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Research Note: Cholesterol Content of Commercially Produced Eggs in Georgia1
RESEARCH NOTES Research Note: Cholesterol Content of Commercially Produced Eggs in Georgia 1 R. SCOTT BEYER and LEO S. JENSEN Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication March 9, 1989)
1989 Poultry Science 68:1703-1706 INTRODUCTION
Much research has been conducted to determine the cholesterol content of eggs (Naber, 1983; Hargis, 1988). The data from many of these studies have been used to compile an estimate of the average cholesterol content of eggs (Feeley et al., 1972), which is currently set at 274 mg/egg (Consumer and Food Economics Institute, 1976). Most of these studies were not conducted to determine the absolute value for cholesterol in eggs but to assess the relative differences among treatments. More recently in a study by Holden et al. (1989), the cholesterol level of eggs was estimated at 208 mg/egg. Earlier work in the authors' laboratory (Beyer and Jensen, 1989) revealed that, in general, the cholesterol content of eggs has been overestimated using a common colorimetric method for cholesterol detection. Analysis by HPLC indicated that the cholesterol content was about 200 mg/egg. Many recent reports have appeared in the popular press about producing eggs with a cholesterol level below die USDA standard. The importance of accuracy of values shown in tables for the cholesterol content of eggs cannot be overemphasized. Such tables are
'Supported by State of Georgia and Hatch funds allocated to the Georgia Agricultural Experiment Stations, University of Georgia.
commonly used by dieticians and others for estimating daily cholesterol intake. The purpose of mis work was to obtain a more accurate assessment of the cholesterol content of eggs produced by commercial sources in Georgia. MATERIALS AND METHODS
Egg samples produced during December were solicited by mail from 33 egg producers in the state of Georgia chosen at random. Nineteen samples of two dozen eggs each were received. Enclosed with each request for eggs was a short questionnaire form which included requests for the following information: 1) age of the hens; 2) percentage of egg production of flock; 3) breed or strain; 4) protein, fat, and ME content of the diet fed to the flock; 5) whether any animal by-products used in the diet and if so, what kind were used; and 6) whether the hens had been molted previously. Immediately upon arrival, any broken or cracked eggs were discarded and the remaining eggs were weighed and boiled for 5 min. The yolks were carefully separated from the albumen, weighed, and frozen at -20 C for further analysis. After all the egg samples had been received, the yolks from each farm were thoroughly blended together into a homogenous sample. Samples of the egg yolks were extracted, saponified, and analyzed for cholesterol by an
1703
Downloaded from http://ps.oxfordjournals.org/ at Georgetown University on May 24, 2015
ABSTRACT A survey of the cholesterol content of eggs obtained from commercial sources in Georgia was conducted. Data on flock age, egg-production rate, strain, molting status, as well as dietary protein, fat, ME, and the content of animal by-products were obtained from producers via a questionnaire. Mean egg cholesterol level, determined by an HPLC procedure, was 195 mg/egg, which is substantially lower than that commonly included in tables of egg composition. The total cholesterol content correlated positively with egg weight and yolk weight and negatively with egg production and dietary protein levels, but no significant (P<.05) correlations among the variables were evident when cholesterol was expressed as milligrams per gram of yolk. Molted flocks had a higher level of total cholesterol than nonmolted flocks due to a larger egg size. The addition of animal by-products did not increase the cholesterol content of eggs, compared to those flocks which were not fed animal by-products. (Key words: eggs, egg weight, yolk weight, egg production, cholesterol)
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RESEARCH NOTE TABLE 2. Correlations between response data and egg cholesterol content, all samples received (December 1988) Weight ME
Eggs (g)
1.00 .82** 1.00
Age
Age, wk Egg production, % Protein, % Fat, % ME, kcal/kg Egg weight, g Yolk weight, g Cholesterol, mg/g of yolk Cholesterol, mg/egg
1.00 -.68** -.46* .13 -.02 .76** .85**
1.00 .48* .01 -.25 -.65** -.57**
1.00 .38 .15 .52* -.53*
1.00 -.26 -.09 .14
1.00 .07 .05
.19 -.31 .81** -.65**
-.18 -.53*
-.42 -.11
.14 .23
Yolks (g)
.18 -.04 .78** .79**
Cholesterol mg/g of yolk
mg/egg
1.00 .58**
1.00
*P<.05. **KS.01.
HPLC method referred to previously (Beyer and Jensen, 1989). All samples were run in quadruplicate, and the mean value was used for statistical analysis. Product-moment correlations between the variables were determined by using the Statistical Analysis System (SAS Institute, 1982). RESULTS AND DISCUSSION
The response data and cholesterol content for all of the individual samples received are shown in Table 1. Sample 10 from a flock of hens which were just beginning to lay was excluded from subsequent statistical analysis. This sample had the highest cholesterol content on a milligram per gram basis; however, it had the lowest total amount of cholesterol because of the small egg size. The mean egg weight, yolk weight, and cholesterol content of the samples are shown at the bottom of Table 1. The average cholesterol content of the samples was 195.4 mg/egg. This is substantially below the USDA estimate but in close agreement with earlier reports by the authors about an egg sample from a Leghorn flock at the University of Georgia (Beyer and Jensen, 1989). Seeking to discern other factors that might influence cholesterol levels in eggs, correlations among all response variables were estimated (Table 2). Total cholesterol per egg was correlated positively with hen age, egg weight, yolk weight, and cholesterol concentration (when expressed as milligrams per gram of yolk) and correlated negatively with
egg production (percentage) and dietary protein levels. Expressed as total cholesterol per egg, however, many of the variables became interrelated. For example, as the hens aged, the egg weight increased, thus raising the total yolk and cholesterol content in the eggs. Therefore, it is more meaningful to examine the correlations when cholesterol is expressed as milligrams per gram of yolk. None of the variables examined were significantly correlated with cholesterol expressed as milligrams per gram of yolk. The four molted flocks had more total cholesterol/egg than the nonmolted flocks (219.0 versus 188.7 mg/egg). This, however, was due to a greater egg size (65.2 versus 60.8) associated with age and molting. When expressed as milligrams per gram of yolk, the two groups had similar cholesterol levels (12.0 vs. 11.6 mg/g yolk). The majority of the flocks (fifteen) were of one strain, so no correlations between the cholesterol content of the eggs and the strain were made. Animal by-products are the only source of dietary cholesterol. The response data indicated that eleven of the samples were from hens fed animal by-products, mostly meat meal. Egg cholesterol (milligrams per gram of yolk) was similar between flocks fed diets with and without animal by-products (11.9 versus 11.5 mg/g). Caution should be taken when interpreting these data, though, since the authors do not know if the respondents considered poultry oil or animal fat as animal by-products.
The results of the present survey indicated that the average cholesterol content of today's
Downloaded from http://ps.oxfordjournals.org/ at Georgetown University on May 24, 2015
Variable
Egg production Protein Fat
1706
BEYER AND JENSEN
eggs is substantially lower than the estimate used by the USDA. Eggs collected from nineteen producers varied in the cholesterol content, according to egg weight, yolk weight, hen age, egg production, and dietary protein. When cholesterol was expressed as milligrams per gram of yolk, no significant correlations with egg weight, yolk weight, hen age, egg production, or dietary protein were noted. REFERENCES
Downloaded from http://ps.oxfordjournals.org/ at Georgetown University on May 24, 2015
Beyer, R. S., and L. S. Jensen, 1989. Overestimation of the cholesterol content of eggs. J. Agric. Food Chem. 37: 917-920.
Consumer and Food Economics Institute, 1976. Composition of foods, dairy and egg products, raw-processed-prepared. USDA Agric. Hand. 8-1:1-167. Feeley, R. M., P. E. Criner, and P. K. Watt, 1972. Cholesterol content of foods. J. Am. Diet. Assoc. 61:134-149. Hargis, P. S., 1988. Modifying egg yolk cholesterol in the domestic fowl-A review. World's Poult. Sci. J. 44: 17-29. Holden, J., J. Exler, C. McCharen, and J. Lockard, 1989. A nationwide study of the cholesterol, proximate, vitamin and mineral levels in large eggs. Fed. Am. See. Exp. Biol. 3:A658. (Abstr.) Naber, E. C , 1983. Nutrient and drug effects on cholesterol metabolism in the laying hen. Fed. Proc. 42: 2486-2493. SAS Institute, 1982. SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC.
1989 Poultry Science 68:1703-1706 INTRODUCTION
Much research has been conducted to determine the cholesterol content of eggs (Naber, 1983; Hargis, 1988). The data from many of these studies have been used to compile an estimate of the average cholesterol content of eggs (Feeley et al., 1972), which is currently set at 274 mg/egg (Consumer and Food Economics Institute, 1976). Most of these studies were not conducted to determine the absolute value for cholesterol in eggs but to assess the relative differences among treatments. More recently in a study by Holden et al. (1989), the cholesterol level of eggs was estimated at 208 mg/egg. Earlier work in the authors' laboratory (Beyer and Jensen, 1989) revealed that, in general, the cholesterol content of eggs has been overestimated using a common colorimetric method for cholesterol detection. Analysis by HPLC indicated that the cholesterol content was about 200 mg/egg. Many recent reports have appeared in the popular press about producing eggs with a cholesterol level below die USDA standard. The importance of accuracy of values shown in tables for the cholesterol content of eggs cannot be overemphasized. Such tables are
'Supported by State of Georgia and Hatch funds allocated to the Georgia Agricultural Experiment Stations, University of Georgia.
commonly used by dieticians and others for estimating daily cholesterol intake. The purpose of mis work was to obtain a more accurate assessment of the cholesterol content of eggs produced by commercial sources in Georgia. MATERIALS AND METHODS
Egg samples produced during December were solicited by mail from 33 egg producers in the state of Georgia chosen at random. Nineteen samples of two dozen eggs each were received. Enclosed with each request for eggs was a short questionnaire form which included requests for the following information: 1) age of the hens; 2) percentage of egg production of flock; 3) breed or strain; 4) protein, fat, and ME content of the diet fed to the flock; 5) whether any animal by-products used in the diet and if so, what kind were used; and 6) whether the hens had been molted previously. Immediately upon arrival, any broken or cracked eggs were discarded and the remaining eggs were weighed and boiled for 5 min. The yolks were carefully separated from the albumen, weighed, and frozen at -20 C for further analysis. After all the egg samples had been received, the yolks from each farm were thoroughly blended together into a homogenous sample. Samples of the egg yolks were extracted, saponified, and analyzed for cholesterol by an
1703
Downloaded from http://ps.oxfordjournals.org/ at Georgetown University on May 24, 2015
ABSTRACT A survey of the cholesterol content of eggs obtained from commercial sources in Georgia was conducted. Data on flock age, egg-production rate, strain, molting status, as well as dietary protein, fat, ME, and the content of animal by-products were obtained from producers via a questionnaire. Mean egg cholesterol level, determined by an HPLC procedure, was 195 mg/egg, which is substantially lower than that commonly included in tables of egg composition. The total cholesterol content correlated positively with egg weight and yolk weight and negatively with egg production and dietary protein levels, but no significant (P<.05) correlations among the variables were evident when cholesterol was expressed as milligrams per gram of yolk. Molted flocks had a higher level of total cholesterol than nonmolted flocks due to a larger egg size. The addition of animal by-products did not increase the cholesterol content of eggs, compared to those flocks which were not fed animal by-products. (Key words: eggs, egg weight, yolk weight, egg production, cholesterol)
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RESEARCH NOTE TABLE 2. Correlations between response data and egg cholesterol content, all samples received (December 1988) Weight ME
Eggs (g)
1.00 .82** 1.00
Age
Age, wk Egg production, % Protein, % Fat, % ME, kcal/kg Egg weight, g Yolk weight, g Cholesterol, mg/g of yolk Cholesterol, mg/egg
1.00 -.68** -.46* .13 -.02 .76** .85**
1.00 .48* .01 -.25 -.65** -.57**
1.00 .38 .15 .52* -.53*
1.00 -.26 -.09 .14
1.00 .07 .05
.19 -.31 .81** -.65**
-.18 -.53*
-.42 -.11
.14 .23
Yolks (g)
.18 -.04 .78** .79**
Cholesterol mg/g of yolk
mg/egg
1.00 .58**
1.00
*P<.05. **KS.01.
HPLC method referred to previously (Beyer and Jensen, 1989). All samples were run in quadruplicate, and the mean value was used for statistical analysis. Product-moment correlations between the variables were determined by using the Statistical Analysis System (SAS Institute, 1982). RESULTS AND DISCUSSION
The response data and cholesterol content for all of the individual samples received are shown in Table 1. Sample 10 from a flock of hens which were just beginning to lay was excluded from subsequent statistical analysis. This sample had the highest cholesterol content on a milligram per gram basis; however, it had the lowest total amount of cholesterol because of the small egg size. The mean egg weight, yolk weight, and cholesterol content of the samples are shown at the bottom of Table 1. The average cholesterol content of the samples was 195.4 mg/egg. This is substantially below the USDA estimate but in close agreement with earlier reports by the authors about an egg sample from a Leghorn flock at the University of Georgia (Beyer and Jensen, 1989). Seeking to discern other factors that might influence cholesterol levels in eggs, correlations among all response variables were estimated (Table 2). Total cholesterol per egg was correlated positively with hen age, egg weight, yolk weight, and cholesterol concentration (when expressed as milligrams per gram of yolk) and correlated negatively with
egg production (percentage) and dietary protein levels. Expressed as total cholesterol per egg, however, many of the variables became interrelated. For example, as the hens aged, the egg weight increased, thus raising the total yolk and cholesterol content in the eggs. Therefore, it is more meaningful to examine the correlations when cholesterol is expressed as milligrams per gram of yolk. None of the variables examined were significantly correlated with cholesterol expressed as milligrams per gram of yolk. The four molted flocks had more total cholesterol/egg than the nonmolted flocks (219.0 versus 188.7 mg/egg). This, however, was due to a greater egg size (65.2 versus 60.8) associated with age and molting. When expressed as milligrams per gram of yolk, the two groups had similar cholesterol levels (12.0 vs. 11.6 mg/g yolk). The majority of the flocks (fifteen) were of one strain, so no correlations between the cholesterol content of the eggs and the strain were made. Animal by-products are the only source of dietary cholesterol. The response data indicated that eleven of the samples were from hens fed animal by-products, mostly meat meal. Egg cholesterol (milligrams per gram of yolk) was similar between flocks fed diets with and without animal by-products (11.9 versus 11.5 mg/g). Caution should be taken when interpreting these data, though, since the authors do not know if the respondents considered poultry oil or animal fat as animal by-products.
The results of the present survey indicated that the average cholesterol content of today's
Downloaded from http://ps.oxfordjournals.org/ at Georgetown University on May 24, 2015
Variable
Egg production Protein Fat
1706
BEYER AND JENSEN
eggs is substantially lower than the estimate used by the USDA. Eggs collected from nineteen producers varied in the cholesterol content, according to egg weight, yolk weight, hen age, egg production, and dietary protein. When cholesterol was expressed as milligrams per gram of yolk, no significant correlations with egg weight, yolk weight, hen age, egg production, or dietary protein were noted. REFERENCES
Downloaded from http://ps.oxfordjournals.org/ at Georgetown University on May 24, 2015
Beyer, R. S., and L. S. Jensen, 1989. Overestimation of the cholesterol content of eggs. J. Agric. Food Chem. 37: 917-920.
Consumer and Food Economics Institute, 1976. Composition of foods, dairy and egg products, raw-processed-prepared. USDA Agric. Hand. 8-1:1-167. Feeley, R. M., P. E. Criner, and P. K. Watt, 1972. Cholesterol content of foods. J. Am. Diet. Assoc. 61:134-149. Hargis, P. S., 1988. Modifying egg yolk cholesterol in the domestic fowl-A review. World's Poult. Sci. J. 44: 17-29. Holden, J., J. Exler, C. McCharen, and J. Lockard, 1989. A nationwide study of the cholesterol, proximate, vitamin and mineral levels in large eggs. Fed. Am. See. Exp. Biol. 3:A658. (Abstr.) Naber, E. C , 1983. Nutrient and drug effects on cholesterol metabolism in the laying hen. Fed. Proc. 42: 2486-2493. SAS Institute, 1982. SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC.