Fish Microbiology and Quality Assurance

16. Sensory evaluation for assessing the quality of raw fish

The quality of fish gradually deteriorates after capture and becomes unfit for consumption if proper storage conditions are not followed. However, the freshness of fish can be judged by its appearance, odour and texture. The spoilage of any species of fish which follows a definite pattern can be recognized and described using the senses of sight, touch, smell and taste, and freshness scale established by assigning numbers to spoilage stages. The sensory grades and scores are useful only within a limited situation for immediate assessment of freshness by a consumer or a buyer for further processing.

Guide to EEC Freshness Grades

The EEC recognizes four freshness grades for fish namely, Extra grade (E), grades A, B and C based following sensory characteristics. The freshness grading for sardines and mackerel is given below.

I. SARDINES

		E	A	B	Unfit (C)
Skin		Bright, shining, iridescent (not red fish) or opalescent, no bleaching	Waxy, slight loss of bloom, very slight bleaching	Dull, some bleaching	Dull, gritty, marked bleaching and shrinkage
Outer slime		Transparent, water white	Milky	Yellowish – gray, some clotting	Yellow – brown, very clotted and thick
Eyes		Convex, black pupil, translucent cornea	Plane, slightly opaque pupil; slightly opalescent	Slightly concave gray pupil, opaque cornea	Completely sunken, gray pupil; opaque discoloured cornea
Gills		Dark red or bright red, mucous translucent	Red or pink; mucous slightly opaque	Brown / grey and bleached; mucous opaque and thick	Brown or bleached; mucous yellowish gray and clotted
Peritoneum (in gutted fish)		Glossy; Brilliant; difficult to tear from flesh	Slightly dull; difficult to tear from flesh	Gritty; fairly easy to tear from flesh	Gritty; easily torn from flesh
Gill and Internal Odours	All except plaice	Fresh; seaweedy; shellfishy	No odour; neutral odour; trace musty; mousy; milky; caprylic; garlic or peppery	Definite musty; mousy milky; caprylic; garlic or peppery; bready; malty; beery; lactic; slightly sour	Acidic; butyric; fruity; turn ; amines; sulfide fecal
	Plaice	Fresh oil; metallic; fresh cut grass; earthy; peppery	Oily; seaweedy; aromatic; trace musty; mousy or citric	Oily; definite musty; mousy or citric; bready; malty; beery; slightly rancid; painty	Muddy; grassy; fruity; acidic; butyric; rancid; amine; sulfide fecal

II. MACKEREL

	E	A	B	Unfit ( C )
Skin	Strong blue & turquoise colour; iridescence over all body; well defined lateral line; reticulations on upper surface; clear distinction between upper & lower surfaces	Loss of bright colour with fading of reticulations; pale golden tinge on lower surface	Golden tinge overall body; skin wrinkles on flexing; washed out appearance of colours; patchy irridescence	Yellow slime; little distinction between upper and lower surfaces
Texture of body	Stiff	Firm	Some softening	Limp and floppy
Eyes	Bulging with protruding lens; shiny jet black/ blue pupil with metallic brown iris; transparent eye cap	Convex slight clouding of lens and wrinkling of iris; clouding of eye cap	Plane cloudy lens with black specks in iris; pale golden eye cap	Sunken eye covered with yellow slime
Gills appearance	Uniformly dark red/ purple with free blood and water clear slime	Loss of colour with red/ brown slime; pale margins to gills	Further loss of colour with patchy bleaching; increase in red/ brown slime	Bleached; thick yellow slime
Gill odour	Fresh seaweed; sharp halogens; pepper; fresh cut grass; metallic; blood; fresh sweet oil	Dull; muddy; musty; mousy; cardboardy; fish oil	Yeast; sour; rotten fruits; “wet dogs”; old grass cuttings; strong oily	Compost heap; rotten turnips; sour cheese; ammonia; sulfides; rancid oil

Procedure

The raw fish procured from the fish landing center/ fish market is evaluated for general appearance, odour, texture and flesh including belly flaps using the following quality attributes and assigning score on a number scale with highest score to fresh fish and lowest to poor quality fish.

Instructions

1. Choose the best description to characterize the freshness attribute
2. Write the corresponding value in score sheet
3. Based on the total score (sum of the score for all attributes) grade the freshness quality of fish.

EVALUATION OF RAW FISH

General appearance	Score (5)
Eyes perfectly fresh; convex black pupil; translucent cornea; bright red gills; no bacterial gills; outer slime watery white; bright opalescent sheen; no bleaching	5
Eyes flat; very slight grayness in pupil; slight loss in colour of gills	4
Eyes slightly sunken; gray pupil; slight opalescent of cornea; some discoloration of gills; some mucus; outer slime opaque and somewhat milky; loss of slight opalescent and some bleaching	3
Eyes sunken; milky white pupil; opaque cornea; thick knotted outer slime with some bacterial discoloration	2
Eyes completely sunken; shrunken head covered with thick yellow bacterial slime; gills showing bleaching or dark brown discoloration and covered with thick bacterial mucus; outer slime thick yellow brown; bloom completely gone; marked bleaching and shrinkage	0
Odour	Score (10)
Fresh seaweedy odour	10
Loss of fresh seaweedyness; shellfish odour	9
No odours; neutral odour	8
Slightly musty; mousy; milky; garlic or peppery odour	7
Bready; malty; beery; yeasty odour	6
Lactic acid; sour milk of oily odour	5
Acidic or butyric acid; grassy old boot; slightly sweet; sweety or chloroform odour	4
Stale cabbage water; sour sink; wet matches; phosphine like odour	3
Ammonical with strong odours	2
H2S and other sulfide odours with strong ammonical odour	1
Indole; ammonia; fecal and putrid odours	0
Texture	Score (5)
Firm; elastic to the finger touch; fish not yet in rigor	5
Firm and elastic and fish passing out of rigor	4
Softening of flesh and some grittiness near tail	3
Softer flesh; definite grittiness and scales easily rubbed off the skin	2
Very soft flabby; retains the finger indentations; marked grittiness and flesh easily fall torn form backbone	1
Flesh including belly flaps	Score (5)
Bluish translucent flesh; no reddening along the backbone; no discoloration of belly; kidney blood light red	5
Waxy appearance; no reddening along backbone; loss in original brilliance of kidney blood; some discoloration of belly flap	3
Some opacity; some reddening along backbone; brownish kidney blood; some discoloration of belly flap	2
Opaque flesh; very marked red or brown discoloration along back bone; marked discoloration of flaps	0

SCORE SHEET FOR RAW FINFISH

Name of the fish : Date :

Place of catch : Date of catch:

Method of catch : Transportation condition:

Characteristics	Scores assigned	Scores obtained
		Sample 1	Sample 2	Sample 3	Sample 4
RAW FISH General appearance Odour Texture Flesh including belly flaps	5 10 5 5

GRADING

Grade	Score points	Remarks
A	90% and above	Good for processing
B	70 to 89%	Edible purpose
C	Less than 70%	Not suited for consumption