Gastrophysical and chemical characterization of structural changes in cooked squid mantle

Abstract

Squid (Loligo forbesii and Loligo vulgaris) mantles were cooked by sous vide cooking using different temperatures (46 • C, 55 • C, 77 • C) and times (30 s, 2 min, 15 min, 1 h, 5 h, 24 h), including samples of raw tissue. Macroscopic textural properties were characterized by texture analysis (TA) conducted with Meullenet-Owens razor shear blade and compared to analysis results from differential scanning calorimetry. The collagen content of raw tissues of squid was quantified as amount of total hydroxyproline using ultra-high-performance liquid chromatography. Structural changes were monitored by Raman spectroscopy and small-angle X-ray scattering and visualized by second harmonic generation microscopy. Collagen in the squid tissue was found to be highest in arms (4.3% of total protein), then fins (3.0%), and lowest in the mantle (1.5%), the content of the mantle being very low compared to that of other species of squid. Collagen was found to be the major protein responsible for cooking loss, whereas both collagen and actin were found to be key to mechanical textural changes. A significant decreased amount of cooking loss was obtained using a lower cooking temperature of 55 • C compared to 77 • C, without yielding significant textural changes in most TA parameters, except for TA hardness which was significantly less reduced. An optimized sous vide cooking time and temperature around 55-77 • C and 0.5-5 h deserves further investigation, preferably coupled to sensory consumer evaluation. Practical Application: The study provides knowledge about structural changes during sous vide cooking of squid mantle. The results may be translated into gastronomic use, promoting the use of an underutilized resource of delicious and nutritious protein (Loligo vulgaris and Loligo forbesii).

Cephalopods as Challenging and Promising Blue Foods: Structure, Taste, and Culinary Highlights and Applications

“…For L. forbesii , the results from SHGM linked to the investigations by TA, differential scanning calorimetry (DSC), as well as cooking-loss measures, and the major responsible layers controlling texture were identified as collagen and actin, with an ideal cooking temperature to be around 55 °C, while being >46 °C but <77 °C. Cooking loss was linked to the denaturation of collagen (and, to some degree, myosin), whereas mechanical texture was, in general, linked to collagen and actin, with visual imaging from SHGM validating the results from DSC, suggesting that controlling the denaturation of collagen is key for obtaining both tenderness and juiciness of squid mantle [ 32 ]. Microscopy, using light microscopy and transmission electron microscopy combined with TA, was also used to investigate refrigeration effects.…”

“…For the cooked mantle, the mechanical texture is considerably stronger in the longitudinal direction (across circular muscle fibres) than in the transversal direction. Specifically, cooking at 60 °C and 100 °C reveals a greater effect on the mechanical texture of the longitudinal direction than on the transverse, which was attributed to the orientation of the circular collagen fibres of squid [ 31 ] and may also additionally be linked to the denaturation of actin fibres [ 32 ].…”

“…Cephalopod structure has been investigated by multiple techniques, some giving direct access to structural information such as microscopy and scattering techniques, and others more indirectly such as spectroscopy as well as chemical and thermal analysis. Some relevant studies include electrophoresis [ 38 , 40 , 41 , 42 , 43 , 44 , 45 ], microscopy [ 29 , 32 , 42 , 43 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ], spectroscopy [ 41 , 53 ], small-angle x-ray scattering [ 32 ], differential scanning calorimetry [ 32 , 43 , 54 ], and chemical analysis in relation to collagen quantity and quality determination [ 28 , 38 , 40 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ]. The reader is referred to the literature for a detailed description, and the following section is limited to highlighting results obtained from the most common techniques that include microscopy, spectroscopy, and chemical analysis.…”

“…Other types of microscopy have also been applied to study the structure of squid and octopus; some examples include second-harmonic-generation microscopy (SHGM) applied to investigate the structural changes inside the mantle caused by low-temperature long-time cooking [ 32 ]. For L. forbesii , the results from SHGM linked to the investigations by TA, differential scanning calorimetry (DSC), as well as cooking-loss measures, and the major responsible layers controlling texture were identified as collagen and actin, with an ideal cooking temperature to be around 55 °C, while being >46 °C but <77 °C.…”

“…Studies into cephalopod structure using microscopy further investigated the impact of drying methods (freeze-drying vs. heat pump) [ 42 , 43 ], enzymatic tenderisation [ 46 ], deep frying [ 47 ], soaking post cooking and drying [ 49 , 50 , 51 ], as well as low-temperature long-time cooking [ 32 , 52 ].…”