AFB1 Microbial Degradation by Bacillus subtilis WJ6 and Its Degradation Mechanism Exploration Based on the Comparative Transcriptomics Approach.

Aflatoxin pollution poses great harm to human and animal health and causes huge economic losses. The biological detoxification method that utilizes microorganisms and their secreted enzymes to degrade aflatoxin has the advantages of strong specificity, high efficiency, and no pollution inflicted onto the environment. In this study, Bacillus subtilis WJ6 with a high efficiency in aflatoxin B1 degradation was screened and identified through molecular identification, physiological, and biochemical methods. The fermentation broth, cell-free supernatant, and cell suspension degraded 81.57%, 73.27%, and 8.39% of AFB1, respectively. The comparative transcriptomics analysis indicated that AFB1 led to 60 up-regulated genes and 31 down-regulated genes in B. subtilis WJ6. A gene ontology (GO) analysis showed that the function classifications of cell aggregation, the organizational aspect, and the structural molecule activity were all of large proportions among the up-regulated genes. The down-regulated gene expression was mainly related to the multi-organism process function under the fermentation condition. Therefore, B. subtilis WJ6 degraded AFB1 through secreted extracellular enzymes with the up-regulated genes of structural molecule activity and down-regulated genes of multi-organism process function.

Silver metallization-triggered liposome-embedded AIE fluorophore for dual-mode detection of biogenic amines to fight food freshness fraud.

To combat food freshness fraud, it is urgent to develop a method which could realize the detection of biogenic amines (BAs) present in food. In our study, we developed a colorimetric and ratiometric fluorescence dual-mode sensor which integrated with silver metallization-based response system of AIE liposome + OPD + RSM + Ag+ toward BAs in foods for fighting freshness fraud. With the hydrolysis from the alkaline of BAs to resorcinol monoacetate (RSM), the production resorcinol (RS) could metallize silver ion (Ag+) to silver atoms (Ag0) which could lead to a BAs concentration-dependent decrease of the oxidation product 2,3-diaminophenothiazine (DAP) of Ag+ to o-phenylenediamine (OPD). As a result, the dual-mode sensor has a low detection limit and wide linear range in the spiked detection of soy products, pork and milk samples for BAs. Thus, providing a reliable method for food safety and forestalling food freshness fraud.

Effects of pullulanase enzymatic hydrolysis on the textural of acorn vermicelli and its influencing mechanism on the quality.

The effect of pullulanase enzymatic hydrolysis time on the textural properties of acorn vermicelli was investigated by texture analyzer. And the influencing mechanism was revealed by exploring the physicochemical properties of acorn starch under the optimum enzymatic hydrolysis time by texture analyzer, scanning electron microscopy, X-ray diffraction and brabender viscograph. After acorn starch was hydrolyzed by pullulanase for 14 h, acorn vermicelli had excellent textural properties. In addition, the enzymatic hydrolysis transformed the acorn starch from spherical particles with smooth surface to polygonal particles with rough surface, as well as transformed the crystal structure of acorn starch from C-type to B-type. Compared with native acorn starch, enzyme hydrolyzed acorn starch had higher amylose content, better freeze-thaw stability, lower swelling power and, breakdown viscosity, stronger gel strength and, higher light transmittance. These excellent properties contributed to the exceptional textural properties and quality of acorn vermicelli. The results of this study may provide valuable information on the preparation of acorn vermicelli.

Preparation of Pickering emulsion gels based on κ-carrageenan and covalent crosslinking with EDC: Gelation mechanism and bioaccessibility of curcumin.

Pickering emulsions stabilized by zein/carboxymethyl dextrin nanoparticles were added to the κ-carrageenan-based gel matrix to prepare emulsion gels via EDC - induced covalent crosslinking. Texture, WHC and freeze-thaw stability of the emulsion gels increased after crosslinking. The Confocal laser scanning microscope and SEM suggested that droplet clusters could be observed in gel with higher concentration of emulsion. The rheological measurements indicated that the viscosity and gel-like structure were relied on crosslinking agent and emulsion concentration. The photothermal stability of curcumin was significantly enhanced after crosslinking. In addition, in vitro digestion study suggested that the bioaccessibility of curcumin in emulsion gel crosslinked was lower compared to emulsion gel without crosslinking agent. These studies might facilitate the preparation of emulsion gels with excellent stability for bioactive compounds delivery in food and pharmaceutical applications.

Preparation and characterization of zein/carboxymethyl dextrin nanoparticles to encapsulate curcumin: Physicochemical stability, antioxidant activity and controlled release properties.

In this work, zein/carboxymethyl dextrin nanoparticles were successfully fabricated at different zein to carboxymethyl dextrin (CMD) mass ratios. Zein/CMD nanoparticles with the negative charge and the smallest size (212 nm) were formed when the mass ratio of zein to CMD was 2:1, exhibiting improved encapsulation efficiency of curcumin (85.5%). Electrostatic interactions, hydrogen bonding and hydrophobic interactions were main driven forces for nanoparticles formulation and curcumin encapsulation. Fourier transform infrared spectroscopy determined curcumin might be partially embedded in CMD during encapsulation. The spherical structures of zein/CMD nanoparticles and curcumin-loaded zein/CMD nanoparticles were observed by transmission electron microscopy. The photothermal stability and antioxidant activity of curcumin were significantly enhanced after be loaded in zein/CMD nanoparticles. Furthermore, encapsulation of curcumin in zein/CMD nanoparticles significantly delayed the release of curcumin in simulated gastrointestinal fluids. These results indicated that zein/CMD nanoparticles could be effective encapsulating materials for bioactive compounds in food industry.

Preparation, characterization, and encapsulation capability of the hydrogel cross-linked by esterified tapioca starch.

The modified starch-based hydrogels were prepared by crosslinking modified starch with sodium trimetaphosphate. Modified starch was obtained by esterification of tapioca starch with maleic anhydride. The degree of substitution (DS) increased significantly from 0.078 to 0.258 as the content of maleic anhydride increased from 6.67% to 33.33%. Fourier transform infrared spectroscopy demonstrated that starch was successfully esterified. In addition, the thermal properties of modified starch-based hydrogels were investigated by differential scanning calorimeter and thermogravimetry analysis, which proved that hydrogels had better thermal stability. Esterified starch-based hydrogels showed excellent pH sensitivity by measuring of swelling degree. When DS was 0.250, the adsorption capacity and encapsulation efficiency of starch-based hydrogels were 399.23 µg/g and 80%, respectively, which exhibited satisfactory embedding properties for curcumin. Therefore, esterified tapioca starch-based hydrogels could be as the encapsulating materials to protect bioactive substances, which provided a theoretical basis for their application in food field and pharmaceuticals industry.

Chitosan hydrochloride/carboxymethyl starch complex nanogels stabilized Pickering emulsions for oral delivery of ß-carotene: Protection effect and in vitro digestion study.

ß-Carotene was encapsulated in the Pickering emulsions stabilized by chitosan hydrochloride - carboxymethyl starch (CHC-CMS) nanogels. During ultraviolet radiation and storage, the retention of ß-carotene in Pickering emulsions was higher than that of other formulations, such as Tween 80 stabilized emulsions (TEs) and bulk oil. The Pickering emulsions were found to be stable during thermal treatment. Meanwhile, lipid oxidation was delayed in Pickering emulsions compared to TEs and bulk oil. The vitro digestion results suggested that the free fatty acids (FFA) released were below 30% for all Pickering emulsions, which indicated that a physical barrier was formed by CHC-CMS nanogels to restrain the lipid hydrolysis. The bioaccessibility of ß-carotene in Pickering emulsions was higher than that in bulk oil. This research helped establish a connection between the physicochemical properties of CHC-CMS stabilized Pickering emulsions with their applications in the protection effect and oral delivery of bioactive compounds.

Exploration of the binding between ellagic acid, a potentially risky food additive, and bovine serum albumin.

Ellagic acid (EA), a natural plant polyphenol, is usually used as a functional additive in variety of health foods. However, the potential toxicity of EA to human health should be paid enough attention. To clarify its biological toxicity in vivo, this study explored the binding mechanism of EA with bovine serum albumin (BSA) by means of spectroscopic approaches and molecular docking insimulative physiological conditions. The results showed that the mixture of BSA with EA could spontaneously cause the formation of BSA-EA complex through electrostatic interaction under simulative physiological conditions (0.01 mol·L-1Tris-HCl, 0.015 mol L-1 NaCl, pH = 7.4). Molecular docking experiments revealed that EA was primarily bound to the hydrophobic pocket of the site I (subdomain IIA) of BSA. It has been reported that the binding of small functional molecules to serum albumins remarkably impacts their absorption, distribution, metabolism, and excretion features. Therefore, this study might be helpful for human to have an in-depth understanding of the biological effect of EA in vivo and guide human to take it safely and reasonably.

Physicochemical Properties, Crystallization Behavior and Oxidative Stabilities of Enzymatic Interesterified Fats of Beef Tallow, Palm Stearin and Camellia Oil Blends.

Properties, crystallization behavior and oxidative stabilities of enzymatically catalyzed interesterified fats were investigated in this study. Interesterified fats were catalyzed by Lipase Lipozyme RM IM, through reaction from beef tallow (BT), palm stearin (PS) and camellia oil (CO)under the mass ratio of 7.55: 2.45: 4 (BT: CO: PS) using 3.65% (w/w) of Lipozyme RM IM at 72.6°C for 3.85 h. After reaction, interesterified fats with 36.8°C sliding melting point (SMP) was obtained. Physicochemical properties (fatty acid profile, triacylglycerol profile, solid fat content (SFC), melting and crystallization curve, polymorphic forms) of interesterified fats were characterized. Results proved that interesterified fats blends after interesterification were improved with desirable ß' type crystals and preferable SFC. Triacylglycerol constituent of interesterified fats displayed a decrease in OOO, PSS/SPS, LLL, SSS and increased in PSO/POS/SPO, POO/OPO, POP/PPO, PLO/PLP/PPL by comparison of physical blends without interesterification. Additionally, it is estimated that interesterified fats have a moderate antioxidative stability about 352 days-shelf life at 20°C through the traditional accelerated oxidation test. In conclusion, interesterified fats with desirable properties could be suitable for plastic fats use.

Effects of pectin with different molecular weight on gelatinization behavior, textural properties, retrogradation and in vitro digestibility of corn starch.

Effects of pectin with different molecular weight (Mw) on gelatinization behavior, textural properties, retrogradation, and in vitro digestibility of corn starch (CS) were investigated. The pectin addition led to the decrease of peak, setback, and final viscosities of CS, and a further decrease was provided with the pectin of high Mw, whereas the pasting temperature was increased. The syneresis of starch gel during freeze-thaw process was reduced by the addition of pectin. High Mw pectin significantly lowered the hardness of the starch gel from 238.9 and 350.2 N to 222.7 and 318.5 N after 7 and 14 days storage (P < 0.05), respectively. Compared with the retrograded CS alone, the relative crystallinity of starch-pectin mixtures significantly decreased (P < 0.05), but the crystal type of starch remained unchanged. A significant increase was observed in both the proportion of slowly digestible starch and resistant starch for retrograded starch-pectin mixtures.

Combining sestc engineered A. niger with sestc engineered S. cerevisiae to produce rice straw ethanol via step-by-step and in situ saccharification and fermentation.

The development of agricultural residue ethanol has a profound effect on the environment protection and energy supply. To increase the production efficiency of straw ethanol and reduce operation progress, the single-enzyme-system-three-cellulase gene (sestc) engineered Aspergillus niger and sestc engineered Saccharomyces cerevisiae were combined to produce ethanol using the pretreated rice straw as the substrate. The present results showed that both the step-by-step and in situ saccharification and fermentation can effectively produce ethanol using rice straw as the carbon substrate. The conversion rates of ethanol were 12.76 and 14.56 g per 1 kg of treated rice straw, respectively, via step-by-step and in situ processes. In situ process has higher ethanol conversion efficiency of rice straw and fewer operation processes as compared with step-by-step process. Therefore, in situ saccharification and fermentation is a more economical and effective pathway to convert rice straw into ethanol. This study provides a reference to the conversion of lignocellulosic residues into ethanol with a combination of two kinds of sestc engineered strains.

Improving Acetic Acid Production by Over-Expressing PQQ-ADH in Acetobacter pasteurianus.

Pyrroquinoline quinone-dependent alcohol dehydrogenase (PQQ-ADH) is a key enzyme in the ethanol oxidase respiratory chain of acetic acid bacteria (AAB). To investigate the effect of PQQ-ADH on acetic acid production by Acetobacter pasteurianus JST-S, subunits I (adhA) and II (adhB) of PQQ-ADH were over-expressed, the fermentation parameters and the metabolic flux analysis were compared in the engineered strain and the original one. The acetic acid production was improved by the engineered strain (61.42 g L-1) while the residual ethanol content (4.18 g L-1) was decreased. Analysis of 2D maps indicated that 19 proteins were differently expressed between the two strains; of these, 17 were identified and analyzed by mass spectrometry and two-dimensional gel electrophoresis. With further investigation of metabolic flux analysis (MFA) of the pathway from ethanol and glucose, the results reveal that over-expression of PQQ-ADH is an effective way to improve the ethanol oxidation respiratory chain pathway and these can offer theoretical references for potential mechanism of metabolic regulation in AAB and researches with its acetic acid resistance.

Fermentation Process and Metabolic Flux of Ethanol Production from the Detoxified Hydrolyzate of Cassava Residue.

With the growth of the world population, energy problems are becoming increasingly severe; therefore, sustainable energy sources have gained enormous importance. With respect to ethanol fuel production, biomass is gradually replacing grain as the main raw material. In this study, we explored the fermentation of five- and six-carbon sugars, the main biomass degradation products, into alcohol. We conducted mutagenic screening specifically for Candida tropicalis CICC1779 to obtain a strain that effectively used xylose (Candida tropicalis CICC1779-Dyd). By subsequently studying fermentation conditions under different initial liquid volume oxygen transfer coefficients (kLα), and coupling control of the aeration rate and agitation speed under optimal conditions, the optimal dissolved oxygen change curve was obtained. In addition, we constructed metabolic flow charts and equations to obtain a better understanding of the fermentation mechanism and to improve the ethanol yield. In our experiment, the ethanol production of the wild type stain was 17.58 g·L-1 at a kLα of 120. The highest ethanol yield of the mutagenic strains was 24.85 g·L-1. The ethanol yield increased to 26.56 g·L-1 when the dissolved oxygen content was optimized, and the conversion of sugar into alcohol reached 0.447 g·g-1 glucose (the theoretical titer of yeast-metabolized xylose was 0.46 g ethanol/g xylose and the glucose ethanol fermentation titer was 0.51 g ethanol/g glucose). Finally, the detected activity of xylose reductase and xylose dehydrogenase was higher in the mutant strain than in the original, which indicated that the mutant strain (CICC1779-Dyd) could effectively utilize xylose for metabolism.