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Analysis of the Nutritional Content of Myocastor coypus
(2000) 13, 117}125 doi:10.1006/jfca.1999.0865 Available online at http://www.idealibrary.com on
JOURNAL OF FOOD COMPOSITION AND ANALYSIS
ORIGINAL ARTICLE Analysis of the Nutritional Content of Myocastor coypus Richard T. Tulley* , Fatemeh M. Malekian*, Jennifer C. Rood*, Mary B. Lamb*, Catherine M. Champagne*, Stephen M. Redmann Jr*, Ruth Patrick*, Noel Kinler-, and C. T. Raby? *Pennington Biomedical Research Center, Baton Rouge, LA 70808-4124, U.S.A.; -Louisiana Department of Wildlife and Fisheries, New Iberia, LA 70560, U.S.A.; and ?Louisiana State Department of Agriculture and Forestry, Baton Rouge, LA 70821, U.S.A. Received May 4, 1998, and in revised form December 8, 1999
The present investigation was designed to determine the nutritional content of Myocastor coypus (nutria). Proximates, total petroleum ether extractable fatty acids, cholesterol, iron, sodium, calcium, vitamins A and C were determined. In comparing male versus female and young versus old nutria there were no di!erences in protein and moisture; however, there were signi"cant di!erences in total petroleum ether extractable fat, ash, and cholesterol content. Average results for meat from all animals were 1.3 g for total petroleum ether extractable fat, 1.0 g ash, 22.1 g protein, 36 mg for cholesterol, 1.7 mg for iron, 67 mg for sodium, and 5.2 mg for calcium per 100 g wet weight. Nutria petroleum ether extractable fat was generally richer in saturated (43%) than mono (33%) and polyunsaturated fat (24%). As expected, nutria was not a good source of vitamins A and C. In summary, nutria is an excellent nutritional source of protein which is low in fat and cholesterol. Thus, nutria meat provides a healthy alternative food which complies with current healthy and dietary recommendations for low fat, low cholesterol diets. 2000 Academic Press
Key =ords: nutria; nutritional content; fat; cholesterol; fatty acids.
INTRODUCTION Myocastor coypus (nutria) is a small herbivorous animal which is indigenous to South America and is also quite prevalent in the marshes of the southeastern United States, having been brought to the United States from South America to Avery Island, Louisiana in the 1930s. The animals escaped and since have spread across the southeastern United States (McCann et al., 1996). The nutria belongs to the same animal order as the squirrel. It is similar to, but smaller than the North American beaver, and hence is sometimes called the swamp beaver. The total length of the animal is 50}80 cm, of which the tail comprises 30} 50 cm. The nutria is entirely vegetarian (Kinsel, 1958). Its intestinal tract is designed so that it can eat large amounts of foods which are not easily digested, such as its main sources of food, water plants and reeds. The nutria has devoured large areas of marshland in south Louisiana which has led to the destruction of levees and coastal To whom correspondence and reprint requests should be addressed. Tel. 504-763-2524. Fax: 504-7632525. E-mail: [email protected] 0889}1575/00/020117#09 $35.00/0
2000 Academic Press
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erosion. Nutria are posing an ecological problem in many other southeastern states in the United States such as Texas and Oregon, and even as far away as Thailand. For this reason, o$cials have begun to look for ways to increase the value of the nutria, thereby providing an economic incentive to trappers to increase the harvest of nutria. Nutria have long been used as a food source in their native South America and also in parts of Europe and Asia (Grzimek, 1975). In the 1960s, the Louisiana State University Agricultural Experiment Station published a booklet containing information on the collection, preparation, and cooking of nutria (Glasgow and McCollough, 1963). Also included were numerous recipes. With the widespread availability of common meat sources, nutria meat has not been utilized to its full potential. Recently, there has been renewed interest because of the detriment the nutria poses to the environment and also because of its potential to provide the public with an inexpensive alternative meat source. Although the nutritional quality of nutria has been reported by others (Bugawva and Dimitroski, 1987; Kostron and Kukla, 1969; Niedzwiadek et al., 1986; Palanska et al., 1985; Sperber et al., 1982), those analyses were performed on farm-raised animals and/or in Europe. There is a scarcity of data on the species which is indigenous in Louisiana swamps and bayous. It would be expected that the diet of these animals is substantially di!erent than that of farm-raised animals leading to di!erences in the nutrient content of the meat. Therefore, the object of this study was to determine the nutritional content of meat from wild nutria and to compare it to other meat sources. MATERIALS AND METHODS Reagents Petroleum ether, sodium hydroxide, iso-octane, potassium hydroxide, cyclohexane, Ultrex nitric acid, and ICP standards were obtained from J. T. Baker (Phillipsburg, NJ). Ethanolic pyrogallol was purchased from Baddley Chemical Inc. (Baton Rouge, LA). Boron tri#uoride (14% w/v)/methanol solution, ascorbate oxidase, and ophenylenediamine were purchased from Sigma Chemical Company (St. Louis, MO). Sodium chloride was obtained from CMS (Houston, TX) and pyridine from Pierce Chemical Company (Rockford, IL). Otawa sand and 26 mm cellulose "ber thimbles were purchased from Fisher Scienti"c (Pittsburgh, PA). Bis(trimethylsilyl)-tri#uoroacetamide (BSTFA) containing 1% w/v TMCS (Regisil, Alltech Assoc., Inc., Deer"eld, IL) was purchased from Alltech (Dear"eld, IL). Dithiothreitol was purchased from Aldrich Chemical Company (Milwaukee, WI). C:23:0 methyl ester and 5-alpha cholestanol were obtained from NuCheck Prep, Inc. (Elysian, MN). Capture and Slaughter A total of 63 nutria were captured by hand, utilizing airboats and a long-handle net, on the Marsh Island Wildlife Refuge, Iberia Parish, LA. Once captured, animals were placed in individual holding cages and transported to the New Iberia Field O$ce of the Louisiana Department of Wildlife and Fisheries. Animals were captured on December 14, 1994 and processed on the next day. Nutria were sacri"ced and immediately sexed, tagged, and weighed to the nearest 10 g. The skin was removed, animal eviscerated, and the remaining carcass weighed. The carcass was deboned and the resulting meat defatted by removing the small amount of subcutaneous fat present. Although all major muscle groups were deboned (hind legs, front legs, and back strap), a small amount of meat remained on the carcass.
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The deboned sample of meat was weighed (to the nearest 2 g) and packaged in labeled ziplock storage bags. The meat samples and corresponding data were delivered to the Pennington Biomedical Research Center, frozen on dry ice, and stored at !203C (1}2 days) until composited. Compositing Prior to compositing, the meat samples were arranged into four groups based on age and sex of the animals from which they were obtained. The animals heavier than 4000 g total weight were classi"ed as &&adult'' with the remainder classi"ed as &&young''. The four groupings were young males, young females, adult males, and adult females. The meat from three animals was used to form a composite for each group. For economical reasons, the meat from 42 of the 63 animals was included in this study. A total of 14 composites representing 42 animals were made as follows: 3 groups of young males, 4 groups of young females, 4 groups of adult males, and 3 groups of adult females. The meat samples were removed from the freezer and placed overnight in the refrigerator at 43C to thaw, then cut into pieces measuring 8}10 cm with a stainlesssteel bladed knife and homogenized using a Robot Coupe Model R-2 food processor (Ridgeland, MS). The homogenized samples were then aliquoted into glass jars and frozen at !203C until the day of analysis. Analyses Quality control. Quality control samples were prepared from mixed food samples which were blended and homogenized until they were homogeneous, and then divided into aliquots in 20 mL glass bottles. These bottles were then capped and stored at !803C. On each day of analysis, a glass bottle containing the pooled food control was removed from the ultralow freezer, thawed, and analyzed in triplicate for each analyte reported. Values for all analytes had to be within two standard deviations of the mean for an analysis to be accepted. ;nits. All values were analyzed on a wet basis and results expressed as per 100 g wet wt. ¹otal petroleum ether extractable fat. Total petroleum ether extractable fat was determined gravimetrically according to AOAC method number 945.16 using petroleum ether on a Soxtec fat extraction apparatus (Tecator, Spring"eld, MD). The dried fat extract was dissolved in 20 mL of petroleum ether and divided into two fractions. One fraction was used for the determination of cholesterol and the other for fatty acid analysis. Reproducibility measurements for the fat measurement resulted in a coe$cient of variation of 4.2% at a level of 3.87 g/100 g. Protein. Protein was determined using thermal conductivity on a Model 2410 Nitrogen Analyzer (Perkin Elmer, Norwalk, CT) according to AOAC method number 992.15. Protein was calculated from nitrogen content by using a factor of 6.25. The coe$cient of variation (cv.) for this assay is 10.8% at 4.0 g/100g protein. Ash. Ash was determined using a microwave mu%e furnace (MAS 7000, CEM, Matthews, NC) according to AOAC method number 920.153. At a mean of 0.6 g/ 100 g the cv. for this assay is 14.3%.
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Moisture. Moisture was determined automatically on a Lab Wave 9000 microwave solid analyzer (CEM, Matthews, NC) (AOAC C985.14). At a mean of 0.6 g/100 g reproducibility of this method showed a cv. of 0.3%. ¹otal petroleum ether extractable fatty acids. Fatty acids in the petroleum ether extract were determined by gas chromatography of the fatty acid methyl esters according to a modi"cation of an AOCS method (Firestone, 1993). The composition of the fatty acid methyl esters were determined by gas chromatography on a HewlettPackard 5890 Gas Chromatograph (Atlanta, GA) using a fused silica capillary column (30;0.25 mm) with a 0.20 lm coating (C2-4110, Supelco, Inc, Bellefonte, PA). Individual fatty acids were quanti"ed and then grouped into the appropriate saturated (SFA), monounsaturated (MUFA), or polyunsaturated fatty acid (PUFA) categories. Coe$cient of variations for SFA, MUFA, and PUFA were 15.1, 16.0, and 19.6%, respectively, at 696, 872, and 650 mg/100 g. Petroleum ether extractable cholesterol. Cholesterol in the petroleum ether extract was analyzed by the method of Thompson and Merola (1993) on a Hewlett-Packard 5890 Gas Chromatograph (Atlanta, GA) using a fused silica capillary column (30;0.25 mm) with 0.25 lm coating (Supelco, Inc., Bellefont, PA). Reproducibility of the procedure shows a cv. of 4.0% at 10.7 mg/100 g. Sodium, calcium, and iron. Sodium, calcium, and iron were analyzed by inductively coupled plasma emission spectrometry (ICP) using a Perkin Elmer P1000 ICP (Norwalk, CT) following ashing on a MAS 7000 microwave mu%e furnace (CEM, Matthews, NC). Samples were ashed for 2}4 h at 5003C and diluted to 10 mL in a solution of 0.15 mol/L nitric acid. The samples were then "ltered through 0.2 lm syringe "lters (C77524 Uni#o 25, Schleicher and Schuell, Keen, NH). Each sample was analyzed in duplicate on the ICP which was calibrated on mixed standards of 1, 10, and 100 lg/mL in each mineral. Accuracy of sodium and calcium were veri"ed by using a commercially available assayed control (Bio Rad, Hercules, CA). This same material also served as instrumental quality control material. Calcium had cvs. of 3.5 and 4.4% at 62 and 114 mg/L, respectively; sodium's cvs. were 3.3 and 3.7% at 55 and 175 mmol/L, respectively.
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Statistics Statistics presented, including summary statistics (sample mean and S.D.) reported in Tables 2}5, were computed using SAS release 6.12 for Windows (SAS Institute Inc., Cary, NC). To make comparisons among age and sex categories for carcass component weights and for each of the chemical analytes, factorial analysis of variance (ANOVA) models were implemented in SAS. Stated signi"cance levels for comparisons among combinations of sex and age categories are adjusted using the Tukey} Kramer method to control the overall Type I error rate.
RESULTS AND DISCUSSION Analysis of Composites Table 1 lists the total weight, carcass weight, and weight of the meat for each sample used in the four composite groups (young male, young female, adult male, and adult female). Once selected, young nutria weighed less than or equal to 3790 g while adult nutria weighed greater than 4460 g. Table 2 presents the mean weights of each group. There were no signi"cant di!erences between the young male and young female groups for total weight, carcass weight, or meat weight as determined by TABLE 1 Makeup of nutria composite samples (n"3 for each group) Age Young Young Young Young Young Young Young Adult Adult Adult Adult Adult Adult Adult
Sex and no. (N"3)
Mean total weight (g)
Mean carcass weight (g)
Mean meat weight (g)
Male 1 Male 2 Male 3 Female Female Female Female Male 1 Male 2 Male 3 Male 4 Female Female Female
3020 2790 2900 3110 3470 3210 3000 5660 5730 5860 5840 5090 5130 5120
1485 1500 1385 1385 1625 1865 1335 3000 2845 2815 2795 2335 2335 2415
476 550 488 452 540 504 398 946 762 980 732 298 702 792
1 2 3 4
1 2 3
TABLE 2 Average weight of each group Total weight (g)
Carcass weight (g)
Meat weight (g)
Group
Mean
S.D.
Mean
S.D.
Mean
S.D.
Young male (N"9) Young female (N"12) Adult male (N"12) Adult female (N"9)
2903 3198 5772 5113
698 605 436 464
1453 1552 2864 2362
404 474 257 266
505 473 855 597
142 104 177 255
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Tukey}Kramer post-ANOVA tests. However, there were di!erences between adult males and females for total weight, carcass weight, and meat weight (P(0.05). The di!erences between the young and adult large groups within each sex were signi"cant for total weight and carcass weight (P(0.001), and for meat weight among males but not females (males: P(0.001, females: P"0.23). Table 3 lists proximate analysis for the nutria. There are no signi"cant di!erences between young and adult nutria for moisture and protein. Moisture (data not shown) and protein are very consistent between the sexes without regard to age. Signi"cant di!erences between young and old nutria are noted for petroleum ether extractable fat (P(0.005). Ash is higher in adult animals than in young animals (P(0.01) but the level is similar between males and females. Total petroleum ether extractable fat varies with sex and age, but generally ranges from 1.4 to 1.6 g/100 g, except in adult males, which have about half as much fat (0.8 g/100 g) as their younger counterparts and adult females. The decline in fat with age in male nutria may be due to an increase in male sex hormones as the animals mature. These hormones are known to increase lean body mass and decrease fat levels. Fat levels in females do not di!er signi"cantly with age. Fat contributes 52}58 kJ/100 g in all groups except for adult males, in which fat generates 29 kJ/100 g. Table 4 shows the breakdown for petroleum ether extractable cholesterol, SFA, MUFA, and PUFA. Signi"cant di!erences in cholesterol are seen with age, with levels being higher in young than adult animals (P(0.05). The predominant fatty acids are SFA, followed by MUFA, and then PUFA. Signi"cant di!erences in MUFA (P(0.10), and PUFA (P(0.005) (on a mass basis) are found with respect to age. SFA are the predominant fatty acids in both age classes, increasing percentage-wise with age. This is o!set by a decline in the percent PUFA with age. Table 5 lists the vitamin and mineral content found in nutria. No di!erences between age categories are noted for vitamin A and sodium; however, signi"cant di!erences with age are noted for iron (P(0.001), calcium (P(0.05), and vitamin C (P(0.10). Iron increases with age to nearly double that in the young animals, while vitamin C and calcium decline with age. TABLE 3 Proximate analysis of nutria grouped by sex and age Weight in grams per 100 g (S.D.) Moisture %
Group Young male (3 composites, 12 animals) Young female (4 composites, 12 animals) Average young (7 composites, 21 animals) Adult male (4 composites, 12 animals) Adult female (3 composites, 9 animals) Average adult (7 composites, 21 animals) Average all groups (14 composites, 42 animals) Means and
S.D.
76.1 (0.70) 75.9 (0.70) 76.0 (0.65) 75.1 (0.56) 76.1 (0.06) 75.5 (0.67) 75.7 (0.69)
Ash 0.9 (0.00) 0.95 (0.06) 0.9 (0.05) 1.0 (0.10) 1.1 (0.06) 1.0 (0.08) 0.99 (0.09)
Protein 22.1 (0.35) 22.0 (0.70) 22.0 (0.54) 22.5 (0.41) 21.9 (0.85) 22.2 (0.66) 22.1 (0.59)
Fat 1.6 (0.25) 1.4 (0.17) 1.5 (0.20) 0.8 (0.18) 1.4 (0.12) 1.0 (0.34) 1.3 (0.36)
are in parentheses. All data are expressed on a wet wt. basis.
kJ/100 g (S.D.) Protein 368 (6.3) 368 (11.8) 368 (9.2) 377 (6.9) 364 (14.3) 372 (11.2) 372 (10.0)
Fat 58 (10.2) 54 (7.4) 56 (8.2) 29 (7.1) 52 (5.2) 39 (13.4) 47 (13.7)
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ANALYSIS OF NUTRIA TABLE 4 Lipid analysis of nutria grouped by sex and age Group
mg/100 g Cholesterol
Young male (3 composites, 12 animals) Young female (4 composites, 12 animals) Average young (7 composites, 21 animals) Adult male (4 composites, 12 animals) Adult female (3 composites, 9 animals) Average adult (7 composites, 21 animals) Average all groups (14 composites, 42 animals) Means and
S.D.
41 (2.57) 40 (6.15) 40 (4.6) 29 (8.36) 36 (0.51) 32 (7.05) 36 (7.17)
% Fatty acid
SFA
MUFA
PUFA
270 (73) 220 (79) 240 (75) 140 (58) 260 (30) 190 (75) 220 (77)
230 (73) 180 (72) 200 (70) 100 (35) 190 (25) 140 (53) 170 (68)
190 (54) 150 (54) 170 (53) 60 (33) 110 (19) 90 (36) 130 (61)
SFA
MUFA
40 (0.5) 40 (0.4) 40 (0.5) 46 (1.9) 46 (1.6) 46 (1.6) 43 (3.4)
33 (3.2) 33 (2.1) 33 (2.4) 34 (2.6) 34 (2.1) 34 (2.2) 33 (2.3)
PUFA 28 (3.5) 27 (2.3) 27 (2.6) 20 (3.0) 20 (1.0) 20 (2.2) 24 (4.5)
are in parentheses. All data are expressed on a wet wt. basis.
TABLE 5 Vitamin and mineral content of nutria grouped by sex and age Group Young male (3 composites, 9 animals) Young female (4 composites, 12 animals) Average young (7 composites, 21 animals) Adult male (4 composites, 12 animals) Adult female (3 composites, 9 animals) Average adult (7 composites, 21 animals) Average all groups (14 composites, 42 animals) Means and
S.D.
Vitamin A (lg/00 g)
Vitamin C (mg/100 g)
Iron (mg/100 g)
Calcium (mg/100 g)
3.1 (1.61) 2.6 (0.57) 2.8 (1.04 2.3 (0.54) 3.2 (0.71) 2.7 (0.73) 2.7 (0.87)
0.3 (0.25) 0.8 (0.25) 0.6 (0.36) 0.2 (0.04) 0.4 (0.10) 0.3 (0.12) 0.4 (0.29)
1.1 (0.02) 1.3 (0.19) 1.2 (0.17) 2.4 (0.08) 1.9 (0.18) 2.2 (0.28) 1.7 (0.54)
5.9 (1.45) 5.4 (0.43) 5.6 (0.92) 5.0 (0.17) 4.3 (0.09) 4.7 (0.38) 5.2 (0.83)
Sodium (mg/100 g) 69 (13.2) 60 (13.6) 64 (13.2) 74 (4.1) 65 (15.1) 70 (10.5) 67 (11.9)
are in parentheses. All data are expressed on a wet wt. basis.
Other investigators have performed analyses on nutria in Europe. Sperber et al. (1982) found that fat averaged 9.4% with the body fat depots removed and protein ranged from 16.5 to 19.2%, reported on a wet-wt. basis. Kostron and Kukla (1969) found protein levels of 19.7% and fat levels of 15.2%. Although the techniques of stripping fat from depots may di!er than those used in the current study, it appears that in both of these studies, the fat levels were higher and protein lower than we found in our study. It is possible that the method used for fat analysis in this study, petroleum ether extraction, may not have extracted all fats such as membrane phospholipids, slightly reducing the amount analyzed. In our laboratory, however,
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TULLEY E¹ A¸. TABLE 6
Comparison of nutritional content of nutria versus other meats as determined by the MENU database Meat source Chicken USDA 05011 Ground beef USDA 13309 Cod USDA 15015 Squirrel USDA 17183 Deer USDA 17164 Rabbit USDA 17180 Turkey USDA 05167 Nutria Current study
Moisture (%)
Ash (mg/100 g)
Protein (g/100 g)
Fat (g/100 g)
75.5
1.0
21.4
3.1
56.1
1.0
16.6
26.6
81.2
1.2
17.8
0.7
73.8
1.2
21.2
3.2
73.6
1.2
23.0
2.4
74.5
1.1
21.8
2.3
74.2
1.0
21.8
2.9
75.7
1.0
22.1
1.3
this method gives comparable results to the chloroform/methanol extraction on meat samples. Another possibility for the di!erences in fat found is that the diet of wild nutria in Louisiana, primarily plants and grasses, contributes to lower fat and higher proteins levels compared to farm-raised nutria in Europe. A comparison of the nutritional content of nutria with other meat (chicken, cod, turkey, ground beef, sirloin, lean sirloin, squirrel, deer, rabbit, and pork) performed using the Menu database (Moore et al., 1993) is shown in Table 6. The Menu database is a derivative of the USDA Handbook 8 values. The most signi"cant "ndings are the low fat levels found in nutria meat compared to other meat sources. The petroleum ether extractable fat is lower than reported fat levels in chicken, ground beef, squirrel, deer, rabbit, pork, and turkey. Only cod has lower levels of fat, although the petroleum ether extractable fat is comparable in young male nutria. We do not know what methods were used for obtaining the USDA data for these meats, although we suspect that the results are a composite of multiple analytical methods and labs. Protein content of nutria compares favorably to all the meats listed. Of all the meats listed, nutria contains the lowest amount of cholesterol, at least in our petroleum ether extracts. Even though saturated fatty acid is the predominant fatty acid in petroleum ether extracted nutria meat, the levels are actually less than all meat sources but cod. MUFA are lower than all meats listed, except cod; PUFA are lower than all meats listed. As an iron source, nutria is superior to cod and chicken but not as good as the other meats listed. Nutria is in the mid-range of the meats listed for calcium. In summary, nutria is an excellent nutritional meat source which is high in protein and low in fat and cholesterol. All studies have indicated that the meat of nutria is very tasty, tender, and of a high quality (Kostron and Kukla, 1969; Sperber et al., 1982; Palanska et al., 1985; Niedzwiadek et al., 1986). The overall quality of the meat has been favorably compared to that of poultry, rabbits, and veal (Palanska et al., 1985). Nutria meat as a dietary source complies with current health and dietary recommendations for low fat, low cholesterol diets. The widespread availability of the animal should make it a readily accessible food source in speci"c regions such as Louisiana; however, many pre-conceived notions as to its acceptability as a food source need to
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be overcome. The future acceptance of nutria as a major meat source remains to be determined. This work was supported by funds provided by the Louisiana Department of Wildlife and Fisheries.
REFERENCES AOAC (1995). O.cial Methods of Analysis, 16th edn. (P. Cunni!, Ed.) AOAC International, Arlington, VA. Bugawva, A. A., and Dimitrovski, Y. D. (1987). Fatty acid composition of coypu lipids.
JOURNAL OF FOOD COMPOSITION AND ANALYSIS
ORIGINAL ARTICLE Analysis of the Nutritional Content of Myocastor coypus Richard T. Tulley* , Fatemeh M. Malekian*, Jennifer C. Rood*, Mary B. Lamb*, Catherine M. Champagne*, Stephen M. Redmann Jr*, Ruth Patrick*, Noel Kinler-, and C. T. Raby? *Pennington Biomedical Research Center, Baton Rouge, LA 70808-4124, U.S.A.; -Louisiana Department of Wildlife and Fisheries, New Iberia, LA 70560, U.S.A.; and ?Louisiana State Department of Agriculture and Forestry, Baton Rouge, LA 70821, U.S.A. Received May 4, 1998, and in revised form December 8, 1999
The present investigation was designed to determine the nutritional content of Myocastor coypus (nutria). Proximates, total petroleum ether extractable fatty acids, cholesterol, iron, sodium, calcium, vitamins A and C were determined. In comparing male versus female and young versus old nutria there were no di!erences in protein and moisture; however, there were signi"cant di!erences in total petroleum ether extractable fat, ash, and cholesterol content. Average results for meat from all animals were 1.3 g for total petroleum ether extractable fat, 1.0 g ash, 22.1 g protein, 36 mg for cholesterol, 1.7 mg for iron, 67 mg for sodium, and 5.2 mg for calcium per 100 g wet weight. Nutria petroleum ether extractable fat was generally richer in saturated (43%) than mono (33%) and polyunsaturated fat (24%). As expected, nutria was not a good source of vitamins A and C. In summary, nutria is an excellent nutritional source of protein which is low in fat and cholesterol. Thus, nutria meat provides a healthy alternative food which complies with current healthy and dietary recommendations for low fat, low cholesterol diets. 2000 Academic Press
Key =ords: nutria; nutritional content; fat; cholesterol; fatty acids.
INTRODUCTION Myocastor coypus (nutria) is a small herbivorous animal which is indigenous to South America and is also quite prevalent in the marshes of the southeastern United States, having been brought to the United States from South America to Avery Island, Louisiana in the 1930s. The animals escaped and since have spread across the southeastern United States (McCann et al., 1996). The nutria belongs to the same animal order as the squirrel. It is similar to, but smaller than the North American beaver, and hence is sometimes called the swamp beaver. The total length of the animal is 50}80 cm, of which the tail comprises 30} 50 cm. The nutria is entirely vegetarian (Kinsel, 1958). Its intestinal tract is designed so that it can eat large amounts of foods which are not easily digested, such as its main sources of food, water plants and reeds. The nutria has devoured large areas of marshland in south Louisiana which has led to the destruction of levees and coastal To whom correspondence and reprint requests should be addressed. Tel. 504-763-2524. Fax: 504-7632525. E-mail: [email protected] 0889}1575/00/020117#09 $35.00/0
2000 Academic Press
118
TULLEY E¹ A¸.
erosion. Nutria are posing an ecological problem in many other southeastern states in the United States such as Texas and Oregon, and even as far away as Thailand. For this reason, o$cials have begun to look for ways to increase the value of the nutria, thereby providing an economic incentive to trappers to increase the harvest of nutria. Nutria have long been used as a food source in their native South America and also in parts of Europe and Asia (Grzimek, 1975). In the 1960s, the Louisiana State University Agricultural Experiment Station published a booklet containing information on the collection, preparation, and cooking of nutria (Glasgow and McCollough, 1963). Also included were numerous recipes. With the widespread availability of common meat sources, nutria meat has not been utilized to its full potential. Recently, there has been renewed interest because of the detriment the nutria poses to the environment and also because of its potential to provide the public with an inexpensive alternative meat source. Although the nutritional quality of nutria has been reported by others (Bugawva and Dimitroski, 1987; Kostron and Kukla, 1969; Niedzwiadek et al., 1986; Palanska et al., 1985; Sperber et al., 1982), those analyses were performed on farm-raised animals and/or in Europe. There is a scarcity of data on the species which is indigenous in Louisiana swamps and bayous. It would be expected that the diet of these animals is substantially di!erent than that of farm-raised animals leading to di!erences in the nutrient content of the meat. Therefore, the object of this study was to determine the nutritional content of meat from wild nutria and to compare it to other meat sources. MATERIALS AND METHODS Reagents Petroleum ether, sodium hydroxide, iso-octane, potassium hydroxide, cyclohexane, Ultrex nitric acid, and ICP standards were obtained from J. T. Baker (Phillipsburg, NJ). Ethanolic pyrogallol was purchased from Baddley Chemical Inc. (Baton Rouge, LA). Boron tri#uoride (14% w/v)/methanol solution, ascorbate oxidase, and ophenylenediamine were purchased from Sigma Chemical Company (St. Louis, MO). Sodium chloride was obtained from CMS (Houston, TX) and pyridine from Pierce Chemical Company (Rockford, IL). Otawa sand and 26 mm cellulose "ber thimbles were purchased from Fisher Scienti"c (Pittsburgh, PA). Bis(trimethylsilyl)-tri#uoroacetamide (BSTFA) containing 1% w/v TMCS (Regisil, Alltech Assoc., Inc., Deer"eld, IL) was purchased from Alltech (Dear"eld, IL). Dithiothreitol was purchased from Aldrich Chemical Company (Milwaukee, WI). C:23:0 methyl ester and 5-alpha cholestanol were obtained from NuCheck Prep, Inc. (Elysian, MN). Capture and Slaughter A total of 63 nutria were captured by hand, utilizing airboats and a long-handle net, on the Marsh Island Wildlife Refuge, Iberia Parish, LA. Once captured, animals were placed in individual holding cages and transported to the New Iberia Field O$ce of the Louisiana Department of Wildlife and Fisheries. Animals were captured on December 14, 1994 and processed on the next day. Nutria were sacri"ced and immediately sexed, tagged, and weighed to the nearest 10 g. The skin was removed, animal eviscerated, and the remaining carcass weighed. The carcass was deboned and the resulting meat defatted by removing the small amount of subcutaneous fat present. Although all major muscle groups were deboned (hind legs, front legs, and back strap), a small amount of meat remained on the carcass.
ANALYSIS OF NUTRIA
119
The deboned sample of meat was weighed (to the nearest 2 g) and packaged in labeled ziplock storage bags. The meat samples and corresponding data were delivered to the Pennington Biomedical Research Center, frozen on dry ice, and stored at !203C (1}2 days) until composited. Compositing Prior to compositing, the meat samples were arranged into four groups based on age and sex of the animals from which they were obtained. The animals heavier than 4000 g total weight were classi"ed as &&adult'' with the remainder classi"ed as &&young''. The four groupings were young males, young females, adult males, and adult females. The meat from three animals was used to form a composite for each group. For economical reasons, the meat from 42 of the 63 animals was included in this study. A total of 14 composites representing 42 animals were made as follows: 3 groups of young males, 4 groups of young females, 4 groups of adult males, and 3 groups of adult females. The meat samples were removed from the freezer and placed overnight in the refrigerator at 43C to thaw, then cut into pieces measuring 8}10 cm with a stainlesssteel bladed knife and homogenized using a Robot Coupe Model R-2 food processor (Ridgeland, MS). The homogenized samples were then aliquoted into glass jars and frozen at !203C until the day of analysis. Analyses Quality control. Quality control samples were prepared from mixed food samples which were blended and homogenized until they were homogeneous, and then divided into aliquots in 20 mL glass bottles. These bottles were then capped and stored at !803C. On each day of analysis, a glass bottle containing the pooled food control was removed from the ultralow freezer, thawed, and analyzed in triplicate for each analyte reported. Values for all analytes had to be within two standard deviations of the mean for an analysis to be accepted. ;nits. All values were analyzed on a wet basis and results expressed as per 100 g wet wt. ¹otal petroleum ether extractable fat. Total petroleum ether extractable fat was determined gravimetrically according to AOAC method number 945.16 using petroleum ether on a Soxtec fat extraction apparatus (Tecator, Spring"eld, MD). The dried fat extract was dissolved in 20 mL of petroleum ether and divided into two fractions. One fraction was used for the determination of cholesterol and the other for fatty acid analysis. Reproducibility measurements for the fat measurement resulted in a coe$cient of variation of 4.2% at a level of 3.87 g/100 g. Protein. Protein was determined using thermal conductivity on a Model 2410 Nitrogen Analyzer (Perkin Elmer, Norwalk, CT) according to AOAC method number 992.15. Protein was calculated from nitrogen content by using a factor of 6.25. The coe$cient of variation (cv.) for this assay is 10.8% at 4.0 g/100g protein. Ash. Ash was determined using a microwave mu%e furnace (MAS 7000, CEM, Matthews, NC) according to AOAC method number 920.153. At a mean of 0.6 g/ 100 g the cv. for this assay is 14.3%.
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Moisture. Moisture was determined automatically on a Lab Wave 9000 microwave solid analyzer (CEM, Matthews, NC) (AOAC C985.14). At a mean of 0.6 g/100 g reproducibility of this method showed a cv. of 0.3%. ¹otal petroleum ether extractable fatty acids. Fatty acids in the petroleum ether extract were determined by gas chromatography of the fatty acid methyl esters according to a modi"cation of an AOCS method (Firestone, 1993). The composition of the fatty acid methyl esters were determined by gas chromatography on a HewlettPackard 5890 Gas Chromatograph (Atlanta, GA) using a fused silica capillary column (30;0.25 mm) with a 0.20 lm coating (C2-4110, Supelco, Inc, Bellefonte, PA). Individual fatty acids were quanti"ed and then grouped into the appropriate saturated (SFA), monounsaturated (MUFA), or polyunsaturated fatty acid (PUFA) categories. Coe$cient of variations for SFA, MUFA, and PUFA were 15.1, 16.0, and 19.6%, respectively, at 696, 872, and 650 mg/100 g. Petroleum ether extractable cholesterol. Cholesterol in the petroleum ether extract was analyzed by the method of Thompson and Merola (1993) on a Hewlett-Packard 5890 Gas Chromatograph (Atlanta, GA) using a fused silica capillary column (30;0.25 mm) with 0.25 lm coating (Supelco, Inc., Bellefont, PA). Reproducibility of the procedure shows a cv. of 4.0% at 10.7 mg/100 g. Sodium, calcium, and iron. Sodium, calcium, and iron were analyzed by inductively coupled plasma emission spectrometry (ICP) using a Perkin Elmer P1000 ICP (Norwalk, CT) following ashing on a MAS 7000 microwave mu%e furnace (CEM, Matthews, NC). Samples were ashed for 2}4 h at 5003C and diluted to 10 mL in a solution of 0.15 mol/L nitric acid. The samples were then "ltered through 0.2 lm syringe "lters (C77524 Uni#o 25, Schleicher and Schuell, Keen, NH). Each sample was analyzed in duplicate on the ICP which was calibrated on mixed standards of 1, 10, and 100 lg/mL in each mineral. Accuracy of sodium and calcium were veri"ed by using a commercially available assayed control (Bio Rad, Hercules, CA). This same material also served as instrumental quality control material. Calcium had cvs. of 3.5 and 4.4% at 62 and 114 mg/L, respectively; sodium's cvs. were 3.3 and 3.7% at 55 and 175 mmol/L, respectively.
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Statistics Statistics presented, including summary statistics (sample mean and S.D.) reported in Tables 2}5, were computed using SAS release 6.12 for Windows (SAS Institute Inc., Cary, NC). To make comparisons among age and sex categories for carcass component weights and for each of the chemical analytes, factorial analysis of variance (ANOVA) models were implemented in SAS. Stated signi"cance levels for comparisons among combinations of sex and age categories are adjusted using the Tukey} Kramer method to control the overall Type I error rate.
RESULTS AND DISCUSSION Analysis of Composites Table 1 lists the total weight, carcass weight, and weight of the meat for each sample used in the four composite groups (young male, young female, adult male, and adult female). Once selected, young nutria weighed less than or equal to 3790 g while adult nutria weighed greater than 4460 g. Table 2 presents the mean weights of each group. There were no signi"cant di!erences between the young male and young female groups for total weight, carcass weight, or meat weight as determined by TABLE 1 Makeup of nutria composite samples (n"3 for each group) Age Young Young Young Young Young Young Young Adult Adult Adult Adult Adult Adult Adult
Sex and no. (N"3)
Mean total weight (g)
Mean carcass weight (g)
Mean meat weight (g)
Male 1 Male 2 Male 3 Female Female Female Female Male 1 Male 2 Male 3 Male 4 Female Female Female
3020 2790 2900 3110 3470 3210 3000 5660 5730 5860 5840 5090 5130 5120
1485 1500 1385 1385 1625 1865 1335 3000 2845 2815 2795 2335 2335 2415
476 550 488 452 540 504 398 946 762 980 732 298 702 792
1 2 3 4
1 2 3
TABLE 2 Average weight of each group Total weight (g)
Carcass weight (g)
Meat weight (g)
Group
Mean
S.D.
Mean
S.D.
Mean
S.D.
Young male (N"9) Young female (N"12) Adult male (N"12) Adult female (N"9)
2903 3198 5772 5113
698 605 436 464
1453 1552 2864 2362
404 474 257 266
505 473 855 597
142 104 177 255
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Tukey}Kramer post-ANOVA tests. However, there were di!erences between adult males and females for total weight, carcass weight, and meat weight (P(0.05). The di!erences between the young and adult large groups within each sex were signi"cant for total weight and carcass weight (P(0.001), and for meat weight among males but not females (males: P(0.001, females: P"0.23). Table 3 lists proximate analysis for the nutria. There are no signi"cant di!erences between young and adult nutria for moisture and protein. Moisture (data not shown) and protein are very consistent between the sexes without regard to age. Signi"cant di!erences between young and old nutria are noted for petroleum ether extractable fat (P(0.005). Ash is higher in adult animals than in young animals (P(0.01) but the level is similar between males and females. Total petroleum ether extractable fat varies with sex and age, but generally ranges from 1.4 to 1.6 g/100 g, except in adult males, which have about half as much fat (0.8 g/100 g) as their younger counterparts and adult females. The decline in fat with age in male nutria may be due to an increase in male sex hormones as the animals mature. These hormones are known to increase lean body mass and decrease fat levels. Fat levels in females do not di!er signi"cantly with age. Fat contributes 52}58 kJ/100 g in all groups except for adult males, in which fat generates 29 kJ/100 g. Table 4 shows the breakdown for petroleum ether extractable cholesterol, SFA, MUFA, and PUFA. Signi"cant di!erences in cholesterol are seen with age, with levels being higher in young than adult animals (P(0.05). The predominant fatty acids are SFA, followed by MUFA, and then PUFA. Signi"cant di!erences in MUFA (P(0.10), and PUFA (P(0.005) (on a mass basis) are found with respect to age. SFA are the predominant fatty acids in both age classes, increasing percentage-wise with age. This is o!set by a decline in the percent PUFA with age. Table 5 lists the vitamin and mineral content found in nutria. No di!erences between age categories are noted for vitamin A and sodium; however, signi"cant di!erences with age are noted for iron (P(0.001), calcium (P(0.05), and vitamin C (P(0.10). Iron increases with age to nearly double that in the young animals, while vitamin C and calcium decline with age. TABLE 3 Proximate analysis of nutria grouped by sex and age Weight in grams per 100 g (S.D.) Moisture %
Group Young male (3 composites, 12 animals) Young female (4 composites, 12 animals) Average young (7 composites, 21 animals) Adult male (4 composites, 12 animals) Adult female (3 composites, 9 animals) Average adult (7 composites, 21 animals) Average all groups (14 composites, 42 animals) Means and
S.D.
76.1 (0.70) 75.9 (0.70) 76.0 (0.65) 75.1 (0.56) 76.1 (0.06) 75.5 (0.67) 75.7 (0.69)
Ash 0.9 (0.00) 0.95 (0.06) 0.9 (0.05) 1.0 (0.10) 1.1 (0.06) 1.0 (0.08) 0.99 (0.09)
Protein 22.1 (0.35) 22.0 (0.70) 22.0 (0.54) 22.5 (0.41) 21.9 (0.85) 22.2 (0.66) 22.1 (0.59)
Fat 1.6 (0.25) 1.4 (0.17) 1.5 (0.20) 0.8 (0.18) 1.4 (0.12) 1.0 (0.34) 1.3 (0.36)
are in parentheses. All data are expressed on a wet wt. basis.
kJ/100 g (S.D.) Protein 368 (6.3) 368 (11.8) 368 (9.2) 377 (6.9) 364 (14.3) 372 (11.2) 372 (10.0)
Fat 58 (10.2) 54 (7.4) 56 (8.2) 29 (7.1) 52 (5.2) 39 (13.4) 47 (13.7)
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ANALYSIS OF NUTRIA TABLE 4 Lipid analysis of nutria grouped by sex and age Group
mg/100 g Cholesterol
Young male (3 composites, 12 animals) Young female (4 composites, 12 animals) Average young (7 composites, 21 animals) Adult male (4 composites, 12 animals) Adult female (3 composites, 9 animals) Average adult (7 composites, 21 animals) Average all groups (14 composites, 42 animals) Means and
S.D.
41 (2.57) 40 (6.15) 40 (4.6) 29 (8.36) 36 (0.51) 32 (7.05) 36 (7.17)
% Fatty acid
SFA
MUFA
PUFA
270 (73) 220 (79) 240 (75) 140 (58) 260 (30) 190 (75) 220 (77)
230 (73) 180 (72) 200 (70) 100 (35) 190 (25) 140 (53) 170 (68)
190 (54) 150 (54) 170 (53) 60 (33) 110 (19) 90 (36) 130 (61)
SFA
MUFA
40 (0.5) 40 (0.4) 40 (0.5) 46 (1.9) 46 (1.6) 46 (1.6) 43 (3.4)
33 (3.2) 33 (2.1) 33 (2.4) 34 (2.6) 34 (2.1) 34 (2.2) 33 (2.3)
PUFA 28 (3.5) 27 (2.3) 27 (2.6) 20 (3.0) 20 (1.0) 20 (2.2) 24 (4.5)
are in parentheses. All data are expressed on a wet wt. basis.
TABLE 5 Vitamin and mineral content of nutria grouped by sex and age Group Young male (3 composites, 9 animals) Young female (4 composites, 12 animals) Average young (7 composites, 21 animals) Adult male (4 composites, 12 animals) Adult female (3 composites, 9 animals) Average adult (7 composites, 21 animals) Average all groups (14 composites, 42 animals) Means and
S.D.
Vitamin A (lg/00 g)
Vitamin C (mg/100 g)
Iron (mg/100 g)
Calcium (mg/100 g)
3.1 (1.61) 2.6 (0.57) 2.8 (1.04 2.3 (0.54) 3.2 (0.71) 2.7 (0.73) 2.7 (0.87)
0.3 (0.25) 0.8 (0.25) 0.6 (0.36) 0.2 (0.04) 0.4 (0.10) 0.3 (0.12) 0.4 (0.29)
1.1 (0.02) 1.3 (0.19) 1.2 (0.17) 2.4 (0.08) 1.9 (0.18) 2.2 (0.28) 1.7 (0.54)
5.9 (1.45) 5.4 (0.43) 5.6 (0.92) 5.0 (0.17) 4.3 (0.09) 4.7 (0.38) 5.2 (0.83)
Sodium (mg/100 g) 69 (13.2) 60 (13.6) 64 (13.2) 74 (4.1) 65 (15.1) 70 (10.5) 67 (11.9)
are in parentheses. All data are expressed on a wet wt. basis.
Other investigators have performed analyses on nutria in Europe. Sperber et al. (1982) found that fat averaged 9.4% with the body fat depots removed and protein ranged from 16.5 to 19.2%, reported on a wet-wt. basis. Kostron and Kukla (1969) found protein levels of 19.7% and fat levels of 15.2%. Although the techniques of stripping fat from depots may di!er than those used in the current study, it appears that in both of these studies, the fat levels were higher and protein lower than we found in our study. It is possible that the method used for fat analysis in this study, petroleum ether extraction, may not have extracted all fats such as membrane phospholipids, slightly reducing the amount analyzed. In our laboratory, however,
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Comparison of nutritional content of nutria versus other meats as determined by the MENU database Meat source Chicken USDA 05011 Ground beef USDA 13309 Cod USDA 15015 Squirrel USDA 17183 Deer USDA 17164 Rabbit USDA 17180 Turkey USDA 05167 Nutria Current study
Moisture (%)
Ash (mg/100 g)
Protein (g/100 g)
Fat (g/100 g)
75.5
1.0
21.4
3.1
56.1
1.0
16.6
26.6
81.2
1.2
17.8
0.7
73.8
1.2
21.2
3.2
73.6
1.2
23.0
2.4
74.5
1.1
21.8
2.3
74.2
1.0
21.8
2.9
75.7
1.0
22.1
1.3
this method gives comparable results to the chloroform/methanol extraction on meat samples. Another possibility for the di!erences in fat found is that the diet of wild nutria in Louisiana, primarily plants and grasses, contributes to lower fat and higher proteins levels compared to farm-raised nutria in Europe. A comparison of the nutritional content of nutria with other meat (chicken, cod, turkey, ground beef, sirloin, lean sirloin, squirrel, deer, rabbit, and pork) performed using the Menu database (Moore et al., 1993) is shown in Table 6. The Menu database is a derivative of the USDA Handbook 8 values. The most signi"cant "ndings are the low fat levels found in nutria meat compared to other meat sources. The petroleum ether extractable fat is lower than reported fat levels in chicken, ground beef, squirrel, deer, rabbit, pork, and turkey. Only cod has lower levels of fat, although the petroleum ether extractable fat is comparable in young male nutria. We do not know what methods were used for obtaining the USDA data for these meats, although we suspect that the results are a composite of multiple analytical methods and labs. Protein content of nutria compares favorably to all the meats listed. Of all the meats listed, nutria contains the lowest amount of cholesterol, at least in our petroleum ether extracts. Even though saturated fatty acid is the predominant fatty acid in petroleum ether extracted nutria meat, the levels are actually less than all meat sources but cod. MUFA are lower than all meats listed, except cod; PUFA are lower than all meats listed. As an iron source, nutria is superior to cod and chicken but not as good as the other meats listed. Nutria is in the mid-range of the meats listed for calcium. In summary, nutria is an excellent nutritional meat source which is high in protein and low in fat and cholesterol. All studies have indicated that the meat of nutria is very tasty, tender, and of a high quality (Kostron and Kukla, 1969; Sperber et al., 1982; Palanska et al., 1985; Niedzwiadek et al., 1986). The overall quality of the meat has been favorably compared to that of poultry, rabbits, and veal (Palanska et al., 1985). Nutria meat as a dietary source complies with current health and dietary recommendations for low fat, low cholesterol diets. The widespread availability of the animal should make it a readily accessible food source in speci"c regions such as Louisiana; however, many pre-conceived notions as to its acceptability as a food source need to
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125
be overcome. The future acceptance of nutria as a major meat source remains to be determined. This work was supported by funds provided by the Louisiana Department of Wildlife and Fisheries.
REFERENCES AOAC (1995). O.cial Methods of Analysis, 16th edn. (P. Cunni!, Ed.) AOAC International, Arlington, VA. Bugawva, A. A., and Dimitrovski, Y. D. (1987). Fatty acid composition of coypu lipids.