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.