Investigation of isomerization and oxidation of astaxanthin in ready-to-eat Litopenaeus vannamei during accelerated storage.

Astaxanthin (AST), the natural pigment in Litopenaeus vannamei, is susceptible to oxidation and isomerization, leading to the fading of the orange-red color in ready-to-eat (RTE) shrimps. This study specifically investigated the changes mechanism in AST content, including geometric and stereoisomers, as well as oxidation degradation, throughout the storage process of RTE shrimps. The results showed that the total amount of AST decreased by 46.76 % after 45 days of storage at 40 °C. The levels of geometric isomers (all-E, 9-Z, 13-Z) and stereoisomers (3S,3'S, 3S,3'R, 3R,3'R) gradually decreased over time. Notably, 9-Z and 3S,3'S isomers, known for their strong antioxidant activity, were reduced by 83.57 % and 61.64 % respectively. Additionally, AST underwent oxidative degradation, forming short-chain compounds (astaxanthinal or astaxanthinone), with the main products being Apo-14'-astaxanthinal and Apo-7-astaxanthinone DHA ester. These findings provide a theoretical foundation for further research on the degradation mechanism of AST, and offer valuable insights into the color protection of RTE shrimps.

Effect of ultra-high pressure heat-assisted technology combined with L-cysteine on the color of ready-to-eat shrimp during storage.

This study used ultra-high pressure processing (HPP) heat-assisted technology combined with L-cysteine (L-cys) to process ready-to-eat (RTE) shrimp. Subsequently, the effects of physical field and chemical modifications on the color of RTE shrimp were studied. The results showed that the RTE shrimp treated with HPP-Heat-L-cys showed better performance in terms of brightness value (65.25) and astaxanthin (AST) content (0.71 µg/g) during storage, maintaining the original color of RTE shrimp effectively. In addition, it was observed that the application of HPP-Heat-L-cys significantly delayed phenol oxidation, lipid oxidation, and Maillard reaction compared with traditional HPP or heat treatments. Specifically, the total phenolic content of RTE shrimp treated with HPP-Heat-L-cys was higher than that of other samples, but the TBARS and browning index were lower. Furthermore, HPP-Heat-L-cys could delay the production of dark products (such as 2-methylanthraquinone, p-benzoquinone, lipofuscin and melanin), ultimately safeguarding the color stability of RTE shrimp during storage.

Molecular mechanism of color deepening of ready-to-eat shrimp during storage.

Color deepening occurs during storage of ready-to-eat (RTE) shrimps, which seriously affects their marketing cycle. This study investigated the molecular mechanisms of color deterioration in RTE shrimps during accelerated storage, shedding light on the pattern of change in colored products and content. The findings revealed significant occurrences of phenolic oxidation, lipid oxidation, and Maillard browning reactions during accelerated storage. Qualitative and quantitative analyses were conducted on the colored products resulting from these chemical reactions. Multivariate mathematical models were employed to analyze the phenolic oxidation products (2-methylanthraquinone and p-benzoquinone), lipid oxidation products (lipofuscin-like pigments and hydrophobic pyrroles), and Maillard browning products (pyrazines and melanoidins). These products were identified as the main contributors to the deepening of the color of RTE shrimps during storage. The outcomes of this research could enhance our understanding of the color change mechanism in thermally processed marine foods, providing valuable insights for quality maintenance and industrial advancement.

Konjac glucomannan-assisted fabrication of stable emulsion-based oleogels constructed with pea protein isolate and its application in surimi gels.

Konjac glucomannan (KGM) is widely used as a stabilizer for the structuring of highly unsaturated oils. This study aimed to investigate the changes in structure and functional properties of soybean oil - based oleogels (emulsion template method) prepared with different amounts of KGM-modified pea isolate protein (PPI). The findings revealed that the oleogels formed three - dimensional networks through van der Waals interactions and hydrogen bonding between the stretched PPI and KGM. As the amount of KGM increased, the oil droplets were more uniformly dispersed within the continuous PPI - KGM rigid network, especially when the ratio of PPI to KGM was 4:1. This formulation also showed the highest thixotropy (73.2 %) and the best oil binding capacity (94 %). Cryo - SEM revealed that the oleogel - prepared surimi gels successfully enclosed oil droplets in a dense matrix through a dual stabilization mechanism. Additionally, the incorporation of oleogels significantly improved the textural properties of surimi in comparison to directly adding oil.

Effects of calcium chloride on the gelling and digestive characteristics of myofibrillar protein in Litopenaeus vannamei.

In this study, the effects of CaCl2 (0, 25, 50, 75, and 100 mM) on the gelling and digestive properties of the myofibrillar protein (MP) in Litopenaeus vannamei were investigated. The results showed that increasing CaCl2 concentration led to changes in the tertiary structure of MP. Specifically, compared with the control group, a 64.31 % increase in surface hydrophobicity and a 45.90 % decrease in the sulfhydryl group were observed after 100 mM CaCl2 treatment. Correspondingly, the water holding capacity and strength of the MP gel increased by 24.46 % and 55.99 %, respectively. These changes were positively correlated with the rheological properties, microstructure pore size, and content of non-flowable water. The mechanical properties of MP gel were improved, and the microstructure became more compact with the increase in CaCl2 concentration. Furthermore, the particle size of the digested MP gels decreased in the presence of CaCl2, which improved the digestion characteristics of MP gels.

pH-shift strategy improving the thermal stability and oxidation stability of rice starch/casein-based high internal phase emulsions for the application in fish cake.

The thermal stability of the different pH-shift rice starch/casein-based high internal phase emulsions (SC-HIPE) were evaluated in the present study to verify potential in improving the quality of fish cake. The results showed that the pH-shift treatment improved thermal stability (from 27.23% to 76.33%) and oxidation time (from 5.01 h to 6.86 h) of SC-HIPE, which showed the smaller droplet size (decreased from 15.14 to 1.64 µm) and higher storage module. The breaking force of FC with thermal stable SC-HIPE (average 64.95 g) was higher than that with thermal unstable SC-HIPE (51.05 g). The cohesiveness, adhesiveness and chewiness could be improved by adding thermal stable SC-HIPE, compared with pork fat. Additionally, combining sensory evaluation, the thermal stable SC-HIPE improved the gel quality, thus it could be completely replaced pork fat in the preparation of FC, which provided theoretical guidance for the preparation and application of fat substitutes.

Differential distribution of surface proteins/lipids between wheat A- and B-starch granule contributes to their difference in pasting and rheological properties.

The distribution of surface proteins/lipids and their effect on physicochemical properties of wheat A- and B-starch were investigated. Small B-starch with higher surface protein (~1.8 %) and lipid (~0.4 %) contents did not differ significantly from specific surface area of large A-starch (~0.2 % protein and ~0.1 % lipid), indicating surface lipids/proteins for starch are characteristic of their biological origin, not directly related to granule size. The surface of A-starch granule was an integrated membrane structure (lipids covered by proteins). B-starch showed a greater decrease in peak and trough viscosity (130 and 82 cP) than A-starch (99 and 52 cP) after removing surface proteins, perhaps because the presence of residual surface lipid as a membrane protected the rigidity of A-starch granule. B-starch showed a greater increase in consistency coefficient (K) (47.01 Pa·sn) than A-starch (20.33 Pa·sn) after removing surface lipids, possibly because the greater loss of surface lipid as complex with amylose in B-starch retarded retrogradation and reduced K. These results show that different distributions and contents of surface proteins/lipids between wheat A- and B-starch granule contribute to the pasting and rheological properties.

High-intensity ultrasound improved the physicochemical and gelling properties of Litopenaeus vannamei myofibrillar protein.

The effects of high-intensity ultrasound on the physicochemical and gelling properties of Litopenaeus vannamei (L. vannamei) myofibrillar protein (MP) were investigated. MP solutions were subjected to ultrasound treatment (power 100 W, 300 W, and 500 W). It was found that the carbonyl and free amino contents of MP increased significantly with increasing ultrasound power, accompanied by enhanced emulsification properties. The increase of free radical and carbonyl content indicated that ultrasound induced the oxidation of MP. With the increase of ultrasound power, it was found that the total sulfhydryl content of the shrimp MP decreased, but the surface hydrophobicity increased significantly, which might be closely related to the conformational changes of MP. Meanwhile, a significant increase of ß-sheet but a decrease of α-helix in the secondary structure of MP was observed with increasing ultrasound power, indicating that ultrasound treatment induced the stretching and flexibility of MP molecules. SDS-PAGE showed that L. vannamei MP consisted of myosin heavy chain, actin, myosin light chain, paramyosin and tropomyosin. Ultrasound treatment could lead to some degree of oxidative aggregation of MP. The results of rheological properties indicated that ultrasound treatment enhanced the viscoelasticity of MP and further improved the gel strength of MP gel. This study can provide a theoretical basis for the functional modification of shrimp MP and the processing of its surimi products.

Effect of phytic acid combined with lactic acid on color and texture deterioration of ready-to-eat shrimps during storage.

To retard the deterioration of texture and color of ready-to-eat (RTE) shrimps during storage, phytic acid (PA) and lactic acid (LA) were used to soak the shrimp prior to cooking. The factors affecting texture (water holding capacity, protein oxidation and degradation, and microstructure) and color (Maillard reaction and lipid oxidation) were determined separately. The free radical and copper ion content were also determined in order to investigate the regulation mechanism of phytic acid and lactic acid on the texture and color of RTE shrimps. It was found that the inhibitor-treated RTE shrimps showed better texture and color properties than the control group, and the compound inhibitor (PA + LA) showed a better inhibition effect than single inhibitor. In addition, PA and LA prevented the oxidation of RTE shrimps by scavenging free radicals and chelating copper ions, which in turn enabled the regulation of color and texture deterioration.

Nanocomplexes of curcumin and glycated bovine serum albumin: The formation mechanism and effect of glycation on their physicochemical properties.

Bovine serum albumin (BSA) and BSA-glucose conjugates (GBSAⅠ and GBSAⅠI) with different extent of glycation were complexed with curcumin (CUR). The formation mechanism of BSA/GBSA-CUR complexes and the effect of glycation on their physicochemical properties were investigated. Fluorescence quenching and FTIR analysis indicated that the BSA/GBSA-CUR nanocomplexes were formed mainly by hydrophobic interactions. XRD analysis demonstrated that CUR was present in an amorphous state in the nanocomplexes. BSA with a greater extent of glycation (BSA < GBSAⅠ

Inhibition of ultraviolet-induced sea cucumber (Stichopus japonicus) autolysis by maintaining coelomocyte intracellular calcium homeostasis.

Apoptosis plays a critical role in sea cucumber autolysis. To investigate the ultraviolet (UV)-induced apoptosis, sea cucumbers with and without injection of BAPTA-AM (cytosolic calcium chelator) were exposed to UV (15 W/m2) for 30 min. The results showed that UV irradiation caused several changes in sea cucumber coelomocytes, including calcium imbalance, abnormal morphology of endoplasmic reticulum, upregulation of pro-apoptotic proteins CRT, CHOP, and caspases 9 and 3, and downregulation of anti-apoptotic protein Bcl-2. A comparison between the two groups showed that injection of the calcium chelator into sea cucumbers helped maintain coelomocyte intracellular calcium homeostasis and suppressed other abnormal changes caused by ER stress, indicating apoptosis in sea cucumbers is mediated by calcium imbalance and follows the activation of the ER stress pathway. Therefore, this study broadens understanding of the apoptotic mechanism involved in sea cucumber autolysis, which is helpful in developing preservative agents for sea cucumbers.

CACLA-Based Trajectory Tracking Guidance for RLV in Terminal Area Energy Management Phase.

This paper focuses on the trajectory tracking guidance problem for the Terminal Area Energy Management (TAEM) phase of the Reusable Launch Vehicle (RLV). Considering the continuous state and action space of this guidance problem, the Continuous Actor-Critic Learning Automata (CACLA) is applied to construct the guidance strategy of RLV. Two three-layer neuron networks are used to model the critic and actor of CACLA, respectively. The weight vectors of the critic are updated by the model-free Temporal Difference (TD) learning algorithm, which is improved by eligibility trace and momentum factor. The weight vectors of the actor are updated based on the sign of TD error, and a Gauss exploration is carried out in the actor. Finally, a Monte Carlo simulation and a comparison simulation are performed to show the effectiveness of the CACLA-based guidance strategy.

Effect of hydroxyl radical induced oxidation on the physicochemical and gelling properties of shrimp myofibrillar protein and its mechanism.

Protein oxidation is considered as an important factor affecting the texture quality of surimi. In this work, the myofibrillar protein (MP) from shrimp (Penaeus vannamei) was subjected to a hydroxyl radical generating system at various concentrations of H2O2, to simulate the oxidative environment during surimi processing. After the hydroxyl radical oxidation, it was found that the carbonyl content, surface hydrophobicity, and MP aggregation increased. Meanwhile, the a-helix decreased, but ß-sheet increased after oxidation. The moderate oxidation led to a dense network microstructure, increased water holding capacity (WHC) and decreased water mobility, which ultimately enhanced textural (hardness and springiness increased by 0.51- and 0.06-fold, respectively) and rheological properties of MP gel (MPG). However, excessive oxidation could reduce the mechanical properties of MPG. The microstructure, WHC and water distribution played a key role in the mechanical properties of MPG. This study can provide a theoretical basis for processing of shrimp surimi products.

Effects of natural phenolics on shelf life and lipid stability of freeze-dried scallop adductor muscle.

Effects of natural phenolics on the shelf life of dried scallop adductor muscle predicted by accelerated shelf life testing (ALST) combined with Arrhenius model were investigated. This allows the food industries to reliably and rapidly determine the shelf life of dried shellfish species treated with antioxidants. The shelf life of dried scallop adductor muscle treated with antioxidants of bamboo leaves (AOB) and tea polyphenols (TP) was more than 1.70-fold that of dried control scallop adductor muscle. Thus, the highly nutritional value of dried scallop adductor muscle, based on its lipid constituents, is maintained during storage. OXITEST method further confirmed the improvement of lipid stability of antioxidant treated dried scallop adductor muscle by protecting polyunsaturated fatty acids, especially eicosapentaenoic and docosahexaenoic acids, against autoxidation. Moreover, the natural phenolics employed effectively limited lipid oxidation by breaking the autoxidative chain reaction and/or inhibiting free radical formation in dried scallop adductor muscle during storage.

[Development of transcutaneous jaundice predictor for the neonates].

Neonatal jaundice is a common neonatal disease. Severe jaundices lead to kernicterus that affects intellectual development of infants or even causes death. Timely and early prediction is vital to the treatment and prevention. This paper presents a jaundice predictor, which uses C8051F020 as the core of single-chip microcomputer (SCM) system with prediction algorithms proven by a large number of clinical trials. The jaundice predictor can reduce the incidence rate of jaundice, alleviate the condition of infants with jaundice, improve the quality of perinatal, with predicting pathologic neonatal jaundice effectively and calling attention to the prophylactic treatment. In addition, compared with the existing transcutaneous jaundice meters, the new predictor has a smaller size, a lighter weight, more user-friendly, and easier to use by hand-holding.