Silver nanoparticles and silver-graphene oxide nanocomposites were fabricated using a rapid and green microwave irradiation synthesis method. Silver nanoparticles with narrow size distribution were formed under microwave irradiation for both samples. The silver nanoparticles were distributed randomly on the surface of graphene oxide. The Fourier transform infrared and thermogravimetry analysis results showed that the graphene oxide for the AgNP-graphene oxide (AgGO) sample was partially reduced during the in situ synthesis of silver nanoparticles. Both silver nanoparticles and AgGO nanocomposites exhibited stronger antibacterial properties against Gram-negative bacteria (Salmonella typhi and Escherichia coli) than against Gram-positive bacteria (Staphyloccocus aureus and Staphyloccocus epidermidis). The AgGO nanocomposites consisting of approximately 40 wt.% silver can achieve antibacterial performance comparable to that of neat silver nanoparticles.
The enzymatic hydrolysis of palm kernel cake protein (PKCP) with trypsin to obtain PKCP hydrolysates (PKCPH) was optimized using response surface methodology (RSM). A central composite design (CCD) was used to study the influence of four independent variables, namely pH, hydrolysis temperature (°C), substrate concentration (w/v) and enzyme/substrate (w/w) ratio on the degree of hydrolysis (DH%). The hydrolysis was carried out using different combinations of four hydrolytic parameters at five levels for 6h. The CCD consisted of 24 experimental points and six replicates of the central points. The data were analyzed using Design-Expert Software. The results showed that all of the variables evaluated significantly influenced the DH% in a second polynomial model, and different combinations of parameters were generated to obtain three different levels of DH (30%, 40% and 50%), namely PKCPH 30, PKCPH 40 and PKCPH 50. The PKCPH with different DH% showed significantly different antiradical properties (p<0.05). The PKCPH 50 preparation had the lowest EC 50 value for DPPH radical scavenging capacity (0.14mg/ml). In the ABTS + radical scavenging capacity and PCL-ACW (photo chemiluminescence-antiradical capacity of water soluble substances) assays, PKCPH 50 showed the highest Trolox equivalent antioxidant capacity value (326.67±5.77μmol TEAC/g) and ascorbic acid equivalent value (11.43±0.03μg AAE/mg) of the preparations tested. Moreover, the protein hydrolysates also exhibited a notable reducing effect in a dose-dependent manner. Optimum conditions for enzymatic hydrolysis of PKCP were established in this study to produce an antiradical agent.
A hybrid nanocomposite cellulose membrane containing graphene oxide and silver nanoparticles was produced via a two step synthesis method. First, regenerated cellulose membranes containing different percentages of graphene oxide (GO) were produced by coagulating the mixture in an acid coagulating bath. Afterward, silver nanoparticles (AgNPs) were in situ synthesized onto the membranes using the modified Tollens' method. The presence of GO on the cellulose membranes significantly enhanced the deposition of AgNPs due to the electrostatic interaction between the positively charged silver ammonia complex and negatively charged oxygenated functional groups of GO before the reduction to AgNPs.The AgNPs content of the membrane with 1 wt% of GO was approximately 26 times greater than that of the neat cellulose membrane. More interestingly, the presence of GO significantly lowered the release of Ag ions and leaching of AgNPs into the aqueous solution. The produced composite membranes exhibited strong antibacterial activity against S. aureus and E. coli.
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