748 Nippon Shokuhin Kogyo Gakkaishi Vol.36, No.9, 748•`753 (1989) •k Article•l (42)

Texturization of Surimi using a Twin-Screw Extruder

Kiyotaka AOKI*, Fusao HARA*, Manabu OHMICHI*,

Noboru NAKATANI* and Hideaki HOSAKA*

* Ahjikan Co., Ltd. Laboratory, 5-5-24,Shokosenta Nishi- k u, Hiroshima 733

A product fibrously texturized was obtained from surimi by extrusion cooking with a

twin-screw extruder. Raw material called surimi (fish meat sol), in Japan, was

preconditioned to lower the moisture content down to 1.5•`2.0 (dry base). Conditions of the

extruder in this experiment were as follows. The range of the screw speed and the barrel

temperature were 150 rpm and 160•`180•Ž, respectively. The rate of the feeder was 30kg/h.

The temperature of the die was kept around 10•Ž by using tap water. Properties of the

product obtained were examined with a microscope and a Rheometer as well as by visual

observations. The product had a clear fibrous structure, whose direction was directly related

to the extruding direction.

Studies on texturization of plant proteins

separated from soy beans have been carried

out by many researchers since the 1960s1)～4).

However, the texturization of marine products

such as surimi (fish meat sol) has never been

studied, to the best of the authors' knowledge,

because it was assumed that the texturization

of them was almost impossible by means of a

twin-screw extruder.

The heat energy of the plastic extrusion is

carried out heating elements fixed around a

barrel and by frictional heat produced by the

shearing force of the screw5). Both energies

are supposed to be almost equal. SEK6),

HAYAKAWA7) and HASAKA8) have proven that

frictional heat produced by the shear force of

the extruder had also a powerful influence on

the texturization plant proteins. YACU9)

found that the frictional heat converted from

mechanical energies of the extruder was

proportiona1 to that of the geometrical view

factor and of the apparent viscosity. He

showed that it also was in proportion to the

square of the screw speed. LEVIN10) found

that there was an expontial relation between

the apparent viscosity and moisture content.

The texturization marine products such as

surmi could not be performed satisfactory at

the initial stage of this study. The main

reason seemed to be that frictional heat

from shear force was reduce due to the high

moisture content of surimi. In the case of soy

beans, the tensile strength of the product

texturized using an extruder showed a maxi-

mum value at between 0.7 to 1.0 (kg-water/kg-

dry material; dry base) moisture content.

Therefore, the moisture of surimi was de-

hydrated around 1.5 or 2.0 (dry base) to

approximate the desired level of moisture

content for extrusion cooking.

In the case of dehydrated surimi (1.5～

2.0, dry base) treated using the twin-screw

extruder, the product obtained showed fibrous

textures somewhat like those of crabs or squid.

Although proteins of any fish and animal meat

usually coagulate due to heating, we found

that a very interesting phenomenon in this

experiment. Once surimi was cooked and

melted in the barre1, it could be rearranged

into another material with a fibrous texture.

Material and Methods

1. Material

Frozen surimi preparared from Alaska pollack,

a special grade, was used. Usually surimi was

prepared in the following way. First, the

(43) AOKI et al. : Texturization of S urimi using an Extruder 749

bones were removed from the Alaska pollack,

together with the skin and the other internal

organs. Next, the meat was minced and then

washed with water. Standard surimi contains

75.1% (w/w) of moisture, 16.6% (w/w, N•~

6.25) of protein, 7.7% (w/w) of carbohydrates

and 0.6% (w/w) of ash.2

. Extruder

The twin-screw extruder employted was a

type of the intermeshing co-rotaing model

(Kowa Kogyo CO., Ltd., Type KEI 45-25).

Each screw was 45 mm_??_and L/D was 25. The

elements of the cut flight screw and kneading

screw were placed at points of 1070 and 1135

mm from the feed port, respectively. The die

had a jacket-type cooling system. The opening

of the die was doughnut in shape and its

external diameter was 35mm and internal

diameter 29mm.

3. Extrusion cooking

Surimi amounting to 20kg was mixed and

kneaded with 0.5kg of salt and 0.8kg of starch

using a silent cutter. The kneaded surimi was

gelated using a twin-screw extruder. This

operation was carried out at a feed rate of

30kg/h, a screw of 100rpm and a barrel

temperature of 150•Ž. The gelated surimi was

then divided into four groups, which were dried

to 1.5, 1.7, 1.9 and 2.0 (dry base) using a fan,

respectively. Each dried matter was crushed

into smaller sizes like soy bean using the silent

cutter. The crushed surimi was fed into the

extruder through a screw feeder (30kg/h) . The

screw speed was 150rpm. The barrel tempera-

ture was varied from 160 to 180•Ž. The die

was kept around 10•Ž by running tap water .

4. Measurement of barrel and die tem-

perature

Thermocouples were used as the temperature

measuring device. They were inserted through

holes in the side of the barrel and die head .

The position of thermocouples of Fig .3 b were

600mm (A) , 800mm (B), 960mm (C), 1050

mm (D) and 1160mm (E) distant from the

feed port.

5. Measurement of physical properties of

products

Two kinds of samples with a rectangular

shape parallel and crosswise to the extrusion

direction were prepared from the ribbon-like

products (Fig.1). One of them, sample A,

was used for measuring the tear strength of

the vertical direction along the extruding flow.

Another, sample B, was used for the parallel

direction. The size of each sample is 20 (L)•~

10 (W)•~3 (T) mm. The tear strength of the

longer sides of each sample was determined by

a Rheometer (Fudoh Kogyo CO., Ltd., type

NRM-2002 J) with a 0.3mm piano wire. The

tear strength value of each sample was the

average of ten pieces measured.

6. Microscopic observation

The surface of the two pieces of the sample

was thinly peeled in the parallel and vertical

direction to the extruding flow. One thinly

peeled piece was examined with a stereo

microscope (Olympus Optical CO., Ltd., type

SZH-131). Another was examined with a

acanning electron microscope (Hitachi CO.,

Ltd., type SEM-405). The procedure of pre-

paration for the scanning electron microscope

was as follows: first, the peeled flake was

adhered onto a board of aluminum with silver

paste. Next, it was coated with gold (about

300 •ð in thickness) by means of a spatter ion

Fig.1 Measurement of tear strength

Sample A was used for measuring strength

of vertical direction along extruding flow .Sample B was used for measuring strength

of parallel direction.

750 日本食品工業学会誌 第36巻 第9号 1989年9月 (44)

coating.

Results and Discussion

1. Die In case of high moisture content materials

such as surimi treated using an extruder, anirregular extrusion, called flash, often occur-red. The flashed matter was a mixture ofvapour from raw materials and things cooked

or partially texturized. The low viscosity ofraw materials seemed to be the cause of theflash, by reason that the low viscosity couldnot produce sufficient frictional heat in thebarrel. In order to prevent the flash, a coolingsystem of the die was developed. This systemhelped the die to retain a much higher pressureand to give a stronger shear force to thematerial. In this way, the stability of extru-sion cooking was considerably improved.

2. Adjustment of moisture content Even the extruder with the cooling system

could not perfectly texturize surimi in a steadystate, with a flash sometimes occurred. Inorder to improve the stability of extrusion,surimi was dehydrated to increase the visco-sity. As surimi had usually 3.0 (dry base) ofthe moisture content, it was dehydrated downto 1.5 or 2.0 (dry base) by preheating anddrying. The stable operation of extrusioncooking was easily obtained by using de-hydrated surimi. The texturized ribbon-like

product was produced through the die with thecooling system. In case of products being tornusing hands along the extruding direction, the

products showed a fibrous structure shown inFig.2. Figs.3a and 3b show the variation of

tmperature at typical points of the extruder

during operation. Surimi kept at the labora-

Fig. 3a Variation of temperature at each

of thermocouples

Temperature of thermocouples

Set temperature

Fig. 2 Texturized products were torn

along the extruding flow with hands

Fig.3b Variation of temperature at

position of thermocouples

•Z

: Thermocouple A

•ž

: Thermocouple B

_??_

: Thermocouple C

•œ: The rmocouple D

•Ÿ: Thermocouple E

( 45 ) AOKI et al. : Texturization of Surimi using an Extruder 751

tory was transfered into the extruder through

the screw feeder and heated to 170•Ž using the

heat bands of the barrel and by frictional heat

produced in the barrel. Subsequently, the

heated surimi is likely to be melted just before

the die inlet. To confirm the fibrous structures

and its alignment, each tear strength in the

parallel and vertical direction to the extruding

flow was determined by the Rheometer. Fig.4

shows tear strengths of products made from

raw materials containing a moisture from 1.5

to 2.0 (dry base). Tear strength in the vertical

direction was almost the inverse of the

moisture content of the raw materials; while

in the parallel direction, the tear strength

showed little relationship to the moisture

content. The tear strength in the vertical

direction was much greater than that in the

parallel direction. The fiber direction of the

texturized product seemed to be directly related

to the extruding direction.

3. Barrel temperature

The barrel temperature was varied from 160

to 180•Ž. The heat from the barrel had

influence on the alignment and orientation of

the texturized products. Fig.5 shows that the

tear strength of the vertical direction of the

product was clearly dependent upon the barrel

temperature. According to the rise of the

barrel temperature, the tear strength of the

parallel direction was scarcely varied. So the

orientation of the texturized products was

lowered under 165•Ž, but rapidly increased to

over 165•Ž. The barrel temperature must be

set lower than 175•Ž, because the product

begins to turn brown at temperatures over

175•Ž.

4. Observation with a stereo and electron

microscope

Fig.6 shows the extruded products observed

by a stereo microscope. It shows a pattern

like grained wood. On the other hand, the

surface of the kamaboko made from surimi

according to the traditional way in Japan had

Fig.5 Effect of barrel temperature on tear

strength of the extruded products

•œ: Vertical direction

•Ÿ: Parallel direction

Fig.4 Tear strength of extruded products

from raw materials containing the

moisture from 1.5 to 2.0 (dry base)•Z

: Vertical direction•ž

: Parallel direction

Fig .6 Stereo micrograph of the texturized

products (•~30)

752 日本食品工業学会誌 第36巻 第9号 1989年9月 (46)

almost an uniform structure, and was not

fibrous. A characteristic of the extruded

products had a fibrous structure in the parallel

and vertical direction to the extruding flow. A

distinctive feature of the extruded product was

the multilayer structure composed of thin

layers (about 10ƒÊm in the thickness). This is

the reason why it could be easily peeled off in

extremely thin layers. Thin layers peeled

consisted of numerous fine fibers which form

two dimensional structures. The multilayer

structures are always invisible like chemical

film synthesized from plastic. The thin layer

structure is also observed with a scanning

electron microscope. Figs.7 and 8 clearly

show that the extruded product has fibrous

structures with only one direction which is the

same one as that of the extruding flow.

Fig. 7 Scanning electron micrograph of

the texturized products (•~1000)

(cutting surface of parallel direc-

tion)

Conclusion

During the course of extrusion of viscousfluid like surimi, back flow often occurred dueto the low viscosity of the material.Therefore, adjustment of the moisture contentof surimi was carried out to get the desiredviscosity by preheating and drying. Preheatingcontributed to coagulate proteins as well as toremoval of water in the raw materials. Bothdehydration and coagulation gave adequatefrictional resistance to surimi and the barrel.Surimi preheated can be successfully texturizedusing the twin-srew extruder.

The fibrous texturized products suggest that

proteins of the surimi should be rearrangedthrough melting conditions. The extrusion inthe steady state was suddenly stopped toobserve conditions inside of the barrel by

pulling out the two screws. The observationof the products adhered to the screw confirmedthat the texturization of the surimi alreadyhad started at the outlet of the screw before itwas transported to the die as shown in Fig.9.This fact seemed to indicate that surimi hadcompletely melted in the barrel. Namely, inthe case of the extrusion cooking of surimi, itis very important to completely melt the rawmaterials. The necessary heat energy formelting them was carried out by the heaters

Fig.8 s canning electron micrograph of

the surface of the texturized pro-

ducts (•~50)

Fig.9 Outlet of the screws with the

texturized products

(47)AOKI et al.: Texturization of Surimi using an Extruder753

surrounding the barrel and the frictional heat

derived from mechanical energies like shear

force and kneading.

The shape of the die also has an important

influence on the adequate pressure and filling

capacity of the outlet of the barrel. A well-

designed die must gradually increase internal

pressure in the barrel as raw materials

approach the die. Therefore, it is necessary to

design a die with an efficient opening ratio.

The texture of the pｒoduct made from surimi

was similar to the tissue of lobsters, crabs and

squid. We hope that the product obtained

from surimi using the twin-screw extruder will

be of some help to food industry.

Achnowledgments: The authors are gratefulto Mr. Hidee MATSUEDA, Kowa Kogyo,

Ohsaka, for his teehnical advice about the

extruder and Associate Prof. Kiyotaka SATOHat Hiroshima Univ. for his assistance regarding

scanning electron micrograph analysis.

References

1) van ZUILICHEN, D.J., ALBLAS, B.,REINDERS, P.M. and STOLP, W.: "Thermal

processing and quality of foods" ZeuthenP.et al(Ed.)(Elsevier ApPlied SciencePublishers, Essex, England), p.33 (1983).

2) KITABATAKE, N., MEGARD, D. and CHEFTEL,

J.C.: J. Food Sci., 50, 1260 (1985).3) HARPER, J. M.: Food Technol., 40 (3), 70

(1986).4) NoGUCHl, A, and ISODE, S.: Nippon Shoku-

hin Kbgyo Gakkaishi, 33, 798 (1986).5) MARTELLI F.G.: "Twin-screw extruders:

A basie understanding" (Van NostrandReinhold Co., New York, N.Y.), (1983).

6) SEK, J.P. and JANSEN, L.P.B.M.: "Ther-

mal processing and quality of foods"Zeuthen P, et al. (Ed.) (Elsevier AppliedScience Publishers, Essex, England), p.272 (1983).

7) HAYAKAWA, I.: Chemical Engineering, 30(8), 30 (1985).

8) HOSAKA, H.: J. the Japanese Society ofFood Engineering, 6(3), 152 (1986).

9) YACU, W.A.: "Thermal processing and

quality of foods"Zeuthen P.et. al. (Ed.)(Elsevier Applied Science Publishers,Essex, England), p.62 (1983).

10) LEVIN, L., SYMES, S. and WEIMER, J.: J.F.Proc.Eng., 8 (2), 97 (1986).

(Received. Nov.9, 1988)

二軸型エクス トルーダーによる魚 肉す り身の組織化

青木清隆*・ 原 房雄*･大 道 学*

中谷 登*･保 坂 秀明*

*(株)あ じかん 研究所

(〒733 広 島市西区商工セ ンター5丁 目5-24)

二軸型エ クス トルーダーで魚 肉す り身 を処理 し,繊 維

状の組織化製 品が得 られた.魚 肉す り身 のような高水分

系の水産加工 品は,従 来,加 熱す ると熱変性 して,エ ク

ス トルージョンク ッキ ングでは溶 融 しないと思われて い

たが,低 水 分に水分調整す ることによ 参溶融 して再構成

し,繊 維状 の組織化製品 をつ くることに成功 した.

エクス トル ダーの操作条件は,予 備操作 により原料す

り身の含有 率を1.5～2.0(dry base)と して供給量30

kg/h,ス ク リュー回転数150rpm,バ レル温度160～

180℃ で,ダ イを冷却 して得な った.得 られた製品 は可

視的 にも明 らかに繊維性の組織性状が認 め られ,物 性を

測定す ると押 し出 し方 向に強 い方両性があ った.ま た,

顕微鏡での観察で も繊維状 の組織が確認 された.