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© 2014 Conscientia Beam. All Rights Reserved. 

THE EFFECT OF STEAMING PROCESS ON FAT SOLUBLE VITAMINS' 

CONTENT AND FATTY ACID PROFILE IN BLUEFISH AND RAINBOW 

TROUT FILLETS 

 

Stancheva M.1 --- Merdzhanova A.2 --- Galunska B.3 --- Dobreva A.D.4 

1,2,3,4Department of Chemistry, Faculty of Pharmacy, Medical University of Varna, Varna, Bulgaria 

 

ABSTRACT 

Fatty acid composition and all-trans-retinol, alpha-tocopherol, and cholecalciferol content was determined 

and compared in raw and steamed Bluefish and Rainbow trout. Total lipids were extracted by Bligh and 

Dyer method followed by GC-MS. All-trans-retinol, cholecalciferol and alpha-tocopherol were analyzed 

simultaneously using HPLC. In comparison with raw fish fillets, analyzed fat soluble vitamin’s content in 

steamed fish filletsfor the Trout and Bluefish decreased significantly to about 54.2% and 49.8% for retinol 

and 32.6% and 43.5% for alpha-tocopherol, respectively. After steaming, the cholecalciferol amounts in 

processed fillets decreased significantly only in Rainbow trout (23.5%), whereas in Bluefish the losses were 

non-significant. After cooking, the polyunsaturated fatty acid content changed significantly in the Rainbow 

trout (45.8%), whereas the variations in the Bluefish were minor. The major PUFA in all samples were 

linoleic acid (LA) and docosahexaenoic acid (DHA). PUFA/SFA ratios were between 1.01 and 1.68 for 

both species. Steaming increases PUFA/SFA ratio by 8.33% in Rainbow trout, but does not affect this 

ratio in Bluefish. 

Keywords: Black sea, Fish nutrition, Human health, Oncorhynchus mykiss, Pomatomus 

saltatrix, Thermal processing. 

 

1. INTRODUCTION 

The Rainbow trout and Bluefish are commercially important fish species in Bulgaria. The 

Rainbow trout (Oncorhynchus mykiss) is one of the most widely farmed fishes in our country. It is a 

predator which inhabits cold and clear freshwater ponds. Because of its rapid growth and rich and 

diverse composition of meat, the trout is preferred fish for breeding and consumption [1]. The 

Bluefish (Pomatomus saltatrix) is important pelagic fish for the Black Sea fish markets. This species 

feeds primarily on fish (anchovy, horse mackerel) and on crustaceans (shrimps) [2]. On the other 

hand, the distinctive flavor of Rainbow trout and Bluefish makes them favorite dishes. 

Fish is a rich source for essential nutrients such as fat soluble vitamins and Polyunsaturated 

Fatty Acids (PUFA) [3-5]. Fatty fish is the most important source of vitamin D and long-chain 

omega-3 (n3) PUFAs, and is favorable with respect to both cardiovascular disease and fetal 

Animal Review 
2014 Vol. 1, No. 1, pp. 1-10 
ISSN(e): 2409-6490 
ISSN(p): 2412-3382 
© 2014 Conscientia Beam. All Rights Reserved. 
 

 

 



 
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development. It is well known that fat soluble vitamins control the diversity of biologically 

important processes in the human body. All-trans-retinol (vitamin A) play role in photoreception, 

bone growth, reproduction etc. Alpha-tocopherol (vitamin E) acts as an antioxidant, protecting 

membrane structures, essential fatty acids, and vitamin A from oxidation. Cholecalciferol (vitamin 

D3) plays a crucial role in the regulation of the calcium-phosphate balance stimulating calcium 

absorption and thus regulating bone metabolism. 

The majority of researches on fish and human health have focused on the link between 

cardiovascular diseases and the consumption of fish or long chain n3 PUFAs as eicosapentaenoic 

acid (C20:5, EPA) and docosahexaenoic acid (C22:6, DHA) [6]. Consumption of at least two fish 

servings per week is recommended by the American Heart Association and FAO/WHO [3, 5]. In 

Bulgaria the consumption of fish is very low (4.5kg annual per capita) compared to the average 

European levels (23 kg annual per capita) [7]. Meanwhile, in the Western society and Bulgaria 

consumption of raw fish is rare. Temperature processing of fish tissue enhances its taste, 

inactivates pathogenic microorganisms and increases its shelf life. During cooking, chemical and 

physical reactions occur and the content of thermo labile compounds as fat-soluble vitamins and 

PUFA in fish tissue is reduced. Steaming is known as a mild and often recommended cooking 

method used in healthy diets. There are no research data in Bulgaria on the effect of steaming on 

fat soluble vitamins' content, total lipids and fatty acids (FA) composition of these fish species. 

The aim of the present study is to evaluate the effect of the steaming process on the total 

lipids, the fat soluble vitamins' content and the fatty acid composition in these two traditionally 

consumed in Bulgaria fish species – the Rainbow trout and the Bluefish. 

 

2. MATERIALS AND METHODS 

2.1. Sample Collection and Cooking Method 

A total of twelve fresh Rainbow trout (fish farm, Plovdiv region) and Bluefish specimens were 

purchased from Varna local fish market during the autumn season. Biological and biometrical 

characteristics of the species were determined and noted (Table 1). 

 

Table-1. Biometric and biologic characteristics of studied fishes (mean ± SD) 

Fish species 
Mean total 
weight [g] 

Mean total 
length [cm] 

Habitat Food habits 

Bluefish (n=6) 60.5 ± 2.3 16.0 ± 2.1 Pelagic Carnivorous 

Rainbow trout(n=6) 325.0 ± 15.0 28.0 ± 3.4 Pelagic Omnivorous 

 

All fishes were immediately frozen and stored at -20oC. Prior to analysis the frozen samples 

were thawed at 4oC, for 12 hours. The edible tissue was filleted with the skin. The fillets were 

totally randomized and then divided in two batches: first group of fillets (n=6 for each fish 

species) were analyzed in raw state, a second group was analyzed after steaming (n=6 for each 

fish species). The fish fillets from the first group were homogenized at 800 rpm for 3 minutes 

using Moulinex blender. The homogenized tissue was used to prepare the parallel samples. The 



 
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second group was placed in a steamer above a glass pot of boiling water (500 ml) and cooked for 

10 minutes. The steamed fillets were placed for 5 minutes on absorbent papers and then processed 

as described for group one. The Steamed samples were weighed and the observed losses were 

noted. 

 

2.2. Moisture Analysis 

Test portions of homogenized fish tissue (2.000±0.005g) were dried at 105±2oC in an air 

oven, to constant weight for 16-18 hours [8]. All samples were cooled in desiccator and 

weighted. The change in the moisture [%] was calculated as weight loss. 

 

2.3. Extraction of Fat Soluble Vitamins and HPLC Analysis 

The sample preparation was performed using the method of Dobreva, et al. [9]. An aliquot of 

the homogenized sample (1.000±0.005 g) was weighed into a glass tube with a screw cap and 1% 

of methanolic L-ascorbic acid and 1M methanolic potassium hydroxide was added. Six parallel 

samples of edible fish tissue were prepared and subjected to saponification at 80oC for 20 min. The 

components of interest were extracted with n-hexane and the extract was evaporated under 

nitrogen. The dry residue was dissolved in methanol and injected (20μl) into the liquid 

chromatography system. The three fat soluble vitamins were analyzed simultaneously using 

HPLC system (Thermo Scientific Spectra SYSTEM) equipped with RP analytical column ODS2 

Hypersil™ 250х 4,6mm, 5um. All-trans retinol and cholecalciferol were detected by UV, alpha-

tocopherol by fluorescence detection. The mobile phase composition was 97:3 = MeOH:H2O and 

the flow rate was 1ml/min. The qualitative analysis was performed by comparing the retention 

times of pure substances: at λmax = 325nm for retinol; λmax = 265nm for cholecalciferol and alpha-

tocopherol fluorescence at λex = 288nm and λem = 332nm. The quantitation was done by the 

method of external calibration comparing the chromatographic peak areas of the corresponding 

standards (Retinol solution, Fluka; DL-alpha Tocopherol, Supelco; Cholecalciferol, Supelco). The 

results are expressed as µg per 100 g wet weight (µg.100g-1ww). 

 

2.4. Lipid Extraction and Fatty Acid Analysis 

Portions of freshly prepared homogenate (5.000±0.001g) were extracted in triplicate with 

chloroform: methanol (1:2 v/v) according to Bligh and Dyer procedure [10]. BHT (2-terth-

Butyl-4-hydroxyanisole) was added to all samples as antioxidant. After phase separation the 

chloroform layers were evaporated on a rotary vacuum evaporator (Bushi 5200) until dryness and 

quantified gravimetrically. The total lipid (TL) content of edible tissue was determined for each 

group (n=6) and the results are presented as g per 100g wet weight (g.100g-1ww). The dry 

residue of the chloroform fraction was methylated by base-catalyzed transmethylation using 2M 

KOH in methanol and n-hexane [11]. The hexane layer was separated and analyzed by GC-MS. 

Gas chromatography was performed by a model FOCUS Gas Chromatograph with auto sampler 

A3000, equipped with Polaris Q MS detector (Thermo Scientific, USA). The capillary column 



 
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used was a TR-5 MS, 30m length, 0.25mm i.d. Helium was used as a carrier gas at a flow rate 1 

ml/min. Peaks were identified according to two parameters: Retention Time (RT) based on 

available FAME mix standard (SUPELCO 37 F.A.M.E. Mix C4 - C24) and mass spectra (ratio 

m/z) – compared to internal Data Base (Thermo Sciences Mass Library, USA). Results are 

expressed as the percentage of each fatty acid with respect to the total fatty acids [12]. 

 

2.5. Statistical Analysis 

The obtained data were analyzed using Graph Pad Prism 5 software. Column statistics were 

used for calculation of means and standard deviations and results are presented as average ± SD. 

To estimate the differences between two groups - raw and steamed samples unpairedt-test 

statistical analysis was applied. Thus the comparison was made between moisture, total lipids, fat 

soluble vitamins and individual FA and FA groups. The differences were considered significant at 

p<0.05. 

 

3. RESULTS AND DISCUSSION 

3.1. Moisture Content 

The raw samples of Rainbow trout fillets showed high moisture content (78.5%) followed by 

the Bluefish (62.6%). During the process of steaming a significant decrease in moisture, compared 

to raw tissue was revealed (16.2%) for Rainbow trout (65.8%, p<0.001) and 5.6% for Bluefish 

fillets (59.1%, p<0.001). These results are consistent with Sikorski and Kolakowska for trout, and 

possibly due to the fact that the fish food experienced water loss in its tissues during the cooking 

process [13]. Larsen et al. presented a similar result for moisture content of steamed King 

salmon [14]. 

 

3.2. Fat Soluble Vitamins' Content 

All-trans-retinol and alpha-TP are known to be unstable when heated in the presence of air. 

The steaming method of cooking affects strongly the content of these vitamins. Retinol and 

alpha-TP contents in steamed fish fillets for both Rainbow trout and Bluefish decrease 

significantly p<0.001, compared to their content in the raw fish samples - by about 54.2% and 

49.8% for retinol and 32.6% and 43.5% for alpha-TP, respectively (table 2). 

 

Table-2.Vitamin contents in raw and steamed fish fillets, µg.100g-1ww, (mean ± SD) 

 
Fish 
species 

All-trans-retinol Alpha-tocopherol Cholecalciferol 

raw steamed raw steamed raw steamed 

Rainbow 
trout 

58.95±2.6 26.99±1.4*** 1648.90±68.8 1112.17±40.3*** 14.92±1.1 11.42±0.6** 

Bluefish 38.48±2.4 19.35±1.7*** 427.08±37.1 241.38±24.7*** 11.18±1.2 10.40±0.5 

*** p<0.001 steamed vs raw; ** p<0.01 steamed vs raw 

 



 
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Rainbow trout and Bluefish are amongst the fishes comprising highest amounts of 

cholecalciferol. Our data for cholecalciferol content in raw fish tissue (table 2) are in accordance 

with the data given by Mattila et al. for vitamin D3 content (0.28 - 47.7 µg.100g-1 raw tissue) in 

fishes [15]. The amount of cholecalciferol decreased significantly (p<0.01) by 23.5% only in 

Rainbow trout, whereas in Bluefish fillet the losses were non-significant, after steaming (table 2). 

There is a discrepancy in the literature regarding the effect of various types of cooking on the fat 

soluble vitamin contents in fish tissue [16-18]. Erkan et al. found out losses of about 75% for 

retinol and 55% for alpha-tocopherol in steamed horse mackerel [18]. Our results, regarding 

retinol and alpha-TP changes after steaming, are comparable with those of Erkan, et al. [18]. 

Mattila et al. reported losses below 10% for cholecalciferol in fish samples undergoing a baking 

process [16]. We also established slight non-significant losses (6.9%) for cholecalciferol in 

Bluefish fillets after steaming. In contrast Ersoy and Ozeren reported no significant differences in 

fat soluble vitamins A and E in edible tissue of African catfish after various types of cooking - 

baking, grilling, microwaving and frying [17]. 

 

3.3. Total Lipid Content 

The TL content in raw Rainbow trout was 11.50 g.100g-1ww and 15.54 g.100g-1ww for 

Bluefish. After steaming a significant (p<0.001) decrease in TL content was observed for both 

species - 9.02 g.100g-1ww for Rainbow trout and 13.34 g.100g-1ww for Bluefish. According to 

other authors, changes in the lipid amounts after steaming depend on fish species, temperature 

treatment, portion size and heatable surface area [13, 19]. The obtained results are consistent 

with those quoted by other authors, who observed loss of fat due to spreading during heat 

treatment in Rainbow trout and steamed King salmon fillets [14, 20]. To provide more useful 

and precise information of the actual lipid losses after steaming in the samples it was necessary to 

calculate the True Retention Factor (%TR). %TR is based on the measuring of weight change and 

proportion of TL in steamed and raw fish samples. This factor is calculated by the True Retention 

Method as follows: %TR = (nutrient content per g of cooked food X g of food after cooking) / 

(nutrient content per g of cooked food X g of food before cooking) X 100 [21]. In this study the 

observed weight changes for Bluefish after heat treatment were higher (from 100 g raw sample to 

87 g after steaming) in comparison to these for Rainbow trout (from 100 g raw sample to 90 g 

after steaming). On this basis %TR were calculated - 72.1% for Rainbow trout and 71.1% for 

Bluefish. These results are in good agreement with the data for average retention factor for fat in 

steamed carp (70%) presented by Kalyoncu, et al. [22]. 

 

3.4. Fatty Acid Composition 

Twenty-eight FA (from C12:0 to C 24:1) were identified and compared among the different 

species. There was a wide variation and significant differences (p<0.05) among the FA profiles of 

fish species and after steaming in terms of total and individual saturated and unsaturated FAs. 

The FA pattern in raw trout followed the order: PUFA>SFA>MUFA. Statistically compared to 



 
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the raw trout, steamed fillets showed significant increase in the values of total PUFA and MUFA 

(p<0.001), whereas the SFA amounts decreased slightly (p<0.05). The FA pattern has changed in 

the following way PUFA>MUFA>SFA after steaming. Only minor increase in MUFAs (p<0.05) 

was observed in Bluefish and PUFA>SFA>MUFA pattern did not change after steaming. 

Therefore we may assume that the Bluefish FAs content is more stable after steaming than the 

Rainbow trout FAs content. Gladishev et al. reported increased PUFA levels after heat treatment 

in four fish species and suggested that this may be due to the higher degree of hydrolysis of fish 

tissue lipids [19]. The FA profiles of analyzed fish species before and after steaming are shown in 

table 3. As a result the steaming leads to significant changes in the levels of the individual FAs 

within the FA groups. 

 

Table-3. FA profiles (% total FA) of raw and steamed Rainbow trout and Bluefish (mean ± SD) 

Fatty Acid 
 

Rainbow trout Bluefish 

raw steamed raw steamed 

C 12:01 0.40±0.02 1.92±0.12*** 0.42±0.03 0.51±0.02 

C 14:0 3.35±0.65 4.13±0.75*** 4.17±0.36 4.47±0.34** 

C 16:0 12.95±1.23 14.09±1.34*** 22.65±1.57 23.00±1.55** 

C 17:0 0.51±0.01 0.35±0.04 0.47±0.05 0.43±0.03 
C 18:0 3.35±0.51 2.24±0.12*** 3.46±0.55 3.40±0.15 

C 20:0 2.68±0.35 2.00±0.10 0.54±0.02 0.46±0.02 

C 21:0 nd nd 0.33±0.01 0.27±0.01 
C 22:0 1.95±0.40 0.75±0.05*** 0.57±0.02 0.47±0.03 

C 23:0 0.00 0.28±0.02 0.30±0.01 0.25±0.01 
C 24:0 3.20±0.60 1.50±0.33*** 0.54±0.03 0.45±0.04 

Σ SFA 28.90 27.28* 33.73 33.93 

C 14:1 3.16±0.52 3.40±0.51 0.33±0.02 0.27±0.01 

C 16:1 4.15±0.45 5.57±0.84*** 6.92±0.54 7.01±0.45 
C 17:1 0.50±0.03 0.35±0.05 0.47±0.02 0.42±0.02 

C 18:1 n 9 11.50±1.22 13.62±1.06*** 15.45±1.35 16.15±1.25*** 

C 20:1 2.03±0.67 2.68±0.54 2.81± 0.55 2.71±0.20 

C 22:1 n 9 2.74±0.53 2.69±0.50 3.70±0.41 3.71±0.61 
C 24:1 1.30±0.37 0.51±0.04 0.91±0.06 0.83±0.04 

Σ MUFA 25.39 28.82*** 30.59 31.04* 

C 18:3 n6 3.19±0.64 0.56±0.03*** 0.40±0.01 0.30±0.01 

C 18:2 n6 13.56±1.15 21.66±1.67*** 16.60±1.15 16.10±1.05 
C 18:3 n3 6.16±0.80 1.22±0.31*** 1.50±0.20 1.78±0.21 

C 20:5 n3 1.56±0.10 0.60±0.02*** 0.43±0.02 0.35±0.04 

C 20:4 n6 3.73±0.22 5.33±0.54*** 2.82±0.34 2.82±0.35 
C 20:2 1.46±0.14 0.45±0.01 0.40±0.02 0.35±0.01 

C 20:3 n3 nd 0.41±0.02 0.38±0.01 0.45±0.01 
C 20:3 n6 1.98±0.51 0.45±0.01 0.35±0.01 0.25±0.01 

C 22:6 n3 11.23±1.05 14.45±0.98*** 11.30±1.12 11.60±1.26 
C 22:2 1.90±0.08 0.70±0.05 0.50±0.03 0.40±0.02 

Σ PUFA 44.47 45.82*** 34.60 34.23 

Σ n3 18.95±1.53 16.68±1.34*** 13.96±1.25 14.10±1.23 

Σ n6 22.46±1.67 28.00±1.84*** 20.04±1.71 19.45±1.64 

EPA+DHA 12.79±0.92 15.05±0.85*** 11.73±1.03 11.95±1.10 

Σ n3/ Σ n6 0.84±0.06 0.60±0.05*** 0.70±0.06 0.73±0.05 

PUFA/SFA 1.54±0.05 1.68±0.07 1.03±0.08 1.01±0.04 

*** p<0.001 steamed vs raw; ** p<0.01 steamed vs raw; * p<0.05 steamed vs raw 

 



 
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3.4.1. Saturated Fatty Acids 

The SFA group of steamed Rainbow trout shows increased levels of palmitic C16:0, myristic 

C14:0 and lauric acid C12:0 (p<0.001), whereas the levels of stearic acid C18:0 and the very long-

chain FAs – lignoceric acid C24:0 and behenic acid C22:0 were significantly reduced (p<0.001). 

These changes reflect the overall reduction of SFAs in the steamed trout. A similar trend was 

observed in the Bluefish SFA levels after steaming, but the differences were very small. 

 

3.4.2. Monounsaturated Fatty Acids 

The amounts of unsaturated FA as MUFAs vary especially in wild fish [18, 23, 24]. Oleic 

acid (C18:1 n9) is the main MUFA in both species Fish are able to biosynthesize this FA, but the 

oleic acid also has an exogenous origin and usually its content reflects the type of fish diet. [23, 

24] In our study the levels of C18:1 n9 were increased significantly (p<0.001) after steaming in 

both species. The second abundant MUFA was palmitoleic acid C16:1 n7. Steaming results in 

significant increase in the levels of C16:1 n7 only for trout (p<0.001). The increase of both C18:1 

n9 and C16:1 n7 acid levels after steaming contributed to higher extent to the elevation of total 

MUFA content in the Rainbow trout. Larsen et al. reported insignificant effect of the steaming on 

King salmon MUFA contents, while Su and Babb found significant changes in MUFA levels in 

steamed scallops [14, 25]. There are several possible reasons for the discrepancies and differences 

among the reported results, but one of the most important is the lack of standardized times and 

temperatures for any cooking method. 

 

3.4.3. Polyunsaturated Fatty Acids 

In this study PUFA in both fish species were dominated by linoleic acid C18:2 (LA) from n6 

and DHA from n3 series. In the steamed Rainbow trout LA content increases up to  47.30 % of 

total PUFAs (p<0.001), whereas in  Bluefish its value was unchanged EPA and DHAn3 are 

highly polyunsaturated and more vulnerable to the oxidation even at ambient temperature 

compared to LA n6 and their contents strongly depend on the storage conditions. Conversely, the 

levels of the second abundant n6 FA - arahidonic acid (AA) were constant in raw and steamed 

Bluefish (8.15 % of total PUFAs), whereas the Rainbow trout showed slight increase by 3.22 % 

(p<0.01) compared to raw samples. Su and Babb reported increase in DHA and AA contents and 

decrease of EPA content in steamed scallops [25]. Some discrepancies were found when 

comparing the obtained results with the results involving amounts of EPA and DHA quoted by 

other authors. In the present study the sum of EPA plus DHA in raw trout and Bluefish 

accounted to 28.8 % and 34.0% of total PUFA respectively (table 3). The results obtained by 

Kalyoncu et al. and Steffens and Wirth for these FAs in trout were lower (with 10%) [22, 26]. 

The feeding habits, the method of fish farming and the different locations are probably the main 

reasons for the discrepancies in the results. Significant changes in EPA and DHA levels were 

observed in the steamed trout (32.8 % of total PUFA) due to the increase of DHA value 

(p<0.001), while no differences were found for the Bluefish (table 3). The Lack of negative 



 
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influence of the cooking procedure on the DHA levels of trout fillets has high practical 

importance. Due to this fact, compared with Bluefish, the steamed trout is a better source of these 

n3 PUFAs. Kolakowska et al. suggested that the different heat treatment procedures had no 

substantial influence on the percentage of EPA and DHA in Baltic herring [20]. In other 

researches the same authors reported that heating for 20 min at 160oC could reduce DHA and 

EPA contents in the Rainbow trout [13]. The reported changes in EPA + DHA levels for both 

species could be caused by the changes in their lipid extractability. Other important results in this 

study showed that the total sum of n6 PUFAs was elevated in steamed Rainbow trout (up to 

61.00 % of total PUFA) in comparison with the raw one (50.5% of total PUFA, p<0.001), whereas 

the opposite trend was observed in Bluefish (p<0.001) after steaming (table 3). The n3 series 

showed significantly decreasing (below 6.0%, p<0.001) in steamed Rainbow trout, while in 

Bluefish this series remains unaffected. As a result, steaming can be preferred without significant 

loss of n3 PUFAs in Bluefish. The n3/n6 PUFA ratio is a key factor for balanced synthesis of 

eicosanoids in the organism [27]. Previous studies revealed that n3/n6 ratio in freshwater fishes 

varies between 0.5 and 5.6, whereas in marine fishes it is between 0.7 and 14.4 [26, 28]. The 

obtained results in this study for raw species (from 0.7 up to 0.84) are in agreement with the 

above mentioned results. The observed differences in omega PUFA levels result in a decrease of 

n3/n6 ratio only in Rainbow trout, while it remains stable in Bluefish after steaming (table 3). 

Gladishev et al. and Su and Babb reported a decrease in n3/n6 ratio in steamed and boiled fish 

species and thus support our results [19, 25]. According to the current WHO recommendations, 

n3/n6 PUFA should not be lower than 0.2 [2, 27]. In both analyzed fish species before and after 

steaming this ratio remains significantly above the cut-of value. The Department of Health 

recommended PUFA/SFA ratios greater than 0.45 [29]. Simopoulos and Cleland [27] reported 

that several studies had found inverse association of the PUFA/SFA ratios with cardiovascular 

diseases [27]. In our study, the most balanced PUFA/SFA ratio was obtained for Bluefish (table 

3). We found that the steaming increases PUFA/SFA ratio by 8.33 % in the Rainbow trout, 

whereas this parameter remains unchanged in the Bluefish. Our results reveal that steaming does 

not induce a reduction of PUFA/SFA ratio below 0.45 in both species. 

 

4. CONCLUSIONS 

The Nutritional quality of the Rainbow trout and the Bluefish are fairly similar, with 

relatively high levels of unsaturated FAs and fat-soluble vitamins. No significant changes in 

PUFA amounts, FA distribution and cholecalciferol content for the Bluefish compared to the 

Rainbow trout were observed after steaming. The positive beneficial effect of fish lipids based on 

EPA and DHA n3 PUFA, n3/n6 and PUFA/SFA ratios, and fat soluble vitamins content are 

preserved after that treatment. The steaming method can be recommended as a mild and less 

aggressive cooking method suitable for healthy dietetic regimes. Since FA composition and fat 

soluble vitamins' content are important components of the nutritional value of fishes, their 



 
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changes during the various regimens of processing need special interest and further 

investigations. 

 

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