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Poult Sci 2008. 87:64-70. doi:10.3382/ps.2007-00124
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METABOLISM AND NUTRITION

Utilization of Oil By-Product from the Purification Process of Conjugated Linoleic Acid as Feeding Supplements for the Accumulation of Conjugated Linoleic Acid in the Egg Yolk

J. H. Kim*,1, N.-J. Choi{dagger},1, H. G. Park*, I. H. Kim{ddagger}, H. G. Lee§, M. K. Song§, K. Y. Whang|| and Y. J. Kim*,2

* Department of Food and Biotechnology, Korea University, Chungnam, 339-700, Korea; {dagger} Hanwoo Experiment Station, National Livestock Research Institute, Gangwon, 232-952, Korea; {ddagger} Department of Animal Resource and Science, Dankook University, 330-714 Chungnam, Korea; § School of Agricultural Biotechnology, Seoul National University, 151-912, Seoul, Korea; § Department of Animal Science, Chungbuk National University, 361-703, Chungbuk, Korea; and || Division of Biotechnology, Korea University, Seoul, 136-713, Korea

2 Corresponding author: yk46{at}korea.ac.kr


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
This study was performed to examine an efficient way to use oil by-product which is obtained during the purification process of conjugated linoleic acid (CLA) from safflower oil. The CLA by-product (CBP) was fed to the laying hens to accumulate CLA in the egg yolk. Egg yolk samples from 3 different dietary groups were analyzed: control; CBP, 2%; and CLA-80 (which contained 80% free form of CLA), 2%. Fatty acids from the yolk were analyzed by gas chromatography, and the parameters of egg quality were determined. During the feeding trial, there was little alteration in the egg quality and egg production of the tested groups. The CLA contents in the test group with CBP, which contain CLA as glyceride form, significantly increased in the first week of feeding and had the highest level among the tested groups throughout the feeding trials, whereas the CLA group showed an increase in CLA contents from the third week. Moreover, the contents of total CLA isomers in CLA-80 and CBP oils were decreased by 12.92 and 0.51% after heat treatment in 48 h, and the contents of linoleic acid (LA) isomer in LA-80 (which contained 80% free form of LA) and LA by-product (LBP) oils were decreased by 19.63 and 5.78%, respectively. It was confirmed that a major form of fats in CBP was mainly esterified forms, whereas the fats in CLA-80 and LA-80 were composed of free fatty acids. There was no significant difference in the egg quality and production among the tested groups. It is meaningful that the oil by-product could be utilized as a source for functional foods of animal origin without influencing egg quality and production.

Key Words: conjugated linoleic acid • by-product • egg quality • egg production • glyceride


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Conjugated linoleic acid (CLA) is a generic name of the mixture of positional and geometric isomers of linoleic acid (LA), which is mainly found in food products derived from ruminant animals. The conversion of LA to CLA occurs in the rumen as a by-product of the multiple step biohydrogenation which yield monounsaturated fatty acids and saturated fatty acids as major products (Chin et al., 1992). It was shown that CLA had diverse physiological effects, such as anticarcinogenic activity (Ip, 1997), body fat reduction (Park et al., 1997; West et al., 1998), regulation of immunoglobulin production (Sugano et al., 1998), and antiobesity effect with hypolipidemic activity (Yeung et al., 2000).

Because CLA level in food supply is quantitatively minimal, a variety of research using CLA sources as feed additives has been performed to produce CLA-enriched animal products (Hwangbo et al., 2006; Kim et al., 2007). However, most of the commercially available CLA is the mixture of isomers produced from LA, and the application of CLA has been limited due to the high cost of purification (Kim et al., 2003). Therefore, it is meaningful to find economic alternatives to elevate the CLA level in the food products to meet the physiologically effective level.

The CLA by-product (CBP), which contained high level of CLA (about 80%) formed during the purification process, has been wasted. It was hypothesized that CBP which contained high levels of esterified form of CLA could be more easily absorbed to the intestine of animals compared with the free form, and thus CBP could be used to promote the efficiency of the CLA accumulation in the egg yolk. The form of digested fats may influence the composition of the newly formed chylomicrons, because triglyceride is resynthesized in the intestinal mucosa using monoglycerides (MG) from dietary lipids (Ramirez et al., 2001). If CBP contains high level of esterified CLA, it could be good source for CLA accumulation in the yolk. The CLA absorption into the epithelial cells of the animals would be more active in the esterified form compared with the free form because the esterified form of fatty acids favor the synthesis of chylomicrons in the intestinal cells.

Even though the beneficial effects of CLA have been widely known, the efficient level could hardly be reached by staple food consumption. It was suggested that the CLA consumption of Western people from the daily diet was less than one-third of the level that can exert physiological effects in humans (Ip et al. 1994). The present study was conducted to accumulate CLA efficiently in the egg yolk using CBP as a CLA source with little alteration of egg quality and productivity. It would be meaningful if oil by-products could be utilized as an economic source for functional foods of animal origin.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Birds and Diets
Sixty-three 30-wk-old White Leghorn laying hens were randomly distributed into 3 groups of 21 hens each and maintained in individual laying cages during 5 wk. The hens were assigned to the 3 dietary groups: control (no additional fat); CBP, 2%; and CLA-80 (which contained 80% free form of CLA, Lipozen Inc., Pyongtaek, Korea), 2%, respectively. The ingredients and chemical composition including oil supplements of the experimental diets are shown in Table 1Go. Feed and water were available ad libitum in each dietary group. The photoperiod was set at 17L:7D during the experiment. Eggs were collected and counted daily to obtain data of egg production, and feed consumption for each replicate was recorded daily for the entire study. Collected eggs were broken open to determine the egg quality twice per week during the feeding trials, and contents were then frozen at –50°C for further analyses. All animal-based procedures were in accordance with the Guidelines for the Care and Use of Experimental Animals of Korea University.


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  		Table 1. Formulation and chemical composition of the experimental diets
 
Sample Collections and Egg Quality
Eggs were collected during the experimental periods and stored at –50°C for subsequent analysis. Egg parameters including egg weight, Haugh units, and egg yolk color were measured with a QCM+ device (Technical Services and Supplies, York, UK), and eggshell thickness and strength were measured with an FHK device (Fujihara Co. LTD, Saitama, Japan). Egg yolk index was determined according to the method of Sauter et al. (1953).

GC Analysis
All the chemicals used for GC analysis were analytical grade and purchased from Sigma (St. Louis, MO). Lipid from egg yolks was extracted with hexane/isopropanol (3:2 vol/vol). Fatty acids were converted to methyl esters as described in our previous study with some modifications (Kim et al., 2003). Briefly, 0.5 mL of toluene and 2 mL of 5% KOH-MeOH were added to the lipid, and the samples were vortex-mixed and heated at 70°C for 8 min and then cooled in cold water. Two milliliters of 14% BF3-MeOH was then added to the sample, and heated at 70°C for additional 8 min. The sample was cooled, and then 3 mL of 5% NaCl was added to the sample and mixed. Five milliliters of distilled water and 0.5 mL of hexane were added to extract the fatty acid methyl ester. The mixture was vortexed and centrifuged at 5,000 x g for 10 min, and then the upper phase was collected and dried with sodium sulfate. Samples were analyzed for total fatty acids including CLA isomers using an HP5890 gas chromatograph with a flame ionization detector (Hewlett Packard 5890 Series II). Fatty acid methyl esters were separated using a Supelcowax-10 fused silica capillary column (100 m x 0.32 mm i.d., 0.25 µm film thickness; Supelco Inc., Bellefonte, PA) with 1.2 mL/min of helium flow. The GC was operated at a temperature of 140°C for 5 min, followed by heating at 2°C/min to 240°C, and holding for 30 min. Both the injector and detector were maintained at 260°C. One microliter of sample was injected into the column in the split mode (50:1). The peak of each CLA isomer (cis-9 trans-11, trans-10 cis-12, cis cis, and trans trans isomers) and other fatty acids were identified and quantified by comparison with the retention time and peak area of each fatty acid standard (Sigma) respectively. Fatty acid content was expressed as % of total fatty acids. Heptadecanoic acid (C17:0) was included as an internal reference before the extraction of lipids to determine the recovery of the fatty acids in each sample. The recovery of methylated fatty acids calculated in a comparison to the internal standard was higher than 80%.

Esterification Level Analysis of Oils
Thin-layer chromatography (TLC) was used to confirm the contents of esterified form of fats used in feeding trials. The LA-80 (which contained 80% free form of LA) and LA by-product (LBP; Lipozen Inc.) were used in TLC analysis as the comparative groups of CLA-80 and CBP, respectively. The CBP and LBP were obtained from the purification procedure of CLA and LA respectively, the concentration of which were 80%. Each diluted solution of CLA-80, CBP, LA-80, and LBP (80 µL/0.7 mL of hexane) was submitted to TLC on silica gel plates (20 x 20 x 0.25 Silica Gel 60 plates, Merck) using a solvent system of hexane-diethylether-methanol-acetic acid (80:15:3:2, vol/vol). Molybdatophosphoric acid solution (10%) was used as a color former.

Heat Stability and POV Measurements of Oils
The CLA-80, CBP, LA-80, and LBP oils (10 g each) were placed in 50-mL beakers and held in an oven at 95 ± 1°C for up to 0, 12, 24, and 48 h. Immediately after each storage period, changes of main fatty acids contents of oil samples were analyzed by GC and measured for POV as described by Raghavan and Hultin (2005) with some modification.

Statistical Analysis
Statistical differences were determined by ANOVA, with mean separations performed by the Duncan multiple range test using the GLM procedure of the SAS statistical software package (SAS Institute, 1996). Egg yolk samples were analyzed in triplicates and the variation between samples is expressed as the pooled SEM or mean ± SEM, where applicable.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Egg Quality and Productivity
The dietary group fed with CLA alone showed significant adverse effects on layer performance and egg quality as shown in Table 2Go. Feed intake was relatively lower in oil supplementation groups compared with the control group, but the difference was not statistically significant (P > 0.05). This may be partly due to the adverse effects of CLA on the animal (Yeung et al., 2000), and it seemed that the esterification of fat did not affect such effect. Although there was no significant difference, laying rate, strength and thickness of eggshell, and yolk height were decreased in eggs from the CLA-fed group, but these effects were not evident in the eggs from the CBP-fed group. Reduction of feed intake by CLA supplementation has been reported in most of the research with poultry, and the same result has been observed in other experimental animals (Ahn et al., 1999; Szymczyk and Pisulewski, 2003; Shang et al., 2004). These results may be due to the fatty acid composition in egg yolks not being adversely affected by CBP. Therefore, the present results suggest that supplementation of CBP had no adverse effects on egg quality and productivity compared with free form of CLA.


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  		Table 2. Effect of different dietary oil supplementation on performance and egg quality of hens during the experiment
 
Fatty Acid Profiles of the Egg Yolk
The change in fatty acid composition of the egg yolks was observed for 5 wk of feeding trial. Total CLA contents in the test group with CBP significantly increased from the first wk of feeding, whereas the CLA group showed an increase from the third week (Figure 1Go). Moreover, CLA contents in the CBP group throughout the experimental period were higher than that in the CLA group and increased up to 8.71% of total fat in the fourth week. These results indicated that CLA in CBP was used more efficiently to promote the accumulation of CLA in the egg yolk. It was confirmed by TLC analysis that the major forms of fats in CBP were esterified forms including monoglycerides, diglycerides, and triglycerides (TG) with little free fatty acids (FFA), whereas the fat in the CLA group was FFA (Figure 2Go). Ramirez et al. (2001) observed the positional distribution of fatty acids in dietary TG and determined that the major form absorbed to the intestine was 2-monoglycerides (2-MG) and the form of glycerides influenced the composition of chylomicrons. The TG is resynthesized in the intestinal mucosa using 2-MG from dietary lipids after absorption. Typically, the sn-2 position of fatty acids in TG is favored for absorption into the intestine, whereas no specificity has been found for the fatty acids in the sn-1 and sn-3 positions. Therefore, CLA in 2-MG form as a digestion product in the intestine could be more favored compared with free CLA in the micelles in the formation and resynthesis of TG. Ultimately, it may induce effective absorption of dietary fat into the intestine of animals. Thus, the use of esterified fats as a vehicle for unsaturated fatty acids is considered to be efficient (Fown et al., 1994; Carnielli et al., 1995; Innis et al., 1997; Lien et al., 1997). Further studies on the specific position of FFA in TG are to be performed.


Figure 1
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  		Figure 1. The changes of conjugated linoleic acid (CLA) contents in egg yolk after feeding. Chickens (n = 21) were fed with different oils for 5 wk. Control = basal diet; CBP = CLA by-product (2%); CLA-80 = 80% free form of CLA (2%). Error bars represent standard deviations of each data point (n = 3).

 

Figure 2
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  		Figure 2. The contents of esterified form of fats used in feeding trials. CLA-80 = 80% free form of conjugated linoleic acid (CLA); CBP = CLA by-product; LA-80 = 80% linoleic acid (LA); LBP = LA by-product. The LA and LBP were analyzed for the accurate comparison between oils and oil by-products but not used in feeding trials. Data represent mean values from 3 experiments. FFA = free fatty acids; STD = standard.

 
The ratio of saturated fatty acids (SFA) to polyunsaturated fatty acids (PUFA) in the egg yolk is an important parameter in terms of the nutritional balance and related to the incidence of degenerative diseases such as cardiovascular disease and atherosclerosis. It was higher with the CLA-fed groups along the test period than control, and the difference was more pronounced toward the end of the test period. This is the typical tendency of fatty acid profile shown when CLA level was increased. The level of monounsaturated fatty acids decreased and stearic acid increased due to the inhibition of {Delta}-9 desaturase by CLA (Miyazaki and Ntambi, 2003). This tendency was more evident with CBP group compared with CLA-80 group, but there was no significant difference between CLA-80 group and control group at the early stage of the experimental period, and there was no significant change in the value for CBP group throughout the test period (Figure 3Go). Aydin et al. (1999) suggested that egg quality is influenced by the change of yolk water content, and the ion movement through vitelline membrane is affected by the shift in fat compositions of the membrane, and this effect was thought to be minimized when the fats are in the glyceride form. Layer performance is highly associated with the related lipid metabolism to meet the metabolic demands of laying hens for yolk formation (Mark et al., 2003). In our study, it seemed that the change in the ratio of SFA to PUFA influenced the egg production rate to some extent in the test groups, although there was no significant difference (P > 0.05). As shown in Table 3Go, many research reported that dietary CLA supplementation decreased the level of monounsaturated fatty acid but increased that of SFA in egg yolk (Ahn et al., 1999; Yang et al., 2002). It was the most remarkable in CBP group, which showed the highest level of CLA. The C18:2 n-6 and C18:3 n-3 were not affected significantly by supplementation of CLA.


Figure 3
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  		Figure 3. The changes of saturated fatty acid (SFA)/polyunsaturated fatty acid (PUFA) ratio in egg yolk after feeding. Chickens (n = 21) were fed with different oils for 5 wk. Control = basal diet; CBP = CLA byproduct (2%); CLA-80 = 80% free form of CLA (2%). Error bars represent standard deviations of each data point (n = 3).

 

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  		Table 3. Fatty acids composition in egg yolk (% of fat)1
 
Therefore, it is reasonable to conclude that the supplementation of CBP, which is constituted of mainly esterified form of CLA, is efficient in the accumulation of the CLA in the egg yolk compared with purified free-form CLA. Also, there was no adverse effect on layer performance and egg quality. It is meaningful to utilize oil byproduct as a CLA source, and this study indicated that the esterified form is more efficient than free form as a functional fat additive in the feed for the healthy egg production.

Heat Stability and POV of Oils
To investigate the stability of the oil by-products, CLA-80, CBP, LA-80, and LBP were heated in an oven at 95°C for 48 h. The LA-80 and LBP were included in this study to compare the stability between FFA and oil by-products. Decreases in CLA contents of CLA-80 and CBP after heat treatment were 12.92 and 0.51%, respectively. The decreases were 19.63 and 5.78% in LA-80 and LBP, respectively (Figure 4Go). Considering less degree of change in CLA content in CBP after heating compared with the change in LA contents in LBP, it was thought that CLA in CBP was more stable than LA in LBP. In fact, unsaturated fatty acids with conjugated double bonds are chemically stable compared with fatty acids without conjugation. In addition, hydroperoxide production from the group of CBP and LBP was not higher than that of CLA-80 and LA-80, although a tendency of each sample was similar (Figure 5Go). These results indicated that the oil by-product has significantly higher stability against lipid oxidation induced by high temperature compared with the purified form of CLA and LA. The degree of lipid oxidation by heat treatment was affected by the form of fats, and FFA was thought to be more susceptible compared with the esterified form (Campbell et al., 2003). On the other hand, Chen et al. (1997) reported that CLA as the FFA form was very unstable similar to that of docosahexanenoic acid. The free form of CLA may readily donate an electron or a hydrogen ion to form free CLA radical intermediates due to resonance delocalization. Moreover, the free CLA radicals have been shown to be rapidly decomposed to furan fatty acids (Yurawecz et al., 1995). In the present study, it was demonstrated that heat-stability of oil by-products measured by the stability of main fatty acids content and POV was adequately preserved. Effects of dietary oil by-products such as CBP and LBP on the egg quality during storage need to be examined, and the effect on the cooking quality should also be studied in further studies.


Figure 4
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  		Figure 4. The changes of major fatty acid content in fats used in feeding trials after heat treatment. CLA-80 = 80% free form of CLA, 2%; CBP = CLA by-product; LA-80 = 80% linoleic acid (LA); LBP = LA by-product. The LA and LBP were analyzed for the accurage comparison between oils and oil by-products but not used in feeding trials. Error bars represent standard deviations of each data point (n = 3).

 

Figure 5
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  		Figure 5. The changes of hydroperoxide values in fats used in feeding trials after heat treatment. CLA-80 = 80% free form of CLA; CBP = CLA by-product; LA-80 = 80% linoleic acid (LA); and LBP = LA by-product. The LA and LBP were analyzed for the accurate comparison between oils and oil by-product but not used in feeding trials. Error bars represent standard deviations of each data point (n = 3).

 


   ACKNOWLEDGMENTS
 
This work was supported by research grant (10027407-2006-01) from the Ministry of Commerce, Industry and Energy, Republic of Korea.


   FOOTNOTES
 
1 The first two authors equally contributed to this work. Back

Received for publication March 20, 2007. Accepted for publication September 29, 2007.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
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