Soya bean meal-based formulated feeds have recently become available for snakehead culture in Vietnam. This study was conducted to determine the appropriate replacement of fish meal (FM) protein by another soya product, soya protein concentrate (SPC), in snakehead (Channa striata) diets. Five iso-nitrogenous (45% crude protein) and isocaloric (19 KJ g À1 ) practical diets were formulated to replace 0% (control), 40%, 60%, 80% and 100% of protein FM by protein SPC (100% FM, 40% SPC, 60% SPC, 80% SPC and 100% SPC respectively). A digestibility experiment was also conducted with the same formulated diets with addition of 1% chromic oxide. Fish fed 100% FM and 40% SPC diets had significantly better growth and survival compared with other treatments. Feed intake, feed conversion ratio, protein efficiency ratio and net protein utilization, trypsin and chymotrypsin activities of experimental fish fed 100% FM and 40% SPC diets were significantly higher than those fed other diets. The apparent digestibility coefficient (ADC) of the diet and diet components, ADC diet , ADC protein and ADC lipid , of fish fed diet 40% SPC and 100% FM treatment were significantly higher than those of other treatments. The cost/kg fish produced in diets 100% FM and 40% SPC was much lower compared with other treatments. Dietary inclusion levels of SPC in diet above 40% significantly affected fish survival, growth, digestibility and trypsin and chymotrypsin activities, although fish chemical composition was not greatly affected.

A green approach, including using phytochemicals in pomelo peel extract (PPE) and direct sunlight, was used to synthesize silver nanoparticles (AgNPs). PPE was prepared by treating pomelo peel with a citric acid solution at 85°C for 2 h. PPE was then mixed with AgNO3 and exposed to sunlight to induce the formation of AgNPs. Time-dependent UV-vis spectra of the reaction mixture demonstrated that AgNPs are formed under sunlight irradiation faster than underheating at 90°C. Characterization techniques, including X-ray diffraction, transmission electron microscopy, and scanning electron microscopy, confirmed the formation of AgNPs with sizes of 20–30 nm. AgNPs synthesized in PPE were more stable toward electrolyte-induced aggregation than those synthesized using the conventional NaBH4/citrate method. The AgNPs synthesized in PPE showed antibacterial activities comparable to those of AgNO3 at the same silver concentration against four pathogenic bacterial strains. The obtained PPE containing AgNPs, pectin, and other phytochemicals can be utilized further to produce antibacterial and antioxidant films in food packaging and medical applications.

This study reports a synthesis of copper nanoparticles (CuNP) deposited on polyethylene terephthalate (PET) filters and antibacterial evaluation of the obtained filters against Escherichia coli and Salmonella enterica. CuNP were synthesized by a two-step method involving adsorption of [Cu(OH) 4 ] 2ions onto a PET filter and subsequent chemical reduction by ascorbic acid without using other capping agents. The synthesized CuNP were 105±26 nm (mean±SD) in size and agglomerated into clusters on the PET fibres. Increasing the immersion time of the filters in [Cu(OH) 4 ] 2solutions yielded higher amounts of deposited CuNP. SEM images and mass measurements revealed significant changes in the PET fibre surface under the alkaline medium. Passing bacterial suspensions of E. coli and S. enterica through the CuNP-deposited PET filter reduced them by 5.55 and 2.30 log values, respectively. This method of depositing CuNP onto PET material may be further developed for a wide scope of applications, not only in antibacterial filters, but also in catalytic, packaging and biomedical fields.

Copper (I) oxide nanoparticles (Cu2O NP) were synthesized by reducing CuSO4 with glucose in the presence of polyvinyl alcohol as a capping agent. We used three different synthetic procedures with a fast reaction (procedure 1p), a fast-then-slow reaction (procedure 2p), and a slow-then-fast reaction (procedure 3p). The reaction rates were controlled by changing the temperature and the speed of adding reagents. The synthesized Cu2O NP were subsequently incubated for 24 h in a pH 6 solution (Cu2O NP6) or a pH 8 solution (Cu2O NP8) at 5°C. XRD and SEM images analysis revealed that the 1p procedure produced smaller NP, while the 2p procedure produced larger but more uniform NP. The 3p procedure produced the largest NP with a higher size variation. The 24-hour acidic postsynthesis incubation resulted in an etching effect, which reduced the size and size variation of Cu2O NP6. To evaluate the antibacterial activity, E. coli suspensions were mixed with the obtained Cu2O NP (32, 96, or 160 ppm) for different time intervals (1 or 24 h) and then grown on Petri dishes at 37°C for 24 h. Higher doses, smaller sizes of Cu2O NP, and longer contact times with the bacterial suspension resulted in higher inactivation efficiencies. Cu2O NP6 showed higher antibacterial effects at low doses, possibly due to the etching effect and the positive surface charge. Increasing the Cu2O doses from 32 to 96 and 160 ppm noticeably increased the antibacterial effect of the Cu2O NP8, but not significantly for Cu2O NP6. We suggested that the Cu2O NP6 suffered from agglomeration at high doses due to their high surface activity and low surface charges.

This study aimed to fabricate a nontoxic coating containing copper nanoparticles (CuNPs) to protect fruits from pathogenic Colletotrichum gloeosporioides causing anthracnose on several tropical fruits. We used a green approach, in which CuNPs were synthesized by reducing CuSO4 with ascorbic acid in the presence of gelatin and glycerol as the capping agents. The formation of CuNPs was confirmed by UV-vis absorption spectra of the reaction mixture, which showed a surface plasmon resonance peak at 578–594 nm. The x-ray diffraction spectrum of the CuNPs indicated the presence of mostly metallic copper with some minor impurities of Cu2O, CuO, and Cu(OH)2. Transmission electron microscopy (TEM) images and dynamic light scattering studies showed that the sizes of 90% of CuNPs were in 100–300 nm range. A 30–50 nm capping layer of gelatin surrounding CuNPs can be observed in the TEM images. Comparing FTIR spectra of the used reagents and CuNPs confirmed the depletion of ascorbic acid, as well as the gelatin layer protecting CuNPs. The synthesized CuNPs showed dose-dependent antifungal activity against C. gloeosporioides with 100% growth inhibition at 200 ppm copper. Gelatinized tapioca starch was then added to the CuNPs solution to obtain a film-forming mixture to produce stand-alone composite films on Petri dishes and coatings on mangoes. C. gloeosporioides could not grow on the surface of nutrient agar in contact with the films containing 245 ppm CuNPs, while they grew normally on control films without CuNPs. For the in vivo antifungal tests on mangoes, both the control and the CuNPs-containing coatings equally inhibit fungal growth, possibly due to the low oxygen permeability of the protein and starch components in the films. This study thus demonstrated the potential applications of composite coatings using biodegradable polymers that contain CuNPs in postharvest protecting fruits from phytopathogenic fungi.

In this study, dialdehyde starch (DAS) was prepared by oxidizing corn starch using potassium periodateas the oxidant.The aldehyde contentsin DAS weredetermined using titration with hydroxylamine and were found proportional to the molar ratio of KIO4:C6H10O5.Fourier transform infrared spectroscopy was used to confirm the breakage of the bond between C2 and C3in anhydroglucose units and the formation of -CHO group in DAS. X-ray diffractometry showed a decrease in crystallinity of starch after periodate oxidation. Thermogravimetric analysis showed reduced thermal stability of DASin comparison with the native starch. The prepared DAS was blended with gelatin to form films by casting method. Increasing aldehyde contents in DAS from 0 to 12.2% resulted in decreased moisture contents, solubility in water, and the swelling capacity of gelatin-DAS films. The value of tensile strength and elongation at break of the gelatin-DAS films rose when the aldehyde content was low (0-3.5%), but declined when the aldehyde content was high (3.5-12.2%). Slight periodate oxidation is, therefore, an effective way to enhance the mechanical characteristics of blend films from DAS and other biopolymers.

The purpose of this study is to produce antibacterial filters based on a commercial polyethylene terephthalate (PET) filter with pores larger than bacterial cells. The antibacterial agent was copper nanoparticles (CuNP) which were synthesized and deposited on the PET filter by reducing copper(II) ions using sodium hypophosphite (NaH2PO2) as the reducing agent and polyvinylpyrrolidone (PVP) as the capping agent. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed the presence of 150–300 nm CuNP on the surface of PET filters. We evaluated the amounts of deposited CuNP using a colorimetric method and the antibacterial-filtration capacity of CuNP/PET filters against Escherichia coli using the colony counting method. The reaction conditions were optimized successively using the one-factor-at-a-time approach for the concentration of copper precursor, the concentration of PVP, and the reaction time. The results showed that an initial 1 M CuSO4, 0.8% w / v PVP, and 10-20 min of reaction resulted in a CuNP/PET filter with the highest antibacterial activity: 5.2 log cfu/mL reduction for Escherichia coli and 5.6 log cfu/mL reduction or Staphylococcus aureus. SEM images demonstrated the damages of the bacterial cells after passing through the CuNP/PET filter. ICP-MS analysis of the first liter of filtrate showed that the copper concentration of released copper was 0.6 ± 0.1  ppm, which is below the WHO standard for drinking water. Therefore, these CuNP/PET filters are promising for point-of-use disinfection of water, where clean potable water is not sufficient.

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