Hugo Enrique Ramírez-Guerra

The study aimed to evaluate the low molecular-mass nitrogen compounds (LMMNC) arginine (Arg), taurine (Tau), and trimethylamine oxide (TMAO) (individually or their mixtures) cryostabilizing effect over jumbo squid (Dosidicus gigas) myofibrillar protein (JSMP) frozen at -20°C for 0, 30, and 90 days. Washed muscle (three times, 1:3, muscle:water) was lyophilized (sample). Washing water was ultrafiltrated (<1 kDa cut-off) and permeate lyophilized (<1 kDa fraction). LMMNC, Control+ (with 0.05) TS in most treatments. LMMNC, especially Taurine and TMAO, protects JSMP from freezing denaturation, stabilizing its structure.

Physicochemical and structural properties of soluble jumbo squid (Dosidicus gigas) elastin recovered from skin by-products were evaluated. The molecular weight of isolated elastin was ~40 kDa with an isoelectric point (pI) between 9 and 10. Aspartic, glutamic, arginine, proline, glycine, and lysine amino acids were the most abundant in squid elastin, whereas the hydroxyproline absence, ~0.7% cysteine content, and the calculated 0.35 isoleucine/leucine ratio were used as purity index. Total and reactive sulfhydryl contents were similar (247.0 ± 5.1 vs 242.0 ± 7.5 μmol mg⁻¹ of protein, P ≥ 0.05) in purified squid elastin but surprisingly higher than previously reported in other elastins. On the other hand, the secondary structures of squid elastin analyzed by Fourier transform infrared spectroscopy (FTIR) were ~45% β-sheets, ~15% α-helices, ~10% β-turns, and ~30% undefined structures. In addition, squid elastin experienced glass transition at 82.01 ± 0.01ºC, denaturation temperature at 110.45 ± 0.64ºC, and aggregation at 197.5 ± 0.23ºC. In conclusion, the prevalence of charged amino acids and pI of squid elastin can facilitate its solubilization in hydrophilic systems, whereas the secondary structure profile and thermostability are desirable features in proteins used for biopolymer designs such as food biofilms or barrier systems.

Chemical properties of fish gelatins differ from those of conventional mammalian sources, representing an attractive technological alternative for the food industry. Ray filleting generates a considerable amount of skin waste that can be used as a collagen source for gelatin extraction. Thus, this research evaluated the HCl and CH₃COOH effect, at 0.01, 0.025, 0.05, 0.075, 0.1, 0.15, and 0.2 M, on extraction yield, molecular weight distribution, and gel strength (GS) of whiptail stingray (Dasyatis brevis) skin gelatins. Results showed differences (P < 0.05) between acid type and concentration used. CH₃COOH (0.15 M) gave the highest extraction yield (7.0% vs. 5.5% at 0.15 M HCl) and GS (653 ± 71 g vs. 619.5 ± 82 g at 0.2 M HCl). Gelatin electrophoretic profile from CH₃COOH revealed α-/β-components and high molecular weight (> 200 kDa) polymers. Ray gelatin GS was higher than commercial bovine gelatin, suggesting its possible use for technological food applications.

Collagen is the major connective tissue (CT) protein and one of the main constituents of the jumbo squid (Dosidicus gigas). Therefore, physicochemical changes of pepsin-solubilized collagen (PSC) and insoluble collagen (IC) were studied after cooking (100°C/30 min) of muscle (mantle, fins, and arms). Different pyridinoline (Pyr) contents (the major cross-linking molecule in collagen fibers) were found in the fresh muscle of the three anatomical regions. After the cooking process, a decrease from 10 to 30% in the thermal resistance of collagen was observed, depending on the anatomical region and fraction evaluated. Furthermore, the electrophoretic profile, Fourier transform infrared (FTIR) spectroscopy, and the amino-acid profile revealed that structural changes occurred in the two different collagen fractions caused by the thermal process, and the changes were greater in the mantle. Under the conditions applied in this study, collagen fractions from the squid arms showed more stability during the cooking process due to the high cross-linking degree of their fibers.

In marine organisms primarily intended for human consumption, the quality of the muscle and the extracted oils may be affected by lipid oxidation during storage, even at low temperatures. This has led to a search for alternatives to maintain quality. In this sense, antioxidant compounds have been used to prevent such lipid deterioration. Among the most used compounds are tocopherols, which, due to their natural origin, have become an excellent alternative to prevent or retard lipid oxidation and maintain the quality of marine products. Tocopherols as antioxidants have been studied both exogenously and endogenously. Exogenous tocopherols are often used by incorporating them into plastic packaging films or adding them directly to fish oil. It has been observed that exogenous tocopherols incorporated in low concentrations maintain the quality of both muscle and the extracted oils during food storage. However, it has been reported that tocopherols applied at higher concentrations act as a prooxidant molecule, probably because their reactions with singlet oxygen may generate free radicals and cause the oxidation of polyunsaturated fatty acids in fish oils. However, when tocopherols are included in a fish diet (endogenous tocopherols), the antioxidant effect on the muscle lipids is more effective due to their incorporation into the membrane lipids, which can help extend the shelf life of seafood by reducing the lipid deterioration that occurs due to antioxidant synergy with other phenolic compounds used supplements in fish muscle. This review focuses on the most important studies in this field and highlights the potential of using tocopherols as antioxidants in marine oils.

Summary: Collagen fibres, stabilised by lysyl oxidase (LOX), play an important role in jumbo squid because they are responsible for the union between various cells; therefore, a close interdependence between their functions and muscle firmness during ice storage has been suggested. In this study, the relationship between LOX activity, pyridinoline (Pyr) content and muscle texture (SF) during ice storage of jumbo squid mantle was evaluated. LOX activity was confirmed within the range of 4.1–7.1 × 10⁻³ U g⁻¹ of protein, leading to an increase in Pyr content, detected in the range of 0.85–1.32 mmol mol⁻¹ of collagen after 5–20 days. The SF of the muscle became harder during the ice storage time, increasing from 21.08 to 37.95 N. It was therefore possible to establish the relationship between LOX activity, collagen cross‐links (Pyr content) and texture patterns during ice storage of jumbo squid muscle, which increased after 20 days.