Cephalopods encompass a group within the phylum mollusc and include squid, octopus, and cuttlefish. Cephalopods are found in all salty waters around the globe, and there are about 800 existing species, of which about 30 different species are used as human food. Cephalopods constitute about 5% of the global marine catch, and the volume is increasing. Almost all cephalopods on the world market are from wild stocks, and aquaculture is only very slowly progressing due to difficulties in artificially breeding cephalopods. Foods are complex systems due to their biological origin. Biological materials are soft matter hierarchically structured on all scales from molecules to tissues. The structure reflects the biological constraints of the organism and the function of the tissue. The structural properties influence the texture and hence the mouthfeel of foods prepared from the tissue, and the presence of flavour compounds is similarly determined by biological function. Cephalopods, such as squid, cuttlefish, and octopuses, are notoriously known for having challenging texture due to their muscles being muscular hydrostats with highly cross-linked collagen. Similar with other marine animals such as fish and crustaceans, cephalopods are rich in certain compounds such as free amino acids and free 5′-ribonucleotides that together elicit umami taste.
1. Cephalopod Texture
The structural properties of cephalopod muscular tissue as described above determine the textural properties of the tissue considered as food
[1]. Texture is the sensory perception of the elements of food structure and as such intimately dependent on the hierarchical and multiscale structuring of the food matrix
[2] as a piece of complex soft matter
[3]. In many ways, the cephalopod muscle is one of the most intriguing pieces of soft material used for food
[4].
Texture Analysis
Cephalopod structure has been extensively investigated scientifically since the 1970s using the texture analysis (TA) methodologies of food pioneered in the 1960s by Dr Alina Surmacka Szczesniak (2002). Several authors have investigated squid and octopus texture by TA to study multiple effects. Historically, the TA of cephalopods has included methods including compression or puncture test by a cylindrical probe, shear force by a knife or razor blade, and collagen gel strength test. Sample cutting and orientation of muscle tissue samples analysed by TA highly affect the outcome. Specifically, in the case of squid, the direction of the shearing and sampling area of the mantle affects the TA due to the biological structural variation across the mantle thickness
[5] and along the longitudinal direction
[6][7] and due to the direction of dominant circular muscle fibres in the mantle
[8][9][10][11].
Table 1 provides an overview of the studies dealing with TA of the textural properties of cephalopods, primarily with regard to studies of textural changes of cephalopods caused by cold and freeze storage. For other specific results, the reader is referred to the quoted literature.
Table 1. Overview table of applied TA test types applied to analysing the mechanical texture of different species of cephalopods.
Family |
Species |
Cut |
Test Type |
Parameters |
Fixture |
Reference |
Squid |
D. gigas |
Fins (gel) |
Compression |
Stress and strain |
Cylindrical probe (dia. 38 mm), deformation 75%, load cell 100 N |
[12] |
|
D. gigas |
Mantle |
Double compression |
Flexibility, firmness |
Cylindrical probe (dia. 5 mm) |
[13] |
|
D. gigas |
Mantle (cooked) |
Double compression |
Hardness, springiness, cohesiveness; shear force |
Cylindrical probe (dia. 50 mm), deformation 75%; Warner–Bratzler shear blade |
[14] |
|
D. gigas |
Mantle (dried) |
|
Firmness |
Cylindrical probe (dia. 3 mm) |
[15] |
|
D. gigas |
Mantle (gel) |
Double bite |
Hardness, cohesiveness, elasticity |
Knife blade, load cell 100 N |
[16] |
|
D. gigas |
Mantle (gel) |
Double compression |
Gel strength, elasticity, cohesiveness |
Cylindrical probe, deformation 75% |
[17] |
|
D. gigas |
Mantle, fins, arms (cooked) |
Shear force |
Shear force |
|
[18] |
|
I. argentinus |
Mantle |
Shear force |
Shear force |
|
[19] |
|
I. argentinus |
Mantle (cooked) |
|
Hardness, elasticity, chewiness |
|
[20] |
|
I. argentinus |
Mantle (raw) |
Shear force |
|
Wedge plunger |
[21] |
|
I. argentinus |
Mantle (raw, enzymes) |
|
Toughness |
|
[22] |
|
I. coindetii |
Mantle |
Tensile |
Stress and strain |
Two hooks |
[23] |
|
I. illecebrosus, L. pealei |
Mantle (raw, cooked) |
Shear force |
|
Modified Kramer shear cell |
[24] |
|
L- vulgaris |
Mantle (raw) |
Compression test |
Toughness |
Cylindrical probe (5 kg load cell) |
[25] |
|
L. duvauceli |
Mantle (cooked) |
Double compression |
Hardness 1, hardness 2, cohesiveness, gumminess, springiness, chewiness; shear force |
Cylindrical probe (dia. 50 mm), 50 N load cell, deformation 40%; Warner–Bratzler shear blade, 50 N load cell |
[26] |
|
L. duvauceli |
Mantle (raw, cooked) |
Double compression |
Cohesiveness, springiness, stiffness |
Cylindrical probe (dia. 50 mm), deformation 40% |
[27] |
|
L. duvauceli |
|
Shear force |
Shear force |
Warner–Bratzler shear blade |
[28] |
|
L. edulis, I. argentinus |
Mantle (raw) |
Shear force |
Toughness |
Plunger knife blade |
[29] |
|
L. forbesii, L. vulgaris |
Mantle (raw, cooked) |
Shear force |
Hardness, work |
Warner–Bratzler shear blade |
[30][31] |
|
L. pealei |
Mantle (cooked) |
Shear force |
Force, energy |
Single blade; punch and die |
[8] |
|
L. pealei, I. illecebrosus |
Mantle (raw, cooked) |
Tension |
Stress and strain |
Tensile grips |
[9][32] |
|
L. vulgaris |
Mantle (raw) |
Penetration |
Firmness, elasticity, work |
Flat bottom stainless-steel cylinder (dia. 6 mm) 100 kg load cell. |
[33] |
|
L. vulgaris |
Mantle (raw) |
Texture profile analysis |
Hardness, cohesiveness, springiness, gumminess, chewiness |
Cylindrical compression probe |
[25] |
|
L. vulgaris |
Mantle (raw, enzymes) |
Compression test |
Toughness |
Cylindrical probe using 40% compression (5 kg load cell) |
[34] |
|
O. sloanipacifcus |
Mantle (raw, dried) |
Rupture |
Shear force |
Razor blade |
[35] |
|
S. lessoniana |
Mantle (cooked) |
Tension |
Stress and strain |
|
[36] |
|
T. pacificus |
Mantle (raw) |
Compression |
Hardness |
Cylindrical probe (dia. 2 mm) |
[37] |
|
T. sagittatus |
Mantle (cooked) |
Shear force |
Toughness |
Warner–Bratzler shear blade |
[38] |
Octopus |
E. moschata |
Mantle |
Penetration |
Toughness |
Cylindrical probe (dia. 2 mm) |
[39] |
|
O. vulgaris |
Mantle |
Penetration |
Toughness |
Cylindrical probe (dia. 2 mm) |
[40] |
|
O. vulgaris |
Arm (raw) |
Texture profile analysis |
Hardness, cohesiveness, springiness, gumminess, chewiness |
Cylindrical compression probe |
[25] |
|
O. vulgaris |
Arm (raw) |
Compression test |
Toughness |
Cylindrical probe (5 kg load cell) |
[25] |
Cuttlefish |
S. aculeata |
Mantle (raw) |
Shear force |
Shear force |
Warner–Bratzler shear blade |
[28] |
|
S. officinalis |
Mantle (raw) |
Texture profile analysis |
Hardness, cohesiveness, springiness, gumminess, chewiness |
Cylindrical compression probe |
[25] |
|
S. officinalis |
Mantle (raw) |
Compression test |
Toughness |
Cylindrical probe (5 kg load cell) |
[25] |
|
S. pharaonis |
Mantle (raw) |
Shear force |
Toughness |
Plunger knife blade |
[41] |
2. Food Safety
2.1. Biogenic Amines
An increase in ammonia and drip loss have been correlated with the decrease in overall quality rating and increase in the quality index score of squid and cuttlefish, with the (trimethylamine) TMA content markedly increased after 10 and 8 days of storage in squid and cuttlefish, respectively
[28]. The food safety of squid can be managed by high-pressure processing (HPP). Specifically, HPP has been proven to lower the formation of autolytic activity and level of TMA
[42]. HPP was also investigated for octopus, showing that TMA and dimethylamine (DMA) produced in chopped raw octopus treated at 600 MPa were significantly reduced by 42.5% and 62.2%, respectively, as compared with the levels in the control. The production of biogenic amines (BAs) increased by up to 1.82 mg/g in the control after 12 days of refrigerated storage, while the BA levels in the 450 and 600 MPa treated octopus were 1.40 and 1.35 mg/g, respectively
[43].
2.2. Trace Elements
The concentrations of essential and non-essential elements in cephalopods have been determined to be within the prescribed limits set by various authorities, except for Cu and As. Regarding the content of toxic metals Hg, Cd, and Pb, the consumption of cephalopods is not a cause of concern, with the lowest concentrations found in Loliginidae, and for the nutritional essential elements, cephalopod mollusc consumption makes an important contribution to the daily dietary intake of Cu, Zn, and Se. However, considerably higher contents are found in the hepatopancreas (i.e., the liver) than in the muscle of cephalopods, except for Hg and As, which are equally distributed in the two types of tissue. In particular, Cd present in the hepatopancreas is of dietary concern
[44], which also seems to be the case, comparing tissue with digestive glands from other marine species, e.g., in the case of crustaceans
[45]. It is therefore strongly recommended that the liver of cephalopod be not regularly consumed although it is showing a great umami taste potential in other investigations
[46].
3. Cephalopod Gastronomy and Gastrophysics
3.1. Cephalopod Cooking and Cookbooks
Although different types of cephalopods have been used in food cultures around the world, there is no particular, well-defined universal cephalopod cuisine or cephalopod gastronomy
[47]. Moreover, there are surprisingly few modern cookbooks specifically devoted to cephalopods
[48][49][50], and they are mostly dealing with squid. In older accounts, octopus seems to be a favourite dish. The Roman gourmet Marcus Gavius Apicius (25 BCE−37 CE) is credited for the oldest known cookbook
De re coquinaria from the Antique, which contains a recipe for octopus with pepper, lovage, ginger, and the Roman fish sauce garum
[51]. From the Middle Ages, there are some recipes in handwritten manuscripts from the fourteenth century
[52], e.g., a Catalan recipe for octopus filled with its own arms together with spices, parsley, garlic, raisins, and onions, and prepared over an open fire or in an oven. From the sixteenth century, a Catalan recipe describes the preparation of baked octopus and an Italian one using boiled, roasted, and marinated octopus
[52].
While the preferred taste and texture of prepared cephalopods are very dependent on the food culture, there are some general trends. For example, Japanese eaters prefer a mild flavour as close to the natural flavour as possible, and they will therefore only add subtle flavours, e.g., from marinating liquids. Moreover, Japanese cuisine often uses squid that is either raw or extremely lightly cooked. In other places in Southeast Asia such as Vietnam, Thailand, and China, eaters prefer cephalopods with more spicy, powerful, and fishy flavours. In Southern Europe, cephalopods are almost always prepared either by grilling, steaming, or frying. In South America, marinating squid in salt and acid juices a la ceviche strikes a middle balance between raw and prepared/cooked.
Generally, the taste and flavour of fresh cephalopods are reasonably mild and quite easily blend in with other flavours. Therefore, in gastronomic uses of cephalopods, one may risk suppressing the subtle flavours of the cephalopods with stronger tasting ingredients, such that one is left with the texture as the only surviving characteristic of the cephalopod used.
Building on traditional, in particular Mediterranean cuisines, there appears in Europe to be an increasing interest among chefs to explore cephalopod cooking and take it into a more modernist setting
[53]. This trend may be fuelled by a search for using marine food sources in a more sustainable fashion
[54]. A deeper understanding of the gastrophysical properties of cephalopod muscular structure as reviewed in the present paper may aid in this search.
3.2. Culinary Gastrophysical Investigations of Cephalopods
A majority of scientific investigations into cephalopods include studies of raw tissue rather than cooked. Investigated cooking techniques of cephalopods have most frequently included boiling
[55][56][39][40] and drying
[57][58]. Other types of culinary preparations have involved tenderisation techniques of cephalopods using natural autolysis
[59]; ultrasonic treatment
[60]; and marination with NaCl and acetic acid
[39], alkaline soaking
[35], liver extract
[61], collagenase
[62], and spleen and bromelain extract
[63]. However, it is often a predefined cooking treatment that is applied to study the physical, chemical, or microbiological changes rather than applying a gastrophysical approach to optimise the culinary treatment in question. Gastrophysical exploration of cephalopods is therefore limited, but a few examples include the investigation of
L. forbesii [64][65][66]. Other studies involving cephalopods in a culinary context investigated (commercial) food preparations, ranging from frankfurters prepared from the mantle of
Dosidicus gigas [67], ready-to-eat Indian squid (
L. dauvacelli Orbigny) masala
[68], and battered and fried squid rings
[69].
The present authors have, in recent years together with several collaborators, including scientists, chefs, and innovators, developed a multipronged gastrophysical research programme with a focus on a single species,
L. forbesii, that is common in Nordic waters but not part of the traditional Nordic food culture. Part of the motivation for undertaking such a programme can be seen as a contribution to the so-called New Nordic Cuisine. Another part pertains to the current search for sustainable food to promote a transition towards a more green and sustainable eating behaviour
[70]. Some of which is reported in the present research in a more general context, researchers tried to cover all aspects of squid food science and gastronomy, basically from the state of molecular structure, materials properties and chemical characteristics, preparation procedures, taste, flavour, and texture, to human food preferences and culinary innovation. Currently, this broad programme is being supplemented by an ethical dimension via participation in an international research programme dealing with humane slaughtering methods of cephalopod.