In this study, braised pork belly was frozen at different temperatures (−18, −38, and −80 ℃), and the resulting quality changes were evaluated in terms of water-holding capacity, texture, color, moisture distribution and microstructure. The results showed that freezing led to a significant reduction in the moisture content of braised pork belly. After thawing, the water-holding capacity of the −80 ℃ frozen group was 86.49%, which was significantly higher than that of the −18 ℃ and −38 ℃ groups (P < 0.05), and was close to that of the fresh sample (89.30%). The results of low-field nuclear magnetic resonance (LF-NMR) confirmed that freezing at low temperatures delayed the migration of immobilized water (T₂₂) to free water (T₂₃), thereby maintaining the water-holding capacity of the product. In terms of texture, the hardness, springiness and chewiness of the lean part were significantly lower than those of the control group (P < 0.05), while those of the fat part showed an increasing trend. The texture quality of the −80 ℃ frozen group was significantly better than that of the other groups (P < 0.05). Microstructural observations revealed that freezing at −80 ℃ effectively inhibited the growth of ice crystals and reduced damage to muscle fiber structure (P < 0.05). The porosity between muscle fiber bundles was only 6.47%, significantly lower than that of the −18 ℃ (11.67%) and −38 ℃ (9.25%) groups. After thawing, the fat droplets were more uniformly distributed in the −80 ℃ group, with a smaller relative area of 30.53% compared with the −18 ℃ (39.74%) and −38 ℃ (32.67%) groups. The b* value of the lean layer and the L* value of the fat layer in the −18 ℃ freezing group were significantly higher than those in the other treatment groups (P < 0.05). Different freezing temperatures had no significant effect on the a* value of braised pork belly or the b* value of the fat layer (P > 0.05). In conclusion, freezing at −80 ℃ was more effective in preserving the water-holding capacity and textural properties of braised pork belly, thereby maintaining its overall quality.

To investigate the regulatory effect of 1-methylcyclopropene (1-MCP) treatment on the quality and edible period of kiwifruit during cold storage and subsequent shelf life, ‘Jintao’ kiwifruit was treated with three concentrations of 1-MCP (0 (control), 0.3, and 0.6 μL/L). The fruits were stored at 0 ℃ for five months and then transferred to shelf-life conditions at 20 ℃. Key quality parameters including fruit firmness, total soluble solids (TSS) content, titratable acidity (TA) content, soft fruit rate, decay incidence, and edible period were systematically measured and analyzed. The results showed that both 1-MCP treatments effectively delayed the quality deterioration of ‘Jintao’ kiwifruit during cold storage by maintaining high firmness, suppressing the rapid accumulation of TSS, slowing down the reduction in TA, and significantly reducing the respiration intensity and ethylene production. During the shelf-life, the edible period of both the control and 0.3 μL/L groups was 7 days compared to only 5 days for the 0.6 μL/L group. Notably, treatment with 0.6 μL/L 1-MCP resulted in the occurrence of “zombie fruit” accompanied by significantly increased soft rot incidence, with the decay incidence by the end of shelf life being 74.44%, 1.59 times that of the control group. In conclusion, 0.3 μL/L 1-MCP treatment is beneficial for maintaining the quality and extending the edible period of ‘Jintao’ kiwifruit after long-term cold storage. In contrast, 0.6 μL/L 1-MCP treatment leads to abnormal ripening symptoms such as shortened edible period and increased decay incidence, as well as poor quality stability, making it unsuitable for long-term cold storage of kiwifruit.

In order to study the effect of superchilling storage on the sensory quality and postmortem lactic acid metabolism in pork, pork tenderloin was stored at superchilling (−1 ℃) or chilling (4 ℃) temperature immediately after slaughter. At 0.5, 2, 6, 12, 24, 72, 120 and 168 h, quality indicators including drip loss, color and pH, as well as the activities of major enzymes involved in glycolysis and related metabolic pathways were determined. The results showed that superchilling storage effectively reduced the quality deterioration of pork and slowed down the rate of glycolysis and lactic acid metabolism. During 0.5–12 h postmortem, some of the nine enzymes tested including hexokinase, phosphofructokinase and lactate dehydrogenase were significantly inhibited (P < 0.05). From the perspective of post-mortem metabolism, superchilling temperature can effectively inhibit the activity of glycolytic enzymes, delay the accumulation of lactic acid and the reduction in meat pH, and improve the quality deterioration of pork during storage.

An extraction and purification method for soluble polyphenol oxidase (sPPO) and membrane-bound polyphenol oxidases (mPPO) from Agaricus bisporus was developed involving temperature-induced phase partitioning, fractional precipitation with ammonium sulfate, and DEAE anion exchange chromatography. The purity, molecular mass and enzymatic reaction kinetics of purified PPO were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Native-PAGE and Michaelis-Menten equation. The specific activities of sPPO and mPPO toward catechol were 6912.88 and 19092.94 U/mg, and increased by 12.20 and 10.86 times, respectively, compared with that of crude PPO. The results of enzymatic reaction kinetics showed that the catalytic activities of sPPO and mPPO toward different substrates were greatly different and were higher toward catechol. mPPO had a stronger affinity to the substrate catechol and a higher reaction rate than sPPO. The optimum pH and temperature for both PPO enzymes were 6.8 and 30 ℃, respectively. This study may lay a foundation for future research on mass spectrometry identification and enzymatic properties two forms of PPOs from A. bisporu and inhibition of enzymatic browning caused by PPO.

In order to study the effect of intermittent ozone treatment on the storage quality and preservation of kiwifruit, ‘Hayward’ kiwifruit were fumigated with different concentrations (0, 21.4, 42.8 and 64.2 mg/m³) of ozone once every seven days during storage at (0.0 ± 0.5) ℃. Quality indexes and the antioxidant enzyme activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) were measured regularly during storage. The results showed that compared with the control group, ozone treatment at all concentrations effectively reduced fruit mass loss rate, soft fruit rate and decay rate, inhibited the increase of total soluble solid (TSS) and malondialdehyde (MDA) contents, delayed the decrease of titratable acid (TA) content and fruit hardness, and maintained higher vitamin C (VC), total phenol and flavonoid contents. The preservative effect of ozone at 42.8 mg/m³ was better than those at 21.4 and 64.2 mg/m³ concentrations. After 140-day storage, the hardness and VC content in the 42.8 mg/m³ treatment group were 76.92% and 43.10% higher than those in the control group, respectively. The peak values of catalase (CAT) and peroxidase (POD) activity were 36.53% and 89.31% higher than those of the control group, respectively. Ozone treatment also effectively controlled the soft fruit rate and decay rate of kiwifruit during the shelf-life period. On the 9th day, the decay rate of the 42.8 mg/m³ treatment group was 16.67%, which was 63.77% lower than that of the control group. It is concluded that intermittent ozone treatment at a concentration of 42.8 mg/m³ can effectively slow down the senescence process and improve the storage quality and nutritional value of kiwifruit.

The effects of immersion freezing and air freezing at different temperatures (-18 and -38 ℃) on the quality of braised beef with potato were studied by physicochemical measurements, microstructural observation and sensory evaluation. The results showed that freezing at -38 ℃ maintained better quality of braised beef with potato compared with freezing at -18 ℃, and immersion freezing was significantly superior to air freezing. The freezing time of beef and potato in the dish under -38 ℃ immersion freezing was shortened by 96.02% and 97.34%, respectively, compared with air freezing at -18 ℃, and the time required to pass through the maximum ice crystal formation zone for beef and potato was 9.67 and 10.92 min, respectively, suggesting improved freezing rate of the dish. Under this condition, the L^*, a^* and b^* values of beef and potato were closer to those of the unfrozen dish; the hardness and elasticity of beef were significantly higher than those of the other frozen treatment groups (P < 0.05), and the shear force was 25.35 N, which was closer to that of the unfrozen sample (26.70 N), indicating good toughness of beef; the hardness of potato was 341.95 g, which was significantly higher than that of (P < 0.05) air-frozen samples, indicating good texture. Scanning electron microscopy (SEM) showed that beef muscle fibers were not broken after immersion freezing at -38 ℃, the gap between muscle fiber bundles was the smallest, arranged in an orderly manner; the cell contour of potato was clear and compact. The overall sensory score of the immersion-frozen sample was higher than that of the air-frozen one, and the sensory scores of beef and potato in the dish after -38 ℃ immersion freezing were 88.80 and 86.80 points, respectively, indicating higher acceptability. These findings provide a theoretical basis for the development of freezing preservation technologies for industrialized Chinese dishes.

In order to investigate trends in the odor profiles of different parts (cap and stipe) of Tricholoma matsutake during the shelf-life, the present study used an electronic nose and gas chromatography-ion mobility spectrometry (GC-IMS) combined with principal component analysis (PCA) and cluster analysis to analyze the changes of volatile flavor substances in T. matsutake at different points of the shelf-life. The results showed that a total of 48 volatile organic compounds (VOCs), including 10 aldehydes, 6 alcohols, 5 ketones, 4 sulfur-containing compounds, 9 esters, 2 acids, 3 alkenes, 9 other volatile substances such as heterocyclic compounds, and 15 unidentified volatile compounds, were detected. The stipe contained a richer variety of volatile substances than the cap. In general, the types and contents of volatile substances in T. matsutake continued to decrease during the shelf-life period. The inflection point of volatile substances occurred after around 24 h for the cap, and after both around 12 and 48 h for the stipe. In conclusion, the combination of electronic nose and GC-IMS can be used to quickly and intuitively analyze the differences in volatiles between the cap and stipe of T. matsutake at different time points of the shelf-life, thereby helping to determine the freshness of T. matsutake.

To investigate the effect of static magnetic field-assisted freezing (SMAF) on beef quality, quality traits of beef Longissimus dorsi muscle frozen at -18 ℃ and different magnetic field intensities (0, 2, 4, 6, 8 and 10 mT) were comparatively analyzed. The results showed that compared with the control group, SMAF-6, 8, and 10 treatments significantly shortened the phase transition time by 15%, 25%, and 6.7%, respectively (P < 0.05). SMAF treatment effectively improved the water-holding capacity (WHC) of beef (thawing loss, cooking loss and centrifugal loss), and reduced the color difference (ΔE value) (P < 0.05), but had no significant effect on the pH or thiobarbituric acid reactive substance value (P > 0.05). In addition, the results of shear force and myofibrillar fragmentation index (MFI) were consistent, indicating that SMAF treatment maintained the shear force of beef. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that SMAF treatment could reduce the decrease in protein content of meat after freezing and thawing. In summary, freezing under appropriate static magnetic field intensity (8 mT) can save time, improve the WHC of muscles, reduce the protein loss, and thus improve beef quality.

This study compared the effectiveness of genetic algorithm-back propagation neural network (GA-BPNN) and response surface methodology (RSM) in optimizing the high-pressure ultrasound-assisted enzymatic extraction of collagen from sheep skin to determine the optimal process parameters. The results showed that GA-BPNN had superior performance in model fitting and prediction compared to RSM. The optimal extraction parameters were as follows: high pressure holding time of 23 min, ultrasound time of 22 min, enzyme dosage of 3.2%, and hydrolysis time of 222 min. Under these conditions, the extraction rate of collagen from sheep skin was (80.5 ± 1.6)%, which is 40% higher than that of the traditional papain method. The results of ultraviolet-visible (UV-Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy demonstrated that the structure of the extract collagen was complete.