FISH FEEDS PROCESSING AND TECHNOLOGY

FISH FEEDS PROCESSING AND TECHNOLOGY

J.P. MELCION

1. GENERAL FLOW-SHEET (Fig.1)

2. GRINDING

2.1. Definitions

The purpose of grinding is to reduce the raw materials into small particles in order:

1. to facilities the mixing operation,

2. to improve their nutritional utilization.

The yield of a grinder is the output (t/h) or the specific production (t/Kwh); the particle analysis describes the quality of the ground product: it can be measured by sieving.

The most commonly used equipments in grindings materials are hammermills, because of their rusticity and flexibility.

2.2. Hammermill description (Fig.2)

Hammermill consists of stationary or swinging hammers mounted on a rotor driven at speed usually from 1500 to 3 000rpm (50–100m/sec). The materials are first contacted by hammers, until the sizes of particles would be near the desired size. A negatives draw of air through the hammermill will assist in moving the sized particle towered the screen.

2.3. Grinding parameters

-   related to the grinder (tab.1)

-   related to the materials:

1. moisture: the specific production is reduced from 12 to 25 % when the moisture increases from 12–14 to 17–18 ‰

2. type of raw materials (Fig.3)

The particles sizes will be different with each type of material within the same grindings conditions.

A very small particles size is important for fish Feeds (0.5mm).

3. MIXING

3.1 Definitions

Blending consists to associate ground and proportioned raw materials, in order to distribute them homogeneously within the mixture.

Mixing quality is homogeneity: it can be measured with tracers.

The word “homogeneous” means every element of a mixture must be present in a feed sample, as small as the sample will be.

For a given ingredient, there is a relationship between the number and the size ratio of the particules.

3.2. Mixing equipments (fig. 4)

The horizontal ribbons mixer is the most commonly used equipment for mixing dry materials (until 18% moisture).

Running condition:

Degree filling: 50 – 100 % of the total volume

- mixing time: 4–5mn

- full bottom discharge

- use of premix for inclusion under 0.5 to 1‰

3.3. Demixing

Particle segregation may occur during transportation, conveying and delivery of the feed when the sizes and densities of the ingredients particles are quite different.

4. “DRY”PELLETING

4.1. Definitions

Pelleting can be defined, as the agglomeration of small particles into a larger solid with a given shape and texture, by means of a mechanical process in combination with moisture, heat and pressure.

The quality of the pellets is expressed as hardness, durability, water stability, sinkability, rehydratiom. Water stability is to be considered because of the leaching effect of water: loss of nutritive elements (soluble nitrogen, vitamins), and ponds eutrophisation.

4.2. Principle and equipment(fig. 5 and 6)

The pellet mill:

The rolls act to compress the material and to extrude it through the holes of the die. Steam is eventually added to the meal with conditioner.

4.3. Factors affecting pelleting

The main factors are (tab. 2)

-   Ingredients characteristics (fat, starch).

-   Moisturizing or steaming of the meal prior to pelleting (1 – 3%)

-   Diameter (2 – 4mn) and die thickness (compression ratio 12): the higher the die thickness for the same diameter, the harder are the pellets, but the lower is the specific production.

-   Binders: the feeds may disintegrate into water unless ingredients such as wheat gluten or pre-gelatinized starches are included to help form a continuous matrix producing adhesion between particles. their use is optimal.

4.4. Further operations (fig. 7)

4.4.1. Cooling

The temperature of the pellets leaving the pellet mill is high (60 to 80 ° C): they must be cooled prior other operation or delivery. Equipment: vertical or horizontal coolers.

4.4.2. Crumbling (fig. 8)

Crumble rolls are used to take relatively small pellets and break them into smaller particles for special feeding applications, especially for fingerlings and young fishes (d=0, 025 x fish length).

4.4.3. Screening

Fines from cooled pellets are usually removed prior to delivery. Particles from the reground pellets are separated by screening into various sizes according to the fingerlings sizes.

4.4.4. Coating

Some dry pellets or expanded products (salmon) are coated with fat in order to include to the diet essential fatty acids or liposolubles vitamins,and to form an hydrophobic layer out of the product. Liquid fat is applied by spraying a mist of liquid over the product as it enters a rotating drum or screw.

5. EXTRUSION-COOKING

5.1. Principle

Extrusion cooking can be defined as to squeeze a mealy product through a small hole, the die, under action of very high pressure (30 to 120 bars) with the aid of one or two screws, which compress and shear the material before it passes through the die. A part of mechanical energy is converted into heat, generated by friction: the product is cooked at variable intensities, depending from from the degree of treatement and the additional heating (80 to 250 C). The water, which under pressure in the meal, evaporates on leaving the die, creating the very low density and expanded structure. On emergence,the product is cut by a rotating knife, cooled and dried to approximately 10 to 12% moisture for safe storage.

5.2. Extruders (fig. 9)

-   mono screws and twin-screws

-   3 sections : feeding, compressing, melting.

The equality of the extruder feeds is expressed by:

-   Geometry expansion ratio, density,

-   Functional properties: water stability, rehydration, floatability,

-   Biochemical modifications : starch, available amino-acids.

5.3. Extrusion variables

Extrusion-cooking is a process of difficult to control because of numerous parameters. Its mechanism are practically unknown.

5.4. Application to feeds for marine animals (appendix 1)

6. WET GRANULATION(or PELLETIZING) (fig. 10)

Diets are normally prepared by mixing the ingredients into a dough like mass (25 to 40 % moisture), extrusion of the dough through a mincer plate or similar forming device, at low pressure and temperature (30 – 60 c).

Ingredients are:

1. Fresh or refrigerated by-products and fish offals, blended with oilseed cakes or fish meals,extruded into moist strands and refrigerated until requried. This type of feed obliges to dispose of fresh meet and to be produced on the farm. It is suitable for sea-trout, turbot, sole.

2. Meals from meat, fish, oilseeds and cereals, mixed with solution of binders wheat gluten fig - 8% alginates associated with Ca++ to produce a firm water soluble gel. Products must be dried, or added with additives (2–4% propylen-glycol) to keep them from microorganism spoilage if stored and use as a wet from. Binders may be useful fools for preparation of experimental shrimp feeds, mainly at larval stages.

FIGURE 1

DIAGRAMME GENERAL/GENERAL FLOW-SHEET

FIGURE 2
Broyeur a Marteaux                           Hammermill

TABLEAU 1 / TABLE 1

FIGURE 4

MELANGEURS A CUVE FIXE ET MOBILE D'AGITATION MECHANICAL MIXERS

FIGURE 5 : THE DIE AND ROLLER ASSEMBLY ENSEMBLE FILIERE & ROULEAU DE PRESSE

FIGURE 6 : PRESSE A AGGLOMERER
PELLET MILL

FIGURE 7

TYPICAL FLOW DIAGRAM . EXEMPLE TYPIQUE DE DIAGRAMME

FIGURE 8 CRUMBLE ROLLS / CYLINDRES EMIETTEURS

TABLEAU 2 / TABLE 2

FIGURE 9a

COUPE EXTRUDEUR MONOVIS

VIEW OF A SINGLE - SCREW EXTRUDER

FIGURE 9b

COUPE EXTRUDEUR BIVIS
AVEC CONTRE-FILET EN POSITION TERMINALE

VIEW OF A TWIN SCREWS EXTRUDER (with
reverse flight screw in terminal position)

MELANGEUR et GRANULATEUR par voie humide
MIXER and WET PELLETIZER
FIGURE 10
SECHOIR en lit fluidisé
Fluidised bed DRYER

APPENDIX 1

PREPARATION BY EXTRUSION-COOKING OF IMPROVED FEEDS FOR MARINE ANIMALS

The feeding behaviours of marine animals are quite different and often badly known. Extrusion-cooking is a way to obtain unusal physical caracteristics of feeds measured by the rehydration, the water stability, the consistency and the floating or sinking ability.

Extrusion-cooking at moderate temperatures (80 – 90°C) and water additions (22 p. 100) of a gluten containing meal gives favourable water stability (76 – 89 p. 100) to shrimp feeds.

On the contrary, salmon and turbot feeds need expansion to increase water and/or oil absorption.

Expansion would be given by extrusion at fairly high temperature (180°C) of a meal added with pregelatinized starches. Rehydration capacity of the product is between 250–330 p. 100.

A good floatability is usual with such a feed, well adapted to salmon and trout behaviour, but the problem of the sinking ability of a turbot feed is difficult to solve.

Compared with other techniques, extrusion-cooking is expensive and has a tremendous effect on the vitamins of the feed, but it seems to be actually well adapted to produce foods for salmonids and flat fishes.

CARACTERISTIQUES PHYSIQUES RECHERCHEES DES ALIMENTS POUR ANIMAUX AQUATIQUES
(Requested physical properties of feeds for aquatic species)

(a) Salmo Gairdneri, Onchorynchus Kisutch, Salmo salar,
(b) Scophtalmis maximus,
(c) Dicentrarchus labrax, Sparus sp:, Chrysophrys sp:,
(d) Solea solea,
(e) Penaeus Japonicus.