Iranian Journal of Chemical Engineering (IJChE)

Abstract Objective: C-Phycocyanin (C-PC) is a blue-colored protein antioxidant produced in the microalgae Spirulina platensis (S. platensis) that is used in the food, cosmetic and pharmaceutical industries. The purification methods are often time-consuming and expensive. In this study, Foam fractionation (FF) was used as a simple, rapid, cost-effective, and environmentally friendly method for the purification of C-PC.
Methods: C-PC pigment solution was extracted from dry S. plantensis biomass in phosphate buffer. FF method for the purification of C-PC was optimized using the response surface methodology (RSM). A UV-Vis spectrophotometer was used to determine the identifying absorbance peaks of the C-PC solutions.
Results: The RSM obtained an optimal setting at a pH = 6, aeration rate of 3.5 vvm, and operation time of 21 min for achievement of the highest purification fold (PF), purity index (PI), and C-PC recovery percentage (R) of about 1.56 ± 0.02, 0.59 ± 0.02, and 45.59 ± 0.72%, respectively.
Conclusion: In FF method there are no additional chemicals, also it is fast and has low operating costs, which make it an attractive method.

Abstract The application of the agro-industrial waste as the feedstock helps to decrease the operational cost of the fermentation process. Soapstock is a by-product of the vegetable oil refinery and enriched with fatty acids including linoleic acid which has a high potential application in the production of biosurfactants. In this study, a dual carbon source system, including glucose and free fatty acids recovered from a sunflower soapstock, was used for the synthesis of sophorolipid (SL) by Candida catenulata. The production of SL showed a major dependence on the initial carbon sources and the concentration of urea as the nitrogen source. The inoculum size was another influential factor in the fermentation process. The optimization of these factors was evaluated by the one-factor-at-a-time and the response surface methodology (RSM). The one-factor-at-a-time approach gained the best SL productivity (Y₁) of about 52.08 mg L^-1 h^-1 and SL-to-biomass yield (Y₂) of 712 mg_SL g_cell^-1 at the inoculum size of 4% vv^-1, 100 g L^-1 of glucose, 80 g L^-1 of soapstock, and 7.5 g L^-1 of urea. While the RSM, due to considering interactional effects of the factors, obtained the best condition at 100 g L^-1 of glucose, 100 g L^-1 of the soapstock, 9.3 g L^-1 of urea, and an inoculum size of 6.3% vv^-1 with the Y₁ and Y₁ values of about 58.10 mg L^-1 h^-1 and 713 mg_SL g_cell^-1, respectively. The characterization of the produced SLs by the GC-MS analysis indicated that a di-acylated C16:1 acidic sophorolipid with an m/z ratio of 679 amu was the main product.

Abstract Nisin is a natural heat resistance preserver with wide applications in food industries. The main drawback of nisin is its weak activity against most Gram-negative bacteria. In this study, the antibacterial activities of nisin against Salmonella typhimurium, Klebsiella pneumoniae, Citrobacter freundii, and Escherichia coli improved via the Maillard reaction with xanthan. The nisin-xanthan conjugates analyzed by the ultraviolet, fluorescence, and Fourier transform infrared spectroscopies. The results showed temperature, reaction duration, and nisin-to-xanthan ratio affected the quality of the obtained conjugates. In relevant to the results, the antibacterial activity of 100 mg L-1 of the conjugates was increased against S. aureus, S. typhimurium, and E. coli when the nisin to xanthan ratio was increased from 1:1 to 4:1 and reached 88.8, 98.7, and 97.7%, respectively. The increase in temperature from 90 ᵒC to 110 ᵒC enhanced the antibacterial effects against all test bacteria, especially for persistent Gram-negative cells, namely C. freundii and K. pneumoniae. The longer Maillard reaction after 110 min at 110 ᵒC did not improve the antibacterial activity of the conjugates against all test bacteria. The best antibacterial activity was observed at a temperature of 110 ᵒC for 110 min for a nisin-to-xanthan ratio of 4:1.

Abstract In this study, hydrodynamic characteristics such as gas holdup (ε), liquid phase velocity, and mass transfer coefficient (kLa) for air-diesel system were modeled for bubble column (BCR), airlift (ALR), and airlift with the net draft tube (ALR-NDT) reactors at different superficial gas velocities ranging from 0.008 to 0.085 m s-1. A 3D two-fluid Eulerian-Eulerian model was developed using computational fluid dynamic (CFD) technique to model the three configurations of column reactors and predict the hydrodynamic parameters. The results of 3D-CFD modeling showed a good agreement with the experimental data where average error was less than 14 and 9% for ε and kLa, respectively. Although the vortex occurred in BCR and ALR at high gas velocities, however optimum liquid and gas circulation and distribution observed in ALR-NDT. Furthermore, the formation of dead zone (kLa = 0) in the reactors was studied, and the results revealed that ALR-NDT has a lower volume of dead zones (about 8%) in comparison with BCR and ALR. In order to reduce the dead zone in BCR and ALR systems, the location of gas diffuser and draft tube were investigated. The dead zone was decreased by 12% with shifting of gas diffuser to the bottom of the BCR. Also, by increasing the distance of gas diffuser from draft tube, the dead zone was decreased by 40% specifically near the walls of ALR. Meanwhile, the simultaneous shifting of gas diffuser and draft tube to lower position in ALR had no effect on dead zone formation and its distribution.