Functional and sensory properties of hen eggs with modified fatty acid compositions

Abstract

Foaming, emulsifying, gelling, and sensory properties of fresh and stored hen eggs fed with a diet supplemented with flax oil (FO), rapeseed oil (RO), fish oil (FISH), and by-product from black currant processing (BC) were investigated. With these diets, the ω6/ω3 fatty acid ratio of eggs varied from 1.5 to 5.8, while the ratio for eggs in the control group was 6.2. Compared to eggs in the control group, FO supplementation in the feed had statistically significant influences on the foaming properties of the fresh eggs. Eggs stored for 21 days lost part of their foaming properties in FISH oil supplemented group, but the foaming properties in all test groups were technically acceptable. The emulsifying properties of eggs in FO and FISH supplemented feeding groups were statistically different compared to control group. In boiled eggs, flax oil and fish oil supplementation induced off flavours in eggs, but no changes between the control group and test groups were found in the sensory properties of mayonnaise preparations. These results suggest that the egg processing industry may produce egg-based products using oil-supplemented eggs without major problems in functional or sensory properties.

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Introduction

Several studies have shown that it is possible to control the changes in fatty acid composition of egg yolk lipids by modifying the dietary fat of the hens. The production of healthier eggs by increasing the amount of the long-chain unsaturated fatty acids is a modern way to improve the nutritional value of eggs. Typical oils added to the diet of the hens are fish, flax, canola, and algae oils.^1–5 In recent studies, with tailored combinations of dietary fats, more specific eggs with modified fatty acid compositions have been developed.^6,7 Moreover, it is possible to increase the amount of other health-promoting ingredients in egg yolks with dietary changes. Typical ingredients used in diets are minerals, vitamins, and different types of antioxidants.^8–10

The egg albumen is known to produce foams with high foamability and foam stability.¹¹ Capacity and stability of foam are the most important indexes of foaming properties.¹² Both of these attributes are closely associated with the functional properties of eggs. The beating, blending, and homogenising method and the temperature of the foam are the principal factors that influence egg foams.¹³ Other parameters like the effects of pH,^14,15 and the effects of typical processing steps used in egg industry^16–18 have been extensively studied. Several methods for measuring food foams have been developed both for laboratory and industrial measurements.^19–23 In the egg industry, the methods used in measuring foam properties should be fast and easily repeated, and the volume of material should be as low as possible.

Foaming is usually related to the functional properties of proteins, and it is generally accepted that pure lipids do not foam.²⁴Yolk lipids are exclusively associated with lipoproteins and to some extent to other components of yolk.²⁵ These interactions are largely responsible for the functional properties of egg yolks. Egg yolk is a complex structure organized in large spheres, granules, and low-density lipoprotein micelles and globular proteins. In this structure, lipids and proteins form a dispersion in water phase, where the apolipoproteins act as emulsifying and stabilizing agents.²⁶

The possible effect of a modified lipid composition on the foaming and emulsifying properties of eggs is poorly understood. Pankey and Stadelman²⁷ found some differences in the volumes of sponge cakes made with eggs from hens of oil-supplemented trial groups, but they considered the practical significance of the differences only slight. Pikul et al.²⁸ concluded that various levels of rapeseed in the diet of laying hens did not have any major influence on the foaming properties of egg albumen. Meluzzi et al.^29,30 and Franchini et al.³¹ reported some minor changes in functional properties of eggs of hens fed with vegetable lipids, fish oil, and vitamins.

The modification of egg yolk lipids by ω3-enriched feeds has been reported to induce sensory problems in eggs. These problems are typically related to “fishy” or “paint-like” aroma.³² Other possible reasons that may effect these unwanted changes are the strain and age of the hens^33,34 and the storage of eggs.¹

In the present study, the fatty acid composition of eggs was modified by adding flax oil (FO), rapeseed oil (RO), and fish oil (FISH) to the diet of the hens. In addition, by-product from black currant (BC) processing was tested as a source of ω6 fatty acids in the diet. On the basis of the literature, these supplementations were supposed to modify both the ω3 and ω6 fatty acid compositions of eggs. The fatty acid compositions of feeds and eggs were determined in all test groups, and the fatty acid compositions of mayonnaise preparations were determined in control, FO, RO and FISH groups. To find out the possible changes in the functional properties of these modified eggs, foaming capacity, and stability of the fresh and stored eggs were determined, and emulsifying properties of fresh eggs were evaluated using methods typical for egg industry. Sensory analysis was performed with fresh eggs, and with mayonnaise preparations in control, FO, RO and FISH groups.

Materials and methods

Animals, diets, and egg handling

White Leghorn hens, 44–56 weeks old, were randomly divided into five feeding groups (18 in each). Hens were fed a standard laying diet (control group) or a diet supplemented with 5% flax oil (FO), 5% rapeseed oil (RO), 5% fish oil (FISH) or 20% of dried black currant by-product (BC) containing 2.3% of oil for three weeks. All the supplements used in diets were gifts from local companies (Elixi Oil Ltd, Somero, Finland; Raisio Yhtymä Ltd, Raisio, Finland; Marli Ltd, Turku, Finland; Scannfish Ltd, Naantali, Finland).

The compositions of the diets are presented in Table 1. The hens were fed ad libitum.Eggs intended for later analyses were stored at 12 °C in 60% humidity for three weeks.

Table 1 The composition of control and FO diets

	Control (%)	FO (%)	RO (%)	FISH (%)	BC (%)
a Premix: protein 43.0%; fibre 3.3.%; fat 7.4%; ash 18.5%; methionine 1.35%; cystine 0.55%; lysine 2.60%; Ca 4.00%; P 1.90%; ME 11.7 MJ kg^−1; vitamin A 75 000 IU kg^−1; vitamin D3 15 000 IU kg^−1; vitamin E 150 mg kg^−1; Cu 60 mg kg^−1; Se 1.4 mg kg^−1. b According to the analysis of BC by-product.
Premix^a	17	16.2	16.2	16.2	13.6
Barley	50	47.5	47.5	47.5	40
Oats	24	22.8	22.8	22.8	19.2
CaCO3	9	8.5	8.5	8.5	7.2
Oil supplement		5	5	5	(2.3)^b
BC					20
Total	100	100	100	100	100

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Fatty acid analysis, analysis of foaming, gelling, and emulsifying properties, and mayonnaise preparations

The fatty acids of feeds, eggs, and mayonnaise samples were analysed as described in Rokka et al.³⁵ In the fatty acid analysis of eggs, five yolks from both feeding groups were pooled and homogenised.

The foaming indexes and foam stabilities were measured from fresh eggs and from eggs stored for 21 days. The foaming properties were analysed as described in Rokka et al.³⁵ Briefly, twelve eggs from each feeding group were collected. Six eggs were broken and the albumens were separated, pooled and homogenised (albumen group). The contents of another six eggs were processed analogously (whole egg group). 100 ml of homogenised liquid albumen and 150 ml of homogenised liquid whole egg were used to foaming tests. Foam formation and analysis were performed in duplicate samples. Samples were whipped with Hobart N-50 mixer equipped with a volume-readable bowl (50 ml intervals). The samples were whipped for 3 min, and the volume of the formed foam was measured. The foam index was calculated as follows: (foam volume − original liquid volume)/(original liquid volume) × 100.

Foam stability was measured according to the slightly modified method of Phillips et al.¹⁹ A 6 mm hole was drilled to the bottom of bowl. During the whipping the hole was covered with a piece of tape. After whipping, the tape was removed and the liquid drained through the hole was weighed in 5, 10, 30, and 60 min after finishing whipping. The emulsifying and gelling properties of the samples were analysed by a modified method of Sathe and Salunke³⁶ and Quinn and Paton.³⁷ Briefly, three eggs from each feeding group were broken, pooled and homogenised. The tubes with the samples were filled up to 125 ml with distilled water. Rapeseed oil (125 ml) was added, and the mixture was blended for 1 min at 10 000 rpm. The mixture was immediately centrifuged at 2400 rpm for 5 min, and the height of the emulsion was measured. The results for the emulsion activity are given as the percentage of the emulsion height of total dispersion height. The measurements for the emulsion stability were performed equally, except that samples were, before the centrifugation, heated to 80 °C for 30 min and cooled down to room temperature.

For mayonnaise preparations, six fresh egg yolks from feeding groups were pooled. 20 g of yolk were mixed with 2 g of mustard. To this mixture, 14 ml of apple wine vinegar were slowly added with simultaneous mixing. Finally, 175 ml of sunflower oil were added to the mixture. Mustard, apple wine vinegar, and sunflower oil were purchased from local store.

Sensory analysis

Prior to sensory evaluation, the eggs were boiled for 10 min and then cooled to room temperature.

In a multiple comparison test, twelve trained panellists evaluated the yolks for odour, taste, and general acceptance, as described in Rokka et al.³⁵ In a triangular test, twelve trained panellists were informed that two of three eggs are similar. Panellists were asked to compare the odour, taste, and other sensory properties of the egg yolks. According to these properties, the panellists were asked to indicate which egg is different. In every test, two of the eggs came from a control group and the third egg came from a modified group.

In the evaluation of the sensory properties of mayonnaise, six mayonnaise preparations were made: one with control group, RO group, FISH group, and BC group yolks, and two with FO group yolks. Twelve trained panellists were asked to evaluate the odour and taste of different mayonnaises and rank them from 1 (best) to 6 (worst) according to these sensory properties. The panellists were also advised to describe the differences between the samples.³⁸

Statistical analysis

In statistical analysis, results from the control group eggs were analysed against the results of different feeding groups using one-way ANOVA.

Results and conclusions

Fatty acid compositions of the feeds, eggs, and the mayonnaises

The main fatty acid composition of feeds and egg yolks in all feeding groups are presented in Table 2. Compared to control group, typical changes were found in eggs analyzed in oil supplementation groups. In FO group, the amount of α-linolenic acid increased more than 11-fold compared to the control group, and in FISH group the amount of DHA increased up to 3.7% of fatty acids. These results agree with the other results of experiments with plant oil or fish oil supplementation.^39–41

Table 2 The main fatty acid compositions of feed, eggs, and mayonnaise preparations in control and test groups. Statistically significant differences between control group and each test group are marked with letters a (p < 0.05) and b (p < 0.005)

Feed (n = 3)
	Control (%)	FO (%)	RO (%)	FISH (%)	BC (%)
C16:0 (palmitic)	19.0	11.1^b	11.2^b	15.5^b	15.6^b
C16:1/C17:0 (anteiso, tr)	1.4	0.6^a	0.6^a	1.5	0.9
C18:0 (stearic)	3.1	3.6^a	3.1	3.9^a	4.1
C18:1 (oleic)	22.9	18.2^a	42.3^b	36.9^b	21.1^a
C18:2 ω6 (linolic)	42.6	24.5^b	26.6^b	27.9^b	40.0^a
C20:4 ω6 (arachidonic)	0.0	0.0	0.00	0.0	0.00
C18:3 ω3 (alfa linolenic)	6.8	39.7^b	11.0^b	5.7	8.6^b
C18:3 ω6 (gamma linolenic)	0.0	0.0	0.0	0.0	4.7^b
C20:5 ω3 (EPA)	0.0	0.0	0.0	0.9^b	0.0
C22:6 ω3 (DHA)	0.0	0.5^b	0.50^b	1.4^b	0.0
ω3 tot.	6.8	40.2	11.5	7.9	9.0
ω6 tot.	42.6	24.5	26.6	27.9	44.7
ω6/ω3	6.3	0.6	2.3	3.5	5.0

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Eggs (n = 3)
	Control (%)	FO (%)	RO (%)	FISH (%)	BC (%)
C16:0 (palmitic)	26.6	23.6^a	23.4^a	27.2^a	25.0
C16:1/C17:0 (anteiso, tr)	2.5	2.1^a	1.7^a	3.0^a	2.0
C18:0 (stearic)	10.1	10.5	8.8^a	9.4^a	9.9
C18:1 (oleic)	41.6	37.0^a	41.4^a	35.1^a	37.9^a
C18:2 ω6 (linolic)	12.1	13.9^b	12.5^a	11.00^b	15.9^b
C20:4 ω6 (arachidonic)	1.6	0.9^b	1.5^a	0.9^b	1.6^a
C18:3 ω3 (alfa linolenic)	0.7	7.8^b	1.9^a	0.8^a	1.9^a
C18:3 ω6 (gamma linolenic)	0.0	0.0	0.0	0.0	0.3^b
C20:5 ω3 (EPA)	0.0	0.0	0.1	0.8	0.1
C22:6 ω3 (DHA)	1.5	1.8^a	1.9^a	3.7^b	1.7^a
ω3 tot.	2.2	9.6	4.1	6.00	3.1
ω6 tot.	13.7	14.8	14.00	11.8	18.1
ω6/ω3	6.2	1.5	3.4	2.0	5.8

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Mayonnaise (n = 3)
	Control (%)	FO (%)	RO (%)	FISH (%)
C16:0 (palmitic)	7.1	6.8	6.8	6.9^a
C16:1/C17:0 (anteiso, tr)	0.2	0.2^a	0.2^a	0.1^a
C18:0 (stearic)	4.7	5.0^a	4.8	4.5^a
C18:1 (oleic)	23.3	19.7^a	21.9	24.8
C18:2 ω6 (linolic)	60.3	65.0	62.7	59.1^a
C20:4 ω6 (arachidonic)	0.2	0.3	0.1^a	0.1 ^a
C18:3 ω3 (alfa linolenic)	0.6	0.6	0.6	1.0^a
C18:3 ω6 (gamma linolenic)	0.0	0.0	0.0	0.0
C20:5 ω3 (EPA)	0.3	0.0^a	0.1^a	0.0^a
C22:6 ω3 (DHA)	0.1	0.1	0.2	0.1
ω3 tot.	1.0	0.8	0.8	0.7
ω6 tot.	60.5	65.3	62.8	59.2
ω6/ω3	62.0	87.6	80.5	81.7

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In the BC group, the feed contained 4.7% of gamma-linolenic acid. However, in eggs the corresponding value was only 0.3%, indicating that the BC seed oil was only partly available for the hens. In general, flax, rapeseed and fish oil supplements in hens' diets changed the fatty acid composition of eggs to be nutritionally more beneficial. In this study, the calculated ω6/ω3 content varied from 1.5 to 3.4. According to nutritional recommendations, the optimal ω6/ω3 ratio varies a little, but values close to 1 are suggested.⁴²

In mayonnaise preparations, the amount of sunflower oil was so high that the differences in the fatty acid composition of egg yolk had no practical effect on the fatty acid composition of mayonnaise.

Foaming indexes of fresh and stored eggs

The foaming indexes of albumen and whole egg for the control and test groups are presented in Table 3. The pH values for tested albumen foams varied between 9.01–9.25, and for whole egg foams between 7.34–7.59.

Table 3 Foaming indexes of albumen and whole egg foams in control, FO, RO, FISH, and BC groups. Before whipping, the original masses for albumen and whole egg were 100 g and 150 g, respectively. Statistically significant differences between control group and each test group are marked with letter a (p < 0.05)

	Control (n = 4)				FO (n = 4)
	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days
Foam volume (ml)	950	875	430	470	900	850^a	500	515
Foam left (g)
5 min	100	100.0	150	150	100	100	150	150
10 min	100	89	150	150	98	95	150	150
30 min	58	50	138	121	56	59	145	126
60 min	36	36	94	79	36	37	97	75
t½ (min)	33	28	73	62	33	34	75	58

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	RO (n = 4)				FISH (n = 4)
	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days
Foam volume (ml)	950	875	500	470	900	875	430	530
Foam left (g)
5 min	100	100	150	150	100	100	150	150
10 min	99	99	150	150	99	94	150	150
30 min	54	59	131	122	64	51	135	120
60 min	35	39	83	79	41	33	93	70^a
t½ (min)	34	35	86	64	39	29	71	55

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	BC (n = 3)
	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days
a nd = not determined.
Foam volume (ml)	950	875	425	500^a
Foam left (g)
5 min	100	100	150	150
10 min	99	99	149	150
30 min	59	58	133	142^a
60 min	34	32	74	85^a
t½ (min)	34	35	nd^a	74

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In albumen foams, the index values varied from 900 to 950 in all oil supplemented feeding groups in fresh eggs. Compared to value of control group (950), the data from these experiments indicates that supplementation with RO and FISH oils or BC by-product have no influence on the foaming capability or foam stability of fresh egg albumen. Statistical difference was found with FO oil supplementation (p < 0.05). Between the fresh and stored eggs, slight but not significant changes in albumen foam volume were found in all groups. Hammershoj and Qvist²³ concluded that the storage of eggs in a cold environment did not have a great impact on the albumen foaming properties. Rokka et al.³⁵ reported similar results with eggs from hens fed a diet supplemented with oil from Camelina sativa. In Mattila et al.,⁴³vitamin D-enriched eggs showed similar foaming properties as the control group eggs.

In contrast, Silversides and Budgell⁴⁴ showed that albumen whipping volume increased substantially with time when stored for ten days. In our study, the storage time was quite long (21 days), and the storage conditions and increasing periods of storage time may decrease the egg weight and albumen weight and increase the yolk weight.^45–47 Moreover, moderate unfolding of egg albumen proteins has been shown to improve the foaming capacity, foam stability, and foam rheological properties.^15,48 In certain cases, a decrease in pH has reduced the volume of albumen foams.⁴⁹

We may conclude that in our study the detected changes in foaming properties of albumens are not based on the changes in fatty acid compositions of yolks. The possible reasons may include slight differences in pH-values and dry matter contents of samples. The contamination of the albumen samples with yolk is unlikely.

Whole egg foam indexes showed values 425–500 for fresh eggs in the control group and in all test groups. For stored eggs, the corresponding values were 400–530. All of the whole egg foams were weak, and the measurements were difficult to carry out. Compared to control group, best foam stability was found in BC group. In FISH oil group, the whole egg foams of stored eggs lost part of their capability to maintain foam stability. This result agrees with Scholtyssek and El-Bogdady.⁵⁰ As a contaminant, egg yolk reduces the volume of egg-white foams, and especially the triglycerides in egg yolk are more detrimental to albumen foams than the cholesterol and phospholipid fractions.¹³ Possible interactions in the phospholipid-protein complexes in egg yolk may have some influence in the functional properties of yolks.¹² Kivini et al.⁵¹ found no significant differences in the main phospholipid moieties of eggs from several vegetable or fish oil supplemented feeding groups. The content of α-linolenic acid increased significantly only in the phosphatidylcholine fraction of linseed oil group eggs. Wang and Wang¹⁸ found that yolk phospholipids do not give significant foaming reduction even in relatively high concentrations.

In the present study, the foaming capacity in all feeding groups was at a technologically acceptable level for use in the further processing of eggs.

Emulsifying and gelling properties of eggs

The results of the emulsifying and gelling measurements are presented in Table 4. In general, only small variations between the fresh eggs from the control group and FO, RO, and FISH groups in emulsion activity, emulsion stability, and gel-forming capacity were found. These results agree with Rokka et al.³⁵ and Mattila et al.⁴³ However, in FISH group the results show worse emulsion activity (p < 0.005) and emulsion stability (p < 0.005) with fresh eggs, and we cannot exclude the possibility that the changes in fatty acid compositions have an effect on the emulsifying properties of these eggs. Yolk LDLs, mainly located in yolk plasma, are proved to be the main contributors to the emulsifying properties of egg yolk, through the interactions between the amphiphilic apoproteins and phospholipids.²⁷ DHA a is common fatty acid in phospholipids, thus participating the emulsion formation. In FISH group egg yolks, the level of DHA was higher than in control group eggs, which may have effect on emulsifying activity of egg yolks. Le Denmat et al.⁵² reported that at pH 7 egg yolk granules have better emulsifying properties than plasma. On the contrary, Laca et al.⁵³ fractionated egg yolk to granule, lipidic paste and watery fractions, and found that lipidic paste showed the better emulsifying properties than granules. Taking consider all the complex interactions between all the components in egg yolk, the role of individual fatty acids in emulsion formation is unclear and is under further investigation.

Table 4 Mean values of emulsion activity (g oil emulsified/g), emulsion stability, and gel-forming capacity (hardness/N) of eggs in control, FO, RO, and FISH groups. Statistically significant differences between control group and each test group are marked with letters a (p < 0.05) and b (p < 0.005)

Control					FO
	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days
Emulsion activity (n = 5)			67.4	63.9			67.2	65.2^b
Emulsion stability (n = 5)			53.9	23.8			42.9^a	36.5^b
Gel-forming capacity (n = 5)	4.2	6.4			5.4^b	7.7^a

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RO					FISH
	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days	Albumen fresh	Albumen 21 days	Whole fresh	Whole 21 days
Emulsion activity (n = 5)			67.1	64.8^a			69.5^b	63.2^a
Emulsion stability (n = 5)			57.4	24.4			35.4^b	23.1
Gel-forming capacity (n = 5)	5.2^b	6.7			4.9^a	8.2^b

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With stored eggs, statistically significant differences were found in emulsion activity in FO (p < 0.005), RO (p < 0.05) and FISH (p < 0.005) groups, but as a technological point of view, these differences are negligible.

Egg yolk itself is considered to be one of the most complex protein-based emulsifier systems. Yolk emulsions are mainly stabilized by low density lipoproteins (LDL). Other constituents of egg as an emulsifying agent are high density lipoproteins (HDL), phosvitin, and livetin.^54,55 With the FO oil supplementation, the main difference in the fatty acids of the eggs is the increase in α-linolenic acid. Correspondingly, the RO oil supplementation increases the oleic oil contents, and the FISH oil supplementation the EPA and DHA contents. Probably, the relative distribution of fatty acids in the different lipid components of eggs is similar in ω-3 enriched eggs and in control group eggs, and thus has minor or no effect on the emulsifying properties of eggs.⁵¹

In gelling, albumen proteins typically create a network via noncovalent cross-linkages, such as hydrophobic interactions, hydrogen bonds, or electrostatic interactions, and (to some extent) covalent interactions.⁵⁶ When modifying the fatty acid composition of egg yolk, it should be evident that the relationships between albumen proteins do not change and the gelling properties remain equal, both in control and modified eggs. However, the reasons for the wide variations in gel forming capacities between the eggs stored for different times and from different feeding groups remain unclear.

Sensory properties of eggs

Table 5 shows the results of the multiple comparison test of eggs from the test groups. Eggs from the RO group, FO group, and BC group showed similar sensory properties as the eggs from the control group. All these eggs were acceptable to senses. Eggs from the FISH group showed clearly worse sensory properties in all evaluations. All these results agree well with earlier results.^32,2–5 In this study, only the level of flax oil in feed was optimized to avoid sensory problems, but, according to the panelists comments, flax oil induced some fishy-like aromas in eggs. In several studies with fish and marine oils rich in DHA, undesirable odours and flavors are typically found, when the hens are fed more than 1.5% of oil in feed.^5,57 Using vitamin E as antioxidant, Meluzzi et al.²⁹ found that after 28 d storage the levels of vitamin E were close to levels of fresh eggs, suggesting that vitamin was not used to prevent lipid oxidation. In our study, we used exceptional high level of fish oil (5%) with 150 mg kg⁻¹ of vitamin E, to find prominent increase in the levels DHA in eggs. As expected, the undesirable changes in sensory properties were found in boiled eggs, but not with mayonnaise preparations.

Table 5 Mean values of the multiple comparison test of feeding groups as compared to control group yolks (n = 8). Statistically significant differences between control group and each test group are marked with letter a (p < 0.05)

	FO	RO	FISH	BC
Odour	0.0	−0.2	−1.2^a	−0.3
Taste	−0.1	0.3	−1.8^a	0.2
General acceptance	0.2	−0.2	−1.2	−0.1

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In triangle tests, 9 of 10 panellists recognized the right egg in FO group. The corresponding result for RO group was 1 of 10, for FISH group 9 of 10, and for BC group 6 of 10. These results corroborate the results of multiple comparison tests.

Sensory properties of mayonnaise

The rankings of the evaluators for the mayonnaise preparations showed great variations (Table 6). RO group (average ranking 3.0), both FO groups (average rankings 2.8 and 3.4), and FISH group (average ranking 3.9) mayonnaise preparations were evaluated as having better sensory properties than the control group preparations (average ranking 4.0). BC group preparation was evaluated to be on the same level as control group preparation. Due to the large deviations in all average ranking values, no statistical differences were found between the groups. All the panellists considered the ranking of the samples to be difficult because the taste of the vinegar covered all the other tastes very efficiently. This agrees with the results of McClements and Demetriades,⁵⁸ who concluded that most of the initial flavour of mayonnaise comes from molecules present in water phase. Depree and Savage⁵⁹ evaluated that, in lower fat formulations of mayonnaise, the chemical interactions within the mayonnaise will change and this will affect the flavour stability of the products. And, as in all fat-containing foods, mayonnaise is susceptible to auto-oxidation of the unsaturated and polyunsaturated fats, thus inducing problems in the sensory quality of the product. However, in this study, the content of the fat was similar in the control and test products, and the modified fatty acid composition of the eggs did not change the sensory properties of mayonnaise products. These results suggest that it is possible to prepare mayonnaise from the ω3-enriched eggs without problems in sensory properties.

Table 6 The rankings of the evaluators for the mayonnaise preparations made from yolks from different feeding groups (n = 8)

	Control	RO	FO1	FISH	FO2	BC
Average ranking	4.0	3.0	3.4	3.9	2.8	4.0
sd	1.5	1.3	1.7	1.9	1.4	1.7

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This study was conducted to investigate how the addition of oil supplements to the diets of laying hens affected the functional properties of eggs and egg products. Sensory properties of these eggs and egg products were evaluated, too. Oil supplementations of feeds modify the fatty acid composition of eggs to be nutritionally more beneficial. BC by-product supplementation increased the amount of γ-linolenic acid in feed, but in eggs the level of γ-linolenic acid was negligible. Most probably, to increase the availability of gamma linolenic acid for hens, the black currant seeds should be broken, or even press the oil from the seeds before use in the feed.

With high level of fish oil supplementation of feed, the results show decrease in the emulsion stability, but the emulsion activity was even better than in control group eggs. All the other oil-supplemented test groups showed similar or even better emulsifying properties when comparing to results from control group eggs. Moreover, both foaming and gelling play an important role in further applications of processed eggs. Based on the data presented in this paper, modifying the diet of hens with flax, rapeseed, and fish oils does not affect the foaming or gelling properties of eggs. Foaming and foam stability measurements of eggs in black currant group also showed similar results as in control group.

As has been shown in several earlier studies, fish oil supplementation induced some off-flavors in boiled eggs. However, even with this exceptional high level of fish supplementation of feed, the sensory properties of different eggs and egg products were on acceptable level in all other studies. It appears evident that the processing industry may produce egg-based products using oil-supplemented eggs without major problems in functional or sensory properties, thus offering some new business opportunities for egg industry in the area of enriched eggs.

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Footnote

† Current address: Finnish Funding Agency for Technology and Innovations TEKES, P.O. Box 236, FI 20101 Finland

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