Steamed stuffed buns are fermented wheat flour products. However, they have often suffered from quality deterioration of the dough during freezing, frozen storage, and subsequent re-steaming. The quality defects are also characterized by the texture hardening, reduced elasticity, surface cracking, and sensory acceptance. Mechanical damage caused by ice crystal growth can also weaken the gluten network, leading to the retrogradation of starch. This study aims to systematically investigate the synergistic regulation of soluble soybean polysaccharides (SSPS) and lard (LD) on the quality improvement of frozen and re-steamed stuffed bun dough. Three types of steamed buns were selected as the typical fillings—pork (representing a high-fat and high-protein system), cabbage and mushroom (representing a high-moisture and high-fiber system), as well as red bean paste (representing a high-sugar and high-starch system). The applicability of the additives was evaluated in complex food matrices. A multi-dimensional analytical approach was employed to characterize the physicochemical properties and microstructural evolution of the dough. The textural characteristics were quantified using a Texture Analyzer, while the water mobility and distribution were monitored via low-field nuclear magnetic resonance (LF-NMR). Furthermore, the protein secondary structures and starch crystallinity were identified using Fourier transform infrared spectroscopy (FTIR) and X-ray Diffraction (XRD), respectively. The microscopic morphology of the dough was visualized using scanning electron microscopy (SEM). The results demonstrated that the combined addition of SSPS and LD significantly improved the eating quality of the re-steamed stuffed bun dough, compared with the control or single-addition groups. Texture profile analysis indicated that the hardness and chewiness were reduced significantly, whereas the elasticity and resilience were enhanced (P<0.05). LF-NMR analysis revealed that the additives significantly altered the state of water within the dough matrix. Specifically, the bound water content in pork, cabbage, and mushroom, and red bean paste bun doughs increased by 29.14%, 26.23%, and 43.97%, respectively. The synergistic effect of SSPS and LD effectively inhibited water migration to reduce the proportion of free water, thereby mitigating the mechanical damage to the gluten network caused by ice crystallization. At the molecular level, chemical analysis showed that the SSPS-LD treatment promoted the conversion of free sulfhydryl groups (-SH) into disulfide bonds (S-S), significantly increasing the disulfide bond content. The additives facilitated the polymerization of gluten proteins, thus enhancing the stability of the network through covalent cross-linking. FTIR spectra further indicated that the gluten secondary structure was represented by a transition from disordered random coils to ordered structures, specifically an increase in the proportion of β-sheets. XRD patterns confirmed that while the crystal pattern remained unchanged, the crystallinity of the starch was significantly reduced in the SSPS-LD group, indicating an effective inhibition of starch retrogradation. Microstructural observations via SEM verified that the SSPS-LD group possessed a denser, more continuous, and uniform gluten network, with significantly improved pore distribution, compared with the coarse and porous structure of the control group. In conclusion, the SSPS primarily enhanced the water retention to form the strong hydrogen bonding networks with gluten and starch. While the LD functioned as a lubricant to interact with amylose for the lipid-starch complexes, which hindered the starch recrystallization. The synergistic effect of SSPS and LD was realized to stabilize the overall network structure via combined covalent and non-covalent cross-linking. These findings can provide a solid theoretical basis for polysaccharide-lipid interactions to reduce the quality deterioration in functional ingredients and wheat flour products of complex food systems.

Frozen whole wheat bread can often cause the quality decline after reheating. This study aims to explore the effects of reheating modes on the gluten protein aggregation, eating quality, and flavor of the frozen whole wheat steamed bread. Bread samples with the different additions of the whole wheat flour were frozen at -18 ℃. A systematic comparison was also implemented to explore the effects of natural thawing, steam reheating, microwave reheating, and microwave steam reheating on the bread quality. The whole wheat bread was characterized by Fourier transform infrared spectroscopy (FTIR), fluorescence spectroscopy, scanning electron microscopy (SEM), low field nuclear magnetic resonance (LF-NMR), and GC-IMS. The results showed that the steam recuperating energy effectively maintained the texture characteristics of frozen whole wheat bread, with the best hardness index (3 032.86 N). The structural characterization showed that the steam reheating treatment was significantly reduced the content of -SH in the gluten protein of whole wheat bread (P<0.05). The oxidation of free -SH in gluten protein also promoted to form the disulfide bonds. The elasticity and resilience of the product (P<0.05) were improved significantly after treatment. Natural thawing also promoted the protein aggregation behavior to maintain the electrostatic repulsion of gluten proteins. Hydrophobic analysis showed that the surface hydrophobicity of gluten protein was significantly improved (P<0.05), as the amount of whole wheat flour (WWF) added increased. The exposure of hydrophobic groups was exacerbated after reheating, due to the unstable gluten network structure caused by WWF during freezing; Among them, microwave reheating also exhibited low hydrophobicity, due to the short-term elevated temperature and starch gelatinization masking hydrophobic groups. While the steam reheating expanded the gluten network under hot steam, indicating the higher surface hydrophobicity. The scanning electron microscope showed that the exposure outside was represented for the starch particles in the whole wheat bread, naturally thawed after frozen storage. The gluten network and starch particles were wrapped more closely with each other after the steam reheating and microwave steam reheating, compared with microwave reheating. Grain size analysis showed that there was the a minimum grain size of gluten protein in the whole wheat bread of 0WWF, 50WWF, and 100WWF, which were 558.50, 592.86, and 615.30, respectively, under steam reheating. The microwave steam composite treatment was reduced the conformational changes of the whole wheat proteins after the freezing. The fluorescence spectra of proteins showed the high fluorescence intensity in both microwave and steam reheating, indicating that microwave steam reheating was a relatively mild treatment. At the same time, the LF-NMR analysis showed that the high proportion of whole wheat was reduced the free water content. The mMore water existed in the bound state, indicating that microwave reheating and microwave steam reheating were conducive to the water quality of whole wheat bread. In addition, the flavor analysis confirmed that steam reheating shared the little effect on the whole wheat bread; Microwave reheating and microwave steam reheating were reduced the concentration of irritating flavor substances, such as the diethylene glycol dimethyl ether, benzaldehyde, ethylbenzene, butyraldehyde, and 2-hexanone, with the increasing concentration of fruity flavor substances, such as the propyl propionate and 3-methylethyl butyrate. The sensory evaluation showed that the microwave steam reheating effectively maintained the color, shape, and taste quality of whole wheat bread with the different amounts of whole wheat flour (0, 50, and 100WWF), especially when 100% whole wheat flour was added. There was the synergistic effect of microwave rapid internal heating and steam humid environment; Microwave reheating shared the higher scores in the appearance and odor dimensions, due to the heating speed. But the overall quality was still better in the microwave steam group. This finding can also provide an important theoretical basis to optimize the reheating process of frozen whole wheat flour products.

With its high aspect ratio and renewable characteristics, nanocellulose not only exhibits excellent biodegradability, but also forms hydrogen bonds between abundant hydroxyl groups (-OH) on the surface and group materials when used as a reinforcing filler. It can also significantly enhance the mechanical properties and thermal stability of the composites. In this work, soy hull nanocellulose (SHNC) was prepared by ultrasonic-assisted acid hydrolysis, and PVA/PUL/SHNC composite film were prepared by solution casting method using soy hull nanocellulose, polyvinyl alcohol (PVA) and pullulan (PUL) as raw materials. The chemical structure of the composite film was characterized by Fourier transform infrared spectroscopy (FT-IR), and the changes of the vibration peaks of the characteristic functional groups were analyzed to verify the molecular interaction and chemical compatibility between the components. The crystallinity of the composite film was tested by X-ray diffractometer (XRD), and the microscopic morphology of the composite film was observed by scanning electron microscope (SEM), including key morphological parameters such as surface uniformity, phase separation phenomenon and cross-sectional layered structure. In terms of thermal stability evaluation. The thermogravimetric analyzer (TGA) was used to test the temperature programmed test of the material. The thickness, mechanical properties, contact angle, water content, water vapor permeability, storage stability and bacteriostatic effect on Escherichia coli of the composite film were tested. Finally, the composite film was applied to the preservation of chilled chicken at 4 ℃ to verify the preservation effect of the composite film on chilled chicken. The results of FT-IR and XRD showed that there was a strong hydrogen bond between SHNC and PVA, PUL, and no crystal was formed. SEM analysis showed that there was a good compatibility between SHNC and the composite film components. The surface and cross section showed a dense structure, and no phase separation or structural defects, such as rupture and holes, were observed. At the same time, SHNC increased the tensile strength and elongation at break of the composite film by 67.1% and 100.7%, respectively, indicating that SHNC had a significant enhancement effect on the mechanical properties of the composite film (P<0.05). TGA test results showed that the maximum thermal degradation temperature of PVA/PUL/SHNC-3 composite film containing SHNC was 317.58 ℃, which was significantly higher than that of PVA/PUL/SHNC-0 (302.41℃) (P<0.05). This is due to the formation of intermolecular hydrogen bonds between SHNC and PVA, PUL to stabilize the structure of the composite film. In addition, SHNC also significantly improved the hydrophobicity of the composite film (P<0.05). The water contact angle experiment showed that SHNC increased the water contact angle of the composite film from 38.8° to 66.4°, confirming the significant optimization of its hydrophobicity (P<0.05). Similarly, SHNC was uniformly dispersed in the composite film, creating a curved channel for the movement of water, which could effectively hinder the migration of water. Therefore, the water vapor permeability of the composite film was reduced from 0.408 8 g·mm/(m²·h·kPa) without SHNC to 0.271 5 g·mm/(m²·h·kPa), showing excellent water vapor barrier properties. Bacteriostatic experiments showed that the minimum inhibitory concentration of PVA/PUL/SHNC composite film against Escherichia coli was 3 % SHNC. Moreover, the preservation experiment showed that the PVA/PUL/SHNC-3 composite film separated cold fresh chicken from the outside world through its excellent barrier properties, effectively prevented the raw contact with bacteria in the air and slowed down the protein and lipid oxidation of cold fresh chicken, effectively slowed down the growth of the total number of colonies in cold fresh chicken, the increase of TVB-N value and pH value, maintained the freshness of cold fresh chicken and significantly prolonged the shelf life (P < 0.05). Therefore, the composite film prepared by blending SHNC with PVA and PUL has the potential to be developed as a packaging material for cold fresh chicken, and provides a reference for the development of new methods for the preservation and storage of cold fresh meat.

Hydrogels have attracted much attention for fresh preservation in the field of food at present, because of their low toxicity, biocompatibility, and degradability. However, mechanical properties and fatigue resistance have limited the application in food preservation. In this study, the multifunctional nanocellulose/polyvinyl alcohol/sodium alginate (SCNFs/PVA/SA) composite hydrogels were prepared with excellent mechanical properties and fatigue resistance using low-temperature (-20 ℃) cyclic freezing-thawing. The raw materials were also taken as soy hull nanocellulose (SCNFs), polyvinyl alcohol (PVA), and sodium alginate (SA). The microstructure of the composite hydrogel was observed by scanning electron microscopy (SEM). The chemical structure and crystallinity were identified by Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD). The thermal stability was obtained by a thermogravimetric analyzer (TGA). The mechanical properties of the composite hydrogel were determined by a texture analyzer. Finally, the composite hydrogels were used for the preservation applications of fresh pork at 4 ℃. The SEM images showed that the regular and uniform three-dimensional network structure was formed inside the composite hydrogel, which was conducive to the mechanical stability of the composite hydrogel. The FT-IR results showed that the SCNFs, PVA, and SA with the high aspect ratio formed hydrogen and ester bonds in the composite hydrogel. More functional groups were exposed in the cyclic freezing-thawing process at -20 ℃, indicating the high cross-linking density between the monomers. The XRD results further proved that the crystallinity in the composite hydrogels was enhanced by the presence of hydrogen bonds and the addition of SCNFs. The TGA results showed that the SCNFs increased the thermal stability of the composite hydrogels. The reason was that the SCNFs strengthened the hydrogel matrix, or the interaction of internal hydrogen bonds enhanced the stability of the composite hydrogels. At the same time, the composite hydrogel shared low density, water content, and water solubility, but with excellent swelling degree. The uniform three-dimensional network was formed internally, where the SCNFs were cross-linked with PVA and SA by hydrogen and ester bonds. The -20 ℃ low-temperature cyclic freezing-thawing also caused the chain entanglement among monomers, indicating the high crosslinking density. The mechanical tests showed that the elongation at break and tensile strength of the composite hydrogel were 230% and 17 kPa, respectively. The compressive strength was 70 kPa under 70% stress, indicating great toughness (170 kJ/m³). Furthermore, the composite hydrogel still had excellent mechanical properties (tensile strength of 12 kPa) after five cycles of stretching under the 70% strain, indicating excellent fatigue resistance. The high tensile strength and fatigue resistance were attributed to the uniform three-dimensional network structure of the composite hydrogel after the addition of SCNFs. The pork preservation showed that the composite hydrogel maintained the stability of pork color to prevent the loss of internal moisture of pork in the rapid change of the internal pH value of pork. At the same time, the composite hydrogel was used to isolate the outside air, in order to inhibit the growth of bacteria inside pork and the oxidation of unsaturated fatty acids and protein inside pork. The composite hydrogel was also used to extend the shelf life of pork to 10 days. Therefore, the high tensile, toughness, and fatigue-resistant composite hydrogel can be expected for the food packaging, in order to extend the shelf life of frozen meat products. The composite hydrogel can also fully meet the needs of refrigerated meat products. A new type of preservation material can be served to ensure food quality and safety. In addition, the composite hydrogel can also be applied in the food preservation industry of packaging and refrigerated meat products, due to the low cost, simple preparation, and strong reproducibility.