The denaturation of proteins (particularly myosin) due to freezing can lead to the deterioration of Penaeus vannamei. The purpose of this study was to verify the antifreeze protective effects of polyphenols screened by a molecular docking technique, and to explore their interactions with myosin after freezing treatment. It was found that the screened polyphenols could significantly increase the freezing rate and unfreezable water content of shrimp paste. The results of fluorescence spectra indicated that the hesperetin to myosin quenching process included both dynamic and static quenching, and it was primarily bound to myosin through hydrophobic interactions; The quenching of myosin by both dihydroquercetin and mangiferin was static quenching, and they were bound to myosin mainly by hydrogen bonds and van der Waals forces; All three of these polyphenols had only one binding site on myosin. Surface hydrophobicity indicated that all four polyphenols were engaged in non-covalent binding (hydrophobic interactions) with myosin. Infrared spectra demonstrated that the addition of these four polyphenols significantly increased the α-helix content of myosin. They also reduced the myosin particle size, zeta potential, and protein degeneration degree. Scanning electron microscopy revealed that the four polyphenols reduced the degree of aggregation, while more uniformly distributing the myosin particles. These observations provide a basis for the screening of polyphenols and further research into the protective mechanism of polyphenols on frozen myosin.

Freeze-thaw (F/T) and electrochemistry both are environment-friendly and efficient sludge treatment technologies. In this study, the sludge samples were frozen at - 15 °C, and 20% g/gTss activated carbon (AC) was added to the dissolved sludge. Finally, the uniformly mixed sludge was treated at a voltage of 15 V for 25 min. During the experiment, the effect of F/T on the floc structure was analyzed by a laser particle analyzer and scanning electron microscope. F/T treatment improved the dewatering performance of the sludge and promoted the aggregation of sludge flocs into larger particles either. At the same time, the median diameter (D50) increased from 45.27 to 128.94 μm. AC was added to the thawed sludge solution before electrochemical treatment (EP). The conductivity of AC enhanced the effect of EP, thereby cracking the sludge flocs. Therefore, the three-dimensional excitation-emission matrix (3D-EEM) intensity of tightly bound extracellular polymeric substances (TB-EPS) decreased significantly. The protein in TB-EPS decreased from 54 to 33%, and the D50 was also reduced to 105.3 μm. The final specific resistance of filtration and water content were reduced by 96.39% and 32.17%, respectively. The dehydrated cake elemental analysis showed that increased AC improved the sludge cake\'s combustion efficiency significantly. Moreover, the preliminary economic analysis indicated that the cost of this research was low, which implied the potential application value of combined treatment.

Extracellular polymeric substances (EPS) are important components of activated sludge, whose content and composition have important effects on the macro-physical properties of sludge. In this study, the response of EPS in sludge to temperature (-40-200 °C) was systematically investigated using XAD resin fractionation, variable-temperature infrared spectra (VTIS) and two-dimensional correlation spectroscopy (2D-COS). The relationships between the molecular structure of EPS and the macro-physical properties (rheological property and dewatering performance) of waste activated sludge (WAS) at varying temperature were also established. During the freezing treatment, the solubilization of biopolymers and destruction of the hydrophilic functional groups (hydroxy, amino and carboxyl) resulted in the production of small organic matters, which enhanced EPS hydrophobicity and reduced electrostatic repulsion of sludge, and subsequent dewaterability improvement. For the hydrothermal treatment, the EPS transformation showed a two-stages reaction including stage I (70-120 °C) and stage II (>120 °C). Stage I (70-120 °C), a plenty of hydrophilic functional groups (hydroxy, amino and carboxyl) in EPS were exposed via the solubilization of biopolymers, which enhanced electrostatic repulsion of sludge and EPS hydrophilicity, and subsequence in deterioration of sludge dewaterability and fluidity. However, at stage II (>120 °C), the high temperature caused hydrolyzation of macromolecular organic matters in completely, in which the secondary structure of the protein was destroyed, causing the peptide chain to unfold. In addition, the reduction of α-helix and β-sheet content and intensified Maillard reaction decreased electrostatic repulsion of sludge, thus resulted in the improvement of sludge dewaterability and fluidity. This study enriched the theoretical basis of the optimal control of sludge treatment based on temperature regulation.

Auricularia auricula-judae is an edible nutrient-rich mushroom, which is a traditional medicinal resource in China. It is known that environment stimuli will affect the production of melanin by A. auricula-judae, but the mechanism of the effects of freezing treatment on melanin accumulation remains unknown. In the present study, the synthesis of melanin in A. auricula-judae was analyzed by physiological assays and a proteomics approach. Our findings showed that a longer freezing treatment causes a lighter color of A. auricula-judae fruiting bodies. The proteomic analysis showed that proteins involved in glycolysis/gluconeogenesis, tyrosine metabolism, ribosome, and arginine biosynthesis might contribute to the color differences in the A. auricula-judae after freezing treatment. This work will be expected to provide valuable information on the physiological and molecular mechanisms of freezing treatment on the color quality of A. auricula-judae.

The effect of freezing combined with alkali treatment on physicochemical property of konjac glucomannan (KGM) with different molecular weight was investigated in this work. The properties and structure of degraded KGM was characterized by means of intrinsic viscosity measurement, atomic force microscope (AFM) and Fourier transformation infrared (FT-IR). The results suggested that the intrinsic viscosity of KGM solution gradually decreased during the ultrasonic treatment. The AFM observation indicated that KGM with lower viscosity average molecular weight had smaller height and lateral diameter of molecules. The main repeating units of the KGM chain could not be destroyed no matter how long the KGM was sonicated. Rheometrical studies revealed that with increasing alkali concentration from 0% to 0.36%, both viscosities and shear stress of deacetylated konjac glucomannan (Da-KGM) system were increased and moduli G\' were substantially higher in either freezing or unfreezing samples. Da-KGM system performed a solid-like behavior (G\' > G\'\') along the frequency range after freezing treatment. With increasing sonication time, both viscosity and shear stress of unfreezing samples were decreased while had an inverse effect for freezing treated samples. The modulus G\' and G\'\' declined for unfreezing samples but rise significantly for freezing treated samples with increase of sonication time.

The aim of this study was to investigate the influence of length of freezing time (-18°C for 5 or 24 h) on the quality characteristics of tofu. The yield and moisture content of tofu obtained from frozen soybean were lower than control tofu. Tofu made from frozen soybeans showed higher hardness, gumminess and chewiness than the control. Freezing treatment also made the microstructure of the tofu more uniform than the control. However, after 24-h freezing, hardness decreased and the microstructure of tofu appeared to form pores. Sensory evaluation showed that mouth-feel decreased with an increase of freezing time. Among all of tofu frozen at -18°C, 5-h freezing treatment showed the highest overall acceptability. These results indicate that the length of time that soybeans are frozen before making tofu affects the quality of tofu.

To ensure the safety of produce, including blueberries, elimination of potential pathogens is critical. This study evaluated the efficacy of antimicrobial washes when coupled with frozen storage against Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes on wild blueberries. Inoculated blueberries were sprayed with antimicrobial solutions at different concentrations for various contact times (chlorine dioxide -2.5, 5, 10, and 15 ppm for 10 s, 1, 5, and 10 min; chlorine -100, 150, and 200 ppm for 10s, 1, 5, and 10 min; lactic acid 1 and 2% for 5, 10 and 20 min) and following treatment, stored at -12 °C for 1 week. Compared to antimicrobial washing alone, the additional freezing significantly reduced pathogens (P < 0.05). Concentrations of all three antimicrobials combined with freezing reduced L. monocytogenes to undetectable levels (detection limit < 1 log CFU/g). The greatest reduction of E. coli O157:H7 (4.4 log CFU/g) and Salmonella (5.4 log CFU/g) was achieved by 2% lactic acid or 200 ppm Cl2 followed with frozen storage. These antimicrobials maintained the visual quality of blueberries and did not leave detectable residues. In conclusion, antimicrobial washes, when combined with frozen storage, effectively reduce the risk of pathogen contamination on blueberries.

The effect of freezing on functionality of native and sodium dodecyl sulfate (SDS)-treated wheat starches was investigated, with the aim of understanding the role of water absorption during freezing process. SDS is one of most efficient detergents to remove non-starch components (such as proteins and lipids) for starches but does not cause any apparent damage on granular structure. Slow swelling could be converted to rapid swelling by SDS washing, indicating higher water absorption. Freezing process induced slight roughness on starch granules but the non-starch components content was little affected. Combined SDS+freezing treatment significantly decreased both amylose and proteins non-starch components contents, which was accompanied with high gelatinization temperatures, melting enthalpy, and pasting viscosities. A smaller bread specific volume was obtained from SDS+freezing-treated starches while the crumb firmness significantly increased (p<0.05). SDS mainly extracted the surface components from starch granules, leading to high water absorption and making granules sensitive to the freezing treatment.

The impact of freezing on the wheat starches with different particle size was studied using a range of characterization methods including X-ray diffraction, differential scanning calorimetry, the Rapid Visco Analyser and a reconstitution dough system. Wheat starches were fractionated into A- and B-type granules, and then subjected to freezing/thawing treatment for 3 cycles. The freezing treatment did not cause apparent damage on A-type granular surface but induced cracked structure on B-type granules. It facilitated materials such as amylose, proteins, and lipids leaching from starch granule and an increase in gelatinization temperatures, melting enthalpy, and pasting viscosities. A smaller bread specific volume was obtained from freezing-treated B-granules while the crumb firmness significantly increased (p>0.05). No marked differences were observed in the counterparts of A-granules after freezing treatment. It seemed that the B-type granules were more sensitive to the freezing/thawing treatment, thus facilitating structural transformations from dough to bread. Results indicated that the deterioration in frozen bread quality derived from starch could be minimized by increasing the A-granules content.