid composition of beef have been extensively studied, as mentioned previously. For lambs, it has been mentioned that grazing may increase the 18:0 concentration in adipose tissue, while grain concentrates may increase 18:1 and 18:2 (Enser, 1995). Regarding the eects of grain diet vs forage diet on bovine tissue fatty acid composition, some dierences have been found between published studies. Westerling and Hedrick (1979) reported that the 16:0 percentage in intramuscular fat
Fig. 2. Saturated, monounsaturated and polyunsaturated fatty acid percentages for the range plants diet (with means weighted for each plant's estimated contribution to the total diet) vs the grain diet and for muscle tissue from range goats vs that from grain-fed goats: calculated from Fig. 1 data.
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was similar between animals fed an 82.4% corn diet and those grazed on predominantly fescue grass, whereas the 18:1 percentage was greater in grain-fed animals and 18:0, 18:2 and 18:3 percentages were higher in foragefed animals. In the study by Marmer et al. (1984), however, the 18:2 percentage of intramuscular fat was higher in animals fed a 79% corn diet than in animals fed a forage diet (primarily winter wheat). The dierences between these studies may be related to fatty acid composition dierences that could have been present between the two grain diets and/or the two forage diets (fatty acid pro®les of diet samples were not mentioned in these studies). In the present study (of goats), the 18:2 percentage was much higher for the grain ration while the 18:3 percentage was much higher for the range plant diet (Fig. 1). However, the combined percentage of the two fatty acids was not markedly dierent between the range and grain diets (57% vs 51%) (Fig. 2). For intramuscular fat vs diets, the combined percentage was much lower for intramuscular fat (<10% in range goats as well as grain-fed goats) than for the diets (>50% in both diets) (Fig. 2), because much of the dietary 18:2 and 18:3 would have been hydrogenated in the rumen to 18:1 and 18:0. In conclusion, this study has determined that intramuscular fat from Boer x Spanish goats grazed on pasture without any grain supplementation is more saturated than intramuscular fat from goats fed a grain diet. This trend with intramuscular fat seemed to generally re¯ect the fatty acid saturation or unsaturation dierences between the two diets. Further studies are needed on the relationship between the fatty acid pro®les of diet specimens (dierent grain diets and various range plants) and those of tissue samples from goats that have undergone the dietary treatments. In addition, what eect the time-on-feed (grain diet) may have on the composition of goat meat fatty acids needs to be investigated in future studies.
References Byers, F. M., & Schelling, G. T. (1993). Lipid in ruminant nutrition. In: D. C. Church, Ruminant animal: digestive physiology and nutrition (pp. 298±312). Prospect Heights, IL: Waveland Press Inc. Chang, J. H. P., Lunt, D. K., & Smith, S. B. (1992). Fatty acid composition and fatty acid elongase and stearoyl-CoA desaturase activities in tissues of steers fed high oleate sun¯ower seed. Journal of Nutrition, 122, 2074±2080. Chilliard, Y. (1993). Dietary fat and adipose tissue metabolism in ruminants, pigs, and rodents: a review. Journal of Dairy Science, 76, 3897±3931. Ekeren, P. A., Smith, D. R., Lunt, D. K., & Smith, S. B. (1992). Ruminal biohydrogenation of fatty acids from high-oleate sun¯ower seeds. Journal of Animal Science, 70, 2574±2580. Enser, M. (1995). Meat lipids. In R. J. Hamilton, Developments in oils and fats. Bishopbriggs, Glasgow: Blackie Academic and Professional. Folch, J., Lees, M., & Sloane-Stanley, G. H. (1957). A simple method for the isolation and puri®cation of total lipid from animal tissues. Journal of Biological Chemistry, 226, 497±509. Marmer, W. N., Maxwell, R. J., & Williams, J. E. (1984). Eect of dietary regimen and tissue site on bovine fatty acid pro®les. Journal of Animal Science, 59, 109±121. Melton, S. L. (1983). Eect of forage feeding on beef ¯avor. Food Technology, 37(5), 239±248. Metcalfe, L. D., & Wang, C. N. (1981). Rapid preparation of fatty acid methylesters using organic base-catalyzed transesteri®cation. Journal of Chromatographic Science, 19, 530±535. Rhee, K. S. (1992). Fatty acids in meats and meat products. In C. K. Chow, Fatty acids in foods and their health implications (pp. 65±93). New York: Marcel Dekker Inc. Rhee, K. S., Ziprin, Y. A., Bishop, C. E., & Waldron, D. F. (1997). Composition and stability of goat meat patties as aected by breed type and feeding regimen. Journal of Food Science, 62, 949±953, 962. Rhee, K. S., Ziprin, Y. A., Ordonez, G., & Bohac, C. E. (1988). Fatty acid pro®les of the total lipids and lipid oxidation in pork muscles as aected by canola oil in the animal diet and muscle location. Meat Science, 23, 201±210. SAS (1990). SAS user's guide: statistics. SAS Institute Inc., Cary, NC. Warren, L. E. (1981). Diets of various breeds of sheep and goats grazing in common on selected plant communities in west Texas. M.S. thesis. Angelo State University, San Angelo, Texas. Westerling, D. B., & Hedrick, H. B. (1979). Fatty acid composition of bovine lipids as in¯uenced by diet, sex and anatomical location and relationship to sensory characteristics. Journal of Animal Science, 48, 1343±1348.