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Praca oryginalna Original paper
Conservation of genetically different animals, among them birds, existing in small populations and threatened with extinction is required for economic, scientific, cultural and historical reasons (2). There are eight flocks of ducks included in the duck conservation pro-gram in Poland. The conservative flocks of ducks kept in situ are a source of genetic variability which allows breeding work to be continued (10). From the point of view of breeding maintaining genetically diversified conservative flocks of birds it is necessary to give rise to genetic variation in the selected populations.
These conservative flocks were used in the deve-lopment of new breeding and experimental strains and synthetic lines as well as in the search for heterosis effects in commercial sets (9). Ducks kept in small populations are particularly susceptible to the intense effects of inbreeding and genetic drift (15). These
unique populations are characterized by good produc-tion traits, which are the basis of studies on traits such as egg quality (12, 14).
The eggs of ducks were studied to determine the interbreed variability of the species (11) and their use-fulness for the food industry (20). Generally, avian eggs are recognized as one of the main sources of protein for human nutrition. Even though eggs of domestic fowl constitute an important source of protein in the human diet (21), duck eggs containing approx. 53% egg white and 35% yolk are not used for consumption and processing in Poland. In Poland and many other European countries hen eggs are most frequently used for human consumption (7).
Although the morphological traits of duck eggs from conservative flocks (e.g.: egg specific gravity, eggshell thickness, egg shape index and egg white and yolk
Effect of genotype on some egg quality parameters
of ducks from different conservative flocks
ANDRZEJ OKRUSZEK, JULIUSZ KSI¥¯KIEWICZ*, JANINA WO£OSZYN, JADWIGA BIERNAT**, GABRIELA HARAF, AGNIESZKA ORKUSZ
Department of Animal Food Technology, Engineering and Economics Faculty, Wroclaw University of Economics, Komandorska 118/120, 53-345 Wroc³aw, Poland
*Department of Farm Animal Genetic Resources Conservation, National Research Institute of Animal Production, 32-083 Balice n. Kraków, Poland
**Department of Bromatology, Pharmacy Faculty, Wroclaw Medical University, Nankiera 1, 50-140 Wroc³aw, Poland
Okruszek A., Ksi¹¿kiewicz J., Wo³oszyn J., Biernat J., Haraf G., Orkusz A.
Effect of genotype on some egg quality parameters of ducks from different conservative flocks Summary
The objective of the study was to compare the chemical composition and fatty acid profile of eggs of two-year-old light type ducks: Orpington (O1) and crossbreed ducks Khaki Campbell × Orpington (KhO) as well as Pekin type ducks P9, A1 and A2 from conservative flocks, collected at the onset (the 6th week) of the
second laying period. There were no significant differences in the water content (in egg whites and yolks), cholesterol content in yolk lipids and pH value of egg whites in the investigated eggs. The eggs of A1, A2 and P9 contained more (P £ 0.05; 0.01) protein in egg white (11.01%, 10.97% and 10.85% respectively) and yolk (16.34%, 16.26% and 16.24% respectively) than O1 and KhO eggs (10.74% and 16.07% as well as 10.66% and 16.21% respectively). Furthermore the A2 eggs were characterized by the lowest of lipid contents in yolk (27.19% v/s 29.45-30.99%) and pH yolk value (6.27 v/s 6.31-6.40). In P9, A1 and A2 eggs, yolk lipids contained more C 16:0, C 20:5 ù-3 (EPA), C 22:4 ù-6 and C 22:6 ù-3 (DHA) and less CLA 18:2 ù-6 and trans isomer fatty acids (C 16:1 trans-9 and C 18:1 trans-11) than those of O1 and KhO eggs. The unsaturated fatty acids (UFA) were predominant in yolk lipids of eggs for all flocks (69.02%-72.28%). The A1 yolk lipids contained the most UFA, PUFA (19.74%) and SFA (27.41%). A higher concentration of PUFA from ù-6 group was observed in A1 (15.42%) and KhO (15.32%) eggs. Egg yolks collected from P9, A1 and A2 ducks were characterized by a higher level of ù-3 PUFA fatty acids (4.34%, 4.32% and 4.71% respectively) in comparison to KhO and O1 eggs (3.97% and 4.10% respectively). The more favorable ratio of ù-6/ù-3 PUFA was counted for KhO (3.86) and A1 (3.57) eggs, but for the investigated flocks it was close to the recommended values of human diets.
Medycyna Wet. 2008, 64 (4A) 418
index) have already been thoroughly studied in previous investigations conducted, among others, by Ksi¹¿kiewicz and Bednarczyk (11) and Kisiel and Ksi¹¿kiewicz (8) there is still not enough information on the chemical composition, physicochemical proper-ties of fresh egg content and especially on the profile of fatty acids in lipids of yolk.
The objective of the study was to evaluate chemical composition, physicochemical properties and quantity of fatty acids and cholesterol in egg yolk lipids collected from two-year-old ducks from five conservative flocks of ducks at the onset (6th week) of the second laying
period.
Material and methods
The study was conducted on duck eggs from five con-servative flocks, maintained in situ method as a gene bank at the Dworzyska Waterfowl Breeding Farm. The experi-mental material consisted of eggs (20 from each flock) collected from two-year-old light type ducks: O1 Orping-ton, yellow brown variety, from the parental flock impor-ted from France in 1971 and KhO crossbreed ducks being a cross of 50% Khaki Campbell (Kh1) and 50% O1 (Orpington) as well as Pekin type: P9 Pekin parent stock Jansen Comp., France, 1978; A1 and A2 progeny of a commercial stock imported from England in 1977 at the 6th week of laying. The eggs from each flock were
randomly sampled twice each one day.
The ducks were kept in a windowless poultry house in a controlled environment with no access to an outside run. All birds were fed ad libitum with the same all-mash diets for breeding ducks. The all-mash contained 173.45 g crude protein, 33.09 g fibre; 33.35 g fat and 11.15 MJ metaboli-zable energy per 1 kg of feed.
The analyses were made after 24 h of cold storage (3.0--4.0°C). The basic chemical composition of egg white and yolk was analyzed by the standard methods by AOAC (1). The pH of egg white and yolk were measured with the use a digital Metrohm pH-meter 654 series (Metrohm Ltd. CH-9100 Harisau,
Switzerland), equipped with a combination type of pH electrode Food-trode series (Hamilton Company in Reno, Nevada USA).
The cholesterol con-tent in the yolk was determined using the enzymatic Human test in an extract prepared ac-cording to the Folch et al. (5) procedure as modi-fied by Wasburn and Nix (24). The absorbance was detected with a Hewlett--Packard 8452A UV/VIS spectrophotometer, at a wavelength of 500 nm.
The composition of fatty acids was determined using gas chromatography technique with an Agilent Tech. 6890N Chromatograph (Agil. Tech. Inc., St. Clara, USA), equip-ped with a flame-ionization detector (FID). The methyl esters of fatty acids were separated on a fused silica CP-Sil 88 (Chromopack, Netherlands) capillary column (100 × 0.25 mm), with helium as the carrier gas. The separation was conducted at the programmed temperature column and FID from 165°C to 200°C (at increments of 2°C/min) and 253°C, respectively. The identification of fatty acids was accom-plished by comparison with external standards. The fatty acids were calculated as % of total fatty acids with the ChemStation v. 4.0 Agilent Technologies program.
The data were analyzed statistically (arithmetic mean and standard deviation) for a one-way analysis of variance (ANOVA) in a non-orthogonal scheme. Significant diffe-rences between the average values were determined by Duncans multiple range test. The statistical analyses were processed with the Statistica data analysis software system, version 7.1.
Results and discussion
It was confirmed that chemical composition and physicochemical properties of the investigated eggs depended on the kind of flock (tab. 1). The A2, A1 and P9 eggs were characterized by higher (P £ 0.05; P £ 0.01) protein content in egg whites (11.01%, 10.97% and 10.85% respectively) and yolks (16.34%, 16.26% and 16.24% respectively) than O1 and KhO eggs (10.74% and 16.07% as well as 10.66% and 16.21% respectively). The lipid content in yolks was significantly lower in the A2 eggs (27.19%) than the A1 (30.62%), P9 30.99% (P = 0.01) and KhO (P £ 0.05) 29.67% (tab. 1). The protein and lipid contents in yolks were lower (»1.70% and »5.60% respectively) in comparison with data published by Romanoff and Romanoff (23). Whereas the percent-age content of lipids in yolk eggs of light type ducks established by Kisiel and Ksi¹¿kiewicz (8) amounted
ti a r T k c o l F e p y t t h g i L Pekintype M E S oEffflfeocctk 1 O KhO P9 A1 A2 n a e M Mean Mean Mean Mean % , e ti h w g g e n i t n e t n o c r e t a W 87.45 86.40 86.57 86.68 86.38 0.22 ns % , k l o y n i t n e t n o c r e t a W 49.93 49.45 49.42 49.96 49.03 0.19 ns % , n i e t o r p e ti h w g g E 10.74 aa10.66Bb 10.85 a10.97a A11.01A 0.04 ** % , n i e t o r p k l o Y aa16.07Bb 16.21 a16.25a a16.26a A16.34A 0.03 * % , s d i p il k l o Y 29.45 a29.67a A30.99A A30.62A aa27.19Bb 0.39 * g / g m , k l o y n i l o r e t s e l o h C 17.60 17.10 17.59 17.58 17.73 0.31 ns e ti h w g g e H p 19.05 19.01 19.00 19.01 19.00 0.01 ns k l o y H p 1a6.39a 1a6.40a 16.31 16.34 1a6.27b 0.02 *
Tab. 1. Chemical composition and physicochemical properties of duck eggs
Explanations: SEM standard error of mean; * P £ 0.05; ** P £ 0.01; ns not significant; means with different superscript letters differ significantly a, b p £ 0.05; A, B p £ 0.01
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to »36.20% and was higher for data results obtained in the present investigations.
The pH value of yolks of eggs from light type ducks O1 and KhO was higher (P = 0.05) compared to Pekin type ducks A1, A2 and P9 (tab. 1). The pH value of egg whites and yolks of eggs from pedigree ducks of two parental flocks (A44 and A55) and three maternal flocks (P66, P77 and K11), collected at the start (2nd week) of the first laying period, ranged from
8.54 A55 up to 8.61 K11 and from 6.00 P66 up to 6.08 P77 pH unit respectively (17) and were on average lower by 0.44 and 0.30 pH unit respectively than for the analyzed flocks.
No significant effect of duck origin on the water con-tent of egg whites and yolks, cholesterol concon-tent in yolk lipids and pH egg whites, was established (tab. 1). The proportion of water content in O1, KhO, P9, A1 and A2 egg yolks was similar to those established by Petersen et al. (19) for Lohman LSL and Lohman Brown hen eggs. However the water content of egg whites and yolks for all investigated duck eggs
diffe-red in comparison to the data results published by Dziadek et al. (3) for table eggs from three commercial lines of laying hens (ISA Brown, Shaver 579 and Lohman Brown). The cho-lesterol content in yolk lipids of eggs from all investigated flocks was evidently lower (from 2.90 mg/g A2 up to 3.53 mg/g KhO respective-ly) in comparison with the data results obtained by Ksi¹¿kie-wicz and Kisiel (13) for eggs of 54-week-old light type ducks from conservative flocks (O1, Kh1, KhO).
The kind of duck flock in-fluenced the profile of fatty acids in yolks (tab. 2). The UFA were predominant in yolk lipids from all investigated flocks, which amounted to 69.02% O1, 70.68% A2, 71.37% P9, 71.86% KhO and 72.28% A1, respective-ly, of the total content of fatty acids.
The main components of the UFA were MUFA, among them C 18:1 cis-9. The yolk lipids of KhO, P9, A1 and A2 eggs contained more (P £ 0.05, P £ 0.01) C 18:1 cis-9, ã C18:3 ù-6 and C 16:0 (except KhO) and less (P £ 0.05, P £ 0.01) C 16:1 trans-9, C 18:1 trans-11 and CLA 18:2 ù-6 and long-chain PUFA C 20:5 ù-3 (EPA) C 22:4 ù-6 and C 22:6 ù-6 (DHA) fatty acids than the lipids of O1 eggs. The UFA/SFA ratio in yolk lipids of Pekin type ducks (P9, A1 and A2) were similar (2.63, 2.64 and 2.59 respectively), whereas in the yolks from light type ducks (O1 and KhO) it was more favorable (2.62 and 2.77 respectively).
The data on O1, KhO, P9, A1 and A2 yolk lipids were lower for C 16:0 and C 18:1 cis-9 and higher for C 18:2 ù-6, C 20:4 ù-6 and C 22:6 ù-3 (DHA) than the data previously published by Maldjian et al. (16) concerning the content of fatty acids in yolks of com-mercial ducks eggs. Furthermore, the yolk lipids of the investigated eggs contained less SFA C 16:0 (harmful for human health) and C 18:0 (which is bio-logically neutral) and more long-chain PUFA main-ly C 20:4 and C 22:6 (except O1) than yolk lipids of eggs from 18-week-old Warren line hens (22) and Japanese quails (18).
From the nutritional perspective, it is important to determine the ù-6/ù-3 ratio, which should account for
) % ( d i c a y tt a F k c o l F e p y t t h g i L Pekintype M E S oEffflfeocctk 1 O KhO P9 A1 A2 n a e M Mean Mean Mean Mean 0 : 6 1 C 22.78B 22.49B 23.62A 23.98A 23.92A 0.13 ** 1 : 6 1 C cis-9 3.55B 3.57B 3.86AD 4.19AC 3.50B 0.06 ** 1 : 6 1 C rtans-9 1.41a 1.40a 1.35A 1.34A 1.27b 0.05 ns 0 : 8 1 C 3.54A 3.48A 3.59A 3.43A 3.40A 0.05 ** 1 : 8 1 C cis-9 42.82B 45.07A 44.80A 44.50A 44.18A 0.18 ** 1 : 8 1 C rtans-11 2.86a 2.53b 2.49b 2.51b 2.50b 0.05 ns 2 : 8 1 C w 6- 9.58A 9.55A 9.18A 9.33A 9.54A 0.09 ns gC18:3w 6- 0.19Bb 0.23A 0.24Ac 0.24Ac 0.21ad 0.02 ** 2 : 8 1 A L C w 6- 0.33AC 0.32Aa 0.27Db 0.23B 0.25B 0.01 ** aC18:3w 3- 2.10A 1.46Bb 1.62Ba 1.45Bb 2.16A 0.06 ** 4 : 0 2 C w 6- 3.98B 4.99ADE 4.63ADFa 5.39AC 4.31ADb 0.09 ** 5 : 0 2 C w 3- (EPA) 0.13Bb 0.15Ba 0.18A 0.17A 0.17A 0.01 ** 4 : 2 2 C w 6- 0.20b 0.23a 0.21 0.23a 0.21b 0.01 * 6 : 2 2 C w 3- (DHA) 1.87B 2.36ADb 2.54Aad 2.70ACc 2.38ADb 0.05 ** SUFA 69.02 71.86 71.37 72.28 70.68 SMUFA 50.64 52.57 52.50 52.54 51.45 SPUFA 18.38 19.29 18.87 19.74 19.23 SSFA 26.32 25.97 27.21 27.41 27.32 SUFA/SSFAraito 12.62 12.77 12.63 12.64 12.59 S w 6- 14.28 15.32 14.53 15.42 14.52 S w 3- 14.10 13.97 14.34 14.32 14.71 w S -6/Sw-3raito 13.48 13.86 13.35 13.57 13.08
Tab. 2. Fatty acid composition in egg yolks of duck eggs
Explanations: as in tab. 1; UFA unsaturated fatty acids; MUFA monounsaturated fatty acids; PUFA polyunsaturated fatty acids; SFA saturated fatty acids
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4-6 : 1 (4, 6). In the present study, the ratio of PUFA ù-6/ù-3 was more favorable in the KhO eggs (3.86). In the eggs of remaining duck flocks the ratio was lower (3.08 A2, 3.35 P9, 3.48 O1 and 3.57 A1).
Based on the results of our study it can be conclu-ded that the basic chemical composition, values of pH egg white and yolk as well as the fatty acid profile in yolk lipids of eggs from the analyzed flocks (the same feeding, housing conditions and age), were different and dependent on the birds origins. The eggs from Pekin type ducks (P9, A1 and A2 flocks) contain more proteins in egg whites and yolks and lipids in yolk (except A2) in comparison to that from light type ducks (O1 and KhO flocks). Furthermore the yolk lipid extracts from eggs of Pekin type ducks contained more C 16:0, C 18: 1 cis-9 (except KhO flocks) and C 20:5 ù-3 (EPA) as well as lower trans isomeric mono-unsaturated fatty acids C 16:1 trans 9 and C 18: 2 trans 11 in comparison to yolk lipids of light type ducks. Summing up the data results of the conducted in-vestigations, it can be said that from the perspective of chemical composition and profile of fatty acids of yolk lipids eggs of ducks from the A2 flock were slightly favorable. It is also evident that eggs from A2 flocks have been characterized by a higher nutritional value than eggs from remaining investigated duck flocks.
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Authors address: dr in¿. Andrzej Okruszek, Katedra Technologii ¯ywnoci Pochodzenia Zwierzêcego, Wydzia³ In¿ynieryjno-Ekonomiczny, Akademia Ekonomiczna, ul. Komandorska 118/120, 53-345 Wroc³aw; e-mail: andrzej.okruszek@ae.wroc.pl
