Effect of solution plasma process on microorganism sterilization, physicochemical properties and nutrients of milk.

Solution plasma process (SPP) was used for sterilizing Staphylococcus aureus (S. aureus) in raw milk (RM). The sterilization efficacy analysis and kinetics analysis showed bacterial concentration and the distance between electrodes were negatively correlated with the sterilization effect, while discharge voltage was positive. The better sterilization effect was achieved at 4 kV. The electrochemical indices analysis indicated that pH value of RM had no changed. The DO content decreased. The conductivity increased with the increasing discharge voltage. The nutrient content analysis revealed that the content of acidity, lactose, fat, and protein decreased. RM after SPP treatment exhibited higher values of sourness and slightly lower values of astringency than the control. The higher discharge voltage and narrower distance between electrodes presented the stronger effect. The structural characterization of CMs and MFGs was carried out using a laser particle sizer, FTIR, 1H NMR, XRD, and AFM. The results showed that the main chemical structure of CMs was unchanged basically. The SPP with the narrower distance between electrodes and lower discharge voltage significantly reduced the size and aggregation of MFGs at the molecular level. At 4 kV/2 mm, the particle sizes of CMs and MFGs were reduced from 238 nm and 523 nm to 224 nm and 302 nm, respectively. The average diameter of MFGs was reduced from 45 nm to 18 nm. Therefore, SPP is a potential method in the milk industry and provides a new idea for the preservation and processing of beverage.

Effect and Mechanism of L-Arginine against Alternaria Fruit Rot in Postharvest Blueberry Fruit.

This study aimed to explore the impact of L-arginine (Arg) on the development of resistance to Alternaria tenuissima (A. tenuissima) in blueberries. The metabolism of reactive oxygen species, pathogenesis-related proteins (PRs), and jasmonic acid (JA) biosynthesis pathways were analyzed, including changes in activity and gene expression of key enzymes. The results indicated that Arg treatment could prevent the development of Alternaria fruit rot in postharvest blueberries. In addition, it was also found to induce a burst of hydrogen peroxide in the blueberries early on during storage, thereby improving their resistance to A. tenuissima. Arg treatment was observed to increase the activity of antioxidant enzymes (peroxidase, catalase, superoxide dismutase, and ascorbate peroxidase) and related gene expression, as well as the total levels of phenolics, flavonoids, and anthocyanin in the blueberries. The activity and gene expression of the PRs (chitinase and ß-1,3-glucanase) were elevated in Arg-treated blueberries, boosting their resistance to pathogens. Additionally, a surge in endogenous JA content was detected in Arg-treated blueberries, along with upregulated expression of key genes related the JA biosynthesis pathway (VcLOX1, VcAOS1, VcAOC, VcAOC3, VcOPR1, VcOPR3, VcMYC2, and VcCOI1), thereby further bolstering disease resistance. In conclusion, Arg treatment was determined to be a promising prospective method for controlling Alternaria fruit rot in blueberries.

Effects of arsenic on the transport and attachment of microplastics in porous media.

Understanding the impact of arsenic (As(III), inorganic pollutant widely present in natural environments) on microplastics (MPs, one type of emerging contaminants) mobility is essential to predict MPs fate and distribution in soil-groundwater systems, yet relevant research is lacking. This study explored the effects of As(III) copresent in suspensions (0.05, 0.5, and 5 mg/L) on MPs transport/attachment behaviors in porous media containing varied water contents (θ = 100 %, 90 %, and 60 %) under different ionic strengths (5, 10, and 50 mM NaCl) and flow rates (2, 4, and 8 m/day). Despite solution ionic strengths, flow rates, porous media water contents, sizes, and surface charges of MPs, with coexisting humic acid, and in actual water samples, As(III) of three concentrations increased MPs transport in quartz sand and natural sandy soil. The increased electrostatic repulsion between MPs and sand caused by the altered MPs surface charge via the adsorption of As(III) together with steric repulsion from As(III) in solution contributed to the promoted MPs mobility in porous media. The occupying attachment sites by As(III) partially contributed to the increased mobility of MPs with negative surface charge in porous media. Clearly, As(III) coexisting in suspensions would enhance MPs transport in porous media, increasing MPs environment risks.

Transport and release behaviors of PFOA in saturated and unsaturated porous media with biochar amendment.

The widespread usage of perfluorooctanoic acid (PFOA) in daily consumer products and its high mobility in porous media have resulted in ubiquitous contamination of PFOA in the natural environment. Developing techniques to immobilize and inhibit the transport of PFOA thus is critical to reduce its potential risks. In present study, biochar, one type of environmental-friendly material produced from cellulose, was utilized in porous media to test its addition on inhibiting the transport and release of PFOA before and after aging process. We found that although PFOA had high mobility in saturated/unsaturated porous media, biochar addition could significantly inhibit PFOA transport in porous media with different saturations due to its high adsorption capacity towards PFOA. The inhibited transport of PFOA by biochar also held true in solution with copresence of natural organic matter and in actual river water. Moreover, we found that negligible PFOA was released from porous media with biochar amendment even after exposure to freeze-thaw/dry-wet treatment. PFOA adsorbed onto biochar could be completely desorbed and the biochar could be reused for subsequent cycles after desorption. Clearly, amendment of porous media with biochar would be a feasible and cost-effective method to immobilize PFOA in natural environment and reduce its environmental risks.

Cotransport of different electrically charged microplastics with PFOA in saturated porous media.

The fate and transport behavior of microplastics (MPs), emerging colloidal contaminant ubiquitous in natural environments, would be greatly affected by other copresent pollutants. PFOA (emerging surfactant pollutant) would interact with MPs after encounter with them in natural environments, which could alter the transport behavior of both pollutants. Relevant knowledge is still lacking, affecting accurate prediction the fate and distribution of these two emerging contaminants in natural porous media. The cotransport behavior of different surface charged MPs (negatively/positively charged, CMPs/AMPs) with PFOA (three concentrations ranging from 0.1 to 10 mg/L) in porous media in both 10 and 50 mM NaCl solutions thus was investigated in the present study. We found PFOA inhibited CMPs transport in porous media, while enhanced AMPs transport. The mechanisms leading to the altered transport of CMPs/AMPs caused by PFOA were found to be different. The decreased electrostatic repulsion between CMPs-sand induced by the decreased CMPs negative zeta potentials via the adsorption of PFOA led to the inhibited transport of CMPs in CMPs-PFOA suspension. The enhanced electrostatic repulsion between AMPs-sand due to the decreased positive charge of AMPs via the adsorption of PFOA together with steric repulsion induced by suspended PFOA resulted in the increased transport of AMPs in AMPs-PFOA suspension. Meanwhile, we found that the adsorption onto MPs surfaces also impacted the transport of PFOA. Due to the lower mobility of MPs than PFOA, the presence of MPs despite their surface charge decreased the transport of PFOA of all examined concentrations in quartz sand columns. This study demonstrates that when MPs and PFOA are co-existing in environments, their interaction with each other will alter the fate and transport behavior of both pollutants in porous media and the alteration is highly correlated with the amount of PFOA adsorbed onto MPs and original surface properties of MPs.

Freeze-thaw treatment of bacteria significantly affects bacterial transport behaviors in both saturated and unsaturated porous media: Deep investigation the roles of flagella and extracellular polymeric substances.

The effects of freeze-thaw (FT) treatment and mechanisms on bacteria transport/retention in porous media with different moisture contents remain unclear. The transport/retention behaviors of bacteria with different FT treatment cycles (0, 1, and 3) in sand columns with different moisture contents (100 %, 90 %, 60 %, and 30 %) in NaCl solutions (10 and 100 mM) thus were investigated. Regardless of moisture content and solution chemistry, FT treatment increased bacteria deposition in sand columns, consistent with the results of QCM-D and visible parallel plate flow chamber (PPFC) systems. Via deep investigation of the contribution of flagella through using genetic-modified bacteria strain without flagella and that of extracellular polymeric substances (EPS) through analyzing its overall quantity, composition as well as the secondary structure of its two major components (proteins and polysaccharides), the mechanisms of FT treatment controlling bacterial transport/deposition were revealed. Although FT treatment induced flagella loss, it was not the major contributor to driving to the enhanced FT-treated cell deposition. Instead, FT treatment stimulated EPS secretion and increased its hydrophobicity (via increasing hydrophobicity of both proteins and polysaccharides), mainly contributing to the enhanced bacterial deposition. Even with copresent humic acid, FT treatment still enhanced bacterial deposition in sand columns with different moisture contents.

Transport of plastic particles in natural porous media under freeze-thaw treatment: Effects of porous media property.

Freeze-thaw (FT) cycles would alter physical and chemical properties of soil and thus influence the transport of plastic particles (one type of emerging contaminant with great concerns). This study was designed to investigate the effects of FT treatment on the mobility of plastic particles (nanoplastics as representative) in columns packed with natural soils (i.e. loamy sand and sandy soil, quartz sand employed as comparison). We found that FT treatment of different types of porous media would induce different transport behaviors of plastic particles. Specifically, FT treatment of quartz sand did not affect plastic particles mobility. While FT treatment of loamy sand and sandy soil increased plastic particles transport. The increased pore sizes and disintegration of small soil particles from soils (the detached soil would serve as mobile vehicle for the transport of plastic particle) led to the facilitated mobility of plastic particles in two types of soils after FT treatment. The presence of preferential flow paths induced by FT treatment also drove to the enhanced mobility of plastic particles in sandy soil with FT treatment. This study clearly showed that the mobility of model plastic particles in two types of natural soils was greatly enhanced by FT treatment.

Degradation of polymeric polyproanthocyanidins from black chokeberry by microwave-assisted nucleophilic technique of sulfite/catechin: Reaction kinetics, antioxidation and structural analysis.

Microwave was employed to enhance the degradation of polymeric proanthocyanidins from black chokeberry using the nucleophilic technique of sulfite/catechin. Based on the degradation effect and kinetics, it was found that increasing the microwave time, microwave power, microwave temperature, sulfite concentration, and mass ratio of raw material to catechins was favourable for the degradation reaction. The degradation kinetics conformed to a random first-order degradation model. The antioxidant activity of the degraded products was analysed using DPPH and O2- assay, which suggested that the scavenging effect of the products was improved. FT-IR and 1H NMR analyses showed that the main functional groups were not destroyed. Using MALDI-TOF/MS to study the components of the degradation products, it was found that the molecular weight distribution became narrower, and the compositions were more single. Polyproanthocyanidins were reduced to oligomers. This study suggested that microwave-assisted nucleophilic techniques could produce oligomeric proanthocyanidins with remarkably improved functionalities.

Effect of pH value and the distance between the electrodes on physicochemical properties of chitosan under SPP treatment.

Solution plasma process (SPP) was employed to degrade chitosan. The effects of the initial pH value and the distance between the electrodes on the steady shear flow behavior, structural characterization, molecular conformation, and antioxidant activity of chitosan were investigated. The results revealed that a lower initial pH value and a narrower distance between the electrodes were beneficial to the decrease in viscosity and increase in shear-thinning capacity. Structural characterization of the chitosan by FT-IR and 1H NMR showed that chemical structure of chitosan was not destroyed at different process parameters. The results of XRD, HPSEC-MALLS, SEM, and AFM indicated that SPP degradation clearly decreased the crystallinity, molecular weight, molecular size, and molecular aggregation of chitosan. At initial pH values of 2.8 and 5.8, the molecular weight was 27.16 and 44.25 kDa, at the distance between the electrodes of 4 and 8 mm, it was 35.88 and 66.17 kDa, respectively. The results of DPPH and hydroxyl radical scavenging assays demonstrated that a lower initial pH value and a narrower distance between the electrodes enhanced the antioxidant activity.

Transport and deposition behaviors of microplastics in porous media: Co-impacts of N fertilizers and humic acid.

Due to the interaction of fertilizers with microplastics (MPs) and porous media, fertilization process would influence MPs transport and distributions in soil. The co-impacts of N fertilizers (both inorganic and organic N fertilizers) and humic substance on MPs transport/retention behaviors in porous media were examined in 10 mM KCl solutions at pH 6. NH4Cl and CO(NH2)2 were employed as inorganic and organic N fertilizers, respectively, while humic acid (HA) was used as model humic substance. We found that for all three sized MPs (0.2, 1 and 2 µm) without HA, both types of N fertilizers decreased their transport/increased their retention in porous media (both quartz sand and soil). N fertilizers adsorbed onto surfaces of MPs and sand/soil, lowering the electrostatic repulsion between MPs and porous media, thus contributed to the enhanced MPs deposition. MPs with N fertilizers in solutions more tightly attached onto porous media and thus were more difficult to be re-mobilized by low ionic strength solution elution. Via steric repulsion and increasing electrostatic repulsion between MPs and porous media due to adsorption onto their surfaces, HA could increase MPs transport with N fertilizers in solutions.

Bacteria have different effects on the transport behaviors of positively and negatively charged microplastics in porous media.

Bacteria, biological colloids with wide presence in natural environments, would interact with plastic particles (emerging colloids with great concern recently) and thus would influence the fate and distribution of plastics in environment. In present research, the impacts of bacteria (both Gram (-) E. coli and Gram (+) B. subtilis) on the transport/deposition of model microplastics (MPs) in porous media were examined in NaCl salt solutions (5 and 25 mM, pH = 6). Both negative carboxylate-modified MPs (CMPs) and positive amine-modified MPs (AMPs) were concerned. We found that under both solution conditions, the presence of both types of bacteria decreased CMPs transport and enhanced retention of CMPs in sand columns. In contrast, the presence of bacteria (regardless of cell type) yet increased AMPs transport and decreased their deposition in sand columns under both ionic strength conditions. The mechanisms leading to the altered transport of CMPs and AMPs by bacteria were different. The formation of larger sized CMPs-bacteria clusters and the extra deposition sites resulted from bacteria adsorbed on quartz sand contributed to the decreased CMPs transport and enhanced their deposition in sand columns. Whereas, the formation of AMPs-bacteria clusters with overall negatively surface charge improved AMPs transport in quartz sand.

Different electrically charged proteins result in diverse transport behaviors of plastic particles with different surface charge in quartz sand.

The influence of proteins on the transport and deposition behaviors of microplastics (MPs) in quartz sand was examined at both low (5 mM) and high ionic strength (25 mM) in NaCl solutions at pH 6. Carboxylate- and amine-modified polystyrene latex microspheres with size of 200 nm were employed as negatively (CMPs) and positively surface charged MPs (AMPs), respectively, while bovine serum albumin (BSA) and bovine trypsin were utilized as representative negatively and positively charged proteins, respectively. The results showed that for two examined protein concentrations (both 1 and 10 mg/L TOC) under both ionic strength conditions, the presence of BSA increased the transport of both CMPs and AMPs, while the presence of trypsin decreased the transport of CMPs yet increased the transport of AMPs in porous media. The mechanisms driving to the changed transport of MPs induced by two types of proteins were found to be different. Particularly, steric interaction induced by BSA corona adsorbed onto CMPs surface as well as the repel effects resulted from BSA suspending in solutions were found to contribute to the enhanced CMPs transport with BSA copresent in suspensions. The increased sizes and the decreased electrostatic repulsion of CMPs due to the adsorption of trypsin onto CMPs, together with the addition of extra deposition sites due to the adsorption of trypsin onto quartz sand drove to the decreased CMPs transport with trypsin copresent in suspensions. The increased electrostatic repulsion due to the adsorption of BSA onto AMPs surfaces caused the enhanced AMPs transport with BSA in solutions. While, the decreased electrostatic attraction of AMPs due to the adsorption of trypsin onto AMPs, as well as the competition of deposition sites due to the adsorption of trypsin onto quartz sand contributed to the increased AMPs transport with trypsin copresent in suspensions. The results showed that the presence of different types of proteins would induce different transport behaviors of microplastics with different surface charge in porous media. Since proteins are widely present in aquatic systems, to more accurately predict the fate and transport of MPs in natural environments, the effects and mechanisms of proteins on the transport of MPs should be considered.

Different surface charged plastic particles have different cotransport behaviors with kaolinite ☆particles in porous media.

The wide utilization of plastic related products leads to the ubiquitous presence of plastic particles in natural environments. Plastic particles could interact with kaolinite (one type of typical clay particles abundant in environments) and form plastic-kaolinite heteroaggregates. The fate and transport of both plastic particles and kaolinite particles thus might be altered. The cotransport and deposition behaviors of micron-sized plastic particles (MPs) with different surface charge (both negative and positive surface charge) with kaolinite in porous media in both 5 and 25 mM NaCl solutions were investigated in present study. Both types of MPs (negatively charged carboxylate-modified MPs (CMPs) and positively charged amine-modified MPs (AMPs)) formed heteroaggregates with kaolinite particles under both solution conditions examined, however, CMPs and AMPs exhibited different cotransport behaviors with kaolinite. Specifically, the transport of both CMPs and kaolinite was increased under both ionic strength conditions when kaolinite and CMPs were copresent in suspensions. While, when kaolinite and positively charged AMPs were copresent in suspensions, negligible transport of both kaolinite and AMPs were observed under examined salt solution conditions. The competition deposition sites by kaolinite (the portion suspending in solution) with CMPs-kaolinite heteroaggregates led to the increased transport both CMPs and kaolinite when both types of colloids were copresent. In contrast, the formation of larger sized AMPs-kaolinite heteroaggregates with surface charge heterogeneity led to the negligible transport of both kaolinite and AMPs when they were copresent in suspensions. The results of this study show that when plastic particles and kaolinite particles are copresent in natural environments, their interaction with each other will affect their transport behaviors in porous media. The alteration in the transport of MPs or kaolinite (either increased or decreased transport) is highly correlated with the surface charge of MPs.

Influence of biofilm on the transport and deposition behaviors of nano- and micro-plastic particles in quartz sand.

Biofilm, community of bacteria ubiquitously present in natural environment, may interact with plastic particles and affect the transport of plastic particles in environment. The significance of biofilm (Escherichia coli) on the transport and deposition behaviors of three different sized plastic particles (0.02 µm NPs, 0.2 µm MP and 2 µm MP) were examined under both 10 mM and 50 mM NaCl solutions by comparing the breakthrough curves and retained profiles of plastic particles in bare sand versus those in biofilm-coated sand. Regardless of ionic strengths, the presence of biofilm increases the deposition of all three sized plastic particles in porous media. Via employing X-ray microtomography imaging (XMT) and Scanning electron microscope (SEM), we find that the presence of biofilm could narrow the flow path especially near to the inlet of the column and increase the surface roughness of porous media (by decreasing DLVO repulsive interaction), which contributes to the enhanced the deposition of plastic particles. Extracellular polymeric substances (EPS) present on the biofilm are found to contribute to the enhanced deposition of plastic particles. Packed column experiments, quartz crystal microbalance with dissipation (QCM-D) as well as parallel plate flow chamber experiments all show that three major components of EPS, proteins, polysaccharide, and humic substances all contribute to the enhanced deposition of plastic particles. O-H and N-H groups present on cell surfaces are highly likely to form hydrogen bond with plastic particles and increase the deposition plastic particles. Elution experiments show that decreasing solution ionic strength could release small portion of plastic particles from both bare and biofilm-coated sand columns especially from the segments near to the column inlet (with slighter lower percentage from biofilm-coated columns based on the total mass of retained plastics). In contrast, increasing flow rate does not obviously detach the plastic particles that already deposited onto porous media. The results of this study clearly show that the presence of biofilm in natural environment could enhance the deposition and decrease the transport of plastic particles.

Transport behaviors of plastic particles in saturated quartz sand without and with biochar/Fe3O4-biochar amendment.

As an environmentally friendly material, biochar has been widely used to remediate soil/water contaminants such as heavy metals and organic pollutants. The addition of biochar or modified biochar to porous media might affect the retention of plastic particles and thus influence their fate in natural environment. In this study, both biochar and magnetic biochar (Fe3O4-biochar) were synthesized via a facile precipitation method at room temperature. To determine the significance of biochar and Fe3O4-biochar amendment on the transport and deposition behaviors of plastic particles, the breakthrough curves and retained profiles of three different sized plastic particles (0.02 µm nano-plastic particles, and 0.2 µm and 2 µm micro-plastic particles) in quartz sand were compared with those obtained in quartz sand either with biochar or Fe3O4-biochar amendment in both 5 mM and 25 mM NaCl solutions. The results show that for all three different sized plastic particles under both examined solution conditions, the addition of biochar and Fe3O4-biochar in quartz sand decreases the transport and increases the retention of plastic particles in porous media. Fe3O4-biochar more effectively inhibits the transport of plastic particles than biochar. We found that the addition of biochar/Fe3O4-biochar could change the suspension property and increase the adsorption capacity of porous media (due to the increase of porous media surface roughness and negatively decrease the zeta potentials of porous media), contributing to the enhanced deposition of plastic particles. Moreover, we found that negligible amount of biochar and Fe3O4-biochar (<1%) were released from the columns following the plastic particle transport when the columns were eluted with very low ionic strength solution at high flow rate (to simulate a sudden rainstorm). Similarly, small amount of plastic particles were detached from the porous media under this extreme condition (16.5% for quartz sand, 14.6% for quartz sand with biochar amendment, and 7.5% for quartz sand with Fe3O4-biochar amendment). We found that over 74% of the Fe3O4-biochar can be recovered from the porous media after the retention of plastic particles by using a magnet and 87% plastic particles could be desorbed from Fe3O4-biochar by dispersing the Fe3O4-biochar into 10 mM NaOH solution. In addition, we found that the amendment of unsaturated porous media with biochar/Fe3O4-biochar also decreased the transport of plastic particles. When biochar/Fe3O4-biochar were added into porous media as one layer of permeable barrier near to column inlet, the decreased transport of plastic particles could be also obtained. The results of this study indicate that magnetic biochar can be potentially applied to immobilize plastic particles in terrestrial ecosystems such as in soil or groundwater.

Influence of Nano- and Microplastic Particles on the Transport and Deposition Behaviors of Bacteria in Quartz Sand.

Plastic particles are widely present in the natural environment and are highly likely to interact with bacteria (the ubiquitous microbes in the natural environment), which might affect the transport and deposition of bacteria in porous media. In this study, the significance of plastic particles from nanoscale to micrometer-scale (0.02-2 µm) on the transport and deposition behaviors of bacteria ( Escherichia coli) in quartz sand was examined under environmentally relevant conditions in both NaCl and CaCl2 solutions at pH 6. The results showed that the presence of different-sized plastic particles did not affect bacterial transport behaviors at low ionic strength (10 mM NaCl and 1 mM CaCl2), whereas, at high ionic strength conditions (50 mM NaCl and 5 mM in CaCl2), plastic particles increased bacterial transport in quartz sand. At low ionic strength conditions, the mobility of both plastic particles and bacteria was high, which might drive the negligible effects of plastic particles on bacterial transport behaviors. The mechanisms driving the enhanced cell transport at high ionic strength were different for different-sized plastic particles. Specifically, for 0.02 µm nanoplastic particles, the adsorption of plastic particles onto cell surfaces and the repel effect induced by suspended plastic particles contributed to the increased cell transport. As for 0.2 µm microplastics (MPs), the suspended plastic particles induced  repel effect contributed to the increased cell transport, whereas, for 2 µm MPs, the competition deposition sites by the plastic particles were the contributor to the increased cell transport.