Effects of nano-TiO2 -LDPE packaging on postharvest quality and antioxidant capacity of strawberry (Fragaria ananassa Duch.) stored at refrigeration temperature.

BACKGROUND: Nano-TiO2 -low-density polyethylene (NTLDPE) packaging was prepared, and the effects of NTLDPE packaging on quality and antioxidant capacity of strawberry fruits were investigated. RESULTS: With increased barrier properties, NTLDPE packaging quickly formed a relative lower O2 and higher CO2 air composition in comparison with LDPE. It was also more efficient in maintaining the overall quality of strawberry fruit, as reflected by lower decay rate and weight loss, as well as retarding the decrease in firmness and titratable acid. Meanwhile, reactive oxygen species (ROS) including superoxide anion and hydrogen peroxide in NTLDPE-packed fruits were 10.8% and 21.9% lower, respectively. Furthermore, the activities of antioxidant enzymes involved in ROS scavenging in NTLDPE-packed fruits were significantly higher at the later period of storage time. Anthocyanin accumulation was inhibited, whereas ascorbic acid and total phenolics contents were better retained and 1-diphenyl-2-picrylhydrazyl radical scavenging activity was 13.2% higher in NTLDPE-packed fruit by the end of storage. CONCLUSION: These data indicate that the beneficial effects of NTLDPE packaging on postharvest quality and antioxidant capacity of strawberry are probably associated with the promotion of ROS scavenging and related antioxidant enzyme activities, and NTLDPE packaging together with refrigeration storage is a promising method for strawberry fruit preservation. © 2016 Society of Chemical Industry.

Impact of nano-CaCO3 -LDPE packaging on quality of fresh-cut sugarcane.

BACKGROUND: In order to evaluate the effects of nano-CaCO3 -based low density polyethylene (nano-CaCO3 -LDPE) packaging on the quality of fresh-cut sugarcane, concentrations of O2 and CO2 within the packages, overall visual quality (OVQ), total bacterial count (TBC), yeast and mould count (YMC), reducing sugar content and total phenolic content, respiration, ethylene production, and the activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), acid invertase (AI) and neutral invertase (NI) were examined during storage at 10 °C for 5 days. RESULTS: The transmission rate of O2 and CO2 of the nano-CaCO3 -LDPE material was lower than that of LDPE, which lead to the more rapid formation of gas environment with low O2 and high CO2 concentration in the package. TBC and YMC counts of fresh-cut sugarcane were significantly retarded by nano-CaCO3 -LDPE packaging. Nano-CaCO3 -LDPE packaging fresh-cut sugarcane exhibited significantly lower activities of PAL, PPO, POD AI and NI than LDPE packaging fresh-cut sugarcanes during the storage. Meanwhile, nano-CaCO3 -LDPE packaging significantly inhibited the increase of browning index and total phenolic content, while improving OVQ. CONCLUSION: Our results indicated that nano-CaCO3 -LDPE packaging together with the cold storage is a promising approach in inhibiting browning and maintaining quality of fresh-cut sugarcane.

Nucleic Acid Plate Culture: Label-Free and Naked-Eye-Based Digital Loop-Mediated Isothermal Amplification in Hydrogel with Machine Learning.

Digital nucleic acid amplification enables the absolute quantification of single molecules. However, due to the ultrasmall reaction volume in the digital system (i.e., short light path), most digital systems are limited to fluorescence signals, while label-free and naked-eye readout remain challenging. In this work, we report a digital nucleic acid plate culture method for label-free, ultrasimple, and naked-eye nucleic acid analysis. As simple as the bacteria culture, the nanoconfined digital loop-mediated isothermal amplification was performed by using polyacrylamide (PAM) hydrogel as the amplification matrix. The nanoconfinement of PAM hydrogel with an ionic polymer chain can remarkably accelerate the amplification of target nucleic acids and the growth of inorganic byproducts, namely, magnesium pyrophosphate particles (MPPs). Compared to that in aqueous solutions, MPPs trapped in the hydrogel with enhanced light scattering characteristics are clearly visible to the naked eye, forming white "colony" spots that can be simply counted in a label-free and instrument-free manner. The MPPs can also be photographed by a smartphone and automatically counted by a machine-learning algorithm to realize the absolute quantification of antibiotic-resistant pathogens in diverse real samples.

Camellia Oleifera shells derived nano cellulose crystals conjugated with gallic acid as a sustainable Pickering emulsion stabilizer.

Lately, emulsions with low-fat and natural stabilizers are predominant. This study extracted the nano cellulose crystals (NCs) from Camellia Oleifera shells, and their gallic acid (GA) conjugates were synthesized by free-radical grafting. Pickering emulsions were prepared using NCs 1 %, 1.5 %, 2.5 %, and gallic acid conjugates NC-GA1, NC-GA2, and NC-GA3 as stabilizers. The obtained nano cellulose crystals exhibited 18-25 nm, -40.01 ±â€¯2.45 size, and zeta potential, respectively. The contact angle of 83.4° was exhibited by NC-GA3 conjugates. The rheological, interfacial, and microstructural properties and stability of the Pickering emulsion were explored. NC-GA3 displayed the highest absorption content of 79.12 %. Interfacial tension was drastically reduced with increasing GA concentration in NC-GA conjugates. Rheological properties suggested that the low-fat NC-GA emulsions showed a viscoelastic behavior, increased viscosity, gel-like structure, and increased antioxidant properties. Moreover, NC-GA3 displayed reduced droplet size and improved emulsion temperature and storage stability (28 days) against phase separation. POV and TBARS values were reduced with the NC-GA3 (P < 0.05). This work confirmed that grafting phenolic compounds on NCs could enhance bioactive properties, which can be used in developing low-fat functional foods. NC-GA conjugates can potentially fulfill the increasing demand for sustainable, healthy, and low-fat foods.

Construction of self-assembled nano cellulose crystals/chitosan nanobubbles composite hydrogel with improved gallic acid release property.

Hydrogels are of great significance in the field of bioactive delivery. This study designed the self-assembly of gallic acid-loaded nano cellulose crystals/chitosan (NC/CS) hydrogels via Nano bubbles (NBs). NC/CS NBs 4:2 hydrogels improved the mechanical properties compared to those without NBs. The hardness of NC/CS (4:2) NBs hydrogels was greatly enhanced by 1.15 ± 0.05. The water-holding and swelling behavior can be tuned at different ratios. NC/CS NBs (4:2) showed the electrostatic interaction analyzed by FTIR, XRD, and XPS. SEM results displayed smoother and smaller pores along dense networks promoted by NBs. The antioxidant activity of hydrogels was increased by adding NBs (P < 0.05). In vitro and vivo release activity of gallic acid was higher in simulated intestinal fluid (SIF) at 4:2, depicting the controlled release mechanism. Thus, current work revealed that NBs and low concentrations of NC can be self-assembled with chitosan chains, producing a highly compact hydrogel structure.

Nanoporous electrode with stable polydimethylsiloxane coating for direct electrochemical analysis of bisphenol A in complex wine media.

Direct electrochemical analysis of bisphenol A (BPA) in alcoholic drinks without proper sample preparation is a major challenge. The current work reports a nanoporous electrode design with ultrathin polydimethylsiloxane (PDMS) coating grafted on the top of an indium tin oxide (ITO) electrode with silica nanochannels membrane and cetyltrimethylammonium bromide micelles (SNCM), using a facile contact heating step. The proposed PDMS@SNCM/ITO electrode was subjected to direct ultra-trace detection of BPA in the linear range of 1.0-100.0 µM and detection limit of 0.23 µM, under optimized pH 8 and an accumulation time of 9.0 min. The analytical utility of the proposed method was checked in real wine samples for BPA detection with successful recovery percentages in the range from 95.20 ± 8.53 to 96.22 ± 10.00. The intrinsic hydrophobic features, exceptional stability, and sensitivity of the proposed electrode show potential for food safety surveillance in complex food matrices.

Generation and stabilization of CO2 nanobubbles using surfactants for extraction of polyphenols from Camellia oleifera shells.

Camellia oleifera shells are abundant in polyphenolic compounds. Green extraction methods of polyphenolic compounds are essential to ensure product quality, efficiency, process cost, environment, and safety. This study investigated the effect of Tween 80 and Rhamnolipid surfactants on the production and utilization of stabilized carbon dioxide nanobubbles (CO2 -NBs). The results confirmed the presence of the CO2 -NBs in ultra-pure water with a concentration of 8.45 ± 1.05 × 108  ml-1 , among which the stable CO2 -NBs possessed a mean size of 40-90 nm and a negative zeta potential (-41.6 ± 1.3 mV). Further, the efficiency of CO2 -NBs combined with ultrasonication (CO2 -NBs-Rh-UAE) was evaluated to extract polyphenols from Camellia oleifera shells (waste). The CO2 -NBs treatment with ultrasonication showed the highest total phenolic content (TPC) and total flavonoid content (TFC) (36.75 ± 0.22 mg GAE/g DW and 24.06 ± 0.22 mg RE/g DW, respectively). Overall, this study demonstrated an innovative approach for producing, stabilizing, and utilizing biosurfactant stabilized CO2 -NBs to extract polyphenolic compounds from the waste agricultural products. These findings highlighted the potential application of biosurfactant-stabilized CO2 -NBs.

Direct detection of Pb2+ and Cd2+ in juice and beverage samples using PDMS modified nanochannels electrochemical sensors.

Direct electrochemical detection in real food samples remains challenging due to the fouling and interference by abundant interference components. Herein, we report an electrochemical sensing platform based on binary assembly of silica nanochannels and polydimethylsiloxane that is able to detect Pb2+ and Cd2+ in real food samples without complex pretreatments. Using differential pulse anodic stripping voltammetry, the electrochemical detection consists of electro-deposition of metal species and subsequent anodic stripping in the modified silica-nanochannels. Under the optimized conditions, the linear ranges were obtained from 4 to 1500 µg L-1 for Pb2+ and 30 to 900 µg L-1 for Cd2+. The relative standard deviations were 2.9% and 3.6% for Pb2+ and Cd2+ of 300 µg L-1. Without tedious pretreatments, the quantitative detection of Pb2+ and Cd2+ in real juice and beverage samples was successfully performed, revealing that the developed sensor possesses excellent anti-interference and practicability properties for unprocessed food.

Interference-free Detection of Caffeine in Complex Matrices Using a Nanochannel Electrode Modified with Binary Hydrophilic-Hydrophobic PDMS.

In the present study, a novel electrochemical sensor for the direct detection of caffeine in the crude sample has been prepared by plasma-triggered polydimethylsiloxane (PDMS) deposition on the indium tin oxide electrodes supported with silica nanochannels. The deposited PDMS contains both the original hydrophobic and oxidized hydrophilic PDMS oligomers. Nanochannels modified with these two kinds of PDMS with opposite wettability only allow the passage of small amphiphilic molecules such as caffeine, while other molecules including hydrophilic, hydrophobic, and large ones were all rejected. With the excellent shielding properties, the modified nanochannel electrode exhibits excellent anti-interference and antifouling capability, which could be directly used for the detection of caffeine in real crude food such as tea, milk, coffee, and coke without sample pretreatments. Moreover, the modified electrode has good repeatability and stability. In contrast, severe interference was observed when conventional electrodes were used directly in these unprocessed samples. The linear ranges of caffeine were determined to be between 50 nmol/L and 700 µmol/L, with a limit of detection of 20 nmol/L. The developed sensor provides a very simple, rapid, and cost-effective way for the interference-free and fouling-free analysis of specific amphiphilic compounds and can be extended to a wide range of applications.

Delaying the biosynthesis of aromatic secondary metabolites in postharvest strawberry fruit exposed to elevated CO2 atmosphere.

Aromatic secondary metabolites are closely related to quality attributes of postharvest fruit. In the present study, 20% CO2 was applied to strawberry fruit to investigate the regulation of elevated CO2 on aromatic secondary metabolites. The results showed that elevated CO2 delayed accumulations of anthocyanins, eugenol and lignin. Phenylalanine and tyrosine, the precursors of the above secondary metabolites, were 18.90% and 35.61%, respectively, lower in CO2-treated fruit compared with the control on day 6. Furthermore, enzyme activities and transcriptional profiles analysis showed pentose phosphate pathway and glycolysis were activated by elevated CO2 whereas the aromatic amino acids (AAAs) pathway was inhibited. These results indicated that elevated CO2 restricted carbon flux into aromatic secondary metabolism by inhibiting the AAAs pathway, leading to the decrease of phenylalanine and tyrosine, and thus, delayed the accumulation of aromatic secondary metabolites. In addition, the effect of elevated CO2 was eliminated after transferred CO2-treated fruit to air.

Chitosan-based melatonin bilayer coating for maintaining quality of fresh-cut products.

This work was designed to develop the chitosan-based melatonin layer-by-layer assembly (CMLLA) via the inclusion method. The structural characterizations and interaction present in CMLLA were investigated by the scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier Transform-Infrared spectroscopy (FTIR). The ratio of chitosan (CH) to carboxymethylcellulose (CMC) greatly influenced the mechanical properties, including the tensile strength, moisture content and color performance. Results showed that both antioxidant and antimicrobial properties of CMLLA were enhanced with the addition of melatonin (MLT). Furthermore, it was demonstrated that the CMLLA with 1.2 % (w/v) CH, 0.8 % (w/v) CMC and 50 mg/L MLT better contributed to the delay of chlorophyll degradation and the maintenance of shelf-life quality. Results from this study might open up new insights into the approaches of quality improvement of postharvest fresh products by incorporating the natural antioxidant compounds into natural polymers.

Recovery of lotus (Nelumbo nucifera Gaertn.) seedpod flavonoids using polar macroporous resins: The updated understanding on adsorption/desorption mechanisms and the involved intermolecular attractions and bonding.

Macroporous resins have been employed in the effective recovery of flavonoids from plants. In this study, S8 polar resins were used to recover flavonoids and procyanidins from lotus seedpods. Adsorption kinetics, isotherms, and thermodynamics studies revealed that the adsorption process involved physico-chemical interactions, including flavonoid-resin and flavonoid-flavonoid electrostatic interactions, π-π aromatic stacking, moderate and strong hydrogen bonding, and repulsive forces. These forces worked complementarily in adsorption, except for the repulsive force, which opposed the adsorption. Further, adsorption temperature determined the adsorption behavior, with multilayer adsorption enhancing adsorption capacity. In dynamic desorption tests, an acetone/water/acetic acid mixture (58.77: 39.34: 1.89) designed by the D-optimal design method was able to desorb 95.57% and 89.85% of total flavonoids and procyanidins, respectively, using less than two bed volumes of solvent. Ultra-performance liquid chromatography triple-time of flight/mass spectrometry (UPLC-TOF/MS) analysis showed that 26 flavonoids, including 5 procyanidins, were detected after the recovery.

Ultrasonic impact on viscosity and extraction efficiency of polyethylene glycol: A greener approach for anthocyanins recovery from purple sweet potato.

Purple sweet potatoes are known for its vibrant purple color due to high level of anthocyanins. A polyethylene glycol based ultrasonic-assisted green extraction (PEG-UAE) of anthocyanins from purple sweet potato was proposed. Different types of PEG were tested for anthocyanin extraction along with PEG concentration, liquid-to-solid ratio, ultrasonic temperature and time were investigated for its impact on viscosity and extraction efficiency. The optimum extraction condition, 42 mL/g of ratio, 83% of PEG 200 concentration, 64 °C of ultrasonic temperature and 80 min of sonication time, resulted in better extraction of anthocyanins (83.78 mg CE/100 g DW) and phenolics (994.88 mg GAE/100 g DW). Using UPLC-Triple-TOF/MS, ten anthocyanin and six non-anthocyanin compounds were identified and characterized, with the highest peak area for cyanidin-3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside (25.9%). Moreover, the anthocyanins and phenolics extraction yield along with antioxidant activity were negatively correlated with PEG viscosity, on which ultrasonication has profound effects.

Effect of heat treatment on lignification of postharvest bamboo shoots (Phyllostachys praecox f. prevernalis.).

In order to evaluate the effects of heat treatment on the quality of postharvest bamboo shoots, the firmness, disease incidence, respiration and ethylene production, ACC synthase (ACS) and ACC oxidase (ACO) activities, lignin and cellulose contents, and the activities of phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) were examined during storage at 20°C after heat treatment at 45°C for 5h. Heat treatment inhibited disease incidence and respiration, retarded ethylene production, and decreased ACS and ACO activities in bamboo shoots. Furthermore, heat treatment significantly delayed the rise in the activities of PAL, CAD and POD, which were associated with the inhibition of the synthesis of lignin and the delayed tissue lignification. These findings suggest that heat treatment could be a potential tool to delay lignification and decrease disease incidence in bamboo shoots during storage at 20°C.