Abstract:In order to explore the impact of pH and temperature on the temporal sweetness profile of eight different sweeteners (sucrose, fructose syrup, maltitol, sorbitol, oligofructose, steviol glycoside 00, steviol glycoside 07 and steviol glycoside 14), this study first determined the concentration of the other seven sweeteners that had equivalent sweetness as 5 g/dL sucrose under neutral conditions at room temperature through paired comparison test, magnitude estimation method and single factor variance analysis. Further, the time-intensity method was used to describe the temporal sweetness profile of eight sweeteners under three conditions including room-temperature-neutral (pH 7.0, 25 ℃), room-temperature-acidic (pH 4.5, 25 ℃) and low-temperature-neutral (pH 7.0, 4 ℃). It was found that both acidity and low temperature could decrease the maximum sweetness intensity for most of the samples. Acidic conditions had a significantly higher reduction effect on fructose syrup and steviol glycoside samples than low-temperature conditions, while low-temperature conditions had a more significant reduction effect on sugar alcohols, sucrose and oligofructose. In addition, the overall sweetness duration of each sample was also inhibited and shortened under acidic and low-temperature conditions, with a more significant impact from low-temperature conditions. Therefore, acidic or low-temperature conditions could both inhibit the sweetness release intensity or release time of different sweeteners, but to varying degrees. Overall, in terms of temporal sweetness profile and change trends under the three conditions, the closest performance to sucrose was sorbitol, followed by fructose syrup and oligofructose.

Abstract:bstract： To investigate the changes in dielectric properties of duck egg white during rapid pickling, duck eggs were pickled directly, or soaked in vinegar (with acetic acid volume fraction of 1.45%) or wine (with ethanol volume fraction of 3.23%) for 20 minutes before pickling. The dielectric properties of the egg white were measured using coaxial probe technology at frequencies from 0.3 to 3.0 GHz after being pickled by different methods for 5, 10, 15, 20, and 25 days. The relationship between the dielectric properties, penetration depth, and salt content of the egg white was analyzed at frequencies of 915 MHz and 2 450 MHz. The results showed that the pickling rate of salted duck eggs increased after soaking in acetic acid and wine, and the pickling rate of the vinegar-soaked group could be accelerated by 40% compared with the control group (direct pickling) (P<0.05). As the frequency increased, the dielectric constant and dielectric loss of egg white decreased. However, the rate of decrease was higher at low frequencies (0.3~1.0 GHz) compared to that at high frequencies (1.0~3.0 GHz). During the pickling process, the dielectric loss increased with the increase of salt content. Moreover, the vinegar-soaked group exhibited higher dielectric loss than both the control group and the wine-soaked group, for the same pickling duration. At 915 MHz and 2 450 MHz, the dielectric constant of the wine-soaked group showed a decreasing trend as the salt content increased, while the control group and vinegar-soaked group showed an opposite trend. As the pickling time increased, the penetration depth of egg white gradually decreased at both 915 MHz and 2 450 MHz. Additionally, the penetration depth at 915 MHz was greater than that at 2 450 MHz. The correlation between penetration depth and salt content in egg whites was fitted with a polynomial equation, and a good correlation (R²>0.90) was found between the two in the wine-soaked group A.

Abstract:This experiment focused on the carcass muscle of squid to study the effects of four thawing methods, including high voltage static electric field thawing (4 ℃, 3.8 kV), static water thawing, flowing water thawing, and thawing in room temperature air, on the quality characteristics of squid muscle. The effects of different thawing methods on the thawing rate, thawing loss rate, cooking loss rate, pH, color, water content, total volatile basic nitrogen (TVB-N), texture characteristics, total viable count (TVC), and other indices were analyzed on muscle quality. The results showed that the muscle quality of squid thawed by high-voltage electrostatic field was better than the other three methods. The thawing rate was 2.89 ℃/min, and the whiteness value was 24.21. Water content was 67.44 g/hg, and TVB-N was 2.76 mg/hg. The total number of colonies was 2.74 lg(CFU/g). Additionally, the thawing loss rate, and cooking loss rate were lower. This method could reduce the loss of muscle juice during thawing, and delay the decline of muscle pH levels, consequently preventing an increase in muscle acidity, and also inhibit the growth of microorganisms. However, the squid thawed by high-voltage electrostatic field had a higher moisture mass fraction but a shorter shelf life.

Abstract:This research prepared a selective adsorbent on the basis of SiO2 glass beads bound with zeranol monoclonal antibody and the method of immunoaffinity microextraction in a packed syringe and high performance liquid chromatograph-tandem mass spectrometry (IA-MEPS-LC-MS/MS) was further developed to detect six kinds of zeranols (ZERs) in milk. Milk samples were centrifuged, and the middle layer was extracted with IA-MEPS syringe and washed by ultra-pure water before eluted with methanol. The eluent was concentrated and then re-dissolved by mobile phase. Finally, the sample was detected by LC-MS/MS, separated on a C₁₈ column with the mobile phase of water and acetonitrile. Matrix-matched external standard method was used for quantification. The linearity of six ZERs was good within 0.1~100.0 ng/mL, and the correlation coefficient was 0.994 3~0.996 2. The average recoveries ranged from 50.40% to 68.34% at the addition level of 1 ng/g, the intra-day and the inter-day RSDs were 4.87%~17.64% and 7.04%~18.75%, respectively. The limit of detection (LOD) and limit of quantification　(LOQ) of this method were 0.05 ng/g and　0.2 ng/g, respectively.

Abstract:To study the effect of catechins concentration on the lipid and protein oxidation, microbial infection degree, color and hardness during the storage period of shrimp paste, the peroxide value (POV), thiobarbituric acid value (TBA), and the carbonyl and sulfhydryl content (mass molar concentration) of protein for samples at different time points were analyzed to examine the inhibitory effects of catechins on the oxidation of lipid and protein in shrimp paste. The degree of microbial infection of shrimp paste was characterized by the level of volatile base nitrogen (TVB-N) and the total colony count. Changes in the edible quality of shrimp paste were determined by the whiteness value, hardness, pH and sensory score. The results showed that the addition of catechins could delay the increase of shrimp paste’s POV value, TBA value, carbonyl molar concentration and the decrease of sulfhydryl molar concentration, while inhibiting the growth and reproduction of microorganisms. During storage, the whiteness of shrimp paste showed an initial increase followed by a decrease, while the hardness showed an increasing trend. There was no significant change in pH value. The results show that the addition of catechins at 0.20 g/kg and above could improve the quality of shrimp paste during storage, indicating a good application prospect.

Abstract:The pre-packaged, caramel-flavored, boiled-and-dried sunflower seeds were used as the experimental object. The accelerated shelf life testing (ASLT) method was adopted to analyze pre-packaged samples with or without deoxidizers. The changes in the acidity value, peroxide value, and sensory indicators of boiled-and-dried sunflower seeds under the conditions of 40 ℃ and 50 ℃ were also investigated. A storage period prediction dynamic model was established, which predicted the product shelf life and evaluated the correlation between the sensory indicators and acidity and peroxide value indicators of the product. The results showed that with the prolongation of storage time, the acid value index of cooked dried sunflower seed products with or without deoxidizer added increased significantly at 40 ℃ and 50 ℃, and the peroxide value index showed an inconsistent fluctuating upward trend. Through fitting regression analysis and constructing a storage kinetics model for boiled-and-dried sunflower seeds, the theoretical shelf life of pre-packaged boiled-and-dried sunflower seeds with deoxidizer added could reach 352 days, while the theoretical shelf life of similar products without deoxidizer added could be 176 days. Furthermore, the sensory performance of sunflower seeds was more sensitive to the change of acid values while the tendency of abrupt change in peroxide values was more consistent with the degree of sensory deterioration of the product in the later stages of storage.

Abstract:Spinach was utilized as the test material to study the effect of delayed pre-cooling on the nutrition and quality of spinach throughout cold chain circulation process. The fresh spinach was placed for 0, 1, 5, and 9 hours, and then implemented differential pre-cooling to 4 ℃, respectively. The spinach was transported and sold with both film and non-film packaging at 4 ℃. The spinach was also kept refrigerated at home for 2 days, and changes in nutrition and quality were measured. The results showed that after 6 days of cold chain circulation at 4 ℃, the spinach that underwent delayed pre-cooling for 0 hours and was packaged with film achieved the best nutritional and quality results. The sensory evaluation was 7.2, and the weight loss rate was 4.25%. And the mass fractions of vitamin C, chlorophyll, and soluble protein were 4.66 mg/hg, 0.73 mg/g, and 0.35 mg/g, respectively. Therefore, the spinach should be pre-cooled in the field within 1 hour after harvesting, and then packaged with anti-fog film and transported at 4 ℃ using cold chain circulation to maintain the freshness and storage quality of spinach.

Abstract:To explore the changes in food quality indicators of air-dried crucian carp products during different processing stages, a low-salt salting and natural air-drying process was adopted to determine quality indicators such as salt mass fraction, water activity, weight loss rate, pH, and more during the processing, supplemented by sensory evaluation. The results showed that during the processing, the salt mass fraction of the air-dried crucian carp products increased gradually, while water activity and weight loss rate showed a decreasing trend. Meanwhile, the pH value decreased gradually in the salting stage and began to rise again in the air-dried stage. On the fourth day of drying, the sensory score reached the highest point, with a salt mass fraction of (3.720±0.079)%, a water activity of 0.67, a weight loss rate of 64.92%, and a pH value of 6.50. In the correlation analysis, water activity was significantly correlated with salt mass fraction and weight loss rate.

Abstract:In order to explore the optimal extraction conditions, composition and antioxidant capacity of total saponins from Clinacanthus nutans, single factor and response surface methodology were used to optimize the ultrasonic-assisted extraction conditions of total saponins from Clinacanthus nutans. The composition of total saponins under the optimal extraction conditions was analyzed by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) and the antioxidant activity was detected. The results indicated that the optimal extraction parameters included 92% volume fraction of ethanol, solid-liquid ratio of 1 g∶44 mL, extraction time of 0.6 h, and extraction temperature of 66 ℃, which yielded a total saponin extraction rate of 2.30%. Five triterpene saponins were then identified. The antioxidant experiment showed that the total saponins of Clinacanthus nutans had strong antioxidant activity, and there was a good correlation between their mass concentration and their ABTS+ scavenging rate, DPPH+ scavenging rate, and Fe3+ reduction ability. The corresponding semi-inhibitory concentrations to free radical scavenging rate were 0.407 mg/mL and 0.562 mg/mL, respectively. The results provide beneficial reference information for further development and utilization of saponins from Clinacanthus nutans.

Abstract:Through investigating the contents of heavy metals arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg) in tsamba produced by different grinding methods in four cities in Tibet (Shannan, Xigaze, Nyingchi and Lhasa), and conducting a comprehensive analysis and evaluation of pollution levels, reliable data support could be provided to enhance the quality and safety level of tsampa production and strengthen quality and safety supervision. A total of 101 samples of tsamba produced in different modes were collected from four cities in Tibet. And inductively coupled plasma mass spectrometry was utilized to detect and analyze five heavy metals in tsamba samples, and to evaluate their quality and safety. Among 101 tsamba samples evaluated using the comprehensive pollution index of tsamba quality grading standard, both electric mill and water mill methods yielded safe levels of heavy metals including As, Cd, Cr, Pb, and Hg in tsamba, based on the evaluation results of single factor pollution index and comprehensive pollution index in the production of tsamba prepared by different grinding methods. Based on the evaluation results of the single factor pollution index and comprehensive pollution index in the production of tsamba in different cities, it could be concluded that the heavy metal Pb in tsamba in Shannan city is basically clean, and As, Cd, Cr, and Hg are all safe. The heavy metal As in tsamba in Xigaze city is basically clean, and Cd, Cr, Pb, and Hg are all safe. The heavy metal Pb in tsamba in Nyingchi city is basically clean, and As, Cd, Cr, and Hg are all safe. The heavy metals Pb, As, Cd, Cr, and Hg in tsamba in Lhasa city are all safe. According to the Nemerow comprehensive pollution level evaluation, the comprehensive pollution index levels of other heavy metals in the four cities are all safe. Therefore, the comprehensive pollution index levels of heavy metals such as As, Cd, Cr, Pb, and Hg in tsamba in four cities of Tibet are all safe.

Abstract:Menaquinone-7 (MK-7) is one of the significant components of vitamin K2. Previous studies found that the highest yield of MK-7 under shake flask culture condition was much higher than that cultured under stirred tank reactor (STR). In order to reduce the differences caused by scaling up from the shake flask to 3 L STR, computational fluid dynamics (CFD) and dynamic absorption method were used to compare the shear stress and oxygen transfer performance of the shake flask and STR at different rotational speeds. The effects of oxygen supply and shear stress on the growth of BS20 and the synthesis of MK-7 were also explored. The results showed that sufficient oxygen supply could promote the growth of BS20 and the synthesis of MK-7, however, excessive shear stress would destroy the bacterial cell and reduce the yield of MK-7. Based on the above results, under the culture condition of the 3 L STR, the lower stirring speed (400 r/min) was used to ensure low shear force, while the oxygen-enriched air (oxygen volume fraction 55%) was used to improve the oxygen supply level. The yield of MK-7 reached 296 mg/L, which was an increase of 152% compared to the control batch (with an oxygen volume fraction of 21%), and reached 79% of the highest level cultured in shake flask. In this study, reducing the stirring speed and increasing the oxygen volume fraction of the supplied air in the STR can effectively improve the performance of the shear-sensitive but highly aerobic fermentation process.

Abstract:The effects of high pressure thermal sterilization (HPTS) combined with glucose on the sterilization effect and the impact on the inner membrane of Bacillus subtilis spores were investigated. The sterilization effect, ion release, intimal permeability, and membrane structure stability of Bacillus subtilis spores were studied through plate counting, conductivity measurement, flow cytometry analysis, and Fourier transform infrared spectroscopy analysis. The results showed that the inactivation rate of spores reached 4.64 lg with HPTS treatment of 600 MPa and 75 ℃, while the addition of 60% mass fraction glucose reduced the inactivation rate of spores by 2 lgs. As the mass concentration of glucose increased, the ion release of spores decreased significantly (P<0.05). The result of flow cytometry showed that the proportion of the positive region (M2) in the sample under 600 MPa and 75 ℃ with 60% mass fraction glucose treatment was 92.88%, indicating a significant increase in the intimal permeability of spores (P<0.05). By analysis of infrared spectroscopy in the 3 000~2 800 cm-1 band, it was found that compared to the HPTS treatment alone, HPTS combining with glucose resulted in a significant reduction in the absorption peak intensity of the characteristic functional group —CH₂/—CH₃ in the inner membrane of spores. Glucose contributed to the stability of inner membrane structure of spores. Therefore, the mass concentration of glucose has an important influence on the inactivation effects of HPTS on Bacillus subtilis spores.

Abstract:To investigate the protective effect and mechanism of chlorogenic acid (CGA) on UVB damaged human immortalized epidermal cells (HaCaT), a cellular ultraviolet damage (photo-aging) model and different treatment methods of CGA were established using MTT assay. The UV absorption of CGA was detected by the microplate reader. The level of apoptotic cell death was determined by flow cytometry analysis. The free radical scavenging ability of CGA was detected by ABTS method. The results showed that when the UVB radiation dose was 21.6 mJ/cm² and the concentrations of CGA were 100.000 and 150.000 μmol/L respectively, after pre-treatment for 1 hour and cell cultivation for 12 hours, CGA exhibited strong absorption in the UVB spectrum range of 280~320 nm. Both 100.000 μmol/L and 150.000 μmol/L CGA could significantly reduce UVB-induced cell apoptosis. The ABTS⁺ free radical scavenging capacity of UVB-treated cells could be effectively increased by 150.000 μmol/L CGA, reaching 53%. Therefore, CGA has strong anti-skin aging activity in the UVB-induced HaCaT photo-aging model, which might be related to its UV absorption and antioxidant ability. This provides a scientific basis for the development and utilization of food resources rich in CGA.

Abstract:To improve the biological activity of food flavone isoorientin (Iso) and provide a basis for preventing liver injury induced by benzo (a) pyrene (BaP), Iso and its silver nanoparticles (Iso-AgNPs) were used to investigate to the damage of HL-7702 human liver cells caused by BaP, a harmful product of food prepared under high temperature. The hepatoprotective effect of Iso-AgNPs was detected by MTT, trypan blue staining, fluorescence labeling, flow cytometry, and Western blotting based on the three programmed death modes including apoptosis, autophagy and pyroptosis. The results showed that compared with Iso, Iso-AgNPs could better inhibit the damage of HL-7702 huamn liver cells activity induced by BaP, promote cell proliferation, and significantly inhibit the apoptosis, autophagy and apoptosis of HL-7702 huamn liver cells. Therefore, Iso-AgNPs could improve the biological activity of Iso and prevent liver cell damage.