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Chemical composition and quality characteristics of chevon from goats fed three different post-weaning diets
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Small Ruminant Research 75 (2008) 177–184
Chemical composition and quality characteristics of chevon from goats fed three different post-weaning diets J.H. Lee ∗ , B. Kouakou, G. Kannan Georgia Small Ruminant Research and Extension Center, Fort Valley State University, Fort Valley, GA 31030, USA Received 19 December 2006; received in revised form 23 October 2007; accepted 23 October 2007 Available online 18 December 2007
Abstract Thirty-six Boer × Spanish intact male goats (BW = 18 ± 0.8 kg; age 4 months) were used to determine the effects of dietary treatments on the chemical composition and quality characteristics of goat meat (chevon). Animals were allotted to three treatment groups (n = 12/treatment) with three pens for each treatment. Each pen of four goats was fed one of three dietary treatments for 90 d: (1) a hay diet, consisting of alfalfa (Medicago sativa) hay alone (H); (2) a 18% CP concentrate diet, consisting predominantly alfalfa meal and yellow corn (C); or (3) a combined diet, consisting of the hay diet for the first 45-d, followed by the concentrate diet (HC). At the end of the feeding trial, goats were slaughtered and Longissimus dorsi (LD) muscle and subcutaneous fat samples were obtained from each carcass to determine chemical and fatty acid compositions. Loin chops were used to evaluate color (CIE L* a* b* ), cooking loss, and Warner-Bratzler shear force (WBSF) values. The LD muscle from goats fed the H diet contained higher (P < 0.05) moisture (77.1 vs. 74.7%), but a lower (P < 0.05) total lipid (1.32 vs. 2.67%) than those from goats fed the C diet. However, the percentages of moisture and total lipid in the LD muscle from HC group were not statistically different from those fed either the H or C group. Compared with goats fed the H diet, goats fed the C diet had: (1) a higher (P < 0.05) level of oleic acid (C18:1n9; 43.9 vs. 38.7%), but a lower (P < 0.05) level of linolenic acid (C18:3n3; 0.12 vs. 0.46%) in the LD muscle lipid; (2) a higher (P < 0.05) level of linoleic acid (C18:2n6; 4.27 vs. 3.11%), but lower (P < 0.05) levels of myristic acid (C14:0) and C18:3n3 (0.44 vs. 0.76%) in the subcutaneous fat. The L* (lightness) and b* (yellowness) values of loin chops from goats fed the H diet were higher (P < 0.05) than those fed the C diet; however, a* values (redness) were not statistically different among the dietary treatments. The WBSF values and cooking losses were not influenced by the dietary treatments. The results indicated that chevon from the H diet had healthier nutritional properties compared with that from the C diet; however, the meat qualities were not different among the treatment groups. © 2007 Elsevier B.V. All rights reserved. Keywords: Goat; Hay; Concentrate; Fatty acid; Meat quality
1. Introduction The demand for goat meat (chevon) has been steadily increasing in recent years among ethnic populations and ∗
Corresponding author at: Fort Valley State University, Agricultural Research Station, 1005 State University Drive, Fort Valley, GA 31030, USA. Tel.: +1 478 827 3077; fax: +1 478 825 6376. E-mail address: [email protected] (J.H. Lee). 0921-4488/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2007.10.003
health conscious consumers, although domestic chevon production is relatively limited compared to other red meats (beef and lamb) in the United States (James and Berry, 1997). The scientific evidences and recommendations by health professionals have increased the concerns about the negative effects of dietary saturated fat to human health and prompted the development of low-fat meat products in the U.S. (James and Berry, 1997). Chevon is particularly attractive to health
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conscious groups due to its lower fat contents compared to other types of red meat and thereby provides an excellent source of low-fat meat entrees (James and Berry, 1997). Development of processed products will expand the existing consumer base in the U.S. However, the seasonal limitations of breeding and forage availability on meat goat production affect the market value of chevon in the U.S. (McMillin and Brock, 2005). The production costs greatly influence the profit margin of meat goat enterprises. Feed cost makes up 50–70% of the total expenditures in livestock production (Wilkinson and Stark, 1987). Meat goats are fed most of their required nutrients from forages to increase the profit to the producers; however, pasture-based production systems have a limitation because of the effect of seasonal variation on the nutrient contents. This often means pasture alone does not always provide adequate nutrition for fast growing animals (Wilkinson and Stark, 1987). On that account, additional protein and energy (hay or concentrate) are offered to maintain acceptable goat performance. Young animals fed either hay alone, hay followed by concentrate, or concentrate alone, just after weaning, may have different performance characteristics and thereby influence the composition and quality of chevon. Different forms and energy levels of diets influence carcass composition and meat properties in food animals (McMillin and Brock, 2005). Meat goats with high-energy intake increased the juiciness, tenderness, and texture of chevon, but the consumer acceptability was lower because of the higher content of fat in meat than that from goats finished on roughage diets (McMillin and Brock, 2005). Carlucci et al. (1998) reported that meat from goats grazed and fed a commercial pellet was more tender and juicier than that from goats fed hay and a commercial pellet. Data on the effects of feeding treatments on chevon quality are limited. The objective of this research was, therefore, to determine the effect goat diet (a hay, concentrate-, or hay followed by concentrate-diet) on chemical composition and quality characteristics of chevon. 2. Materials and methods 2.1. Feeding trials and meat sampling Experimental procedures involving animals were conducted with the approval of the Fort Valley State University (FVSU) Institutional Animal Care and Use Committee. Thirtysix weaned crossbred (Boer × Spanish; 4-month-old) intact male goats (18 ± 0.8 kg, BW) were assigned in a completely randomized design to a feeding trial consisting of three dietary treatments. Each treatment was replicated in three pens, with
Table 1 Ingredients and chemical composition of hay and concentrate diets Item
Ingredient (%) Alfalfa hay Alfalfa meal Yellow corn Soybean meal, 44% TM salt (red salt) Vitamin premix Poultry fat
Diet Hay
Concentrate
100 – – – – – –
– 50.2 35.0 8.8 0.50 0.50 5.00
Chemical composition (%) Dry matter (DM) Crude protein (CP) Ether extract Ash Acid detergent fiber (ADF) Neutral detergent fiber (NDF)
91.7 17.3 2.4 5.9 34.0 45.0
93.6 18.0 7.1 6.5 4.0 29.0
Fatty acid methyl ester (%) C12:0 C13:0 C13:1n9 C14:0 C14:1n5 C15:0 C16:0 C16:1n7 C17:0 C18:0 C18:1n9 C18:2n6 C18:3n3 C20:0 C20:1n9 C20:5n3 C22:0 C22:5n3
0.27 0.23 2.70 0.79 0.14 0.48 20.97 1.67 0.47 3.94 10.00 19.90 21.66 1.16 1.05 0.45 1.15 0.84
0.07 – 0.27 0.49 0.11 0.11 21.32 5.09 0.16 4.86 33.70 25.08 3.69 0.30 0.04 0.09 0.10 0.16
four goats per pen. Experimental animals were housed in feeding pens located at the Georgia Small Ruminant Research and Extension Center, FVSU. Pens were in a closed barn, and each goat was provided 1.25 m2 of floor space with ad libitum access to water. Each pen of four goats was fed one of three dietary treatments for a 90-d feeding period: (1) a hay diet, consisting of alfalfa (Medicago sativa) hay alone (H); (2) a 18% CP concentrate diet (Table 1), consisting predominantly of alfalfa meal, yellow corn, and soybean meal (C); or (3) a combined diet, consisting of the hay diet for the first 45-d, followed by the concentrate diet (HC). In the feeding period, feed was provided ad libitum and the experimental animals (n = 36) were weighted individually biweekly. At the conclusion of the feeding trial, the goats were slaughtered using standard procedures and carcasses kept at 2 ◦ C for 24 h before dissection. Dressing percent or carcass yield of each carcass was reported as that proportion (percentage) of the live
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weight that remains in the carcass. After 24 h of cooling, the carcasses were dissected with each carcass split along the vertebral column into left and right halves, and then sliced into 2.5 cm loin chops using a band saw. Four loin chops (Longissimus dorsi, LD muscle) from the right side of each carcass and subcutaneous fat were removed from the pelvic area and sampled. All the samples were ground in liquid nitrogen, placed in polyethylene bags (NASCO Inc., Fort Atkinson, WI), and stored at −28 ◦ C for proximate and fatty acid analyses. Four more chops from the right side of each carcass were also used to analyze thiobarbituric acid reactive substances (TBARS) and total collagen content. Chops from left side of each carcass were allotted for analysis of color (CIE L* a* b* ), WarnerBratzler shear force (WBSF) values, and cooking losses. 2.2. Chemical composition Proximate composition of LD muscle samples was analyzed according to AOAC (1995) methods. Moisture and ash contents (%) were determined by the oven-drying (AOAC, 950.46) and furnace methods (AOAC, 942.05), respectively. The ether extraction method (AOAC, 920.39) was used to determine total lipid content (%) in the muscle samples. Protein content (%) was estimated by a carbon/nitrogen analyzer (Vario Max CN Elementar Americas Inc., Mt. Laurel, NJ, USA). Total lipids were extracted from either 2.0 g of muscle or 0.2 g of fat samples with chloroform/methanol (2:1 v/v) according to Cherian et al. (1996) using a homogenizer (Cyclone IQ2 , The Virtis Co., Gardiner, NY) for 3× 30 s at 30,000 rpm. The fatty acid composition of the total lipids extracted from each sample was determined by the following preparation. Extracted lipid was saponified and esterified according to the AOCS method (1993) of preparation of fatty acid methyl esters (FAME). The prepared FAME were analyzed using a Hewlett Packard 5890 Series II gas chromatograph (GC), equipped with an automatic sampler HP 7673 (Agilent Technologies Inc., Palo Alto, CA, USA). A 0.25-mm i.d. by 30-m long fused silica SP2330 capillary column (Supelco Inc., Bellefonte, PA, USA) was used to separate the methyl esters, which were detected with a flame ionization detector (FID). The injection temperature was 250 ◦ C, and the column temperature was programmed from 130 to 220 ◦ C at 2 ◦ C/min. Helium was the carrier gas with a flow rate at 30 mL/min, and a split ratio of 30:1. The identification of individual FAME in the sample was achieved by matching the retention time of the unknown FAME with that of known FAME standard mixtures (Alltech Associates Inc., Deerfield, IL; Sigma–Aldrich Corp., Bellefonte, PA, USA). For quantitative analysis of the sample FAME, standards containing known weight percentages of individual FAME, present in levels similar to those in the samples, were analyzed by the GC, and the correction factors relative to palmitic (C16:0) acid were calculated according to the AOCS (1993) for fatty acid analysis. The area of individual sample FAME was corrected using its correction factor. The relative weight percentages of each FAME (C10:0:-C22:6) in each sample were then calculated using their corrected areas (AOCS, 1993).
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2.3. Quality characteristics of loin chops The TBARS assay was performed as described by Buege and Aust (1978). The ground muscle sample (0.5 g) was mixed with 2.5 mL of 0.375% thiobarbituric acid-15% trichloroacetic acid-0.25 N HCl stock solution in a glass test tube. The mixture was heated for 10 min in a boiling water bath (∼100 ◦ C) to develop a pink color. The test tube was cooled with tap water and then centrifuged at 5500 rpm for 25 min. Absorbance of supernatant was measured at 532 nm using a Shimadzu (Model UV-2401 PC) spectrophotometer (Shimadzu Corporation, Columbia, MD, USA). The TBARS were calculated from a standard curve of malondialdehyde (MDA) and expressed as mg MDA/kg sample. Hydroxyproline concentrations were determined using the procedures of Bergman and Loxley (1963) and the total collagen concentrations were expressed in mg/g dry muscle. The L* , a* , and b* color coordinate values were measured on the cut surfaces of loin chops from left side of each carcass after a 30-min bloom time at 4 ◦ C using a HunterLab color instrument with illuminant D65 as the light source. Three measurements were taken from each sample. The average of the three measurements was recorded as color coordinate value of the sample. Hue angle was calculated as tan−1 (b* /a* ), whereas chroma (a measure of color vividness) was calculated as (a*2 + b*2 )1/2 (Hunter and Harold, 1987). After measuring color coordinate values, the chops were vacuum-packed, frozen, and stored at −28 ◦ C until assessment of tenderness and cooking loss. The cuts were thawed at 4 ◦ C and cooked according to the procedures described by Kannan et al. (2002). Briefly, the chops were cooked in a convection oven (Maytag Corporation, Model MER6550B, Newton, IA, USA) to an internal temperature of 71 ◦ C. The internal temperature was measured in a representative chop from each pan using thermocouple thermometers (Fisher Scientific, Suwannee, GA, USA). In a randomly chosen cut from each pan, the thermocouple probe was placed in the geometric center of the LD muscle. Cooked samples were wrapped in aluminum foil and cooled at 4 ◦ C overnight before core removal. The cuts were allowed to come to room temperature by removing them from the refrigerator and placing them on a laboratory countertop for 2 h, and then 1-cm diameter cores were removed parallel to muscle fiber orientation (Kannan et al., 2002). Two cores were taken from each chop and WBSF values assessed using a TA-XT2 texture analyzer fitted with a Warner-Bratzler shear attachment (Texture Technologies Corp., Scarsdale, NY, USA). The instrument was set with a 25-kg load cell and a cross-head speed of 200 mm/min. The difference in weight of samples before and after cooking was expressed as percentage cooking loss. 2.4. Statistical analysis All data were analyzed as a completely randomized design using the GLM procedure of SAS (2000), with individual goats as the experimental units. Least squares means were generated
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Table 2 Proximate composition of Longissimus muscles from goats fed three different diets Component (%)
Moisture Protein Total lipid Ash
Diet
S.E.
H
C
HC
77.09 a 20.78 1.32 b 1.32
74.70 b 21.30 2.67 a 1.38
75.79 ab 20.10 2.02 ab 1.62
0.89 0.41 0.35 0.15
H: hay for 45-d; C: concentrate for 45-d; HC: hay for 45-d plus concentrate for 45-d. Within a row, least squares means that do not have a common letters differ (P < 0.05).
and separated using the PDIFF options of SAS (pairwise t-test). Significant effects were determined at P < 0.05, but differences with P < 0.1 were considered as trends.
3. Results and discussion 3.1. Body weight gain and carcass yield Daily weight gain by the goats was different (P < 0.01) among the experimental diets. The average daily gains (ADG) were 41.4, 134.3, and 64.7 (S.E. = 12.55) g/d for H, C, and HC diets, respectively. Goats fed the C diet gained more weight per day than those fed either the H or HC diet; however, no significant difference was found in the ADG of goats on H and HC diets. Differences (P < 0.01) were also observed in the mean (±S.E.) final live weight, which was greater for the goats fed C diet (30.3 ± 1.39 kg) than for the goats fed either the H or HC diet (21.6 or 22.7 ± 1.39 kg). However, no significant differences were found in the carcass yields of the goats fed the three experimental diets. The mean carcass yield ranged from 37.5 to 38.7%. In general, animals on concentrate-based diets have higher average daily gains than those on pasture (Realini et al., 2004; Haddad, 2005). Carcasses from cattle finished on concentrate were heavier than those finished on pasture (Realini et al., 2004). Goats on high-energy diets had heavier body weight than those on low-energy diet and increased concentrate to forage ratios also increased the weight gain and final body weight of goats (Haddad, 2005). 3.2. Chemical composition Proximate compositions of LD muscles from goats fed the experimental diets are presented in Table 2. No significant differences were found in the protein and ash contents in the LD muscles of goats fed the experimental diets. However, goats fed the C diet had lower (P < 0.05)
amounts of moisture in the LD muscles than those fed the H diet, but had a higher (P < 0.05) total lipid content. No significant differences were found in the moisture and total lipid contents in the LD muscles of goats fed either the C or HC diet. The lower moisture content in the LD muscle from the goats fed the C diet is due to the higher lipid content in this group compared to the goats fed the H or HC. Numerous studies reported higher muscle fat contents in animals that received higher proportions of concentrate in the diet (French et al., 2001; Geay et al., 2001). The LD muscle fat content of concentratefed steers was twofold greater than pasture-fed steers (Marino et al., 2006). The fatty acid composition of the LD muscle and subcutaneous fat from goats fed the experimental diets is presented in Table 3. Nineteen fatty acids were identified in lipids extracted from LD muscle and subcutaneous fat, which consisted of nine saturated (C10:0, C12:0, C14:0, C15:0, C16:0, C17:0, C18:0, C20:0, and C22:0), five monounsaturated (C13:1n9, C14:1n5, C16:1n7, C18:1n9, and C20:1n9), and five polyunsaturated (C18:2n6, C18:3n3, C20:4n6, C20:5n3, and C22:5n3) fatty acids. The major fatty acids in the LD muscle lipids from H-, C-, and HC-fed goats were palmitic (C16:0), stearic (C18:0), and oleic (C18:1n9) acids, which accounted for 73.1, 75.3, and 71.4% of total fatty acids, respectively. In general, meat from pasturefed animals contains a similar proportion of saturated fatty acids, a lower concentration of monounsaturated fatty acids, and a higher percentage of polyunsaturated fatty acids than that from concentrate-fed animals (Webb et al., 2005; Marino et al., 2006). In the present study, the LD muscle lipid from goats fed the C diet contained a lower concentration of saturated fat (36.4 vs. 41.0%) and a higher concentration of monounsaturated fat (42.8 vs. 48.0%) than that from H-fed goats (Table 3). Among the saturated fatty acids (SFA), goats fed the H diet had higher (P < 0.05) percentages of pentadecanoic (C15:0) and margaric (C17:0) acids in LD muscle lipids than those fed the C or HC diet; however, no significant difference was found in margaric acid (C17:0) between goats fed H and HC diets. Saturated fatty acids such as lauric (C12:0), myristic (C14:0), and palmitic (C16:0) acids raise the LDL-cholesterol concentrations in blood, increasing the risk of cardiovascular diseases (Noakes et al., 1996). These three LDL-cholesterol increasing fatty acids made up 24.2, 23.5, and 22.8% of total fatty acids in the LD from goats fed H, C, and HC diets, respectively. Of the monounsaturated fatty acids (MUFA), the mean concentration of oleic acid (C18:1n9) of the LD muscle lipids of goats that consumed the C diet was higher (P < 0.05) than that of goats fed either the H or HC
J.H. Lee et al. / Small Ruminant Research 75 (2008) 177–184
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Table 3 Fatty acid composition of intramuscular and subcutaneous fat of goats fed three different diets Fatty acid (%)
C10:0 C12:0 C13:1n9 C14:0 C14:1n5 C15:0 C16:0 C16:1n7 C17:0 C18:0 C18:1n9 C18:2n6 C18:3n3 C20:0 C20:1n9 C20:4n6 C20:5n3 C22:0 C22:5n3
Intramuscular fat
S.E.
H
C
HC
0.17 0.17 0.09 2.16 0.52 0.70 a 21.87 3.38 1.75 a 12.49 38.73 b 6.93 0.46 a 0.07 0.12 4.65 0.45 1.57 0.37
0.17 0.14 0.06 2.00 0.29 0.47 b 21.40 3.69 1.35 b 10.01 43.85 a 7.92 0.12 b 0.05 0.11 3.46 0.38 0.83 0.37
0.15 0.14 0.06 1.77 0.42 0.51 b 20.60 3.24 1.69 a 11.69 39.12 b 7.07 0.19 b 0.08 0.16 4.19 0.59 1.90 0.63
0.04 0.03 0.01 0.15 0.11 0.06 0.68 0.27 0.10 1.33 1.45 0.61 0.15 0.02 0.05 1.16 0.14 0.62 0.26
Subcutaneous fat
S.E.
H
C
HC
0.20 a 0.21 0.20 a 3.19 a 0.33 1.12 a 25.03 3.40 2.85 a 22.83 36.18 3.11 b 0.76 a 0.01 0.23 a 0.49 0.33 0.09 a 0.18 a
0.10 b 0.08 0.06 c 2.40 b 0.04 0.51 c 25.00 3.03 1.85 b 23.52 39.32 4.27 a 0.44 b 0.01 0.03 b 0.21 0.07 0.04 b 0.09 b
0.16 ab 0.16 0.12 b 2.57 b 0.06 0.76 b 23.95 3.22 2.60 a 23.07 38.62 3.99 ab 0.52 b 0.01 0.05 b 0.39 0.13 0.05 b 0.10 b
0.02 0.05 0.02 0.20 0.09 0.08 0.74 0.30 0.16 1.85 1.47 0.23 0.11 0.00 0.08 0.11 0.09 0.01 0.02
H: hay for 45-d; C: concentrate for 45-d; HC: hay for 45-d plus concentrate for 45-d. Within a row, least squares means that do not have a common letters differ (P < 0.05).
diet. However, no significant difference was detected in the oleic acid (C18:1n9) concentration of the LD muscle lipid from goats fed the H or HC diet. Goats fed the H diet had higher (P < 0.05) levels of linolenic acid (C18:3n3) in LD muscle lipids than goats fed either the C or HC diet; however, there were no differences in the concentrations of linolenic acid (C18:3n3) in the LD muscle lipids between the goats fed C and HC diets. Current recommendations are that the PUFA:SFA (P:S) ratio should be around 0.45 (Webb et al., 2005). The P:S ratios in this study were lower than the recommended ratio, being 0.31 for H-fed, 0.34 for C-fed, and 0.32 for HC-fed goats. Duckett et al. (1993) reported a higher P:S ratio (0.26) for beef from grass-finished steers than for meat from concentrate-finished animals (0.07). The major fatty acids in the subcutaneous fat from goats fed the experimental diets were also palmitic (C16:0), stearic (C18:0), and oleic (C18:1n9), which made up 84.0, 87.8, and 85.6% total fatty acids in H-, C-, and HC-fed goats, respectively. No significant differences were found in the concentrations of total SFA, MUFA, or PUFA in the subcutaneous fat from goats fed H, C, or HC diet (Table 3). Among the SFA in the subcutaneous fat, there were significant differences in the mean concentrations of decanoic (C10:0), myristic (C14:0), pentadecanoic (C15:0), margaric (C17:0), and docosanoic (C22:0) acids among the goats fed the exper-
imental diets. The concentrations of these five fatty acids in the subcutaneous fat of goats fed the H diet were higher (P < 0.05) than in the subcutaneous fat of goats fed the C diet. However, no significant differences were observed in decanoic (C10:0), myristic (C14:0), or docosanoic (C22:0) acid concentrations between goats fed C and HC diets. The mean concentrations of pentadecanoic (C15:0) and margaric (C17:0) acids in the subcutaneous fat of goats fed the C diet were lower (P < 0.05) than in the subcutaneous fat of goats fed the HC diet. Concentrations of subcutaneous MUFA were not statistically different among goats fed the experimental diets, except tridecenoic (C13:1n9) and eicosaenoic (C20:1n9) acids. Concentrations of tridecenoic (C13:1n9) and eicosaenoic (C20:1n9) of the subcutaneous fat of goats fed the H diet were higher (P < 0.05) than those of goats fed either the C or HC diet; however, no significant difference was detected in the eicosaenoic (C20:1n9) acid concentration of the subcutaneous fat between goats fed C and HC diets. Goats fed the H diet had higher (P < 0.05) levels of linolenic (C18:3n3) and docosatrienoic (C22:5n3) acids in subcutaneous fat than goats fed either the C or HC diet. Similar to muscle fat, there were no significant differences in concentrations of linolenic (C18:3n3) and docosatrienoic (C22:5n3) acids in subcutaneous fat between goats fed C and HC diets. Concentration of linoleic (C18:2n6)
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Table 4 Quality characteristics of loin color (L* , a* , b* , chroma, and hue angle), thiobarbituric acid reactive substances (TBARS), total collagen, cooking loss, and Warner-Bratzler shear force (WBSF) values of loin chops from goats fed three different diets Item
Color L* value a* value b* value Chroma value Hue angle TBARS Total collagen (mg/kg) Cooking loss (%) WBSF (kg)
Diet
S.E.
H
C
HC
43.57 a 9.34 12.45 a 15.41 51.78 a
39.81 b 9.91 11.09 b 14.63 47.30 b
42.17 ab 9.89 11.88 ab 15.22 49.37 ab
1.26 1.04
1.18 0.95
1.19 0.98
0.08 0.10
22.66 3.79
28.83 3.73
25.65 3.10
3.11 0.44
1.10 0.54 0.32 0.39 1.72
H: hay for 45-d; C: concentrate for 45-d; HC: hay for 45-d plus concentrate for 45-d. Within a row, least squares means that do not have a common letters differ (P < 0.05).
acid of the subcutaneous fat of goats fed the C diet was higher (P < 0.05) than that of goats fed the H diet, but no difference was detected in the linoleic (C18:2n6) acid concentration of the subcutaneous fat between goats fed H and HC diets. 3.3. Quality characteristics of chevon chops Sensorial characteristics of the chevon chops from goats fed the experimental diets are presented in Table 4. The dietary treatments had significant influences on the LD muscle L* (lightness) and b* (yellowness) values, but not in the a* value (redness). The LD muscle color was lighter (higher L* value; P < 0.05) in the goats fed H diet than those fed the C diet; however, no difference was found in the L* values between goats fed H and HC. Goats fed the H diet also had higher b* (P < 0.05) values in the chops than the goats fed the C diet. However, the b* values of the LD muscles of goats fed the H diet was not different from those fed the HC diet. There were no significant differences in chroma values of the LD muscle from goats fed the experimental diets. However, the hue angle was higher (P < 0.05) in the H group than in the C group. No difference was found in the hue angle between goats fed H and HC diets. Fresh meat color is an important criterion for judging freshness and quality by consumers. Chevon has lower lightness and higher redness than lamb because of the lower intramuscular fat of goat carcasses (Babiker et al., 1990); however, consumers cannot readily perceive the differences between chevon and lamb. Previous researchers
reported that Longissimus muscle of ruminants fed on low-energy diets had a darker colored lean (lower L* values) than those fed high-energy diets (Priolo et al., 2002; Realini et al., 2004). Meat from grass fed lambs was darker (P < 0.05) in color than that from concentrate-fed lambs (Priolo et al., 2002). Steers finished on pasture also had darker Longissimus muscle compared to concentrate finished steers (Realini et al., 2004). However, no differences were found in the instrumental color values of the Longissimus muscle of steers fed on different combinations of forage-concentrate diets for a short period (French et al., 2001). This suggested that in order for the diet to influence meat color, the feeding period should last for an extended period. Dietary treatments did not have significant effects on TBARS values (Table 4). The reaction of malondialdehyde (MDA) with 2-thiobarbituric acid (TBA) is widely used for measuring the extent of oxidative deterioration of lipid in muscle foods (Gray, 1978). Lipid oxidation results in the production of free radicals, which may lead to the oxidation of meat pigments and generation of rancid odors and flavors (Faustman and Cassens, 1990). In the present study, lipid oxidation of meat was not affected by dietary treatments. The results agree with the findings of Marino et al. (2006). Nutritional factors can influence the functional property of collagen. Miller et al. (1987) reported that mature cows fed a high-energy diet for 84 d prior to slaughter produced meat with a higher percentage of heat-labile collagen and lower shear values compared to meat from cows fed a maintenance-energy diet. In contrast, Crouse et al. (1985) found that muscle from cattle fed a highenergy diet contained more soluble collagen, and the meat was less tender compared to cattle fed a low-energy diet. In the present study, dietary treatments did not affect total collagen content of goat LD muscle measured at 24 h postmortem (Table 4). The results of this study are in agreement with those of Kannan et al. (2006), who found that meat from goat fed either a high- or lowenergy diet were not different in the collagen content and solubility. Dietary treatments did not have any effect on the cooking loss of chevon chops (Table 4). Leheska et al. (2002) reported that dietary treatment did not influence drip loss and cooking loss in pork. Juiciness of meat is directly related to the intramuscular lipids and moisture content of the meat, but the water remaining in the cooked product is the major contributor to the sensation of juiciness during eating (Cross et al., 1986). Chevon and its products are reportedly less juicy than lamb and lamb products, a quality attributed to the lower fat content of chevon.
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Evaluation of factors affecting meat tenderness is particularly important in chevon because of its lower tenderness than lamb and beef (Smith et al., 1974). However, the tenderness value of chevon is often in the acceptable range (Webb et al., 2005). The acceptable limit for lamb tenderness is about a 3 kg Warner-Bratzler shear force to Australian and New Zealand consumers (Webb et al., 2005). Shear force values depend on factors such as the treatment of the animals prior to slaughter, postmortem methodologies, the sampled muscle and method of sample preparation (Webb et al., 2005). Warner-Bratzler shear force (WBSF) values of chevon chops after the 24 h postmortem was not influenced by dietary treatments (Table 4). Similar results were reported by Smith et al. (1979) in cattle, who found that nutritional regime did not cause any change in the shear values of steaks. Several researchers found that implementation of a short finishing period or an increase in concentrate proportion during this period had no effect on meat tenderness (French et al., 2001). May et al. (1992) found a longer period was necessary to observe a decrease in WBSF. In these works, the decrease in WBSF was accompanied by an increase in marbling and carcass fatness. Intensive management with high-energy intake by goats increased the juiciness, tenderness, and texture of the chevon, but general acceptability was lower than with grazing systems because the meat had higher fat (Karanjkar et al., 2000). 4. Conclusion Feeding meat goats with a concentrate diet increased the body weight compared with goat fed hay only or hay followed by concentrate feeding, but did not change the carcass yield and quality of chevon. Concentratefed goats had a darker longissimus muscle color than hay-fed goats. Edible tissues from goats fed a concentrate diet had a higher amount of fat than those from goats fed a hay diet. Goats receiving hay, concentrate, or hay followed by concentrate ration did not influence the intramuscular fatty acid profile, which is of interest from a human health perspective. The characteristics related to tenderness of chevon were not affected by the dietary treatments. There may not be any merit in increasing production cost by feeding all concentrate diet to meat goats after weaning, since the diet did not influence meat quality characteristics in this study. References AOAC, 1995. Official Methods of Analysis of the AOAC International, 16th ed. Association of Official Analytical Chemists, International, Gaithersburg, MD.
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AOCS, 1993. Official and Tentative Methods of Analysis, 5th ed. American Oil Chemists’ Society, Champaign, IL. Babiker, S.A., El Khider, I.A., Shafie, S.A., 1990. Chemical composition and quality attributes of goat meat and lamb. Meat Sci. 28, 273–277. Bergman, I., Loxley, R., 1963. Two improved and simplified methods for the spectrophotometric determination of hydroxyproline. Anal. Chem. 35, 1961–1965. Buege, C.E., Aust, S.D., 1978. Microsomal lipid peroxidation. Methods Enzymol. 52, 302–304. Carlucci, A., Girolami, A., Napolitano, F., Monteleone, E., 1998. Sensory evaluation of young goat meat. Meat Sci. 50, 131–136. Cherian, C., Wolfe, F.W., Sim, J.S., 1996. Dietary oils with added tocopherols: effects on egg or tissue tocopherols, fatty acids, and oxidative stability. Poult. Sci. 75, 423–431. Cross, H.R., Durland, P.R., Seidman, S.C., 1986. Sensory qualities of meat. In: Eechtel, P.J. (Ed.), Muscle as Food. Food Science and Technology Series. Academic Press, New York, pp. 279– 320. Crouse, J.D., Cross, H.R., Seideman, S.C., 1985. Effects of sex condition, genotype, diet and carcass electrical stimulation on the collagen content and palatability of two bovine muscles. J. Anim. Sci. 60, 1228–1234. Duckett, S.K., Wagner, D.G., Yates, L.D., Dolezal, H.G., May, S.G., 1993. Effect of time on feed on beef nutrition in beef nutrient composition. J. Anim. Sci. 71, 2079–2088. Faustman, C., Cassens, R.G., 1990. The biochemical basis for discoloration in fresh meat: a review. J. Muscle Foods 1, 217– 243. French, P., O’Riordan, E.G., Monahan, F.J., Caffrey, P.J., Mooney, M.T., Troy, D.J., 2001. The eating quality of meat of steers fed grass and/or concentrates. Meat Sci. 57, 379–386. Geay, Y., Bauchart, D., Hocquette, J.F., Culioli, J., 2001. Effect of nutritional factors on biochemical, structural and metabolic characteristics of muscles in ruminants, consequences on dietetic value and sensorial qualities of meat. Reprod. Nutr. Dev. 41, 1– 26. Gray, J.I., 1978. Measurement of lipid oxidation: a review. J. Am. Oil Chem. Soc. 55, 539–546. Haddad, S.G., 2005. Effect of dietary forage: concentrate ratio on growth performance and carcass characteristics of growing Baladi kids. Small Rumin. Res. 57, 43–49. Hunter, R.S., Harold, R.W., 1987. Uniform color scales. In: The Measurement of Appearance, 2nd ed. Hunter Associates Laboratory, VA, pp. 135–148. James, N.A., Berry, B.W., 1997. Use of chevon in the development of low-fat meat products. J. Anim. Sci. 75, 571–577. Kannan, G., Terrill, T.H., Kouakou, B., Gelaye, S., Amoah, E.A., 2002. Influence of packaging method and storage time on shear value and mechanical strength of intramuscular connective tissue of chevon. J. Anim. Sci. 80, 2383–2389. Kannan, G., Gadiyaram, K.M., Galipalli, S., Carmichael, A., Kouakou, B., Pringle, T.D., McMillin, K.W., Gelaye, S., 2006. Meat quality in goats as influenced by dietary protein and energy levels, and postmortem aging. Small Rumin. Res. 61, 45–52. Karanjkar, L.M., Abdul Hakim, M.A., Patil, G.R., 2000. Performance of Osmannabadi goats reared under three management systems. In: Proceedings of the 7th International Conference on Goats, Tours, Frances, International Goat Association, Little Rock, AR, pp. 346–348. Leheska, J.M., Wulf, D.M., Claooer, J.A., Thaler, R.C., Maddock, R.J., 2002. Effects of high-protein/low-carbohydrate swine diets during
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the final finishing phase on pork muscle quality. J. Anim. Sci. 80, 137–142. Marino, R., Albenzio, M., Girolami, A., Muscio, A., Sevi, A., Braghieri, A., 2006. Effect of forage to concentrate ratio on growth performance, and on carcass and meat quality of Podolian young bulls. Meat Sci. 72, 415–424. May, S.G., Dolezal, H.G., Grill, D.R., Ray, F.K., Buchanan, D.S., 1992. Effects of days fed, carcass grade traits, and subcutaneous fat removal on post-mortem muscle characteristics and beef palatability. J. Anim. Sci. 70, 444–453. McMillin, K.W., Brock, A.P., 2005. Production practices and processing for value-added goat meat. J. Anim. Sci. 83 (E.Suppl.), E57–E68. Miller, M.F., Cross, H.R., Crouse, J.D., Jenkins, T.J., 1987. Effect of feed energy intake on collagen characteristics and muscle quality of matures cows. Meat Sci. 21, 287–294. Noakes, M.N., Nestle, P.J., Clifton, T.M., 1996. Modifying the fatty acids profile of dairy products through feedlot technology lowers plasma cholesterol of humans consuming the products. Am. J. Clin. Nutr. 63, 42–46.
Priolo, A., Micol, D., Agabriel, J., Prache, S., Dransfield, E., 2002. Effect of grass or concentrate feeding systems on lamb carcass and meat quality. Meat Sci. 62, 179–185. Realini, C.E., Duckett, S.K., Brito, G.W., Dalla Rizza, M., De Mattos, D., 2004. Effect of pasture vs. concentrate feeding with or without antioxidants on carcass characteristics, fatty acid composition, and quality of Uruguayan beef. Meat Sci. 66, 567–577. SAS Inst., 2000. SAS/STAT software. Release 8.2. SAS Inst. Inc., Cary, NC. Smith, G.C., Pike, M.I., Carpenter, Z.L., 1974. Comparison of the palatability of goat meat and meat from four other animal species. J. Food Sci. 39, 1145–1146. Smith, M.E., Kastner, C.L., Hunt, M.C., Kropf, D.H., Allen, D.M., 1979. Elevated conditioning temperature effects on beef carcasses form four nutritional regimes. J. Food Sci. 44, 158–163. Webb, E.C., Casey, N.H., Simela, L., 2005. Goat meat quality. Small Rumin. Res. 60, 153–166. Wilkinson, J.M., Stark, B.A., 1987. Commercial Goat Production. The BSP Professional Books, London, 159 pp.
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Chemical composition and quality characteristics of chevon from goats fed three different post-weaning diets J.H. Lee ∗ , B. Kouakou, G. Kannan Georgia Small Ruminant Research and Extension Center, Fort Valley State University, Fort Valley, GA 31030, USA Received 19 December 2006; received in revised form 23 October 2007; accepted 23 October 2007 Available online 18 December 2007
Abstract Thirty-six Boer × Spanish intact male goats (BW = 18 ± 0.8 kg; age 4 months) were used to determine the effects of dietary treatments on the chemical composition and quality characteristics of goat meat (chevon). Animals were allotted to three treatment groups (n = 12/treatment) with three pens for each treatment. Each pen of four goats was fed one of three dietary treatments for 90 d: (1) a hay diet, consisting of alfalfa (Medicago sativa) hay alone (H); (2) a 18% CP concentrate diet, consisting predominantly alfalfa meal and yellow corn (C); or (3) a combined diet, consisting of the hay diet for the first 45-d, followed by the concentrate diet (HC). At the end of the feeding trial, goats were slaughtered and Longissimus dorsi (LD) muscle and subcutaneous fat samples were obtained from each carcass to determine chemical and fatty acid compositions. Loin chops were used to evaluate color (CIE L* a* b* ), cooking loss, and Warner-Bratzler shear force (WBSF) values. The LD muscle from goats fed the H diet contained higher (P < 0.05) moisture (77.1 vs. 74.7%), but a lower (P < 0.05) total lipid (1.32 vs. 2.67%) than those from goats fed the C diet. However, the percentages of moisture and total lipid in the LD muscle from HC group were not statistically different from those fed either the H or C group. Compared with goats fed the H diet, goats fed the C diet had: (1) a higher (P < 0.05) level of oleic acid (C18:1n9; 43.9 vs. 38.7%), but a lower (P < 0.05) level of linolenic acid (C18:3n3; 0.12 vs. 0.46%) in the LD muscle lipid; (2) a higher (P < 0.05) level of linoleic acid (C18:2n6; 4.27 vs. 3.11%), but lower (P < 0.05) levels of myristic acid (C14:0) and C18:3n3 (0.44 vs. 0.76%) in the subcutaneous fat. The L* (lightness) and b* (yellowness) values of loin chops from goats fed the H diet were higher (P < 0.05) than those fed the C diet; however, a* values (redness) were not statistically different among the dietary treatments. The WBSF values and cooking losses were not influenced by the dietary treatments. The results indicated that chevon from the H diet had healthier nutritional properties compared with that from the C diet; however, the meat qualities were not different among the treatment groups. © 2007 Elsevier B.V. All rights reserved. Keywords: Goat; Hay; Concentrate; Fatty acid; Meat quality
1. Introduction The demand for goat meat (chevon) has been steadily increasing in recent years among ethnic populations and ∗
Corresponding author at: Fort Valley State University, Agricultural Research Station, 1005 State University Drive, Fort Valley, GA 31030, USA. Tel.: +1 478 827 3077; fax: +1 478 825 6376. E-mail address: [email protected] (J.H. Lee). 0921-4488/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2007.10.003
health conscious consumers, although domestic chevon production is relatively limited compared to other red meats (beef and lamb) in the United States (James and Berry, 1997). The scientific evidences and recommendations by health professionals have increased the concerns about the negative effects of dietary saturated fat to human health and prompted the development of low-fat meat products in the U.S. (James and Berry, 1997). Chevon is particularly attractive to health
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conscious groups due to its lower fat contents compared to other types of red meat and thereby provides an excellent source of low-fat meat entrees (James and Berry, 1997). Development of processed products will expand the existing consumer base in the U.S. However, the seasonal limitations of breeding and forage availability on meat goat production affect the market value of chevon in the U.S. (McMillin and Brock, 2005). The production costs greatly influence the profit margin of meat goat enterprises. Feed cost makes up 50–70% of the total expenditures in livestock production (Wilkinson and Stark, 1987). Meat goats are fed most of their required nutrients from forages to increase the profit to the producers; however, pasture-based production systems have a limitation because of the effect of seasonal variation on the nutrient contents. This often means pasture alone does not always provide adequate nutrition for fast growing animals (Wilkinson and Stark, 1987). On that account, additional protein and energy (hay or concentrate) are offered to maintain acceptable goat performance. Young animals fed either hay alone, hay followed by concentrate, or concentrate alone, just after weaning, may have different performance characteristics and thereby influence the composition and quality of chevon. Different forms and energy levels of diets influence carcass composition and meat properties in food animals (McMillin and Brock, 2005). Meat goats with high-energy intake increased the juiciness, tenderness, and texture of chevon, but the consumer acceptability was lower because of the higher content of fat in meat than that from goats finished on roughage diets (McMillin and Brock, 2005). Carlucci et al. (1998) reported that meat from goats grazed and fed a commercial pellet was more tender and juicier than that from goats fed hay and a commercial pellet. Data on the effects of feeding treatments on chevon quality are limited. The objective of this research was, therefore, to determine the effect goat diet (a hay, concentrate-, or hay followed by concentrate-diet) on chemical composition and quality characteristics of chevon. 2. Materials and methods 2.1. Feeding trials and meat sampling Experimental procedures involving animals were conducted with the approval of the Fort Valley State University (FVSU) Institutional Animal Care and Use Committee. Thirtysix weaned crossbred (Boer × Spanish; 4-month-old) intact male goats (18 ± 0.8 kg, BW) were assigned in a completely randomized design to a feeding trial consisting of three dietary treatments. Each treatment was replicated in three pens, with
Table 1 Ingredients and chemical composition of hay and concentrate diets Item
Ingredient (%) Alfalfa hay Alfalfa meal Yellow corn Soybean meal, 44% TM salt (red salt) Vitamin premix Poultry fat
Diet Hay
Concentrate
100 – – – – – –
– 50.2 35.0 8.8 0.50 0.50 5.00
Chemical composition (%) Dry matter (DM) Crude protein (CP) Ether extract Ash Acid detergent fiber (ADF) Neutral detergent fiber (NDF)
91.7 17.3 2.4 5.9 34.0 45.0
93.6 18.0 7.1 6.5 4.0 29.0
Fatty acid methyl ester (%) C12:0 C13:0 C13:1n9 C14:0 C14:1n5 C15:0 C16:0 C16:1n7 C17:0 C18:0 C18:1n9 C18:2n6 C18:3n3 C20:0 C20:1n9 C20:5n3 C22:0 C22:5n3
0.27 0.23 2.70 0.79 0.14 0.48 20.97 1.67 0.47 3.94 10.00 19.90 21.66 1.16 1.05 0.45 1.15 0.84
0.07 – 0.27 0.49 0.11 0.11 21.32 5.09 0.16 4.86 33.70 25.08 3.69 0.30 0.04 0.09 0.10 0.16
four goats per pen. Experimental animals were housed in feeding pens located at the Georgia Small Ruminant Research and Extension Center, FVSU. Pens were in a closed barn, and each goat was provided 1.25 m2 of floor space with ad libitum access to water. Each pen of four goats was fed one of three dietary treatments for a 90-d feeding period: (1) a hay diet, consisting of alfalfa (Medicago sativa) hay alone (H); (2) a 18% CP concentrate diet (Table 1), consisting predominantly of alfalfa meal, yellow corn, and soybean meal (C); or (3) a combined diet, consisting of the hay diet for the first 45-d, followed by the concentrate diet (HC). In the feeding period, feed was provided ad libitum and the experimental animals (n = 36) were weighted individually biweekly. At the conclusion of the feeding trial, the goats were slaughtered using standard procedures and carcasses kept at 2 ◦ C for 24 h before dissection. Dressing percent or carcass yield of each carcass was reported as that proportion (percentage) of the live
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weight that remains in the carcass. After 24 h of cooling, the carcasses were dissected with each carcass split along the vertebral column into left and right halves, and then sliced into 2.5 cm loin chops using a band saw. Four loin chops (Longissimus dorsi, LD muscle) from the right side of each carcass and subcutaneous fat were removed from the pelvic area and sampled. All the samples were ground in liquid nitrogen, placed in polyethylene bags (NASCO Inc., Fort Atkinson, WI), and stored at −28 ◦ C for proximate and fatty acid analyses. Four more chops from the right side of each carcass were also used to analyze thiobarbituric acid reactive substances (TBARS) and total collagen content. Chops from left side of each carcass were allotted for analysis of color (CIE L* a* b* ), WarnerBratzler shear force (WBSF) values, and cooking losses. 2.2. Chemical composition Proximate composition of LD muscle samples was analyzed according to AOAC (1995) methods. Moisture and ash contents (%) were determined by the oven-drying (AOAC, 950.46) and furnace methods (AOAC, 942.05), respectively. The ether extraction method (AOAC, 920.39) was used to determine total lipid content (%) in the muscle samples. Protein content (%) was estimated by a carbon/nitrogen analyzer (Vario Max CN Elementar Americas Inc., Mt. Laurel, NJ, USA). Total lipids were extracted from either 2.0 g of muscle or 0.2 g of fat samples with chloroform/methanol (2:1 v/v) according to Cherian et al. (1996) using a homogenizer (Cyclone IQ2 , The Virtis Co., Gardiner, NY) for 3× 30 s at 30,000 rpm. The fatty acid composition of the total lipids extracted from each sample was determined by the following preparation. Extracted lipid was saponified and esterified according to the AOCS method (1993) of preparation of fatty acid methyl esters (FAME). The prepared FAME were analyzed using a Hewlett Packard 5890 Series II gas chromatograph (GC), equipped with an automatic sampler HP 7673 (Agilent Technologies Inc., Palo Alto, CA, USA). A 0.25-mm i.d. by 30-m long fused silica SP2330 capillary column (Supelco Inc., Bellefonte, PA, USA) was used to separate the methyl esters, which were detected with a flame ionization detector (FID). The injection temperature was 250 ◦ C, and the column temperature was programmed from 130 to 220 ◦ C at 2 ◦ C/min. Helium was the carrier gas with a flow rate at 30 mL/min, and a split ratio of 30:1. The identification of individual FAME in the sample was achieved by matching the retention time of the unknown FAME with that of known FAME standard mixtures (Alltech Associates Inc., Deerfield, IL; Sigma–Aldrich Corp., Bellefonte, PA, USA). For quantitative analysis of the sample FAME, standards containing known weight percentages of individual FAME, present in levels similar to those in the samples, were analyzed by the GC, and the correction factors relative to palmitic (C16:0) acid were calculated according to the AOCS (1993) for fatty acid analysis. The area of individual sample FAME was corrected using its correction factor. The relative weight percentages of each FAME (C10:0:-C22:6) in each sample were then calculated using their corrected areas (AOCS, 1993).
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2.3. Quality characteristics of loin chops The TBARS assay was performed as described by Buege and Aust (1978). The ground muscle sample (0.5 g) was mixed with 2.5 mL of 0.375% thiobarbituric acid-15% trichloroacetic acid-0.25 N HCl stock solution in a glass test tube. The mixture was heated for 10 min in a boiling water bath (∼100 ◦ C) to develop a pink color. The test tube was cooled with tap water and then centrifuged at 5500 rpm for 25 min. Absorbance of supernatant was measured at 532 nm using a Shimadzu (Model UV-2401 PC) spectrophotometer (Shimadzu Corporation, Columbia, MD, USA). The TBARS were calculated from a standard curve of malondialdehyde (MDA) and expressed as mg MDA/kg sample. Hydroxyproline concentrations were determined using the procedures of Bergman and Loxley (1963) and the total collagen concentrations were expressed in mg/g dry muscle. The L* , a* , and b* color coordinate values were measured on the cut surfaces of loin chops from left side of each carcass after a 30-min bloom time at 4 ◦ C using a HunterLab color instrument with illuminant D65 as the light source. Three measurements were taken from each sample. The average of the three measurements was recorded as color coordinate value of the sample. Hue angle was calculated as tan−1 (b* /a* ), whereas chroma (a measure of color vividness) was calculated as (a*2 + b*2 )1/2 (Hunter and Harold, 1987). After measuring color coordinate values, the chops were vacuum-packed, frozen, and stored at −28 ◦ C until assessment of tenderness and cooking loss. The cuts were thawed at 4 ◦ C and cooked according to the procedures described by Kannan et al. (2002). Briefly, the chops were cooked in a convection oven (Maytag Corporation, Model MER6550B, Newton, IA, USA) to an internal temperature of 71 ◦ C. The internal temperature was measured in a representative chop from each pan using thermocouple thermometers (Fisher Scientific, Suwannee, GA, USA). In a randomly chosen cut from each pan, the thermocouple probe was placed in the geometric center of the LD muscle. Cooked samples were wrapped in aluminum foil and cooled at 4 ◦ C overnight before core removal. The cuts were allowed to come to room temperature by removing them from the refrigerator and placing them on a laboratory countertop for 2 h, and then 1-cm diameter cores were removed parallel to muscle fiber orientation (Kannan et al., 2002). Two cores were taken from each chop and WBSF values assessed using a TA-XT2 texture analyzer fitted with a Warner-Bratzler shear attachment (Texture Technologies Corp., Scarsdale, NY, USA). The instrument was set with a 25-kg load cell and a cross-head speed of 200 mm/min. The difference in weight of samples before and after cooking was expressed as percentage cooking loss. 2.4. Statistical analysis All data were analyzed as a completely randomized design using the GLM procedure of SAS (2000), with individual goats as the experimental units. Least squares means were generated
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Table 2 Proximate composition of Longissimus muscles from goats fed three different diets Component (%)
Moisture Protein Total lipid Ash
Diet
S.E.
H
C
HC
77.09 a 20.78 1.32 b 1.32
74.70 b 21.30 2.67 a 1.38
75.79 ab 20.10 2.02 ab 1.62
0.89 0.41 0.35 0.15
H: hay for 45-d; C: concentrate for 45-d; HC: hay for 45-d plus concentrate for 45-d. Within a row, least squares means that do not have a common letters differ (P < 0.05).
and separated using the PDIFF options of SAS (pairwise t-test). Significant effects were determined at P < 0.05, but differences with P < 0.1 were considered as trends.
3. Results and discussion 3.1. Body weight gain and carcass yield Daily weight gain by the goats was different (P < 0.01) among the experimental diets. The average daily gains (ADG) were 41.4, 134.3, and 64.7 (S.E. = 12.55) g/d for H, C, and HC diets, respectively. Goats fed the C diet gained more weight per day than those fed either the H or HC diet; however, no significant difference was found in the ADG of goats on H and HC diets. Differences (P < 0.01) were also observed in the mean (±S.E.) final live weight, which was greater for the goats fed C diet (30.3 ± 1.39 kg) than for the goats fed either the H or HC diet (21.6 or 22.7 ± 1.39 kg). However, no significant differences were found in the carcass yields of the goats fed the three experimental diets. The mean carcass yield ranged from 37.5 to 38.7%. In general, animals on concentrate-based diets have higher average daily gains than those on pasture (Realini et al., 2004; Haddad, 2005). Carcasses from cattle finished on concentrate were heavier than those finished on pasture (Realini et al., 2004). Goats on high-energy diets had heavier body weight than those on low-energy diet and increased concentrate to forage ratios also increased the weight gain and final body weight of goats (Haddad, 2005). 3.2. Chemical composition Proximate compositions of LD muscles from goats fed the experimental diets are presented in Table 2. No significant differences were found in the protein and ash contents in the LD muscles of goats fed the experimental diets. However, goats fed the C diet had lower (P < 0.05)
amounts of moisture in the LD muscles than those fed the H diet, but had a higher (P < 0.05) total lipid content. No significant differences were found in the moisture and total lipid contents in the LD muscles of goats fed either the C or HC diet. The lower moisture content in the LD muscle from the goats fed the C diet is due to the higher lipid content in this group compared to the goats fed the H or HC. Numerous studies reported higher muscle fat contents in animals that received higher proportions of concentrate in the diet (French et al., 2001; Geay et al., 2001). The LD muscle fat content of concentratefed steers was twofold greater than pasture-fed steers (Marino et al., 2006). The fatty acid composition of the LD muscle and subcutaneous fat from goats fed the experimental diets is presented in Table 3. Nineteen fatty acids were identified in lipids extracted from LD muscle and subcutaneous fat, which consisted of nine saturated (C10:0, C12:0, C14:0, C15:0, C16:0, C17:0, C18:0, C20:0, and C22:0), five monounsaturated (C13:1n9, C14:1n5, C16:1n7, C18:1n9, and C20:1n9), and five polyunsaturated (C18:2n6, C18:3n3, C20:4n6, C20:5n3, and C22:5n3) fatty acids. The major fatty acids in the LD muscle lipids from H-, C-, and HC-fed goats were palmitic (C16:0), stearic (C18:0), and oleic (C18:1n9) acids, which accounted for 73.1, 75.3, and 71.4% of total fatty acids, respectively. In general, meat from pasturefed animals contains a similar proportion of saturated fatty acids, a lower concentration of monounsaturated fatty acids, and a higher percentage of polyunsaturated fatty acids than that from concentrate-fed animals (Webb et al., 2005; Marino et al., 2006). In the present study, the LD muscle lipid from goats fed the C diet contained a lower concentration of saturated fat (36.4 vs. 41.0%) and a higher concentration of monounsaturated fat (42.8 vs. 48.0%) than that from H-fed goats (Table 3). Among the saturated fatty acids (SFA), goats fed the H diet had higher (P < 0.05) percentages of pentadecanoic (C15:0) and margaric (C17:0) acids in LD muscle lipids than those fed the C or HC diet; however, no significant difference was found in margaric acid (C17:0) between goats fed H and HC diets. Saturated fatty acids such as lauric (C12:0), myristic (C14:0), and palmitic (C16:0) acids raise the LDL-cholesterol concentrations in blood, increasing the risk of cardiovascular diseases (Noakes et al., 1996). These three LDL-cholesterol increasing fatty acids made up 24.2, 23.5, and 22.8% of total fatty acids in the LD from goats fed H, C, and HC diets, respectively. Of the monounsaturated fatty acids (MUFA), the mean concentration of oleic acid (C18:1n9) of the LD muscle lipids of goats that consumed the C diet was higher (P < 0.05) than that of goats fed either the H or HC
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Table 3 Fatty acid composition of intramuscular and subcutaneous fat of goats fed three different diets Fatty acid (%)
C10:0 C12:0 C13:1n9 C14:0 C14:1n5 C15:0 C16:0 C16:1n7 C17:0 C18:0 C18:1n9 C18:2n6 C18:3n3 C20:0 C20:1n9 C20:4n6 C20:5n3 C22:0 C22:5n3
Intramuscular fat
S.E.
H
C
HC
0.17 0.17 0.09 2.16 0.52 0.70 a 21.87 3.38 1.75 a 12.49 38.73 b 6.93 0.46 a 0.07 0.12 4.65 0.45 1.57 0.37
0.17 0.14 0.06 2.00 0.29 0.47 b 21.40 3.69 1.35 b 10.01 43.85 a 7.92 0.12 b 0.05 0.11 3.46 0.38 0.83 0.37
0.15 0.14 0.06 1.77 0.42 0.51 b 20.60 3.24 1.69 a 11.69 39.12 b 7.07 0.19 b 0.08 0.16 4.19 0.59 1.90 0.63
0.04 0.03 0.01 0.15 0.11 0.06 0.68 0.27 0.10 1.33 1.45 0.61 0.15 0.02 0.05 1.16 0.14 0.62 0.26
Subcutaneous fat
S.E.
H
C
HC
0.20 a 0.21 0.20 a 3.19 a 0.33 1.12 a 25.03 3.40 2.85 a 22.83 36.18 3.11 b 0.76 a 0.01 0.23 a 0.49 0.33 0.09 a 0.18 a
0.10 b 0.08 0.06 c 2.40 b 0.04 0.51 c 25.00 3.03 1.85 b 23.52 39.32 4.27 a 0.44 b 0.01 0.03 b 0.21 0.07 0.04 b 0.09 b
0.16 ab 0.16 0.12 b 2.57 b 0.06 0.76 b 23.95 3.22 2.60 a 23.07 38.62 3.99 ab 0.52 b 0.01 0.05 b 0.39 0.13 0.05 b 0.10 b
0.02 0.05 0.02 0.20 0.09 0.08 0.74 0.30 0.16 1.85 1.47 0.23 0.11 0.00 0.08 0.11 0.09 0.01 0.02
H: hay for 45-d; C: concentrate for 45-d; HC: hay for 45-d plus concentrate for 45-d. Within a row, least squares means that do not have a common letters differ (P < 0.05).
diet. However, no significant difference was detected in the oleic acid (C18:1n9) concentration of the LD muscle lipid from goats fed the H or HC diet. Goats fed the H diet had higher (P < 0.05) levels of linolenic acid (C18:3n3) in LD muscle lipids than goats fed either the C or HC diet; however, there were no differences in the concentrations of linolenic acid (C18:3n3) in the LD muscle lipids between the goats fed C and HC diets. Current recommendations are that the PUFA:SFA (P:S) ratio should be around 0.45 (Webb et al., 2005). The P:S ratios in this study were lower than the recommended ratio, being 0.31 for H-fed, 0.34 for C-fed, and 0.32 for HC-fed goats. Duckett et al. (1993) reported a higher P:S ratio (0.26) for beef from grass-finished steers than for meat from concentrate-finished animals (0.07). The major fatty acids in the subcutaneous fat from goats fed the experimental diets were also palmitic (C16:0), stearic (C18:0), and oleic (C18:1n9), which made up 84.0, 87.8, and 85.6% total fatty acids in H-, C-, and HC-fed goats, respectively. No significant differences were found in the concentrations of total SFA, MUFA, or PUFA in the subcutaneous fat from goats fed H, C, or HC diet (Table 3). Among the SFA in the subcutaneous fat, there were significant differences in the mean concentrations of decanoic (C10:0), myristic (C14:0), pentadecanoic (C15:0), margaric (C17:0), and docosanoic (C22:0) acids among the goats fed the exper-
imental diets. The concentrations of these five fatty acids in the subcutaneous fat of goats fed the H diet were higher (P < 0.05) than in the subcutaneous fat of goats fed the C diet. However, no significant differences were observed in decanoic (C10:0), myristic (C14:0), or docosanoic (C22:0) acid concentrations between goats fed C and HC diets. The mean concentrations of pentadecanoic (C15:0) and margaric (C17:0) acids in the subcutaneous fat of goats fed the C diet were lower (P < 0.05) than in the subcutaneous fat of goats fed the HC diet. Concentrations of subcutaneous MUFA were not statistically different among goats fed the experimental diets, except tridecenoic (C13:1n9) and eicosaenoic (C20:1n9) acids. Concentrations of tridecenoic (C13:1n9) and eicosaenoic (C20:1n9) of the subcutaneous fat of goats fed the H diet were higher (P < 0.05) than those of goats fed either the C or HC diet; however, no significant difference was detected in the eicosaenoic (C20:1n9) acid concentration of the subcutaneous fat between goats fed C and HC diets. Goats fed the H diet had higher (P < 0.05) levels of linolenic (C18:3n3) and docosatrienoic (C22:5n3) acids in subcutaneous fat than goats fed either the C or HC diet. Similar to muscle fat, there were no significant differences in concentrations of linolenic (C18:3n3) and docosatrienoic (C22:5n3) acids in subcutaneous fat between goats fed C and HC diets. Concentration of linoleic (C18:2n6)
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Table 4 Quality characteristics of loin color (L* , a* , b* , chroma, and hue angle), thiobarbituric acid reactive substances (TBARS), total collagen, cooking loss, and Warner-Bratzler shear force (WBSF) values of loin chops from goats fed three different diets Item
Color L* value a* value b* value Chroma value Hue angle TBARS Total collagen (mg/kg) Cooking loss (%) WBSF (kg)
Diet
S.E.
H
C
HC
43.57 a 9.34 12.45 a 15.41 51.78 a
39.81 b 9.91 11.09 b 14.63 47.30 b
42.17 ab 9.89 11.88 ab 15.22 49.37 ab
1.26 1.04
1.18 0.95
1.19 0.98
0.08 0.10
22.66 3.79
28.83 3.73
25.65 3.10
3.11 0.44
1.10 0.54 0.32 0.39 1.72
H: hay for 45-d; C: concentrate for 45-d; HC: hay for 45-d plus concentrate for 45-d. Within a row, least squares means that do not have a common letters differ (P < 0.05).
acid of the subcutaneous fat of goats fed the C diet was higher (P < 0.05) than that of goats fed the H diet, but no difference was detected in the linoleic (C18:2n6) acid concentration of the subcutaneous fat between goats fed H and HC diets. 3.3. Quality characteristics of chevon chops Sensorial characteristics of the chevon chops from goats fed the experimental diets are presented in Table 4. The dietary treatments had significant influences on the LD muscle L* (lightness) and b* (yellowness) values, but not in the a* value (redness). The LD muscle color was lighter (higher L* value; P < 0.05) in the goats fed H diet than those fed the C diet; however, no difference was found in the L* values between goats fed H and HC. Goats fed the H diet also had higher b* (P < 0.05) values in the chops than the goats fed the C diet. However, the b* values of the LD muscles of goats fed the H diet was not different from those fed the HC diet. There were no significant differences in chroma values of the LD muscle from goats fed the experimental diets. However, the hue angle was higher (P < 0.05) in the H group than in the C group. No difference was found in the hue angle between goats fed H and HC diets. Fresh meat color is an important criterion for judging freshness and quality by consumers. Chevon has lower lightness and higher redness than lamb because of the lower intramuscular fat of goat carcasses (Babiker et al., 1990); however, consumers cannot readily perceive the differences between chevon and lamb. Previous researchers
reported that Longissimus muscle of ruminants fed on low-energy diets had a darker colored lean (lower L* values) than those fed high-energy diets (Priolo et al., 2002; Realini et al., 2004). Meat from grass fed lambs was darker (P < 0.05) in color than that from concentrate-fed lambs (Priolo et al., 2002). Steers finished on pasture also had darker Longissimus muscle compared to concentrate finished steers (Realini et al., 2004). However, no differences were found in the instrumental color values of the Longissimus muscle of steers fed on different combinations of forage-concentrate diets for a short period (French et al., 2001). This suggested that in order for the diet to influence meat color, the feeding period should last for an extended period. Dietary treatments did not have significant effects on TBARS values (Table 4). The reaction of malondialdehyde (MDA) with 2-thiobarbituric acid (TBA) is widely used for measuring the extent of oxidative deterioration of lipid in muscle foods (Gray, 1978). Lipid oxidation results in the production of free radicals, which may lead to the oxidation of meat pigments and generation of rancid odors and flavors (Faustman and Cassens, 1990). In the present study, lipid oxidation of meat was not affected by dietary treatments. The results agree with the findings of Marino et al. (2006). Nutritional factors can influence the functional property of collagen. Miller et al. (1987) reported that mature cows fed a high-energy diet for 84 d prior to slaughter produced meat with a higher percentage of heat-labile collagen and lower shear values compared to meat from cows fed a maintenance-energy diet. In contrast, Crouse et al. (1985) found that muscle from cattle fed a highenergy diet contained more soluble collagen, and the meat was less tender compared to cattle fed a low-energy diet. In the present study, dietary treatments did not affect total collagen content of goat LD muscle measured at 24 h postmortem (Table 4). The results of this study are in agreement with those of Kannan et al. (2006), who found that meat from goat fed either a high- or lowenergy diet were not different in the collagen content and solubility. Dietary treatments did not have any effect on the cooking loss of chevon chops (Table 4). Leheska et al. (2002) reported that dietary treatment did not influence drip loss and cooking loss in pork. Juiciness of meat is directly related to the intramuscular lipids and moisture content of the meat, but the water remaining in the cooked product is the major contributor to the sensation of juiciness during eating (Cross et al., 1986). Chevon and its products are reportedly less juicy than lamb and lamb products, a quality attributed to the lower fat content of chevon.
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Evaluation of factors affecting meat tenderness is particularly important in chevon because of its lower tenderness than lamb and beef (Smith et al., 1974). However, the tenderness value of chevon is often in the acceptable range (Webb et al., 2005). The acceptable limit for lamb tenderness is about a 3 kg Warner-Bratzler shear force to Australian and New Zealand consumers (Webb et al., 2005). Shear force values depend on factors such as the treatment of the animals prior to slaughter, postmortem methodologies, the sampled muscle and method of sample preparation (Webb et al., 2005). Warner-Bratzler shear force (WBSF) values of chevon chops after the 24 h postmortem was not influenced by dietary treatments (Table 4). Similar results were reported by Smith et al. (1979) in cattle, who found that nutritional regime did not cause any change in the shear values of steaks. Several researchers found that implementation of a short finishing period or an increase in concentrate proportion during this period had no effect on meat tenderness (French et al., 2001). May et al. (1992) found a longer period was necessary to observe a decrease in WBSF. In these works, the decrease in WBSF was accompanied by an increase in marbling and carcass fatness. Intensive management with high-energy intake by goats increased the juiciness, tenderness, and texture of the chevon, but general acceptability was lower than with grazing systems because the meat had higher fat (Karanjkar et al., 2000). 4. Conclusion Feeding meat goats with a concentrate diet increased the body weight compared with goat fed hay only or hay followed by concentrate feeding, but did not change the carcass yield and quality of chevon. Concentratefed goats had a darker longissimus muscle color than hay-fed goats. Edible tissues from goats fed a concentrate diet had a higher amount of fat than those from goats fed a hay diet. Goats receiving hay, concentrate, or hay followed by concentrate ration did not influence the intramuscular fatty acid profile, which is of interest from a human health perspective. The characteristics related to tenderness of chevon were not affected by the dietary treatments. There may not be any merit in increasing production cost by feeding all concentrate diet to meat goats after weaning, since the diet did not influence meat quality characteristics in this study. References AOAC, 1995. Official Methods of Analysis of the AOAC International, 16th ed. Association of Official Analytical Chemists, International, Gaithersburg, MD.
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