Nemipterus virgatus is one of the favorite marine fish in China. It is often required for the green and low-carbon surimi production for national food security. This study aims to investigate the effects of precision feedback microwave heating (PFMH) on the gel properties of Nemipterus virgatus surimi. A systematic analysis was conducted to measure the gel strength, water-holding capacity, textural properties, whiteness, moisture distribution, microstructure, protein distribution, and protein secondary structure of the surimi gels under different temperatures and heating durations of PFMH. Two-stage water bath heating is the control. The results indicated that the gel strength increased by 58.21% (6 855.66 g·mm) in the surimi gels heated by PFMH at 85 °C for 1 min, compared with the control group. The gel strength of surimi gels treated at 80 °C and 90 °C was lower than that of the control group. The hardness, chewiness, and adhesiveness of surimi gels treated with PFMH at 80 and 85 °C were enhanced by 12.70% to 36.39%, 6.37% to 22.04%, and 8.56% to 25.37%, respectively, indicating the high texture properties. There was no discernible color difference, although the whiteness of the surimi gels treated with PFMH decreased by 2.11% to 6.44%. The water-holding capacity of surimi gels treated with PFMH increased by 1.25% to 9.18%, indicating the strong binding between proteins and water to effectively reduce the water mobility. Low-field nuclear magnetic resonance and imaging revealed that the relaxation times of surimi gels treated with PFMH shifted significantly to the left, compared with the control group. The reddest imaging colors were observed in the samples heated at 85 °C for 1 min and at 80 °C for 3 min, indicating the highest proportion of immobile water. The PFMH was used to lock moisture within the surimi gels, thus promoting a uniform distribution of water. Furthermore, microstructural analysis showed that the surface of surimi gels treated with PFMH was smoother than that of the control group, indicating a denser network structure and more orderly pores. The surimi gel treated under PFMH at 85 ℃ for 1 min exhibited the smallest pores with uniform distribution. The highest Df value was 1.969 5 in the surimi gel heated at 85 °C for 1 min, indicating a more compact and uniform microstructure to effectively retain moisture. Confocal laser scanning microscopy showed that the more dispersed particles of protein were obtained in the surimi gel than in the control group. But there was a more uniform distribution of protein and the consistent particle size in the surimi gel treated at 85 ℃ for 1 min. The protein secondary structure reduced the α-helix content to 38.22%, while increasing the β-sheet content to 32.49% after the PFMH treatment at 85 °C for 1 min. The more ordered morphologies of the protein secondary structure effectively facilitated the transition of protein conformations toward a more structured state. Therefore, the PFMH heating also improved the surimi gel quality to reduce the wastewater discharge. The findings can provide theoretical references and technical support for the deep processing of Nemipterus virgatus.

This research aims to systematically investigate the influence of pulsed vacuum drying (PVD) parameters on the drying kinetics, physicochemical attributes, and volatile flavor profiles of red jujube slices. Various PVD parameters were evaluated, including drying temperatures (65, 70, and 75 °C), vacuum holding durations (10, 15, and 20 min), and atmospheric holding durations (2, 4, and 6 min). Hot air drying (HAD) was utilized as the control group. The experimental results demonstrated that the total drying duration was shortened significantly as the drying temperature escalated, whereas it was moderately extended with the prolongation of both vacuum and atmospheric holding times. The drying kinetics were attributed to the complex interplay between thermal energy transfer and the pressure-driven moisture diffusion in the PVD process. Color preservation was one of the most critical quality indicators for fruit processing. Once the treatment group was subjected to a drying temperature of 70 °C, a vacuum holding time of 15 min, and an atmospheric holding time of 6 min (designated as PVD-70 °C-15:6), the color preservation was characterized by the highest luminosity (L* value of 55.50) and the minimum total color difference (∆E* value of 1.97), indicating the most favorable appearance similar to the fresh samples. The macro-level observations were further supported by microstructural analysis via scanning electron microscopy. While the HAD-treated slices displayed a densely packed and collapsed cellular arrangement, leading to maximum hardness and diminished crispness. By contrast, the PVD-70 °C-15:6 samples shared a well-developed, uniform honeycomb-like porous structure to facilitate a better balance between low hardness and moderate crispness after the mitigation of structural shrinkage. Furthermore, the landscape of volatile flavor was dominated by the drying parameters. Radar plot analysis and Principal Component Analysis (PCA) indicated that there were significant (P<0.05) variations in the aromatic profiles under the different treatments. According to the headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), a total of 77 volatile compounds were identified and then quantified, including 11 acids, 14 esters, 42 hydrocarbons, 2 alcohols, 3 aldehydes, 1 ketone, and 4 other compounds; Among them, organic acids, with the relative content from 16.66% to 27.92%, were identified as the predominant contributors to the characteristic aroma of the red jujube slices. Notably, the PVD-70 °C-15:6 treatment demonstrated that the relative content of aldehydes and acids substantially increased by 33.55% and 21.82%, respectively, compared with the HAD control. A relatively stable acidic profile was obtained to promote the synthesis and retention of key aldehyde-based flavor precursors after the fluctuations of cyclic pressure in the PVD process. In the PVD-70°C-15:6 treatment, the optimal overall quality was achieved to effectively balance the drying efficiency with the preservation of the structural, aesthetic, and aromatic integrity of the red jujubes. The findings can also provide a robust theoretical and technical framework for pulsed vacuum drying in high-quality dehydrated functional foods.

The purpose of this study is to investigate the effects of the high-humidity hot-air impingement (HHAI) on the conformational transformation of collagen in the fish swim bladder. The HHAI treatment was also carried out at the different blanching temperatures (100, 110, and 120 ℃), relative humidities (20%, 30%, and 40%), and durations (4, 5, and 6 min). Some parameters were then captured to evaluate the performance of the treatment using an analytical approach. Water distribution and migration were characterized by the low-field nuclear magnetic resonance and nuclear magnetic resonance imaging. Protein structure and thermal stability were characterized by the Fourier transform infrared spectroscopy and the differential scanning calorimetry, respectively. Conformational shifts at the molecular level were further probed after the test. Protein conformation was characterized by fluorescence spectroscopy and ultraviolet spectroscopy. Protein surface properties were characterized by the surface hydrophobicity measurement (8-phenyl-1-naphthalenesulfonic acid fluorescence and contact angle). The microscopic structure was characterized by scanning electron microscopy, in order to link the microstructure to the macroscopic properties. The apparent viscosity and dynamic modulus were characterized by the rheological tests. Boiling water blanching was used as the control. The results showed that the optimal treatment conditions were 110 ℃, 30% humidity, and HHAI for 5 min. The results show that the product quality was enhanced under the optimal parameters. Compared with the control group, the proportion of the bound water reached 57.32%, thereby increasing by 19.77%. There was the most uniform distribution of the moisture. The water-holding capacity of the fish's swim bladder was also enhanced under the optimal parameters. Structural analysis revealed that there was a notable stabilization of the protein matrix. The content of β-sheet in the secondary structure of protein increased by 28.50%, and the thermal denaturation temperature increased by 8.12%, indicating the improved thermal stability. Surface property modifications were equally significant. The contact angle decreased by 34.97%, indicating the enhanced hydrophilicity of the protein. Microstructural and rheological data were provided for the strengthened protein network. The dense and porous microstructure was observed, where the apparent viscosity increased by 272.02%. Moreover, the storage modulus was significantly higher than the loss modulus (P < 0.05), indicating a more stable elastic network of the protein. Importantly, the HHAI non-optimal treatment group also outperformed the control group in all indicators. Specifically, the proportion of bound water increased by 6.29% to 16.04%, the content of β-sheet increased by 0.39% to 5.95%, the thermal denaturation temperature increased by 0.31% to 7.89%, and the apparent viscosity increased by 13.03% to 261.27%, whereas, the contact angle decreased by 8.51% to 34.97%, compared with the control group. Overall, the HHAI treatment significantly improved the quality of the fish swim bladder, compared with the conventional boiling. The water distribution was optimized to stabilize the protein secondary structure, and then enhance the thermal stability and the surface hydrophobicity. The technology effectively promoted the orderly rearrangement of the collagen molecules into a more stable and functional network. This finding can provide the theoretical reference and technical basis for the efficient processing of the fish swim bladder. The potential applicability can also be offered for the collagen-rich aquatic and food materials.

This study aims to investigate the effects of high-temperature high-humidity air impingement cooking (HHAIC) on enzyme inactivation characteristics and quality of Litopenaeus vannamei (L. vannamei). The activities of catalase (CAT), trypsin (TRY), polyphenol oxidase (PPO), and superoxide dismutase (SOD) in L. vannamei were determined under different temperatures (70, 90, 110 ℃) and HHAIC pretreatment durations (0, 45, 90, 135, 180, 225, 270, 315, 360 s). Kinetic models for enzyme inactivation were established using first-order kinetics model, Weibull distribution model, and Logistic model. The cooking process parameters were predicted through the kinetic models and a systematic investigation was made on the impacts of the color, texture, and antioxidant activity. The results showed that higher temperatures accelerated heat transfer rate at the early stage of HHAIC pretreatment. Under different temperatures, the changing trends of the internal temperature of L. vannamei were basically consistent, which could be generally divided into three stages. They were rapid-rate temperature rise stage, reduced-rate temperature rise stage, and constant-rate temperature rise stage, respectively. The relative activities of CAT, TRY, PPO, and SOD all showed a downward trend with the extension of HHAIC durations and the increase of temperature. The Logistic model could better fit the inactivation process of CAT and TRY at lower temperatures. At the same temperature, the coefficient of determination of the first-order kinetic model was the lowest compared with the Weibull distribution model and Logistic model, indicating that the PPO inactivation process did not conform to the simple unimolecule reaction mechanism. The relative activity of SOD (50.28%) was relatively high after 360 s of cooking at 70 ℃, which was related to the high thermal stability of SOD. The performance of the Weibull distribution model indicated a strong fit by the high coefficient of determination and low prediction error. Therefore, the Weibull distribution model exhibited higher accuracy for the inactivation of CAT, TRY, PPO and SOD by HHAIC pretreatment than the first-order kinetic model and Logistic model. The L*, a*, b*, ∆E and chromaticity values all exhibited a tendency to increase initially and then decrease. After four minutes of cooking at 90 ℃, the hue angle of L. vannamei was the smallest (62.51°), indicating that the color of the L. vannamei was most inclined to red under such condition. The hardness, gumminess and chewiness of L. vannamei first increased and then decreased during HHAIC pretreatmen, while the elasticity showed varying degrees of increasing and decreasing trends. After four minutes of cooking at 90 ℃, the hardness (18.56 N) and chewiness (31.70 mJ) of L. vannamei were relatively high, showing that the L. vannamei had better palatability under such condition. The astaxanthin from L. vannamei had a high scavenging capacity for ABTS free radical, while its scavenging capacity for OH free radical was generally weaker than that for ABTS and DPPH free radicals. The DPPH free radical and OH free radical scavenging rates reached the maximum values of 95.61% and 70.80% when cooked for four minutes at 90 ℃, respectively. Overall, the L. vannamei cooked at 90 ℃ for four minutes exhibited better quality, and this condition was determined as the optimal cooking condition after comprehensive consideration. The relative activities of CAT, TRY, PPO, and SOD showed extremely significant negative correlations (P < 0.01) with elasticity, L*, a*, and b* value, DPPH free radical scavenging rate, and OH free radical scavenging rate. The relative activities of CAT and TRY showed a significant negative correlations with chewiness (P < 0.05). However, the relative activities of CAT, TRY, PPO, and SOD showed no significant correlations with ABTS free radical scavenging rate (P > 0.05), while showed a negative correlation overall. In conclusion, this study can provide certain theoretical references and technical bases for the pretreatment and deep processing of L. vannamei products.

This study aims to explore the effects of radio frequency-assisted hot air drying (RF-HAD) on the drying characteristics and physicochemical properties of Litopenaeus vannamei (L. vannamei). Hot air drying (HAD) at 60 ℃ was taken as the control. A systematic investigation was also made to clarify the impacts on drying characteristics, water distribution, color, texture, astaxanthin content, antioxidant capacity, protein secondary structure, and microstructure under various drying temperatures (60, 70, and 80 ℃), and electrode gaps (107, 117, and 127 mm). The results showed that there was a dynamic variation in the internal temperature of L. vannamei during drying. The transverse relaxation time was adjusted to shorten the drying time by 47.22%-72.22%, compared with the HAD. The L. vannamei contained a high amount of the free water initially, and then evaporated, as the drying proceeded, leading to a great reduction in the free water content. At the last stage of drying, the bound water was the main component of the moisture in the L. vannamei, which was more difficult to remove. Therefore, the drying rate decreased, as the drying time increased. The relaxation time of strongly bound water T_2b value was significantly reduced (P<0.05) under the RF-HAD treatment, compared with the HAD. The RF-HAD L. vannamei tissue shared a stronger binding to water. The moisture of each component was removed continuously. At the same time, the immobile water was converted into bound water during RF-HAD. Additionally, the drying rate increased with the decrease of the electrode gap at the same RF-HAD temperature. There was a large proportion of the peak area that was occupied by bound water. Specifically, 107 mm treatment was more conducive to improving the drying efficiency. Besides, the L* value increased by 17.39%-21.70%, compared with the HAD. The RF-HAD treatment has enhanced the brightness of L. vannamei. Specifically, the L. vannamei dried at 60 ℃ with an electrode gap of 117 mm shared a higher L* value (51.23) and lower ∆E value (7.64), in order to better preserve the color of L. vannamei. The cohesiveness and chewiness of the L. vannamei after RF-HAD treatment were reduced by 34.88%-74.48% and 35.75%-79.49%, respectively, compared with the HAD, indicating improved palatability. Furthermore, the higher content of astaxanthin was observed at the same temperature of the RF-HAD, when the electrode gap was 117 mm, compared with 107 or 127 mm. The content of astaxanthin in the RF-HAD treatment groups at 70 and 80 ℃ was lower than that at 60 ℃. Specifically, the L. vannamei dried at 60 ℃ with an electrode gap of 117 mm shared the highest astaxanthin content (20.70 μg/g), indicating the slow degradation of astaxanthin. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging increased by 42.36% and 58.33%, respectively, at 60 ℃ with the electrode gap of 117 mm, compared with the 107 and 127 mm treatments, indicating the stronger antioxidant capacity and protein thermal stability. Scanning electron microscope (SEM) images revealed that the muscle fibers varied more outstandingly at the higher temperature and lower electrode gap. Moreover, the fractal dimension (1.923 0) at 60 ℃ with an electrode gap of 117 mm was quite lower, compared with the 107 and 127 mm treatments. The microstructure of the L. vannamei dried was relatively simple. Pearson’s correlation analysis showed that there was a correlation between the color and texture. Besides, the astaxanthin content was highly significantly positively correlated with the elasticity (P<0.01), although it was highly significantly negatively correlated with the hardness (P<0.01). Meanwhile, there was a significant positive correlation between DPPH scavenging and elasticity (P<0.05). This finding can provide the theoretical reference and technical assistance for the deep processing of the L. vannamei.

In order to explore the effects of different drying methods on the physicochemical properties and microstructure of Penaeus vannamei, the drying characteristics, color, texture, water distribution, astaxanthin content, antioxidant capacity and microstructure of P. vannamei were analyzed after medium-short wave infrared drying (MSWID) or hot air drying (HAD). The results showed that with the increase in drying temperature, the moisture content of P. vannamei decreased gradually, and MSWID could reduce the drying time of P. vannamei by 16.67% and make its color brighter compared with HAD at 70 ℃. The hardness, gumminess and chewiness of P. vannamei were significantly increased with increasing drying temperature (P < 0.05), but the springiness was not significantly affected by drying temperature (P > 0.05). According to magnetic resonance imaging (MRI) results, the rate of water migration during MSWID was faster than that during HAD. Besides, the results of microstructure observation indicated that the muscle fiber of P. vannamei became looser and more porous after MSWID compared with HAD. For both drying treatments, the α-helix relative content of shrimp proteins first increased and then decreased, and the β-fold relative content showed a contrary trend. The astaxanthin content of MSWID dried shrimp was lower than that of HAD dried shrimp, and so was the antioxidant capacity. The quality of MSWID dried P. vannamei was better than that of HAD dried P. vannamei, indicating MSWID to be a promising drying method for P. vannamei.

Here air impingement drying (AID) was introduced to dry the desalted sea cucumber for less drying time and better quality of dried products. A systematic investigation was implemented to clarify the impacts of AID temperature (50, 60, and 70 ℃) and air velocity (4, 6, and 8 m/s) on the moisture distribution, moisture state, microstructure, hardness, and saponin content of desalted sea cucumber. Conventional hot air drying (HAD) was also taken as a control. The results revealed that the drying rate of desalted sea cucumbers increased significantly, as the drying temperature increased. The drying time of desalted sea cucumber was also reduced by 6.67%-33.33% at 6 m/s air velocity and various AID temperatures, compared with the HAD at 60 °C. The air velocity shared an insignificant effect on the drying time of desalted sea cucumbers (P>0.05) at the same temperature (60 ℃), particularly for the extended drying time (12-13 h) with the increased air velocity (4-8 m/s). The microstructure showed that the high AID temperature was beneficial to increase the porous structure of the material surface, leading to accelerated water migration. More and larger porous structures were observed on the surface of AID sea cucumber samples under the same conditions (the temperature was 60 ℃ and the air velocity was 6 m/s), compared with the HAD ones. As such, the AID drying rate was accelerated as well. However, the high air velocity was used to prevent the surface deformation (such as crusting) of desalted sea cucumber, thus reducing the structure porosity, which hindered the water migration and lowered the drying rate. The relaxation time of immobilized water in the AID sea cucumbers moved faster toward the short relaxation time, and then the peak amplitude decreased significantly, compared with the HAD. The low freedom of water molecules also led to a decrease in drying rate, with the extension of drying time. There was a weaker signal of proton density in the AID sea cucumbers. The water content was lower under the same conditions (drying time was 6 h). The water migration rate of AID sea cucumbers was higher than that of HAD, indicating that the AID was beneficial in shortening the drying time. The hardness of dried sea cucumber increased first and then decreased, with the increase in AID temperature and air velocity. The maximum hardness (494.25 N) was recorded at an AID temperature of 60 ℃ and 6 m/s air velocity. The saponin content (1.36-1.79 μg/g dry matter) of AID sea cucumbers increased with the increase in temperature, while there was no significant change in the air velocity. The saponin content of AID sea cucumber samples increased by 50% under the same conditions, compared with HAD. The temperature of 70 ℃ and the air velocity of 6 m/s were the better conditions for the AID sea cucumbers, in terms of drying efficiency and quality. The AID can be expected to improve the drying efficiency and ingredient retention rate of desalted sea cucumbers. The finding can provide theoretical reference and technical support for better drying quality.

This study aims to explore the effects of precision feedback microwave heating (PFMH) on the physicochemical properties of myofibrillar proteins (MPs) of Nemipterus virgatus. The MPs were collected from the Nemipterus virgatus as the research subject. Traditional water bath heating (40 ℃ for 30 min, and 90 ℃ for 20 min) was taken as the control. A systematic investigation was also made on the impacts of PFMH on the protein's turbidity, surface hydrophobicity, fluorescence intensity, ultraviolet (UV) absorbance thermal stability, gel electrophoresis patterns, surface morphology, and surimi gel chemical interactions under various temperatures and heating durations. Results showed that the turbidity and surface hydrophobicity of MPs significantly increased after PFMH treatment, compared with the control group. Both increases also indicated protein aggregation and denaturation, which were critical to understanding the variations in the internal structure of the protein. Specifically, the turbidity of MPs reached 0.78 when heated under S₈₅A conditions, which was an increase of 129.41%, compared with the control group (0.34). Meanwhile, the surface hydrophobicity increased to 177.45 μg, representing a 52.51% increase, compared with the control group (116.35 μg). As such, the PFMH treatment altered the tertiary structure of the protein. The lowest intensity of fluorescence was at S₈₅A, indicating that the PFMH treatment enhanced intermolecular interactions within the protein. Specifically, the PFMH treatment led to the dynamic fluorescence quenching of protein oxidative aggregates in the excited state, resulting in reduced fluorescence intensity. There was a higher fluorescence intensity of myofibrillar protein treated with PFMH at low temperatures (80 °C for 2 and 3 min), compared with the control. The reason was possibly that the rapid PFMH treatment caused some tryptophan residues to be buried within the MPs molecules. Conversely, the UV absorbance exhibited an upward trend, indicating that the PFMH heating induced the conformational changes in the protein structure. The exposure of more aromatic residues led to more effective UV light. Thermal stability was assessed using differential scanning calorimetry (DSC). The results showed that the PFMH treatment significantly enhanced the thermal stability of MPs. Furthermore, the degradation temperature (T_d) of the MPs under S₈₅A conditions reached the maximum of 62.20 ℃, an increase of 13.65%, compared with the control group (54.73 ℃). The enthalpy change (ΔH) decreased from 0.43 J/g in the control group to 0.03 J/g, representing a 93.02% reduction. As such, the PFMH treatment effectively prevented the thermal denaturation and degradation of MPs at elevated temperatures. Gel electrophoresis patterns and atomic force microscopy (AFM) images further revealed the structural changes induced by PFMH treatment. The MPs also unfolded to form a dense gel network structure under the S₈₅A condition. Additionally, the AFM images indicated that the size of MPs aggregates increased, while the quantities decreased after PFMH treatment at 90 °C. Chemical interactions revealed that the maximum content of hydrogen bond was 3.06 g/L after heating at S₈₅A conditions, which was 14.61% higher than that of the control group (2.67 g/L). Meanwhile, the hydrophobic interactions and disulfide bonds increased by 105.60% and 97.80%, respectively. However, the ionic bonds decreased after PFMH treatment, compared with the control group. The cross-linking and aggregation of MPs were promoted to form a more stable and compact protein structure. In conclusion, these findings demonstrated that the PFMH treatment significantly affected the physicochemical properties of MPs in Nemipterus virgatus. The protein denaturation and aggregation also induced the structural changes to enhance the thermal stability and the formation of dense gel networks. The heating processing of surimi products can also offer potential reference data for the future application of PFMH technology.