T u n a has b e e n c a n n e d in c o m m e r c i a l quantities in the U n i t e d States since 1 9 0 3 . T h e tremendous growth w h i c h the tuna industry has under
gone since then has b e e n due to the increasing popularity of c a n n e d tuna, since tuna in any other form, such as fresh or frozen tuna, is used only in negligible amounts b y t h e consuming U . S. public. T h e solid-pack style of c a n n e d tuna has dominated the market during most of these years. T h i s p a c k was, to b e g i n with, m a d e mostly from a l b a c o r e tuna.
T h e disappearance for several years of a l b a c o r e from the tuna-fishing areas along the Pacific C o a s t of t h e U n i t e d States, forced the tuna canners to look elsewhere for tuna, and to b a s e their rapidly expanding production on yellowfin tuna, bluefin tuna, and other species. Skipjack seems at t h e m o m e n t to b e replacing the yellowfin tuna as t h e largest contributor of raw material to the tuna-canning industry.
T h e gradual development of several different styles of pack, such as chunk style, flaked, and grated style, m a d e from the m a n y different species of tuna and tuna-like species, c r e a t e d problems a m o n g canners as well as a m o n g t h e regulatory authorities with regard to t h e identity of tuna raw material, fill of container, etc., which, it was thought, could b e s t b e solved b y t h e establishment of tuna standards. T h e U . S. F o o d a n d D r u g Administration, in cooperation with the canners, therefore, b e g a n in 1 9 4 9 to work on standards of identity, definitions and standards of fill of container for t h e tuna industry. After several years of work, a g r e e m e n t was finally r e a c h e d on details of the standards, so that the F o o d a n d D r u g Administration could issue an order establishing "a definition a n d standard of identity, and standard of fill of container for c a n n e d tuna." T h e text of the Standards was published on F e b r u a r y 13, 1958. T h e s e Standards, w h i c h normally will b e effective one year after publication, limit the species w h i c h m a y b e p a c k e d and designated as tuna to eleven, whose scientific and c o m m o n names are given in T a b l e I I I .
F o r further description and identification of e a c h species, the follow
ing references m a y b e consulted: Godsil a n d H o l m b e r g ( 1 9 5 0 ) , Godsil and Byers ( 1 9 4 4 ) , Godsil ( 1 9 5 4 ) , and Kishinouye ( 1 9 2 3 ) .
This list of species of fish contained in the Standards w h i c h m a y b e
2 3 6 S V E N L A S S E N
canned as tuna and so designated are generally a c c e p t a b l e to the canners and to the fishing industry as a whole. Unfortunately, it has as yet b e e n impossible to identify b y c h e m i c a l or other positive tests a c a n n e d sample of any one of t h e a b o v e species from another or, w h a t is perhaps m o r e important, to differentiate b e t w e e n a c a n n e d sample of any o n e of the a b o v e species a n d a c a n of the several other tuna-like species w h i c h might find their w a y into the tuna market.
TABLE I I I
TUNA SPECIES ACCEPTABLE UNDER FEDERAL STANDARDS
Thunnus thynnus Bluefin tuna
Thunnus maccoyi Southern bluefin tuna
Thunnus orientalis Oriental tuna
Thunnus thynnus orientalis Albacore
Thunnus ohesus Big-eyed tuna
Thunnus alhacares Yellovvfin tuna
Neothunnus rarus Northern bluefin tuna
Euthynnus pelamis Skipjack
Euthynnus alletteratus Little tunny
Euthynnus Uneatus Black skipjack
Euthynnus yaito Kawakana
T h e n e w T u n a Standards specify concisely w h a t part of the tuna m a y b e used for canning b y stating: " T h e optional form of processed tuna consists o f loins and other striated muscular tissue of t h e fish. T h e loin is t h e longitudinal quarter of the great lateral muscle freed from skin, scales, visible blood clots, bones, gills, viscera, and from t h e non-striated part of such muscle, w h i c h p a r t ( k n o w n anatomically as the median superficial m u s c l e ) , is highly vascular, dark in color, b e c a u s e of retained blood, and granular in form." T h e median superficial muscle referred to in t h e above, is t h e so-called dark m e a t or b l o o d meat, w h i c h is typical of m a n y fish, and w h i c h is i m b e d d e d in t h e muscular structure b e t w e e n the dorsal and ventral loin of the tunas.
T h e four different types of p a c k style referred to under methods of manufacture in t h e tentative T u n a Standards are described and defined as follows:
" 1 ) Solid or solid p a c k consists of loins freed from any surface tissue discolored b y diffused hemolyzed blood, cut in transverse segments to w h i c h n o free fragments are added. I n containers o f one-pound or less of net contents, such segments are cut in lengths suitable for packing in one layer. I n containers m o r e than one-pound net content, such segments m a y b e cut in lengths suitable for packing in one or m o r e layers o f e q u a l thickness. Segments are p l a c e d in the can with the planes of their traverse cut ends parallel to the ends of the can. A p i e c e of a segment m a y b e
4 . T U N A CANNING AND P R E S E R V A T I O N O F R A W M A T E R I A L 237
added if necessary to fill a container. T h e proportion of free flakes broken from loins in the canning operation shall not e x c e e d 1 8 % .
" 2 ) Chunks or chunk style consists of a mixture of pieces of tuna in which t h e original muscle structure is retained. T h e pieces m a y vary in size, b u t not less than 5 0 % of the weight of t h e pressed content of a container is retained on a half-inch mesh screen.
" 3 ) F l a k e or flakes consist of a mixture of pieces of tuna in w h i c h more than 5 0 % of the weight of the pressed content of a container will pass through a half-inch m e s h screen, b u t in w h i c h the muscle structure of the flesh is retained.
" 4 ) G r a t e d consists of a mixture of particles of tuna that have b e e n reduced to uniform size, that will pass through a half-inch m e s h screen, and in w h i c h t h e particles are discrete and do not comprise a paste."
T o describe and define a style of p a c k so that it incorporates all essential features of t h e pack, and w h i c h does not permit of any am
biguity in interpretation of wording, is difficult. T h e a b o v e description of style of p a c k seems to h a v e o v e r c o m e this difficulty rather well.
C a n n e d tuna is also subject to color specifications. T h e color designation is obtained b y comparing, in a simple color comparator using filtered light, the reflectance value of the surface of the tuna m e a t prepared, under specified conditions, with that of m a t t e surface neutral reflectance standards of specified Munsell value.
T h e color designations for c a n n e d tuna are white, light, dark, and blended. W h i t e is a designation w h i c h m a y b e used only for albacore, provided t h e reflectance value is m o r e than 6.3 Munsell units. T h e term
"white m e a t " for tuna has always, in the mind of the purchasing public, b e e n associated with albacore, h e n c e this restriction.
Light. T h i s color or shade designation m a y b e used on c a n n e d tuna if its reflectance value is not b e l o w a Munsell value of 5.3. Most tuna c a n n e d in t h e U n i t e d States, and abroad, would pass this requirement.
It sometimes occurs that some lots of c a n n e d yellowfin tuna, and even skipjack, will h a v e a reflectance value a b o v e 6.3 Munsell units, w h i c h would m a k e it as light as white meat. I n such instances, t h e designation will still h a v e to b e light, as the term "white," as indicated, is reserved for a l b a c o r e only.
Dark. T h i s is a color or shade designation w h i c h applies to all c a n n e d tuna with a Munsell value b e l o w 5.3. T u n a of this designation often has a so-called "mahogany b r o w n " color and is often identified with large-size tuna fish. T h e U . S. consumer of tuna has a decided preference for light or white m e a t tuna; dark tuna, w h i c h is often also of coarse texture, has, therefore, only a limited market.
Blended. T h i s is a designation with a limited use in that it m a y b e
2 3 8 SVEN L A S S E N
applied only to c a n n e d tuna flakes consisting of a mixture of tuna flakes of w h i c h not less than 2 0 % b y weight meets the color standard for either white tuna or light tuna and the remainder of w h i c h fall within t h e color standard for dark tuna.
T h e packing m e d i a w h i c h are permitted under t h e Standard for c a n n e d tuna are as follows: ( 1 ) any edible v e g e t a b l e oil other than olive oil, or any mixture of such oils not containing olive oil; ( 2 ) olive oil;
( 3 ) water. W h i l e no further specifications in regard to quality of oils are incorporated in the T u n a Standard, they should obviously b e of such quality that they satisfy all state a n d federal p u r e food laws. S o y b e a n and cottonseed salad oils are the most popular oils used in tuna canning, and w h e n used should b e tested for identity, color, free fatty acids content, rancidity, moisture content, cloud point, smoke point, etc.
W h e n e v e r possible, salad oil to b e used should first b e p a c k e d in an experimental p a c k and tested for flavor reversion. T h e greater care exercised within recent years b y t h e oil mills in the selection and treat
ment of their cotton seeds and soybeans, and improvements in oil refining techniques, have reduced flavor reversions to a comparatively rare occurrence.
Olive oil, w h i c h is used to a limited extent, particularly for the so-called " T o n n o " solid pack, is often imported from the Mediterranean area. S o m e very good olive oil is also produced in California and is used in the tuna-canning industry. B u t whatever the origin, to b e a c c e p t a b l e , the olive oil must b e cold-pressed oil, must b e of good color, and have a fairly low free fatty acids content. T h e typical olive oil flavor, w h i c h is favored b y many, is present to a variable degree in olive oil from different localities. T h i s flavor c a n b e developed to some extent b y the way the olives are processed. Therefore, m u c h practical experience is required in selecting the right olive oil for tuna canning and it cannot usually b e decided u p o n b y the c h e m i c a l analytical report alone.
T h e Standards for c a n n e d tuna permit the seasoning or flavoring with one or m o r e of the following ingredients: ( 1 ) salt; ( 2 ) purified mono-sodium glutamate; ( 3 ) hydrolyzed protein; ( 4 ) hydrolyzed protein with reduced monosodium glutamate; ( 5 ) spices or spice oils or spice extracts;
( 6 ) v e g e t a b l e broths; ( 7 ) garlic.
Salt is needed as a flavoring or seasoning ingredient in all tuna packs except in the so-called "dietetic" low sodium pack. F l a v o r acceptability tests have revealed that a salt content of roughly 1.5% is most a c c e p t a b l e to t h e consumer. Unfortunately, t h e original salt content of t h e tuna m e a t that is p a c k e d often varies within a w i d e range. T h i s forces t h e tuna p a c k e r to carry out frequent salt determinations on t h e cooked tuna m e a t ( o r on the raw t u n a ) so that proper adjustment can b e m a d e in
4. T U N A CANNING AND P R E S E R V A T I O N O F R A W M A T E R I A L 2 3 9
t h e dosage of t h e a u t o m a t i c salt addition m a c h i n e on the canning line.
T h e variations in m e t h o d of t r e a t m e n t during b r i n e freezing and thawing w h i c h t h e tuna is subject to while on b o a r d the tuna clippers influence its salt content. U n d e r favorable conditions the over-all salt c o n t e n t of the tuna loin m e a t m a y b e b e l o w 1 % . T h e salt w h i c h is a d d e d to e a c h c a n on the canning line as it passes the a u t o m a t i c salt dispenser should b e fine-grained, free-flowing, dry salt. A c a n n e r s salt p r o d u c e d b y vacuum concentration of b r i n e is a c c e p t a b l e . I t must b e low in impurities and microorganisms. A m o n g t h e inorganic impurities, m a g n e s i u m and iron are particularly o b j e c t i o n a b l e , iron b e c a u s e of a possible discolor
ation that it m a y cause in the c a n n e d tuna meat, and magnesium b e c a u s e of the possibility that it m a y aid in t h e formation of m a g n e s i u m a m m o n i u m phosphate, t h e so-called "struvite," a harmless b u t neverthe
less most undesirable crystalline formation w h i c h sometimes develops in c a n n e d tuna, salmon, shrimp, lobster, and c r a b . T h e reason for the occasional d e v e l o p m e n t of "struvite" in c a n n e d tuna is still unknown.
T h e addition of purified monosodium glutamate as a seasoning agent is p e r m i t t e d under t h e T u n a Standards. M o n o s o d i u m glutamate has b e e n known as an intensifier of flavors of food. I t is the monosodium salt of the L-form of glutamic acid w h i c h has this extraordinary property; t h e isomeric D-form possesses n o n e of the flavor-intensifying properties ( M a n ning and B u c h a n a n , 1 9 4 8 ) . T h e addition of monosodium glutamate to a can of tuna in amounts of 0.15 to 0.25% of t h e w e i g h t of t h e tuna m e a t brings out satisfactory flavor intensification. Its present use in the tuna canning industry is, however, limited.
Hydrolyzed proteins m a y b e a d d e d t o c a n n e d tuna. S u c h hydrolyzates will usually contain considerable amounts of monosodium glutamate ( B l o c k and Boiling, 1 9 4 5 ) a n d will, therefore, exhibit properties similar to monosodium glutamate. T h e other components of hydrolyzed protein m a y add a bouillon-like flavor to t h e tuna meat, w h i c h m a y a p p e a l to some consumers. T h e hydrolyzed protein with r e d u c e d monosodium glutamate c o n t e n t will p r e s u m a b l y h a v e the bouillon-flavoring character
istics predominating over that w h i c h c a n b e o b t a i n e d b y hydrolyzed protein.
S p i c e or spice oils, or v e g e t a b l e b r o t h and garlic are all seasoning or flavoring agents whose addition is permitted under the T u n a Standards.
T h e y p r o d u c e special taste effects b y modifying t h e original flavor of the tuna m e a t and, therefore, differ from t h e effect p r o d u c e d b y mono
sodium glutamate. S o m e of t h e s e seasoning or flavoring agents have found a favorable reception b y t h e consuming public, particularly a m o n g certain e t h n i c groups.
T h e standards for fill of containers for c a n n e d tuna are b a s e d upon a
2 4 0 S V E N L A S S E N
determination of the pressed weight of their content. U n d e r specified conditions the pressed w e i g h t of a can is determined b y placing the drained content of can in a steel cylinder, inserting a plunger and b y means of a hydraulic press slowly exerting increasing pressure upon the tuna meat. B y increasing the pressure to 3 8 4 l b . per square inch of plunger face in c o n t a c t with the c a n content, a certain amount of liquid will b e pressed out. T h e press c a k e remaining in the cylinder when pressure finally is released is recovered and weighed. T h i s m e t h o d is simple and fast, and correlates fairly well with the amount of tuna m e a t which was originally put into the c a n during canning operations.
TABLE I V
CAN SIZE, PRESSED WEIGHT RELATIONSHIP UNDER FEDERAL STANDARDS
Minimum value Minimum value
for weights of for weights of
pressed cake pressed cake
Can size (average of Can size (average of and form of 24 cans) and form of 24 cans) tuna ingredient Averages tuna ingredient Averages
211 X 109 401 X 206
Solid 2.25 Solid 8.76
Chunks 1.98 Chunks 7.68
Flakes 1.98 Flakes 7.68
Grated 2.00 Grated 7.76
307 X 113 603 X 408
Solid 4.47 Solid 43.2
Chunks 3.92 Chunks 37.9
Flakes 3.92 Flakes 37.9
Grated 3.96 Grated 38.3
S o m e criticism of this m e t h o d has b e e n voiced, one b e i n g that only a small p e r c e n t a g e of t h e total moisture content of the tuna m e a t is b e i n g r e m o v e d b y pressing a n d that t h e moisture r e m o v e d varies with the physical characteristics a n d state of aggregation of the tuna meat, etc.
It has b e e n suggested that a nitrogen determination of can content or a determination of acetone-insoluble solids would b e a simpler and m o r e accurate m e t h o d of evaluating the c a n s content of tuna.
T h e s e a n d other objections o f a m o r e or less substantial c h a r a c t e r have, however, not b e e n a b l e to obscure the fact that press weights, as determined b y the standard procedure, generally speaking, give a reliable index of the amount of cooked tuna m e a t w h i c h was put into t h e can, and, therefore, provides the regulatory authorities with means to deter
m i n e w h e t h e r provisions w i t h regard to fill of container h a v e b e e n complied with. T h e m i n i m u m value for w e i g h t of pressed cake, as an average of 2 4 cans sampled, for the various can sizes, is given in T a b l e I V .
4 . T U N A CANNING AND P R E S E R V A T I O N O F R A W M A T E R I A L 2 4 1
TABLE V
AVERAGE COMPOSITION OF CANNED TUNA
Style of pack Protein (%) Fat (%) Moisture (%)
Ash and carbohydrates
(%)