baseline study - scotland mussels - final report · ten experienced panellists analysed the live...

MusselsAlive Report

JANUARY, 2013 MEAT QUALITY OF ROPE GROWN SCOTTISH

MUSSELS

The report describes the work developed at IPMA in order to

characterize the meat quality of rope grown mussels from

Scotland.

ANA MAULVAULT ANTÓNIO MARQUES SÓNIA PEDRO MARIA LEONOR NUNES

Acknowledgments: MusselsAlive is a research for SME Associations project and has received funding from the EU Seventh Framework Programme FP7 under grant agreement no 243452.

MusselsAlive Report - SCOTLAND

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INDEX

1. TRANSPORT CONDITIONS .................................................................................................................... 3

1.1 Transport box 3

1.2 Biometric data 3

1.3 Mortalities and broken shells 4

2. PERCEIVED FRESHNESS ........................................................................................................................... 6

2.1 Sensorial analyses of live and cooked mussels 6

2.2 Edible meat content 8

2.3 Edible meat coloration 8

3. CHEMICAL COMPOSITION ...................................................................................................................... 9

3.1 Proximate chemical composition 10

3.2 Fatty acids profile 10

3.3 Inorganic elements 13

4. REFERENCES ........................................................................................................................................ 17


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MusselsAlive Report Meat quality of rope grown mussels in Scotland – Winter, Spring and Autumn 2011 – Winter, Spring and Summer 2012

The work developed at IPMA aimed to characterize the meat quality of rope grown mussels from Scotland in

order to evaluate the current status of mussel’s quality provided to European consumers throughout the year.

Mussels were sent by The Scottish Shellfish Marketing Group and received at IPMA (Lisbon) in four

seasons: Winter I (sent on the 1st of March and received on the 2nd of March, 2011), Spring I (sent on the

13th of June and received on the 14th of June, 2011), Autumn (sent on the 14th and received on the 15th of

November of 2011), Winter II (sent on the 25th of January and received on the 26th of January, 2012),

Spring II (sent on the 1st of May and received on the 2nd of May, 2012), and Summer (on the 11th of July

and received on the 12th of July, 2012). Once in Portugal, the mussels were immediately examined and

several parameters were checked namely:

1. Transport box and net bags

2. Biometry

3. Mortality

4. Sensorial analyses of raw and cooked mussels performed by a professional panel

5. Edible meat content

6. Meat chemical assessment

This report is divided in three main sections. The first section is the Transport Conditions and

comprehends the parameters one to three of the above list. The second part describes the results of the

sensorial analyses and the edible content and is entitled Perceived Freshness. Finally, the main results of

the chemical analyses, including proteins, fat, glycogen, ash, moisture, fatty acids, amino acids and inorganic

elements are shown in the third section - Chemical Composition.


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1. TRANSPORT CONDITIONS

1.1 Transport box

Mussels were packed in 10 net bags in Spring (I and II) and Winter (I and II) seasons. The samples

received in Autumn consisted only in a large net bag containing all mussels. In Summer, 15 net bags with

Scottish mussels were sent. Nevertheless, once at the laboratory (in Lisbon, Portugal), the mussels were

divided and distributed into 9 different recipients. In all seasons, samples were transported in Styrofoam

boxes, containing packed ice to keep low temperature, i.e. around 10 ºC upon arrival to Lisbon, in all cases

(Figure 1). Additionally, paper journal was used to maintain moisture in Winter I and Spring I samples.

1.2 Biometric data

As shown in Table 1, each net bag of Winter I mussels had 989.3 ± 15.2 g, corresponding to 75 mussels

each, whereas in Winter II the net bags weighted in average 1028.0 ± 38.8 g and contained 98 mussels. In

Spring I, net bags weighted 960 ± 25.2 g, each having 77 specimens, but in Spring II a higher number of

mussels were found per net bags (100 mussels), each weighting 1096.3 ± 29.5 g. The samples received in

Autumn consisted only in a large net bag containing all mussels sent from Scotland. Nevertheless, once at

the laboratory (in Lisbon, Portugal), the mussels were divided and distributed into 9 different recipients. Each

A B C

D E

Figure 1 - The different layers wrapping the net bags containing mussels: A - Winter I (2011); B – Spring I (2011); C – Autumn (2011); D - Winter II (2012); E – Spring II (2012); F – Summer (2012). 1 - Packed Ice; 2- Insulating plastic layer; 3 – Paper Journal: 4 – Net bag with

live mussels.

1

2 3

4 1

2

3 4

1

2

4

1

2 4 1

2 4

1 2

4

F

4

A


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recipient contained, in average, 67 mussels and weighted 1002.8 ± 2.6 g. Summer sample consisted of 15

net bags, each weighing 894.8 ± 14.9 g which corresponded to an average of 86 mussels per net bag.

Table 1 – Winter (I and II), Spring (I and II), Autumn and Summer mussels’ biometric parameters.

Biometrics Winter I Spring I Autumn Winter II Spring II Summer

Net bag weight (g) 989.3 ± 15.2 960 ± 25.2 1002.8 ± 2.6 1028.0 ± 38.8 1096.3 ± 29.5 894.8 ± 14.9

Mussels/net bag 75.0 ± 4.0 77.3 ± 4.9 69.7 ± 6.2 98.0 ± 4.3 99.8 ± 3.4 85.9 ± 2.8

Mussel weight (g) 18.9 ± 3.7 14.2 ± 5.3 15.6 ± 3.9 10.3 ± 3.8 10.9 ± 2.4 11.4 ± 3.3

Mussel length (mm) 68.3 ± 4.2 59.1 ± 7.2 61.6 ± 5.4 52.8 ± 6.4 52.4 ± 4.9 56.0 ± 6.1

Mussel width (mm) 24.1 ± 2.1 18.4 ± 6.0 21.8 ± 2.2 18.4 ± 2.6 18.0 ± 1.6 19.2 ± 2.3

In general, mussels harvested in Winter II, Spring II and Summer presented lower lengths and weights,

whereas larger specimens were collected in Winter I, Autumn and Spring I.

1.3 Mortalities and broken shells

Each net bag was visually inspected. As shown in Figure 2, mortality percentages during transportation were

very high on Winter I and Spring I (18% and 35%, respectively, not including broken shells), since these

samples only arrived at Lisbon 4 days after being collected. The mortalities observed in Autumn, Winter II,

Spring II and Summer were much lower, never exceeding 10%. When including mussels with broken shells

the mortalities were slightly higher, indicating that mussels should be handled and transported carefully along

the trade chain to avoid such losses. Despite the results obtained, it is important to note that mussels’ net

bags should not be kept inside a closed plastic bags (as observed in Spring II sampling) since this does not

allow animals to breath, causing the decrease of condition index and higher mortality rates during transport.

Figure 2 - Mussel’s mortality rate and mortality including broken mussels (%) in each net bag after transport from Scotland in a Styrofoam box.


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In general, mortality (excluding broken shells) in each season was variable among bags,

with an average of 6 % in Autumn, 2 % in Winter II, 4 % in Spring II and 10% in Summer.


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2. PERCEIVED FRESHNESS

2.1 Sensorial analysis of live and cooked mussels

Ten experienced panellists analysed the live mussels’ shell appearance and smell in Winter I, Spring I,

Autumn, Winter II, Spring II and Summer. The panel also scored odour, flavour and texture of steam-

cooked mussels. At the end, a global rate for each treatment (live and cooked) was attributed to the mussels.

In each season, six mussels were analysed per panellist (3 raw and 3 cooked), totalizing thirty live mussels

and thirty steam-cooked mussels.

2.1.2. LIVE MUSSELS SENSORIAL ANALYSES

The descriptors used to characterize live mussels are indicated in Table 2.

Table 2. Scale of sensorial evaluation of live mussels. 1 2 3 4 5 6

Shell appearance

Closed, cleaned Closed, dirty (algae, mud)

Open, cleaned Open, dirty

Shell Odour Characteristic

sweet fresh

Non-specific

slightly sweet Neutral

Slightly

to ammonia Ammonia Very unpleasant

Global Rate Very Good Good Acceptable Rejected

Fresh live mussels harvested in Winter II, Spring I and Autumn were scored, globally, as very good or good

(100 %, 80 % and 70 %, respectively; Figure 3), whereas Spring II and Summer mussels presented the

lowest scores. Smell was the most important attribute influencing the global appreciation.

Figure 3 - Scores attributed to live mussels harvested in Winter I, Spring I, Autumn, Winter II, Spring II and Summer (shell appearance, smell and global rate). The percentage of answers given by the panellists is evidenced according to the scale classes used (see table 2)

represented by the colour coded bars.


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2.1.2. STEAMED COOKED-MUSSELSSENSORIAL ANALYSES

Mussels were also steam-cooked at 100 ºC during 3 minutes and served to experienced panellists at room

temperature. The scale used to characterize steam-cooked mussels is indicated in Table 3.

Table 3. Descriptors for sensory evaluation of steam-cooked mussels (adapted from Pastoriza et al., 2004).

1 2 3 4 5 6

Odour Characteristic sweet fresh

Non-specific slightly sweet

Neutral Slightly to ammonia

Ammonia Very unpleasant

Taste Characteristic mild

Characteristic slightly mild

Strong Slightly sour

Sour Sickening

Texture Very firm Firm Slightly firm Slightly soft Soft Very soft

Global Rate

Very Good Good Acceptable Rejected

Globally, steam-cooked mussels were better scored than raw ones (Figure 4). Despite the better taste and

texture presented by Spring II mussels, panellists identified, in general, a less characteristic and/or sweet

smell in this sample compared to those collected in the other seasons. For this reason, 40 % of Spring II

mussels were rated only as acceptable. An unpleasant smell (10%) along with a sickening taste (20) lead to

the lowest global rates attributed to Summer samples (rejected by 30% of the panel).

Figure 4 - Score attributed to steam-cooked mussels harvested in Winter I, Spring I, Autumn, Winter II, Spring II and Summer (shell appearance, smell and global rate). The percentage of answers given by the panellists is evidenced according to the scale classes used

(see table 2) represented by the colour coded bars.


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2.2 Edible meat content

The highest percentage of edible weight was found in mussels harvested in Spring II (56 %), whereas

Winter I mussels revealed the lowest percentage (41 %) (Figur 5. Summer mussels from Scotland

presented lower meat yields than those harvested in Norway but higher than those obtained in Irish mussels

in the same season (56 % and 45 %, respectively). Nevertheless, Scottish mussels’ (Winter, Spring, Autumn

and Summer) meat yields were higher than those reported by Fuentes et al. (2009) in different parts of

Spain.

2.1 Edible meat coloration

The edible meat coloration was evaluated using the three LAB parameters: lightness (L*; 0 means black and

100 means white), red/green (a*; negative values means green and positive values indicate red) and

yellow/blue (b*; negative values means blue and positive values indicate yellow). The values were converted

to the RGB range of values and different tones were obtained in each sampled season, with the help of

Adobe® Kuler® tools (Figure 6). Coloration of Winter and Spring mussel meat samples collected in 2011 (I)

and 2012 (II) was similar. Autumn mussels’ meat presented the lightest tone, whereas in Spring (I and II)

samples a darker and more intense tone was observed.

B

A

Figure 5 - A – Winter (I and II), Spring (I and II), Autumn and Summer mussel’s total weight (shell included); mussel’s edible weight; and the proportion of edible weight to the whole animal – meat yield (%). Data is presented as average ± Standard Deviation; B – Comparison

between the meat yield of Summer mussels from Norway (own data), Ireland (own data), and Spain (Fuentes et al., 2009).


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In general, live and steam-cooked mussels harvested in Summer revealed lower

acceptance than those harvested in Winter, Autumn and Spring, mostly due to the

unpleasant smell and taste detected. Spring mussels revealed higher meat yield

percentages (55.5%) a darker and more intense coloration of meat.

WINTER

I and II

SPRING

I and II

AUTUMN

Figure 6 - Scottish mussels’ average edible meat coloration converting LAB values to RGB values (http://kuler.adobe.com).

SUMMER


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3. CHEMICAL COMPOSITION

3.1 Proximate chemical composition

The proximate chemical composition of Winter (I and II), Spring (I and II), Autumn and Summer mussel

samples is shown in Table 4. Regardless of origin and season, mussels reveal high moisture and protein

contents. Winter (I and II), Spring I and Summer mussels had a leaner flesh, but higher moisture contents.

On the other hand, mussels sampled in Autumn and Spring II had higher fat contents. The chemical

composition found in Scottish mussels was similar to those of Norwegian, Irish and Spanish mussels

(Musselsalive data; Fuentes et al., 2009).

Table 4 - Mussels proximate chemical composition (%). Data is presented as average – Comparison between the composition of mussels from Norway (own data), Ireland (own data) and Spain (data from Fuentes et al. (2009). ND - No data.

Parameters Scotland Norway Ireland Galicia

Ebro Delta

Valencia

Winter I Spring I Autumn Winter II Spring II Summer Summer Summer Summer Summer Summer

Moisture 81.9 82.9 78.8 81.7 78.9 80.0 79.5 84.1 79.0 83.8 81.5

Proteins 11.3 9.7 11.8 9.6 10.1 11.2 9.6 7.4 10.0 6.5 10.0

Ash 5.7 2.2 2.1 2.2 2.0 2.2 1.7 2.4 2.2 3.4 3.4

Carbohydrates 0.9 3.8 2.3 2.3 2.7 1.6 2.8 1.7 ND ND ND

Fat 0.4 1.5 2.0 1.5 2.5 1.6 0.9 0.8 1.4 1.7 2.2

3.2 Fatty acids profile

The fatty acid profiles of Scottish mussels harvested in Winter (I and II), Spring (I and II), Autumn and

Summer are shown in Figure 7. Summer mussels revealed the highest content of saturated fatty acids (SFA)

and monounsaturated fatty acids (MUFA) with 47.2% and 25.1%, respectively, whereas the highest

percentages of polyunsaturated fatty acids (PUFA) were observed in mussels harvested during Winter I and

Spring I (52.8% and 51.5%, respectively). Total concentration of omega-3 PUFA was also higher in Spring I

(45.5%), while the highest percentage of omega-6 PUFA was found in Winter I samples (6.8%). However, the

best ratio of n-3/n-6 was obtained in Spring II samples (14.2) and lower in Winter I (6.6).


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In the SFA group (Figure 8), palmitic acid (16:0) was the predominant fatty acid in all samples, reaching the

highest value in Summer (26.1%) and the lowest in Winter I. Palmitic acid has been reported in numerous

studies as the major SFA in mussels (e.g. Alkanani et al., 2007).

Regarding MUFA, palmitoleic acid (16:1n-7+n-9) was the most abundant fatty acid (Figure 9), with the

highest content in Spring II mussels (16.9%) and the lowest in Winter I (7.1%).

Figure 7 – Fatty acids profiles of Winter (I and II), Spring (I and II), Autumn and Summer mussels harvested in Scotland.

Figure 8 – Saturated fatty acids of Winter (I and II), Spring (I and II), Autumn and Summer mussels harvested in Scotland.


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Eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids were the most important

PUFA in all samples (Figure 10). Higher levels of EPA were found during Spring (I and II, respectively,

23.2% and 26.6%), whereas the lowest values were observed in Summer (10.5%). Concerning DHA, the

percentages were lower than those of EPA, varying between 4.1% (Summer) and 10.0% (Winter I).

3.3 Inorganic elements

3.3.1. ESSENTIAL ELEMENTS

Almost all elements considered as essentials, i.e. those provided through the diet and required to maintain

normal physiological functions can be found in Scottish mussels. Figure 11 shows the elemental composition

of Winter (I and II), Spring (I and II), and Autumn mussels.

Figure 9 – Monounsaturated fatty acids of Winter (I and II), Spring (I and II), Autumn and Summer mussels harvested in Scotland.

Figure 10 – Polyunsaturated fatty acids of Winter (I and II), Spring (I and II), Autumn and Summer mussels harvested in Scotland.


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Globally, higher concentrations of Cl, Zn and Sr were found in mussels harvested in Winter II, whereas

Summer mussels presented higher contents of Ca and Br. Autumn samples revealed the highest contents

Figure 11 – Macro and trace elements concentration in Scottish mussels harvested in Winter (I and II), Spring (I and II), Autumn and Summer.


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of K, S and Cu. Fe was higher in Winter I samples, whereas Spring II showed higher Rb levels. The

concentration of Se did not greatly vary among seasons.

Considering this dichotomy, risk assessment of essential elements has to take into account the two ends of

the toxicity spectrum: those associated with intakes that are too high (toxicity), and those associated with

intakes that are too low (nutritional deficiencies). The USA Food and Nutrition Board of the Institute of

Medicine (IOM) has dealt with nutritional deficiency problems, as well as with their toxicity, by setting dietary

reference intakes (DRI), which includes the recommended dietary allowance (RDA), adequate intake (AI)

and tolerable upper intake level (UL) for essential elements. Table 5 shows the RDA/AI and UL of some

essential elements, together with a small description of their functions and adverse effects if consumed in

excess.

Table 5 - Dietary reference intakes for essential elements (mg/day) from food and water (adapted from Barrento, 2010).

Element Function RDA/AI UL Adverse effects of excessive consumption

Potassium

K

Required for normal cellular function 4700* ND Hyperkalemia

Sodium

Na

Required to maintain extracellular volume and plamsa osmolality

1500* 2300 Elevated blood pressure, increased risk factor for CVD and renal diseases

Calcium

Ca

Blood clotting, muscle contraction, nerve transmission, bone and tooth formation

1000* 2500 Kidney stones, hypercalcemia, milk alkali syndrome and renal insufficiency

Iron

Fe

Prevents anemia 18 (♀)

8 (♂)

45 Gastrointestinal distress

Copper

Cu

Component of enzymes in iron metabolism

0.9 10 Gastrointestinal distress, liver damage

Zinc

Zn

Component of multiple enzymes and proteins, involved in the regulation of gene expression

8 (♀)

11 (♂)

40 Reduced Cu levels

Selenium

Se

Protection against oxidative stress, regulation of thyroid hormone action, reduction and oxidation of vitamin C and other molecules

0.055 0.4 Hair and nails brittleness and loss

Magnesium

Mg†

Cofactor of enzyme systems 320 (♀)

420 (♂)

ND No evidence of adverse effects from consumption of naturally occurring Mg in foods;

Mg containing supplements may cause osmotic diarrhea

Manganese

Mn

Involved in the formation of bone, as well as in enzymes from amino acid, cholesterol and carbohydrate metabolism

1.8* (♀)

2.3* (♂)

11 Elevated blood concentration and neurotoxicity

Abbreviation: (RDA) recommended dietary allowance; (AI) adequate intake; (UL) tolerable upper intake levels. RDA values are in bold type while AI are in ordinary type followed by an asterisk (*). All reference intakes shown are for adult males (♂) and females (♀) aged 19 to 50 years. (ND) not determinable due to lack of data of adverse effects in this age group and concern with regard to lack of ability to handle excess amounts. Source of intake should be from food only to prevent high levels of intake (IOM, 1997; 2001; 2004); (†) female and male adults aged between 31 and 50 years.


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RDA is set to meet the daily dietary needs of almost all (97 to 98 %) healthy individuals in a particular life

stage (e.g. infants, children, pregnancy and lactation) and gender group. The AI is believed to cover the

needs of all individuals in a life stage group, but lack of data prevent being able to specify with confidence

the percentage of individuals covered by this intake. The UL is the highest level of daily nutrient intake that is

likely to pose no risk of adverse health effects to almost all individuals in the general population.

Considering that an adult may eat the equivalent to 100 g of mussels’ edible meat per meal

(approximately, 13 mussels), this product is an excellent source of Se and a good source of Zn, Cu

and Fe.

3.4.1. CONTAMINANTS

In addition to essential elements, toxic elements, such as Hg, Cd, Pb and As, can also be found in some

marine species. Such elements are available in water from natural sources, such as rocks, as a result of

human activities like emissions from industrial processes. These elements are taken up by marine organisms

through the diet and gills, and tend to accumulate in species occupying higher trophic levels, like fish and

shellfish (EFSA, 2004, 2005). Regular consumption of contaminated seafood can cause poisoning and

promote diseases. In the European Union, the European Commission has set maximum levels for Cd, Pb

and Hg but not yet for As (EC No. 1881/2006; Table 6). To ensure an efficient protection of public health,

products containing contaminants exceeding the maximum levels should not be placed on the market either

as such, after mixture with other foodstuffs or used as an ingredient in other foods (EC No. 1881/2006).

Table 6 - Maximum level (ML, ppm) for Hg, Cd and Pb in bivalves according to the EC regulation No 1881/2006 of 19 December 2006, setting maximum levels for certain contaminants in foodstuffs.

Element ML

(ppm) Adverse Effects Observations

Arsenic

As ND

No data on the possible adverse effects of organic arsenic compounds in food were found. Inorganic arsenic is a known toxic substance.

There is no established maximum level for Arsenic.

Cadmium

Cd 1.0

Nephrotoxicity, osteoporosis, carcinogenicity and genotoxicity, teratogenicity, and endocrine and reproductive effects.

Long biological half-life in mammals. In humans, steady-state concentrations in the renal cortex are reached after about 40 years.

Lead

Pb 1.5

Neurotoxicity, anaemia, renal toxicity and subsequent carcinogenicity and cardiovascular effects; impairment of the reproductive system.

Pb in seafood is inorganic, and is bound to proteins. Bioaccumulation in marine animals is low compared to mercury. Main sites of Pb accumulation in seafood: internal organs, skin and bone, but not in muscle.

Mercury

Hg 0.5

Neurotoxicity. High exposure in uterus has resulted in cerebral palsy or severe mental retardation in the neonate.

Organic Hg is considered to be more toxic than other forms of Hg following ingestion. Methyl-Hg is the predominant form of Hg in fish (> 90 %).


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Despite the, relatively, higher concentrations of Cd and Pb found in Spring I samples (Figure 12), the values

are still well below the levels set by the EU (Table 5), thus indicating that mussels harvested in Scotland are

safe for consumption all year round. Presently, the EU has not established a maximum level for As, but the

concentrations obtained in Scottish mussels have shown to be very low compared to other seafood products

(Muñoz et al., 2009), thus not representing any risk to consumers.

Overall, Scottish mussels are a lean and safe seafood product, as very low contamination

levels were found in Scottish mussels.

Figure 12 – Contaminants concentration in Scottish mussels harvested in Winter (I and II), Spring (I and II), Autumn and Summer.


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4. REFERENCES

Alkanani, T., Parrish, C. C., Thompson, R. J., & Mckenzie, C. H. (2007). Role of fatty acids in cultured

mussels, Mytilus edulis, grown in Notre Dame Bay, Newfoundland. Journal of Experimental Marine Biology

and Ecology, 348, 33–45.

Barrento, S. (2010). Nutritional quality and physiological responses to transport and storage of live

crustaceans traded in Portugal. Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto

(PhD thesis in English). 261p.

EFSA (2004). Opinion of the scientific panel on contaminants in the food chain on a request from the

Commission related to cadmium as undesirable substance in animal feed (Question N° EFSA-Q-2003-033).

The EFSA Journal, 72, 1-24.

EFSA (2005). Opinion of the scientific panel on contaminants in the food chain on a request from the

European Parliament related to the safety assessment of wild and farmed fish. Question N° EFSA-Q-2004-

22. The EFSA Journal, 236, 1-118.

Fuentes, A., Fernández-Segovia, I., Escriche, I. & Serra, J. A. (2009). Comparison of physico-chemical

parameters and composition of mussels (Mytilus galloprovincialis Lmk.) from different Spanish origins. Food

Chemistry, 112(2), 295-302.

Muñoz, O., Devesa, V., Suñer, M.A., Vélez, D., Montoro, R., Urieta, I., Macho, M.L., Jalón, M., 2000. Arsenic

in cooked seafood products: study on the effect of cooking on total and inorganic arsenic contents. Journal of

Agricultural and Food Chemistry, 49: 4132-4140.

Pastoriza, L., Bernárdez, M., Sampedro, G., Cabo, M. L. & Herrera, J. J. R. (2004). Elevated concentrations

of oxygen on the stability of live mussel stored refrigerated. European Food Research Technology, 218,

415–419.

baseline study - scotland mussels - final report · ten experienced panellists analysed the live...

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