The use of pseudo-infinite methanol in increasing the rate of esterification and transesterification reactions was studied using oil palm trunk (OPT) and sugarcane bagasse (SCB) derived solid acid catalysts. The catalysts were prepared by incomplete carbonisation at 400°C for 8h, followed by sulfonation at 150°C for 15h and characterised using TGA/DTA, XRD, FT-IR, SEM-EDS, EA and titrimetric determinations of acid sites. Under optimal reaction conditions, the process demonstrated rapid esterification of palmitic acid, with FAME yields of 93% and 94% in 45min for OPT and SCB catalysts, respectively. With the process, moisture levels up to 16.7% accelerated the conversion of low FFA oils by sulfonated carbon catalysts, through moisture-induced violent bumping. Moisture assisted transesterification of palm olein containing 1.78% FFA and 8.33% added water gave FAME yield of 90% in 10h, which was two folds over neat oil.
The objective of this research was to study the kinetics of synthesis of a commercially important ester - Isopropyl Palmitate (IPP) using immobilized lipase (Lipozyme IM). It was studied in a packed bed differential reactor. In order to establish the kinetics of the reaction, parameters such as linear velocity of the fluid through the reactor, particle size, substrate concentration, substrate molar ratio, temperature and water activity were studied. Operational and storage stability of the enzyme were also assessed. The reaction followed Michaelis-Menton kinetics as observed from the relationship of initial rate of the reaction as a function of substrate concentration. It was found that the optimum substrate concentration was 0.15M palmitic acid and isopropyl alcohol in 1:1 stoichiometric ratio. Inhibition by excess of isopropyl alcohol has been identified. The optimum temperature for the esterification reaction was found to be around 50 degrees C. The activation energy of this process was determined to be 43.67 kJ/mol. The optimum water content was 0.50%. The reaction rates were measured in the absence of any significant external diffusional limitations. Since internal diffusional limitations could not be eliminated, the kinetics observed is only apparent.
Fatty acid desaturase enzymes are capable of inserting double bonds between carbon atoms of saturated fatty acyl-chains to produce unsaturated fatty acids. A gene coding for a putative Δ9-fatty acid desaturase-like protein was isolated from a cold-tolerant Pseudomonas sp. A8, cloned and heterologously expressed in Escherichia coli. The gene named as PA8FAD9 has an open reading frame of 1185 bp and codes for 394 amino acids with a predicted molecular weight of 45 kDa. The enzyme showed high Δ9-fatty acid desaturase-like protein activity and increased overall levels of cellular unsaturated fatty acids in the recombinant E. coli cells upon expression at different temperatures. The results showed that the ratio of palmitoleic to palmitic acid in the recombinant E. coli cells increased by more than twice the amount observed in the control cells at 20 °C using 0.4 mM IPTG. GCMS analysis confirmed the ability of this enzyme to convert exogenous stearic acid to oleic acid incorporated into the recombinant E. coli membrane phospholipids. It may be concluded that the PA8FAD9 gene from Pseudomonas sp. A8 codes for a putative Δ9-fatty acid desaturase protein actively expressed in E. coli under the influence of temperature and an inducer.
In this study, the effects of limited and excess nitrate on biomass, lipid production, and fatty acid profile in Messastrum gracile SE-MC4 were determined. The expression of fatty acid desaturase genes, namely stearoyl-ACP desaturase (SAD), omega-6 fatty acid desaturase (ω-6 FAD), omega-3 fatty acid desaturase isoform 1 (ω-3 FADi1), and omega-3 fatty acid desaturase isoform 2 (ω-3 FADi2) was also assessed. It was found that nitrate limitation generally increased the total oil, α-linolenic acid (C18:3n3) and total polyunsaturated fatty acid (PUFA) contents in M. gracile. The reduction of nitrate concentration from 1.76 to 0.11 mM increased the total oil content significantly from 32.5 to 41.85% (dry weight). Palmitic (C16:0) and oleic (C18:1) acids as the predominant fatty acids in this microalgae constituted between 82 and 87% of the total oil content and were relatively consistent throughout all nitrate concentrations tested. The expression of SAD, ω-6 FAD, and ω-3 FADi2 genes increased under nitrate limitation, especially at 0.11 mM nitrate. The ω-3 FADi1 demonstrated a binary up-regulation pattern of expression under both nitrate-deficient (0.11 mM) and -excess (3.55 mM) conditions. Thus, findings from this study suggested that limited or excess nitrate could be used as part of a cultivation strategy to increase oil and PUFA content following media optimisation and more efficient culture methodology. Data obtained from the expression of desaturase genes would provide valuable insights into their roles under excess and limited nitrate conditions in M. gracile, potentially paving the way for future genetic modifications.
Bioprospecting for biodiesel potential in microalgae primarily involves a few model species of microalgae and rarely on non-model microalgae species. Therefore, the present study determined changes in physiology, oil accumulation, fatty acid composition and biodiesel properties of a non-model microalga Messastrum gracile SE-MC4 in response to 12 continuous days of nitrate-starve (NS) and nitrate-replete (NR) conditions respectively. Under NS, the highest oil content (57.9%) was achieved despite reductions in chlorophyll content, biomass productivity and lipid productivity. However, under both NS and NR, palmitic acid and oleic acid remained as dominant fatty acids thus suggesting high potential of M. gracile for biodiesel feedstock consideration. Biodiesel properties analysis returned high values of cetane number (CN 61.9-64.4) and degree of unsaturation (DU 45.3-57.4) in both treatments. The current findings show the possibility of a non-model microalga to inherit superior ability over model species in oil accumulation for biodiesel development.
In the present study, we investigated the effect of long-acyl chain SFA, namely palmitic acid (16:0) and stearic acid (18:0), at sn-1, 3 positions of TAG on obesity. Throughout the 15 weeks of the experimental period, C57BL/6 mice were fed diets fortified with cocoa butter, sal stearin (SAL), palm mid fraction (PMF) and high-oleic sunflower oil (HOS). The sn-1, 3 positions were varied by 16:0, 18:0 and 18:1, whilst the sn-2 position was preserved with 18:1. The HOS-enriched diet was found to lead to the highest fat deposition. This was in accordance with our previous postulation. Upon normalisation of total fat deposited with food intake to obtain the fat:feed ratio, interestingly, mice fed the SAL-enriched diet exhibited significantly lower visceral fat/feed and total fat/feed compared with those fed the PMF-enriched diet, despite their similarity in SFA-unsaturated fatty acid-SFA profile. That long-chain SFA at sn-1, 3 positions concomitantly with an unsaturated FA at the sn-2 position exert an obesity-reducing effect was further validated. The present study is the first of its kind to demonstrate that SFA of different chain lengths at sn-1, 3 positions exert profound effects on fat accretion.