BACKGROUND: The quality deterioration of Antarctic krill (Euphausia superba) after thermal processing limits its industrial application. This study sought to improve the texture characteristics of Antarctic krill after heat treatment through pre-soaking using L-lysine (Lys) solution and sodium tripolyphosphate (STPP). Moreover, the effects of Lys on heat-treated Antarctic krill were explored.RESULTS: Lys significantly reduced the cooking loss and improved the texture characteristics of Antarctic krill during heat treatment. The low-field nuclear magnetic resonance results showed that Lys reduced the water loss of Antarctic krill during heat treatment. Additionally, the surface hydrophobicity, Fourier transform infrared spectroscopy, and endogenous fluorescence spectroscopy results showed that Lys could inhibit the structural damage of Antarctic krill protein under the thermal denaturation condition and enhance the thermal stability of the protein. The scanning electron microscopy results showed that Lys could protect the structural integrity of Antarctic krill muscle fibers during heat treatment.CONCLUSION: The cooking loss in the Lys added groups was better than the sodium tripolyphosphate added group, and 2.0% Lys solution could minimize the cooking loss of Antarctic krill. The secondary and tertiary structures of the Antarctic krill protein were actively protected by Lys during heat treatment. Overall, the study will provide insights into the application of Lys in the food industry as a natural additive and an alternative to phosphate.

Antarctic krill (Euphausia superba) is an important source of biomass and high-quality protein. However, heat treatment of Antarctic krill negatively impacts its quality and compromises its utilization in the food industry. This study aimed to investigate the mechanisms underlying changes in Antarctic krill meat characteristics and physicochemical properties treated at different temperatures and holding times.Findings indicate that at higher temperatures and holding times, hardness and cooking loss of Antarctic krill meat increased dramatically. The low-eld nuclear magnetic resonance (LF-NMR) analysis revealed that the loss of immobile water increased, whereas SDS-PAGE analysis showed that the content of myosin heavy chain decreased signi cantly, and that protein degradation occurred. Fourier transform infrared spectroscopy (FT-IR) and intrinsic uorescence spectra indicated that α-helix motifs were transformed into β-sheets, and that more hydrophobic groups were exposed. The scanning electron microscopy (SEM) results showed that Antarctic krill meat formed corrugated folded regions after heat treatment without forming a three-dimensional water-entrapped structure, which led to signi cant water loss, resulting in rapid deterioration Antarctic krill meat. These results provide the basis for a deeper understanding of processing characteristics of Antarctic krill meat.

BACKGROUND In this work, low‐field nuclear magnetic resonance (LF‐NMR) and magnetic resonance imaging were used to investigate the changes in protons (from water and oil) distribution of mackerel during the frying process. The relationship between proton migration and some physicochemical indexes was established by partial least squares regression (PLSR). The changing mechanism of the quality characteristics and physicochemical properties of fish meat under different frying conditions was analysed by LF‐NMR combined with PLSR, which provided theoretical support for the development of canned mackerel food. RESULTS LF‐NMR results showed that three kinds of T2 protons assigned to protein–water interaction (T21), multilayer bound water (T22), oil and free water (T23), respectively. As the frying temperature increased, protons from the T22 peak significantly decreased, while protons from the T23 peak remarkably increased. The microstructure of fried mackerel was destroyed; cooking loss, oil content, a* value, b* value, hardness and chewiness increased; and the protein content and L* value decreased. Furthermore, PLSR analysis revealed that significant correlation was observed between the cooking loss, TPA parameter (chewiness), colour parameter (L*) and LF‐NMR parameters. CONCLUSION Different frying temperatures and times had a strong effect on the physicochemical properties of mackerel. Good prediction models could be established by proton migration using the LF‐NMR technique and PLSR for fried mackerel. Quality control of fried fish could be realized by monitoring the change in LF‐NMR data. © 2021 Society of Chemical Industry

Summary The object of this study was a high‐protein Antarctic krill ball which was made of mixed shrimp surimi (Antarctic krill and white shrimp). The effects of four different exogenous additives on gel properties and spatial structure of mixed shrimp surimi systems during processing were investigated by texture profile analysis, low‐field nuclear magnetic resonance, magnetic resonance imaging, Fourier‐transform infrared spectroscopy, scanning electron microscopy and rheology analysis, according to product formulation and processing conditions. Different exogenous additives improved distinctly the mixed shrimp surimi system. The use of the four exogenous additives combined had a synergistic promotional effect. Acetylated distarch adipate, egg white powder and soy protein isolate played a vital role in producing high‐protein Antarctic krill balls. The relatively limited improvement of transglutaminase could be attributed to processing temperature and the presence of autolytic enzymes originated intrinsically from Antarctic krill surimi.

Heat treatment reduces the quality of Antarctic krill (Euphausia superba), thus greatly limiting its industrial application. Although L-Lys immersion pretreatment can effectively improve the quality of heat-treated Antarctic krill meat, the underlying mechanism is unclear. This study aimed to investigate the effect of different L-Lys concentrations (0, 25, 50, 100, and 200 mM) on the aggregation behavior and structure of Antarctic krill myofibrillar protein solution before and after heat treatment. Compared with the untreated group, L-Lys decreased the surface hydrophobicity and particle size of the heat-treated Antarctic krill protein by 2.38 times and 18.27 times while increasing the solubility by 3.59 times. Furthermore, L-Lys intervention inhibited the formation of disulfide bonds in myofibrillar protein of the heat-treated Antarctic krill, enhanced the intermolecular hydrogen bonding force, improved the orderliness of the secondary structure, and "exposed" the tyrosine residues of the protein molecule. As a result, the polarity of the microenvironment was enhanced while the tertiary structure of the protein was altered, thus inhibiting thermal aggregation behavior and improving the water-holding capacity and tenderness of heat-treated Antarctic krill. This study reveals the mechanism of L-Lys inhibition of thermal aggregation behavior of Antarctic krill myofibrillar protein. Our results provide insights into the development and utilization of Antarctic krill protein in the food industry.