Sensory Evaluation of Fish Freshness

Transcription

1 Workshop: Use of sensory techniques in quality control of food 1 Sensory Evaluation of Fish Freshness Emilía Martinsdóttir ttir Icelandic Fisheries Laboratories Skúlagata 4, IS-101 Reykjavík, k, Iceland Tel: , emilia@rf.is

2 The content of the lecture Methods for sensory evaluation of fish importance of freshness use of sensory evaluation The QIM-method How to develop a QIM-scheme Reference manual Use in industry Conclusions

3 Why is sensory evaluation of fish important! Sensory evaluation of fish freshness gives valuable information on quality Fish is very perishable, can be kept on ice 8-20 days depending on species Spoilage is species related - Many different species Freshness and changes in sensory attributes are critical parameters during food production Time and temperature is of main importance Fish is transported all over Fish is sold via e-commerce

4 Sensory evaluation in the fishery chain Fishing vessel FIsh auction Landing Sensory evaluation of whole fish Fish processing plant Fresh fillets Frozen fillets Retailers Retailers Sensory evaluation of raw and cooked fillets Sensory evaluation of cooked fillets Consumers Consumers

5 Methods for sensory evaluation of fish freshness in the industry EU scheme Grading scheme for whole fish EU scheme is commonly accepted in the EU countries E, A, B / unfit QIM (Quality Index Method) Bremner,1985 Demerit points 0-3 added to give an index Torry scheme for both whole and cooked fish Shewan, 1953 scoring system (10-1)

6 EU-scheme White fish: Haddock, cod saithe, pollock, redfish, whiting, ling, hake, Ray s bream, anglerfish pouting and poor cod, bogue, picarel, conger, gurnard, mullet, plaice, mergrim, sole, dab, lemon,sole, flounder, scabbard fish Criteria Freshness category Not Extra A B Admitted Skin Bright, iridescent pigment Pigmentation bright but Pigmentation in the Dull pigmentation (save for redfish) or not lustrous process of becoming opalescent; no discoloured and dull discolouration Skin mucus Aqueous, transparent Slightly cloudy Milky Yellowish, grey, opaque mucus Eyes Convex (bulging), black, Convex and slightly Flat, opalescent cornea, Concave in the centre, bright pupil, transparent sunken; black, dull pupil, opaque pupil grey pupil, milky cornea slighly opalescent cornea cornea Gills Bright colour, no mucus Less coloured, Brown / green becoming Yellowish, milky mucus transparent mucus discoloured, thick, opaque mucus Peritoneum on Smooth, bright, difficult Slighly dull, can be Speckled, comes away Does not stick gutted fish to detach from flesh detached from flesh easily from flesh Smell of gills and abdominal cavity >whitefish other Seaweedy No smell of seaweed, Fermented, slightly sour Sour than plaice: neutral smell >plaice: Fresh oily, peppery Oily, seaweedy or Oily, fermented, stale, Sour earthy smell slightly sweetish slightly rancid Flesh Firm and elastic, smooth Less elastic Slightly soft (flaccid), Soft (flaccid), scales surface less elastic, waxy easily detached from (velvery) and dull surface skin, surface rather wrinkled

7 Disadvantages of grading schemes like the EU-scheme Grouping several, different sensory terms into one quality grade Sensory characteristics disagree with other subdescriptions of the quality grade confusion of the grader, increased time decreases the objectivity of the evaluation Not species related

8 QIM-scheme for Sea bass Quality parameter Description Score Skin Colour/ Bright, iridescent pigmentation 0 appearancerather dull, becoming discoloured (head) 1 Green, yellowish, mainly near the abdomen 2 Odour Fresh seaweedy, neutral 0 Cucumber, metal, hey 1 Sour, dish cloth 2 Rotten 3 Texture In rigor 0 Finger mark disappears rapidly 1 Finger leaves mark over 3 seconds 2 Eyes Pupils Clear and black, metal shiny 0 Grey 1 Mat, grey 2 Form Convex 0 Flat 1 Sunken 2 Gills Colour Blood red/orange 0 Pale red, pink/light brown 1 Grey-brown, brown, grey 2 Mucus Transparent 0 Milky, clotted 1 Brown, clotted 2 Odour Fresh, seaweed, neutral 0 Metal, grass 1 Sour, mouldy,dish cloth 2 Rotten 3 Flesh, fillecolour Translucent, bluish 0 Waxy, milky 1 Opaque, yellow, brown spots 2 Viscera Solution Whole 0 Beginning to dissolve 1 Viscera dissolved 2 Quality Index 0-22

9 Advantages of the Quality Index Method (QIM) The relevant attributes are all evaluated and given scores according to their imporance The inspector has to evaluate each attribute Minor differences in judgements in one attribute do not influence the total score Useful to teach inexperienced people Useful to train and harmonise inspectors Linear relationship between Quality Index and storage time in ice

10 QIM scheme is developed for a new each fish species Development of QIM scheme selection of experienced QIM assessors purchasing of super fresh fish controlled storage experiment day-to-day description of the sensory attributes draft scheme validation and linear regression end-of-shelf life practical implementation QI score y = 0,6921x + 1,5676 R 2 = 0, Days in ice

11 Practical session With max 5 experienced QIM assessors experienced in sensory assessments good vocabulary experienced panel leader day-to-day description five fishes a time (do not re-use them) discussion during observation write down all comments from everyone continue one day after fish is definitely spoiled

12 Draft scheme Select the attributes which changed during the storage time group the descriptions with major changes add scores 0 very fresh, to max 3 at end of changes make a draft QIM scheme

13 Changes in sensory attributes during storage of ocean perch Eyes Cornea: Clear Score = 0 Form: concave Score = 0 Eyes Cornea: milky Score = 2 Form: sunken Gills Colour : Blood red Score = 0 Mucus: Clear Score = 0 Mucus: Discoloured, clotty Score = 2 Score = 2

14 Right score for each description? Individually assessment of all attributes over the storage period How do they change do they increase are all the scores 0, 1,2 3, used Score 2,0 1,5 1,0 0,5 0,0 Score 3,0 2,5 2,0 1,5 1,0 0,5 0,0 Texture Days in ice Gills odor Days in ice

15 Right score for each description? Multivariate analyses of all data. Make a PCA analyses of all results and decide if an attribute contributes enough to the total QIM score and to the storage time PC2 Texture Eyes form X-loadings Skin colour Gills colour Eyes pupils Skin mucus Skin odour Abdomen blood Abdomen odour Days in ice Gills mucus Gills odour X-expl: 82%,4% PC1

16 new storage experiment Validation use the draft QIM scheme individually discuss the scoring after every session adjust the descriptions and scores determine end-of-shelf life simultaneously use sensory evaluation of cooked samples by expert panel Torry scheme Quantitative Descriptive Analyses (QDA)

17 Torry scheme for the evaluation of cooked cod Odour Flavour Score Sweet, cooked milk Watery, metallic 10 Shellfish, cooked meat Sweet, meaty 9 Faint, neutral Sweet but more faint 8 Wood, vanilla Neutral 7 End of shelf life Average score = 5.5 Cooked potatoes Insipid 6 Boiled clothes A little sour, faint 5 TMA Sour milk, TMA Bitter,sour, TMA, 4

18 Changes in Quality Index and eating quality (Torry-score) during storage of iced haddock Quality index-qi Torry score Linear relationship -QI can be used to predict Torry-score QIM used on whole raw fish could replace sensory evaluation of cooked samples Storage time (days) 2 QI-May QI-Dec Torry-May Torry-Dec QIM is more rapid and is performed earlier in the production chain.

19 QDA evaluation of end-of-shelf life for salmon Score Negative QDA flavour changes Days in ice Sour Musty, earth Rancid increase of negative attributes detection of spoilage flavours significant difference at days (for positive as well as negative flavours)

20 Finalising the QIM scheme Describe the assessment of the fish Make professional photographs on relevant attributes use one batch, make photographs every day no commercial pictures calculate reliability of the calibration curve how many fishes per batch prediction of storage time st.dev. Firm texture Convex form of eye

21 Linear relationship between QI and storage time in ice Scientific development of QIM for various species Quality Index increases linearly with the storage time. For use in the industry - Evaluate QI Predicted storage time in ice is defined as the number of days that the fish has been stored in ice. Shelf life is defined as the number of days that whole, fresh (gutted) fish can be stored in ice until it becomes unfit for human consumption -Storage studies An estimate can be calculated for the remaining shelf life (= shelf life-predicted storage time).

22 QIM in Quality and Production Management Quality Index Remaining shelf-life Plaice Predicted storage time in ice Remaining shelf- life Salmon Estimated shelf life

23 QIM-manual in 11 languages English, Dutch, Danish, French, German, Greek, Icelandic, Italian, Norwegian, Portuguese and Spanish! Sensory evaluation of fish The Quality Index Method (QIM) for 12 fish species Guidelines for sensory evaluation of fish Facilities for sensory evaluation Sample preparation of cooked samples and procedure for the sensory evaluation Selection and training of panellists Shelf life of whole fish Using QIM in process- and quality management

24 Conclusions QIM is developed and recommended by fish research institutes Rapid, objective sensory method QIM is used in research Use in fish auctions has increased Interest of the fish sector has increased For further progress and development of QIM Implementation in fish auctions and fish processing plants training of assessors implementation of QIM (at the first point of sale) stimulated if the EU Council regulation (2406/1996) would incorporate QIM Develop schemes for more fish species!!

25 Conclusions QIM-schemes could be developed for other food quality control same language for buyers and sellers photographs

26 QIM-homepage QIM-EUROFISH QIMCHAIN-project Information on QIM method All QIM-schemes presented New articles on QIM Attribute Description Score Appearance Skin Bright, iridescent pigmentation 0 Rather dull, becoming discoloured 1 Dull 2 Stiffness In rigor 0 Firm, elastic 1 Soft, 2 Very soft 3 Eyes Cornea Clear 0 Opalescent 1 Milky 2 Form Convex 0 Flat, slightly sunken 1 Sunken, concave 2 Pupil Black 0 Opaque 1 Grey 2 Gills Colour Bright 0 Less coloured, some discoloured 1 Discoloured, brown spots 2 Brown, discoloured 3 Smell Fresh. seaweedy, metallic 0 Neutral, grassy, musty 1 Yeast, bread, beer, sour milk 2 Sulphuric, very sour 3 Mucus Clear 0 Milky 1 Milky, dark, opaque 2 Flesh, fillets Colour Translucent, bluish 0 Waxy, milky 1 Opaque, yellow, brown spots 2 Blood Colour Red 0 Dark red 1 Brown 2 Quality index 0-23

27 Thank you for your attention! Acknowledgements : Rian Schelvis-Smit and Joop Luten RIVO Grethe Hyldig DIFRES Kolbrún Sveinsdóttir IFL