Squid Meat and Its Processing
T O Y O - O TAKAHASHI
Tokai Regional Fisheries Research Laboratory, Fisheries Agency, Ministry of Agriculture a n d Forestry, Tsukishima, Chou-ku, Tokyo, Japan
I. Introduction 339 II. Basic Differences between Squid and Fish Meat 340
III. General Composition of Squid Meat 341 IV. Components of the Meat Extract 341
V. Proteins 342 A. Fibrous Protein Appearing in Water Extract 342
B. Actomyosin 343 C. Myosin and Nonmyosin Fractions 343
D. Tropomyosin 343 VI. Nutritive Value of the Meat 344
VII. Spoilage 344 VIII. Dried Meat 345
A. Sun-Dried Squid 345 B. Reversibility of Dried Squid Pretreated with Various Reagents . . 347
IX. Heat Processed Meat 348 A. Changes in Meat 348 B. Procedure 349 C. Odor 350 X. Stripping the Skin 350
References 350
I. Introduction
In few other countries of the world is the squid as m u c h utilized and appreciated in various forms of food as in J a p a n . Annual c a t c h of squid from t h e seas adjacent to J a p a n averaged 5 1 3 , 0 0 0 m e t r i c tons for the period 1 9 5 9 - 6 1 , forming about 8 % of total landings o f h e r domestic marine fisheries ( F A O , 1 9 6 2 ) . O f nine important species of squid com
mercially fished, the great majority of nearly 9 0 % is "surumeika" (Om
mastrephes sloani pacificus S t e e n s t r u p ) . I n this article, the term "squid"
refers to this species unless otherwise specified.
A b o u t one half the c a t c h is processed into dry products, and almost the same quantity is m a r k e t e d as r a w fish. T h e rest ( a b o u t 1 0 % ) of the landings is either refrigerated or processed into various types of food, such as salted, smoked, pastes, or "shiokara."
T h e latter is a fermented product m a d e of sliced squid m e a t fer- 339
3 4 0 TOYO-O TAKAHASHI
merited with salt and the liver. T h e intestines and stomach of skipjack are also processed in this form.
S q u i d liver extract is used as human food, b u t after condensation or dehydration serves as feed for livestock. D r y i n g oil of fairly fine quality is produced from the liver oil.
T h e viscera of squid are rich in amino acids a n d particularly rich in vitamins B2 and B12; it is a good material for domestic poultry feed
( K a w a t a et al, 1 9 5 5 ) . T a k a h a s h i ( 1 9 5 9 a , b ) found the contents of zinc, manganese, and copper in squid viscera to b e higher t h a n in fish and other molluscan meat.
T h e a p p e a r a n c e o f the m e a t and its peculiar taste and odor m a y not always b e encouraging. Nevertheless its flesh is e q u a l to fish in nutritive value and m a y even surpass it. Provided that ways o f processing and cooking the m e a t can b e found that suit regional habits, it m i g h t very well c o m e to b e highly appreciated b y m o r e of the world's population than is the case at present.
II. Basic Differences between Squid and Fish Meat
Since squid is taxonomically remote from fish, one would expect con
siderable differences, c h e m i c a l as well as histological, b e t w e e n these two groups of marine animals. R e c e n t work has b e e n successful in bringing to light a n u m b e r of b a s i c differences in this respect through histological and c h e m i c a l studies relative to processing.
T a n a k a ( 1 9 5 8 a ) studied histological changes microscopically and observed several such differences. A c c o r d i n g to his observations, t h e trunk of the squid is surrounded b y fibrous layers, e a c h 2 0 0 - 5 2 0 μ thick;
each fiber is very slender and about 5 μ in diameter. B e t w e e n every other layer is a narrower layer consisting of short fibers running perpendicular to the others. T h e flesh tissue of the arms is composed o f fibrous struc
tures m u c h more complicated than those of the trunk. T h i s explains w h y the trunk is not so easily torn off lengthwise as it is across, and w h y the arms are too tough to b e readily b i t t e n off.
T h e skin on the trunk comprises four layers of m e m b r a n e s . B e t w e e n the first and second outer layers are pigment cells that appear to contain melanin or similar pigments ( T a n i k a w a and Akiba, 1 9 5 2 ) ; t h e s e are sup
posed to b e responsible for the discoloration of squid m e a t products in one or another form. T h e fourth layer is m a d e up of connective tissues running longitudinally. T h e inner surface of t h e trunk is also covered with a thin m e m b r a n e . T h e skin of t h e arms has nearly t h e same struc
ture as that of the trunk.
Chemically, squid m e a t differs from fish in m a n y ways. T h e isoelectric point, obtained at maximum precipitation a n d minimum swelling of t h e
m e a t ( N o g u c h i et al, 1 9 5 1 ; O k a d a and T a d a , 1 9 5 3 ) was found to b e m o r e acid than that of fish meat. O k a d a and T a d a ( 1 9 5 3 ) reported that squid m e a t in salt solution swells m o r e than m e a t of horse m a c k e r e l (Trachurus japonicus). A c c o r d i n g to A m a n o ( 1 9 5 2 ) , the H g C l2 reaction cannot b e as readily used for measuring freshness of squid m e a t as of fish meat, since w a t e r extract of the m e a t reacts with H g C l2 regardless of the degree o f freshness. T h e characteristics s e e m to correlate with differ
ences in the proteins of the meats. T h e difference in the components of squid m e a t extract and of fish m e a t extract accounts for the peculiar taste of t h e meat.
III. General Composition of Squid Meat
I n ordinary fish, t h e ratio o f edible parts to t h e w h o l e is roughly 4 0 - 7 0 % . T h e ratio in t h e squid, on the other hand, is as l a r g e as 8 0 %
(trunk 5 0 % , arms 3 0 % ) with the liver forming 1 0 % of the whole. W a t e r content of squid m e a t ( 7 7 - 8 0 % ) is almost t h e same as t h a t o f white m e a t fish, such as c o d and flatfish; the oil content is about 1 - 1 . 5 % . T h e arms contain a larger amount of w a t e r than t h e trunk. T a n i k a w a et al.
( 1 9 5 6 a ) found that squid caught in summer contained m o r e w a t e r b u t less crude protein than that caught in autumn. K a w a t a and T a k a h a s h i ( 1 9 5 5 a ) reported that no seasonal variations occur in the ratio of weights of various parts of the body, e x c e p t t h e viscera, to the b o d y weight, and that considerable c h a n g e in t h e oil content of the liver occurs, b e i n g m a x i m u m in O c t o b e r and N o v e m b e r with m i n i m u m moisture and nitro
gen. T a k a h a s h i ( 1 9 6 0 ) showed that the w e i g h t of the viscera changes radically from N o v e m b e r to M a r c h . T h e viscera also show m a x i m u m fat content, with m i n i m u m moisture a n d total nitrogen, in N o v e m b e r .
IV. Components of the Meat Extract
F i s h with dark meat, such as skipjack, show a higher amount o f extractives t h a n white m e a t fish, such as flatfish ( S i m i d u , 1 9 4 8 ) . T h e extract from squid meat, 0 . 6 - 0 . 9 % on a nitrogen basis, is close to that of dark m e a t fish ( S i m i d u a n d T a k e d a , 1 9 5 2 ; Yoshimura et al, 1 9 5 2 , 1 9 5 3 ; E n d o et al, 1 9 5 4 ; K i t a b a y a s h i et al, 1 9 5 4 ; Könosu et al, 1 9 5 8 ) .
In examining t h e distribution of nitrogen extractives in various species of squid, Simidu and T a k e d a ( 1 9 5 2 ) found m o n o a m i n o nitrogen to b e abundant in squid so long as the m e a t tastes sweetish. E n d o et al ( 1 9 5 4 ) reported that tasty m e a t often contains m o r e glycine than less tasty meat. P a p e r chromatographic examinations w e r e carried out b y A m a n o and Bito ( 1 9 5 1 ) , I n o u e et al ( 1 9 5 3 ) and Yoshimura and S h i b a t a ( 1 9 5 3 ) to determine the amino acids present. Könosu et al ( 1 9 5 8 ) determined 17 amino acids microbiologically; these comprised a b o u t a fourth o f t h e
342
TOYO-O TAKAHASHInonprotein nitrogen
(776.3
m g . % ) in t h e meat. O f these acids, proline (67.3 m g . % ) is t h e most a b u n d a n t followed b y histidine, arginine, glycine, and alanine in that order.
O t h e r extractives present in substantial amount a r e trimethylamine oxide ( T M A O )
(0.42%,
K o j i m a and K u s a k a b e ,1956; 1.13%,
K ö n o s u et al,1958),
b e t a i n e(0.54%,
K o j i m a and K u s a k a b e ,1956),
a n d taurine(1.26 ^ο
in c o m m e r c i a l dried meat, Kojima a n d K u s a k a b e ,1955).
I n addition, octopine was d e t e c t e d in these extracts ( I s h i b a s h i , 1953; Kojima et al.,
1955),
guanine, carnitine, adenine, xanthine, and hypoxanthine (Ishibashi,1953).
T h e last one was also reported b y K o j i m a et al.,1956,
and trimethylamine b y Könosu et al., 1958. Squid muscle is furthermore a good source of organic phosphates ( S a i t o et at,
1960).
V. Proteins
F o r m a n y years detailed studies have b e e n c o n d u c t e d b y the staff of the T o k a i R e g i o n a l Fisheries R e s e a r c h L a b o r a t o r y in respect to specific properties o f proteins in squid meat. A significant discovery was m a d e b y O k a d a a n d T a d a (1954): streaming birefringence appears in a water extract of squid m e a t centrifuged at
4000
r.p.m. for30
minutes. W o r k b y Matsumoto, in the years1957-1959,
clarified, to some extent, the characteristic features of the proteins showing streaming birefringence in the w a t e r extract a n d those of actomyosin prepared from salt extract, and the relationship b e t w e e n these substances.A. FIBROUS PROTEIN APPEARING IN W A T E R EXTRACT
T h e streaming birefringence is attributable to the presence in the extract of a fibrous protein. T h i s c o m p o u n d has never b e e n extracted with w a t e r from any other animal muscle. T h e discovery m a d e b y O k a d a is therefore suggestive o f either the existence of a water-soluble fibrous protein that has remained unknown, or a peculiar dissolution of acto
myosin that takes p l a c e in the aqueous extracts. I n this connection Matsu
moto has established t h e following facts.
( i ) I n muscles of other animals, t h e amount o f water-extractable protein nearly equals the amount of the nonmyosin fraction ( t h e residue obtained after removing t h e myosin fraction precipitated in a 1:10 dilution of t h e salt-extracted p r o t e i n s ) . I n the c a s e of squid meat, how
ever, the water-extractable proteins, upon b e i n g repeatedly extracted, are
2.4r-4
times as a b u n d a n t as t h e amount of t h e nonmyosin fractions ( M i g i t a and Matsumoto,1954).
(it) I n K C l solution the water-extractable proteins from squid m e a t h a v e a minimum solubility at
0.05-0.1
μ, with the solubility curve resem-bling that o f t h e myosin A found b y Szent-Györgyi ( M i g i t a and Matsu- moto, 1 9 5 4 ) .
(Hi) W h e n t h e precipitate o b t a i n e d from t h e w a t e r extract with a small amount ( 0 . 0 3 - 2 μ ) o f K C l is suspended in water, it exhibits stream
ing birefringence ( M i g i t a and Matsumoto, 1 9 5 4 ) .
(iv) O n adding A T P ( a d e n o s i n e t r i p h o s p h a t e ) , this precipitate ( M - a c t o m y o s i n ) shows characteristic viscosity changes a c c o m p a n i e d b y liberation o f P 04 in the solution as w e l l as superprecipitation in t h e gel state, all characteristics w h i c h closely r e s e m b l e those o f actomyosin ( M a t s u m o t o , 1957; 1958a,d; 1 9 5 9 a , b ) .
O n the basis o f these findings M a t s u m o t o has suggested that at least a part o f t h e actomyosin in squid m e a t is water-soluble and makes an appearance in t h e water-extract solution ( M a t s u m o t o , 1 9 5 7 ) .
B . ACTOMYOSIN
I n comparing t h e actomyosin o f squid m e a t with that of carp, Matsu
moto ( 1 9 5 8 b ) pointed out t h e following important differences b e t w e e n them.
(i) Although Szent-Györgyi ( 1 9 4 7 ) was successful in precipitating r a b b i t actomyosin in a solution obtained b y prolonged extraction with a high p H medium, t h e m e t h o d is not a p p l i c a b l e to squid meat. Suitable conditions for preparing actomyosin from squid are short-time extraction
( 1 0 m i n u t e s ) at p H about 6.5 ( M a t s u m o t o , 1 9 5 8 b ) .
(it) W h e n one precipitates the myosin fraction in salt extract of squid m e a t b y t h e m e t h o d o f D y e r et al. ( 1 9 5 0 ) , t h e p H o f the dilution has a marked effect u p o n t h e amount o f t h e precipitate formed; the effect b e comes greater not only with decreasing freshness of t h e r a w material, b u t with prolonged storage o f the salt solution prior to dilution ( M i g i t a et al, 1 9 5 8 ) .
C . MYOSIN AND NONMYOSIN FRACTIONS
T a k i n g t h e a b o v e characteristics into consideration, Matsumoto ( 1 9 5 8 c ) determined t h e protein composition of squid meat. According to his results, t h e composition is almost t h e s a m e as that of white m e a t fish: the myosin fraction comprises a b o u t 7 7 - 8 5 % , t h e nonmyosin frac
tion 1 2 - 2 0 % , and t h e stroma protein 2 - 3 % o f t h e total protein content.
D . TROPOMYOSIN
C o m p a r i n g crystalline tropomyosin prepared from squid m e a t with that from r a b b i t and carp, Yoshimura ( 1 9 5 5 a ) reported appreciable differences b e t w e e n t h e m in r e g a r d to amino a c i d composition, electro- phoretic mobility, a n d sedimentation constants.
3 4 4 TOYO-O TAKAHASHI
According to Kitabayashi ( 1 9 5 6 ) , w h o determined the tropomyosin content in squid meat, t h e amount ( 3 6 mg. p e r 1 0 0 g. fresh material on a nitrogen b a s i s ) b y far exceeds that found in various fishes ( 4 - 7 m g . ) .
K u b o ( 1 9 6 1 ) isolated two kinds of crystalline protein from t h e tropo
myosin fraction in t h e squid mantle, and determined their solubility, amino acid composition, terminal residue, a n d molecular size and shape.
I t is concluded from the results that one is identical to Yoshimura's tropomyosin or tropomyosin B , while t h e other belongs to t h e water- insoluble or tropomyosin A group.
VI. Nutritive Value of the Meat
E v e n in J a p a n w h e r e squid m e a t is widely consumed, most people underestimate its nutritive value a n d regard it as almost indigestible. I t is true that squid meat, w h e n dried or boiled for long, b e c o m e s a little too hard to b e readily digested. Nevertheless, it offers as m a n y calories as white m e a t fish ( T a n i k a w a and Suno, 1 9 5 2 ) a n d its amino acid com
position is c o m p a r a b l e to that of fish ( S u g i m u r a et al., 1 9 5 4 ; Konosu et al., 1 9 5 6 ) . T h u s , squid m e a t m a y b e considered nutritionally a perfect source of protein.
In attempting to c o m p a r e the digestibility o f squid m e a t with that of the flatfish Limanda herzensteini, T a n i k a w a and Suno ( 1 9 5 2 ) tested vari
ous forms of the fresh, cooked, and dried meats in the presence of pepsin.
However, the results showed little or no difference in digestibility b e t w e e n the pairs of c o m p a r a b l e samples. According to Yoshimura and Nara ( 1 9 5 4 ) , w h o fed animals sample meats, the digestion and absorp
tion rates for dried squid w e r e a little less t h a n those for beef.
K a w a t a et al. ( 1 9 5 5 ) found that squid m e a t prepared from the m e a t stripped of skin b y autolysis during pretreatment is b y far superior to sardine and herring meats, though inferior to that of codfish.
VII. Spoilage
F o r some time after capture, the dorsal surface of the squid shows a dark brown color due to certain pigment cells. W i t h subsequent de
crease in freshness, these cells contract and the m e a t turns white. W h e n t h e m e a t shows an alkaline reaction, the cells d e c o m p o s e and the pig
m e n t particles redden the meat. T h u s the freshness of t h e squid can b e roughly estimated b y the c h a n g e in skin color with progressive deterio
ration.
T h e first stage of putrefaction in squid as well as fish ( M o t o h i r o and T a n i k a w a , 1 9 5 2 ) should b e set at 3 0 mg. volatile basic nitrogen ( V B N ) p e r 1 0 0 g. meat. O n t h e basis of extensive observations, Shimidu et al.
( 1 9 5 5 ) reported the decomposition to p r o c e e d as follows: as soon as the
squid begins to decompose, t h e amount of V B N increases rapidly, in part from T M A O and in part from monoamino acids. T h e y found histamine and acetylcholine to b e hardly detectable in putrid products of the meat.
T a n i k a w a et al. ( 1 9 5 4 ) observed mustiness in raw squid meat, which is a sign of spoilage. I t occurs at high humidity ( 8 5 % or m o r e ) w h e n the V B N reaches 3 0 m g . % and t h e p H is a b o v e 6.5. T h e pigment cells in t h e epidermis then b r e a k down, and the w h o l e surface of t h e m e a t turns red.
Squid caught in summer deteriorate faster than those captured in autumn. T a n i k a w a et al. ( 1 9 5 6 a ) attribute this to differences in t h e bio
chemical factors controlling the freshness and the spoilage pattern in these two seasons, w h i c h are in turn due to differences in muscle com
position, content of b o u n d water, a n d optimum p H value for autolytic enzymes.
VIII. Dried Meat
As stated earlier, about one half t h e squid landed in J a p a n a r e dried for domestic consumption and for export as well. F o r t h e J a p a n e s e table, the dried squid is either simply grilled or softened in water, with or with
out t h e aid of chemicals, and seasoned. O t h e r varieties of dried squid processed with several seasonings a r e also available on t h e food market.
A. S U N - D R I E D SQUID
Almost all squid is dried b y exposure to t h e sun ( F u k u d a and Ishida, 1 9 5 4 ) . T h e trunk is first cut open to remove the entrails; t h e eyeballs are also removed, b u t not the arms. After washing, t h e material is left outdoors until t h e w a t e r content drops to 1 8 - 2 2 % , a c o m m o n value in commercial products. I n summer it m a y take 3 days or m o r e for t h e squids to attain this level of moisture content. D u r i n g drying t h e shape of the half-wet m e a t is b y and large retained.
1. Special Features
Several studies have b e e n m a d e on t h e relationship b e t w e e n the degree of freshness of the raw material and t h e quality of the final prod
ucts. T a n i k a w a et al. ( 1 9 5 6 b ) concluded from extensive studies that drying should start as soon as possible after capture and while the V B N level in the b o d y is less than 5 - 1 0 m g . % and the p H b e l o w 5.4; only third-grade products are obtained from squid left at 1 5 - 2 0 ° C . overnight after capture, in w h i c h the V B N level is around 2 0 - 3 0 m g . % with a p H of 5.8.
U n d e r adverse w e a t h e r conditions with high temperature and humid
ity, and particularly rainy days, t h e squid, no matter h o w fresh t h e y are,
3 4 6 TOYO-O TAKAHASHI
rapidly lose their freshness during the drying w h i c h n o w proceeds very slowly. Furthermore, the rain leaches water-soluble protein from t h e meat, resulting in a finished product o f poor a p p e a r a n c e and undesirable odor ( s e e b e l o w ) . Serious rain damage m a y b e partly averted b y dipping the cut up material, prior to drying, in one of t h e following solutions: ( 1 ) a c e t i c acid ( O s h i m a and Satodate, 1 9 3 7 ) , ( 2 ) nitrofura- zone ( I g a r a s h i and T a k e d a , 1 9 5 4 ) , or ( 3 ) dehydroacetic a c i d ( T a n i k a w a et al., 1 9 5 6 c ) . T h e s e measures obviously arrest microbial spoilage. F o r prolonged rain the sprayed products m a y b e protected b y a tent ( T a n i kawa et al, 1 9 5 6 c ) .
2. Chemical Components of Dried Squid
T h e quality of dried squid is graded b y organoleptic inspection and analysis of water content. Yoshimura ( 1 9 5 5 b ) noted an obvious correla
tion b e t w e e n the amount of trimethylamine oxide in dried m e a t and the inspected quality, since t h e higher the quality the greater t h e oxide content. T h e shape o f the individual pigment cells in the skin of the dried m e a t m a y b e used as another key to determining quality of dried squids. T h e pigment cells in top-grade products w e r e all elliptical, whereas the periphery o f t h e ellipse erodes with increasing degree of spoilage until finally t h e ellipse is wholly deformed ( T a c h i k i , 1 9 5 1 ) .
As was mentioned, rain-spoilt dried squid has an offensive odor. This is due to the formation of organic acids such as formic, acetic, phenylace- tic, and isobutyric and to bases such as ammonia, T M A , piperidine, indole, and certain amines ( Y a m a n i s h i et al., 1956a, 1 9 5 8 ) .
3. Surface Blotches
W h i t e powder blotches m a y cover t h e surface of dried squid. T h i s is usually taken for mold, and creates a misconception in the m i n d of the public. I n effect, however, this powder is nothing but a mixture of betaine, taurine, aspartic and glutamic acids, and certain other amino acids ( T a n i k a w a et al., 1 9 5 3 ) . T h e s e substances are liable to form on the m e a t in a b u n d a n c e if the drying process is suspended for a time and the half-dried m e a t is left under conditions of low temperature and high humidity.
4. Softening Procedures
Several efforts h a v e b e e n m a d e to soften dried squid m e a t upon re- constitution in water. Oshima et al. ( 1 9 2 6 ) reported that sodium hy
droxide is most effective, followed b y sodium carbonate. Sodium hydrox
ide dissolves pigment cells of the skin. T h i s reddens t h e meat. T o avert such an undesirable effect, a solution of .0.2 Ν sodium hydroxide is
mixed with a 0 . 5 % lime in t h e ratio 1:2. Another effective m e d i u m is 2 % solution of sodium b i c a r b o n a t e ( O k u d a et al., 1 9 5 4 ) . T a k a h a s h i and T a k e i ( 1 9 5 6 ) tested various other compounds and c o n c l u d e d that solu
tions of 2 % lactic acid, 1 % tartaric acid, or 1 % a c e t i c a c i d are most suitable.
I t is nonetheless most desirable to prepare dried squid in such a w a y that simple reconstitution in w a t e r renders a fully a c c e p t a b l e soft prod
uct. I n general, the degree of dryness does not in itself determine the suitability for reconstitution ( T a k a h a s h i and T a k e i , 1 9 5 6 ) . S q u i d w h i c h has b e e n rapidly dried within a couple days absorbs w a t e r m o r e readily than pieces submitted to a protracted period of drying. W h e n dried in the temperature r a n g e 5 0 - 5 9 ° F . ( 1 0 - 1 5 ° C ) , t h e c a p a c i t y to take up w a t e r is far greater than w h e n dried at 7 2 - 8 4 ° F . ( 2 2 - 2 9 ° C ) . W h e n dried products are stored at 5 ° F . ( — 1 5 ° C . ) for 3 weeks, t h e y retain t h e c a p a c i t y to b e reconstituted readily; holding t h e m for a b r i e f period at 3 7 - 4 3 ° F . ( 3 - 6 ° C . ) or higher destroys this valuable property.
B . REVERSIBILITY OF D R I E D SQUID PRETREATED WITH VARIOUS REAGENTS S q u i d m a y b e pretreated before drying in solutions of anions with high hydrating power, such as sodium citrate and dibasic sodium phos
phate; this yields a product with a rather high c a p a c i t y to b e reconstituted in water. T h i s t r e a t m e n t is given over a period of 8 - 2 4 hours at low tem
perature. A solution of 0 . 4 - 1 . 0 % is employed. M e a t treated accordingly remains close to t h e original raw m e a t in texture, after reconstitution.
Salts of ions with low hydrating p o w e r such as iodide, thiocyanate, etc. are not efficient. T h e y t e n d to r e d u c e t h e water-absorbing capacity.
A few active compounds are sodium lauryl sulfate, sodium lauryl sulfonate, a n d sodium pyrophosphate. T h e first two b e l o n g to a group of reagents c a p a b l e o f b r e a k i n g the cross-linkages of the protein mole
cule. O t h e r compounds w i t h similar characteristics failed to give a positive effect, namely, urea, sodium ß-naphthalene sulfonate, and some forms o f alcohol. C h e m i c a l s that counteract t h e precipitation of pro
teins, such as various types o f sugar a n d sodium caprinate, w e r e not effective; nor was sodium hydroxide, although it m a d e t h e protein swell, nor w e r e t h e salts o f organic acids related to sodium citrate, such as sodium malate.
I t c a n therefore b e safely c o n c l u d e d that it is feasible to restore t h e initial softness o f squid m e a t b y t r e a t m e n t with dibasic sodium phosphate or sodium citrate. I n this case, however, t h e cut pieces must b e sub
j e c t e d to immersion for a greater length o f time, causing loss of protein in the finished product. F r o m t h e c o m m e r c i a l point of view such a method is undesirable. A c c o r d i n g to T a k a h a s h i a n d T a k e i ( 1 9 5 6 ) , such a dis-
3 4 8 TOYO-O TAKAHASHI
advantage c a n b e effectively overcome b y immersing the material in higher concentrations for a briefer period of t i m e — 5 minutes in 1 0 % solution o f dibasic sodium phosphate or in 2 - 5 % soda.
T h e water absorbed b y dried squid showing a high degree of reversi
bility upon reconstitution is less available for evaporation and less express
ible than the water taken up b y samples of dried squid less prone to recon
stitute well ( T a k a h a s h i and Takei, 1 9 5 6 ) . A negative correlation has b e e n noted b e t w e e n w a t e r content of dried m e a t reverted in water and hydro- thermal shrinkage temperature of the meat. T h e s e findings suggest that the inter- or intra-linkages in protein molecules or larger aggregates are related to the water-reversibility of the dried meat.
IX. Heat Processed Meat
A. CHANGES IN M E A T
W h e n fresh squid m e a t is overheated, it contracts and hardens and b e c o m e s almost u n a c c e p t a b l e as food. W i t h a view to obtaining means of alleviating such toughness of the boiled meat, T a k a h a s h i and T a k e i ( 1 9 5 6 ) studied t h e changes in physical properties of squid m e a t during heating up to boiling temperatures. T a k a h a s h i ( 1 9 6 2 ) continued this work and found that boiling in urea ( 1 0 Μ ) or alkaline solution ( p H 1 0 ) decreased t h e toughness.
W h e n trunk m e a t is h e a t e d in w a t e r without stripping the skin off either side, it shows n o t i c e a b l e contraction (lengthwise, 6 0 % of the initial length; b r e a d t h wise, 7 5 % ) . O n boiling completely stripped meat, the lengthwise contraction can b e r e d u c e d to some extent ( T a n a k a , 1 9 5 8 b ) . T h e longitudinal hydrothermal shrinkage occurring in non- stripped m e a t is b e l i e v e d to b e due to the collagen in the skin, t h e lateral shrinkage to t h e muscle fibers in the meat. M i c r o s c o p i c examina
tions b y T a n a k a ( 1 9 5 8 b ) revealed that w h e n cooked, t h e squid m u s c l e fibers bend, thus reducing e a c h c o m p o n e n t fiber a little in diameter.
W h e n very fresh m e a t is c o o k e d at a temperature of a b o u t 1 0 0 ° C , transverse contractions o c c u r b u t little; staler meat, cold-stored for a day or two after death, shows hydrothermal shrinkage of about 7 5 % . T h e shrinkage temperature varies with the freshness of the squid; in fresh m e a t contraction does not occur until the cooking temperature reaches 6 5 - 7 0 ° C , while stale m e a t starts to shrink even at 2 0 ° C . After b o t h freezing a n d drying, shrinkage starts at a higher temperature than is normally the case.
As the cooking temperature rises to 5 0 - 6 0 ° C , squid m e a t begins to lose weight as well as w a t e r content; at 1 0 0 ° C . the m e a t has a b o u t one half its initial weight and t h e w a t e r content has b e e n r e d u c e d about 1 5 % .
A strip of squid m e a t cut laterally and held at zero tension shows t h e same peculiar p h e n o m e n o n as keratin fibers, namely, t h e sudden appear
a n c e of contracting forces at around 5 0 ° C . ( L u n d g r e n , 1 9 5 4 ) . O n t h e other hand, if t h e m e a t strip is enlongated 1 0 % and then heated, t h e stretching force required first decreases with the rise o f temperature, then remains constant at 5 0 - 6 0 ° C , and abruptly mounts at 6 5 - 6 7 ° C . At still higher temperatures, the m e a t reaches a condition in w h i c h t h e stretching force is a straight line function of temperature, with a positive slope. T h e s e forces m a y b e altered b y the addition of sodium ß-naphtha- lene sulfonate or urea to the system. I n t h e case of t h e former t h e slope of the curve remains unchanged, b u t with urea t h e slope o f t h e curve is changed.
I n boiling water, trunk m e a t completely loses its longitudinal break
ing strength ( F ) . Transversely, however, F b e c o m e s greater t h a n in fresh meat. A possible inference from t h e facts is that, lengthwise, F de
pends mainly on collagen fibers in the skin and that, crosswise, muscle fibers are dominant. Numerous studies h a v e b e e n m a d e on t h e effect of different compounds on these basic stretch reactions. T h e s e have re
sulted in recommendations for alleviating t h e toughness of boiled squid meat, namely, t h e use of urea, alkali, diabasic sodium phosphate, or pyrophosphate. M e r e l y heating in a sodium chloride solution m a y very well b e equally effective.
B . PROCEDURE
Most squid is c a n n e d in J a p a n . T h e cephalopoditic part of t h e squid to w h i c h the visceral mass is a t t a c h e d is removed from the mantle cavity.
T h e visceral mass is cut off from t h e cephalopoditic part. T h e mantles and cephalopoditic parts are w a s h e d separately. After washing, t h e y are h e a t e d at about 4 5 - 5 0 ° C . in a salt water ( B e . 1 0 ° ) ( 4 0 ° salinometer) tank for 15 minutes; the skin of t h e parts then peels off easily. T h e pealed meats are h e a t e d in boiling salt solution ( B e . 3 ° ) ( 1 2 ° salinom
e t e r ) for 1 0 minutes. After boiling, the eyes are r e m o v e d from t h e cephalic part. T h e meats are carefully washed. Sections of various parts of the b o d y are put in the c a n in certain proportions. T h e brine used is 4 B e . for the m i n c e d style. G l u t a m a t e is generally added. After precook
ing as above, t h e p e e l e d meats of the m a n t l e cavity and cephalopoditic part are m i n c e d through a c h o p p e r to y$-inch m e s h ) . T h e m i n c e d m e a t is p a c k e d in 3-lb. cans and hot brine.
Seasoned squid m e a t is popular in J a p a n and K o r e a . T h e seasoning solution is prepared b y mixing 2 kg. "miso" ( s o y p a s t e ) , 2.5 kg. sugar, 1 kg. salt, 2 5 liters "shoyu" ( s o y b e a n s a u c e ) , and 1 0 liters water. T h e seasoning solution is put in e a c h c a n in measured quantities.
3 5 0 TOYO-O TAKAHASHI C . ODOR
I n regard to the objectionable odor of boiled squid meat, Yamanishi et al. ( 1 9 5 5 , 1 9 5 6 b ) proved the major c h e m i c a l constituent to b e a sul
fur-containing amine with a piperidine nucleus, w h i c h emanates from proteinaceous fractions of the meat. T o suppress the odor, they recom
m e n d cooking the m e a t with onions.
X. Stripping the Skin
T h e skin of squid consists of four layers with pigment cells distributed b e t w e e n the first and second. Since the melanin-like pigments contained in these cells are apt to discolor the material in t h e course of processing, the skin is often stripped off at the beginning to obviate such damage.
T h o u g h the skin m a y b e stripped with relative ease as far as the second or third layer, manual stripping is burdensome in a large n u m b e r of animals. W h e n the m e a t is heated, interstices are formed b e t w e e n the second and third layers and b e t w e e n the third and fourth layers of the skin. I n this w a y it b e c o m e s more readily r e m o v a b l e ( T a n a k a , 1 9 5 8 b ) . T a k i n g advantage of this phenomenon, the most usual t e c h n i q u e ( M a t - suura and T a k e d a , 1 9 5 2 ) is to stir the squid in w a r m water at approxi
mately 5 0 ° C . for a length of time. D u e to this stirring the squid rub against e a c h other and the skin is stripped off b y itself. O n e deficiency of the method, however, is a c h a n g e induced thermally in t h e myosin fraction even at this low temperature. T h i s is particularly detrimental when the natural properties of the m e a t are necessary in the squid sub
sequently used in the manufacture of fish jelly. T o k e e p the denatura- tion of the myosin fraction at a minimum, O k a d a ( 1 9 5 3 ) suggested blanching the material for only 2 - 5 seconds in w a t e r h e a t e d to 8 0 - 1 0 0 ° C.
This m e t h o d is fairly effective, b u t again it is not free of some obvious disadvantages in the practical handling of the bulk of activities. In addi
tion, a sodium acetate b a t h ( I g a r a s h i et ah, 1 9 5 3 ) and a lactic acid bath ( T a n i k a w a et al., 1 9 5 5 ) have b e e n suggested as effective means of facilitating removal of the skin and still retaining t h e myosin charac
teristics.
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