Valentina FERRANTE
Maria G. MANGIAGALLI
Susanna LOLLI
Luigi GUIDOBONO CAVALCHINI
Department of Animal Sciences, DSA,
Faculty of Veterinary Medicine,
University of Milan,
Milan, Italy
Eggs are a rich source of lipids and proteins. Nourishment supplying is not, nowadays, the only function of the food: consumers’ interest is oriented to food healthiness and dietetic value, animal welfare, environmental impact of animal productions and product traceability. In order to evaluate the link between egg production systems and egg quality, physical parameters and fatty acid profile have been investigated. Eggs from four different production systems labelled as standard, alternative, litter-floor and n-3 enriched have been analysed. There were significant differences in SAFA, MUFA and PUFA concentration. Eggs from the different production systems showed significantly different levels in n6/n3 ratio; EPA and DHA underline the occurring differences between n-3 enriched eggs and eggs from hens fed regular diets. Physical parameters like egg weight, albumen weight, shell weight and total lipids concentration are not significantly influenced by the production-feeding method.
Introduction
Gallus gallus domesticus egg is one of the most common foods all over the world. It can be considered the cheapest nutritionally complete food; it is a rich source of lipids and amino acids (Surai and Sparks, 2001). Yolk fatty acids have a central role in egg nutritional properties evaluation. The yolk weight of a typical chicken 60g egg is 20g of which 50% is solid matter and 50% is water; it contains 6g of lipids and 3g of proteins (Speake et al., 1998). Egg lipid classes are: Triacylglycerols (65%), Phospholipids (28.3%), Free Cholesterol (5.2%), Cholesterol ester and free fatty acids (traces) (Thapon and Bourgeois, 1994). Lipid classes display a stubborn resistance to change, on the contrary their constituent: fatty acids are more compliant to manipulation. Egg yolk fatty acid profile variations may be linked to differences in feed composition, genetic strain, liver physiological reaction (desaturation and elongation) and PUFA incorporation efficiency into Very Low Density Lipoprotein (VLDP) lipids (Speake et al., 1998). Egg lipids have a high biological and nutritional value: they are the major energy source and provide different essential components for embryo tissue development and functionality (Noble et al., 1996). PUFAs have specific regulatory functions being involved in the synthesis of a range of biologically active compounds such as eicosanoids (Surai and Sparks, 2001). According to Uauy and Castillo (2003) blood pressure, vasoconstriction and vasodilatation, thrombocyte aggregation, inflammatory reaction and leukocyte activity together with bronchial constriction and uterine contractility are some of the cell and tissue physiological functions regulated by these autocrine and paracrine mediators.
Food function is nowadays not merely limited to nourishment supplying; consumers’ interest is oriented to food healthiness (Mine and Kovacs-Nolan, 2004) and nutritional value, animal welfare, environmental impact of animal productions and products’ traceability. The Total Quality concept defines in the third point of the list the nutritional quality of an animal product as related to the composition of proteins and lipids and the presence of macro and trace elements and the absence of allergenic compounds (Nardone and Valfrè, 1999). According to Aumaitre (1999) fatty acid profile can be considered an ‘additional chemical factor’ defining the quality of animal productions.
The quality of the product involves not only product characteristics but animal welfare and production systems (feed, facilities, transport) too; traceability and farm assurance procedures are powerful tools to certify these different aspects. Furthermore, sustainability of animal production concept is strictly related to the satisfaction of human and animal welfare requirements (Spedding, 1995).
Layer hens housing condition is traditionally an intensive system: all over the world battery cages can be considered the most common housing system in high scale production. Battery cages are the replay to a low cost production demand. Housing systems have a strong impact on egg production costs. According to Drakley et al. (2002) battery cages are an efficient egg production system when considering feed conversion, ease of management and egg cleanliness and hygienic quality. Furthermore parasites in cages are less common than in extensive systems and considering the immediate separation between birds and their droppings: cages are more hygienic both for the birds and their product: the egg. Welfare friendly egg production systems with their space allowance offer the birds the possibility to express their specie specific behavioural patterns; however in cages there is generally very low mortality, and feather pecking and cannibalism are rare (Drakley et al. 2002). The importance of eggs alternative productions systems is growing due to European Union legislation and particularly to the Council Directive 1999/74/EC of 19 July 1999 laying down minimum standards for the protection of laying hens and to the Commission Directive 2002/4/EC of 30 January 2002 on the registration of establishments keeping laying hens, covered by Council Directive 1999/74/EC; layers’ cages will be prohibited from the 1st of January 2012.
Advantages and disadvantages are present in every housing system considering the commonly used welfare indicators: behaviour, physiology, health, production (characterized by a high number of variables). Housing system evaluation should analyse design criteria related to welfare needs (e.g. space allowance) and performance criteria as indicator of good welfare (e.g. production and physiology) (Rushen and De Pasillè, 1992). There is a close link within housing system, welfare and production being the physiological and behaviour response to distress, an impairing effect on organism whole efficiency and, as consequence, on productive efficiency. Egg production can be affected under a quantitative and a qualitative point of view. However links with egg nutritional characteristics and housing system and birds welfare are rare and contrasting. The objective of the present work was to compare the fatty acids profiles within market eggs from hen housed in different systems and fed with a n-3 enriched diet.
Materials and Methods
Eggs and production systems
Sixty-nine brown eggshell fresh market eggs have been collected; they were grouped by production system and by enrichment. Eighteen eggs marketed as standard were produced in battery cages (group 1), eighteen eggs labelled ‘alternative’ were produced in housing system with slat floor and outdoor pen (group 2), fifteen eggs labelled as litter-floor were produced in litter floor housing system (group 3), eighteen eggs were labelled as n-3 enriched (designer), group 4, and produced in battery cages.
Information about the birds, the housing facilities and the feeds composition were collected from the producing farms and are summarized in Table 2 and 3. Hens producing designer n-3 eggs received a diet with 3% encapsulated fish oil: the fatty acid composition is reported in Table 3 (vitamin E inclusion: 240 mg/Kg). Eggs were one day old and stored one day at 5°C.
Physical parameters
Physical parameters were recorded weighing singularly the whole egg, the yolk (separated with a yolk separation cup for cooking use), the albumen and the shell (membranes included).
Total lipids and fatty acid profile
The total lipids were extracted from singular yolk samples in a suitable excess of chloroform/methanol (2:1, vol.:vol) (Folch et al., 1957; Christie, 1982). Fatty acids were trans-methylated by refluxing in methanol: toluene: sulphuric acid (20:10:1, vol.:vol.:vol.) in the presence of pentadecanoic acid standard (Hamilton et al., 1992).
Fatty acid quantification was obtained by gas chromatography by injection via a CP9010 autosampler (Chrompack, Speck Analytical, London) onto a capillary column (Carbowax, 30 m x 0.25 mm, film thickness 0.25 μm; Alltech ltd., Carnforth, UK) in a CP9001 Chrompack gas chromatograph connected to a data processing system: EZ-Chrom data handling system (Speck Analytical, UK). The identification of the peaks was determined by comparison with the retention times of external standard fatty acid methyl ester mixtures. The amount of each fatty acid was calculated comparing fatty acids peaks areas to the peak area of Pentadecanoic fatty acid (standard) (Christie et al, 1970).
Statistical analysis
Statistical analyses were performed by the analysis of variance (ANOVA) using General Linear Model procedure of SAS® statistic package (SAS, 1998). The used model was undertaken to assess the differences between eggs from different production systems. The source of variation was the origin of the eggs. Student’s t-test was applied to the calculations of the least square means difference.
Results
Some characteristics of the four production systems are summarized in Table 1: differences in housing conditions and space allowance are reported. Table 2 deals with the feeds used in the four considered systems as communicated by the producers showing the variability occurring in feed chemical characteristics. All the hens were ad libitum fed. The encapsulated fish oil, n-3 source, fatty acid concentration is reported in Table 3.
The average fatty acid concentration for the four groups and the occurring differences are shown in Table 4.
Alternative eggs have the highest concentration of palmitic acid; the difference is highly significant when compared to standard eggs and to litter floor eggs. Standard eggs have the lowest palmitic acid concentration; there are statistically significant differences with designer n-3 eggs (P≤0.001). Alternative eggs and Litter floor eggs show significant differences. The statistical analysis revealed significant effects of the production system on stearic acid concentration with the lowest concentration in litter floor eggs and the highest concentration in alternative eggs (P≤0.01).
Oleic acid highest concentration has been recorded in litter floor eggs, highly significant differences are present between litter floor eggs and standard, alternative and designer n-3 eggs (P≤0.01).
The eggs produced by hens reared in litter floor facilities have the lowest concentrations in linoleic acid; they show highly significant differences with the eggs from the other production systems (P≤0.01). Standard eggs with their high concentration in linoleic acid show highly significant differences when compared to alternative, litter floor and designer eggs (P≤0.01). The differences between n-3 enriched eggs and litter floor eggs are highly significant.
Linolenic acid concentration is higher in standard eggs than in the other classes, alternative eggs differ significantly in linolenic acid concentration from litter floor eggs. Designer n-3 eggs show a significantly lower concentration in arachidonic acid compared to the other production systems’ eggs.
EPA and DHA concentration of n-3 enriched eggs is clearly higher than in the eggs of the other groups, the existing differences are highly significant.
Saturated Fatty Acids (SAFA) concentrations were calculated, a statistically significant influence of the production system was observed: alternative eggs showed the highest concentration in SAFA when compared to standard litter floor and n-3 eggs (P≤0.001).
Poli Unsatured Fatty Acids (PUFA) showed the highest concentration in battery caged and designer eggs (P≤0.001) compared to alternative and litter floor eggs recording the PUFA lowest concentration.
The n-6/n-3 ratio was calculated; it ranked, from the lowest to the highest, designer n-3, battery cage, litter floor and alternative eggs.
The results in Table 5 show physical parameters variations: only yolk weight showed statistically significant differences for production system.
Litter floor egg yolk weight had the lowest value; it differed significantly from the weights of the yolks of the eggs from standard and alternative production systems.
Discussion
The experimental trial shows how fatty acid profiles differ in different labelled table eggs. Focusing on fatty acid concentration it is important to underline that every considered fatty acid is characterised by different values for every housing system.
Palmitic acid concentration was recorded with the highest value in alternative eggs. SFA have been calculated to be positively correlated with circulatory system and heart pathologies. However stearic acid, as reported by Cobos et al. (1995) seems not to raise cholesterol level in humans. SFA profile of egg yolk, according to Jakobsen (1999), is not influenced by the SFA concentrations of the diets. Ayerza and Coates (2001) calculated that diets rich in linolenic acids affect the palmitic acid concentration in egg yolk: an inverse proportion was described. Alternative eggs showed the highest concentration in stearic acid too, SAFA concentration stresses these results too. Jiang et al., in 1991, stressed the hypocholesterolemic effect of oleic acid. In this research the highest concentration of this monounsatured fatty acid (MUFA) have been recorded in litter floor eggs. It has been known for decades that oleic acid is the most represented fatty acid in hen egg; our results are a further confirmation of this trend. Linoleic acid primarily and linolenic acid are the essential fatty acids (EFA) for poultry (Watkins, 1995); they play an important role in chick development, and in male reproduction both for their properties and for their function of precursors of ω-6 (linoleic) and n-3 (linolenic) PUFAs. The highest concentration of linoleic and linolenic acid has been recorded in standard eggs produced in battery cages. In contrast, Bergami et al. (1978) found higher level of linoleic acid in non-cage systems. The different concentrations of arachidonic acid must be underlined due to the key role of this fatty acid in prostaglandine metabolism (Watkins, 1995). According to Jiang et al. (1991) a negative relationship has been calculated between arachidonic acid and longer chain n-3 fatty acids. The clear evidence of the high concentration in n-3 fatty acids (EPA and DHA) in designer eggs confirm the efficacy of fish oil supplementation (3% diet formula) with high vitamin E inclusion (240mg/kg of feed) in order to avoid fishy smell and flavour and to limit the oxidation due to lipid saturation level. Watkins (1995) reported that EPA and DHA present in fish oil have a lowering effect on total n-6 PUFA in different chick tissues, in this experiment these results could be confirmed by the low concentration of arachidonic acid in n-3 enriched eggs. This kind of designer egg is produced in order to supply through a common food n-3 fatty acid important for human health particularly DHA. According to Surai et al. (2001) there are two ways to enrich eggs in n-3: the first one consists in enriching eggs in linolenic acid including flaxseed and linseed or their oils in the diets of the hens; the second, considering particularly critic life period (e.g. childhood and old age) when DHA synthesis might not be efficient, in supplying an egg directly enriched in DHA by inclusion of DHA (fish oil) in the hen diet. The concentration of total lipids is an important aspect to take into consideration while analysing egg quality: in our egg grouped by production system the highest value was calculated in standard labelled eggs (N.S.). According to Taylor (1996) who studied eggs produced in cages and aviaries founding no significant differences in average egg weight, the main part of physical parameters showed no significance in the recorded weights differences except for yolk weight lower in litter floor eggs (younger hens) (Etches, 1996; Sauveur, 1988). As reported by Stadelman and Pratt (1989) some experiments of the late seventies studied the effect of environment on egg yolk lipids concluding that there were differences between caged and free-range hen eggs.
Egg yolk fatty acid component is mainly affected by feeding programmes (Milinsk, 2003), dietary lipids, genetics and age (Cobos et al., 1995). Anyway improvement in housing and husbandry systems may positively influence hens’ welfare bettering birds’ life quality and production. In previous researches on table eggs from deep litter, slat floor and mesh floor housing systems no significant differences in egg weight, chemical profiles and yolk colour were found, on the other hand significant differences were recorded in hygienic aspects and in external egg shell bacterial contamination.
It is important to underline that eggs produced in battery cages were characterized by a higher nutritional value due to the highest concentration in PUFA and the lowest n-6/n-3 ratio (except n-3 designer eggs). On the other hand alternative and litter floor eggs showed the lowest PUFA levels and the highest n-6/n-3 ratio.
These results are confirmed by the analysis carried out by Zaniboni and colleagues (2006) who considered organic, litter floor, alternative and battery cage production systems.
The present study shows how different label market eggs are very similar in weight parameters (whole egg, yolk, albumen, shell) but differ significantly in fatty acids concentration, a characteristic strictly linked to birds’ diets formulae (Milinsk et al., 2003; Zaniboni et al., 2006 ) but heavily influencing the nutritive value of the egg.
The results from fatty acids profile analysis showed that table eggs fatty acid profiles are characterised by high variability within different labelled eggs. The number of variables in the analysed production systems influencing eggs’ fatty acid profile was very high: differences were present in the hen genetic strain and age, in the housing conditions and in the diet compositions and fatty acid profiles.
Designer n-3 eggs produced by hen with a 3% encapsulated fish oil inclusion in the diet are a valid dietary DHA supplier.
References are available on request.
